A novel method for screening high glycerol- and ester-producing brewing yeasts (Saccharomyces cerevisiae) by heat shock treatment

Abstract The screening of high glycerol-producing brewing yeasts ( Saccharomyces cerevisiae ) was attempted by heat shock treatment. The shochu yeast BAW-6 was grown in HS-medium, and the culture was treated by heat shock (45°C, 20 min). Surviving cells were isolated as heat shock-resistant (HSR) mutants. Glycerol production in the HSR mutants increased 1.8- to 2.0-fold over that in the parental strain. In some HSR mutants, the production of isoamyl acetate, ethyl caproate, ethyl caprylate, and ethyl capriate also increased significantly compared to their production in the parental strain. The glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) and alcohol acetyltransferase (EC 2.3.1.84) activities in selected HSR mutants were about 2-fold those in the parental strain. By contrast, NAD + -dependent glycerol dehydrogenase (EC 1.1.1.6) activity showed no difference. The ratio of oleic to stearic acid in the intracellular fatty acids was lower in the mutant strain HSR6-7 (6.52) than in the parental strain BAW-6 (8.88), and the incorporation of fatty acids from the medium was less in the HSR mutant than in the parental strain. High glycerol-producing sake and wine yeasts were also obtained from the sake yeast K-7 and wine yeast OC-2 by heat shock treatment. These results showed that heat shock treatment is an effective method for the improvement of brewing yeasts.