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ARTICLE IN PRESS Radiation Physics and Chemistry 77 (2008) 983– 989
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Effect of gamma-irradiation and refrigerated storage on the improvement of quality and shelf life of pear (Pyrus communis L., Cv. Bartlett/William) A.M. Wani , P.R. Hussain, R.S. Meena, M.A. Dar Nuclear Research Laboratory, Bhabha Atomic Research Centre, Zakura, Srinagar 190006, India
a r t i c l e in fo
abstract
Article history: Received 29 November 2007 Accepted 9 April 2008
Gamma-irradiation alone and in combination with refrigeration was tested consecutively for 3 years for extending the shelf life of pear. Matured green pears were irradiated in the dose range of 0.8–2.0 kGy and stored under ambient (temperature 2572 1C, RH 70%) and refrigerated (temperature 371 1C, RH 80%) conditions. Dose range of 1.5–1.7 kGy extended the storage life of pear by 14 days under ambient conditions. Control unirradiated pears were almost fully ripe within 8 days, while as the pears irradiated in the dose range of 1.5–1.7 kGy were fully ripe within 22 days of ambient storage. Irradiation dose of 1.5–1.7 kGy significantly inhibited the decaying of pears upto 16 days of ambient storage. Irradiation in combination with refrigeration prevented the decaying of pears upto 45 days as against the 35% decay in unirradiated samples. Irradiation dose of 1.5–1.7 kGy also gave an extension of 8 and 4 days during additional ambient storage of the pears following 30 and 45 days of refrigeration, respectively. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Pear Gamma-irradiation Refrigerated storage Physico-chemical parameters Shelf life extension
1. Introduction The state of Jammu and Kashmir, owing to its topography is famous for cultivation of number of temperate fruits. The main temperate fruits presently being grown in the state include apple, pear, plum, apricot, peach, cherry, strawberry and sea buckthorn. Pear occupies second leading position after apple both in terms of cultivation and production. There are about a dozen varieties of pear grown in Kashmir valley. The commercially exploited varieties are William pear, Kashmeri Nakh, Fertility and d’Anjou. William pear is highly perishable in nature and has a short shelf life due to its active metabolism, high respiration rate and rapid ripening behavior at optimal temperatures. The fast ripening behavior and senescence of the fruit are the major constraints in the marketing chain of the produce (Haggag, 1987). Due to inappropriate post-harvest management practices and lack of proper scientific storage and transportation facilities, huge postharvest losses of the order of 20–40% are encountered during handling, packaging, and transportation of the produce. Microbial contamination of fresh produce also results in losses and pose potential health risks. Therefore, the post-harvest treatment of pear has become necessary to provide longer life to the fruit, which at the same time establishes price for the grower during the glut season. Many studies have been carried out in order to develop preservation methods. Among the methods tested, gamma-
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irradiation has proved to be effective in reducing bacterial and mold contamination as well as delaying the ripening of climacteric fruits (Kader, 1986). Our earlier study (Wani et al., 2007) revealed that a gamma-ray dose of 1.5–1.7 kGy was effective in extending the shelf life by 2 weeks for ambient storage of the fruit. Combinatory treatments have also widely been investigated as they often result in synergistic effects. Gamma-irradiation in combination with other treatments (e.g., heat, washing, waxing) decreased the microbial contamination level leading thus to an improvement of the shelf life (Spalding and Reeder, 1986; Lacroix et al., 1991). Other reports revealed that pear could in general tolerate a dose of around 1 kGy. Bartlett pears irradiated within 1.0 and 2.0 kGy resulted in a delay in ripening by 2 days, while irradiation with 3 and 4 kGy resulted in abnormal ripening (Maxie et al., 1966). Sattar et al. (1971) reported that Leconte pear could be successfully irradiated when it is slightly unripe and with a dose of 2–3 kGy, ripening could be delayed by 2–3 days. In the present study, carried out consecutively for 3 years, the effect of gamma-irradiation alone and in combination with refrigerated storage was investigated with respect to shelf life extension of pear. The assessment of the treatments is based on the evaluation of physico-chemical parameters, overall acceptability, microbial load and decay percentage.
2. Materials and methods The study was conducted consecutively for 3 years during 2004–2006. Fruit selection was done from same orchard and harvesting was carried out in the first week of August for all the 3
ARTICLE IN PRESS A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
2.1. Raw material preparation Pear (Cv. Bartlett/William) fruits of uniform shape and size, firm texture and proper maturity (120 days after full bloom) were procured from the pear orchards of Shalimar, Kashmir. Fruit was pre-cooled by keeping at 2 1C for 24 h in a cold storage chamber. The pre-cooled fruit was manually graded in order to have uniformity and packed in cardboard boxes. Four boxes each containing 75 fruits spaced uniformly on cardboard trays were taken for each treatment including control.
2.2. Gamma-irradiation treatment The precooled and packaged fruit was subjected to gammairradiation in the dose range of 0.8–2.0 kGy using PANBIT irradiator having Co-60 as the gamma-ray source. The fruit was irradiated at minimum dose rate of 235, 215 and 195 Gy/h during year 2004, 2005 and 2006, respectively. To ensure uniformity of dose, boxes were turned by 1801 half way through the irradiation time and the over dose ratio (Dmax/Dmin) was determined and found to be 1.6. The dose rate was determined by Fricke dosimetry. After irradiation separate batches of fruit were kept under ambient (temperature 2572 1C, RH 70%) and refrigerated (temperature 371 1C, RH 80%) storage conditions for periodic evaluation of physico-chemical parameters namely firmness, titratable acidity, chlorophyll, physiological loss in weight (PLW), overall acceptability (OAA), percent full ripe fruits, decay percentage and microbial load as yeast and mold count.
2.3. Quality analysis Firmness of fruits was determined by hand pentrometer model ‘‘FT-327’’ (EFFGI, Italy) provided with a 6 mm round plunger. Triplicate samples of 15 fruits were selected randomly and evaluated for firmness on three sides of each whole fruit and mean value was expressed in kg. The fruits initially used for firmness were subjected to juice extraction using an Omini mixer (Philips make). Ten milliliters of juice was used for determining the acidity (% malic acid) as per the method of Ranganna (1986). Chlorophyll was determined spectrophotometrically using the method of Witham et al. (1971). Loss in weight was determined by periodical weighing of samples. Overall acceptability based on color, texture and taste was done by a panel of five judges on round table basis using four-point scale where 4 ¼ excellent, 3 ¼ Good, 2 ¼ fair and 1 ¼ poor. Fifteen fruits were selected randomly, coded and served to judges for evaluation of color, texture and taste. Microbial load as yeast and mold count was determined by the serial dilution method using potato dextrose agar media (Aneja, 1996). Percentage of full ripe fruits and decay percentage was determined visually from known number of fruits. For each parameter, triplicate samples were used.
