Abstract: The objective of this study was to investigate the changes of phenols and their relationship with browning during shade drying of Thompson seedless grapes. We determined total phenolic content, phenolic composition and browning degree, and identifyied substrates for enzymatic browning. The results showed that total phenolic content in Thompson seedless grapes decreased during the drying process and that browning degree increased progressively. Totally 14 phenolic compounds were detected in Thompson seedless grapes, six of which such as proanthocyanidin B2, p-hydroxycinnamic acid, catechin, trans-caffeic acid, cis-resveratrol and ferulic acid were substrates for enzymatic browning. The most important substrate was catechin. The browning degree of Thompson seedless grapes was significantly correlated with the contents of total phenols, procyanidin B2, p-hydroxycinnamic acid, catechin, trans-caffeic acid and cis-resveratrol (P < 0.05, P < 0.01). The results of thisse studyies provide a theoretical basis for improving the quality of seedless raisins.

Key words: drying, Thompson seedless grapes, phenolic substrates, browning