Abstract

Extensive reviews of research are available on the use of ascorbic acid, and its consequent degradation pathways, in physiological conditions or food matrices. However, very little information can be found for wine-related systems. This review highlights the relevant chemistry and reactivity of ascorbic acid with a focus on its behavior and potential behavior in a wine environment. The review describes the use of ascorbic acid as a complementary antioxidant preservative to sulfur dioxide along with the metal-catalyzed and radical-dependent manner by which it achieves this role. The relevant degradation products of ascorbic acid in aerobic and anaerobic conditions are presented as well as the interaction of these degradation products with sulfur dioxide and other wine-relevant sulfur compounds. Limitations in existing knowledge, especially regarding the crossover between the antioxidant and pro-oxidant roles of ascorbic acid, are identified.

The ability of ascorbic acid to induce browning of (+)-catechin in a model wine system has been studied. A significant increase in absorbance at 440 nm was observed over 14 days when ascorbic acid was incubated at 45 degrees C with (+)-catechin in a model wine base. The onset of browning was delayed for about 2 days, although the length of the lag period was dependent on the amount of molecular oxygen in the headspace of the reaction system. The lag period was not observed when a preoxidized solution of ascorbic acid was used, suggesting that a product of ascorbic acid oxidation is responsible for the onset of browning. Hydrogen peroxide, when added directly to (+)-catechin in the model system, was not capable of producing the same degree of browning as that generated by ascorbic acid. Liquid chromotography evidence is presented to show that different reaction products are produced by ascorbic acid and hydrogen peroxide.

Background and Aims The long‐term effectiveness of copper(II) to remove sulfidic off‐odours remains the subject of debate. This study was undertaken to assess the extent of copper removal after its addition to white wine that contained a variable concentration of hydrogen sulfide and to investigate the activity of the residual copper in a reaction relevant to white wine ageing. Methods and Results After the addition of sulfide to white wine, copper(II) was added to give an increasing mole ratio of hydrogen sulfide to copper(II). After settling for 1–5 days, negligible copper was removed after racking or filtering (0.45 or 0.20 μm), as determined by flame atomic absorption spectroscopy. Model wines were used in an attempt to ascertain the wine components that may interfere with the removal of the copper sulfide precipitate. Residual copper in the white wine after racking was active in mediating the production of a phenolic pigment. Conclusions Copper sulfide is not easily removed from white wine once formed. Model studies confirmed that tartaric acid is a critical factor influencing the extent of copper sulfide precipitation. Significance of the Study This study demonstrates that after addition of copper(II) to wines containing sulfide, the presence of residual copper is unavoidable and remains active in mediating reactions.