Combinatory breeding of sake yeast strains with mutations that enhance Ginjo aroma production

Isoamyl acetate and ethyl caproate are the primary aroma compounds responsible for the fruity fragrance characteristic of Ginjo sake. Simultaneous high-level production of both compounds is crucial to achieving a balanced aroma and complex flavor. Isoamyl acetate is predominantly produced by hda1∆/hda1∆ and LEU4(G516S)/LEU4(G516S), while ethyl caproate is produced in high quantities by FAS2(G1250S)/FAS2(G1250S). In this study, to maximize the production of both aroma compounds, genome editing was employed to generate sake yeast strains combining these mutations. After small-scale fermentation tests were conducted to evaluate the production of aroma compounds, we found that the isoamyl acetate-enhancing effect of hda1∆/hda1∆ was almost completely masked by FAS2(G1250S)/FAS2(G1250S). In contrast, the effects of LEU4(G516S)/LEU4(G516S) were not entirely masked by FAS2(G1250S)/FAS2(G1250S), resulting in 2.4- and 5.4-fold greater production of isoamyl acetate and ethyl caproate, respectively. This study highlights the utility of genome editing in the combinatorial breeding of sake yeast.