Polyphenols influence enzymatic activity. A) The alcohol dehydrogenase activity of wine yeast extracts in the presence of resveratrol (2 mg/L) and quercetin (9 mg/L). B) Cytosolyc aldehyde dehydrogenase Ald6p activity under the same conditions. C) Mitochondrial aldehyde dehydrogenase Ald4p activity under the same conditions. D) Lipid peroxidation levels on day 6 of a fermentation on synthetic grape juice with and without resveratrol. Experiments were done in triplicate, and the mean and standard deviation are provided. *p < 0.05, **p < 0.01, unpaired t-test, two-tailed.