Breeding of freeze-tolerant baker's yeast by the regulation of trehalose metabolism

Accumulation of trehalose, which is a disaccharide composed of 2 molecules of glucose, is generally considered to be a critical determinant in improvi ng the stress tolerance of the baker's yeast Saccharomyces cerevisiae. To r etain this accumulation in yeast cells, we constructed diploid homozygous t rehalase (trchalose-hydrolyzing enzyme)-deficient mutants by the gene disru ption method from commercial baker's yeast. During fermentation, degradatio n of intracellular trehalose was inhibited in the trehalase-deficient mutan ts. Their freeze tolerance was maintained at a higher level than that of th e parent strain. Due to the improved freeze tolerance exhibited by the treh alase-deficient mutants, these strains may be suitable for use in the bakin g process of frozen dough.