Study On Effect And Mechanism Of Ultraviolet-C On Quality Maintenance Of Chinese Bayberry Fruit

Chinese bayberry is a fruit native to South China,it is very popular with consumers because of its unique flavor and tasete.Chinese bayberry is not only rich in nutritive properties including vitamins and minerals,but also contains natural antioxidants such as anthocyanin,phenolics and flavonoids etc.,which are beneficial to health.But Chinese bayberry fruit is susceptible to mechanical injury due to its soft texture and lack of epicarp protection,since the fruit matures in the hot and rainy season,this environment is conductive to growth and reproduction of microorganisms,the fruit is easily attacked by pathogen and leading to extensive decay,this situation is not satisfying to conditions of transport and consumers' demand.Although chemical fungicides can control postharvest pathogen of fruit effectively,they are limited to application owing to consumer concern over food safety,so there is an urgent need to search green and safe alternatives to maintan the quality of Chinese bayberry.This dissertation took Chinese bayberry(Myrica rubra Sieb.et Zucc.Cv.Dongkui)as experimental materials.The present study was designed to compare the effect of Ultraviolet-C(UV-C)under different doses on Chinese bayberry postharvest decay as the basis,and then investigate changes on its quality,secondary metabolism,on active oxygen metabolism and disease resistance,in order to explore preservation mechanisms involved and supply a gist for the new preservation technique and its development and application of Chinese bayberry.The results were as follows:1.UV-C treatments under different doses could inhibit the rise of decay index of Chinese bayberry at different degrees,UV-C at 3.0kJ/m~2 was most effective in reducing fruit decay index among them,so 3.0kJ/m~2 was chosen as the most suitable dose for UV-C treatment on preservation of Chinese bayberry.In consideration of quality indicators which are also valuable to preservation,the study found that UV-C at 3.0kJ/m~2 simutaneously inhibited high respiration rate,retarded decline of firmness and Vitamin C contents,enhanced fruit sugar acid rate during storage,maintained fruit nutritive contents and its good quality.Moreover,UV-C treatment significantly enhanced anthocyanin,carotenoids and flavonoids contents,and these secondary metabolites contributied to slow down cell senescence and improve disease resistance,which interpreted the reason of UV-C treatment reducing fruit decay.2.UV-C treatment at 3.0kJ/m~2 was able to promote accumulation of secondary metabolites containing anthocyanin,phenolics,carotenoids and flavonoids in Chinese bayberry,and enhance the activities of key enzymes in phenylpropanoid metabolism including PAL?C4H?4-CL and DFR.Data analysis shown that there existed a high positive correlation between activity and partial phenylpropanoid metabolites contents,also there was a positive correlation between antioxidant capacity and phenylpropanoid metabolites contents,thess results illustrated that UV-C treatment improved fruits antioxidant capacity by increasing phenylpropanoid metabolites accumulation after promoting activites of key enzymes in phenylpropanoid metabolism.3.UV-C treatment at 3.0kJ/m~2 regulated activities of active oxygen metabolism related enzymes(SOD,CAT,POD and APX),improved free radical reduction capacity,made a reduction on accumulation of superoxide anion radicals significantly,and mitigated fruits decay comparing untreated fruits at the same period,dueing to the decrease of free radicals damage.Therefore,UV-C treatment at 3.0kJ/m~2 could maintain the balance of active oxygen metabolism in postharvest Chinese bayberry fruit and then retard fruits senescence progress.4.UV-C treatment at 3.0kJ/m~2 significantly inhibited Chinese bayberry fruits decay mainly causing by P.citrinum?and enhanced activities of defense enzymes including PAL?POD?PPO?chitinase and ?-1,3-glucanase to improve disease resistance of fruits,which prevented pathogenic infection.On the other hand,UV-C treatment at 3.0kJ/m~2 decreased spore germination rate,germ tube growth and mycelia growth vitesse of P.citrinum,and reduced the number of fugus and yeast on the Chinese bayberry surface,which shown UV-C treatment has a direct antimicrobial function.Hence,UV-C treatment at 3.0kJ/m~2 directly improved postharvest Chinese bayberry disease resistance and had a direct effect of antimicrobial function,which made Chinese bayberry fruits more effectively defend against P.citrinum and other pathogenic infection,and then inhibite fruits decay during storage.