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*Corresponding author’s e-mail: psrijaya@gmail.com

Impact of gamma irradiation and osmotic dehydration on qualitycharacteristics of guava (Psidium guajava ) slicesM. Srijaya* and B. Shanthti Priya

Food Technology Division, Department of Food and Nutritional Sciences,Sri Sathya Sai Institute of Higher Learning, Anantapur-515 001, Andhra Pradesh, India.Received: 04-07-2016 Accepted: 07-07-2017 DOI:10.18805/ajdfr.v36i03.8964

ABSTRACTA multi-target (combination preservation) technique has been extensively applied to develop minimally processed andcompletely stabilized shelf stable food produces. A combination of irradiation and osmotic dehydration decrease the needfor thermal treatments for enhancing the shelf life and microbial safety of cut fruits and vegetables. The present study aimsat identifying combined effect of -irradiation pre-treatment and osmotic dehydration treatment on guava. The guavaspacked in LDPE pouches were irradiated at 0.25 kGy, and 1.0 kGy dosages at the dose rate of 2.75 kGy/hr. The guavaslices with and without irradiation were infused for osmotic dehydration process. Optimization of the process time (3,6and 9 hr) was also investigated. Further, stored guava slices were analyzed for their physico – chemical, antioxidant andmicrobial analysis. Mass transfer kinetics of guava slices osmotically dehydrated in sucrose solutions were significantlyaffected by irradiation dosage and sucrose concentration and treatment duration. The evaluation of hurdle approach onguava slices showed that, combination treated slices were significantly less susceptible to nutrient and colour changesduring storage. The synergy between the irradiation and dehydration also resulted in adequate microbiological stability ofthe slices.

Key words: Guava, Gamma irradiation, Osmotic dehydration.

INTRODUCTIONFruits and vegetables are potent sources of essential

dietary nutrients such as vitamins, minerals and fibre. Theyare acclaimed universally as protective foods and increasedconsumption has been associated with reduced risk ofcoronary artery diseases, cerebro-vascular disease andmuscular degenerative diseases. (Javaria et al., 2012).

India is the second largest fruit and vegetablesproducer in world with an annual production of 44 millionmetric tons. In India, post harvest losses of fruits andvegetables are estimated to be 25%. This is due to lack ofproper retailing and inadequate storage capacity. Preservingfood to extend its shelf-life, while ensuring its safety andquality is of primary concern. The development of the hurdleconcept has lead to renewed interest in the use of moretraditional preservation methods and the ways they can becombined with newer technologies (Ashok and Singh, 2012).

Synergies are more likely the individual hurdlestargeting different functions within the cell, thus permittinggentler preservation treatment, with potentially less impacton the quality of the product (Leistner, 2000). Gammairradiation has been proven to inhibit microbial growth, delayripening and extend the shelf life of minimally processedfruits and vegetables (Prakash et al., 2000a).Osmotic

dehydration is one of the potential preservation techniquesfor producing high quality products. This provides minimalthermal degradation of nutrients due to low temperature waterremoval process (Sodhi et al., 2006). The adaptation ofosmotic dehydration as a best process hurdle can be ascribedto two aspects. It is a low temperature water removal processand hence, minimum loss of color and flavour retention ismore when sugar syrup is used as an osmotic agent (Islamand Flink, 1982).

Guava is considered as common man’s fruit andcalled as the apple of the tropics (Adsule and Kadam, 1995).Guava fruit is an excellent source of nutrients and consideredas a good source of antioxidant dietary fiber owing to itshigh content and extractable polyphenols (Jimenez et al.,2001).

A combination of irradiation and osmoticdehydration decrease the need for thermal treatments forenhancing the shelf life and microbial safety of cut fruitsand vegetables. Hence, the current study aimed at identifyingcombined effect of ã-irradiation pre-treatment and osmoticdehydration treatment on guava slices and to examine theefficacy of combination treatments on the mass transferkinetics, physico-chemical, antioxidant and microbial qualityof guava slices.

