Analysis Of Influencing Factors Of ‘Ruixue’ Apple Browning And Preliminary Screening Of Postharvest Anti-browning Agents

‘Ruixue’apple has excellent comprehensive traits and has broad development prospects in China.However,the variety was found to be prone to peel browning during the development period and storage period,which reduced its appearance quality and commodity value.In this study,the effects of different periods（development period and storage period）,different tree vigor（strong and weak）,different crown parts（upper,middle and lower parts of the tree,inner and outer parts,shade and sunny sides,branch group types）,different fruit parts and different types of fruit bags on the browning of bagged‘Ruixue’apple peel were analyzed,the suitable agents for reducing the browning of bagged‘Ruixue’apple peel were preliminarily screened by different chemical treatments after harvest.The main results are as follows:1.The browning of bagged‘Ruixue’apple during development and storage is different.The initial browning of‘Ruixue’apple peel occurred 30 days before harvest and the browning process was significantly accelerated 10 days before harvest and the browning rate increased by 2.5 times during this period.In the early storage period（1 month after storage）,the browning rate increased by 73.24%compared with the harvest period.In the middle storage period（3 months after storage）,the browning rate was relatively stable.In the late storage period（5 months after storage）,the browning rate increased by 93.17%compared with the middle storage period.2.The difference of tree vigor and crown position had an effect on the peel browning of bagged‘Ruixue’apple.The results showed that the peel browning time of‘Ruixue’apple with strong tree vigor was 20 days earlier than that of‘Ruixue’apple with weak tree vigor,the browning rate and browning index were higher than those of‘Ruixue’apple with weak tree vigor before harvest and during storage.The fruits growing in the middle and lower parts were the first to brown.During storage,the browning rate showed a trend of lower>middle>upper.The browning index of the lower fruit peel was 114.84%,91.28%and27.39%higher than that of the middle,35.74%,29.11%and 44.58%higher than that of the upper during the early,middle and late storage.The browning rate and browning of‘Ruixue’apple in the inner bore from pre-harvest to mid-storage.3.Different fruit bags had great influence on peel browning of‘Ruixue’apple.Four kinds of fruit bags were selected:white single-layer bag（W1）,green single-layer bag（G1）,inner green outer white double-layer bag（W2）and inner white outer green double-layer bag（G2）.The conventional double-layer three-color bag（CK1）and no bagging（CK2）in apple production were used as controls.The results showed that the browning order was G1,G2,W2 and W1.The browning rate and browning index in the harvest period showed G2>W2>G1>W1.The browning rate and browning index of CK1 were the highest,CK2 was unbrowning.Compared with CK1,the browning rate of the four fruit bags‘Ruixue’apple peel decreased by 9.78%,18.66%,20.39%and 20.78%,respectively,no peel browning occurred in CK2.The browning rate in the early and middle storage period showed the trend of CK1>W2>G2>G1>W1>CK2.During the harvest period,there was no significant difference in the single fruit weight of several fruit bags‘Ruixue’apple（P<0.05）.The color of G2 fruit bag was significantly different from CK1 and CK2.The fruit hardness,soluble solids and titratable acid of W2 fruit bag were at the highest level,which were 7.14,14.23%and 0.31%,respectively.The fruit surface of CK1 was the most smooth and clean,followed by G2 and W2,W1 and G1 were slightly better than CK2.4.During the harvest period,the browning of each part of the bagged‘Ruixue’apple fruit was different and browning rate of stem cavity was the highest at 63.00%,calyx-end was the lowest at 23.50%,the cheeks was 35.00%.Under the electron microscope,it was observed that the damage degree of pericarp cell structure in browning parts was higher than that in non-browning parts.Among the browning parts,the pericarp cells in the stem cavity were most seriously damaged,and the calyx-end was the lightest.The difference of browning in different parts of fruit was significantly correlated with polyphenol oxidase（PPO）activity and superoxide anion（·O₂^-）production rate and with malondialdehyde（MDA）content and peroxidase（POD）activity.5.Postharvest chemical treatment had a certain inhibitory effect on the browning of bagged‘Ruixue’apple peel.‘Ruixue’apple was soaked in 2%citric acid and 2%ascorbic acid for 30 minutes after harvest.During the whole storage period,the browning rate and browning index of the two treatments were lower than those of the cold storage control and significantly lower than those of the normal temperature control,the effect of citric acid treatment was better than that of ascorbic acid.Citric acid and ascorbic acid treatment could maintain the peel color of‘Ruixue’apple during storage,delay the decrease of hardness,soluble solids and titratable acid of‘Ruixue’apple,passivate oxidase activity.