Exogenous Application Of Brs To Delay Carambola Fruit Quality Deterioration And Its Effects On Respiratory Metabolism And Endogenous Hormone Changes

Carambolas fruit is one kind of non-climatic fruit,which is easy to be subjected to fruit damage,rot and quality deterioration during storage and transportation,due to its thin peel and crispy texture.Brassinolide（BRs）is a kind of hormone,with the effects of delaying fruit and vegetable ripening,enhancing stress resistance and ohter physiological aspects.The role of BRs in the control of postharvest quality deterioration and its possible mechanism was studied,which had important application value and theoretical significance.In this study,Averrhoa carambola Linn.Cv.Xiangmi was used as the experimental material to study the effects of BRs on the preservation of the Carambola fruit at room temperature（25℃±2）.The possible physiological and biochemical mechanism of BRs effects on delaying fruit deterioration were also studied,from the aspects of respiration and its related enzyme activities,endogenous hormones and antioxidant enzymes.The main results were as follows:1.The proper concentration of BRs and 1-MCP treatment on carambola fruit preservation were screened out,where the optimal concentration of BRs was 2.8mg·L^-1,and 1-MCP（0.4 g 1-MCPacted on about 2 kg carambola packaged in 0.02 nm microporous antifoging bag）also worked well on fruit preservation.Both of BRs and1-MCP could prolong the shelf-life of carambola fruit ranging from 4 to 6 days under room temperature.2.Exogenous BRsand 1-MCP could delay the the color change and deterioration of carambola fruit to a certain extent.It was a critical period for carambola to turn yellow during storage on 7^th day,where the control group had reached grade 4.5 on 7^th day,while the fruit after BRs and 1-MCP treatment was only at grade 3.Both treatments not only delayed the carambola fruit ripening,but also inhibited the decrease of the fruit hardness.After 11 days of storage,the hardness of the carambola decreased significantly in the control group,which was only about 62%of the initial hardness.However,hardness in the fruit treated with BRs and 1-MCP decreased by about 44.8%,the hardness being significantly higher than that of control fruit.BRsand1-MCP treatment also increased the soluble solids content of carambola fruit and delayed the decrease of soluble protein content.Fruit treated with BRsmaintained a higher Vc level than that treated with 1-MCPand the control.3.Results from HPLC analysis and sensory analysis by customer?s preference showed that people favoured the carambola fruit with high sugar content.In the sensory evaluation by customers,no significant difference was found among the BRs treatment,1-MCP treatment and the control,even both treatments delayed the ripening process of the carambola fruit.4.BRsand 1-MCP inhibited the respiration rate of carambola.On the 11^th day of storage,the respiration rate of carambola in the CK group reached the level of 11mg·h^-1·kg^-1,while that of fruit after BRs and 1-MCP treatment was only 5 mg·h^-1·kg^-1,level.5.The respiration rate related enzymes of carambola were studied.The results showed that BRsand 1-MCPsignificantly inhibited the activity of hexokinase,but increased the activity of succinate dehydrogenase,glucose-6-phosphate dehydrogenase and cytochrome oxidase.6.The effects of BRson the antioxidant activity of carambola were studied.The results showed that the content of MDA、H₂O₂ and the activity of PPO,in BRsand1-MCPtreated fruit was significantly lower than that of the control,and the activities of POD,SOD,CAT and AAO were significantly enhanced compared to the control.7.Both endogenous BRsand 1-MCPtreatments increased the contents of endogenous hormones IAA and GA₃ during fruit storage,but had no significant effect on ABA content.BRstreatment showed a more significant effect on endogenous hormones changes than that of 1-MCP.The results showed that BRstreatment could significantly increase IAA content.On the 5^th day of storage,CK was only about 1/3of BRs.1-MCP treatment also significantly increased the content of GA₃,but less impact on ABA content was observed.8.The correlation analysis results showed that the phenotypic indexes such as hardness,yellowing index and respiration rate were significantly correlated with IAA,GA_3,ABA and MDA content.The content of IAA and GA₃ showed a positive correlation.