ReviewArticle Second-Generation Bioethanol from Coconut...

Review ArticleSecond-Generation Bioethanol from Coconut Husk

Maria Bolivar-Telleria 1 Caacuterita Turbay 1 Luiza Favarato 1

Tarcio Carneiro 1 Ronaldo S de Biasi2 A Alberto R Fernandes1

Alexandre M C Santos1 and Patricia M B Fernandes 1

1Biotechnology Core Federal University of Espırito Santo Vitoria ES Brazil2Military Institute of Engineering Rio de Janeiro RJ Brazil

Correspondence should be addressed to Patricia M B Fernandes patriciafernandesufesbr

Received 2 March 2018 Revised 12 August 2018 Accepted 3 September 2018 Published 27 September 2018

Guest Editor Zhang Lei

Copyright copy 2018 Maria Bolivar-Telleria et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Coconut palm (Cocos nucifera) is an important commercial crop inmany tropical countries but its industry generates large amountsof residue One way to address this problem is to use this residue coconut husk to produce second-generation (2G) ethanol Theaim of this review is to describe the methods that have been used to produce bioethanol from coconut husk and to suggest waysto improve different steps of the process The analysis performed in this review determined that alkaline pretreatment is the bestchoice for its delignification potential It was also observed that althoughmost reported studies use enzymes to perform hydrolysisacid hydrolysis is a good alternative Finally ethanol production using different microorganisms and fermentation strategies isdiscussed and the possibility of obtaining other added-value products from coconut husk components by using a biorefinery schemeis addressed

1 Introduction

Modern life demands highmobility and as a result transportis one of the largest and fastest growing energy demand-ing sectors [1] Also increase in competitive agribusinessautomatization leads to a high energy demand [2] Howeverdue to concern on the negative impact of fossil fuels onthe environment the use of biofuels emerges as a promisingalternative that is gradually becoming technically and eco-nomically feasible [3]

Modern ethanol industry began in the 1970s whenpetroleum-based fuel became expensive and environmentalconcerns arose In 1975 the Brazilian government launcheda pioneer program known as ldquoProalcoolrdquo (Pro-Alcohol) withtwo main objectives to reduce the impact caused by oil priceincreases and at the same time mitigate the fall of sugarprice in the international market [4 5] Between 1980 and2002 over five billion dollars were invested on sugarcaneagriculture and industry to expand alcohol fuel production[5] ldquoProalcoolrdquo is known worldwide for its positive effecton biofuel promotion [6] Nowadays in Brazil 20 to 25of anhydrous ethanol is used as an additive in gasoline

Moreover since 2003 flex-fuel vehicles which can usealcohol gasoline or gasoline+alcohol are on the market [5]

Ethanol is the leading liquid biofuel used for trans-portation First-generation ethanol has a simple productionprocess using sugar or grain as raw material (sugarcane juicein Brazil and corn in the USA and EU for example) while 2Gethanol (bioethanol) has more complex steps of productionand uses lignocellulosic material as a substrate [7] Amongthe major byproducts generated by agroindustries lignocel-lulosic biomass is one of the most abundant conflict-freewith food production and is available throughout the yearat low prices [8 9] All of these characteristics show thatlignocellulose waste might be considered the most feasibleoption for fossil fuel replacement having a significant poten-tial for bioethanol productivity while giving a destination foran environmental liability

In Brazil GranBio and Raızen are pioneering companiesthat utilize sugarcane coproducts as a substrate enhancingethanol production without increasing the cultivated area[10 11] In 2003 Raızen was able to produce more than 40million liters per year [11] In the USA three companiesproduce cellulosic ethanol in commercial scale POET-DSM

HindawiBioMed Research InternationalVolume 2018 Article ID 4916497 20 pageshttpsdoiorg10115520184916497

2 BioMed Research International

Advanced Biofuels DuPont and ABENGOA [12] There aremany projects around the world focusing on the use oflignocellulosic residues for biofuel production [13] Theseresidues can come from homes or city dumps companies inCanada are investing in the construction and operation of arenewable fuel plant using local residential kitchen and yardwaste Phuketrsquos Provincial Administration Organization inThailand is building a waste-to-biofuel facility that will usethemunicipal solidwaste of the entire island as feedstock [14]Chinarsquos State Development amp Investment Corporation beganthe construction of its first ethanol plant in the Liaoningprovince with 300000 tons capacity and is planning to buildfive ethanol plants in other provinces [15] Nowadays biofuelshave an important part in the global liquid fuel market andover a hundred companies in different countries base theirproduction on various types of 2G biofuels [13] Coconuthusk is a very promising substrate that can be used as rawmaterial for 2G ethanol production since coconut palmplays an important role in the economy of several tropicalcountries [16] The food industry uses coconuts to obtainvarious products leaving the husk as waste It is important tonote that coconut husk has a high lignin content that duringhusk decomposition penetrates the soil and can reach thewater table imposing a great environmental risk Since it isdiscarded in high volumes (coconut husk encompasses 80to 85 of the weight of the fruit [17 18] while sugarcanebagasse corresponds only to 27 to 28 dry weight) it ismandatory to find a safe destination for this wasteThereforethe use of coconut husk for 2G ethanol production may bea solution to reduce the environmental impact Moreover ifthe technology is cheap and simple enough it can be used bysmall producers

The three main components of a biomass (cellulosehemicellulose and lignin) form a recalcitrant structure mak-ing it difficult for enzymes to have complete access to cellulosefor conversion to monosaccharides To make this feasiblethe first major step in bioethanol production is biomasspretreatment (biological physical or chemical) in which thelignin content is reduced to release the fermentable sugarsfrom the rigid structure and therefore prepare the biomassfor enzymatic conversion [19] Different types of biomasseshave different amounts and types of sugars (hemicelluloseand cellulose) and lignin so knowing its composition iscrucial for the process Moreover the abundance of theresidue must be taken into account so that the whole processis economically feasible

The second major step in 2G ethanol production is thehydrolysis that unlocks and saccharifies the polysaccharidesthat are present in the biomass to fermentable sugars [20]Generally enzyme cocktails are used to catalyze reactions toobtain simple sugars such as glucose andmannose for furtherfermentation by microorganisms This process also calledsaccharification is very important and the requirementsof these enzyme complexes which act synergistically addmajor costs to the overall process The main challenge is toobtain a cost-effective technology of enzymatic hydrolysis foreconomically viable biofuels [20]

The fermentation process is the next step in which amicroorganism such as the yeast Saccharomyces cerevisiae

ferments the sugars that are present in the treated biomassand produces ethanol [21] To increase the economic feasi-bility of this process industries show great interest in usingyeast strains that are more tolerant and resistant to variouskinds of stresses and that are also able to use pentoses thatcome fromhemicellulose degradation such as xylose asmoststrains naturally only consume hexoses

Currently the process for 2G bioethanol production inlarge scale is being improved since it still has cost productionissues that derive from the procedures needed to over-come the recalcitrance of the lignocellulose (pretreatmentand enzymatic hydrolysis) in order to obtain fermentablesugars [22] To transform the bioethanol production into asustainable and economically viable process it is importantto integrate it in a biorefinery which is a great supporterof a biobased economy In a biorefinery almost all typesof biomass residues can be converted to different classesof biofuels biomaterials and other marketable bioproductsthrough jointly applied conversion technologies [23]

Although many articles address the use of coconut huskas a raw material for bioethanol production few of themcompare the results obtained using different methods Thiswork intends to give an overview on different approachesalready tested to obtain ethanol from coconut husk tofacilitate the development of a process that can effectivelyproduce ethanol from coconut residue

2 The Coconut Plant and Industry

Coconut palm tree is a perennial crop grown in tropicalclimate countries which present ideal conditions for itscultivation such as soil with proper water capacity anddrainage andwarm ambient temperatures [24 25] Due to thecoconut structure many valuable products can be obtainedfrom it such as meat (copra) oil water milk and fibers[25] therefore this fruit is of great economic importanceThere are two major varieties the tall (Typica) mainly usedto obtain coconut meat and milk and the dwarf (Nana) themost cultivated in Brazil used for coconut water extraction[24 25]

Coconut harvesting time is determined by its purposeand is usually carried out in two stages of ripeningThe greenfruits are destined to the coconut water market while maturefruits are destined to the dry coconut market (for meat milkand oil) [26]Therefore depending on the plantation site theresidue ismade of green ormature coconut husks which havedifferent compositions (Table 1)

The coconut fruit has a smooth green epidermis (epi-carp) a medium region with bundles of fibers (mesocarp)and a stony layer that surrounds its edible part (endocarp)(Figure 1)

The estimated annual worldwide coconut production in2015 was around 55 million tons and the main producingcountries are Brazil India Indonesia the Philippines andSri Lanka [16 17] Indonesia is responsible for 331 of thetotal world production [24] and the coconut industry playsa significant economic role in this country as well as inother tropical countries However as mentioned before 80

BioMed Research International 3

Table 1 Chemical composition of green and mature coconut husk ()

Substrate Reference Cellulose Hemicellulose Lignin

Green coconut husk

[27] 3931 1615 2979[28] 4340 1990 4580[29] 3280 1590 na[30] 3323 2914 2544

Mature coconut husk

[31] 3047 2542 3315[32] 2958 2777 3104[33] 3218 2781 2502[30] 2958 2777 3104

na not available or present

(a) (b)

Figure 1 Green coconut and its structures (a) Green coconut (b) Green coconut without epicarp and liquid albumen i epicarp ii mesocarpiii endocarp iv solid albumen

to 85 of the weight of the fruit is not used and is simplydiscarded resulting in large amount of waste [17 18] Alsothe coconut husk is rich in phenolic compounds whichare toxic to humans and animals and are released in theenvironment as a result of natural deterioration [39] Actuallyonly a small percentage of the total fiber residue is designatedfor the production of fertilizers and handmade productslike mats nets and brooms [17 40] and unfortunately thetraditional process to obtain the coir fiber is highly pollutingas it is performed in surface waters and again liberatespolyphenols [17 40] Due to high residue volumes and thehusk slow decomposition the coconut industry turns intoan environmental and handling problem [41] A possibleand sustainable solution for the coconut husk residue is theproduction of 2G bioethanol

Currently around 20 published scientific papers describethe study of coconut husk as raw material for bioethanolThis means that it is an interesting opportunity to contributeto this field of study allowing hopefully in a near futurethat small and local producers to produce biofuels for their

personal use and for the development of a sustainable coconutchain production As mentioned earlier coconut producingcountries are part of the third-world economy in this wayturning trash into jobs and income generation is a veryimportant matter

3 Methods Used in CoconutConversion to Ethanol

31 Coconut Husk Pretreatment for Bioethanol ProductionThe threemain components of lignocellulosic biomass cellu-lose hemicellulose and lignin form a strong matrix whichgives it recalcitrance meaning low enzyme digestibility [42]Biomass used for bioethanol production has to undergoa pretreatment to remove lignin and hemicellulose andovercome recalcitrance by increasing porosity and reducingcellulose crystallinity making it available for biological orchemical hydrolysis An effective pretreatment must returnhigh sugar concentration but always avoiding their loss anddegradation also it has to minimize formation of inhibitors


and be able to undergo fermentation without detoxificationto reduce process steps water and energy consumption inorder to decrease costs [43ndash45] The pretreatment is a veryimportant step as it has an impact on the next stages suchas hydrolysis fermentation and downstreamprocessing [43]Since biomass composition varies from one substrate toanother different pretreatments have to be tested to find thebest for each specific substrate

The first step in the pretreatment is the substrate prepa-ration to make the enzymatic hydrolysis more effective bymechanically reducing cellulose crystallinity [45] In the caseof coconut husk it is dried ground and sieved to obtain apowder [31]

The most used pretreatment for coconut husk is alkalinefollowed by acid but there are also other methods beingtested that will be discussed in this section (Table 2)

Depending on biomass composition and the type andconditions of the pretreatment products that inhibit enzy-matic hydrolysis and fermentation such as weak acids fur-fural 5-hydroxymethyl furfural (HMF) and phenolic com-pounds are formed [42] After the pretreatmentmost authorswash the pretreated coconut husk to extract inhibitors fromthe biomass [27ndash29 46 47] This approach might not be thebest as it increases the number of process steps and uses morewater which affect the cost and moreover a high content ofsugars are lost during these washes [29 48]

311 Alkaline Pretreatment The main effect of alkaline pre-treatment is delignification of the biomass and reduction ofcrystallinity [29 43ndash45] For these pretreatments sodiumpotassium calcium and ammonium hydroxides and ammo-nia are used [44 45] All revised studies that used alkalinepretreatment in coconut husk used NaOH and most of themuse high temperatures [27ndash29 33 46 48ndash50]