Asian J. Dairy & Food Res, 36(3) 2017 : 197-205Print ISSN:0971-4456 / Online ISSN:0976-0563

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Table 1: Treatments for guava slicesTreatment Treatment code Description of treatmentno1. GCA osmotically dehydrated at 400 Brix concentration2. GI1A low dose (0.25 kGy) gamma irradiated, osmotically dehydrated at 400 Brix concentration3. GI2A high dose (1.0kGy) gamma irradiated, osmotically dehydrated at 400 Brix concentration4. GCB osmotically dehydrated at 600 Brix concentration5. GI1B low dose (0.25 kGy) gamma irradiated, osmotically dehydrated at 600 Brix concentration6. GI2B high dose (1.0kGy) gamma irradiated, osmotically dehydrated at 600 Brix concentration

MATERIALS AND METHODSGuavas were obtained from local market. To ensure

homogeneity of sample, they were selected according to theirquality attributes such as uniform degree of maturationbased on skin color (greenish yellow) and total soluble solidscontent.Gamma irradiation treatment: Irradiation treatment wascarried out in a cobalt -60 chamber (Model : Gamma chamber5000, BARC, Mumbai). The dose rate was 2.75 kGy/hr. Theguavas were packed in LDPE pouches and irradiatedseparately at 0.25 kGy (I1), and 1.0 kGy (I2) dosagesrespectively. After radiation treatment, the guava sampleswere prepared for osmotic dehydration process. The gammairradiated guavas were blot dried with absorbent tissue paperto remove external moisture. They were manually cut with astainless steel knife into 0.25 cm thick circular slices.Optimization of infusion media: Food grade sucrosesolutions of 400 Brix (A) and 600 Brix (B) were preparedand food grade KMS (Potassium meta bisulphite) and citricacid were also added at 5% level to the infusion media.Preliminary infusion process was conducted in 400B and600B solution with three variant temperatures viz., 3 hrs, 6hrs and 9 hrs at 300C. After the specified dehydration time,the samples were separated from the osmotic solution, rinsedwith spray of plain water and dried on a filter paper. Apreliminary sensory testing was performed by the selectedpanelists comprised of 10 members. They were asked to scorethe quality attributes such as appearance, texture, color, tasteand over all acceptability using 9 point hedonic scale.Preliminary quantitative analysis was also carried out todetermine the moisture content of the samples. After theanalysis, 9 hours soaking time with 400B and 600Bconcentration were found best to obtain the fruit withdesirable characteristics. Table 1 shows the differenttreatments given to the guava slices for storage .Osmotic dehydration: The prepared guava slices weresuspended in 400B and 600B infusion media at pre selectedtime (9 hours) and temperature (300C). The ratio of the fruitsand infusion media was maintained as 1:8 in order to ensurecomplete immersion of samples. The solutions were stirredat an interval of 30 min to stimulate an ongoing osmoticprocess. Samples were withdrawn from osmotic solutionsafter the determined time (9 hrs), drained and dried with

filter paper to remove adhering solution from the surface ofthe slices. The weight of the samples (i.e. slices) and volumeof the osmotic solution were measured prior to immersionand after infusion. After osmotic dehydration, samples werepacked in Ziploc (LDPE) pouches and stored in refrigeratorat 12+20C and periodically evaluated.Mass transfer mechanisms

Per cent moisture loss (ML), per cent massreduction (MR), and solid gain (SG) were calculated by themass balance equations.

SG (Solid gain) = moisture loss (%) – mass reduction (%)The external color of the fruit slices were

determined during storage by using Konika MINOLTA, CR– 10 colour reader as given by Hajare et al., (2006). Theresults were expressed in colour lightness (L*), Chroma (C*),a* (greenness to redness) and b* values(blueness toyellowness). Moisture was analyzed by method given byBerwal et al., (2004). Total soluble solids (0Brix) weredetermined by using digital refractometer (ATAGO PR-1,Japan) according to AOAC methods (1995). The Titrableacidity and non-enzymatic browning of the samples wereanalyzed by using the method developed by Ranganna (1986)and Berwal et al., (2004);Vitamin C content by Ranganna,(1986); Total phenol content by Singleton and Rossi,(1965).The yeast and mold count of the fruit was determinedby pour plate method using potato dextrose agar (PDA) as amedia as described by Aneja (2001).

To investigate the significant differences amongstthe average values of treatment, two way ANOVA wasapplied. In order to find out the significant difference betweenthe samples, critical difference test was applied (Gupta, 1995).RESULTS AND DISCUSSION

Maximum reduction in water content of guava sliceswas observed in GI2A slices. Overall the infusion processfor all the treatments resulted with nearly half the moisturecontent of fresh guavas (87%) (Table2). Gamma irradiationtreatment affected the rate of water removal and solute gain

Initial moisture – moisture at time% ML = Initial moisture × 100

Initial mass – mass at time (T)% MR = Initial moisture × 100

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Table 2: Effect of gamma irradiation and osmotic dehydration on mass transfer mechanisms of guava slices.Treatment ML (%) MR (%) SG(%)GCA 46.4 25 21.4GI1A 52 44 8GI2A 62 47 15GCB 47 10 37GI1B 56 45 11GI2B 58 55 3

irrespective of dosage. The above stated fact can be attributedto the effect of gamma irradiation as a pre-treatment. Thereduction in the moisture of the infused fruits may also beattributed to large osmotic driving force difference betweenthe cell sap of the guava fruit and surrounding hypertonicsucrose solution. An increase in osmotic sucrose solutionconcentration increased this gradient and in turn the drivingforce.

