Evaluation of the Addition of Yeast Mannoprotein to <i>Oenococcus oeni</i> Starter Cultures to Improve Wine Malolactic Fermentation

Malolactic fermentation (MLF) in wine is driven by the lactic acid bacterium <i>Oenococcus oeni</i> in most cases. Although this bacterium is resistant to wine stress conditions, it often faces difficulties completing MLF. Previous studies indicate that yeast mannoproteins may improve <i>O. oeni</i> growth and survival in wine. However, very little is known about this topic. This study evaluated the effect of the addition of mannoprotein extracts to culture media on <i>O. oeni</i> growth and its survival to stress conditions and MLF performance. Three commercial mannoprotein extracts were characterized in terms of polysaccharide and protein richness and were used for <i>O. oeni</i> culture media supplementation. The addition of mannoprotein extracts improved the survival of the two evaluated <i>O. oeni</i> strains, PSU-1 and VP41, after acid shock (pH 3.2) in comparison to that of the control. The transcriptional response of four genes involved in mannose metabolism was different depending on the strain, indicating the complexity of sugar metabolism in <i>O. oeni</i>. PSU-1 cells grown with two of the mannoprotein extracts performed faster MLF compared with the control condition, indicating that mannoprotein addition may improve the performance of <i>O. oeni</i> starter cultures, although this effect depends on the strain.