Soares et al [50] proposed a pretreatment with diluteNaOH (1 (wv)) at room temperature to decrease the forma-tion of inhibitors using high-solid loadings (18 (wv)) andno detoxification of the pretreated biomass to obtain highersugar concentration In a later work Soares et al [48] suggestthe use of a fed-batch pretreatment and saccharification withhigher solid loadings (25 and 30 (wv))

312 Acid Pretreatment Acid pretreatment is a widely usedand effective method for obtaining high yields of sugarsfrom lignocellulosic biomass Fatmawati and Agustriyanto[47] and da Costa Nogueira et al [29] pretreated coconuthusks with diluted acid (15 and 3 (wv) of H

2SO4) and

autoclaved at 121∘C De Araujo et al [51] tried an acidpretreatment followed by an alkaline treatment of the washedneutralized fibers both at high temperature

313 Other Pretreatment Approaches Pretreatments usingalkaline conditions combined with other techniques havebeen tested for coconut husk One approach consists ofpresoaking the coconut husks in a NaOH solution andthen microwaving them [52 53] Other pretreatments usea combination of alkaline and oxidative conditions [31 51]where an H

2O2solution is adjusted to pH 115 with NaOH

Goncalves et al [30] used a two-step method to removedifferent components from the husk First they utilizedoxidative conditions (NaClO

2ndashC2H4O2) to remove the

lignin Then they performed autohydrolysis to extract thehemicellulose

Other pretreatments reported for coconut husk are theuse of high temperature for autohydrolysis [29 32 53] use ofaqueous glycerol and acidified aqueous glycerol at 130∘C [54]and use of the surfactant Tween 80 during acid alkaline andhydrothermal pretreatment to increase enzymatic hydrolysis[29]

32 Hydrolysis The next step in bioethanol productionis breaking cellulose and hemicellulose into simple sugarmonomers that can be fermented Cellulose is hydrolyzedto glucose while hemicellulose hydrolysis releases a mixtureof pentoses and hexoses [44] There are different hydrolysisstrategies like dilute and concentrated acid alkaline hot-compressed water and enzymatic [55] Enzymatic hydrolysisis the most widely used as it is the most ecofriendly has noformation of inhibitors requires less energy and is operatedat mild conditions (40-50∘C and pH 4-5) so there are nocorrosion problems [20 44 56] On the other hand alkalineand acid hydrolysis present high toxicity high utility costlower sugar yields and corrosion along with the formationof inhibitors [44 56]

A cocktail of enzymes composed of cellulases and hemi-cellulases that work in synergy is needed to effectivelyhydrolyze the cellulose and hemicellulose (Figure 2) [3444 56] These enzymes are naturally produced by variousfungi and bacteria The fungus Trichoderma reesei is onethe most used industrially to produce cellulases [57] Thesestrains have been engineered to produce a large amount ofchosen cellulases (native homologous or engineered) so theyhave a high specific activity on crystalline cellulose [58 59]Currently the most advanced cocktails in the market areCellic CTec3 from Novozymes (Bagsvaeligrd Denmark) andAccellerase TRIO from DuPont Genencor (CA USA)[58]

Enzymatic hydrolysis is the economic bottleneck of lig-nocellulosic bioethanol production because of its high costEnzyme production costs comprise 25 to 50 of bioethanolproduction cost [60] Efforts have been made to decreaseenzyme price and it has dropped from US$ 5 per gallon orUS$ 075 per liter of bioethanol to US$ 010ndash018 per gallonor US$ 0027 per liter of bioethanol [34]

Producing better enzymes with higher efficiency usinglower doses are important to make lignocellulosic bioethanoleconomically feasible There are many factors that affect theefficiency of enzymatic hydrolysis including temperaturepH mixing rate enzyme loading pretreatment presentinhibitors substrate type and concentration (can lead to inhi-bition) and end-product inhibition (glucose) [44 56] As aresult the development of enzymes with (i) stability at highertemperatures and pH (ii) increased tolerance to pretreatmentinhibitors and end-product inhibition (iii) better efficiency(iv) higher adsorption and (v) catalytic efficiency is highlyneeded [20] For example new thermophilic strains suchas M thermophila C1 are used to produce cellulases with


Table2Com

paris

onof

pretreatmentm

etho

dsandinhibitorsform

eddu

ringpretreatment

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[52]

Cocon

uthu

skMicrowave-assis

ted-alkalin

e2450

MHz

na

[27]

Youn

gcoconu

thusk

Step

1NaO

H20-30

(wv)

Step

2NaO

H25(w

v)

Step

1100∘C

2and3h

Step

2170∘C

3hna

[53]

Cocon

uthu

sk

Microwave-assis

ted-alkalin

e2450

MHz20

min

na

Autohydrolysis

121∘ C

1043

bar15min

H2SO41

(vv)

40∘C

150r

pm24h

TS2

NaO

H5

(wv)

40∘C

150r

pm24h

TS2

[31]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)followed

byalkalin

edelignification(N

aOH4

(wv))

H2O225∘C

1hNaO

H100

rpm100∘C

1hna

[61]

Cocon

uthu

skdefattedgrapes

eedand

pressedpalm

fiber

NopretreatmentDire

ctno

n-enzymatichydrolysiswith

subcriticalwater

FurfuralH

MF4-hydroxybenzoicacid

andvanillin

[47]

Cocon

uthu

skH2SO41

(vv)

121∘ C

1hTS

75

na

[32]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Autohydrolysis

160-200∘C

10-50m

inT

S10

Aceticacidfurfuraland

HMF

[28]

Cocon

utfib

erNaO

H3

(wv)

121∘ C

90m

inna

[46]

Cocon

uthu

skNaO

H25m

olsdotLminus1

Soakingin

NaO

H30m

inAu

tocla

ved125∘C

30min

Phenoliccompo

unds

[49]

Green

coconu

thusks

NaO

H5

121∘ C

40m

inT

S5

Aceticacid


Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib

erHydrothermalcatalyzedwith

NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18

Aceticacidformicacidpheno

liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk

Acid-alkaline(H2SO406m

olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH

MF4-hydroxybenzoicand

vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc

eticacidformicacidpheno

liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present


-Glucosidase -Glucosidase

Non-reducing ends

EndoglucanaseCellobiohydrolaseII

Cellobiohydrolase I

Reducing endsCrystalline

Region RegionRegionCrystallineAmorphous

Figure 2 Hydrolysis mechanism of cellulose by cellulase cocktail components Endoglucanases cleave the inner region of cellulose thereducing and non-reducing regions are hydrolyzed by cellobiohydrolases (I and II) and the cellobiose is hydrolyzed to glucoses by 120573-glucosidase [34] Adapted fromWang et al [35]

broader pH and temperature ranges that also contain richerhemicellulases [58]

In the case of bioethanol production from coconut huskmost studies use enzymatic hydrolysis where the use ofcommercial cocktails is the most common approach [27 2931ndash33 46ndash54] Another method is to isolate fungi from thesubstrate to be used for bioethanol production hoping tofind a microorganism with high specificity for that biomassas was done by Albuquerque et al [46] for fresh androtting coconut husk The best isolates (Penicillium variableand Trichoderma sp) were used to produce enzymes bysubmerged fermentation

Some studies have beenmade to test the use of surfactantsto improve enzymatic hydrolysis in coconut husk but usingdifferent approaches Da Costa Nogueira et al [29] usedTween 80 during different pretreatments while de Araujo etal [51] used rhamnolipids produced by Pseudomonas aerugi-nosa during enzymatic hydrolysis Rhamnolipids are biosur-factants that unlike chemical surfactants are biodegradableand that makes them an environmentally friendly option

Non-enzymatic hydrolysis methods have also been testedfor coconut husk Acid hydrolysis using sulfuric acid 1 23 and 4 (vv) and high temperature after an alkaline pre-treatment was performed by Jannah andAsip [28]MoreoverPrado et al [61 62] employed subcritical water hydrolysiswhich utilizes pressure to maintain the water in a liquid stateusing coconut husk without any pretreatment

33 Fermentation Microbial fermentation is the next stepin the production of lignocellulosic bioethanol in which thefermentable sugars such as glucose and mannose obtainedin the saccharification are converted to ethanol [63]

Saccharomyces cerevisiae has traditionally been used toproduce alcohol in brewing and wine industries [21] Thisyeast produces high yields of ethanol with high productivity[64 65] Nowadays other yeasts and bacteria are also used for

bioethanol production [9] Using other microorganisms withdifferent characteristics from S cerevisiae or a combination ofmicroorganisms (cofermentation) can increase ethanol yieldFor example using yeasts that naturally ferment pentosessuch as the xylose consuming Pichia (Scheffersomyces) stipitisCandida shehatae and Pachysolen tannophilus [66] or bacte-ria such as Zymomonas mobilis which presents fermentationunder anaerobic conditions high ethanol tolerance andhigh ethanol-producing capacity [67] can increase the finalethanol concentration

Another approach to overcome the challenges in lig-nocellulosic bioethanol production is the development ofgenetically engineered microorganisms that are capable offermenting pentoses and hexoses Engineered yeast strainswith these characteristics are more economically viable forindustrial production of bioethanol [68] With developmentof new DNA editing technology the metabolic potentials ofmicroorganisms are being explored and harnessed in plentynew ways The development of strains that can fermentxylose themain pentose in coconut husk is done by insertinggenes related to the degradation pathway of this pentoselike overexpressing genes related to the pentose phosphatepathway (such as TKL1 and TAL1) [69 70] Other strategiesare decreasing the formation of xylitol as it is a harmfulderivative for the complete fermentation of the pentoses andpreventing the ubiquitination of hexose transporters sincethey also act to carry pentoses but suffer degradation whenthe concentration (or absence) of glucose decreases [71 72]Ethanol production can also be improved by preventing theformation of glycerol another fermentation product It hasbeen shown that the deletion of genes in this pathway likeGPD2 and FPS1 is related to an improvement in the finalethanol production since they redirect the metabolic flow tothe alcoholic fermentation [73 74] Another approach is theinterruption of the ADH2 gene related to the transformationof ethanol into aldehyde as it has higher affinity for ethanol


compared to other isoenzymes [75] Genetic engineering canalso be used to obtain microorganisms that are more tolerantto stresses like inhibitors produced during the pretreatmentand a high ethanol concentration that is present at the endof the process This can be done by inserting genes suchas Saccharomycopsis fibuligera TPS1 (6-phosphate-trehalosesynthase) into Saccharomyces cerevisiae or fine-tuned pro-teins such as RNApol2 responsible formRNA expression [7677] Genetic engineering offers the advantage over traditionalmethods of increasingmolecular diversity in a direct specificand faster way

34 Hydrolysis and Fermentation Strategies There are threemain strategies for hydrolysis and fermentation separatehydrolysis and fermentation (SHF) simultaneous hydrolysisand fermentation (SSF) and semi-simultaneous hydrolysisand fermentation (SSSF) In SHF the hydrolysis is done ata higher temperature which is optimal for the enzymes andlater the fermentation is performed at a lower temperatureoptimal for the microorganism On the other hand in SSFthe enzymatic hydrolysis and the fermentation are executedat the same time at an intermediate temperatureThis strategyhelps to reduce processing times sugar inhibition andequipment cost since only one vessel is needed [78] Themajor problem is that the temperature is not optimal for theenzymes and sometimes for the microorganisms (the use ofmicroorganisms with higher optimal temperature solves thislast problem)

A way to obtain the advantages of both SHF and SSFis to include a prehydrolysis step before inoculation whichis performed at an optimal temperature for the enzymefollowed by an SSF This method is called SSSF Some ofthe advantages of using SSSF are no carbon deficiency inearly stages as presented during SSF [78] higher enzymaticactivity during prehydrolysis because of optimal enzymetemperature and reduction of slurry viscosity which enableshigher solid loadings and easier stirring and pumping [79]

4 Results and Discussion

41 Coconut Husk Pretreatment for Bioethanol Production Astrategy to evaluate the effectiveness of a pretreatment is tocompare the composition of the biomass before and afterthe procedure This is a key parameter to know whetherthe technique removes the lignin degrades the hemicellu-lose and conserves the cellulose However since the sugarconcentration after hydrolysis depends on many factors thebiomass with the most changes will not yield necessary thehighest sugar turnout Therefore both the coconut huskcomposition after pretreatment and the sugar concentrationafter hydrolysis should be taken into account in any study

Alkaline pretreatment seems to be the best approachto obtain sugars from coconut husk probably because ithelps to remove the lignin from the substrate The results ofdelignification with NaOH are reported by Goncalves et al[33] and Jannah and Asip [28] As for hemicellulose contenttwo studies show an increase [27 29] while other two showa decrease [33 49] This is probably due to the conditions

used on each work The highest increase in cellulose contentwas observed by Goncalves et al [33] and Cabral et al [49]Of the studies with composition analysis after pretreatmentGoncalves et al [33] obtained the best results using NaOHpretreatment with high cellulose increase and high delig-nification On the other hand Vaithanomsat et al [27] andda Costa Nogueira et al [29] observed only a small increasein cellulose content and delignification in comparison withother methods

