Influence of major polyphenols on antioxidant activity in Mencía and Brancellao red wines

The purpose of this work was to examine the relationship of the total polyphenol index (TPI) as measured spectrophotometrically and individual phenols as determined by HPLC to antioxidant activity in red wines made from two Vitis vinifera grape varieties grown in NW Spain (viz. Mencía and Brancellao) during bottled storage in the dark for 12 months. Antioxidant activity was determined by using various methods based on inhibition of the coupled oxidation of the β-carotene/linoleic acid mixture. Also, free radical scavenging activity was determined with 2,2-diphenyl-1-picrylhydrazyl (DPPH). Antioxidant activity as measured by DPPH after storage for 3 months was higher in Mencía wines than in Brancellao wines (4.5 ± 0.60 vs. 3.7 ± 0.30 mmol/L trolox equivalents). Beyond 3 months of storage, radical scavenging activity increased in both types of wine (from 4.5 ± 0.60 to 6.0 ± 0.80 mmol/L in Mencía wines and from 3.7 ± 0.30 to 4.7 ± 0.71 mmol/L trolox equivalents in Brancellao wines). The significant correlation found between antioxidant activity and TPI in all wines (r > 0.88) is indicative of the significance of condensation and polymerisation products to the total antioxidant activity of the wines. The relatively high correlation of total flavonols (r = 0.89) and acylated anthocyanins (r = 0.70) as measured by HPLC with to the overall antioxidant capacity suggests that these two polyphenol classes can substantially influence the antioxidant properties of these wines. The linoleic acid/β-carotene assay exposed a higher antioxidant capacity in Brancellao wines than in Mencía wines after 3 months of storage (6.0 ± 0.80 vs. 4.7 ± 0.70). Most of the studied wines lost an average 45% antioxidant activity during bottled storage. Antioxidant activity as measured with the linoleic acid/β-carotene assay was closely correlated with both hydroxycinnamic acids (r = 0.90) and flavanols (r = 0.71 and 0.61 for monomeric and polymeric forms, respectively).