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 oxidation. Although in different time scales, both enzymatic and chemical oxidations of catechin promoted an initial increase and a following decrease in the chain-breaking activity. The latter was associated with the formation of brown pigments. Similar changes were detected during storage at -18 degrees C of nonoxidized and enzymatically oxidized apple purees. The initial increase in antioxidant activity upon oxidation was attributed to the formation of procyanidins with larger aromatic structure and to synergy effects among them. The formation of tannins, the reactivity of which is sterically hindered, was proposed as a possible explanation for the decrease in antioxidant capacity in the advanced phases of oxidation.