Mangoes (Mangifera indica L.; family Anacardiacae) are known as luxuries and expensive fruit in the markets of many industrialized countries. Asia accounts for 77% of global mango production and the Americas and Africa account for 13 and 19%, respectively (Yadav and Parmar, 2014). India is the global leader in mango production (Yadav and Patel, 2013). The high cost of mangoes in importing countries is due primarily to air freight charges. Mature fruits may take from three to eight days to ripen and this short period certainly limits the commercialization at long distance. Sea transport is less expensive and enables transportation of larger volumes and it thus would aid in the expansion of mango export industries. At the present stage of development, however, sea shipment does not guarantee good quality fruit on arrival for successful marketing. Mangoes are classified as climacteric fruits and ripen rapidly after harvest. Mango is generally harvested when physiologically mature and ripen under suitable conditions of air temperature and humidity. Therefore, if freshly harvested fruit is allowed to ripen at normal ambient conditions (this can vary between 22-32°C and 40 -65% RH), ripening processes increase rapidly within the week (Yadav et al., 2013a).
The ripe fruit may stay edible for a few days thereafter. It is because of this fact that fruits must be stored under specific storage conditions, not only to maintain weight loss but also to prolong ripening. Mango is susceptible to chilling injury and an optimum air temperature of 12-13°C is gene-rally recommended (Gomez-Lim, 1993). Irradiation of fruits has been successfully shown to delay ripening (Pimentel and Walder, 2004). Irradiation is also a physical process for the treatment of foods akin to conventional process like heat-ing or freezing. It prevents food poisoning, reduces wastage to contamination and at the same time preserves quality (Mahindru, 2009). Therefore, the new knowledge is criti-cal because it is important to maintain a balance between the optimum doses required to achieve safety and the mini-mum change in the quality of the fruit. In view of the above fact, it becomes quite clear that investigation for mango fruit is very important not only to reduce the ripening but also control the weight loss. So, irradiation can be used in combination with low temperature to assess the effects of different doses of gamma irradiation and storage tempe-rature on reduction of the physiological loss in weight and ripening phenomena of fruit. The loss in weight of fruits is likely to reduce the quality of fruit drastically.
Therefore, one of the main objectives of any post harvest treatment is to reduce the extent of physiological loss in weight. The Alphonso variety of mango is famous for its excellent table fruit quality. This is a leading commercial mango cultivar of India and Pakistan and is taking position in the export market. The ripen fruits have attractive colour, and excellent sugar: acid blend. To study the com-bined effect of irradiation dose and storage temperature on prevention of mango was the main objective of study.
MATERIALS AND METHODS
The research was conducted during the months of June-July, in the year 2010 at Cold Storage, Post-Harvest Technology Unit and the laboratory of N. M. College of Agriculture, Navsari Agricultural University, Navsari (Gujarat), India. Export grade mangoes of cv. Alphonso were harvested on 12th June 2010. The selected mangoes from class I as per the quality parameters were specified and described in “post harvest manual for mangoes” published by APEDA (Anon., 2007). There were sixteen treatment combinations of irradiation dose (I1 -0.00, I2 -0.20, I3 -0.40 and I4 -0.60 kGy) and storage temperature (S1-Ambient, S2-9°C, S3-12°C and S4-CA storage at 12°C). The fruits were exposed to gamma radiation for different doses from the radio isotope 60Co at ISOMED plant, Board of Radiation and Isotope Technology, Bhabha Atomic Research Centre, Mumbai. The fruits were packed in CFB box and kept at various temperatures, that is, at ambient, 9°C (90% RH), 12°C (90% RH) and at control atmospheric storage (12°C, O2 2%, CO2 3% and RH 90%). The dimensions of CFB box were 370 x 275 x 90 mm and gross weight of box with fruits was 3.0 kg. One CFB box had nine fruits for each treat-ment, each treatment was replicated thrice. The individual fruit weight was from 250-350 g. During the irradiation process, the fruit boxes were kept in the irradiation chamber through a conveyor system. The source rack with its 60Co pencils was raised from the storage pool by automated control system. The product packages are then moved around the radiation source in such a way that they are exposed to radiation for predefined time. Transportation of fruits for irradiation at BARC was carried out in an air conditioned vehicle. Four fruits from each treatment of each replication were earmarked during the investigation for measuring physiological loss in weight. Fruits were weighted on first day of treatment and subsequently their weight was recorded at six day interval up to the end of shelf life. The physiological loss in weight (PLW) was expressed in percentage and calculated as proposed by Yadav et al. (2013a).
