Aging Capacity of Wine and the Comparison of Four Antioxidant Capacity Assays

Aging capacity of wine is an essential facet of wine quality. It is widely accepted that wine oxidation is the main factor leading to the depletion of wine flavor and it limits the aging capacity of wine. During bottle aging, small amounts of air go through the cork or screw cap. Then, oxidation reactions are catalyzed by the iron(Ⅱ) and iron(Ⅲ) ions. The catechol phenols react with oxygen first which produces quinones and hydrogen peroxide. Then, hydrogen peroxide reacts with ethanol and yields acetaldehyde. The quinones and acetaldehyde alter the color and aroma characters of wine by reactions with important wine flavor substances and in the case of acetaldehyde giving oxidized aroma at high levels. SO2, ascorbic acid, and thiols are sacrificial antioxidants in wine that function by recycling the quinones back to catechol phenols, and in the case of SO2 by binding acetaldehyde, rendering it non-volatile. As a result, the antioxidants in wine contribute to the aging capacity of wine by reversing the effect of oxidation reactions. This research was performed with four antioxidant capacity assays, the SO2 addition method, an iron species assay, the DPPH assay and the FRAP assay, by testing commercial wine samples. FRAP assay and DPPH assay both respond to catechol phenols, SO2, thiols, and ascorbic acid in wine and reflects the overall antioxidant capacity of wine. The iron species method determines the antioxidant ability of wine by measuring the iron (Ⅱ) decreasing of the wine after air exposure. The SO2 addition method determines the SO2 in wine, such as weakly bound SO2, strongly bound SO2, and free SO2. Correlations among the four assays were studied understanding the relationships between the assays and shed light on how the reactions of each assay affected its ability to reveal the antioxidant capacity of the wine samples. Future direction of developing a new method to predicting the aging capacity of wine is elaborated