Physico-chemical Properties of Dehydrated Guava

7/30/2019 Physico-chemical Properties of Dehydrated Guava

1/7

T MAHENDRAN : QUALITY OF INSTANT GUAVA DRINK POWDER

*Corresponding author : [email protected]

PHYSICO-CHEMICAL PROPERTIES AND SENSORY CHARACTERISTICSOF DEHYDRATED GUAVA CONCENTRATE: EFFECT OF DRYING METH-OD AND MALTODEXTRIN CONCENTRATION

T MahendranDepartment of Agricultural Chemistry, Faculty of Agriculture, Eastern University of Sri Lanka, Chenkalady

Accepted: 20th May 2010

ABSTRACT

Dehydration of guava juice into powdered particles gives a considerable reduction in volume and is aneffective method of prolonging the shelf life. Therefore, a research study was conducted to determinethe effect of different drying methods and the addition of drying aids on the physico -chemical proper-ties and sensory characteristics of dehydrated guava concentrate. Instant guava-drink-powder sampleswere obtained by dehydrating the concentrated guava juice using freeze drying, spray drying and tun-nel drying techniques. Guava juice at 10.5Brix was used to prepare the fruit powders. A significant

reduction (p


2/7

Tropical Agricultural Research & Extension 13(2): 2010

fruit juice powders since it satisfies the demand andis also reasonably cheap. The addition of dryingaids is necessary during spray drying of fruit juices,adding amount not exceeding the operational limitsof the equipment or altering the flavour properties.

Fruit juice powders obtained by spray drying pre-sent problems in their functional properties such asstickiness and solubility (Bhandari et al. 1997).Much of the published work in this field is of asomewhat general nature. Published data on theeffects of drying methods on the physico-chemicaland organoleptic properties of the guava powderare limited and fragmentary. Therefore, the objec-tives of this study were to produce guava powdersusing freeze drying, spray drying and tunnel dryingmethods and to evaluate the effects of drying on thequality characteristics of the fruit powders. A con-sumer preference test was conducted to determine

the sensory attributes of the reconstituted guavajuice and to compare the final product with thecommercial products available in the market.

MATERIALS AND METHODS

Fully ripe, firm guava (P. guajava var. Allahabad)fruits without bruises were obtained from a com-mercial horticultural station in Brazil. Fruits werewashed in the running water and trimmed. Imma-ture, rotten and damaged fruits were discarded. Thefruits were mashed in a fruit mill and transferred toa water bath (Model: Gyromax-929, UK) and the

temperature was maintained at 30C with agitation.The pulp was heated at 50C for 30min. and500ppm of pectic enzyme (Pectinex Ultra SP-1,BBI Enzymes, UK) was added to the pulp. The en-zyme inactivation was accomplished by heating thepulp to 90C for 5min. The pulp was pressed andthe cloudy juice obtained was treated with fine clar-ifier Baykisol-30 (hydrogel in association with 15%active silicic acid) at the concentration of 0.5 ml/l.The treated juice was kept at the temperature of201C for 30min and passed through the micro-filters (Applieo Membranes Inc., USA) of 50mdiameter. The clear guava juice was concentrated

by reverse osmosis process.

Concentration of guava juice by reverse osmosisThe reverse osmosis was carried out in a plate andframe model (HR-98, Spain) of 0.72m2 filtrationsurface composed polysulphone/polyethylene com-posite layer membranes (95% NaCl rejection). Ac-cording to Matta et al. (2004), the tests were per-formed at 20, 40 and 60 bar aiming at the evalua-tion of the influence of trans-membrane pressure inpermeate flux and in the concentrated product. Thetemperature was maintained at 250.5C and thepump flow rate was kept at 650l/h throughout the

concentration process.

Drying Methods1. Freeze drying: The concentrated guava juicewas frozen on trays for 5h at 30C. After freezing,the samples were transferred to a freeze drier(Model-20 SRC, USA) and dried at 250.5C for

48h at 10mbar Hg pressure. The powder was ob-tained by grinding the dried material in a blenderand stored in dark glass airtight containers at201C until further tests were carried out.

