498 Chiang Mai J. Sci. 2010; 37(3)

Study of Spray Drying of Pineapple Juice UsingMaltodextrin as an AdjunctWeerachet Jittanit*, Siriwan Niti-Att and Onuma TechanuntachaikulDepartment of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University,50 Phaholyothin Road, Chatuchak, Bangkok 10900, Thailand.*Author for correspondence; e-mail: fagiwcj@ku.ac.th

Received: 31 August 2009Accepted: 24 September 2009

ABSTRACTA number of pineapple powder specimens were produced using a spray dryer

under various drying conditions. Fresh pineapple juices were added with maltodextrin (MD)at 15, 20 and 25% before exposing to the drying temperatures at 130, 150 and 170oC with thefeed rate 0.020, 0.022 and 0.035 litre per minute respectively. Then, the qualities of pineapplepowders and reconstituted pineapple powders were investigated in the aspects of moisturecontent, solubility, color, pH and the consumer acceptance. The results indicated that thepineapple juice should be added with MD at 15% and dried at 150oC. Furthermore, themoisture content and solubility of the pineapple powder produced under this condition were5.1% and 6.2 minutes respectively while its solution had the lightness 58.8, redness 5.2, yellowness25.1 and pH 3.5.

Keywords: spray drying, pineapple, pineapple powder, instant pineapple juice, maltodextrin.

1. INTRODUCTIONPineapple is the most important fruit of

Thailand and many developing countries dueto its export values. Generally, the pineapplesare exported as the canned-fruit, concentratedjuice and dried pineapple slices. Althoughthere are a number of pineapple products inthe market, the food industry still keepsdeveloping new product from pineapple.The benefit of new product development isthe elevation of the fresh pineapple demandand consequently help reducing the pineappleloss caused by the microorganisms, chemicaland enzymatic reactions during the peak ofharvesting season [1,2]. Pineapple powder isan interesting product because of its long

shelf life at ambient temperature, convenienceto use and low transportation expenditure.Pineapple powder can be consumed as aninstant juice powder or a flavoring agent. Sofar, there have been merely few studies aboutthe production of pineapple powder.

Some researchers claimed that drying offruit juice could produce the fruit powderthat reconstituted rapidly to a fine productresembling the original juice [2]. It is becausethe product temperature is rarely raised above100oC during drying process [3]. Nonetheless,there are some difficulties in drying the fruitjuice with high sugar content like pineapple dueto their thermoplasticity and hygroscopicity

Chiang Mai J. Sci. 2010; 37(3) : 498-506www.science.cmu.ac.th/journal-science/josci.htmlContributed Paper

Chiang Mai J. Sci. 2010; 37(3) 499

at high temperatures and humidities causingtheir packaging and utilization in trouble[3-5]. These characteristics are attributed tolow molecular weight sugars such as fructose,glucose and sucrose and organic acids such ascitric, malic and tartaric that are the majorsolids in fruit juices [4]. The low glass transitiontemperature (Tg), high hydroscopy, lowmelting point, and high water solubility ofthese solids lead to a highly sticky productwhen spray dried [6]. These solids normallyhave low glass transition temperatures.Additionally, Roos and Karel [7] stated thatthese materials are very hygroscopic inamorphous state and loose free flowingcharacter at high moisture content.

The thermoplasticity and hygroscopicityproblems occurring in drying the fruit juicewith high sugar content can be overcome byadding some carriers such as maltodextrin(MD) and Arabic gum [2,5,8]. The dryingcarriers or adjuncts are high molecular weightcompounds that have high Tg; as a result, theycan raise the Tg value of feed and thesubsequent powder [9]. According to Cano-Chauca et al. [5], MD is a carrier which is themost popular in spray drying due to itsphysical properties such as high watersolubility. Gabas et al. [2] described that MDconsists of b-D-glucose units linked mainlyby glycosidic bonds and are typically classifiedby their dextrose equivalent (DE). Bhandariet al. [8] and Silva et al. [10] pointed out thatMD could improve the stability of fruitpowder with high sugar content because itreduced stickiness and agglomerationproblems during storage. Also, Shrestha et al.[9] indicated that the increasing amount ofMD could increase the product recovery andthe lightness of the orange juice powder.

