Study On Browning Mechanism Of Fruit And Green Protection Technology Of Fruit Stem Of Daqing Grape

The browning of stems,softening of berries and fungal pollution of Daqing grapes lead to the destruction of the original stable metabolic balance of the body,and ultimately lead to fruit browning easily,which affects consumers’purchasing decisions.Therefore,the regulation mechanism of anti-browning and the green technology of fruit stem are of great significance to the development of the industry.This article used the Daqing grape as the research object,from the physical and chemical indicators of fruit and stem,through the analysis of stress,high concentrations of CO₂antistaling agent SO₂and respiratory inhibitors 1-methylacrylic composite fumigation treatment on the storage of low temperature Daqing grape and stem physiological and quality changes of different composite processing inhibitory control Daqing grape fruit and stalk browning.The dynamic changes of gene expression levels of two isoenzymes in the polyphenol oxidase（PPO）family,two isoenzymes in the peroxidase（POD）family and phenylalanine ammonia lyase（PAL）family were further analyzed.Through the correlation analysis of physical and chemical indexes and the comprehensive evaluation indexes of gene expression levels and color difference,the browning mechanism of Daqing grape fruit and the green technology of stem were explored.The specific research contents and results are as follows:（1）The changes of storage quality of Daqing grape under different compound treatments were studied,and the changes of browning index,respiratory intensity,soluble solid,titratable acid,MDA content,relative conductivity,total phenol content,PPO,POD,PAL and LOX activity were clarified.The results showed that T4treatment group（80%CO₂pretreatment,800 ppm SO₂and 1.0μL/L 1-MCP composite）not only inhibit the increase of browning index,but also inhibit the respiratory intensity,reduce the consumption of substances in grape,and maintain the hardness and taste during storage.Moreover,the oxidation degree of membrane lipid was reduced and the integrity of membrane was maintained.At the same time,the activities of PPO,POD and LOX were significantly inhibited in T4 treatment group,and the PAL activity was maintained at a higher level,which stimulated the production of resistant substances.（2）The gene expression levels of PPO,POD and PAL in Daqing grapes at different periods were studied,and the correlation between gene expression levels and comprehensive evaluation indexes of color difference was analyzed.The results showed that the correlation levels of PPO-2001,PPO-7001 and POD-9001 genes were significant at 0.01 level（double-tail）.PAL-1377 gene was positively correlated with the comprehensive evaluation index of color difference,and negatively correlated with the two-tailed gene at 0.05 level.There was no correlation between POD-6001 gene and the comprehensive evaluation index of color difference.（3）The changes of storage quality of Daqing grape stem under different compound treatments were studied,and the changes of browning index,chlorophyll content,respiratory intensity,relative conductivity,MDA content,total phenol content,PPO,POD,PAL and LOX activity were clarified.The results showed that T4treatment significantly inhibited the degradation of chlorophyll and the increase of browning index,and effectively maintained the original bright green appearance of Daqing grape stem.At the same time,T4 treatment effectively inhibit the activities of PPO,POD and PAL,and further prevent the production of brown substances,so that the stem of Daqing grape keeps bright green.