PLW percent = W1 – W2/ W1 x 100
Where W1 = initial weight and W2 = final weight.
The ripening was measured by the number of fruits having change in colour from greenish to yellow and soft in texture which were counted at six day intervals up to eating ripeness and expressed in percentage over total number of fruits taken for study. After 12th day of storage, few treatments had 0.00 values for PLW and ripening due to completion of their shelf life and unripening, therefore, individual mean value of irradiation and storage temperature was different from the original. So, only interaction effect was interpreted. Statistical analysis of the two year data was done by following the Fisher’s analysis of variance technique (Panse and Sukhatme, 1967) at Information Technology Centre, Department of Agricultural Statistics, N. M. College of Agriculture, Navsari Agricultural Univer-sity, Navsari. Values were expressed as the mean standard deviation. The statistical significance of the differences was examined using analysis of variance. Results at probability value of less than 0.05 were considered signififcant.
RESULTS AND DISCUSSION
The data indicated that the physiological loss in weight of fruits increased with the advancement of storage period and significantly influenced by irradiation, storage temperature and their interaction. It is evident from Figure 1 that the physiological loss in weight was significantly influenced by various treatments of gamma rays. Consistently and significantly, minimum PLW was observed in treatment I3 (0.40 kGy) at 6th, 12th, 18th, 24th, 30th and 36th days of storage, that is, 2.155, 3.856, 5.790, 3.810, 2.410 and 2.900 percent, respectively and the maximum PLW was observed in I1 (0.00 kGy) at different storage conditions. Similarly, stora-ge temperature affects the PLW and Figure 2 shows that the significantly minimum PLW was observed in treat-ment S2 (9°C) at 6th, 12th, 18th, 24th, 30th and 36th day of fruit storage (1.095, 2.209, 3.270, 4.670, 6.070 and 5.120%, respectively). Whereas, maximum PLW percent was re-corded in fruits kept at ambient temperature (S¬1) at diffe-rent storage conditions. Interaction between irradiation andstorage temperature was found significant and irradiated fruits significantly reduced the PLW over unirradiated fruits at all conditions of the storage.
The shelf life extended up to 36 day, and on this day, only fruits exposed to 0.40 and 0.60 kGy irradiation and stored at 9°C has shelf life and the minimum reduction in PLW percent was recorded at six day interval in the fruits exposed with 0.40 kGy irradiation and stored at 9°C (I3S2), that is, 5.660% at 36th day, 4.720% at 30th day, 3.480% at 24th day, 2.750% at18th day, 1.777% at 12th day and 0.920 at 6th day of storage (Figure 2). The remaining treatments were discarded due to the lost of their shelf life at every stage of over ripening. The PLW was possibly on account of loss of moisture through transpiration and utilization of some reserve food materials in the process of respiration (Mayer et al., 1960). It is evident from the data that the physiological loss in weight of mango fruit was sig-nificantly influenced by the various exposed dose of gamma rays and different storage temperature (Figure 3). The irra-diation significantly reduced PLW during storage period over control which might be attributed to reduction in utilization of reserve food material in the process of respiration (Purohit et al., 2009). The delay in respiration rate as a result of irra-diation is also reported by Singh and Pal (2009) in guava. Similar findings were also observed by Yadav et al. (2013c), Prasadini et al. (2008) and El-Salhy et al. (2006) in mango. Similarly, in the different storage conditions, the highest physiological loss in weight was observed in fruits subjected to ambient temperature. Lower physiological loss in weight was noted in 9 and 12°C and in CA (12°C) storage tem-perature which might be due to lesser water vapour defi-cit as compared to ambient condition and the low tem-perature which had slowed down the metabolic activities like respiration and transpiration (Yadav et al., 2013b). The observations are in accordance with the results of Roy and Joshi (1989) and Waskar and Masalkar (1997) in mango; Nagaraju and Reddy (1995) and Aina (1999) in banana and Gutierrez et al. (2002) in guava.