Also the studies that presented highest sugar concentra-tions after hydrolysis used alkaline pretreatment with NaOH(the results will be discussed in the hydrolysis section) [27ndash29 48 50] It was observed that higherNaOHconcentrationstemperature and processing time produce more inhibitorswhich may affect the next steps of the process [33 48]

Soares et al [50] selected mild alkaline conditions (1NaOH (wv) room temperature and shorter reaction time)to decrease the formation of inhibitors They also proposedno detoxification of the pretreated biomass and the useof high-solid loadings (18 (wv)) which improved sugarrelease over most of the other studies and consequentlyethanol concentration In a later study Soares et al [48] usedthe same mild conditions but did a fed-batch pretreatmentand saccharification increasing the solid loadings to 25 and30 (wv) which increased the final sugar and ethanolconcentration However rising the solids loading up to 30also led to a diminution in the yield (g ethanolg sugar) butalso showed one of highest sugar concentrations

The use of high-solid loadings (ge 15 solids (wv))during the pretreatment andor hydrolysis stages bringseconomic benefits such as less energy consumption duringthe processes including distillation and use of smaller vesselsand equipment which translates to lower capital cost [80]Unfortunately it also implies many setbacks including ahigher concentration of inhibitors mass transfer limitationsand reduction of ethanol yield as solid loadings rise [80 81]As solid loadings increase free water decreases and viscosityrises as a result there is a reduction in the effectivenessof the pretreatment and enzymatic efficiency because ofpoor diffusion and solubilization [80ndash83] High viscosity alsobrings handling problems as mixing pumping and pouringbecome harder [82]There are different approaches to reduceviscosity such as the use of surfactants [84] and employinga fed-batch process which unfortunately shows a decline inconversion whenmore solids are introduced [81] as observedby Soares et al [48]

DaCostaNogueira et al [29] compared alkaline acid andautohydrolysis pretreatments and the alkaline pretreatmentshowed the highest final sugars concentration The composi-tion of the husk was almost unchanged by the autohydrolysispretreatment and the composition after acid pretreatmentwas not shown They also showed that adding Tween80 during alkaline pretreatment can increase final sugarsconcentration by obtaining a higher digestibility during theenzymatic hydrolysis but no difference was seen when acidand autohydrolysis pretreatments were performed with orwithout the surfactant [29]

Ding et al [53] showed best results for microwave-assisted-alkaline pretreatment followed by alkaline then


acid and lastly autohydrolysis Unfortunately all pretreat-ments in this study led to a low sugars concentrationThe delignification obtained by microwave-assisted-alkalinepretreatment was significant and led to a significant increasein cellulose and hemicellulose concentration Other worksthat used autohydrolysis also obtained better results usingother pretreatments [29 32]

The studies that usedH2O2in alkaline conditions showed

a large difference in the sugars concentration This mightbe due to the delignification with NaOH performed byGoncalves et al [31] after the pretreatment which resultedin higher delignification and increased cellulose and sugarconcentration relative to the values reported by de Araujo etal [51]

On the other hand it was observed that dilute acidpretreatment is not the best strategy for obtaining sugarsfrom green coconut fibers [29] A possible explanation fordilute acid pretreatment not being the best strategy forobtaining sugars from green coconut fibers is that coconuthusk has a high lignin content Studies have shown thatacidic pretreatment at high temperature forms lignin dropletsthat adhere to the biomass interfering with the enzymatichydrolysis [85] De Araujo et al [51] reported no significantremoval of lignin using acid pretreatment followed by analkaline treatment at high temperature which agrees with thelow delignification reported by Fatmawati and Agustriyanto[47]

Another interesting pretreatment proposed by Goncalveset al [30] for coconut husk is the use of oxidative conditions(NaClO

2- C2H4O2) for delignification and autohydrolysis

for hemicellulose removal The authors obtained a highsugar content after hydrolysis a high delignification and areduction of hemicellulose as desired but most lignin wasconserved In terms of lignin removal and cellulose increasetheir results are similar to those of Goncalves et al [33]with NaOH at high temperature but they also obtained ahigher hemicellulose eliminationThey also reported a higherdifference in crystallinity than in other studies [29 31ndash33]

42 Inhibitors of the Enzymatic Hydrolysis and Fermen-tation The main inhibitors found in pretreated coconuthusk are HFM furfural phenolic compounds formic acidand acetic acid the last one in the highest concentrations(Table 2) [29 33 46 48ndash50] Soares et al [50] showed arelationship between an increase in NaOH concentrationin the pretreatment and the inhibitor concentration Afteralkaline pretreatment acetic and formic acids and phenoliccompounds are themain inhibitors produced but noHMForfurfural were detected [29 50] On the other hand Goncalveset al [33] showed a rise of HMF furfural and total phenoliccompounds with increasing pHThese differences seen in theinhibitors found are due to differences in the pretreatmentAlso pretreated coconut husks that still have solid albumenpresent very high levels of fatty acids that act as stronginhibitors [48]

43 Hydrolysis Table 3 presents a compilation of theresults published so far As it can be observed each workuses a different approach making it difficult to determine

the best methodology for enzymatic hydrolysis Differentpretreatments (which affect the type and concentrationof inhibitors) amount of total solid loadings and typeof enzymatic cocktail and doses are used in each study(Table 3) Nevertheless it is expected that the enzymatichydrolysis efficiency will be affected by the pretreatmentmethod It has been shown that mature coconut fiber hasthe highest enzymatic conversion yield after NaOH pre-treatment at high temperatures (9072)[33] followed byautohydrolysis pretreatment (8410) [32] and at last thealkaline hydrogen peroxide pretreatment with a posteriorNaOH delignification (7621) (Table 3)[31] Interestinglythe highest glucose concentration was reported for thepretreatment with the lowest hydrolysis yield [31] and thelowest glucose concentration was determined for the pre-treatment with the highest yield [33] (Table 3) This mightbe explained by a difference in initial cellulose compositionfor the enzymatic hydrolysis after the pretreatment and bythe cellobiose concentration after hydrolysis which is notreported

There are also differences in the enzymatic performancedepending on the severity of the pretreatment conditions Forexample coconut husk pretreated with 4 (wv) NaOH giveslower sugar titers than with 1 (wv) NaOHdue to enzymaticinhibition Also the longer the pretreatment the lowest thefinal sugar concentration [50]

Other factors might also influence enzymatic activity Asan example Albuquerque et al [46] used different hydrostaticpressures to improve the performance of fungi cellulasesisolated from coconut husk in comparison to industrialcellulases Actually coconut fungi cellulases displayed betterenzymatic activity on filter paper and on coconut huskhydrolysis than commercial cellulases at atmospheric pres-sure and at 300MPaThese findings show that isolating nativestrains from the biomass can lead to highly specific cellulaseswhich lead to better results than commercial enzymesThey also demonstrated that high pressure can be used aspretreatment of cellulosic fibers as it promoted ruptures inthe coconut fibers that helped in the later saccharificationprocess High hydrostatic pressure establishes interestingphysical and consequently biological changes that can be usedin biomass pretreatment and fermentation areas on biofuelssynthesis and in the use of residual lignocellulosic materialswith greater efficiency

In the end themain objective is to have the highest sugarsconcentration with the highest conversion yield possibleSome authors report very low total reducing sugars afterhydrolysis of coconut husk like Fatmawati and Agustriyanto(12 gsdotLminus1) [47] andDing et al (28 gsdotLminus1) [53] (Table 3) whichare far from the 8 (ww) of glucose minimum requiredto make the distillation economical [81] Nevertheless threestudies achieved over 8 (ww) of sugars and all of themused alkaline pretreatment [28 48 50] While two of thestudies used enzymatic hydrolysis [48 50] Jannah andAsip [28] performed an acid hydrolysis showing the highestsugars concentration with 4 (vw) sulfuric acid but noinformation about inhibitors was reported (Table 3) Soares etal [48] reached the highest sugars concentration using high-solids loadings in a fed-batch pretreatment and enzymatic


Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra

te)minus1and15IUsdot(g

substrate)minus1

50∘C

140r

pm72h

pH48

TS5

228gglucosesdotLminus1

SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g

substrate)minus1and130I

Usdot(g

substra

te)minus1

30∘C

48hTS

4

Aprox19gglucosesdotLminus1lowast

SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon

osaccharidessdot(100

gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap

rox16gglucosesdotLminus1lowast

SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g

substrate)minus1and100XUsdot(g

substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g

substrate)minus1and100FX

Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g

substrate)minus1and40

IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)


saccharification but they also observed a decrease of theconversion yield which is characteristic of this kind ofconditions

As for the use of surfactants to enhance hydrolysis daCosta Nogueira et al [29] only obtained higher digestibilitywhen using Tween 80 during the alkaline pretreatmentwhereas de Araujo et al [51] found that adding rhamnolipidsduring hydrolysis improved cellulose conversion Comparingboth studies da Costa Nogueira et al [29] showed a higherhydrolysis yield in all conditions presenting the best resultsfor the coconut husk pretreated with NaOH and Tween 80

While using subcritical water hydrolysis Prado et al[61] obtained best results at 250∘C and 20MPa but observedan increase in the concentration of inhibitors (HMF andfurfural) relative to processes at lower temperatures whereonly hemicellulose is degraded In this study three differentsubstrates were used and the results showed that coconuthusk and palm fiber have similar final sugars concentrations(117 and 119 respectively) but a defatted grape seed dis-plays a much lower concentration (64) On the other handusing CO

2during the subcritical water hydrolysis resulted

in a lower concentration of monosaccharides for coconuthusk [62] which is detrimental for ethanol production Theadvantages of subcritical water hydrolysis are the absence ofpolluting reagents a reduction of process steps no corro-sion less residue generation and lower sugar degradation[61] As a downside high temperature and pressure arenecessary

Up to now enzymatic hydrolysis has been the preferredmethod for coconut husk hydrolysis but after reviewing allresults it is evident that further investigation of the use ofacid hydrolysis is necessary An important factor that mustbe taken in account is the concentration of inhibitors afteracid hydrolysis It must be observed that the substances thatare considered inhibitors of enzymatic hydrolysis may notbe important in the case of acid hydrolysis if they do notaffect the fermentation process Measuring the concentrationof other sugars would also be interesting to evaluate thereal potential of acid hydrolysis compared to enzymatichydrolysis Other factors to take into account are the costsand the handling complexity of the process of acid hydrolysisincluding corrosion due to acid conditions

44 Fermentation Results on which hydrolysis and fermen-tation approach is best for ethanol production differ as itis affected by many factors such as the enzymatic loadingused substrate solid loadings pretreatment inhibitors themicroorganism used and prehydrolysis time in SSSF [78]

Ebrahimi et al [54] used a SSF approach and obtaineda much higher ethanol concentration (similar to Goncalveset al [31]) when using acidified aqueous glycerol comparedto the just aqueous glycerol (Table 4) Goncalves et al[31ndash33] compared SSF and SSSF for different pretreatmentswith coconut husk using three microorganisms In all threestudies SSSF presented higher ethanol yield final sugarsconcentration and productivity (Table 4) They also provedthat S cerevisiae P stipitis and Z mobilis are suitable forfermenting the coconut husk hydrolysates showing similarsugar consumption patterns and kinetic parameters (ethanol

yield concentration and productivity) for each separatepretreatment For sequential alkaline hydrogen peroxide-sodium hydroxide [31] and autohydrolysis [32] pretreat-ments P stipitis showed slightly higher ethanol concentrationand ethanol productivity than the other microorganismsbut the ethanol yield was a bit lower The highest ethanolconcentrations (11-12 gsdotLminus1) yield (84-92) and productivity(023-032) for all strains were achieved with the NaOH pre-treatment using high temperature with very little differencesbetween microorganisms [33] It is important to point outthat the sugars concentration after hydrolysis reported onTable 3 for these three studies might not be of the same quan-tity as the one produced by SSF and SSSF asmany interactionsmodify the enzymatic activity so direct comparison of theethanol producedwith the glucose concentration obtained byhydrolysis is not recommended

Soares et al [50] compared ethanol production of coconuthusk hydrolysate with two different S cerevisiae strains acommercial strain Ethanol Red and a genetically modifiedstrain GSE16-T18 This engineered strain can ferment xyloseand resists fermentation inhibitors leading to enhancedethanol production (Table 4)