2.4. Statistical analysis Completely randomized design experiment was used for statistical analysis as discussed by Cochran and Cox (1975) with pp0.05.
3. Results and discussion William pear at harvest had 78.271.75 mm length, 61.270.81 mm breadth, 166.475.19 g average weight, 8.670.45 kg firmness, 11.070.261 B total soluble solids, 0.2870.03% titratable acidity and 10.470.55 mg/100 g chlorophyll. Results of the change in quality parameters of the fruit due to irradiation during storage are discussed as under.
3.1. Firmness Firmness of pears decreased with storage. The decrease in firmness was significantly (pp0.05) higher under ambient conditions than refrigerated conditions. Among the treatments, control unirradiated pears exhibited lower firmness throughout the storage under both the conditions. Firmness of controlunirradiated pears was 1.070.03 kg after 14 days of ambient storage and 1.770.01 kg after 45 days of refrigerated storage (Fig. 1). Dose range of 1.5–1.7 kGy recorded significantly (pp0.05) higher firmness values after 14 days of ambient as well as 45 days of refrigerated storage. Decrease in firmness is associated with the conversion of insoluble pectic fraction to the soluble forms as a result of ripening. Also the activities of enzymes namely protopectinase and pectinmethyl esterase responsible for hydrolyzing and solubulization of pectic substances increase during ripening. Since irradiation is known to delay the ripening and senescence of climacteric fruits (Kader, 1986) and combination with low temperature gives a synergistic effect. Thus, slower decrease in firmness of irradiated samples during storage is related to the delayed enzymatic activities, thereby resulting in reduction in the rate of increase in soluble pectic fractions as a result of delayed ripening. Hence the normal conversion of insoluble to soluble pectins during storage appears to have been markedly retarded both by irradiation and low temperature (Massey et al., 1964; El Assi et al., 1997; d’Amour et al., 1993; Howard et al., 1995; Wills et al., 1996; Kovacs et al., 1997; Prakash et al., 2002). However, decrease in firmness values of samples irradiated at 2.0 kGy could be possibly due to radiation injury to the fruit, resulting in severe degradation of pectic substances.
Firmness (kg)
years of study. The results showed similar behavior for all the 3 years; however, the data presented for each parameter is the average of the means of 3 years of study.
7 days 14 days
7 6 5 4 3 2 1 0 0
0.8 0.9
1.1 1.2 1.3 1.4 1.5 1.6 1.7
1
2
Dose (kGy)
Firmness (kg)
984
30 days 45 days
7 6 5 4 3 2 1 0 0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 1. Effect of gamma-irradiation doses on firmness of pear during storage under ambient (a) and refrigerated (b) conditions.
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985
Acidity (%)
7 days 14 days
Acidity (%)
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0
0.8 0.9
PLW (%)
Chlorophyll content of the control unirradiated samples was significantly (pp0.05) lower than irradiated samples throughout the storage under both the conditions. Further refrigerated storage of pears resulted in higher retention of chlorophyll than ambient storage. Chlorophyll content of control unirradiated pears was 1.170.04 mg/100 g after 14 days of ambient storage and 2.070.11 mg/100 g after 45 days of refrigerated storage (Fig. 3). Among the treatments, dose range of 1.5–1.7 kGy recorded significantly (pp0.05) higher values of chlorophyll under both the storage conditions. The loss of chlorophyll during storage is attributed to the change of chloroplasts into chromoplasts containing yellow and red carotenoid pigments. The loss of chlorophyll is mediated through several processes involving the action of the enzyme chlorophyllase and photodegradation. However, major loss of chlorophyll is mediated through an increase in the activity of the enzyme chlorophyllase during ripening which degrades the molecule. The other two enzymes
0
7 days 14 days
10 8 6 4 2 0
10
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
8 6 4 2 0 0
0.8 0.9
2
Fig. 3. Effect of gamma-irradiation doses on chlorophyll of pear during storage under ambient (a) and refrigerated (b) conditions.
3.3. Chlorophyll
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
12
0
Chlorophyll (mg/100g)
The acidity values of pears also showed a declining trend during storage under both the conditions and decrease was significantly (pp0.05) higher under ambient conditions. Control unirradiated pears recorded lower acidity values of the order of 0.1970.01% after 14 days of ambient storage and 0.2270.02% after 45 days of refrigerated storage (Fig. 2). Statistical analysis of the data revealed that the acidity values of all the samples except those irradiated at 1.7 kGy were marginally (pX0.05) different with respect to each other, but significantly (pp0.05) different when compared with control unirradiated samples after 14 days of ambient storage. On the other hand, the acidity values of all irradiated samples under refrigerated conditions differed marginally ((pX0.05) even after 45 days of storage. The loss in acid values is largely due to the utilization of organic acid as respiratory substrates and as carbon skeleton for the synthesis of new compounds during ripening. Also accumulation of sugars during ripening contributes to decrease of acidity as a result of increase in TSS acid ratio (Stanley, 1991). The retention of acidity is an indication of delay in ripening due to synergistic effect of irradiation and low-temperature storage.
Chlorophyll (mg/100g)
3.2. Acidity
7 days 14 days
16 14 12 10 8 6 4 2 0 0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 4. Effect of gamma-irradiation doses on physiological loss in weight (PLW) of pear during storage under ambient conditions.
chlorophyll oxidase and peroxidase also contribute to chlorophyll degradation during ripening (Stanley, 1991). Also, the rate of biochemical reaction double for every 10 1C rise in temperature, which in turn enhances the ripening thereby causing chlorophyll degradation. The retention of higher values of chlorophyll incase of samples irradiated in the dose range of 1.5–2.0 kGy can be attributed to the inhibitory effect of both irradiation as well as low temperature on the activity of chlorophyllase enzyme. Further, the free radicals produced during irradiation may act as stress signals and may trigger some stress responses resulting in slower degradation of chlorophyll (Fan and Thayer, 2001).
3.4. Physiological loss in weight (PLW)
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 2. Effect of gamma-irradiation doses on acidity of pear during storage under ambient (a) and refrigerated (b) conditions.
