Effect of Drying Rate on Cytochemical Localization of Phenolic Substance and Polyphenol Oxidase and Browning in Thompson Seedless Grape

In order to explore effect of drying rate on cytochemical localization of phenolic substance and polyphenol oxidase and the relationship for browning in Thompson seedless grape. Transmission electron microscopy was used to observe the precise position of phenolics and polyphenol oxidase and browning index of Thompson seedless grape under both rapid and slow modes. The results showed that phenols were distributed in vacuoles and polyphenol oxidase was distributed in cytoplasm, chloroplast membrane, mitochondrial membrane, tonoplast membrane and cell membrane. When the mass loss of slow dehydration was 40% and the mass loss of rapid dehydration was 60%, the outflow of phenols and brown reaction with polyphenol oxidase, the increase of browning index and the breaking down of compartmentalization. Compared with the slow dehydration, the rapid dehydration of non-nuclear white grapes can maintain cell integrity better, can reduce the occurrence of seedless white grapes browning better. These results can provide a theoretic reference for the application of rapid dehydration in the drying of Thompson seedless grapes.