Once again the largest concentrations of ethanol wereobtained in processes that used alkaline pretreatment andused SFH [28 48 50] but only two [28 48] are above the4 (ww) considered as theminimumethanol concentrationfor an economically feasible production [81] Soares et al[48] obtained the highest sugars concentration using a fed-batch pretreatment and hydrolysis approach but the ethanolconcentration was smaller than that obtained by Jannahand Asip [28] This is probably due to the fact that thesugars concentration reported by Jannah and Asip [28] isjust glucose while Soares et al [48] used the total sugarsconcentration This shows the importance of the way dataare presented since Jannah and Asip [28] are probablypresenting less sugars than the ones that can be fermentedand Soares et al [48 50] are showing a mix of sugars thatmay include some that are nonfermentable The best way toreport sugar concentration would be by showing separatelythe concentration of glucose since it is the main sugarin the liquor and that of total fermentable sugars (whichvaries depending on the microorganism used) Soares et al[48 50] determine ethanol yield based on the concentrationof fermentable sugars while Jannah and Asip [28] do notcalculate the conversion yield For coconut husk all reportedethanol yields are based on the relationship between themass of ethanol produced divided by the mass of fermentablesugars detected by HPLC ignoring the ambiguity of usingtotal reducing sugars as a parameter [27 31ndash33 50] TRS is theeasiest way to measure sugars but includes nonfermentablesugars making it difficult to compare different processes andto evaluate the real efficiency of fermentation

Vaithanomsat et al [27] and Cabral et al [49] showed aninitial sugar concentration for fermentation higher than thatreported after hydrolysis with no further explanation on howthat increase occurred

Currently the use of genetically modified organismsand the use of microorganisms other than Saccharomycescerevisiae or a mix of them (coculture) have been scarcely


Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip

itis1017gsdotLminus1

Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1

Zmobilis730gsdotLminus1

Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of

initialglucoseinstead

ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d


studied in the case of ethanol made from coconut husk Sincethis biomass has a high hemicellulose content the use ofmicroorganisms that are able to ferment pentoses may helpto increase the ethanol production

45 Comparison with Other Biomasses Bioethanol produc-tion conditions analyzed in studies similar to the present one(where various works about a biomass are compared) but forsugarcane bagasse [86 87] wheat straw [88] and corn stover[89] were examined

Zhao et al [89] did a profound analysis of the literaturefor articles published during the last 10 years that usedcorn stover as a raw material for bioethanol productionBy analyzing a high number of works on the subject (474)they were able to draw some conclusions that are hard todo when analyzing a much smaller sample and confirmedsome of the observations obtained on this study Regardingthe pretreatment they saw that two-thirds of the papersused acid steam explosion ammonia-based and alkalineprocesses In the beginning acid and steam explosionwere themost popular but their use is declining while solvent-basedand combined techniques are gaining ground Comparedto coconut husk which presented best results with alkalinepretreatment corn stover showed highest ethanol productionwith alkaline solvents and ammonia pretreatment (19-22)and lowest with fungi (11) This low effectiveness withbiological pretreatment was also reported for sugarcanebagasse [86]

The best results found by Cardona et al [86] in 2010 forsugarcane bagasse were using acid hydrolysis (48 (ww)TRS and 19 g etanolsdotLminus1) but Bezerra and Ragauskas [87] in2016 found the highest sugar and concentration with steamexplosion (577 g glucosesdotLminus1 and 256 g ethanolsdotLminus1) EventhoughCardona et al [86] saw ahigher glucose concentrationwhen using alkaline pretreatment they argue that costs aretoo high for the process to be viable at large scale Talebniaet al [88] reported steam explosion as the most suitablepretreatment for wheat straw because it has a lower reactiontime higher solid loadings and aminimumuse of chemicalsThe best results for wheat straw were obtained with nativenon-adapted S cerevisiae (312 g ethanolsdotkgminus1 99 ethanolyield)

As pointed out in this study for coconut husk Zhao et al[89] also remarks that most of the studies for corn stover arefocused on the pretreatment Fermentation is only reportedin half of the studies and most use yeasts (92) and the restbacteria (8) Also purification is usually not described andwhen it is they mostly use distillation

Equal to the findings for coconut husk enzymatic hydrol-ysis is used in most of the studies [86ndash89] Zhao et al [89]report that 95 of the articles for corn stover used enzymatichydrolysis and as also seen on this work the enzyme dosesdiffer significantly from study to study

Parallel to the findings of this study Zhao et al [89]confirm that ethanol production varies greatly from onestudy to another even when using similar processes Forcorn stover ethanol conversion for most studies rangedbetween 80 and 100 with no significant difference while

using different microorganisms for fermentation [89] Theyalso observed that xylose fermentation was a key factor forhigher ethanol production confirming the importance of notextracting the hemicellulose for fermentation and the need touse microorganisms that can ferment these sugars

Most studies analyzed for this kind of technology aredone in laboratory scale (98 for corn stover [89]) includingcoconut husk Zhao et al [89] observed that in the caseof corn stover some pilot scale processes used smallerconcentrations of chemicals than the concentration used inlaboratory studies No full scale plants for this kind of workare reported on the articles analyzed [86ndash89]This is probablybecause it is not in the interest of industry to report its know-how and results

46 Techno-Economic Overview on Bioethanol ProductionSince there are no published data on the costs of bioethanolproduction from coconut husk an extrapolation based onresults from other biomasses was performed Most of thetechno-economic analyses on the production of biofuels weresimulations for a few lignocellulosic feedstock pretreatmentsand enzymatic hydrolysis [19 90ndash94] Eggeman and Elander[90] made the economic analysis using different pretreat-ments for corn stover and found a similar minimum ethanolselling prices (MESPs) using dilute acid hot water ammoniafiber explosion (AFEX) ammonia recycle percolation (ARP)and lime pretreatments Similar results were found by da Silvaet al [19] for hot water and AFEX pretreatment but a higherMESP was obtained using dilute acid pretreatment On theother hand Chovau et al [92] find dilute acid pretreatmentas the best option

The main factors that affect the MESP are plant size[91 95] feedstock price and transportation [91 93 95ndash98]composition of the feedstock [91] pretreatment [94] enzymecost and loading [91 93 96ndash98] conversion from cellulose toglucose [91 93] ethanol yield [95] fermentation of pentoses[93] investment costs [93 95] and energy cost [96ndash98]Ethanol yield is relevant since a higher yield means that lessfeedstock is required and overhead costs are smaller [95]

The MESP is also significantly affected by the locationof the production not only due to the availability priceand transportation cost of the feedstock but because ofthe local technology the cost of raw material (especiallyenzyme) the cost of energy and the local policies Zhao et al[93] compared the MESP of a process using the technologyavailable in China which included using local enzymes withlower activity so that higher loadings were needed and onlyhexoses were fermented and technology from the UnitedStates of America using economic parameters from ChinaThey observed that the MESP for their process with Chinesetechnology was above the local price of fuel ethanol while theMESP obtained using more advanced technology was lowerthan the local price of fuel ethanol

As observed by Chouvau et al [92] the MESP reportedby different authors varies greatly (from $021L to $121L)according to the assumptions involved Most authors use afuture expected cost for the enzymes that is much lower thanthe present cost and leads to a significant decrease of MESP[90ndash92] Chovau et al [92] observed an increase in reported


MESP with higher enzyme cost when comparing variousstudiesThey also estimated from these studies that about 13of the MESP is due to enzyme cost Some studies proposeproducing enzymes at the plant [92 95] but Chovau et al[92] reported higher costs for enzymes produced in-site dueto energy consumption higher investment and lower plantcapacity As an alternative to enzymeuse acid hydrolysismaybe used but recycling of acid is expensive and rises the costs[95]

Feedstock price also greatly affects the MESP represent-ing between 30 and 40 of it [92] Corn stover price includesthe grower payment which is a compensation to the farmerfor the fertilizers that he will use to recover the nutrients thatwould have been obtained from decomposition of the cornstover on the field [92]This makes corn stover expensive andits price can vary greatly as fertilizer prices change annuallyand regionally In addition to reduce the transportation costwhich is significant the plant has to be close to the sourceSince feedstock price has a large impact on the MESP itis important to use a realistic approach to this item whenperforming an economic simulation

Macrelli et al [97] studied the costs of using sugarcaneto produce 1G and 2G (bagasse and leaves) in the same plantusing steampretreatment and enzymatic hydrolysis By doingso they achieved a lower MESP than when producing just2G ethanol This kind of scheme is already used by Raızenas they produce sugar and later use the bagasse to produce2G ethanol [11] Therefore they use the whole sugarcane andthey do not have the extra transportation cost that most 2Gethanol plants have

Duque et al [98] andQuintero et al [99]made an analysisusingAspen Plus for plants using agricultural residues fromColombia using acid pretreatment enzymatic hydrolysis andpurification Quintero et al [99] added an energy generationfacility powered mostly by lignin while Duque et al [98] didnot include any heat exchange networks Later Duque et al[98] proposed to add such facility as their utilities represented453 of the variable cost Quintero et al [99] also showthe importance of including an energy generation system bycomparing the MESP with and without this system Theyobtained a lowerMESP for all the biomasses when generatingtheir own energy

5 Future Perspectives

Bioethanol production from coconut husk might be a wayto benefit rural development as it is mainly obtained bysmall producers This way producers or cooperatives inrural areas might obtain a fuel for personal use enhancingenergy security [1] and reducing waste volume hence theenvironmental impact that the husks discarding brings Inorder to make this possible it is crucial to have a simple andlow-cost process by developing an appropriate pretreatmentand access to cheaper enzymes Since coconut husk is anagroindustrial residue it should enhance competitivenessand social acceptance [8] as well as not presenting the ethicalissue found when food crops are used to produce biofuels

Producing bioethanol from coconut husk still has manychallenges starting from the low concentration of sugars

achieved in most of the studies less than the 8 (ww) ofglucose needed to get a minimum of 4 (ww) of ethanolto have an economically viable process [81] After surpassingthese sugar and ethanol concentrations the scale-up of theprocessmust be donewhere new challenges await such as thedecrease of sugar and ethanol yield due to physical differencesbetween scales [100 101] along with other technical andfinancial issues that may arise

For now most of the studies for bioethanol produc-tion from coconut husk have focused on the pretreatmentand hydrolysis steps less than half of the articles haveaddressed the fermentation to ethanol It is important toinclude fermentation data because even hydrolysates withhigh sugar concentration may present problems when put tofermentation due to the presence of inhibitors

It would be helpful to standardize the way research dataare reported in order to facilitate the comparison of differentprocesses and steps but this is not always possible In thecase of the pretreatment step one should include the biomasscomposition before and after pretreatment As for the hydrol-ysis as commented before stating the glucose concentrationin the hydrolysate as well as the total fermentable sugarsthat can be consumed by the microorganism used wouldhelp to determine the effectiveness of the hydrolysis and thefermentation Stating the ethanol yield based on fermentablesugars also helps to compare the fermentation with otherstudies andmay be useful to alert to a possible problemdue toinhibitors It is always helpful to report the concentration ofinhibitors to determine if the simple sugars are being furtherdegraded Moreover it is important to report the amount ofsugar and ethanol obtained from a given mass of coconuthusk so that the efficiency of the process may be determined

Nowadays the most economical way to produce 2Gbioethanol is the biorefinery scheme which is importantfor strengthening and supporting the growing biobasedeconomy

51 Biorefinery The world is entering a new scenariowhere many countries are taking substantial steps towardsa biobased economy New bioproducts are beginning toreplace fossil based products greenhouse gas emissions aredecreasing and innovative policies are emerging to supportthese changes [102] To establish the foundation of a biobasedeconomy the use of biomass resources must be efficient andsustainableThat goal can be achieved by biorefinery systems

In an energy driven biorefinery system the biomass isprimarily used to produce energy (biofuel power andorheat) and other byproducts are upgraded to more added-value products to optimize the economic and ecological per-formance of the whole production process [103] Larragoiti-Kuri et al [104] propose a biorefinery using corn cob asa substrate that produces bioethanol and lactic acid fromthe cellulose fraction xylitol and succinic acid from xylose(hemicellulose) and lignosulfonates from lignin They opti-mized product distribution by using economic potentialspecific energy intensity and safety indexes as criteria

Advances in biorefineries allow the development ofalternative products to avoid the accumulation of differentresidues (Figure 3) As an example 13-propanediol obtained


Cellulose

C5 andC6 carbons

Lignocellulosic Hemicellulosebiomass

Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products

Butanol ethanol and methanol

Alanine aspartic acid glutamc acid glycine lysineproline serine and threonine

Acetic acid aconitic acid adipic acid ascorbic acid citric acidformic acid fumaric acid glutaric acid 3 hydroxypropionic

acid itaconic acid lactic acid levulinic acid malic acidmalonic acid oxalic acid propionic acid and succinic acid

Glucaric acid and xylonic acid

Arabinitol sorbitol and xylitol

Acetaldehyde acetic anhydride acetoin acetone ethyleneglycol ethylene oxide 25 furan dicarboxylic acid furfural

glycerol 3-hydroxybutyrolactone and levoglucosan

Benzene phenol toluene xylene phenolic acids catechols vanillin vanillicacid cinnamic acid benzoic acid and syringaldehyde

Adsorbents carbon fiber dimethylsulfoxide (DMSO) food additive fuel by pyrolysis orgasification lignosulfonates polymer modifiers adhesives and resins