The statistical analysis of the data revealed that PLW of samples irradiated to 0.8–1.4 kGy and 2.0 kGy differed marginally (pX0.05) with respect to each other, but differed significantly (pp0.05) when compared to control after 7 days of ambient storage (Fig. 4). The dose range of 1.5–1.7 kGy recorded significantly (pp0.05) lower weight loss over the same storage period. As the storage period increased, weight loss also increased and was significantly (pp0.05) higher (14.871.25%) in unirradiated samples after 14 days of ambient storage. Minimum weight loss
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(10.270.75%) was recorded in sample irradiated at 1.7 kGy over the same storage period. The reduced weight loss observed in the dose range of 1.5–1.7 kGy is due to the effect of gamma-irradiation on the respiration rate and in delaying the onset of climacteric, ripening process and senescence (Massey et al., 1964; Dong et al., 1994; Lester and Whitaker, 1996). However, increase in weight loss in case of samples irradiated to 2.0 kGy is attributed to the severe membrane degradation at higher irradiation dose (Lester and Wolfenbarger, 1990; Vosine et al., 1991; Hayashi et al., 1992; Mitsuhashi et al., 1998). 3.5. Overall acceptability Overall acceptability based on color, texture and taste was significantly (pp0.05) higher in irradiated pears than control unirradiated ones after 14 and 45 days of storage under ambient and refrigerated conditions, respectively. Overall acceptability recorded a declining trend with storage and the decrease was significantly (pp0.05) higher in samples kept under ambient storage conditions. The overall acceptability of control-unirradiated samples was 1.470.03 after 14 days of ambient storage and 2.370.06 after 45 days of refrigerated storage (Fig. 5). Dose range of 1.5–1.7 kGy exhibited significantly (pp0.05) higher overall acceptability throughout the storage under both the conditions. The higher decrease in overall acceptability of control samples is related to the fast decrease in firmness, degradation of chlorophyll and loss of volatiles due to rapid ripening and senescence. The delay in rate of chlorophyll degradation and process of ripening and senescence by irradiation and low temperature resulted in retention of overall acceptability of pears in comparison to control samples during storage. 3.6. Yeast and mold count
OAA
Yeast and mold count of pears was markedly reduced by both irradiation and low-temperature storage. No yeast and mold count was recorded in samples irradiated at dose beyond 1.4 kGy after 7 days of ambient storage. As the storage period advanced, yeast and mold count increased and was significantly (pp0.05) higher in unirradiated samples under both the storage conditions (Fig. 6).
7 days
6 5 4 3 2 1 0 0
OAA
4 = excellent, 3 = good, 2 = fair, 1 = poor
14 days
6 5 4 3 2 1 0
0.8 0.9
30 days 45 days
0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
4 = excellent, 3 = good, 2 = fair, 1 = poor
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 5. Effect of gamma-irradiation doses on overall acceptability (OAA) of pear during storage under ambient (a) and refrigerated (b) conditions.
Yeast and mold count (log cfu/g of sample)
A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
Yeast and mold count (log cfu/g of sample)
986
7 days 14 days
6 5 4 3 2 1 0 0
0.8 0.9
1
8 7 6 5 4 3 2 1 0
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 6. Effect of gamma-irradiation doses on yeast and mold count of pear during storage under ambient (a) and refrigerated (b) conditions.
The statistical analysis of the data revealed that yeast and mold count of samples irradiated at doses of 0.8 and 0.9 kGy were marginally (pX0.05) different from those of control samples after 45 days of refrigerated storage. The irradiation alone and in combination with refrigeration resulted in 1.9 and 1.6 log reduction in yeast and mold count of pears. The yeast and molds identified were Candida sp., Penicillium sp. and Botrytis sp., respectively.
3.7. Percentage of full ripe fruits and decay The results of percentage of full ripe fruits indicate that ripening was significantly (pp0.05) faster in control samples than in irradiated samples. The control unirradiated samples were almost fully ripe after 8 days of storage. Samples irradiated in the dose range of 1.5–2.0 kGy exhibited significantly (pp0.05) slower ripening and were almost fully ripe after 22 days of ambient storage (Table 1(a)). Control samples started decaying after 8 days of storage and were fully decayed after 14 days. No decay was recorded in samples irradiated in the dose range of 1.5–1.7 kGy up to 16 days of storage under ambient conditions. The decay percentage values reported in Table 1(b) indicate the onset of decay in the fruits and the rest were in marketable condition. The samples irradiated at dose levels other than 1.5–1.7 kGy were fully decayed after 22 days of storage. The samples irradiated at 1.5–1.7 kGy started decaying after 16 days and were almost fully decayed after 26 days of storage (Table 1(b)). Under refrigerated conditions, no decay was recorded upto 30 days in all the treatments including control. The samples were then taken out from the cold storage and kept under ambient conditions to monitor the further decay. In control samples decaying was observed at day 4 and were fully decayed within 8 days of additional ambient storage. No decay was recorded in samples irradiated at 1.6 and 1.7 kGy upto 8 days of additional ambient storage (Table 2(a)). Control unirradiated samples and those irradiated at dose levels of 0.8, 0.9, 1.0 and 2.0 kGy started decaying after 45 days of refrigerated storage and were almost fully decayed within 2, 4 and 5 days of additional ambient storage. No decay was recorded upto 4 days of additional ambient storage following 45 days of refrigeration in samples irradiated to
Table 1 Effect of gamma irradiation doses on ripeness and decay percentage of pear during storage under ambient conditions Dose (kGy)
Total fruits
Days after irradiation 12
14
16
18
20
22
(a) Percentage of full ripe fruits 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
98.571.12k 52.070.21j 47.770.56i 36.171.32h 35.171.44g 33.870.56f 26.370.58e 25.370.82d 10.770.74b 7.970.67a 7.970.67a 11.770.77c
– 71.571.55i 65.571.64h 59.770.65g 52.970.37f 51.270.91e 47.770.66d 43.471.51c 24.971.46b 17.970.82a 17.870.98a 17.870.92a
– 89.671.03i 89.670.95i 76.971.16h 74.271.46g 70.770.44f 66.070.95e 59.770.63d 43.970.79c 36.670.64a 36.171.29a 39.971.23b
– 98.670.66j 99.070.41j 92.970.39i 91.471.75h 87.071.57g 80.371.65f 73.271.20e 60.371.48d 47.171.40a 51.171.03b 55.970.52c
– – – 98.770.68g 98.870.41g 98.970.82g 91.970.87f 88.071.21e 73.271.21d 60.371.49b 58.870.60a 66.970.31c
– – – – – – 98.770.74e 99.070.41e 81.770.36d 73.670.65b 70.470.68a 77.970.26c
– – – – – – – – 91.471.63d 88.171.08b 84.271.40a 89.671.04c
– – – – – – – – 98.570.71a 98.070.41a 98.570.94a 98.870.46b
C D @ 0.05
0.63
0.69
0.60
0.87
0.56
0.40
0.49
0.52
Dose (kGy)
(b) Decay percentage 0 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2 C D @ 0.05
Total fruits
35 35 35 35 35 35 35 35 35 35 35 35
Days after irradiation 8
10
12
14
16
18
22
26
22.071.83 – – – – – – – – – – –
47.770.48c 17.371.63a 23.970.88b – – – – – – – – –
72.471.44g 38.870.48e 52.871.48f 23.670.76d 21.870.97c 17.970.73b – – – – – 6.571.17a
97.271.62h 61.071.52f 70.070.98g 42.471.30e 39.471.29d 36.071.25c 16.071.24b 16.071.30b – – – 14.371.58a
– 85.471.71f 85.871.53f 57.671.01e 56.670.94d 55.870.71c 32.571.83a 33.371.40b – – – 32.071.76a
– 97.670.03i 98.370.21i 81.071.53h 78.871.41g 76.471.49f 54.971.63e 53.771.98d 12.971.19b 12.771.60b 8.771.38a 47.271.44c
– – – 98.671.10g 95.571.41e 96.771.94f 92.171.80d 95.071.65e 45.670.74b 45.070.67b 41.771.98a 83.771.09c
– – – – – – – – 90.671.09c 88.171.85b 79.871.37a –
0.42
0.56
0.74
0.69
0.82
0.95
0.77
Values are average of triplicate observations 7S.D. Means with in treatments in a column not sharing a common superscript letter are significantly (pp0.05) different.
