Effect of enzymatic and chemical oxidation on the antioxidant capacity of catechin model systems and apple derivatives

Changes in the chain-breaking activity of catechin model systems and apple derivatives were studied as a consequence of enzymatic and chemical oxidati on. Although in different time scales, both enzymatic and chemical oxidatio ns of catechin promoted an initial increase and a following decrease in the chain-breaking activity. The latter was associated with the formation of b rown pigments. Similar changes were detected during storage at -18 degreesC of nonoxidized and enzymatically oxidized apple purees. The initial increa se in antioxidant activity upon oxidation was attributed to the formation o f procyanidins with larger aromatic structure and to synergy effects among them. The formation of tannins, the reactivity of which is sterically hinde red, was proposed as a possible explanation for the decrease in antioxidant capacity in the advanced phases of oxidation.