Effects of Heterologous Expression of Genes Related L-Malic acid Metabolism in  Saccharomyces uvarum  on Flavor Substances Production in Wine.
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 WYm1S N  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 WYm1S N  exhibited the best effect on the flavor quality improvement.
Li P, Song W, Wang Y, Li X, Wu S, Li B, Zhang C