The significant minimum reduction in PLW of mango fruits subjected to irradiation and stored at various temperatures, that is, at 9 and 12°C and in CA (12°C) might be due to themutual complementary effect of irradiation and low temperature (Yadav et al., 2013a). Table 1 Indicates that the ripening percentage of fruits were influenced by the advancement of storage period and significantly affected by irradiation, storage tem-perature and their interaction. Irradiated fruits significantly delayed the ripening process over unirradiated fruits at all conditions of the storage. Irradiated fruits still did not fully ripe up to 30th day of storage, stored at 9°C. On this day, fruits exposed to 0.40 kGy recorded minimum unripe fruits; similarly, fruits stored at 9°C showed only 63.14 ripening in fruits. The remaining treatments were discarded due to the lost of their shelf life. The fruits exposed to gamma rays (0.20 and 0.40 kGy) and stored at 9 and 12°C had more than 50% unripe (I3S2 and I3S3) on 30th day of storage, they showed 50.05 and 51.93% ripening, respectively. The remaining of the treatments had high ripening or discarded due to completion of their shelf life.
The fruits exposed to gamma rays and stored at 9 (S2) and 12°C (S3) storage temperature as well as unirradiated fruits kept at 9°C remained unripe (I1S2) at 24th day of storage (Figure 3). Unirradiated and irradiated fruits kept at ambient tempera-ture were discarded due to the end of their shelf life and the remaining were under ripening. At 18th day of storage, unirradiated fruits were discarded due to full ripening at ambient conditions, remaining unripe or showed minute ripening. At 6th and 12th day of storage, ripened fruits (33.530 and 97.480%, respectively) were observed in unirradiated fruits stored at ambient temperature (I1S1). The remaining of the treatments was fully unripe. Ripening percentage is a physiological process which designates the period from harvest until the fruits attain the stage of maximum consumer acceptability. The unirradiated mangoes early showed ripeness whereas, gamma rays exposed mangoes had significantly delayed ripen-ing. The possible mechanisms that have been postulated include: a) irradiations results in decreased sensitivity to ripening action of ethylene and b) alteration in carbohydrates metabolism by regulating certain key enzymes, which interfere with production of ATP which is required for various synthetic processes during ripening (Udipi and Ghugre, 2010). Same findings were noted by Yadav and Patel (2014) and Farzana and Panhwar (2005) in mango and Aina et al. (1999) in banana. The lower and delayed ripening was noted at 9 and 12°C and in CA (12°C) storage as compared to ambient temperature. The decrease in ripening percent and increase in days for ripening at low temperature may be due to desirable inhibition of enzymatic activities leading to reduction in the respiration and ethylene production (Mane, 2009). These results are supported by Mann and Singh (1975) in mango and Deka et al. (2006) in banana. The minimum and delayed ripening in fruits is due to exposure to gamma rays and storage temperature at 9 and 12°C and in CA (12°C) storage as compared to fruits unirradiated and kept at ambient temperature in the present study which might be due to the joint balancing effect of irradiation and low temperature (Yadav and Patel, 2014).
CONFLICT OF INTERESTS
The authors did not declare any conflict of interest.
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