Spray drying is a technique widely usedin the food industry to produce food powderdue to its effectiveness under the optimumcondition [5]. The spray drying parameters

such as drying air temperature and feed rateare influential to the attributes of spray-driedfood such as particle size, bulk density,moisture content, average time of wettabilityand insoluble solids [11-13]. For instance,Greenwald and King [11] pointed out thatthe increased air temperature resulted in higherbulk density of spray-dried products. On theother hand, Chegini and Ghobadian [13]concluded that the raise of drying air tempera-ture increased the particle size, average timeof wettability and insoluble solids butdecreased the bulk density and moisturecontent of the orange juice powder.

Due to the lack of research about spraydried pineapple juice, this study was carriedout with the following objectives; (1) to studythe feasibility of producing the spray-driedpineapple powders and (2) to determine theoptimal quantity of MD and drying conditionfor spray drying of pineapple juice.

2. MATERIALS AND METHODS2.1 Raw Materials

The ripe pineapples (Ananas comosus) ofthe “Smooth cayenne” variety were obtainedat the local market nearby Kasetsart University,Bangkok, Thailand. The pineapples werepeeled, cut, crushed and hydraulically pressedto squeeze out the juice. The soluble solidcontent, color and pH of the fresh pineapplejuice were measured by refractometer, colormeter and pH meter respectively.

Aqueous solutions of MD were preparedby dispersing MD that had dextrose equivalent(DE) 10, pH 4.7, and moisture content 5.2%into 200 gram of hot water. The solution wasmixed with 900 gram of the fresh pineapplejuice using the blender. The amounts of MDfilled into the hot water were 165, 220 and275 grams in order to provide MD content15, 20 and 25% of the combination of hotwater and pineapple juice 1,100 gram. TheMD content 15, 20 and 25% of the feed

500 Chiang Mai J. Sci. 2010; 37(3)

mixture can be approximately converted tobe the ratios of pineapple juice (based on totalsoluble solids) and MD (based on dry weight)at 65:35, 50:50 and 40:60 (pineapple juice:MD)by weight respectively.2.2 Drying Experiment

The samples prepared by the proceduredescribed in the previous section were driedin a “NIRO” small-scale spray dryer model“Mobile Minor 2000”. The schematic diagramof the dryer was shown in Figure 1. Thedrying experiments were carried out usingthe full factorial design of three MD content

levels (15, 20 and 25%) and three drying airtemperatures (130, 150 and 170oC). The feedrate was controlled at 0.020, 0.022 and 0.035litre per minute (lpm) for the drying airtemperatures 130, 150 and 170oC respectivelyin order to keep the temperature of the outletdrying air at approximately 90oC. At the endof drying, the pineapple powders were collected,weighed, and kept in the sealed container forthe quality determination. The total weightvalue of powder collected from each dryingrun was used for the calculation of powderrecovery.

Figure 1. A schematic diagram of the spray dryer.

2.2 Quality DeterminationThe soluble solid content, color and pH

of the fresh pineapple juice were measuredby “ATAGO” hand refractometer, “Minolta”color meter model CM-3500d and “JENCO”pH meter respectively.

For each drying batch of pineapplepowders, the moisture content and thesolubility were measured. The moisture

content was determined by the oven methodusing 2 g of powder and 105oC dryingtemperature for 2 h. After that, the samplewas cooled in desiccator, weighed, redried 2h, and repeated process until change in weightbetween successive dryings at 2 h intervals wasnot over 2 mg. The weight loss after drying inthe oven was used to calculate the moisturecontent of pineapple powder, expressed on

Chiang Mai J. Sci. 2010; 37(3) 501

wet basis (WB). To determine the solubility,the methods of Al-Kahtani and Hassan [14]and Sommanas [15] were applied. Thepowder sample and distilled water weretransferred into a 500 mL beaker with theproportion 37 g of powder per 100 g ofdistilled water. This ratio was based on theaverage production yield (the feed 137 g couldproduce 37 g of powder). After transferringthe specified amount of powder sample anddistilled water into the beaker, a magnetic barwas dropped and then the beaker was locatedon the “FISHER” hot plate stirrer model210T setting at speed level 5 while theheater was not turned on. The measurementwas conducted in the room controllingtemperature at 25oC. The stopwatch wasstarted since turning on the hot plate stirrerand stopped when the powder in thebeaker entirely dissolved. This recorded time,namely solubility was indicated in the unit ofminute.