2. Spray drying: A laboratory scale cocurrentspray drier (Model-Anhydro LAB S1 209, Italy)with vaned centrifugal atomizer driven by an airturbine at speeds upto 40,000 rpm was used. Theinlet temperature of the feed material was 160Cand the outlet (product) temperature was set to 80C by regulating the feed pump speed. The feedstock was atomised uniformly but difficulties were

encountered owing to the slow flow rate throughthe gravity feed systems of the drier. Powder wasseparated from hot air by a cyclone and stored indark glass airtight containers at 20C. Corn malto-dextrin DE-10 (Food Grade) was added to the juicebefore spray drying. Based on the formula devel-oped for spray drying of fruit juices by Bhandari etal. (1993), the following combinations were select-ed for drying:

1. Guava solids wt 70% + Maltodextrin wt 30%2. Guava solids wt 60% + Maltodextrin wt 40%3. Guava solids wt 50% + Maltodextrin wt 50%4. Guava solids wt 40% + Maltodextrin wt 60%

3. Tunnel drying: The tunnel drier (Model 21009,Wisconsin) was a batch type and the drying temper-ature was maintained by passing the hot air into thesystem. An approximately 2cm thick layer of con-centrated guava juice was spread on cheese clothand placed over a wire mesh tray which was placedin the tunnel drier for drying. The air temperaturewas set to 60C for the first 3h and then reduced to50C. The total drying time was 12h as judged bythe appearance of the dried product. The powderwas obtained by grinding the dried material in agrinder (VIK-1017, UK) for 3min and stored in

dark glass airtight bottles at 201C.

Nutritional and Sensory AnalysesGuava juice and powders were analyzed for totalsoluble solids content using a RFM Refractometer(Model:ATAGO-28E) equipped with a percentagesugar scale and expressed as Brix. Measurement oftitratable acidity was conducted using a standard1% phenolphthalein solution, titrated against 0.1NNaOH and the result was expressed as grams ofanhydrous citric acid per 100g of sample. The pHwas measured using a digital pH meter (MettlerToledo, UK) with a glass electrode. The total sug-

ars were determined by standard AOAC (2008)

49


3/7

T MAHENDRAN : QUALITY OF INSTANT GUAVA DRINK POWDER50

method. Vitamin C was analyzed by oxide-reduction reactions using 2,6-dichlorophenol indo-phenol dye.

Moisture content was determined using a vacuum

oven (Model: S/N-29) operated at 70C at 1bar for

24h. The bulk density of the powder was deter-mined by measuring the volume of a determinedweight of the powder in a 100 ml graduated glasscylinder. The particle density was determined bypycnometry, using toluene at 20C. The solubilityof the powder was determined by mixing 10g pow-ders with 100 ml of distilled water at high speed for3 min in a mixer. Then, the solution was centri-fuged (Eppendorf C-5702, Japan) at 20,000 x g for3 min. An aliquot of 50 ml of the supernatant wasplaced in previously weighed petri dishes and ovendried at 105C for 6h. Solubility was calculated by

difference in weight. The viscosity of the juice wasmeasured in a digital Brookfield viscometer(Model: DVII, USA) at 20C with the spindle No:2 at 50rpm. The colour of the powder was evaluat-ed by a colorimeter (Model: HSCOL 1348, UK)using the Hunter system. Results were expressed inL* (lightness), a* (redness), b* (yellowness) val-ues. All the assays were performed in triplicate andthe data from the dried powders were related tofresh juice by allowing for moisture content when-ever necessary.

Twenty trained panelists aged between 18 to 50

years, able to evaluate and differentiate the guavajuice samples, were selected to take part in the sen-sory panel. The panel measured the selected criticalattributes such as characteristic aroma, flavour, col-our, sweetness, consistency and total acceptability.The attributes were evaluated in a non-structuredscale of 10cm. The tests were carried out in indi-vidual sensory booths under the florescent light.Three repetitions were made for each test. Thesamples were prepared by re-constituting driedpowders down to 10.5Brix and served to the panel-lists at 5-7C in white porcelain cups coded bythree randomized numbers. Samples were expecto-

rated and judges were given distilled water andcrackers to cleanse their palates between samples.

