Synergistic, Additive and Antagonistic Interactions of Grapes' Phenolic Compounds and Organic Acids.

The antioxidant interactions between several natural phenolic and non-phenolic compounds (catechin, quercetin, rutin, resveratrol, gallic acid and ascorbic acid) and organic acids (tartaric, citric and dihydroxyfumaric acids) have been investigated through the DPPH method. Main additive and antagonistic interactions have been found for the combinations of catechin, quercetin, resveratrol and gallic acid with tartaric and citric acids; such behavoir can be due to the enhanced stability of the phenolic compounds in the acidic media. Rutin and ascorbic acid demonstrated good synergistic effects with tartaric and citric organic acids, which may rely on the polymerization processes for rutin, and change of the mechanism of action in case of ascorbic acid.