Post harvest diseases fruits and vegetables - Xavier University ...

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FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE Physical Means 205 gloeosporioides (Spalding and Reeder, 1986b), and papayas infected by various postharvest pathogens (Brodrick et al., 1976). Heat and irradiation act synergistically to inactivate spore germination (Barkai-Golan et al., 1969, 1977a; Sommer et al., 1967), shortening the time of exposure needed for either treatment applied alone. The efficiency of the combined treatment is influenced by the sequence and is generally greater when heat precedes irradiation. The interval between heating and irradiation also affects the synergism; for good results, radiation should be applied within 24 h of the hot water treatment (Barkai-Golan et al., 1969; Spalding and Reeder, 1986b). A combination of heating and rinsing of fruits and vegetables has recently been achieved by the development of a fast hot water spray machine which simultaneously cleans the commodity and reduces the pathogen population on its surface (Fallik et al., 1999; 2000); the device is designed to be a part of a sorting line, and it exposes the commodity to hot water (50-70°C) for 10-60 s. This method significantly reduced decay incidence on sweet bell peppers and enabled fruit firmness to be maintained during prolonged storage and marketing. The optimal treatment conditions for this fruit were 55°C for about 12 s, while 59±1°C for 15 s was optimal for Galia melons. The low percentage of decayed fruits, together with the high level of cleanliness, were achieved by the combination of the hot water rinse with brushing that removes dirt, dust and fungal spores from the fruit, calyx and skin. The improved keeping quality of the rinsed and disinfected fruit has also been attributed to the melting of the wax layer, which seals small, almost invisible, cracks in the epidermis (Fallik et al., 1999; 2000). B. IONIZING RADIATION The possibility of utilizing ionizing radiation for extending the shelf life of fresh fruits and vegetables has been studied since the 1950s. These studies were mainly aimed at three directions: (a) control of postharvest diseases; (b) delay of the ripening and senescence processes; and (c) control of insect infestation for quarantine purposes. Most of the studies were carried out with CO^^ gamma rays. Here, we will focus on irradiation as a physical means for decay control and postharvest life extension of fruits and vegetables. This subject has been separately reviewed (Barkai-Golan, 1992). http://arab2000.forumpro.fr
FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE 206 Postharvest Diseases of Fruits and Vegetables Radiation Effects on the Pathogen Ionizing radiation may directly harm the genetic material of the living cell, leading to mutagenesis and eventually to cell death. The nuclear DNA, which plays a central role in the cell, is the most important target molecule in microorganism irradiation, although radiation lesions in other components of the cell may also contribute to cell injury or even result in cell death (Grecz et al., 1983). Several factors affect the response of a pathogen to radiation, the first being the genetic resistance; fungal species may vary widely in their resistance to irradiation (Fig. 34). In general, multicellular spores, such as Alternaria or Stemphylium spores, or bicellular spores, such as those of the Cladosporium or Diplodia, are 100 100 150 0 50 100 150 200 250 300 350 400 Radiation dose (krad) Fig. 34. Dose-response curves or inactivation of postharvest fungi by gamma radiation. 1 - Trichothecium roseum; 2 - Trichoderma viride; 3 - Phomopsis citri; 4 - Penicillium italicum; 5 - P. expansum; 6 - Aspergillus niger; 7 - P. digitatum; 8 - Geotrichum candidum; 9 - Monilinia fructicola; 10 - Botrytis cinerea; 11 - Diplodia natalensis; 12 - Stemphylium botryosum;13 - Rhizopus stolonifer; 14-Alternaria citri; 15-A. alternata; 16- Cladosporium herbarum; 17 - Candida sp. (Reproduced from Barkai-Golan, 1992 with permission of Springer-Verlag GmbH & Co. KG). http://arab2000.forumpro.fr
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