Statistical Analysis

The design for this experiment was a CompletelyRandomized Design (CRD). Data were statisticallyexamined by analysis of variance and the meanswere separated by Duncans Multiple Range Test.Descriptive statistics was done on sensory attrib-utes and the means were compared using the Tuk-eys test (p


4/7


Hunter L* (lightness) values and b* (yellowness)values following production of guava powder(Table 2) was probably the result of non-enzymicbrowning during freeze drying which produced alight yellow product. This is in agreement with the

results of Tashtoush et al. (2007). They obtained adarker guava freeze dried powder from drying ofguava concentrates. The guava juice has high sugarcontent with low in particulates allowing satisfacto-ry puffing during freeze drying which is responsiblefor the colour and shiny nature of the powders. Allthe powders produced by spray drying were a lightyellow colour in appearance irrespective of the col-our of the feed material. There were no significantdifferences (p>0.05) between the L* and a*(redness) values for powders prepared using differ-ent maltodextrin combinations. Chopda and Banrett(2004) reported the production of bright white gua-

va powder after spray drying of puree with malto-dextrin. During spray drying a* decreased as L*increased because oxidation of pigments increas-ingly revealing the white colour of the maltodex-trin. Due to the long drying process at high temper-atures, the guava powder produced by tunnel dryinghad a golden yellow colour but was very sticky anddifficult to remove from the trays and grind. It wasobserved that the deteriorative changes in qualitywere more pronounced during the tunnel drying ofguava juice.

The physical properties such as moisture content,

bulk density, particle density, wetting, dispersion,solubility, particle size and distribution of guavapowder were related to ease of reconstitution. The-se properties are influenced by the nature of thefeed (solid content, viscosity and temperature) andoperational conditions. The bulk and particle densi-ties of the dried guava powders were also compared(Table 2). The tunnel dried powder had significant-ly higher (p


5/7


solubility. When 30% maltodextrin was addedto guava juice, the solubility of powder was 95%whereas adding 60% maltodextrin decreased thesolubility to 86%. These results are in agreementwith Chauca et al. (2004), who reported that higher

concentrations of drying carriers resulted in lowsolubility of the dried mango powder. With respectto the results obtained in a previous study undersimilar conditions by Borges et al. (2002), the solu-bility was 95% with 60% Guava solids + 40%Maltodextrin. The reconstituted drink made fromthe fruit powder with 60% maltodextrin was notclear because the maltodextrin exceeded the solidlimits suggested for making clear solutions. Malto-dextrin as a carrier in juice dehydration by spraydrying is one of the most utilized substances due toits physical properties such as solubility in water.However, due to the change in structure of the pow-

der, it influences the functional solubility. Theproperties of the powdered guava particles changeas a function of maltodextrin concentration; thehigher concentrations leading to decreased solubili-ty of the powder in water. To maintain the guavapowder quality during storage, the physico-chemical state of the dried product has to be main-tained for as long as possible. Any change in itsstructure not only changes the physico-sensorialattributes but also it may have some quality deterio-rating consequences such as increase in rate ofchemical reactions, structural damage and changesin microbial quality.

Ready-to-serve (RTS) guava nectars were preparedfrom fruit powders and were compared with thoseprepared from fresh juice. The fruit powders werereconstituted at the ratio of 1:10 by adding water tothe final total soluble solid contents of 10.5Brix.All the sensory panellists had tasted guava fruit ordrink before and all of them gave higher scores for

its taste. Scores assigned for each sensory attributewere totalled for each sample to give a value fortotal acceptability (Table 3).

Nectar made from the freeze dried concentrated

juice contained the highest ascorbic acid content of117mg/100ml primarily due to greater proportionof guava powder used in the final drink whereas thecommercial nectar contained low level of ascorbicacid (29mg/100ml). There was no significant differ-ence (p>0.05) between the acceptability of the freshjuice and the reconstituted freeze dried powder.This indicated minimal flavour loss during freezedrying. Most of the panellists preferred the flavourand sweetness of the freeze dried nectar and gavescores accordingly. Spray dried powder producedfrom 40% guava juice was unacceptable to 78% ofthe panellists because of the thick consistency and

off-flavour. This may be due to the addition of

maltodextrin at higher concentration than the desir-able level from the sensory standard point. Overall,88% of the panellists were either very satisfied orsatisfied with reconstituted guava nectar and only5% disliked it. The remainder of the panellists ex-pressed neutral opinion. Our results are in contrastto the finding of Askaret al. (1992). They reporteda significant loss in quality in guava powder whichwas unacceptable by most of the consumers. Thismay be due to the difference in sensory methodused by Askar et al. (1992) and more diverse eth-nicity of the consumers participated in the sensory

analysis.