An aliquot of pineapple powder fromeach drying run was reconstituted at theproportion 37 g of powder per 100 g ofdistilled water in order to make them to becomparable with the fresh juice. The pHand color of the solutions were measured.Furthermore, the solutions were exposed tothe sensory evaluation and compared with thefresh pineapple juice in aspects of appearance,color, aroma, taste and overall liking. Thesensory was evaluated using 9-point hedonicscale test by 22 panelists who were theundergraduate students in the faculty. TheFigure 2 illustrates the throughout procedurefrom the raw material preparation until thesolutions of pineapple powder were exposedto the color and pH measurements and thesensory test.

The soluble solid content, color, pH andsolubility were measured in three replicationswhile the moisture content was measured induplicate. The software package of Statistica

5.5 StatSoftTM (supplied by StatSoft, Inc. Tulsa,OK 74104 USA) was used for statisticalanalysis.

Figure 2. A schematic diagram of theexperiments.

3. RESULTS AND DISCUSSION3.1 Fresh Pineapple Juice

The measurement of soluble solidcontent, color and pH of the fresh pineapplejuices revealed that their soluble solid contentsranged 11-12oBrix while the mean of lightness(L*, +), redness (a*, +) and yellowness (b*,+) were 61.3, 3.3 and 18.8 respectively. Theaverage of pH of the fresh pineapple juicesin this study was 2.3.3.2 Pineapple Powder Appearance

From the drying experiment, the ap-pearances of pineapple powders from alltreatments were white color and not

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agglomerate (powdery). However, the intensityof the pineapple aroma of the powder wasdeclining along the increase of MD content.In addition, the preliminary experimentsimplied that when using the MD contents at5 and 10%, the powder product would besticky and agglomerated (toffee). These stickyand agglomerated products would seize onthe surface of the dryer especially in the dryingchamber and cyclone.3.3 Moisture Content, Solubility andPowder Recovery

The outcomes of moisture content,solubility and powder recovery determina-tions for the pineapple powders are presentedin Table 1. The results showed that themoisture contents of the powders were inthe range of 4.0-5.8%. These moisture levelsare close to the moisture content of dried-teapowder that ranged 3-5% [16]. The increasingdrying temperatures and MD content resultedin the lower moisture product. The highdrying air temperature leaded to the hightemperature gradient at the surface of feeddrops. This directly expedited the heat transferrate and also the moisture evaporation fromthe liquid drops in the drying chamber resultingin the low moisture level of dried product.Furthermore, the MD has the capability tohurdle the sugars in the fruit powder thathave highly hygroscopic nature fromabsorbing the humid in the surrounding air[9]. Nevertheless, in this study the feed rateswere diverse for different drying temperaturesin order to keep the temperature of the outletdrying air at approximately 90oC. At this outlettemperature level, the powder products wereusually not burnt or humid. At elevated dryingtemperature, the feed was supplied to thedrying chamber at a higher rate to avoid theproduct burn. On the other hand, at lowerdrying temperature, the feed rate was reduced;otherwise, the powder might be too wet.Thus, the effect of the drying temperature on

the moisture content of pineapple powderwas partially reimbursed by the feed rateincrease.

Regarding the solubility in Table 1, theeffect of drying temperature was unclear.However, it was found that at the same dryingtemperature the solubility in minute would bereduced when raising the concentration ofMD. This result can be explained by thediscovery of Shrestha et al. [9]. They foundthat the addition of MD content raised theTg of powder; however, the increase in Tg

was not linear. Thus, the agglomeration ofMD rich powder will be obstructed; as aconsequence, the specific surface area of thepowder was high in this case leading to thefaster solubility (lower value of solubility inminute) of the powder.

The values in Table 1 indicate that alldrying conditions provided high powderrecovery in the range 72.7-86.6%. Highpowder recovery values were due to theaddition of MD contents > 15% that resultedin the non-sticky products and subsequentlylow amount of product seized in the dryingchamber and cyclone. Besides, there was atrend of less powder recovery along theincreasing MD contents. This occurrence mightbe explained by the method applied for thepowder collection. In this study, all the powderwas collected at the cyclone; nonetheless, thedrying chamber was periodically knocked bythe hard-rubber hammer during theexperiment in order to keep the remainingpowder on the drying chamber surface andits accessories as minimum as possible. As aresult, although the powder recovery was highfor every drying run, there were higheramount of powder stuck in the drying systemfor the drying conditions that had more solidsin the feed (added higher MD) because ofthe limitation of the hammer force applied inthis powder collection method. On the otherhand, if at the end of drying run, all the

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powder on the drying chamber surface wasmanually swept and combined with those

collected at the cyclone, the trend of powderrecovery might change.