Figure 3 Possible products obtained in a biorefinery [36ndash38]

from maize residues is important in the formation of poly-mers Also succinic acid removed from various lignocellu-losic residues is used in the chemical and pharmaceuticalindustries An important alternative to polyethylene is the useof ether amylose derived from various wastes such as sugar-cane potato and corn [105ndash108] From an economic pointof view Gnansounou and Dauriat [95] propose producinga lower diversity of products with stable markets instead ofoffering a larger number of products some of which may beunprofitable

Up to now all studies of the use of coconut husk forbioethanol production have been made in a small scale andonly three studies mention the use of coconut husk as sub-strate for a biorefinery [30 32 33] These works only discussthe possibility of using byproducts of ethanol production toobtain other substances but no tests to obtain other productshave been reported Goncalves et al [33] only suggestedthe use of sugars acetic acid phenolic compounds andlignin found in the coconut hydrolysate to obtain differentproducts using a biorefinery scheme with no further detailLater Goncalves et al [30] proposed using their processto make ethanol from coconut husk to obtain also value-added products They propose that the phenolic compoundsobtained during pretreatment and autohydrolysis be usedas food additives since they are antioxidants while lignincan be used to produce pharmaceutical and veterinarianbioactive compounds and thermoplastic polymers as well as

for energy production through gasification or pyrolysisTheyalso suggest that xylans obtained fromhemicellulose undergoanother autohydrolysis to obtain xylooligosaccharide that canbe employed in food and pet feed They suggest that othersubstances present in the liquors can be used to obtain furtherproducts but no specific applications are mentioned On theother hand studies not focused on ethanol production showthe potential of coconut husks to produce furfural levulinicacid formic acid and acetic acid [109 110]

Other applications for coconut husks different fromethanol production andpossible byproductswere found suchas polymer composites [111 112] and adsorbents to remove awide range of water pollutants [113] As the focus of this workis ethanol production further studies should be made to seeif the biomass remaining after the chosen process to obtainethanol can still be used for these purposes and analyze if thisstrategy is economically viable

6 Conclusion

Lignocellulosic ethanol production is a multistep processwith many factors that can greatly affect its efficiency Thepublished coconut husk studies were performed in differentconditions throughout the ethanol production process so itis important to analyze various parameters to define whichprocedure as a whole has the best resultsThe final objective is


to obtain the highest ethanol concentration permass of initialsubstrate for the lowest price which translates to simplerprocesses with less energy consumption (lower temperaturepressure and process time) and less reagents that at the sametime have to be low-cost

Using the concentration of sugars after hydrolysis asa comparison parameter to determine the best method toproduce bioethanol is not the best strategy since studies thatuse SSF and SSSF do not show the obtained sugars becausethey are consumed as they are produced Additionally mostof the works report sugars concentration as total reducingsugars but not all these sugars are fermentable so estimatesof ethanol production may not reflect reality On the otherhand ethanol yield is related to the transformation of thosesugars into ethanol so comparing these results reflects theability of the microorganism to ferment the sugars that arepresent in the hydrolysate This study showed that alkalinepretreatment is the best method in the case of coconut huskThe highest ethanol yields using coconut husk as a substratewere obtained by Goncalves et al [33] using SSSF Thehighest ethanol concentration was obtained by Jannah andAsip [28] using an alkaline pretreatment and acid hydrolysisachieving yields above the 4 (ww) of ethanol required foran economically feasible distillation

Finally the most significant coconut producers are eco-nomically developing nations and the industrial residuesgenerated by this culture impose a serious environmentalproblem Biorefining this material for the production ofethanol and other molecules with greater added value wouldenable these countries to create new jobs and boost income

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This work was supported by the Fundacao de Amparoa Pesquisa do Estado do Espırito Santo FAPES Grants[48497231] and [5989954912] PMB Fernandes was grantedthe research productivity award from the Conselho Nacionalde Desenvolvimento Cientıfico e Tecnologico CNPq Grant[3047192014-5] M Bolivar-Telleria C Turbay and TCarneiro acknowledge the Coordenacao deAperfeicoamentode Pessoal de Nıvel Superior CAPES and L Favaratoacknowledge CNPq for their scholarships

References

[1] L R Lynd ldquoThe grand challenge of cellulosic biofuelsrdquo NatureBiotechnology vol 35 no 10 pp 912ndash915 2017

[2] R Sims A Flammini M Puri and S Bracco ldquoOpportunitiesfor Agri-Food Chains to become Energy-Smartrdquo FAO USAID2015

[3] B Hahn-Hagerdal M E Himmel C Somerville and CWyman ldquoWelcome to Biotechnology for Biofuelsrdquo Biotechnol-ogy for Biofuels vol 1 2008

[4] R C Leite and L A B Cortez ldquoO Etanol Combustıvel noBrasilrdquo Biocombustıveis no Bras Real e Perspect Ministerio dasRelacoes Exteriores 2008

[5] M A A de Mendonca F R Edivaldo A O P Dos SantosA S Pereira and R C Da Costa ldquoExpansao da producao dealcool combustıvel no Brasil uma analise baseada nas curvas deaprendizagemrdquo in Proceedings of the 46th Congress Rio Branco Acre Brazil 2008

[6] M G da Cruz E Guerreiro and A P Raiher ldquoA Evolucaoda Producao de Etanol no Brasil no Perıodo de 1975 a 2009rdquoRevista Economica do Nordeste vol 43 no 4 pp 141ndash160 1975

[7] K Saha U M R J Sikder S Chakraborty S S da Silva andJ C dos Santos ldquoMembranes as a tool to support biorefineriesApplications in enzymatic hydrolysis fermentation and dehy-dration for bioethanol productionrdquo Renewable amp SustainableEnergy Reviews vol 74 pp 873ndash890 2017

[8] A Scoma L Bertin M A M Reis M Kornaros and MComa ldquoMultipurpose Integrated 2nd Generation Biorefiner-iesrdquo BioMed Research International vol 2016 2016

[9] M Tabatabaei K Karimi R Kumar and I S HorvathldquoRenewable Energy andAlternative Fuel TechnologiesrdquoBioMedResearch International vol 2015 Article ID 245935 2 pages2015

[10] GranBio Investimento SA ldquoGranBiordquo httpwwwgranbiocombren

[11] Raızen ldquoTecnologia em energia renovavel Etanol de segundageracaordquo httpswwwraizencombrenergia-do-futuro-tecno-logia-em-energia-renovaveletanol-de-segunda-geracao

[12] M Peplow ldquoCellulosic ethanol fights for liferdquo Nature vol 507no 7491 pp 152-153 2014

[13] UNCTAD ldquoSecond generation biofuel market State of playtrade and developing country perspectivesrdquo httpunctadorgenpagesPublicationWebflyeraspxpublicationid=1455

[14] J Lane ldquoBiofuels Mandates Around the World 2016rdquohttpwwwbiofuelsdigestcombdigest

[15] J Lane ldquoBiofuels Mandates Around the World 2017rdquohttpwwwbiofuelsdigestcom

[16] FAOSTAT ldquoCoconut production in 2013rdquo httpfaostat3faoorgbrowseQE

[17] J E G Van Dam ldquoCoir processing technologies improvementof drying softening bleaching and dyeing coir fibreyarn andprinting coir floor coveringsrdquo Common Fund Commod 2002

[18] M de Freitas F J Rosa A A T Montenegro et alldquoCaracterizacao Do Po Da Casca De Coco Verde Usado ComoSubstrato Agrıcolardquo Embrapa Agroindustria Tropical Comuni-cation Tecnicon 2001

[19] A R G da Silva C E Torres Ortega and B-G RongldquoTechno-economic analysis of different pretreatment processesfor lignocellulosic-based bioethanol productionrdquo BioresourceTechnology vol 218 pp 561ndash570 2016

[20] S Mohanram D Amat J Choudhary A Arora and LNain ldquoNovel perspectives for evolving enzyme cocktails forlignocellulose hydrolysis in biorefineriesrdquo Sustainable ChemicalProcesses vol 1 no 1 p 15 2013

[21] S H Mohd Azhar R Abdulla S A Jambo et al ldquoYeasts insustainable bioethanol production A reviewrdquo Biochemistry andBiophysics Reports vol 10 pp 52ndash61 2017

[22] L R Lynd X LiangM J Biddy et al ldquoCellulosic ethanol statusand innovationrdquo Current Opinion in Biotechnology vol 45 pp202ndash211 2017


[23] F Cherubini ldquoThe biorefinery concept Using biomass insteadof oil for producing energy and chemicalsrdquo Energy Conversionand Management vol 51 no 7 pp 1412ndash1421 2010

[24] J M NMarikkar andW SMadurapperuma ldquoCoconutrdquo Tropi-cal and Subtropical Fruits Postharvest Physiology Processing andPackaging pp 159ndash177 2012

[25] S A C N Perera H D M A C Dissanayaka H M N BHerath M G M K Meegahakumbura and L Perera ldquoQuan-titative Characterization of Nut Yield and Fruit Componentsin Indigenous Coconut Germplasm in Sri Lankardquo InternationalJournal of Biodiversity vol 2014 Article ID 740592 5 pages2014

[26] H Martins R Fontes and W M Arag120587o ldquoA Cultura doCoqueirordquo httpswwwspocnptiaembrapabr

[27] P Vaithanomsat W Apiwatanapiwat N Chumchuent WKongtud and S Sundhrarajun ldquoThe potential of coconuthusk utilization for bioethanol productionrdquo Kasetsart Journal -Natural Science vol 45 no 1 pp 159ndash164 2011

[28] AM Jannah and F Asip ldquoBioethanol production from coconutfiber using alkaline pretreatment and acid hydrolysis methodrdquoInternational Journal on Advanced Science Engineering andInformation Technology vol 5 no 5 pp 320ndash322 2015

[29] C da Costa Nogueira C E de Araujo Padilha A L deSa Leitao P M Rocha G R de Macedo and E S dosSantos ldquoEnhancing enzymatic hydrolysis of green coconutfibermdashPretreatment assisted by tween 80 and water effect onthe post-washingrdquo Industrial Crops and Products vol 112 pp734ndash740 2018

[30] F A Goncalves H A Ruiz E S Dos Santos J ATeixeira and G R de Macedo ldquoValorization Comparisonand Characterization of Coconuts Waste and Cactus in aBiorefinery Context Using NaClO2ndashC2H4O2 and SequentialNaClO2ndashC2H4O2Autohydrolysis Pretreatmentrdquo Waste andBiomass Valorization pp 1ndash14 2018

[31] F A Goncalves H A Ruiz C D C Nogueira E S D Santos JA Teixeira and G R De Macedo ldquoComparison of delignifiedcoconuts waste and cactus for fuel-ethanol production bythe simultaneous and semi-simultaneous saccharification andfermentation strategiesrdquo Fuel vol 131 pp 66ndash76 2014

[32] F A Goncalves H A Ruiz E S Dos Santos J A Teixeiraand G R De Macedo ldquoBioethanol production from coconutsand cactus pretreated by autohydrolysisrdquo Industrial Crops andProducts vol 77 pp 1ndash12 2015

[33] F A Goncalves H A Ruiz E Silvino dos Santos J ATeixeira and G R de Macedo ldquoBioethanol production by Sac-charomyces cerevisiae Pichia stipitis and Zymomonas mobilisfrom delignified coconut fibre mature and lignin extractionaccording to biorefinery conceptrdquo Journal of Renewable Energyvol 94 pp 353ndash365 2016

[34] M Taha M Foda E Shahsavari A Aburto-Medina E Ade-tutu and A Ball ldquoCommercial feasibility of lignocellulosebiodegradation Possibilities and challengesrdquo Current Opinionin Biotechnology vol 38 pp 190ndash197 2016

[35] M Wang Z Li X Fang L Wang and Y Qu ldquoCellulolyticenzyme production and enzymatic hydrolysis for second-generation bioethanol productionrdquo Advances in BiochemicalEngineeringBiotechnology vol 128 pp 1ndash24 2012

[36] T Werpy and G Petersen ldquoTop Value Added Chemicals fromBiomass Volume I ndash Results of Screening for Potential Can-didates from Sugars and Synthesis Gasrdquo Tech Rep DOEGO-102004-1992 2004

[37] J E Holladay J F White J J Bozell and D Johnson ldquoTopValue-Added Chemicals from Biomass - Volume IImdashResults ofScreening for Potential Candidates from Biorefinery LigninrdquoTech Rep PNNL-16983 2007

[38] R Arora N K Sharma and S Kumar ldquoValorization ofBy-Products Following the Biorefinery Concept Commer-cial Aspects of By-Products of Lignocellulosic Biomassrdquo inAdvances in Sugarcane Biorefinery pp 163ndash178 Elsevier 2018

