Kinetic analysis of antioxidant capacity of wine

A competition kinetics procedure for measuring total antioxidant capacity in wine is described. This procedure is based on the "crocin bleaching test" [28] as modified for analyzing the antioxidant capacity of complex mixtures [24]. The antioxidant capacity of white wines ranged from 0.08 to 1.2 mM equivalents of the reference antioxidant (Trolox C), while for red wines values ranging from 6.4 to 41.9 mM have been obtained. Although a correlation exists between antioxidant capacity and total phenol content of wines, due to the variable reactivity of different phenol groups, the analysis of the phenol content provides only a crude indication of the actual antioxidant capacity. The analysis of antioxidant capacity on different polyphenol classes, separated by solid phase extraction, indicated that anthocyanins are the major antioxidants of young red wines, and tannins of old red wines and white wines. Several vintages of the same grape have been analyzed and the expected decrease of antioxidant capacity upon ageing was not observed, although spectrophotometric analysis clearly demonstrated the shift from anthocyanin monomers to polymers. Artificial ageing by stirring under air produced a rapid decrease (30 min) of antioxidant capacity followed by an increase (up to two weeks), but not any significant modification of the spectrophotometric chemical age factor. Since neither natural nor artificial ageing present a clear-cut relationship with a decrease of antioxidant capacity, we could conclude that the a priori assumption that an old wine contains less antioxidant capacity, although popular, is not fully correct.