Analysis Of The Difference In Browning Of Different Varieties Of Apples And The Mechanism Of Browning

Browning has always been a key factor restricting the deep processing of apples and has become the main reason affecting apple processing.However,mechanical damage such as unavoidable friction or collision during picking,transportation,processing,storage,and sales can cause tissue damage and cause enzymatic and non-enzymatic browning.Red flesh apple is a new apple variety in recent years,and its browning mechanism is rarely studied.Therefore,in this study,‘Gala' apples,‘Jinshuai' apples and the ‘Xinghong',‘Meihong' and ‘Manhong'red-fleshed apples cultivated by our research group were used as the test materials.Through the determination of enzyme activity and the comparison of the cell ultrastructure in the browning process,compare the browning similarities and differences between red-fleshed apples and white-fleshed apples througr a large number of different metabolites obtained by omics test.Use transcriptome data to obtain a large number of differentially expressed genes,perform correlation analysis with the differential metabolites detected by metabolome,analyze the internal changes of the organism from two levels of cause and effect,lo ck key pathways with metabolite changes,and comprehensively explore the browning mechanism of red-fleshed apples.The results showed that the ultrastructure of pulp cells of different browning degrees changed greatly.The cell structure of‘Manhong' is the most stable,and the cell structure of‘Gala' is the most unstable.The degree of browning of ‘Gala',‘Meihong',and ‘Xinghong' all reached the maximum about 15 minutes after fresh cutting,and remained basically unchanged after that,while the browning degree of ‘Manhong' decreased within 1 hour of fresh cutting.The PPO activity of all apple varieties showed a downward trend during the whole browning process.The PPO of red fleshed apples and white fleshed apples is not heat-resistant,and the optimum temperature is generally 35 ?~45 ?.The optimum p H of PPO of red-fleshed apples and white-fleshed apples is about 5~7.By comparing the Michaelis constant(using catechol as the substrate),it is found that ‘Gala' is the most prone to browning,and ‘Meihong' is the least prone to browning.Except for phenolic substances,the metabolism of red flesh apples during browning is similar to that of white flesh apples.B vitamins are the most affected vitamins during apple browning.The pentose phosphate pathway increased during the browning process of ‘Gala' and‘Xinghong'.The pentose phosphate pathway of ‘Manhong' was inhibited to some extent during the browning process.The tricarboxylic acid cycle may increase in the browning process of ‘Jinshuai',‘Manhong' and ‘Xinghong'.In the process of apple browning,the cell membrane system will be destroyed,and the phospholipid bilayer that composes the cell membrane will also be damaged,resulting in an increase in free phospholipid molecules in the cell,as evidenced by most up-regulated phospholipid molecules from ‘Jinshuai',‘Manhong' and ‘Xinghong' up to this point.The main differentially abundant metabolites during the browning process were phenols,amino acids and fatty acids.The differentially expressed genes were mainly related to plant–pathogen interactions.Polyphenol oxidase(PPO)plays a major role during the early browning stage.The subcellular localization results of the MdPPO gene in ‘Meihong' apple showed that it was localized in the chloroplast.The MdPPO gene of ‘Meihong' apple interacts with MdMYBS3 and MdbHLH30.