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A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
8
987
988
Table 2 Effect of gamma-irradiation doses on decay percentage of pear during refrigeration and additional storage under ambient conditions Dose (kGy)
Total fruits
4
6
8
10
12
14
15
14.771.16 – – – – – – – – – – –
46.972.13e 9.8971.47d 9.8470.89d 5.9871.16c 5.8671.06c 5.1471.33c 4.070.52a 3.670.22a – – – 6.771.28b
93.772.23g 41.672.24f 29.471.63e 28.471.54e 26.270.92d 25.271.43d 17.071.87b 16.871.23b 8.371.10a – – 32.372.15e
– 69.372.13h 69.071.16h 67.471.53g 65.471.63f 60.171.58e 59.271.09e 53.771.28c 31.772.11b 14.371.30a 15.271.11a 57.872.01d
– 95.271.76e 95.371.16e 94.471.56d 94.471.62d 92.071.40c 91.670.89c 91.272.26c 57.471.07b 30.171.91a 29.271.63a 93.571.90d
– – – – – – – – 91.871.84c 67.471.03b 62.972.22a –
– – – – – – – – – 91.171.74b 84.471.73a –
0.82
1.0
0.95
0.97
0.56
0.44
C D @ 0.05 Dose (kGy)
Total fruits
45 days of reference
Additional ambient storage (days) 1
2
3
4
5
6
7
(b) Decay percentage 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
35.971.32e 27.071.79d 14.671.79b 16.471.21c – – – – – – – 9.470.94a
65.372.88e 63.072.26d 22.072.91c 20.071.97b – – – – – – – 15.071.93a
91.371.57d 90.672.07d 46.772.38c 30.172.18a – – – – – – – 33.171.90b
– – 71.672.23e 54.072.27d 20.971.80b 18.271.50a 18.772.23a 17.971.73a – – – 47.072.26c
– – 93.771.97g 72.972.10e 43.071.92d 38.672.13c 32.772.18a 34.072.45b – – – 74.171.97f
– – – 91.871.92h 66.571.08g 61.772.47f 55.772.04d 58.671.94e 20.072.28c 16.172.63b 13.071.71a 93.672.08i
– – – – 87.271.36g 84.271.98f 78.672.13d 82.672.66e 30.171.63c 26.371.82b 24.571.47a –
– – – – 96.471.72e 95.271.34d 93.171.35c 92.272.09c 48.271.26b 43.672.02a 42.772.13a –
C D @ 0.05
0.77
1.0
0.82
0.97
1.0
1.12
0.90
0.93
Means with in treatments in a column not sharing a common superscript letter are significantly (pp0. 05) different. Values are average of triplicate samples 7S.D.
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– – – – – – – – – – – –
Additional ambient storage (days)
A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
(a) Decay percentage 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
30 days of reference
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1.5–1.7 kGy (Table 2(b)). Thus, the synergistic effect of gammairradiation and refrigeration in delaying physiological processes and inhibiting microbial proliferation has resulted in delayed decaying of pears.
4. Conclusion The study reveals that gamma-irradiation alone and in combination with refrigeration proved significantly effective in extending the storage life of William pear. Dose range of 1.5–1.7 kGy resulted in shelf life extension of the fruit by 14 days under ambient storage conditions. Irradiation in combination with refrigeration retarded the onset of decay by 45 days as against the 35% decay in unirradiated control samples. Dose range of 1.5–1.7 kGy gave a further extension of 8 and 4 days during additional ambient storage of pears following 30 and 45 days of refrigeration, respectively.
Acknowledgments The authors are thankful to A.K. Sharma, Head Food Technology Division, BARC and his colleagues Ramesh Chandra, A.K. Behray and Brij Bushan for their help and valuable suggestions. References Aneja, K.R., 1996. Experiments in Microbiology, Plant Pathology, Tissue Culture and Mushroom Cultivation, 2nd ed. New Age International (P) Ltd., New Delhi. Cochran, W.G., Cox, G.M., 1975. Experimental Designs. Willey, New York, pp. 95–100. d’Amour, J., Gosselin, C., Arul, J., Castaigne, F., Willemot, C., 1993. Gammairradiation affects cell wall composition of strawberries. J. Food Sci. 58, 182–185. Dong, C.Z., Montillet, J.L., Triantaphylides, C., 1994. Effect of gamma-irradiation on the plasma membrane of suspension-cultivated apples cells. Rapid irreversible inhibition of H+-ATPase activity. Physiol. Plant 90, 307–312. El Assi, N., Huber, D.J., Brecht, J.K., 1997. Irradiation-induced changes in tomato fruit and pericarp firmness, electrolyte efflux, and cell wall enzyme activity as influenced by ripening stage. J. Am. Soc. Horticult. Sci. 122, 100–106. Fan, X., Thayer, D.W., 2001. Quality of irradiated alfalfa sprout. J. Food Prot. 64, 1574–1578.
