Molecular breeding of sake yeast producing aromatic flavor based on isoamyl acetate-hydrolyzing esterase - Monograph [Japanese]

摘要

One of the many flavor compounds, isoamyl acetate has a fruit-like flavor and is an important factor in determining the flavor quality of sake and other alcoholic beverages. Much attention has therefore been given to improve its production. Acetate esters in Saccharomyces cerevisiae are believed to be synthesized from alcohols and acetyl-CoA by alcohol acetyltransferase (AATFase). This enzyme has been purified and characterized. Recently, the ATF1 gene encoding AATFase was cloned from S. cerevisiae and its nucleotide sequence determined. Meanwhile, many researchers have attempted to disrupt the esterase activity in sake yeast to inhibit the hydrolysis of isoamyl acetate in sake mash. Nevertheless, few detailed studies of the esterase in the yeast S. cerevisiae have been conducted. The EST2 gene corresponding to isoamyl acetate-hydrolyzing esterase has not been cloned and purified. The author therefore focused on the genetic analysis of isoamyl acetate-hydrolyzing esterase (EST2) as a means of establishing an efficient system for producing isoamyl acetate in sake brewing with the help of the yeast S. cerevisiae. In the present study, the author describes molecular cloning of the EST2 gene from S. cerevisiae to breed a sake yeast that accumulates large amounts of isoamyl acetate during sake brewing.