Rastogi (2005) concluded that gamma irradiationaffected the cellwall structures leaving the cells morepermeable for moisture and solute transfer. Singh and Pal(2009) indicated ionizing irradiation as a stress factor forfresh fruits. Severity of stress depends on dose level andmaturity of the fruit. The increase in cell permeability dueto increase in irradiation dose was reported by Hayashi etal., (1992). In the present study, a significant influence ofirradiation dosage and sucrose concentration was observedon solute gain of guava slices. In GI2B sample, the solidgain was minimal which could be due to stress induced bygamma irradiation.

Mass transfer of control and gamma irradiatedsamples varied during the course of osmotic dehydration(Table2). There was a simultaneous increase in mass transferas the radiation dose and concentration of sucrose solutionincreased. Guava slices immersed in 600B solution showedhigher mass transfer rates compared to those immersed in400B solution. The increase of mass transfer was due to theconcentration difference between guava and osmotic solutionwhich increased the rate of diffusion of solute and waterexchange with osmotic solution. Lazavides et al., (1997)attributed the increased mass transfer of sugar moleculeswith increasing concentration to possible membrane swellingeffect, which might increase the cell membrane permeability.

Jacob and Paliayath (2012) reported lower moisturecontent of the infused cherries and also gain in solids wasrelatively low in infused and oven dried cherries. In thepresent study, other factors affecting the rate of water removaland solid gain are the temperature of the osmotic solution,immersion time, level of agitation in the solution, the specificcharacteristics (size and shape) of the fruit and the solutionto sample ratio. Several authors have described the role ofthese factors on the mass transfer kinetics during the osmotic

dehydration of fruits and vegetables such as apples, bananas,carrots, tomatoes etc. (Dermesonlouoglou et al., 2005).Fruit colour: There was a significant difference among thetreatments on the initial day of storage (Fig 1). This changecould be correlated to gamma irradiation as well as osmoticdehydration treatment. It was observed that lightness (L)decreased with increase in the radiation dose and also theosmotic solution concentration. Thus, the highest decreasein L values(16%) was observed in GI2B samples. a* valueincreased with osmotic solution concentration. Moreover,gamma irradiation also would have contributed to theincrease in the a* values. It was observed that, highestincrease of a* value was found in 600B solution than 400B.By comparing irradiated and unirradiated infused samples,the a* values significantly increased with radiation treatmentirrespective of dosage. The increase in the a* values couldbe attributed to the browning reactions that occur duringdrying and also concentration of the infusion media. Adamet al., (2000) has reported the change of color occurringduring processing which could be attributed to the Maillard’sbrowning reaction. A similar trend with increase in a* valuewas found for microwave drying of kiwi fruit.

There was remarkable change upon storage on b*values of GI1B samples. There was minimal difference duringstorage on b* values for various treatments. The change inthe b* value can be associated with less yellowness and moreredness. It was reported in a study that air-dried carrot sliceswere found darker with less yellow and red hues as comparedto microwave dried ones (Sumnu et al., 2009).Moisture: The mean values of moisture in guava slices werefound to be in the range of 32 to 46% respectively. Thechange was found to be statistically different (p<0.05) duringinitial period of storage (Table 3). It can been observed that,the treatments moisture contents ranged within the desirablelevels of the Intermediate Moisture Foods (IMF) (30-45%)(Gullibert, 1988). It was also evident on 15th day of storagethat there was an increase in moisture levels in both thedoses of irradiation and low degree Brix concentration.However, GI2B retained the initial moisture content. During30th and 45th day of storage, irrespective of 0Brix and dosagelevel there was over all increase in moisture content.Total soluble solids: Experimental data (Table 4) revealedthat the 0Brix increased during entire storage duration andfound to be statistically significant at p<0.05. TSS wasmaximum in 400B concentration of both irradiated andosmosed samples.TSS content increased maximum in GI2Bsample from 7.30B to 100B (27% increase over initial TSS)after 15 days of storage. This increment followed the sametrend throughout the storage period. Over all during entirestorage period, all osmo-dried guava slices treated withgamma irradiation irrespective of sugar concentration

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Table 3: Effect of gamma irradiation and osmotic dehydration on moisture (%) of guava slices.Treatment Storage duration

