Chemistry of sulfur dioxide and ascorbic acid as an anti-oxidant system in white wine

Abstract

This project has examined in detail the chemistry of ascorbic acid and sulfur dioxide as an antioxidant system in conditions relevant to white wine.

Summary

Ascorbic acid is well known for its use as a complementary antioxidant to sulfur dioxide in white wine. However, the fate of ascorbic acid and its degradation products that are formed under wine conditions are not well understood. Furthermore, there appears to be some ambiguities in the role of ascorbic acid as an antioxidant, particularly in its role in preventing the oxidative colouration of white wine. Such oxidative colouration usually results in the conversion of the white wine from its normal pale yellow or straw colour to a darker yellow or even brown colour.

This project was conducted to gain more insight into the chemistry of ascorbic acid and its degradation products under conditions relevant to white wine. The extensive chemical literature on ascorbic acid was surveyed and a comprehensive review written on ascorbic acid and its chemistry in a wine-like environment. This review is the first cohesive overview of published work on ascorbic acid with the specific focus of its chemistry in wine.

Experiments were conducted on model wine systems utilising a range of predominantly analytical and organic chemistry techniques. Several of the main terminal degradation products of ascorbic acid, in the model wine system adopted, were identified as 3-hydroxy-2-pyrone, 2-furoic acid and furfural. The mechanism for the production of these compounds was identified and involved an oxidative pathway for the first two compounds and an oxygen-independent pathway for the latter.