Ability of Saccharomyces cerevisiae MC87-46 to assimilate isomaltose and its effects on sake taste

Recently, wild strains of Saccharomyces cerevisiae isolated from a variety of natural resources have been used to make bread, beer, wine, and sake. In the current study, we isolated wild S. cerevisiae MC strain from the carnation (Dianthus caryophyllus L) flower and produced sake using its cerulenin-resistant mutant strain MC87-46. Then, we characterized the components, including ethanol, amino acids, organic acids, and sugars, in the fermented sake. Sake brewed with MC87-46 is sweet owing to the high content of isomaltose, which was at a concentration of 44.3 mM. The low sake meter value of −19.6 is most likely due to this high isomaltose concentration. The genomic DNA of MC87-46 encodes for isomaltases IMA1, IMA2, IMA3, IMA4 and IMA5, as well as the isomaltose transporter gene, AGT1. However, these genes were not induced in MC87-46 by isomaltose, and the strain did not possess isomaltase activity. These results show that MC87-46 cannot utilize isomaltose, resulting in its accumulation in the fermented sake. Isomaltose concentrations in sake brewed with MC87-46 were 24.6-fold more than in commercial sake. These findings suggest that MC87-46 may be useful for commercial application in Japanese sake production because of its unique flavour and nutrient profile.