In a previous study, we reported that the high malic acid-producing
strain no. 28 shows lower mitochondrial activity than its
parental strain K1001 (7). In addition, this respiratory-deficient
strain of K1001 also has increased malic acid production. Thus, we
assumed that reduced mitochondrial activity contributes to high
malic acid production because the pyruvic acid produced during
glycolysis is barely metabolized in mitochondria; then, the excess
pyruvic acid is converted to malic acid by cytosolic pyruvate
carboxylase and malate dehydrogenase. Therefore, it is expected
that sake yeasts producing various compositions of organic acids
can be developed by the improvement of mitochondrial activity
taste (6). Thus, analysis of the organic acid production
mechanism and breeding of new sake yeasts that provide different
organic acid combinations is required for the development of the
sake industry.