Preservation of Mango and Mango Pulp by Radiation

Abstract

This Study Was Carried Out To Investigate The Following Points: I- Effect of ionizing radiation alone (0-2 kGy) or in combination with hot water dip

treatment (55 °C/5 min.) on the shelf-life extension, chemical, microbiological, rheological and organoleptic properties of mango fiuits (at mature green stage) stored at I2 ± I oc.

II- Effect of gamma radiation alone (0-2 kGy) or with steam treament (for I2 min.) on the chemical, microbiological, rheological and organoleptic properties of mango pulp stored at 3 ± I °C. III- Isolation, purification and identification of moulds associated with peel surface of mango fiuits and yeasts associated with mango pulp as well as toxin production from some id ntified moulds. The results obtained throughout this research could be summarized in the

following main points:

Part 1: Mango Fruits

Mango fiuits (var. Zebda) belong to the group of"climacteric fiuits" ,that is, those which show a peak of ethylene production during their maturation, called the "climacteric peak". The time at which this phenomenon takes place depends on the fiuits variety, the degree of ripening at which they are picked, the storage conditions; such as temperature and atmosphere, among others, but generally only a few days elapse from the normal, data of hawest to the onest of the climacteric. The irradiation treatlllent is only attained if it is performed immediately before the occurrence of this "climacteric peak". 1- Chemical Characteristics:

- During storage periods there was a significant increase in the percentage of weight loss of mango fiuits. Such increase was higher in unirradiated samples in comparison with irradiated ones. - During storage, there was a significant increase in the activity of polyphenol oxidase

(PPO), phenolic compounds, total carotenoids and colour index in all mango fiuit samples (irradiated and non-irradiated). However,this increase was higher m unirradiated samples in comparison with irradiated samples.. - During storage, the ascorbic acid content in irradiated and unirradiated mango fruits

significantly decreased during storage at 12 ± I °C, 80-85% RH. Particularly in control samples. - During storage total, reducing and non-reducing sugar, total soluble solid (TSS) and

• pH were significantly increased in both irradiated and non-irradiated mangoes. However! the increase was lower in irradiated mango fruits than in control samples. 2- Microbiological Quality:

In general, during storage there was significant increase in total bacterial counts, yeasts and moulds in unirradiated and irradiated mangoes at different rates. The highest increase was observed in unirradiated samples (control). -Fourteen fungal species belonging to five genera were isolated. The species of moulds isolated and classified from contaminated mango fruit.s were Aspergillus jlavus, A. niger, A. oryzae, A. sydowii, A. terreus, A. ustus, •Cladosporium cladosporides, Fusarium oxysporum, Penicillium brevicompactum, P. chrysogenum,P. corylophyliu, P. janthinellum, P. oxalicum and Scopulariopsis brevicaulis. The decimal radiation doses (D10 -values) ofthe isolated moulds spores in physiological saline solution were 0.319, 0.456, 0.582, 0.514, 0.586, 0.708, 1.106, 0.758, 0.449, 0.376, 0.741, 0.402,

0.621 and 0.803 kGy, respectively. The most radio-sensitive mould among the tested moulds was A. jlavus (D 10 - value 0.319 kGy}and the most radio-resistant spores were C. cladosporoides (Dw-value 1.106 kGy). Meanwhile, D 10-values of the isolated moulds spores in substrate (pulp)were 0.513, 0.50, 0.645, 0.391, 0.463, 0:393, 1.060, 0.919, 0.658, 0.456> 0.883, 0.433, 1.113 and 0.440 kGy, respectively. Where, the most radio-sensitive mould in pulp was A. sydowii (D10-value 0.391 kCJ¥) and the most radio-resistant spores• wasP. oxalicum (D10-value 1.113 kGy). -The results of screening of mould isolates for production of aflatoxins B 1, B2, G1 and

G2 and ochratoxin A revealed that no aflatoxins were produced by A. jlavus on synthetic medium or natural substrates (mango pulp). However, P. brevicompactum and P. coryophylium produced ochratoxin A on the synthetic medium but did not on the mangoes pulp.