3.4 Color and pH of the ReconstitutedSpecimens

As mentioned earlier, the pineapplepowders were reconstituted with distilledwater at the proportion 37 g of powder per100 g of distilled water in order to make thesolutions that were similar to the fresh juice.The results of color and pH determinationfor the solutions comparing to the fresh juiceare illustrated in Table 2. It showed thatthe pH of the solutions were significantlyhigher than those of the fresh sample at 5%significant level. This result was unsurprisingbecause the pH value of MD applied in thisstudy was 4.7 while the fresh juice pH was2.3. Furthermore, there were only slightdifferences in the pH among the reconstitutedspecimens. If deeming the proportion of juice(based on total soluble solids) and MD (basedon dry weight) in this study (65:35, 50:50 and40:60), it is clear that MD contents were notvery difference between powder samples.Moreover, these powders were reconstitutedwith distilled water before measuring pH; as

a result, the effects of different proportionsof juice and MD contents on the pH valueswere also diluted.

Regarding the color, it appeared that thelightness, redness and yellowness of thesolutions of pineapple powders weresignificantly different from the fresh juice foralmost all cases. In general, the solutions hadthe less lightness than the fresh sample butthe redness and yellowness were higher.The cause of the lower lightness was that asmall proportion of powder could notdissolve in the solution. Another reason forthe lightness decrease could be the non-enzymatic browning reactions occurring duringthe spray drying [17]. For the higher rednessand yellowness of the solutions, it may be alsoas a result of some non-enzymatic browningreactions such as caramelization and Maillardreactions happening during the drying process.These reactions could take place because ofthe high sugar content in the pineapple juiceand heat supplied to the juice in the dryingchamber [18]. Furthermore, the MD concen-

Drying condition

Drying temperature MD content Moisture content Solubility (minute) Powder recovery

(oC)/Feed rate (lpm) (%) (%) (%)

130/0.020 15 5.8 0.1a 6.2 0.2a 86.620 4.4 0.1b,c 2.7 0.7b,e 75.925 4.3 0.3b 1.9 0.3c 72.9

150/0.022 15 5.1 0.3d 6.2 0.1a 86.620 5.2 0.4d 4.4 0.2d 81.325 4.5 0.0b,c 3.1 0.1e 80.0

170/0.035 15 4.8 0.2c,d 4.6 0.3d 81.420 4.2 0.2b 1.9 0.1c 73.225 4.0 0.2b 2.4 0.2b,c 72.7

Table 1. The moisture contents, solubility and powder recovery of the pineapple powders.

Note: lpm = litre per minute.Moisture content and solubility values are mean standard deviation.Means with the same superscript within same column are insignificant different (P < 0.05).

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tration is another cause of the color differencebetween the fresh and the reconstitutedpineapple juices. However, the color differenceamong reconstituted samples did not haveobvious trend because for these samples

the spray-dried powders were diluted indistilled water. Moreover, the effect of dryingtemperature on the product color was notapparent because the feed rates were alsoincreased at higher drying temperature.

Drying condition Color

Drying temperature MD content pH

(oC)/Feed rate (lpm) (%)

130/0.020 15 57.3 0.1a,e 4.8 0.1a 24.3 0.3a 7.0 3.5 0.1a,c,d

20 52.6 1.5 b 6.3 0.7b,e 25.6 0.5b,c 11.4 3.5 0.0a,c,d

25 67.8 0.8c 3.7 0.2c 23.0 0.6f 7.8 3.6 0.0a,b,d

150/0.022 15 58.8 1.7a,d 5.2 0.3a,d 25.1 0.7a,b 7.1 3.5 0.1a,c

20 57.2 1.6a,e 6.0 1.3e,f 26.4 1.7c 9.1 3.5 0.1a,c,d

25 54.8 1.5b,e 6.9 0.3b 26.7 0.3c 10.8 3.4 0.1c

170/0.035 15 52.4 1.4b 5.6 0.3d,f 24.2 0.6a 10.6 3.6 0.1b,d

20 73.1 0.7f 2.1 0.0g 18.2 0.3e 11.9 3.7 0.1b

25 47.3 1.9g 6.9 0.2b 25.6 0.1b,c 15.9 3.7 0.1b

Fresh pineapple juice 61.3 2.1d 3.3 0.2c 18.8 0.3e - 2.3 0.1e

Table 2. The color and pH of the solutions of pineapple powders comparing to the freshpineapple juice.

