Abstract
Two cerulenin resistant mutants, strains No.19 and No.24, were obtained by treating Kyokai 701 sake yeast with ethyl methane sulfonate. Strain No.19, which is resistant to 25, μM cerulenin, had a high fermentative ability and produced a 5-fold increase in the amount of ethyl caproate produed compared to the parent strain. Strain No.24, which is reistant to 65 μMcerulenin, had a low fermentative ability but produced a 10-fold increase in the amount of ethyl caproate produed compared to the parent strain. Genomic analysis of these mutants indicated that strain No.19 had a hetero type mutation in FAS 2, the gene encoding the asubunit of the fatty acid synthetase, and strain No.24 had a homo-type mutation in this gene. These results suggested that the homo type mutation of the FAS 2 enabled the sake yeast to obtain a high level of resistance to cerulenin and a high ethyl caproate productivity. By transforming the mutant FAS 2 gene into sake yeast, we obtained sake yeasts which have both the high fermentative ability characteristic of the hetero-type mutant and the high ethyl caproate productivity charactaristic of the homo-type mutant. Furthermore, the homo-type mutant strain No.24 and the transformants obtained in this study were used to brew rice flour shochu. These strains fermented sufficiently and produced high levels of ethyl caproate. Using these strains, shochu with an excellent fruity flavor was produced.