989
Haggag, M.N., 1987. Effect of preharvest and post harvest calcium treatment on storage behavior of Le Conte pears. Alexandria J. Agric. Res. 32, 175–188. Hayashi, T., Todoriki, S., Nagao, A., 1992. Effect of gamma-irradiation on the membrane permeability and lipid composition of potato tubers. Environ. Exp. Bot. 32, 265–271. Howard, L.R., Miller Jr., G.H., Wagner, A.B., 1995. Microbiological, chemical, and sensory change in irradiated pico de gallo. J. Food Sci. 60, 461–464. Kader, A.A., 1986. Potential applications of ionizing radiations in post harvest handling of fresh fruits and vegetables. Food Technol. 6, 117–121. Kovacs, E., Van Buren, J.P., Pitifer, L.A., Hoch, H.C., Terhune, B.T., 1997. Effect of irradiation and storage on cell wall structure of Golden Delicious and Empire apples. Acta Aliment. 26, 171–190. Lacroix, M., Jobin, M., Laterille, B., Laponite, M., Gagnon, M., 1991. Hot water immersion and irradiation effect on mangoes keeping quality after air shipment from Thailand and Canada. Microbial Alim. Nutr. 9, 155–160. Lester, G.E., Whitaker, B.D., 1996. Gamma ray induced changes in hypodermal mesocarp tissue plasma membrane of pre- and post-storage muskmelon. Physiol. Plant 98, 265–270. Lester, G.E., Wolfenbarger, D., 1990. Composition of Cobalt-60 gamma irradiation dose rate on grapefruit flavedo tissues and on Mexican fruit fly mortality. Food Prot. 53, 329–331. Massey Jr., L.M., Parsons, G.F., Smock, R.M., 1964. Radiation processing of foods: some effects of gamma radiation on the keeping qualities of apples. J. Agric. Food Chem. 12, 268–274. Maxie, E.C., Sommer, N.F., Muller, C.J., Rae, H.L., 1966. Effect of gamma radiation on the ripening of Bartlett pears. Plant Physiol. 41, 437–442. Mitsuhashi, N., Koshiba, T., Sato, M., 1998. Effect of g-radiation on the plasma and vacuolar membranes of cultured spinach cell. Phytochemistry 48, 1281–1286. Prakash, A., Manley, J., DeCosta, S., Caporaso, F., Foley, D.M., 2002. The effect of gamma irradiation on the microbiological, physical and sensory qualities of diced tomatoes. Radiat. Phys. Chem. 63, 387–390. Ranganna, S., 1986. Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd ed. Tata MacGraw-Hill Publ. Co., New Delhi. Sattar, A., Mumtaz, A., Khan, I., Muhammed, A., 1971. Effect of gamma irradiation on post-harvest behaviour of pears. Sci. Ind. 8, 330–333. Spalding, D.H., Reeder, W.F., 1986. Decay and acceptability of mangoes treated with combination of hot water, imazalil and gamma irradiation. Plant Dis. 70 (12), 1149–1151. Stanley, J.K., 1991. Post-Harvest Physiology of Perishable Plant Products. Van Nestrand Reinhold, New York. Vosine, R., Vezina, I., Willemont, C., 1991. Induction of senescence like deterioration of microsomal membranes from cauliflower by free radicals generated during gamma irradiation. Plant Physiol. 97, 545–549. Wani, A.M., Hussain, P.R., Dar, M.A., Mir, M.A., 2007. Shelf life extension of pear Cv. William by gamma irradiation. J. Food Sci. Technol. 44 (2), 138–142. Wills, R.H., Lee, T.H., Graham, D., Mc Glasson, W.B., Hall, E.G., 1996. Post-Harvest, An Introduction to the Physiology and Handling of Fruits and Vegetables. Westport, CN, USA; AVI Publishing Co. Inc., New York. Witham, F.H., Blaydes, D.F., Devlin, R.M., 1971. Experiments in Plant Physiology. Van Nostrand, New York, p. 245.
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Effect of gamma-irradiation and refrigerated storage on the improvement of quality and shelf life of pear (Pyrus communis L., Cv. Bartlett/William) A.M. Wani , P.R. Hussain, R.S. Meena, M.A. Dar Nuclear Research Laboratory, Bhabha Atomic Research Centre, Zakura, Srinagar 190006, India
a r t i c l e in fo
abstract
Article history: Received 29 November 2007 Accepted 9 April 2008
Gamma-irradiation alone and in combination with refrigeration was tested consecutively for 3 years for extending the shelf life of pear. Matured green pears were irradiated in the dose range of 0.8–2.0 kGy and stored under ambient (temperature 2572 1C, RH 70%) and refrigerated (temperature 371 1C, RH 80%) conditions. Dose range of 1.5–1.7 kGy extended the storage life of pear by 14 days under ambient conditions. Control unirradiated pears were almost fully ripe within 8 days, while as the pears irradiated in the dose range of 1.5–1.7 kGy were fully ripe within 22 days of ambient storage. Irradiation dose of 1.5–1.7 kGy significantly inhibited the decaying of pears upto 16 days of ambient storage. Irradiation in combination with refrigeration prevented the decaying of pears upto 45 days as against the 35% decay in unirradiated samples. Irradiation dose of 1.5–1.7 kGy also gave an extension of 8 and 4 days during additional ambient storage of the pears following 30 and 45 days of refrigeration, respectively. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Pear Gamma-irradiation Refrigerated storage Physico-chemical parameters Shelf life extension
1. Introduction The state of Jammu and Kashmir, owing to its topography is famous for cultivation of number of temperate fruits. The main temperate fruits presently being grown in the state include apple, pear, plum, apricot, peach, cherry, strawberry and sea buckthorn. Pear occupies second leading position after apple both in terms of cultivation and production. There are about a dozen varieties of pear grown in Kashmir valley. The commercially exploited varieties are William pear, Kashmeri Nakh, Fertility and d’Anjou. William pear is highly perishable in nature and has a short shelf life due to its active metabolism, high respiration rate and rapid ripening behavior at optimal temperatures. The fast ripening behavior and senescence of the fruit are the major constraints in the marketing chain of the produce (Haggag, 1987). Due to inappropriate post-harvest management practices and lack of proper scientific storage and transportation facilities, huge postharvest losses of the order of 20–40% are encountered during handling, packaging, and transportation of the produce. Microbial contamination of fresh produce also results in losses and pose potential health risks. Therefore, the post-harvest treatment of pear has become necessary to provide longer life to the fruit, which at the same time establishes price for the grower during the glut season. Many studies have been carried out in order to develop preservation methods. Among the methods tested, gamma-
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irradiation has proved to be effective in reducing bacterial and mold contamination as well as delaying the ripening of climacteric fruits (Kader, 1986). Our earlier study (Wani et al., 2007) revealed that a gamma-ray dose of 1.5–1.7 kGy was effective in extending the shelf life by 2 weeks for ambient storage of the fruit. Combinatory treatments have also widely been investigated as they often result in synergistic effects. Gamma-irradiation in combination with other treatments (e.g., heat, washing, waxing) decreased the microbial contamination level leading thus to an improvement of the shelf life (Spalding and Reeder, 1986; Lacroix et al., 1991). Other reports revealed that pear could in general tolerate a dose of around 1 kGy. Bartlett pears irradiated within 1.0 and 2.0 kGy resulted in a delay in ripening by 2 days, while irradiation with 3 and 4 kGy resulted in abnormal ripening (Maxie et al., 1966). Sattar et al. (1971) reported that Leconte pear could be successfully irradiated when it is slightly unripe and with a dose of 2–3 kGy, ripening could be delayed by 2–3 days. In the present study, carried out consecutively for 3 years, the effect of gamma-irradiation alone and in combination with refrigerated storage was investigated with respect to shelf life extension of pear. The assessment of the treatments is based on the evaluation of physico-chemical parameters, overall acceptability, microbial load and decay percentage.
2. Materials and methods The study was conducted consecutively for 3 years during 2004–2006. Fruit selection was done from same orchard and harvesting was carried out in the first week of August for all the 3
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2.1. Raw material preparation Pear (Cv. Bartlett/William) fruits of uniform shape and size, firm texture and proper maturity (120 days after full bloom) were procured from the pear orchards of Shalimar, Kashmir. Fruit was pre-cooled by keeping at 2 1C for 24 h in a cold storage chamber. The pre-cooled fruit was manually graded in order to have uniformity and packed in cardboard boxes. Four boxes each containing 75 fruits spaced uniformly on cardboard trays were taken for each treatment including control.