CONCLUSIONS

This study examined the feasibility of using differ-ent drying methods to produce instant guava pow-der of acceptable quality at reasonable cost. Con-centrated guava juice without additives cannot be

Table 1: Effect of Different Drying Methods on the Chemical Characteristics of Dehydrated Guava Concentrate

Treatments Moisture(%)

pH Titratableacidity (%)(as citric acid)

Totalsugars (%)

Vitamin C(mg%)

Brix

Concentrated Fresh Guava juice 87.41.21 4.120.12 0.520.01 9.840.10 996.91.80 12.50.17

Freeze-dried 2.360.04c 4.270.10a 0.490.01c 8.610.13c 809.51.72c 35.40.22c

Tunnel-dried 1.910.03a 4.480.11b 0.370.02b 8.150.12b 675.42.14a 30.70.19b

Spray-dried

1. Guava solids 70% + Maltodextrin 30% 2.240.04b 4.380.10b 0.390.01b 8.300.12b 782.12.1b 33.40.21bc

2. Guava solids 60% + Maltodextrin 40% 2.210.03b 4.440.09b 0.360.02b 8.240.09b 768.31.9b 32.10.20bc

3. Guava solids 50% + Maltodextrin 50% 2.170.02b 4.470.11b 0.350.01b 8.170.10b 741.22.0

b 31.50.24b

4. Guava solids 40% + Maltodextrin 60% 2.140.03b 4.560.08bc 0.300.02a 7.830.11a 681.32.3

a 27.40.21a

Values represent the average of triplicate analytical measurements.

Values in the same column bearing different letters are significantly different.

52


6/7


Table 2: Effect of different drying methods on the Physical characteristics of Dehydrated Guava Concentrate

satisfactorily spray dried because of the hygroscop-ic and thermoplastic nature of the product. Freezedrying produced the best quality guava powder interms of colour, flavour and ascorbic acid retentionthough it was quite hygroscopic in nature. Spraydried product had bright and attractive colour incomparison to the darker tunnel dried product. The

latter was rated poorly in the taste panel assess-ments possessing a distinct off-flavour. Spray dry-

ing produced stable powders at room temperatureof 201C. Maltodextrin proved to be the effectiveadditive, reducing the wall deposition markedly andproducing a product of acceptable flavour and withgood free-flowing properties. The freeze dried pow-der showed higher pigment stability than the spraydried powder. The colour parameters L*, a* and b*were found to be significantly affected by dryingmethods. The spray dried, reconstituted juice wasslightly lacking in flavour compared to freshly pre-pared juice but was preferred to tunnel dried mate-rial. This assessment reflects the heat damage indi-cated by the chemical analyses, consequently the

poor quality of the product does not recommend theapplication of tunnel drying. Because freeze dryingis an expensive method to apply commercially,spray drying may be the best alternative for produc-ing guava powder with good stability. In each case,a compromise must be found to the fruit juice toadditive ratio, drying yield and cost of production.

The development of an instant guava juice powdernot only reduces the shipping cost but also curtailswastage because guava powder is more stable thanits liquid counterpart.

REFERENCES

Abadio FDB, Domingues AM, Borges SV andOliveira VM 2004 Physical properties of pow-dered pineapple (Ananas comosus) juice effect of maltodextrin concentration and atom-ization speed. Journal of Food Engineering.64: 285-287.

Adhikari B, Howes T, Bhandari BR and Troung V2004 Effect of addition of maltodextrin on

Treatments Bulk densityg/cm3

Particle den-sity g/cm3

Solubility(%)

Viscosity(mp) L* a* b*

Concentrated Fresh Guava juice 36.9 2.58 10.34

Freeze-dried

0.65c 1.71c

96.2 c

219.1b 81.8b 1.91c 31.36d

Tunnel-dried 0.69d 1.79c 86.3a 196.7a 73.8a 4.29d 17.91a

Spray-dried

1. Guava solids 70% + Maltodextrin 30% 0.61b 1.64b 95.1c 226.9bc 84.4b 1.66b 26.18c

2. Guava solids 60% + Maltodextrin 40% 0.60b 1.60b 94.2bc 233.2bc 86.6b 1.61b 24.28c

3. Guava solids 50% + Maltodextrin 50% 0.57b 1.54b 92.9b 240.8c 88.1bc 1.54b 22.97bc

4. Guava solids 40% + Maltodextrin 60% 0.54a 1.49a 86.1a 249.1d 91.3c 1.43a 20.13b

L* - Lightness, a* - Redness and b* - Yellowness.Values represent the average of triplicate analysis.Values in the same column bearing different letters are significantly different.