[39] W M A M Anku M A Mamo and P P Govender ldquoPhe-nolic Compounds in Water Sources Reactivity Toxicity andTreatment Methodsrdquo in Phenolic Compounds inWater SourcesReactivity Toxicity and Treatment Methods Phenolic Com-pounds -Natural Sources Importance andApplications PhenolicCompounds - Natural Sources Importance and Applications2017

[40] L M Divya G K Prasanth and C Sadasivan ldquoPotential of thesalt-tolerant laccase-producing strain Trichoderma viride PersNFCCI-2745 from an estuary in the bioremediation of phenol-polluted environmentsrdquo Journal of Basic Microbiology vol 54no 6 pp 542ndash547 2014

[41] O A Carrijo R S Liz and N Makishima ldquoFibra da cascado coco verde como substrato agrıcolardquoHorticultura Brasileiravol 20 no 4 pp 533ndash535 2002

[42] S Sun S Sun X Cao and R Sun ldquoThe role of pretreatmentin improving the enzymatic hydrolysis of lignocellulosic mate-rialsrdquo Bioresource Technology vol 199 pp 49ndash58 2016

[43] M Galbe and G Zacchi ldquoPretreatment the key to efficientutilization of lignocellulosic materialsrdquo Biomass amp Bioenergyvol 46 pp 70ndash78 2012

[44] N Sarkar S K Ghosh S Bannerjee and K Aikat ldquoBioethanolproduction from agricultural wastes an overviewrdquo Journal ofRenewable Energy vol 37 no 1 pp 19ndash27 2012

[45] Y Sun and J Cheng ldquoHydrolysis of lignocellulosic materials forethanol production a reviewrdquo Bioresource Technology vol 83no 1 pp 1ndash11 2002

[46] E D Albuquerque F A G Torres A A R Fernandes and PMB Fernandes ldquoCombined effects of high hydrostatic pressureand specific fungal cellulase improve coconut husk hydrolysisrdquoProcess Biochemistry vol 51 no 11 pp 1767ndash1775 2016

[47] A Fatmawati and R Agustriyanto ldquoKinetic study of enzymatichydrolysis of acid-pretreated coconut coirrdquo in Proceedings of the2nd International Conference of Chemical and Material Engi-neering Green Technology for Sustainable Chemical Productsand Processes ICCME 2015 Indonesia September 2015

[48] J Soares M M Demeke M Van de Velde et al ldquoFed-batch production of green coconut hydrolysates for high-gravity second-generation bioethanol fermentation with cellu-losic yeastrdquo Bioresource Technology vol 244 pp 234ndash242 2017

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[52] T-Y Ding S-L Hii L-G-A Ong and T-C Ling ldquoInvesti-gating the Potential of Using Coconut Husk as Substrate for


Bioethanol Productionrdquo in Proceedings of the 2011 InternationalConference on Biotechnology and Environment Management(ICBEM 2011) Singapore 2011

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[54] M Ebrahimi A R Caparanga E E Ordono and O B Villaflo-res ldquoEvaluation of organosolv pretreatment on the enzymaticdigestibility of coconut coir fibers and bioethanol productionvia simultaneous saccharification and fermentationrdquo Journal ofRenewable Energy vol 109 pp 41ndash48 2017

[55] Y Yu X Lou and H Wu ldquoSome recent advances in hydrolysisof biomass in hot-compressed water and its comparisons withother hydrolysis methodsrdquo Energyamp Fuels vol 22 no 1 pp 46ndash60 2008

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[57] I S Druzhinina and C P Kubicek ldquoGenetic engineering ofTrichoderma reesei cellulases and their productionrdquo MicrobialBiotechnology vol 10 no 6 pp 1485ndash1499 2017

[58] AVGusakov ldquoCellulases andhemicellulases in the 21st centuryrace for cellulosic ethanolrdquo Biofuels vol 4 no 6 pp 567ndash5692013

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[60] J Zhuang M A Marchant S E Nokes and H J StrobelldquoEconomic Analysis of Cellulase Production Methods for Bio-Ethanolrdquo Applied Engineering in Agriculture vol 23 no 5 pp679ndash687 2007

[61] J M Prado T Forster-Carneiro M A Rostagno L AFollegatti-Romero F Maugeri Filho and M A A MeirelesldquoObtaining sugars from coconut husk defatted grape seed andpressed palm fiber by hydrolysis with subcritical waterrdquo TheJournal of Supercritical Fluids vol 89 pp 89ndash98 2014

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[66] N Fu and P Peiris ldquoCo-fermentation of a mixture of glucoseand xylose to ethanol by Zymomonas mobilis and PachysolentannophilusrdquoWorld Journal of Microbiology and Biotechnologyvol 24 no 7 pp 1091ndash1097 2008

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[68] MM Demeke F Dumortier Y Li T Broeckx M R Foulquie-Moreno and J M Thevelein ldquoCombining inhibitor toleranceand D-xylose fermentation in industrial Saccharomyces cere-visiae for efficient lignocellulose-based bioethanol productionrdquoBiotechnology for Biofuels vol 6 no 1 2013

[69] TW Jeffries and Y-S Jin ldquoMetabolic engineering for improvedfermentation of pentoses by yeastsrdquo Applied Microbiology andBiotechnology vol 63 no 5 pp 495ndash509 2004

[70] Y Kobayashi T Sahara T Suzuki et al ldquoGenetic improvementof xylose metabolism by enhancing the expression of pentosephosphate pathway genes in Saccharomyces cerevisiae IR-2for high-temperature ethanol productionrdquo Journal of IndustrialMicrobiology and Biotechnology vol 44 no 6 pp 879ndash891 2017

[71] J G Nijland E Vos H Y Shin P P DeWaal P Klaassen andAJ M Driessen ldquoImproving pentose fermentation by preventingubiquitination of hexose transporters in Saccharomyces cere-visiaerdquo Biotechnology for Biofuels vol 9 no 1 2016

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[73] H Valadi C Larsson and L Gustafsson ldquoImproved ethanolproduction by glycerol-3-phosphate dehydrogenase mutants ofSaccharomyces cerevisiaerdquo Applied Microbiology and Biotech-nology vol 50 no 4 pp 434ndash439 1998

[74] C Navarrete J Nielsen and V Siewers ldquoEnhanced ethanolproduction and reduced glycerol formation in fps1998779 mutantsof Saccharomyces cerevisiae engineered for improved redoxbalancingrdquo AMB Express vol 4 no 1 pp 1ndash8 2014

[75] W YeW Zhang T Liu G Tan H Li and Z Huang ldquoImprove-ment of Ethanol Production in Saccharomyces cerevisiae byHigh-Efficient Disruption of the ADH2 Gene Using a NovelRecombinant TALEN Vectorrdquo Frontiers in Microbiology vol 72016

[76] T-S Cao Z Chi G-L Liu and Z-M Chi ldquoExpression of TPS1gene from Saccharomycopsis fibuligera A11 in Saccharomycessp W0 enhances trehalose accumulation ethanol toleranceand ethanol productionrdquo Molecular Biotechnology vol 56 no1 pp 72ndash78 2014

[77] Z Qiu and R Jiang ldquoImproving Saccharomyces cerevisiaeethanol production and tolerance via RNA polymerase IIsubunit Rpb7rdquo Biotechnology for Biofuels vol 10 no 1 2017

[78] L Paulova P Patakova M Rychtera and K Melzoch ldquoHighsolid fed-batch SSF with delayed inoculation for improvedproduction of bioethanol from wheat strawrdquo Fuel vol 122 pp294ndash300 2014

[79] K Ohgren J Vehmaanpera M Siika-Aho M Galbe L Viikariand G Zacchi ldquoHigh temperature enzymatic prehydrolysisprior to simultaneous saccharification and fermentation ofsteam pretreated corn stover for ethanol productionrdquo Enzymeand Microbial Technology vol 40 no 4 pp 607ndash613 2007

[80] A A Modenbach and S E Nokes ldquoThe use of high-solidsloadings in biomass pretreatment-a reviewrdquo Biotechnology andBioengineering vol 109 no 6 pp 1430ndash1442 2012

[81] A A Modenbach and S E Nokes ldquoEnzymatic hydrolysisof biomass at high-solids loadings - A reviewrdquo Biomass ampBioenergy vol 56 pp 526ndash544 2013

[82] H Joslashrgensen J B Kristensen and C Felby ldquoEnzymatic conver-sion of lignocellulose into fermentable sugars challenges andopportunitiesrdquo Biofuels Bioproducts and Biorefining vol 1 no2 pp 119ndash134 2007


[83] J B Kristensen C Felby and H Joslashrgensen ldquoYield-determiningfactors in high-solids enzymatic hydrolysis of lignocelluloserdquoBiotechnology for Biofuels vol 2 article 11 2009

[84] X Ma G Yue J Yu X Zhang and T Tan ldquoEnzymatichydrolysis of cassava bagasse with high solid loadingrdquo Journalof Biobased Materials and Bioenergy vol 5 no 2 pp 275ndash2812011

[85] M J Selig S Viamajala S R Decker M P Tucker M EHimmel and T B Vinzant ldquoDeposition of lignin droplets pro-duced during dilute acid pretreatment of maize stems retardsenzymatic hydrolysis of celluloserdquo Biotechnology Progress vol23 no 6 pp 1333ndash1339 2007

[86] C A Cardona J A Quintero and I C Paz ldquoProduction ofbioethanol from sugarcane bagasse status and perspectivesrdquoBioresource Technology vol 101 no 13 pp 4754ndash4766 2010

[87] T L Bezerra andA J Ragauskas ldquoA review of sugarcane bagassefor second-generation bioethanol and biopower productionrdquoBiofuels Bioproducts and Biorefining vol 10 no 5 pp 634ndash6472016

[88] F Talebnia D Karakashev and I Angelidaki ldquoProduction ofbioethanol from wheat straw an overview on pretreatmenthydrolysis and fermentationrdquo Bioresource Technology vol 101no 13 pp 4744ndash4753 2010

[89] Y Zhao A Damgaard and T H Christensen ldquoBioethanol fromcorn stover ndash a review and technical assessment of alternativebiotechnologiesrdquo Progress in Energy and Combustion Sciencevol 67 pp 275ndash291 2018

[90] T Eggeman and R T Elander ldquoProcess and economic analysisof pretreatment technologiesrdquo Bioresource Technology vol 96no 18 pp 2019ndash2025 2005

[91] A Aden and T Foust ldquoTechnoeconomic analysis of the dilutesulfuric acid and enzymatic hydrolysis process for the conver-sion of corn stover to ethanolrdquo Cellulose vol 16 no 4 pp 535ndash545 2009

[92] S Chovau D Degrauwe and B Van Der Bruggen ldquoCriticalanalysis of techno-economic estimates for the production costof lignocellulosic bio-ethanolrdquo Renewable amp Sustainable EnergyReviews vol 26 pp 307ndash321 2013

[93] L Zhao X Zhang J Xu X Ou S Chang and M WuldquoTechno-economic analysis of bioethanol production fromlignocellulosic biomass in china Dilute-acid pretreatment andenzymatic hydrolysis of corn stoverrdquo Energies vol 8 no 5 pp4096ndash4117 2015

[94] H Chen and X Fu ldquoIndustrial technologies for bioethanol pro-duction from lignocellulosic biomassrdquoRenewableamp SustainableEnergy Reviews vol 57 pp 468ndash478 2016

[95] E Gnansounou and A Dauriat ldquoTechno-economic analysis oflignocellulosic ethanol A reviewrdquo Bioresource Technology vol101 no 13 pp 4980ndash4991 2010

[96] J Littlewood LWang C Turnbull and R J Murphy ldquoTechno-economic potential of bioethanol from bamboo in ChinardquoBiotechnology for Biofuels vol 6 no 1 2013

[97] S Macrelli J Mogensen and G Zacchi ldquoTechno-economicevaluation of 2nd generation bioethanol production from sugarcane bagasse and leaves integrated with the sugar-based ethanolprocessrdquo Biotechnology for Biofuels vol 5 no 1 2012

[98] S H Duque C A Cardona and J Moncada ldquoTechno-economic and environmental analysis of ethanol productionfrom 10 agroindustrial residues in Colombiardquo Energy amp Fuelsvol 29 no 2 pp 775ndash783 2015

[99] J A Quintero J Moncada and C A Cardona ldquoTechno-economic analysis of bioethanol production from lignocellu-losic residues in Colombia A process simulation approachrdquoBioresource Technology vol 139 pp 300ndash307 2013

[100] F R Schmidt ldquoOptimization and scale up of industrial fermen-tation processesrdquo Applied Microbiology and Biotechnology vol68 no 4 pp 425ndash435 2005

[101] L R Formenti A Noslashrregaard A Bolic et al ldquoChallengesin industrial fermentation technology researchrdquo BiotechnologyJournal vol 9 no 6 pp 727ndash738 2014

[102] E de Jong andG Jungmeier ldquoBiorefinery Concepts in Compar-ison to Petrochemical Refineriesrdquo Industrial Biorefineries WhiteBiotechnology p 33 2015

