Microoxygenation

Abstract: Microoxygenation was applied to a red wine for five months following the end of alcoholic fermentation, and its effects on the concentration of anthocyanin and anthocyanin-derived compounds were studied by high-pressure liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Monomeric anthocyanins were detected together with direct anthocyanin-flavanol adducts, ethyl-linked anthocyanin-flavanol compounds, and pyranoanthocyanins. Microoxygenation resulted in wines with a lower concentration of monomeric anthocyanins and a higher concentration of ethyl-linked compounds and vitisin-related pigments than the control wine, while no effect was observed on the concentration of the direct adducts. Differences were also observed in the chromatic characteristics of the wine, with microoxygenated wines showing higher color intensity, a parameter that was highly correlated with the higher presence of pyranoanthocyanins.

Abstract: We recently showed that expressing an H2O-NADH oxidase in Saccharomyces cerevisiae drastically reduces the intracellular NADH concentration and substantially alters the distribution of metabolic fluxes in the cell. Although the engineered strain produces a reduced amount of ethanol, a high level of acetaldehyde accumulates early in the process (1 g/liter), impairing growth and fermentation performance. To overcome these undesirable effects, we carried out a comprehensive analysis of the impact of oxygen on the metabolic network of the same NADH oxidase-expressing strain. While reducing the oxygen transfer rate led to a gradual recovery of the growth and fermentation performance, its impact on the ethanol yield was negligible. In contrast, supplying oxygen only during the stationary phase resulted in a 7% reduction in the ethanol yield, but without affecting growth and fermentation. This approach thus represents an effective strategy for producing wine with reduced levels of alcohol. Importantly, our data also point to a significant role for NAD+ reoxidation in controlling the glycolytic flux, indicating that engineered yeast strains expressing an NADH oxidase can be used as a powerful tool for gaining insight into redox metabolism in yeast.

Abstract: A Merlot wine in 15 L research tanks was subjected to micro-oxygenation at 10 mL O2 per liter of wine per month over a 16 week period with additions of 0, 50, 100, and 200 mg/L SO2. A large decrease in monomeric anthocyanins and flavan-3-ols was seen in wines with a lower concentration of SO2, coupled with an increase in nonbleachable pigments; an increase in tannin, measured using precipitation with methyl cellulose; and a greater size and red coloration of a proanthocyanidin extract obtained using Sephadex LH-20. These changes were largely suppressed in wines initially treated with 200 mg/L SO2 and occurred more slowly in wines stored in bottles in the absence of O2. The concentration of SO2 is shown to regulate the polyphenol chemistry involved in the formation of polymeric pigments and changes in tannin structure affecting wine astringency.