Rootstock Influence on the Biochemical Composition and Polyphenol Oxidase Activity of ‘Thompson Seedless’ Grapes and Raisins

‘Thompson Seedless’ grapes grafted on five rootstocks and own-rooted vines were evaluated for yield, fruit composition, and raisin recovery percentage. Biochemical constituents were analyzed in fresh grapes before drying into raisins and also in raisins. Among different rootstocks, raisin recovery was highest in ‘Thompson Seedless’ grapes grafted on 110 R followed by those on ‘Dogridge’, 1103 P and 99 R. Significant differences were observed in total proteins, reducing sugars, phenol contents, and polyphenol oxidase (PPO) activity in both fresh grapes and raisins made from all rootstock scion combinations. Increase in the content of proteins and reducing sugars was observed in raisins compared to fresh grapes. However, there was a reduction in phenolic concentrations in raisins compared to fresh grapes. PPO activity was highest in ‘Thompson Seedless’ grapes grafted on ‘Dogridge’, while it was least in 110 R.