0 day 15th day 30th day 45th dayGCA 46.6f±0.1 47.2e±0.2 53.0d±0.1 70.0f±0.1GI1A 41.4e±0.1 43.3d±0.2 58.4e±0.1 69.0e±0.0GI2A 32.7a±0.0 48.3f±0.1 63.0f±0.0 67.0d±0.1GCB 40.0d±0.0 28.3a±0.1 48.1c±0.1 53.1b±0.1GI1B 38.0c±0.1 42.4c±0.1 47.1b±0.1 52.1a±0.2GI2B 36.1b±0.1 36.0b±0.1 42.0a±0.1 56.7c±1.1Values are mean ± S.D, n=3.Means within treatments in a column not having common superscripts are significantly different. (p<0.05)

Fig 1: Effect of gamma irradiation and osmotic dehydration on Colour (L,a and b values) of guava slices.

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Table 4: Effect of gamma irradiation and osmotic dehydration on total soluble solids (0Brix) of guava slices.Treatment Storage duration

0 day 15th day 30th day 45th dayGCA 1.8a±0.1 2.0a±0.1 5.7a±0.1 20.2c±0.1GI1A 10.2d±0.2 12.9f±0.0 16.5d±0.0 22.8d±0.1GI2A 10.0d±0.1 11.6e±0.0 11.7c±0.0 12.1b±0.0GCB 7.5c±0.0 8.4b±0.1 9.8b±0.0 10.3a±0.1GI1B 3.7b±0.1 10.0c±0.1 19.7e±0.1 20.5c±0.1GI2B 7.3c±0.0 11.0d±0.0 25.4f±0.1 27.0e±0.0Values are mean ± S.D, n=3.Means within treatments in a column not having common superscripts are significantly different. (p<0.05)

Fig 2: Effect of gamma irradiation and osmotic dehydration on titrable acidity(%) of guava slices

showed maximum increase in TSS in comparison with onlyosmosed slices. The difference in the TSS of the treatmentscould be due to sugar compositional changes resulted due totreatments. Similar study has been reported by Parker et al.,(2010) during the development of papaya nectar using acombination of irradiation and mild heat treatment.Titrable acidity: The percentage acidity of the samplesranged between 0.25% to 0.51% (Fig 2). There wassignificant interaction difference among the treatments andthe storage period. Initial acidity value was highest in GI2Band lowest in GCA among the treatments. As the storageperiod progressed acidity values were invariably found toincrease in all treatment combinations,

Among the treatments highest percentage increasein acidity value from 0.34-8.64% was recorded in irradiatedguava slices of GI2B followed by GI1B sample. It was alsoobserved that irradiation treatment significantly increased

the acidity than un-irradiated controls. An increase in theacidity was reported by Paul et al., (2012) for osmoticallypre-treated and vaccum dried pine apple cubes.Non-Enzymatic browning: Table 5 shows the results ofnon-enzymatic browning (NEB) in guava slices duringdifferent storage periods. The color of the samples exhibitedsignificant variation among the different treatments frominitial to final storage period. The degree of browning washigh in gamma irradiated and osmosed samples whencompared to only osmosed samples.

Valdramidis (2010) stated that non-enzymaticbrowning may result from the condensation of a carbonylgroup with amino acids, reaction of sugars and ascorbic acidoxidation resulting in formation of brown products. Fromthe present study, it is clear that the increase in NEB valuescould be due to the reaction of sugars and ascorbic acid.

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Table 5: Effect of gamma irradiation and osmotic dehydration on non enzymatic browning of guava slices.Treatment Storage duration

0 day 15th day 30th day 45th dayGCA 0.09a±0.02 0.176a±0.05 0.356a±0.06 0.393a±0.05GI1A 0.396b±0.03 0.513b±0.01 0.720b±0.03 0.816c±0.05GI2A 0.803e±0.02 0.906e±0.02 1.03e±0.09 1.256f±0.05GCB 0.086f±0.04 0.176a±0.05 0.35a±0.05 0.533b±0.05GI1B 0.403c±0.05 0.626c±0.05 0.80c±0.04 0.93d±0.017GI2B 0.626d±0.06 0.846d±0.05 0.903d±0.03 0.973e±0.01Values are mean ± S.D, n=3.Means within treatments in a column not having common superscripts are significantly different. (p<0.05)

Fig 3: Effect of gamma irradiation and osmotic dehydration on ascorbic acid content (mg/100g) of guava slices