[103] F Cherubini G Jungmeier M Wellisch et al ldquoToward a com-mon classification approach for biorefinery systemsrdquo BiofuelsBioproducts and Biorefining vol 3 no 5 pp 534ndash546 2009

[104] J Larragoiti-Kuri M Rivera-Toledo J Cocho-Roldan KMaldonado-Ruiz Esparza S Le Borgne and L Pedraza-SeguraldquoConvenient Product Distribution for a Lignocellulosic Biore-finery Optimization through Sustainable Indexesrdquo Industrial ampEngineering Chemistry Research vol 56 no 40 pp 11388ndash113972017

[105] R Parajuli T Dalgaard U Joslashrgensen et al ldquoBiorefining in theprevailing energy and materials crisis A review of sustainablepathways for biorefinery value chains and sustainability assess-mentmethodologiesrdquoRenewableamp Sustainable Energy Reviewsvol 43 pp 244ndash263 2015

[106] T M Carole J Pellegrino and M D Paster ldquoOpportunitiesin the industrial biobased products industryrdquo Applied Bio-chemistry and BiotechnologymdashPart A Enzyme Engineering andBiotechnology vol 115 no 1ndash3 pp 871ndash885 2004

[107] A A Koutinas C Du R H Wang and C Webb ldquoProductionof Chemicals from Biomassrdquo Introduction to Chemicals fromBiomass pp 77ndash101 2008

[108] C R Somerville and D Bonetta ldquoPlants as factories fortechnical materialsrdquo Plant Physiology vol 125 no 1 pp 168ndash1712001

[109] M K D Rambo F L Schmidt and M M C FerreiraldquoAnalysis of the lignocellulosic components of biomass residuesfor biorefinery opportunitiesrdquo Talanta vol 144 pp 696ndash7032015

[110] K Ding Y Le G Yao et al ldquoA rapid and efficient hydrothermalconversion of coconut husk into formic acid and acetic acidrdquoProcess Biochemistry 2018

[111] G E Gopi E Saleem M ldquoExperimental Results of CoconutShell Polymer Matrix Compositesrdquo International Journal ofMechanical and Production Engineering Research and Develop-ment vol 7 no 6 pp 163ndash170 2017

[112] S Kocaman M Karaman M Gursoy and G Ahmetli ldquoChem-ical and plasma surface modification of lignocellulose coconutwaste for the preparation of advanced biobased compositematerialsrdquo Carbohydrate Polymers vol 159 pp 48ndash57 2017

[113] A Bhatnagar V J P Vilar C M S Botelho and R A RBoaventura ldquoCoconut-based biosorbents forwater treatment-Areview of the recent literaturerdquoAdvances in Colloid and InterfaceScience vol 160 no 1-2 pp 1ndash15 2010

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Submit your manuscripts atwwwhindawicom


Advanced Biofuels DuPont and ABENGOA [12] There aremany projects around the world focusing on the use oflignocellulosic residues for biofuel production [13] Theseresidues can come from homes or city dumps companies inCanada are investing in the construction and operation of arenewable fuel plant using local residential kitchen and yardwaste Phuketrsquos Provincial Administration Organization inThailand is building a waste-to-biofuel facility that will usethemunicipal solidwaste of the entire island as feedstock [14]Chinarsquos State Development amp Investment Corporation beganthe construction of its first ethanol plant in the Liaoningprovince with 300000 tons capacity and is planning to buildfive ethanol plants in other provinces [15] Nowadays biofuelshave an important part in the global liquid fuel market andover a hundred companies in different countries base theirproduction on various types of 2G biofuels [13] Coconuthusk is a very promising substrate that can be used as rawmaterial for 2G ethanol production since coconut palmplays an important role in the economy of several tropicalcountries [16] The food industry uses coconuts to obtainvarious products leaving the husk as waste It is important tonote that coconut husk has a high lignin content that duringhusk decomposition penetrates the soil and can reach thewater table imposing a great environmental risk Since it isdiscarded in high volumes (coconut husk encompasses 80to 85 of the weight of the fruit [17 18] while sugarcanebagasse corresponds only to 27 to 28 dry weight) it ismandatory to find a safe destination for this wasteThereforethe use of coconut husk for 2G ethanol production may bea solution to reduce the environmental impact Moreover ifthe technology is cheap and simple enough it can be used bysmall producers

The three main components of a biomass (cellulosehemicellulose and lignin) form a recalcitrant structure mak-ing it difficult for enzymes to have complete access to cellulosefor conversion to monosaccharides To make this feasiblethe first major step in bioethanol production is biomasspretreatment (biological physical or chemical) in which thelignin content is reduced to release the fermentable sugarsfrom the rigid structure and therefore prepare the biomassfor enzymatic conversion [19] Different types of biomasseshave different amounts and types of sugars (hemicelluloseand cellulose) and lignin so knowing its composition iscrucial for the process Moreover the abundance of theresidue must be taken into account so that the whole processis economically feasible

The second major step in 2G ethanol production is thehydrolysis that unlocks and saccharifies the polysaccharidesthat are present in the biomass to fermentable sugars [20]Generally enzyme cocktails are used to catalyze reactions toobtain simple sugars such as glucose andmannose for furtherfermentation by microorganisms This process also calledsaccharification is very important and the requirementsof these enzyme complexes which act synergistically addmajor costs to the overall process The main challenge is toobtain a cost-effective technology of enzymatic hydrolysis foreconomically viable biofuels [20]

The fermentation process is the next step in which amicroorganism such as the yeast Saccharomyces cerevisiae

ferments the sugars that are present in the treated biomassand produces ethanol [21] To increase the economic feasi-bility of this process industries show great interest in usingyeast strains that are more tolerant and resistant to variouskinds of stresses and that are also able to use pentoses thatcome fromhemicellulose degradation such as xylose asmoststrains naturally only consume hexoses

Currently the process for 2G bioethanol production inlarge scale is being improved since it still has cost productionissues that derive from the procedures needed to over-come the recalcitrance of the lignocellulose (pretreatmentand enzymatic hydrolysis) in order to obtain fermentablesugars [22] To transform the bioethanol production into asustainable and economically viable process it is importantto integrate it in a biorefinery which is a great supporterof a biobased economy In a biorefinery almost all typesof biomass residues can be converted to different classesof biofuels biomaterials and other marketable bioproductsthrough jointly applied conversion technologies [23]

Although many articles address the use of coconut huskas a raw material for bioethanol production few of themcompare the results obtained using different methods Thiswork intends to give an overview on different approachesalready tested to obtain ethanol from coconut husk tofacilitate the development of a process that can effectivelyproduce ethanol from coconut residue

2 The Coconut Plant and Industry

Coconut palm tree is a perennial crop grown in tropicalclimate countries which present ideal conditions for itscultivation such as soil with proper water capacity anddrainage andwarm ambient temperatures [24 25] Due to thecoconut structure many valuable products can be obtainedfrom it such as meat (copra) oil water milk and fibers[25] therefore this fruit is of great economic importanceThere are two major varieties the tall (Typica) mainly usedto obtain coconut meat and milk and the dwarf (Nana) themost cultivated in Brazil used for coconut water extraction[24 25]

Coconut harvesting time is determined by its purposeand is usually carried out in two stages of ripeningThe greenfruits are destined to the coconut water market while maturefruits are destined to the dry coconut market (for meat milkand oil) [26]Therefore depending on the plantation site theresidue ismade of green ormature coconut husks which havedifferent compositions (Table 1)

The coconut fruit has a smooth green epidermis (epi-carp) a medium region with bundles of fibers (mesocarp)and a stony layer that surrounds its edible part (endocarp)(Figure 1)

The estimated annual worldwide coconut production in2015 was around 55 million tons and the main producingcountries are Brazil India Indonesia the Philippines andSri Lanka [16 17] Indonesia is responsible for 331 of thetotal world production [24] and the coconut industry playsa significant economic role in this country as well as inother tropical countries However as mentioned before 80




Green coconut husk

[27] 3931 1615 2979[28] 4340 1990 4580[29] 3280 1590 na[30] 3323 2914 2544

Mature coconut husk

[31] 3047 2542 3315[32] 2958 2777 3104[33] 3218 2781 2502[30] 2958 2777 3104


(a) (b)















2SO4) and













Table2Com

paris

onof

pretreatmentm

etho

dsandinhibitorsform

eddu

ringpretreatment

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[52]

Cocon

uthu

skMicrowave-assis

ted-alkalin

e2450

MHz

na

[27]

Youn

gcoconu

thusk

Step

1NaO

H20-30

(wv)

Step

2NaO

H25(w

v)

Step

1100∘C

2and3h

Step

2170∘C

3hna

[53]

Cocon

uthu

sk

Microwave-assis

ted-alkalin

e2450

MHz20

min

na

Autohydrolysis

121∘ C

1043

bar15min

H2SO41

(vv)

40∘C

150r

pm24h

TS2

NaO

H5

(wv)

40∘C

150r

pm24h

TS2

[31]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)followed

byalkalin

edelignification(N

aOH4

(wv))

H2O225∘C

1hNaO

H100

rpm100∘C

1hna

[61]

Cocon

uthu

skdefattedgrapes

eedand

pressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

FurfuralH


andvanillin

[47]

Cocon

uthu

skH2SO41

(vv)

121∘ C

1hTS

75

na

[32]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Autohydrolysis

160-200∘C

10-50m

inT

S10


HMF

[28]

Cocon

utfib

erNaO

H3

(wv)

121∘ C

90m

inna

[46]

Cocon

uthu

skNaO

H25m

olsdotLminus1

Soakingin

NaO

H30m

inAu

tocla

ved125∘C

30min

Phenoliccompo

unds

[49]

Green

coconu

thusks

NaO

H5

121∘ C

40m

inT

S5

Aceticacid


Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib


NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18


liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk


olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH


vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc


liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present



Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018





Green coconut husk

[27] 3931 1615 2979[28] 4340 1990 4580[29] 3280 1590 na[30] 3323 2914 2544

Mature coconut husk

[31] 3047 2542 3315[32] 2958 2777 3104[33] 3218 2781 2502[30] 2958 2777 3104


(a) (b)















2SO4) and













Table2Com

paris

onof

pretreatmentm

etho

dsandinhibitorsform

eddu

ringpretreatment

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[52]

Cocon

uthu

skMicrowave-assis

ted-alkalin

e2450

MHz

na

[27]

Youn

gcoconu

thusk

Step

1NaO

H20-30

(wv)

Step

2NaO

H25(w

v)

Step

1100∘C

2and3h

Step

2170∘C

3hna

[53]

Cocon

uthu

sk

Microwave-assis

ted-alkalin

e2450

MHz20

min

na

Autohydrolysis

121∘ C

1043

bar15min

H2SO41

(vv)

40∘C

150r

pm24h

TS2

NaO

H5

(wv)

40∘C

150r

pm24h

TS2

[31]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)followed

byalkalin

edelignification(N

aOH4

(wv))

H2O225∘C

1hNaO

H100

rpm100∘C

1hna

[61]

Cocon

uthu

skdefattedgrapes

eedand

pressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

FurfuralH


andvanillin

[47]

Cocon

uthu

skH2SO41

(vv)

121∘ C

1hTS

75

na

[32]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Autohydrolysis

160-200∘C

10-50m

inT

S10


HMF

[28]

Cocon

utfib

erNaO

H3

(wv)

121∘ C

90m

inna

[46]

Cocon

uthu

skNaO

H25m

olsdotLminus1

Soakingin

NaO

H30m

inAu

tocla

ved125∘C

30min

Phenoliccompo

unds

[49]

Green

coconu

thusks

NaO

H5

121∘ C

40m

inT

S5

Aceticacid


Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib


NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18


liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk


olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH


vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc


liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present



Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018










2SO4) and













Table2Com

paris

onof

pretreatmentm

etho

dsandinhibitorsform

eddu

ringpretreatment

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[52]

Cocon

uthu

skMicrowave-assis

ted-alkalin

e2450

MHz

na

[27]

Youn

gcoconu

thusk

Step

1NaO

H20-30

(wv)

Step

2NaO

H25(w

v)

Step

1100∘C

2and3h

Step

2170∘C

3hna

[53]

Cocon

uthu

sk

Microwave-assis

ted-alkalin

e2450

MHz20

min

na

Autohydrolysis

121∘ C

1043

bar15min

H2SO41

(vv)

40∘C

150r

pm24h

TS2

NaO

H5

(wv)

40∘C

150r

pm24h

TS2

[31]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)followed

byalkalin

edelignification(N

aOH4

(wv))

H2O225∘C

1hNaO

H100

rpm100∘C

1hna

[61]

Cocon

uthu

skdefattedgrapes

eedand

pressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

FurfuralH


andvanillin

[47]

Cocon

uthu

skH2SO41

(vv)

