Effects Of Low O₂ And High CO₂ Treatment On Postharvest Browning Of Hanfu And Golden Delicious Apples

Apples are prone to browning during postharvest storage,which reduces the fruit quality and shortens the storage period.The browning of the pulp caused by CO₂ injury is the most common one.Different varieties of apples have different tolerances to CO₂.In this study,Hanfu and Golden Delicious apples were used as test materials to study the effects of low O₂ and high CO₂(3%O₂+6%CO₂)controlled atmosphere storage treatments on the browning of the two varieties of apples.The determination and analysis of malondialdehyde(MDA),vitamin C(Vc),polyphenol oxidase(PPO),total phenols,and other browning-related physiological indicators.At the same time,transcriptome sequencing was used to analyze the factors related to pulp browning in the controlled atmosphere storage of Hanfu and Golden Delicious apples.Gene expression,and then put forward the possible reasons for the formation of the difference in CO₂ tolerance between the two apple varieties.The main findings are as follows:1.The measurement results of browning-related physiological indicators showed that low O₂ and high CO₂(3%O₂+6%CO₂)controlled atmosphere storage treatments promoted the increase of the browning rate and browning index of Hanfu apple fruit,and accelerated the content of Vc The reduction in the content of total phenols and to a certain extent reduced the content of total phenols,and significantly increased the content of MDA and PPO activity,which in turn led to an increase in the degree of browning and reduced fruit quality.However,Golden Delicious apples(control or treatment)did not appear browning in the flesh during the whole storage period,and the changes in various physical and chemical indexes were not obvious,and the overall quality remained relatively good.It shows that compared with Golden Delicious apples,Hanfu apples are less tolerant to CO₂.They are susceptible to CO₂ damage during storage,which increases the permeability of apple cell membranes and increases the accumulation of MDA,which in turn accelerates the degree of membrane lipid peroxidation and causes damage to the membrane system.At the same time,the PPO activity is stimulated,and the phenolic substances are oxidized,resulting in browning of the pulp.The occurrence of browning has no direct correlation with the density and size of the fruit itself.2.Transcriptome sequencing results showed that low O₂ and high CO₂ atmosphere treatments significantly increased the up-regulated expression of the key enzyme ACC synthase gene“MD15G1302200”for ethylene synthesis in the resistant variety Golden Delicious apple,and promoted the key genes Pyruvate decaboxylase(PDC)gene and Alcohol for alcohol fermentation.The expression of dehydrogenase(ADH)gene makes it highly resistant to CO₂.For the Hanfu apple,the low O₂ and high CO₂ atmosphere treatment greatly improved the up-regulated expression of the key enzyme genes phenylalanine ammonia lyase(PAL)and polyphenol oxidase(PPO)genes in the Hanfu apple.The lipid degradation related genes,the key genes for tyrosine synthesis,Chorismate mutase(CM)and Arogenate dehydrogenase(ADH),and the ascorbate oxidase gene“MD10G1132000”were significantly up-regulated.This leads to browning of the flesh.In summary,low O₂ and high CO₂(3%O₂+6%CO₂)controlled atmosphere treatments increased the degree of browning of Hanfu apple fruit,reduced fruit storage quality,and improved the metabolic pathways related to browning.The up-regulation of certain key genes promotes the occurrence of browning in the pulp.