Note: lpm = litre per minute, L* = lightness, a* = redness, b* = yellownessL*, a*, b* and pH values are mean standard deviation.Means with the same superscript within same column are insignificant different (P < 0.05).

L* a* b* ΔΔΔΔΔE*

3.5 Sensory EvaluationThe outcome of hedonic scale test is

shown in Table 3. The limit score for eachitem was 9.0 indicating that the sample wasfavored extremely. The sensory evaluationwas found that both drying temperature andMD content affected the characteristics ofthe solutions. As regards to the appearanceand aroma, almost all of the solutions ofpineapple powders showed higher score thanthe fresh juice. It might be the consequenceof the higher sugar content in the solutionsdue to the MD integration. For the color, allsolutions were preferred when comparing

with the fresh one. It should be due to thestronger redness and yellowness of thesamples after exposing to the spray dryingprocess. In term of the taste, the solutions ofpineapple powders produced with 15-20%MD were favored but those with 25% MDwere not when comparing to the fresh one.The cause was that if adding MD > 25%, thetaste of MD would dominate and worsenthe favorite of sample [17]. The overall likingscore revealed that the solutions of pineapplepowders produced from the feed with 15%MD at drying temperature 150oC was themost accepted sample.

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Drying condition Score (maximum = 9.0)

Drying temperature MD content Overall

(oC)/Feed rate (lpm) (%)Appearance Color Aroma Taste

liking

130/0.020 15 4.9 0.9a 4.2 0.7a,b,c,d 5.2 0.9a,b,c,d 5.0 1.0a 4.4 0.8a,b

20 3.6 0.8b 4.9 0.9e,f 4.8 1.0e,f 3.8 0.8b 2.4 1.2c

25 3.2 0.9b 3.9 0.7d,g,h 4.6 1.1d,g,h 3.3 0.9b 3.5 0.8d

150/0.022 15 5.6 0.9c 5.2 0.9e 4.7 0.9e 5.6 0.9c 5.6 1.0e

20 4.6 0.8a 4.7 0.9f,i 4.8 1.0f,i 4.8 1.1a 5.2 0.9e,f

25 3.1 1.0b 3.8 0.8c,g 4.0 0.9c,d,h 3.5 0.8b 3.9 0.8b,d

170/0.035 15 4.7 1.0a 4.2 0.7b,c,h,i 3.0 0.7b,h,i 3.6 0.9b 4.0 0.9b,d

20 5.0 0.9a 4.6 1.0b,f 4.6 0.7b,f 5.2 1.0a,c 4.9 0.9a,f

25 3.7 0.8b 3.7 0.8a,g 3.1 0.7a,g 2.6 0.9d 2.6 1.3c

Fresh pineapple juice 3.3 0.9b 3.5 1.0g 3.9 0.9g 3.6 0.9b 3.7 1.0d

Table 3. The sensory test results of the solutions of pineapple powders and freshpineapple juice.

Note: lpm = litre per minute.Sensory score values are mean standard deviation.Means with the same superscript within same column are insignificant different (P < 0.05).

4. CONCLUSIONSFrom the results, it showed the

practicability of producing the pineapplepowders from the mixture of fresh pineapplejuice and the aqueous solutions of MD byapplying the spray drying method. Afterreconstituting the pineapple powder in thedistilled water, it was found that a number ofsamples obtained the sensory test scores notless than the fresh counterpart in aspects ofappearance, color, aroma, taste and overallliking. Obviously, the drying air temperatureand MD content had significant influence onthe product quality. The pineapple juice addedwith MD at 15% and dried at 150oC achievedthe highest overall liking score. The pineapplepowder made under this condition had themoisture content and solubility 5.1% and 6.2minutes respectively. Moreover, its solution hasthe lightness 58.8, redness 5.2, yellowness 25.1and pH 3.5. These results are useful for thefruit powder producers and researchers.

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