microbial count and shelf life of strawberry juice - PJAR

Pakistan J. Agric. Res. Vol. 25 No. 3, 2012MICROBIAL COUNT AND SHELF LIFE OF STRAWBERRY JUICEAmbreen Akhtar Saddozai, Saeeda Raza* and Shahzad ArshadSaleem**ABSTRACT:- A study was conducted to investigate the influence ofmicrobiological activity on different quality factors of strawberry juiceduring storage. Strawberry was purchased from local market and its juicewas kept for two weeks at room temperature to check its shelf life. Totalplate count (TPC), pH, flavor, color, yeast and moulds were checked weekly.Quality changes of strawberry juice during storage can be caused both bymicrobiological and physiological processes. At day 0; pH 3.2, color bright2 -1red, excellent flavor, TPC 2.7 x 10 cfu g were recorded, while no yeast ormould were found. After one week, the pH 3.6, dull red color, TPC2 -1 3 -1 5 -12.25x10 cfug , yeast 1.7x10 cfu g and mould 1.6x10 cfu g were observed.2While after two weeks (day 14) color was brown while pH 4.0, TPC 1.9x10-1 6 -1 5 -1cfu g , yeast 2.47x10 cfu g and mould 1.6x10 cfu g were noticed. Yeast,mould and pH were increased with the passage of time. Spoilage can becontrolled by keeping the juice in refrigerator and using preservatives.Thus with good storage conditions, the shelf life of the strawberry juice canbe increased satisfactorily.Key Words: Strawberry; Juice; Shelf Life; Total Plate Count; Yeast;Mould; Pakistan.INTRODUCTIONThe garden strawberry, Fragaria× ananassa, is a hybrid species thatis cultivated worldwide for its fruit.The fruit is widely appreciated for itscharacteristic aroma, bright redcolor, juicy texture, and sweet-ness.The garden strawberry was firstbred in Brittany, France, in the1750s via a cross of Fragariavirginiana from eastern NorthAmerica and Fragaria chiloensis,which was brought from Chile byAmédée-François Frézier in 1714.The first garden strawberry wasgrown in France during the late 18thcentury. Prior to this, wildstrawberries and cultivated selectionsfrom wild strawberry spe-cieswere the common sources for thefruit.In worldwide 366,889t strawberryis produced. Straw-berry is oneof the high value crop that has beencultivated in different parts ofPakistan for a long time but itscommercial plantation in Sindhstarted about ten years ago inKhairpur. Based on rough estimatestrawberry plantation is done over250 acres, in different areas ofKhairpur i.e., Ripri, Garihimori,Pano Akil. The varieties grown inPakistan are Chandelier, Corona andStuff. These are mostly sour andsmall in size. Pakistan is producing alimited quantity of strawberries.These are a number of reasons forrestricted production, like the*Food Science and Product Development Institute, National Agricultural Research Centre, Islamabad, Pakistan.** Agricultural Research Institute, Dera Ismail Khan, Pakistan.Corresponding author:ambreen.saddozai@yahoo.com218

MICROBIAL COUNT AND SHELF LIFE OF STRAWBERRY JUICEaddition to being consumed fresh,strawberries can be frozen, as well asdried and used in prepared foods,such as cereal bars. Strawberries area popular addition to dairy products,as in strawberry-flavored ice cream,milkshakes, smoothies, and yogurts.Depending on area, strawberry pie,strawberry rhubarb pie, or strawberryshortcake are also popular.The aim of present studies was toinvestigate the shelf life of strawberryjuice (microbial and physicalchanges) at room temperature.MATERIALS AND METHODStrawberries were purchasedfrom local market of Islamabad,washed thoroughly, processed intojuice and stored at room temperatureto determine the shelf life of preparedjuice at Food Science and ProductDevelopment Institute, NationalAgricultural Research Centre(NARC), Islamabad. The preparedjuices were analyzed for sensoryevaluation by a panel of 10 judges a(Larmond, 1977). The parametersincluded color, taste and flavor. Thejuice was also tested for microbiologicalanalyses i.e., total platecount, yeast and moulds (FAO,1992). According to this method50ml sample was homogenized withButter field's phosphate buffer (pH7.2). Serial dilutions of juice wereprepared by transferring 1ml ofsample in 9ml of sterile phosphatebuffer in test tubes. After eachdilution, the contents were mixed invortex-mixer for 10 sec. One mililitervolumes of each dilution weretransferred to Petri dish with platecount agar and mixed with mediumin triplicate. After solidification Petri0dishes were incubated at 35 C for48h for total plate count and coloniesformed on the surface and in themedia were counted. The total countwas calculated from the mean countof triplicate of Petri dishes,considering the dilutions.For yeast and mould spreadplate method was used. Yeast growthwas checked on plate count agaramended with 40 ppm Chloramphenicol(added as antibacterialagent). Potato dextrose agar wasused to detect moulds. About 0.1mlinoculum of each dilution was placedon the center of solidified potatodextrose agar and plate count agar ina Petri plate and used a sterile bentglass rod for spreading. Theinoculum was spread on the surface0of media and incubates at 25 C for96h.RESULT AND DISCUSSIONThe considerable changes inquality parameter were reported inthe sample (strawberry juice) duringstorage at room temperature (Table1). It is evident that the pH value offresh juice was 3.2. Deirdre et al.(1999) had also reported the pHrange of strawberry juice as 3.4-3.6which shows it is acidic in nature.The pH of the juice increased withthe passage of time. At the start ofstudy, the pH of the sample was 3.2,while after 7 days the pH increased to3.6 and further increase in pH i.e.,4.0 was recorded after two weeks ofstorage (Table 1). The increase in thepH is might be due to the increase inalcoholic contents in the juice duringstorage (Forney et al., 2000).At day 0, the color of the samplewas bright clear red. On day 7, a littlechange in the color was observed.However, a dark red color wasrecorded later. On day 14, brown220