2.2. Gamma-irradiation treatment The precooled and packaged fruit was subjected to gammairradiation in the dose range of 0.8–2.0 kGy using PANBIT irradiator having Co-60 as the gamma-ray source. The fruit was irradiated at minimum dose rate of 235, 215 and 195 Gy/h during year 2004, 2005 and 2006, respectively. To ensure uniformity of dose, boxes were turned by 1801 half way through the irradiation time and the over dose ratio (Dmax/Dmin) was determined and found to be 1.6. The dose rate was determined by Fricke dosimetry. After irradiation separate batches of fruit were kept under ambient (temperature 2572 1C, RH 70%) and refrigerated (temperature 371 1C, RH 80%) storage conditions for periodic evaluation of physico-chemical parameters namely firmness, titratable acidity, chlorophyll, physiological loss in weight (PLW), overall acceptability (OAA), percent full ripe fruits, decay percentage and microbial load as yeast and mold count.
2.3. Quality analysis Firmness of fruits was determined by hand pentrometer model ‘‘FT-327’’ (EFFGI, Italy) provided with a 6 mm round plunger. Triplicate samples of 15 fruits were selected randomly and evaluated for firmness on three sides of each whole fruit and mean value was expressed in kg. The fruits initially used for firmness were subjected to juice extraction using an Omini mixer (Philips make). Ten milliliters of juice was used for determining the acidity (% malic acid) as per the method of Ranganna (1986). Chlorophyll was determined spectrophotometrically using the method of Witham et al. (1971). Loss in weight was determined by periodical weighing of samples. Overall acceptability based on color, texture and taste was done by a panel of five judges on round table basis using four-point scale where 4 ¼ excellent, 3 ¼ Good, 2 ¼ fair and 1 ¼ poor. Fifteen fruits were selected randomly, coded and served to judges for evaluation of color, texture and taste. Microbial load as yeast and mold count was determined by the serial dilution method using potato dextrose agar media (Aneja, 1996). Percentage of full ripe fruits and decay percentage was determined visually from known number of fruits. For each parameter, triplicate samples were used.
2.4. Statistical analysis Completely randomized design experiment was used for statistical analysis as discussed by Cochran and Cox (1975) with pp0.05.
3. Results and discussion William pear at harvest had 78.271.75 mm length, 61.270.81 mm breadth, 166.475.19 g average weight, 8.670.45 kg firmness, 11.070.261 B total soluble solids, 0.2870.03% titratable acidity and 10.470.55 mg/100 g chlorophyll. Results of the change in quality parameters of the fruit due to irradiation during storage are discussed as under.
3.1. Firmness Firmness of pears decreased with storage. The decrease in firmness was significantly (pp0.05) higher under ambient conditions than refrigerated conditions. Among the treatments, control unirradiated pears exhibited lower firmness throughout the storage under both the conditions. Firmness of controlunirradiated pears was 1.070.03 kg after 14 days of ambient storage and 1.770.01 kg after 45 days of refrigerated storage (Fig. 1). Dose range of 1.5–1.7 kGy recorded significantly (pp0.05) higher firmness values after 14 days of ambient as well as 45 days of refrigerated storage. Decrease in firmness is associated with the conversion of insoluble pectic fraction to the soluble forms as a result of ripening. Also the activities of enzymes namely protopectinase and pectinmethyl esterase responsible for hydrolyzing and solubulization of pectic substances increase during ripening. Since irradiation is known to delay the ripening and senescence of climacteric fruits (Kader, 1986) and combination with low temperature gives a synergistic effect. Thus, slower decrease in firmness of irradiated samples during storage is related to the delayed enzymatic activities, thereby resulting in reduction in the rate of increase in soluble pectic fractions as a result of delayed ripening. Hence the normal conversion of insoluble to soluble pectins during storage appears to have been markedly retarded both by irradiation and low temperature (Massey et al., 1964; El Assi et al., 1997; d’Amour et al., 1993; Howard et al., 1995; Wills et al., 1996; Kovacs et al., 1997; Prakash et al., 2002). However, decrease in firmness values of samples irradiated at 2.0 kGy could be possibly due to radiation injury to the fruit, resulting in severe degradation of pectic substances.
Firmness (kg)
years of study. The results showed similar behavior for all the 3 years; however, the data presented for each parameter is the average of the means of 3 years of study.
7 days 14 days
7 6 5 4 3 2 1 0 0
0.8 0.9
1.1 1.2 1.3 1.4 1.5 1.6 1.7
1
2
Dose (kGy)
Firmness (kg)
984
30 days 45 days
7 6 5 4 3 2 1 0 0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 1. Effect of gamma-irradiation doses on firmness of pear during storage under ambient (a) and refrigerated (b) conditions.
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985
Acidity (%)
7 days 14 days
Acidity (%)
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0
0.8 0.9
PLW (%)
Chlorophyll content of the control unirradiated samples was significantly (pp0.05) lower than irradiated samples throughout the storage under both the conditions. Further refrigerated storage of pears resulted in higher retention of chlorophyll than ambient storage. Chlorophyll content of control unirradiated pears was 1.170.04 mg/100 g after 14 days of ambient storage and 2.070.11 mg/100 g after 45 days of refrigerated storage (Fig. 3). Among the treatments, dose range of 1.5–1.7 kGy recorded significantly (pp0.05) higher values of chlorophyll under both the storage conditions. The loss of chlorophyll during storage is attributed to the change of chloroplasts into chromoplasts containing yellow and red carotenoid pigments. The loss of chlorophyll is mediated through several processes involving the action of the enzyme chlorophyllase and photodegradation. However, major loss of chlorophyll is mediated through an increase in the activity of the enzyme chlorophyllase during ripening which degrades the molecule. The other two enzymes
0
7 days 14 days
10 8 6 4 2 0
10
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
8 6 4 2 0 0
0.8 0.9
2
Fig. 3. Effect of gamma-irradiation doses on chlorophyll of pear during storage under ambient (a) and refrigerated (b) conditions.
3.3. Chlorophyll
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
12
0
Chlorophyll (mg/100g)
The acidity values of pears also showed a declining trend during storage under both the conditions and decrease was significantly (pp0.05) higher under ambient conditions. Control unirradiated pears recorded lower acidity values of the order of 0.1970.01% after 14 days of ambient storage and 0.2270.02% after 45 days of refrigerated storage (Fig. 2). Statistical analysis of the data revealed that the acidity values of all the samples except those irradiated at 1.7 kGy were marginally (pX0.05) different with respect to each other, but significantly (pp0.05) different when compared with control unirradiated samples after 14 days of ambient storage. On the other hand, the acidity values of all irradiated samples under refrigerated conditions differed marginally ((pX0.05) even after 45 days of storage. The loss in acid values is largely due to the utilization of organic acid as respiratory substrates and as carbon skeleton for the synthesis of new compounds during ripening. Also accumulation of sugars during ripening contributes to decrease of acidity as a result of increase in TSS acid ratio (Stanley, 1991). The retention of acidity is an indication of delay in ripening due to synergistic effect of irradiation and low-temperature storage.
