Study On The Mechanism Of Inhibiting Pericarp Browning Of Longan By Methyl Jasmonate Treatment

In this study,the effect of MeJA on the browning of postharvest longan pericarp and its mechanism were investigated by using’Chuliang’longan as the test material The main contents include:explore the effects of different concentrations of MeJA treatment on the physiology and quality of postharvest longan fruit,in order to find out the most appropriate treatment concentration;explore the effects of MeJA treatment on the browning of longan pericarp and its relationship with phenolic metabolism,reactive oxygen species（ROS）metabolism,membrane lipid metabolism and energy metabolism,in order to find out the possible mechanism of MeJA inhibiting the browning of longan pericarp.The specific research results are as follows:（1）The fruits of postharvest longan were treated with 10,50 and 100μmol/L MeJA solution,and the water treatment group was used as the control group.The pericarp browning index,pulp breakdown index,pericarp color,cell membrane permeability and soluble solid（TSS）content were determined.The results showed that different concentrations of MeJA could inhibit the browning of pericarp,the breakdown of pulp,the increase of cell membrane permeability and the decrease of soluble solid of postharvest longan,and 100μmol/L MeJA had the best effect.（2）100μmol/L MeJA could regulate the metabolism of phenols in postharvest longan by increasing the contents of total phenols,flavonoids and phenols in the pericarp of longan,delay the occurrence of enzymatic browning and inhibit the browning of longan pericarp by inhibiting the activities of polyphenol oxidase（PPO）,tyrosinase and laccase（LAC）,improving the activities of peroxidase（POD）and phenylalanine ammonlyase（PAL）.（3）100μmol/L MeJA could regulate postharvest longan ROS metabolism,remove excess ROS,and reduce oxidative damage caused by membrane lipid peroxidation with inhibiting cell membrane permeability,malondialdehyde（MDA）content and reactive oxygen species(O₂^·-,H₂O₂)in longan pericarp,increasing the content of non-enzymatic antioxidant substances（ascorbate（ASA）,glutathione（GSH））,activity of reactive oxygen scavenging enzymes（SOD,CAT,APX,GR）,scavenging ability of free radicals（ABTS,DPPH）.（4）100μmol/L MeJA could regulate the lipid metabolism of postharvest longan,maintain the integrity of cell structure and prevent enzymatic browning by inhibiting the increase of the permeability of cell membrane,MDA content and the activities of enzymes related to membrane lipid metabolism（PLD,PLC,PLA₂,lipase,LOX）,improving the contents of phospholipid components（PC,PI,PE,PG）.（5）100μmol/L MeJA could regulate the energy metabolism of postharvest longan fruits,maintain a high energy state to provide the body with the energy required for normal life activities by inhibiting the increase of respiration rate,enhancing energy supply（the content of ATP and ADP）,maintaining high energy charge（EC）and energy metabolization-related enzymes(SDH,CCO,H⁺-ATPase,Ca²⁺-ATPase).The above studies showed that MeJA（100μmol/L）could reduce the oxidation of phenols,enhance the antioxidant capacity,alleviate membrane lipid peroxidation,ensure adequate energy supply,maintain the structural stability of cell membrane,and inhibit the browning of the pericarp of postharvest longan by regulating the metabolism of phenols,ROS,membrane lipid and energy.