121∘ C

1hTS

75

na

[32]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Autohydrolysis

160-200∘C

10-50m

inT

S10


HMF

[28]

Cocon

utfib

erNaO

H3

(wv)

121∘ C

90m

inna

[46]

Cocon

uthu

skNaO

H25m

olsdotLminus1

Soakingin

NaO

H30m

inAu

tocla

ved125∘C

30min

Phenoliccompo

unds

[49]

Green

coconu

thusks

NaO

H5

121∘ C

40m

inT

S5

Aceticacid


Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib


NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18


liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk


olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH


vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc


liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present



Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018



Table2Com

paris

onof

pretreatmentm

etho

dsandinhibitorsform

eddu

ringpretreatment

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[52]

Cocon

uthu

skMicrowave-assis

ted-alkalin

e2450

MHz

na

[27]

Youn

gcoconu

thusk

Step

1NaO

H20-30

(wv)

Step

2NaO

H25(w

v)

Step

1100∘C

2and3h

Step

2170∘C

3hna

[53]

Cocon

uthu

sk

Microwave-assis

ted-alkalin

e2450

MHz20

min

na

Autohydrolysis

121∘ C

1043

bar15min

H2SO41

(vv)

40∘C

150r

pm24h

TS2

NaO

H5

(wv)

40∘C

150r

pm24h

TS2

[31]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)followed

byalkalin

edelignification(N

aOH4

(wv))

H2O225∘C

1hNaO

H100

rpm100∘C

1hna

[61]

Cocon

uthu

skdefattedgrapes

eedand

pressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

FurfuralH


andvanillin

[47]

Cocon

uthu

skH2SO41

(vv)

121∘ C

1hTS

75

na

[32]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

Autohydrolysis

160-200∘C

10-50m

inT

S10


HMF

[28]

Cocon

utfib

erNaO

H3

(wv)

121∘ C

90m

inna

[46]

Cocon

uthu

skNaO

H25m

olsdotLminus1

Soakingin

NaO

H30m

inAu

tocla

ved125∘C

30min

Phenoliccompo

unds

[49]

Green

coconu

thusks

NaO

H5

121∘ C

40m

inT

S5

Aceticacid


Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib


NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18


liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk


olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH


vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc


liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present



Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018



Table2Con

tinued

Reference

Substrates

Type

Con

ditio

nsRe

ported

inhibitors

[33]

Maturec

ocon

utfib


NaO

H160-200∘C

10-50m

inPh

enoliccompo

undsH

MFfurfuraland

aceticacid

[50]

Green

coconu

tmesocarp

NaO

H1-4

(w

v)

25∘C

200r

pm1-24h

TS18


liccompo

unds

(various)NOlevulin

icacid

furfuralor

HMFdetected

[51]

Green

coconu

thusk


olsdotLminus1and

NaO

H4

(wv))

Acid121∘C

15minT

S20

Alkaline121∘ C

30m

inna

Alkalineh

ydrogenperoxide

(H2O2735

(vv)pH

115)

Room

temperature100

rpm1hTS

4

[54]

Cocon

utcoirfib

ers

Acidified

aqueou

sglycerol

130∘C

400r

pm30and60

minT

S33

and5

na

Aqueou

sglycerol

[62]

Cocon

uthu

skdefattedgrapes

eed

sugarcaneb

agasse

andpressedpalm

fiber

NopretreatmentDire

ctno


subcriticalwater

+CO2

FurfuralH


vanillin

[48]

Green

coconu

thusk

NaO

H1-2

(w

v)

200r

pm25∘C

1hAc


liccompo

unds

(various)a

ndfatty

acidsNO

levulin

icacidfurfuralorH

MFdetected

[29]

Cocon

utfib

erNaO

H1and

2(w

v)-+

Tween

80121∘ C

10-30

minT

S10

Aceticacid

andph

enoliccompo

undsN

Ofurfuralor

HMFdetected

H2SO415

and3

(wv)-+

Tween

80121∘ C

10-60

minT

S15

Autohydrolysis-+Tw

een80

121∘ C

10-60

minT

S10

and15

[30]

Green

coconu

tshellmaturec

ocon

utfib

erm

aturec

ocon

utshelland

cactus

NaC

lO2(093

(wv))-C2H4O2(031

(vv))follo

wed

byautohydrolysis

NaC

lO2-C2H4O275∘C

1-4hTS

31

Autohydrolysis

200∘C

50minT

S10

Phenoliccompo

undsH

MFfurfuraland

aceticacid

TStotalsolid

sloading

s(wv)na

notavailableo

rnot

present



Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018




Non-reducing ends


Cellobiohydrolase I








































Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018






























Table3Com

paris

onof

hydrolysismetho

dsandmaxim

umfin

alsugarc

oncentratio

ns

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[52]

Microwave-assisted-

alkalin

eSSF

Cellusclast

15Land

PectinexUltraS

P-L

na

30∘C

150r

pm96h

TS25

np

[27]

2ste

pswith

NaO

HSH

FCellucla

st15Land

Novozym

e188

(Novozym

esASD

enmark)

15FP

Usdot(g

substra


substrate)minus1

50∘C

140r

pm72h

pH48

TS5


SSF

37∘C

72hpH

55TS

5np

[53]

Microwave-assisted-

alkalin

eOnlyhydrolysis

Cellusclast15Land

Pectinex

UltraS

P-L

05

(vv)e

ach

35∘C

150r

pm5

daysT

S1

28g

TRSsdotLminus1

Autohydrolysis

Aprox07g

TRSsdotLminus1

H2SO4

Aprox07g

TRSsdotLminus1

NaO

HAp

rox14

gTR

SsdotLminus1

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSFmature

coconu

tfiber

CellicC

Tec2

andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

mature

coconu

tfiber

Prehydrolysis50∘C

8hSSF30∘C

40h

TS4

[61]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

34g

mon


gsubstrate)minus1

[47]

H2SO4

Onlyhydrolysis

Cellucla

standNovozym

e188(N

ovozym

esAS

Denmark)

033

mLof

each

50∘C

150r

pm72h

pH48

TS01-2

12

gTR

SsdotLminus1

[32]

AutohydrolysisTS

10

SSFgreencoconu

tshell

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4


SSSF

green

coconu

tshell

Prehydrolysis50∘C

12h

SSF30∘C

36h

TS4

[28]

NaO

HSH

FNon

-enzym

atichydrolysiswith

1-4(vw

)H2SO4121∘C

2h84

(wv)g

lucose

[46]

NaO

HSH

F

Cellulase26921

Novozym

e188

(Novozym

esASD

enmark)

and

enzymes

from

coconu

thu

skiso

latedfung

i

75FP

Usdot(g

substra

te)minus1

50∘C

96hpH

550

mM

TRS

[49]

NaO

HSH

FAc

celerase1500

2(vv)

50∘C

150r

pm72h

TS1

87g

TRSsdotLminus1


Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018



Table3Con

tinued

Reference

Pretreatment

Hyd

rolysis

strategy

Enzymes

Enzymec

oncentratio

nCon

ditio

nsMaxim

umSu

gars

concentration

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

CellicCT

ec2andHTec2

30FP

Usdot(g

substra

te)minus175CB

Usdot(g


Usdot(g

substra

te)minus1

30∘C

48hTS

4Ap


SSSF

Pre-hydrolysis

50∘C

12h

SSF30∘C

36hTS

4

[50]

NaO

HSH

FAlternaFuelCM

AX

37575and15

FPUsdot(g

substra

te)minus1

50∘C

200r

pm96h

pH6TS

17

87

(wv)sugars

[51]

Acid-alkaline

Onlyhydrolysis

Cellucla

st15L

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


substrate)minus1

50∘C

150r

pm72h

TS5

Aprox9g

TRSsdotLminus1

Alkalineh

ydrogen

peroxide

TS4

Aprox11gTR

SsdotLminus1

[54]

Acidified

aqueou

sglycerol

SSF

Enzymefrom

Treseei

10FP

Usdot(g

substra

te)minus1

37∘C

120r

pm96h

np

Aqueou

sglycerol

[62]

Nopretreatment

Onlyhydrolysis

Non

-enzym

atichydrolysiswith

subcriticalwater

+CO2

17gmon


gsubstrate)minus1

[48]

NaO

HSH

FAlternaFuelCM

AX

15FP

Usdot(g

substra

te)minus1each

time

50∘C

200r

pm96h

pH6TS

24and29

97(w

v)sugars

[29]

NaO

H+Tw

een

80Au

tohydrolysis

Onlyhydrolysis

TreeseiAT

CC26921

120573-glucosid

ases

and

xylanases

200FP

Usdot(g

substra

te)minus1200CB

Usdot(g


Usdot(g

substrate)minus1

50∘C

150r

pm96h

TS5

05g

TRSsdot(g

substra

te)minus1

01g

TRSsdot(g

substra

te)minus1

[30]

NaC

lO2-C2H4O2

autohydrolysis

Onlyhydrolysis

CellicCT

ec2andHTec2

10FP

Usdot(g

substra

te)minus130CB

Usdot(g


IUsdot(g

substra

te)minus1

50∘C

150r

pm96h

TS4

Aprox24

gglucosesdotLminus1

na

notavailableo

rpresentT

Stotalsolidsloading

s(wv)npnot

presentb

ecause

ofSSFor

SSSFlowast

values

obtained

from

liquo

rafte

renzym

atichydrolysisbu

tnot

used

forfermentatio

n(SSF

andSSSF)
















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018

















Table4Com

paris

onof

ferm

entatio

ncond

ition

sethano

lcon

centratio

nandyield

Reference

Pretreatment

Ferm

entatio

nstrategy

Microorganism

sCon

ditio

nsMaxim

umEtha

nol

concentration(gL

or)

Etha

nolyield

(getha

nolgsugars

or)

[53]

Microwave-assisted-

alkalin

eSSF

Scerevisia

eATC

C36858

30∘C

150r

pm96h

009(w

w)

na

[27]

2ste

pswith

NaO

HSH

FScerevisia

e37∘C

72hpH

55

228(w

v)lowast

Approx

85

SSF

103

(wv)

[31]

Alkalineh

ydrogen

peroxide

+alkalin

edelignification

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e844gsdotLminus1

Pstip

itis9

12gsdotLminus1

Zmobilis8

27gsdotLminus1

Scerevisia

e043

Pstip

itis0

40

Zmobilis0

42

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e932

gsdotLminus1

Pstip


Zmobilis8

91gsdotLminus1

Scerevisia

e045

Pstip

itis0

43

Zmobilis0

44

[32]

Autohydrolysis

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e744gsdotLminus1

Pstip

itis8

47gsdotLminus1


Scerevisia

e044

Pstip

itis0

43

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

40h

Scerevisia

e771gsdotLminus1

Pstip

itis8

78gsdotLminus1


Scerevisia

e045

Pstip

itis0

44

Zmobilis0

45

[28]

NaO

HSH

FScerevisia

e150r

pm11d

ayspH

45-5

59

na

[49]

NaO

HSH

FScerevisia

e30∘C

100r

pm9

h7gsdotLminus1+

na

[33]

Hydrothermal

catalyzedwith

NaO

H

SSF

Scerevisia

ePstipitis

and

Zmobilis

30∘C

agitatio

ndepend

ingon

microorganism

48h

Scerevisia

e1091gsdotLminus1

Pstip

itis1096

gsdotLminus1


Scerevisia

e044

Pstip

itis0

45

Zmobilis0

43

SSSF

30∘C

agitatio

ndepend

ingon

microorganism

36h

Scerevisia

e116

5gsdotLminus1

Pstip

itis112

9gsdotLminus1

Zmobilis116

4gsdotLminus1

Scerevisia

e047

Pstip

itis0

46

Zmobilis0

47

[50]

NaO

HSH

FScerevisia

estrains

Ethano

lRed

andGSE

16-T

1835∘C

100r

pm103

hpH

55

373(vv)

043

[54]

Acidified

aqueou

sglycerol

SSF

Scerevisia

eHansen2055

37∘C

150r

pm72h

897

gsdotLminus1

na

Aqueou

sglycerol

266

gsdotLminus1

na

[48]

NaO

HSH

FScerevisia

eGSE

16-T

1835∘C

100r

pm72h

pH55

433(vv)

041

na

notavailableo

rnot

presentlowastwith

50gsdotL-1of


ofthe2

28gsdotL

-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d+with

aprox16gsdotL-1of

initial

glucoseinstead

ofthe8

7gsdotL-1repo

rted

from

theh

ydrolysisN

oexplanationforthe

riseo

fsugar

concentra

tionwas

foun

d































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018
































Cellulose

C5 andC6 carbons


Aromatics

Lignin

Alcohols

Amino acids

Organic acids

Sugar acids

Sugar alcohols

Other products
















6 Conclusion








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018








Acknowledgments


References
























































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018



































































































Volume 2018

Zoology











Volume 2018

















Advances in




Enzyme Research





Volume 2018


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