Effects Of High Relative Humidity Storage On Delaying Yellowing And Senescence Of Broccoli And The Possible Mechanisms

Broccoli is rich in nutrients,but it would easily to dehydrate and wilt,aging and yellowing after harvest due to its high water content and strong metabolism,which is not easy to store and affects its commodity and nutritional value.Therefore,the study of broccoli postharvest preservation technology has an important practical significance to promote the healthy development of broccoli industry.In this study,broccoli was stored at4°C for 35 days,with relative humidity of 70～75%as control and relative humidity of 96～99%as treatment.The regulation of water loss and yellowing of postharvest broccoli was studied.In addition,the mechanism was further discussed from the aspects of chlorophyll degradation,antioxidant system,polyamine metabolism and energy metabolism in order to provide a theoretical basis for postharvest storage and preservation technology of broccoli.The main results are as follows:1.The effects of high humidity storage on the yellowing and chlorophyll degradation process of postharvest broccoli were studied.The results showed that high humidity storage could down-regulate the expression of chlorophyll degradation enzyme related genes,inhibit the activity of chlorophyllase and Mg-dechelatase,so as to maintain the higher chlorophyll content of postharvest broccoli,and effectively inhibit the increase of water loss ratio,yellowing index,color difference L*value and b*value.High humidity storage can improve the chlorophyll content of postharvest broccoli by regulating the chlorophyll degradation process,which is conducive to the maintenance of postharvest quality of broccoli.2.The effects of high humidity storage on the quality and antioxidant activity of postharvest broccoli were studied.It was founded that high humidity storage could significantly delay the increase of the content of antioxidant active components such as VC,total phenols,flavonoids,glucosinolates and sulforaphane,and maintain a high level of active oxygen metabolism related enzymes（SOD,CAT,APX,POD）activity and related gene expression,so as to improve the DPPH radical and hydroxyl radical scavenging ability,and effectively reduce the production rate of O₂^·-and the accumulation of H₂O₂content in broccoli.High humidity storage effectively delayed the senescence of broccoli by maintaining high antioxidant components and antioxidant capacity.3.The effects of high humidity storage on energy metabolism of postharvest broccoli were studied.It was founded that high humidity storage up-regulated the expression of energy metabolism related enzyme genes（Bo SDH,Bo CCO）and increased the activities of energy metabolism related enzymes,thereby maintaining high ATP,ADP contents and energy charge level of broccoli.By maintaining a high energy level,high humidity storage provides energy for maintaining a high antioxidant capacity,and inhibits cell membrane damage,which plays a certain role in delaying the degradation of chlorophyll.4.The effects of high humidity storage on polyamine metabolism of postharvest broccoli were studied.The results showed that high humidity storage up-regulated the expression of polyamine synthesis related enzyme genes（Bo ADC-O,Bo ODC）,increased the ADC and ODC activities of broccoli,and decreased the DAO and PAO activities,so as to maintain the high polyamine content of postharvest broccoli.High humidity storage delayed senescence and yellowing of broccoli by maintaining high endogenous polyamine content.