Chlorophyll (mg/100g)
3.2. Acidity
7 days 14 days
16 14 12 10 8 6 4 2 0 0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 4. Effect of gamma-irradiation doses on physiological loss in weight (PLW) of pear during storage under ambient conditions.
chlorophyll oxidase and peroxidase also contribute to chlorophyll degradation during ripening (Stanley, 1991). Also, the rate of biochemical reaction double for every 10 1C rise in temperature, which in turn enhances the ripening thereby causing chlorophyll degradation. The retention of higher values of chlorophyll incase of samples irradiated in the dose range of 1.5–2.0 kGy can be attributed to the inhibitory effect of both irradiation as well as low temperature on the activity of chlorophyllase enzyme. Further, the free radicals produced during irradiation may act as stress signals and may trigger some stress responses resulting in slower degradation of chlorophyll (Fan and Thayer, 2001).
3.4. Physiological loss in weight (PLW)
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 2. Effect of gamma-irradiation doses on acidity of pear during storage under ambient (a) and refrigerated (b) conditions.
The statistical analysis of the data revealed that PLW of samples irradiated to 0.8–1.4 kGy and 2.0 kGy differed marginally (pX0.05) with respect to each other, but differed significantly (pp0.05) when compared to control after 7 days of ambient storage (Fig. 4). The dose range of 1.5–1.7 kGy recorded significantly (pp0.05) lower weight loss over the same storage period. As the storage period increased, weight loss also increased and was significantly (pp0.05) higher (14.871.25%) in unirradiated samples after 14 days of ambient storage. Minimum weight loss
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(10.270.75%) was recorded in sample irradiated at 1.7 kGy over the same storage period. The reduced weight loss observed in the dose range of 1.5–1.7 kGy is due to the effect of gamma-irradiation on the respiration rate and in delaying the onset of climacteric, ripening process and senescence (Massey et al., 1964; Dong et al., 1994; Lester and Whitaker, 1996). However, increase in weight loss in case of samples irradiated to 2.0 kGy is attributed to the severe membrane degradation at higher irradiation dose (Lester and Wolfenbarger, 1990; Vosine et al., 1991; Hayashi et al., 1992; Mitsuhashi et al., 1998). 3.5. Overall acceptability Overall acceptability based on color, texture and taste was significantly (pp0.05) higher in irradiated pears than control unirradiated ones after 14 and 45 days of storage under ambient and refrigerated conditions, respectively. Overall acceptability recorded a declining trend with storage and the decrease was significantly (pp0.05) higher in samples kept under ambient storage conditions. The overall acceptability of control-unirradiated samples was 1.470.03 after 14 days of ambient storage and 2.370.06 after 45 days of refrigerated storage (Fig. 5). Dose range of 1.5–1.7 kGy exhibited significantly (pp0.05) higher overall acceptability throughout the storage under both the conditions. The higher decrease in overall acceptability of control samples is related to the fast decrease in firmness, degradation of chlorophyll and loss of volatiles due to rapid ripening and senescence. The delay in rate of chlorophyll degradation and process of ripening and senescence by irradiation and low temperature resulted in retention of overall acceptability of pears in comparison to control samples during storage. 3.6. Yeast and mold count
OAA
Yeast and mold count of pears was markedly reduced by both irradiation and low-temperature storage. No yeast and mold count was recorded in samples irradiated at dose beyond 1.4 kGy after 7 days of ambient storage. As the storage period advanced, yeast and mold count increased and was significantly (pp0.05) higher in unirradiated samples under both the storage conditions (Fig. 6).
7 days
6 5 4 3 2 1 0 0
OAA
4 = excellent, 3 = good, 2 = fair, 1 = poor
14 days
6 5 4 3 2 1 0
0.8 0.9
30 days 45 days
0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
4 = excellent, 3 = good, 2 = fair, 1 = poor
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 5. Effect of gamma-irradiation doses on overall acceptability (OAA) of pear during storage under ambient (a) and refrigerated (b) conditions.
Yeast and mold count (log cfu/g of sample)
A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
Yeast and mold count (log cfu/g of sample)
986
7 days 14 days
6 5 4 3 2 1 0 0
0.8 0.9
1
8 7 6 5 4 3 2 1 0
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
30 days 45 days
0
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dose (kGy)
2
Fig. 6. Effect of gamma-irradiation doses on yeast and mold count of pear during storage under ambient (a) and refrigerated (b) conditions.
The statistical analysis of the data revealed that yeast and mold count of samples irradiated at doses of 0.8 and 0.9 kGy were marginally (pX0.05) different from those of control samples after 45 days of refrigerated storage. The irradiation alone and in combination with refrigeration resulted in 1.9 and 1.6 log reduction in yeast and mold count of pears. The yeast and molds identified were Candida sp., Penicillium sp. and Botrytis sp., respectively.
