Research on the relationship between mitochondrial membrane potential and fermentation profile is being intensely pursued because of the potential for developing advanced fermentation technologies. In the present study, we isolated naturally occurring strains of yeast from sake mash that produce high levels of malic acid and demonstrate that variations in mitochondrial membrane potential correlate with malic acid production. To define the underlying biochemical mechanism, we determined the activities of enzymes required for malic acid synthesis and found that pyruvate carboxylase and malate dehydrogenase activities in strains that produce high levels of malic acid were elevated compared with the standard sake strain K901. These results inspired us to hypothesize that decreased mitochondrial membrane potential was responsible for increased malic acid synthesis, and we present data supporting this hypothesis. Thus, the mitochondrial membrane potential of high malic acid producers was lower compared with standard strains. We conclude that mitochondrial membrane potential correlates with malic acid production.
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