The antioxidant activity of wines determined by the ABTS(+) method: influence of sample dilution and time

The free radical scavenging activity of 42 Spanish commercial wines was determined using the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS(+)). The ABTS(+) radical was generated enzymatically using a horseradish peroxidase and hydrogen peroxide. The presence of wine phenolic compounds caused the absorbance of the radical to decay at 414nm. The measurement conditions were optimised. The total phenolic content of wines ranged from 1262 to 2389mgl(-1) for red wines and 70 to 407mgl(-1) for white wines, expressed as gallic acid equivalents. The phenolic content of Sherry wines was similar to that of white wines. Optimum dilutions for white and Sherry wines were set up as a function of their total phenolic content (for total phenol index, TPI<300mg gallic acid per liter, dilution 2.5:10 to 5:10; for TPI>300mg gallic acid per liter, dilution 1:10 to 3:10). Red wines absorb at the wavelength of measurement and dilutions between 0.35:10 and 0.1:10 are advisable. Reaction kinetics were also monitored and the antioxidant activity, expressed as Trolox Equivalent Antioxidant Capacity (TEAC), was determined at 2 and 15min of reaction. The mean values for TEAC(2min) were 5.01+/-1.40mM for red wines, 0.46+/-0.32mM for white wines and 0.26+/-0.19mM for Sherry wines. At 15min, mean values were 6.93+/-2.41mM for red wines, 0.67+/-0.47mM for white wines and 0.26+/-0.19mM for Sherry wines. The correlation coefficients were better at 2min (r=0.9012) than at 15min (r=0.8462) when compared with TPI. Hence, TEAC(2min) seems to be a more appropriate measure.