Metabolism of SO2 binding compounds by Oenococcus oeni during and after malolactic fermentation in white wine

Sulfur dioxide (SO2) is the key additive for the preservation of wines. Carbonyl and keto compounds in wine can bind to SO2 and decrease its efficacy, resulting in higher total SO2 requirements. Increased consumer demand for low sulfite and organic wines pose production challenges if SO2 binders have not been properly managed during vinification. Malolactic fermentation (MLF) has been known to reduce bound SO2 levels but detailed time course studies are not available. In this work, the kinetics of major SO2 binding compounds and malic acid were followed during MLF in wine with 12 commercially available strains of Oenococcus oeni. Pyruvic acid, acetaldehyde and α-ketoglutaric acid were degraded to various degrees by O. oeni, but galacturonic acid was not. At the time of malic acid depletion, percent degradation of pyruvate, α-ketoglutaric acid and acetaldehyde was 49%, 14% and 30%, respectively. During MLF, the decrease in average bound SO2 levels, as calculated from carbonyl metabolism, was 22%. The largest reduction in wine carbonyl content occurred in the week after completion of MLF and was 53% (107 mg/L to 34 mg/L) calculated as bound SO2. Prolonged activity of bacteria in the wines (up to 3 weeks post malic acid depletion) resulted only in reduced additional reductions in bound SO2 levels.The results suggest that microbiological wine stabilization one week after malic acid depletion is an effective strategy for maximum removal of SO2 binders while reducing the risk of possible post-ML spoilage by O. oeni leading to the production acetic acid and biogenic amines.

► Carbonyls and keto compounds bind to SO2 in wine limiting its preservative activity.
► Kinetics of carbonyl metabolism of 12 Oenococcus oeni tested in white wine.
► Pyruvate, acetaldehyde and α-ketoglutarate were variably degraded by O. oeni.
► Galacturonic acid was not degraded by any of the O. oeni strains.
► Optimum reduction of SO2 binders was achieved by malolactic fermentation + 1 week.