Effects of Heterologous Expression of Genes Related L–Malic acid Metabolism in <i>Saccharomyces uvarum</i> on Flavor Substances Production in Wine

Abstract

During malolactic fermentation (MLF) of vinification, the harsh L–malic acid undergoes transformation into the milder L–lactic acid, and via decarboxylation reactions it is catalyzed by malolactic enzymes in LAB. The use of bacterial malolactic starter cultures, which usually present challenges in the industry as the suboptimal conditions after alcoholic fermentation (AF), including nutrient limitations, low temperatures, acidic pH levels, elevated alcohol, and sulfur dioxide concentrations after AF, lead to “stuck” or “sluggish” MLF and spoilage of wines. Saccharomyces uvarum has interesting oenological properties and provides a stronger aromatic intensity than Saccharomyces cerevisiae in AF. In the study, the biological pathways of deacidification were constructed in S. uvarum, which made the S. uvarum carry out the AF and MLF simultaneously, as different genes encoding malolactic enzyme (mleS or mleA), malic enzyme (MAE2), and malate permease (melP or MAE1) from Schizosaccharomyces pombe, Lactococcus lactis, Oenococcus oeni, and Lactobacillus plantarum were heterologously expressed. For further inquiry, the effect of L–malic acid metabolism on the flavor balance in wine, the related flavor substances, higher alcohols, and esters production, were detected. Of all the recombinants, the strains WYm1SN with coexpression of malate permease gene MAE1 from S. pombe and malolactic enzyme gene mleS from L. lactis and WYm1m2 with coexpression of gene MAE1 and malate permease gene MAE2 from S. pombe could reduce the L–malic acid contents to about 1 g/L, and in which the mutant WYm1SN exhibited the best effect on the flavor quality improvement.

Keywords

• wine
• heterologous expression
• L–malic acid
• higher alcohols
• esters