Evolution of grape polyphenol oxidase activity and phenolic content during maturation and vinification

The activity of polyphenol oxidase (PPO) and content of phenolic compounds were followed during the maturation in two varieties of wine grapes grown in south-eastern Spain and during vinification at different sulphur dioxide concentrations. Both cresolase and catecholase activities (measured at pH 7.0 and 4.5, respectively) increased throughout the studied period and the content of phenolic compounds decreased rapidly when expressed as concentration (mg gallic acid/g total fresh weight), while when expressed as total amount per berry (mg/berry) it remained constant. During wine production, the enzyme activity was highest immediately after crushing of the fresh grapes and was not detected at the end of the fermentation process. The phenolic content also decreased during vinification to a constant level depending on the S02 level used.