Studies On Effect Of Hypobaric Treatment On Quality Of Postharvest Litchi Fruit And Its Mechanism Of Action

In order to explore the effects of hypobaric treatment on postharvest litchi fruit quality and its physiological and biochemical mechanism,'Feizixiao'litchi was used as experimental material to study the effects of different hypobaric treatment such as40,60,80 and 101(atmospheric pressure)k Pa on litchi browning index,mildew rate,titratable acid,Vc and soluble solids,and understand physiological and biochemical mechanism of hypobaric treatment delaying quality deterioration of postharveat litchi fruit during the shelf life at room temperature(25?)in terms of phenols compounds and active oxygen metabolism,energy metabolism,cell ultrastructure and membrane lipid function.The results of study are as follows:1.hypobaric treatment of 60 k Pa significantly decreased browning index and decay rate of litchi fruit,and delayed the quality deterioration of litchi fruit during storage at ambient temperature,compared with CK and other hypobaric treatment conditions.Moreover,the litchi fruits treated by 60 k Pa decompression had higher contents of soluble sugar,titratable acid and V_Cduring storage,and maintained better fruit quality and commodity value of postharvest litchi fruit.2.Postharvest litchi fruit treated by 60 k Pa decompression had lower content of total phenols and higher content of anthocyanins during storage at ambient temperature in comparison with CK.Furthermore,60 k Pa hypobaric treatment obviously inhibited activities of polyphenoloxidase(PPO)and peroxidase(POD)in fruit pericard tissue,thus delaying the enzymatic browning of postharvest litchi fruits and maintaining a bright red color of litchi fruit.At the same time,hypobaric treatment also significantly induced activities of superoxide dismutase(SOD),reduced the production rate of superoxide anion and the content of hydrogen peroxide,and lowered accumulation of malondialdehyde(MDA),which retarded the occurrence of membrane lipid peroxidation and was beneficial to compartmentalization of browning substrate and enzymes.3.In comparison with the control,the activities of succinate dehydrogenase(SDH)and cytochrome oxidase(CCO)of mitochondrial in treated litchi fruit peel tissue maintained at a higher level.Especially,SDH and CCO activities of litchi fruit treated by 60 k Pa decompress significantly were higher than the control and other hypobaric treatment.Moreover,60 k Pa hypobaric treatment delayed the decrease of ATP and ADP content,and the increase of AMP content during shelf life at room temperature and make the litchi fruit maintained higher energy level,which delayed the occurrence of energy shortage in litchi fruit.It was suggested that 60 k Pa hypobaric treatment delayed quality deterioration of postharvest litchi fruit through inhibiting energy shortage of litchi fruit during storage at ambient temperature.4.Change of cell membrane component of postharvest fruit affects integrality fluidity of cell membrane,which have effect on functions of cell membrane.Litchi fruit treated by 60 k Pa decompress had lower contents of palmic acid and stearic acid,and higher contents of linoleic acid and linolenic acid than those of the control and other hypobaric treatment.In the meantime,fluidity of the litchi fruit treated by decompress was significantly higher than those of the control,suggesting that 60 k Pa hypobaric treatment was in favour of preventing the oxidation of unsaturated fatty acids in membrane lipids and reducing the production of saturated fatty acids,and thus membrane lipid fluidity of litchi fruit was kept at higher level.5.Through transmission electron microscope observation on the ultrastructure of litchi pericarp,it was found that the cell structure of litchi fruit pericarp was intact on the day of harvest,and the clear organelle structure could be seen in the cells.With the extension of postharvest shelf life,there was significant differnce in the cell structure between litchi fruits treated in the control and litchi fruits with treated by 60k Pa,the cell membrane of litchi pericarp was broken,serious plasmolysis of litchi fruit pericarp cell was observed in the control fruit,and the organelles basically disappeared.Contrary to the control,slight plasmolysis was observed in the cell wall of litchi pericarp treated by 60 k Pa decompress and the cell structure was relatively intact.In conclusion,the application of decompression technology in postharvest litchi fruit preservation has good prospects for development,and 60 k Pa hypobaric treatment is expected to be an effective measure for postharvest litchi fruit preservation.