Breeding of a high tyrosol-producing sake yeast by isolation of an ethanol-resistant mutant from a trp3 mutant

Abstract

A novel breeding strategy for a high tyrosol-producing sake yeast was developed by isolating an ethanol-resistant mutant from a tryptophan auxotrophic mutant of a sake brewery yeast. Since tyrosol has antioxidant, cardioprotective and taste-sharpening effects, increasing the tyrosol level of alcohol beverages could be beneficial in alcohol production. Since the transporters of aromatic amino acids are degraded by several stresses and mutants defective in the synthesis of aromatic amino acids are sensitive to ethanol, it was hypothesized that the degradation of these transporters should be inhibited in ethanol resistant mutants isolated from the auxotrophic mutants of aromatic amino acids, and that the uptake of aromatic amino acids would be increased in the mutants. Consistent with this hypothesis, sake was brewed with the ethanol-resistant mutant of a tryptophan auxotrophic mutant and the sake was found to contain a lesser content of tyrosine and a higher content of tyrosol relative to the sake brewed with the parental strains. The taste of the sake brewed with the mutant strain could be discriminated from the sake brewed with the parental strains, probably because of the altered concentrations of tyrosol and certain amino acids and organic acids. The results suggest that combining the isolation of an ethanol-resistant mutant and an auxotrophic mutant is an effective method to breed a brewing strain with a modified metabolism of these substances. © 2012 The Institute of Brewing & Distilling.