AMBREEN AKHTAR SADDOZAI ET AL.Table 1.Shelf life of strawberry juiceDay pH Color Flavor Total platecount(cfug -1 )Mould(cfug -1 )Yeast(cfug -1 )Day 0 3.2 Bright, clear red Excellent 2.7×10 2 Nil NilDay 7 3.6 Dull red Satisfactory 2.25×10 2 1.4×10 3 1.7×10 3Day 14 4.0 Brown Unsatisfactory 1.9×10 2 1.6×10 5 2.47×10 6color was recorded. Studies of Pino etal. (2001) and Silas et al. (2006)showed that a progressive changefrom a bright, clear red to dull redand finally to brown darkening in thecolor of strawberry occur during thestorage at room temperature. Theyalso noticed that color changesoccurring in the juice could partiallybe overcome by storage at lowtemperature.Strawberries are well known fortheir exquisite flavor and are widelyused to prepare juices (Bood andZabetakis, 2002). The flavor of freshstrawberry juice was excellent, whileafter 7 days storage, the flavor wassatisfactory. The flavor became unsatisfactoryafter14 days of storage.With the passage of time the flavor ofthe sample was degraded due tocompositional changes in thesample. Strawberry juice flavorcompounds have shown low stabilityduring storage in various studies(Mosqueda-Melgar et al., 2008).Lundahl et al. (2006) observedpronounced losses of ascorbic acid instrawberry juice with marked changein flavor during storage. Alcoholshave been identified as constituentsof the aroma profile in strawberries.The major alcohol identified in strawberryjuice was 1-butanol which wasaffected after a week of storage. Aftera long period of storage at roomtemperature, an increase in 1-butanol concentrations can renderan unpleasant flavor to the product,due to its strong, pungent smell andtaste.Factors such as maturity at themoment of processing or strawberryvariety, could substantially affect thecolor, flavor, pH and microbiologicalcharacteristics of strawberry juice(Forney et al., 2000). The total plate2count decreased from 2.7×10 to2 -12.25 ×10 cfug during one week storageat room temperature. After 22 -1weeks it decreased to 1.9×10 cfugdue to low pH of the sample. Bacterialgrowth is eliminated to a verylarge extent by acidity, bacterialspores will not germinate in juicewith the pH less than 4.5 andvegetative cells of pathogenicbacteria will not grow at pH less than4.0 (Smelt et al., 1982).Moreover, no mould and yeastgrowth was observed in the sample at3 -10 day. After 7 days 1.4×10 cfug3 -1yeast, 1.7×10 cfug mould were5 -1recorded. After 2 weeks 1.6×10 cfug6 -1yeast and 2.47×10 cfug mould wererecorded. The reason of yeast growthis due to the presence of sugars(carbohydrates) in the sample.According to the Gulf standardsthe maximum anticipated andpermitted count of TPC for juices is3 45.0 × 10 and 1 × 10 , respectively221

MICROBIAL COUNT AND SHELF LIFE OF STRAWBERRY JUICE(Table 2). While in the present studythe TPC is lower than the anticipatedvalue as well as permitted value.However the bacterial load isdecreased with the passage of time.This is due to the lower pH than thatof the pH needed for bacterialgrowth.The Gulf standards show thatthe yeast and mould count should3not be more than 1 × 10 cfu ml-1 injuices. Present study shows that atday 0, there was no yeast growth inthe sample but with the passage oftime the yeast growth was observed.The microbiological status of strawberryjuice is not affected very muchduring storage at room temperatureif it is carefully handled. However,some studies have shown a significantincrease in the microbiologicalpopulations of strawberryjuice during storage. The TPC increasedduring storage in somecases. Moreover, mould and yeastgrowth has also been observed byvarious researchers during theirwork on strawberry juice (Amanatidouet al., 2003).The freshly prepared juice gotthe higher score and overall acceptabilitywas 9 (Table 3). But after 7days there was little change incolour, taste and flavor and overallacceptability was 5. After 14 daysoverall acceptability was 1.5. Thisshows the progressive deteriorationTable 2.CountGulf standard for microbiologicalcriteria for juicesMaximum countanticipated-1(cfuml )Maximum countpermittedTotal plate count 5.0 × 10 3 1 × 10 4Yeast 100 1 × 10 3Mould 100 1 × 10 3Table 3.Sensory evaluation ofstrawberry juiceDuration (day) Color Flavor Taste Overallacceptability0 9 9 9 97 6 5 4 514 2 1 Not fit totasteand quality degradation of juicestored at room temperature.It is thus concluded that thestrawberry juice quality is affectedduring storage by microbiologicaland physiological processes. Howeverthe spoilage can be controlled byprocessing and storage underaseptic/sanitation conditions. Theshelf life of the strawberry juice canbe increased in a satisfactory way bykeeping in refrigeration and by usingpreservatives.LITERATURE CITEDAmanatidou, A. Slump, R. A. andSmid, E. J. 2003. Microbialinteractions on minimallyprocessed carrots under elevatedoxygen and carbondioxide concentrations. ActaHorti-culturae, 600: 621-628.Ayala-Zavala, J. F. Wang, S. Y.Wang, C. Y. and González-Aguilar, G. A. 2004. Effect ofstorage tem-peratures onantioxidant capa-city anda r o m a c o m p o u n d s i nstrawberry fruit. LWT-FoodSci. and Technol. 37: 687-695.Bood, K. G. and Zabetakis, I. 2002.The biosynthesis of strawberryflavor (II): Biosynthetica n d m o l e c u l a r b i o l o g ystudies. J. Food Science, 67:2-8.1.5222

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