3.7. Percentage of full ripe fruits and decay The results of percentage of full ripe fruits indicate that ripening was significantly (pp0.05) faster in control samples than in irradiated samples. The control unirradiated samples were almost fully ripe after 8 days of storage. Samples irradiated in the dose range of 1.5–2.0 kGy exhibited significantly (pp0.05) slower ripening and were almost fully ripe after 22 days of ambient storage (Table 1(a)). Control samples started decaying after 8 days of storage and were fully decayed after 14 days. No decay was recorded in samples irradiated in the dose range of 1.5–1.7 kGy up to 16 days of storage under ambient conditions. The decay percentage values reported in Table 1(b) indicate the onset of decay in the fruits and the rest were in marketable condition. The samples irradiated at dose levels other than 1.5–1.7 kGy were fully decayed after 22 days of storage. The samples irradiated at 1.5–1.7 kGy started decaying after 16 days and were almost fully decayed after 26 days of storage (Table 1(b)). Under refrigerated conditions, no decay was recorded upto 30 days in all the treatments including control. The samples were then taken out from the cold storage and kept under ambient conditions to monitor the further decay. In control samples decaying was observed at day 4 and were fully decayed within 8 days of additional ambient storage. No decay was recorded in samples irradiated at 1.6 and 1.7 kGy upto 8 days of additional ambient storage (Table 2(a)). Control unirradiated samples and those irradiated at dose levels of 0.8, 0.9, 1.0 and 2.0 kGy started decaying after 45 days of refrigerated storage and were almost fully decayed within 2, 4 and 5 days of additional ambient storage. No decay was recorded upto 4 days of additional ambient storage following 45 days of refrigeration in samples irradiated to
Table 1 Effect of gamma irradiation doses on ripeness and decay percentage of pear during storage under ambient conditions Dose (kGy)
Total fruits
Days after irradiation 12
14
16
18
20
22
(a) Percentage of full ripe fruits 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
98.571.12k 52.070.21j 47.770.56i 36.171.32h 35.171.44g 33.870.56f 26.370.58e 25.370.82d 10.770.74b 7.970.67a 7.970.67a 11.770.77c
– 71.571.55i 65.571.64h 59.770.65g 52.970.37f 51.270.91e 47.770.66d 43.471.51c 24.971.46b 17.970.82a 17.870.98a 17.870.92a
– 89.671.03i 89.670.95i 76.971.16h 74.271.46g 70.770.44f 66.070.95e 59.770.63d 43.970.79c 36.670.64a 36.171.29a 39.971.23b
– 98.670.66j 99.070.41j 92.970.39i 91.471.75h 87.071.57g 80.371.65f 73.271.20e 60.371.48d 47.171.40a 51.171.03b 55.970.52c
– – – 98.770.68g 98.870.41g 98.970.82g 91.970.87f 88.071.21e 73.271.21d 60.371.49b 58.870.60a 66.970.31c
– – – – – – 98.770.74e 99.070.41e 81.770.36d 73.670.65b 70.470.68a 77.970.26c
– – – – – – – – 91.471.63d 88.171.08b 84.271.40a 89.671.04c
– – – – – – – – 98.570.71a 98.070.41a 98.570.94a 98.870.46b
C D @ 0.05
0.63
0.69
0.60
0.87
0.56
0.40
0.49
0.52
Dose (kGy)
(b) Decay percentage 0 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2 C D @ 0.05
Total fruits
35 35 35 35 35 35 35 35 35 35 35 35
Days after irradiation 8
10
12
14
16
18
22
26
22.071.83 – – – – – – – – – – –
47.770.48c 17.371.63a 23.970.88b – – – – – – – – –
72.471.44g 38.870.48e 52.871.48f 23.670.76d 21.870.97c 17.970.73b – – – – – 6.571.17a
97.271.62h 61.071.52f 70.070.98g 42.471.30e 39.471.29d 36.071.25c 16.071.24b 16.071.30b – – – 14.371.58a
– 85.471.71f 85.871.53f 57.671.01e 56.670.94d 55.870.71c 32.571.83a 33.371.40b – – – 32.071.76a
– 97.670.03i 98.370.21i 81.071.53h 78.871.41g 76.471.49f 54.971.63e 53.771.98d 12.971.19b 12.771.60b 8.771.38a 47.271.44c
– – – 98.671.10g 95.571.41e 96.771.94f 92.171.80d 95.071.65e 45.670.74b 45.070.67b 41.771.98a 83.771.09c
– – – – – – – – 90.671.09c 88.171.85b 79.871.37a –
0.42
0.56
0.74
0.69
0.82
0.95
0.77
Values are average of triplicate observations 7S.D. Means with in treatments in a column not sharing a common superscript letter are significantly (pp0.05) different.
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8
987
988
Table 2 Effect of gamma-irradiation doses on decay percentage of pear during refrigeration and additional storage under ambient conditions Dose (kGy)
Total fruits
4
6
8
10
12
14
15
14.771.16 – – – – – – – – – – –
46.972.13e 9.8971.47d 9.8470.89d 5.9871.16c 5.8671.06c 5.1471.33c 4.070.52a 3.670.22a – – – 6.771.28b
93.772.23g 41.672.24f 29.471.63e 28.471.54e 26.270.92d 25.271.43d 17.071.87b 16.871.23b 8.371.10a – – 32.372.15e
– 69.372.13h 69.071.16h 67.471.53g 65.471.63f 60.171.58e 59.271.09e 53.771.28c 31.772.11b 14.371.30a 15.271.11a 57.872.01d
– 95.271.76e 95.371.16e 94.471.56d 94.471.62d 92.071.40c 91.670.89c 91.272.26c 57.471.07b 30.171.91a 29.271.63a 93.571.90d
– – – – – – – – 91.871.84c 67.471.03b 62.972.22a –
– – – – – – – – – 91.171.74b 84.471.73a –
0.82
1.0
0.95
0.97
0.56
0.44
C D @ 0.05 Dose (kGy)
Total fruits
45 days of reference
Additional ambient storage (days) 1
2
3
4
5
6
7
(b) Decay percentage 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
35.971.32e 27.071.79d 14.671.79b 16.471.21c – – – – – – – 9.470.94a
65.372.88e 63.072.26d 22.072.91c 20.071.97b – – – – – – – 15.071.93a
91.371.57d 90.672.07d 46.772.38c 30.172.18a – – – – – – – 33.171.90b
– – 71.672.23e 54.072.27d 20.971.80b 18.271.50a 18.772.23a 17.971.73a – – – 47.072.26c
– – 93.771.97g 72.972.10e 43.071.92d 38.672.13c 32.772.18a 34.072.45b – – – 74.171.97f
– – – 91.871.92h 66.571.08g 61.772.47f 55.772.04d 58.671.94e 20.072.28c 16.172.63b 13.071.71a 93.672.08i
– – – – 87.271.36g 84.271.98f 78.672.13d 82.672.66e 30.171.63c 26.371.82b 24.571.47a –
– – – – 96.471.72e 95.271.34d 93.171.35c 92.272.09c 48.271.26b 43.672.02a 42.772.13a –
C D @ 0.05
0.77
1.0
0.82
0.97
1.0
1.12
0.90
0.93
Means with in treatments in a column not sharing a common superscript letter are significantly (pp0. 05) different. Values are average of triplicate samples 7S.D.
ARTICLE IN PRESS
– – – – – – – – – – – –
Additional ambient storage (days)
A.M. Wani et al. / Radiation Physics and Chemistry 77 (2008) 983–989
(a) Decay percentage 0 35 0.8 35 0.9 35 1 35 1.1 35 1.2 35 1.3 35 1.4 35 1.5 35 1.6 35 1.7 35 2 35
30 days of reference
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1.5–1.7 kGy (Table 2(b)). Thus, the synergistic effect of gammairradiation and refrigeration in delaying physiological processes and inhibiting microbial proliferation has resulted in delayed decaying of pears.
4. Conclusion The study reveals that gamma-irradiation alone and in combination with refrigeration proved significantly effective in extending the storage life of William pear. Dose range of 1.5–1.7 kGy resulted in shelf life extension of the fruit by 14 days under ambient storage conditions. Irradiation in combination with refrigeration retarded the onset of decay by 45 days as against the 35% decay in unirradiated control samples. Dose range of 1.5–1.7 kGy gave a further extension of 8 and 4 days during additional ambient storage of pears following 30 and 45 days of refrigeration, respectively.
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