These findings supports the work done by Mancilla et al.,(2011), regarding non-enzymatic browning.Vitamin C: Fig.3 indicates the value of ascorbic acid contentat initial stage and at different storage intervals for differenttreatments. Initial values of ascorbic acid content rangedbetween 68.3±0.5 and 76.43±0.251 for GI2B and GCB. Onzero day of the experiment, a sharp decrease in ascorbicacid content was observed in samples pre-treated with -irradiation, irrespective of dosage. In the initial period i.e.upto 15 days of storage, there was retention of vitamin C inall the samples, irrespective of treatments. However, highdose irradiation caused a significant loss in comparison withlow dose treated fruit slices. A possible explanation for thesedifferences could be stress induced enzyme activation duringprocessing like oxidative reactions by enzymes such as,ascorbic acid oxidase, peroxidase found in fruits and non -enzymatic reactions.

In the present study, as the samples were blot driedafter treatments, heat liable loss of vitamin C was avoidedto some extent in the experiment. As a consequence, thedegree of retention was high in the initial storage period.There was a gradual decrease in ascorbic acid content withthe extension of storage period and this decrease wasstatistically significant at different storage intervals. Lowestvalue of ascorbic acid (62.5±1.4 mg/100gm) was recordedin GI1B sample after 30 days of storage. Whereas, highestvalue for ascorbic acid (69.9±0.4mg/100gm) after 30 dayswas recorded in GCB sample.

An additional decrease was observed during 45th

day of storage in all treatments. Percentage decrease overinitial value in vitamin C content of high dose irradiatedguava slices irrespective of degree Brix concentration after45 days where, 50.5% (from initial 70.46±0.20 mg/100 gm

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FIG 4: Effect of gamma irradiation and osmotic dehydration on Polyphenols content (mg/100g) of guava slices

to final 34.86±0.15,mg/100 gm) for GI1A followed by lowdose irradiated samples GI1B ( 72.63±0.30 to final37.53±0.25 mg/100 gm).

Similar trend was observed by Patras et al., (2009)on their study on impact of high pressure processing ontotal antioxidant activity of strawberry and blackberrypurees and stated that osmotic treatment might havecaused significant loss in ascorbic acid content of samplesranging from 37.27% to 52%.

Progressive loss of ascorbic acid with storageduration might be due to increase in water activity (aw). Therate of oxidation of ascorbic acid in low moisture foodsystems was found to increase progressively with wateractivity and was thought to be associated with increasedavailability of water to act as a solvent for reactants andcatalysts (Dennison and Kirk, 1978).Total phenolics: As shown in fig 4, the contents of totalphenolic compounds in the extracts were in the orderGCA>GI1A>GCB>GI2B>GI2A>GI1B. The total content ofphenolics on 15th day in the gamma irradiated samples rangedbetween 42.0±1.0 to 119.0±1 mg GAE/100 gm where as,for the control samples, the contents ranged between29.3±1.5 and 31.7±0.6 mg GAE/100 gm.

The increase in the phenolic content of the irradiatedsamples might be related to an increased extractability ofsome of the antioxidant compounds following irradiationtreatment.

During storage, total phenolics degraded from arange of 29.3 mg GAE/100gm to 78.6 mgGAE/100 gm after15 days of storage indicating 62% loss of phenolics in onlyosmotically dehydrated samples. Stojanovic and Silva (2007)stated that, different osmotic concentration treatments andultra sound induced loss of phenolics by migration into theosmotic solution. Introduction of ultra sound may haveaccelerated formation of free radicals and increased the levelsof polymerization of phenolics that resulted in 43.7% lossof total phenolics.Yeast and mold count: It was observed that the total platecount was below the detectable limits in all the treatedsamples till a storage period of 15 days. This might be dueto the processing effects. Several reports stated the synergisticeffects of gamma – irradiation with dehydration in renderingmicrobiological safety (Mayer et al.,1981). However, verylow yeasts and mold counts were observed after a month ofstorage i.e., 6, 6.47 and 6.301 log cfu/g in GI1A, GCA, GCBsamples respectively. While GI2A, GI1B, GI2B samples didnot exhibit detectable colonies. On 45th day of storage verylow counts were detected in GI2A, GI1B, GI2B whereas, GCA,GI1A, GCB showed low yeast and mold counts. This mightbe attributed to low aw and synergistic effect of gamma-irradiation and osmotic dehydration.

Vibhakara et al., (2007) suggested combination oflow dose irradiation with other hurdles such as acidification

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and regulation of water activity for effective control overmicrobiological profiles of foods. Similar trend in the presentstudy was observed in combination treated guava slices. The

osmotic treatments influenced the total microbial count, butthe impact of both the treatments increased the microbialresistance of sample to a great extent.

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