Post-harvest Epidermal Wax of Grapes and Fruit Storage Quality

To investigate the changes of epidermal wax and its relationship with storage tolerance in harvested grapes, Summer Black grapes and Shine Muscat grapes were selected as the grapes models. The microstructures of the grapes epidermal wax were detected by SEM, and the compositions of the epidermal wax were detected by GC-MS. The changes of fruit weight loss rate, hardness, MDA, total phenol and other quality indexes during storage were analyzed, the effects of epidermal wax on the nutritional quality and storage preservation of grape fruits were studied. The results showed that the content of epidermal wax in the two kinds of grapes showed a "W" trend. The epidermal wax content in Summer Black grapes was significantly higher than that in Shine Muscat grapes (P<0.01), and the contents were 36.66 mg/100 g and 26.90 mg/100 g at the end of storage, respectively. The SEM results showed that the epidermal waxy structure of Summer Black grapes was stacked flake crystal with pores, while the one of Shine Muscat grapes had more uniform structure distribution with small or even no pores during storage. The correlation between the compositions content of the epidermal wax and the storage quality of the two grapes showed different rules. The main compositions of epidermal waxy were fatty acids (49.84%~81.00%), primary alcohols (0.10%~11.68%), esters (0~9.41%), aldehydes (0.43%~8.83%) and alkanes (0.90%~6.66%). With the increase of storage time, the weight loss rate, threshing rate, and MDA content of grapes were increased, while the hardness, the contents of reducing sugar, total phenol and vitamin C were decreased, the storage quality of grapes were reduced. Correlation analysis results showed that high fatty acid content in epidermal wax of Summer Black grapes accelerated lipid peroxidation in fruit cells, which was consistent with a significant positive correlation (P<0.05) between weight loss rate, MDA content, and other factors, which was not conducive to maintaining the fruit nutritional quality. The content of esters in the epidermal wax of Shine Muscat grapes was significantly negatively correlated with vitamin C and total phenol content (P<0.05), significantly reducing the antioxidant capacity of the fruit. This study provides theoretical basis and technical guidance for the application of grape epidermal wax in the storage and preservation of different varieties of grapes.