INCORPORATING COLD CHAIN
CONTRIBUTORS irradiation can induce the expression of a number of defence response genes , and suppress the expression of major genes involved in cell wall disassembly , lipid metabolism and photosynthesis . These gene changes underline the biochemical and physiological changes induced by UV-C such as increased defence ability , delayed softening , better maintenance of nutritional and sensory qualities and extension of shelf-life in tomato fruit .
UV-treatments of tomato fruits reduce the gloss of the tomato surface because those treatments affect the morphology of fruit surface wax ( Charles et al ., 2008a ). UV-treatment may have induced biochemical modifications of the surface wax layers . The overall impact of these changes has two contrasting effects . On the one hand , changes in the physical and biochemical modifications that occur in the epidermal cell in response to UV-treatment may be conducive to an improved ability of the plant tissue to resist pathogen attack .
On the other hand , altered wax layers can affect light reflectance characteristics of the fruit surface , and may also contribute to increased water loss from cuticular transpiration , both leading to changes in the appearance of the fruit . Charles et al . ( 2008b ) treated postharvest tomato fruit with the dose of 3.7 kJ / m 2 of UV-C , which had shown optimal for inducing decay resistance , but whose treatment caused ultrastructural modifications in the pericarp , UV induced plasmolysis of the epicarp cells as well as some cell layers of the mesocarp .
Collapse of these cells led to the formation of a cell wall stacking zone which restricted Botrytis cinerea development to the outer most part of the fruit and hindered its progression toward the inner tissues . Charles et al . ( 2008c ) studied the biochemical nature of cell wall modifications induced by UV-C in postharvest tomato fruit and they found that UV treatment induced the accumulation of phenolic compounds and the formation of lignin and suberin .
Simple phenolic compounds induced by UV-C appear to have a fungistatic effect ; and complex phenolics , lignin and suberin , play a barrier role by physically impeding pathogen ingress by strengthening the cell wall stacking zone . Such a barrier would also reduce diffusion of nutrients and water from the plant tissue required to sustain fungal growth , and toxins and cell wall degrading enzymes from the fungus , which interfere with virulence of the pathogen .
UV-B irradiation appears to be a useful nonchemical way of maintaining postharvest quality and enhancing antioxidant capacity in tomato fruit . Liu et al . ( 2011b ) applied doses between 20 and 80 kJ / m 2 to mature-green tomato of UV-B irradiation . 20 or 40 kJ / m 2 was most effective in maintaining a high level of firmness and delaying the colour development . Furthermore , 20 or 40 kJ / m 2 promoted the accumulation of total phenolic and total flavonoids , and enhanced antioxidant capacity during storage , though UV-B irradiation could reduce the ascorbic acid content .
A dose of 10 kJ / m 2 had similar effects but to a lesser extent . The highest dose of 80 kJ / m 2 resulted in higher lycopene content , but showed negative effects on texture , colour , and other antioxidants . The optimum dose of UV-B for maintaining sensory qualities and enhancing antioxidant capacity was 20 or 40 kJ / m 2 .
Mushrooms UV-C radiation could potentially be used for sanitising fresh mushrooms and may be a useful non-chemical way of maintaining mushroom quality and extending their postharvest life .
Guan et al . ( 2012 ) investigated the effects of UV-C light , applied to both sides of mushrooms , on microbial loads and product quality , during 21 days of storage at 4 ° C . Microflora populations , colour , antioxidant activity , total phenolics , and ascorbic acid were measured at 1 , 7 , 14 and 21 days of storage . Additionally , the inactivation of Escherichia coli O157 : H7 by UV-C was determined .
Results showed that UV-C doses of 0.45 – 3.15 kJ / m 2 resulted in 0.67 – 1.13 log CFU g−1 reduction of E . coli O157 : H7 inoculated on mushroom cap surfaces . UV-C radiation also reduced total aerobic plate counts by 0.63 – 0.89 log CFU g−1 on the surface of mushrooms . In addition , the UV-C treatments apparently inhibited lesion development on the mushroom surface .
During the first 7 days , irradiated mushrooms had lower antioxidant activity , total phenolics , and ascorbic acid content than non-radiated samples . Jiang et al . ( 2010 ) exposed shiitake mushrooms ( Lentinus edodes ) to UV-C light ( 4 kJ / m 2 ) and stored them in modified atmosphere packaging ( MAP ) for 15 days at 1 ± 1 ° C and 95 % relative humidity plus 3 days at 20 ° C . UV-C treatment resulted in the maintenance of a high level of firmness during 15 days at low temperature and reduced the decrease in firmness during shelf-life . Furthermore , treated samples showed higher total flavonoids , ascorbic acid , and delayed the increases in both superoxide anion production rate and H2O2 . CLA
Article originally published October 2012 . Citation of this article should include the corresponding authors as : Carlos Ribeiro et al . 2012 .
Irradiated mushrooms had lower antioxidant activity , total phenolics , and ascorbic acid content than non-radiated
samples .
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