Treatments Colour Sweetness Aroma Flavour Consistency Totalacceptability

Concentrated Fresh Guava juice 8.9c 7.8c 8.3c 8.9c 8.2cd 42.1c

Freeze-dried 8.7c 7.8c 8.0bc 8.8c 7.9c 41.2b

Tunnel-dried 7.4a 6.5a 6.2a 6.4a 7.0b 33.5a

Spray-dried

1. Guava solids 70% + Maltodextrin 30% 8.4b 7.6b 7.8b 8.0b 7.6b 9.4b

2. Guava solids 60% + Maltodextrin 40% 8.2b 7.5b 7.6b 7.9b 7.4b 38.6b

3. Guava solids 50% + Maltodextrin 50% 8.1b

7.4b

7.4b

7.6b

7.1b

37.6b

4. Guava solids 40% + Maltodextrin 60% 7.8a 6.8ab 6.7a 7.0ab 6.3a 34.6a

Sensory quality scores

Table 3: Effect of Different Drying Methods on the Sensory Characteristics of the Reconstituted Guava Drink

Values are the means of two replications with sensory evaluation completed by 20 trained panellists. Values in the same column bearing different letters are significantly different.

Hunter Colour Values

53


7/7


drying kinetics and stickiness of sugar andacid-rich foods during convective drying ex-periments and modelling. Journal of FoodEngineering.64: 53-68.

AOAC 2008 Official Methods of Analysis of

AOAC International. 18th

ed. Association ofOfficial Analytical Chemists, USA.

Askar A, El-Sanahy SK, Barrnett M and SalemaNA 1992 Production of instant guava drinkpowder. Food Technology. 46(5): 154-161

Bhandari BR, Data N and Howes T 1997 Prob-lems associated with spray drying of sugar-rich foods. Drying Technology. 15(2): 671-684.

Bhandari BR, Senoussi A, Dumoulin ED andLebert, A. 1993 Spray drying of concentratedfruit juices. Drying Technology. 11(5): 1081-1092.

Borges SV, Reis ALS, Jorge EC, Pinto PR andOliveira V 2002 Judo de frutas tropicales des-hidratados por spray drying.Alimentaria. 334:125-130.

Brennan JG, Herrera K and Jowitt R 1991 A studyon the factors affecting the spray drying oforange juice.Journal of Food Technology. 26:314321.

Chauca MC, Stringheta PC, Sardigna L and Cal-Vidal J 2004 Mango juice dehydration byspray drying using different carriers and func-tional characterization. Proceedings of the 14th

International Drying Symposium, Sao Paulo,Brazil. 22-25th August 2004. pp. 205-212.

Chopda CA and Banrett DM 2004 Optimization ofguava juice and powder production. Proceed-ings of the 14th International Drying Symposi-

um, Sao Paulo, Brazil. 22-25th August 2004.

pp. 1764-1789.Gupta RG and Nath N 1984 Drying of tomatoes.

Journal of Food Science and Technology.21:372-376.

Imungi JK, Schefield H and Saint-Hilslare U 1994Physical-chemical changes during extractionand clarification of guava juice. Chemistryand Technology. 7: 33-41.

Kalil UL and Sidel TP 1994 Spray drying ofmango juice concentrate. MesopotamiaJournal of Agriculture. 29(1): 8189.

Masters K 1985 Spray Drying Hand Book. 4th ed.

Longman Scientific and Technical, England.pp. 255-258.

Masters K 1990 Spray drying of liquid foods.Chemical Engineering. 367: 149158.

Matta VM, Moretti RH and Cabral LMC 2004Microfiltration and reverse osmosis for clarifi-cation and concentration of acerola juice.Journal of Food Engineering. 64: 477482.

Papadakis S and Bahu R 1992 The sticky issues ofdrying.Drying Technology. 10(4): 76-91.

Tashtoush DK, Vividas UR and Mujumdar GT2007 Effect of spray drying variables on thephysico-chemical characteristics of guava

powder.Drying Technology. 29: 288-290.

54

Physico-chemical Properties of Dehydrated Guava

Documents

Transcript of Physico-chemical Properties of Dehydrated Guava