VIEW ARTICLE    DOI: 10.1094/ASBCJ-53-0058

Reduction of Hydrogen Sulfide Production in Brewing Yeast by Constitutive Expression of MET25 Gene (1). Fumihiko Omura (2), and Yuji Shibano, Institute for Fundamental Research, and Nobuyuki Fukui and Kazuo Nakatani, Institute for Beer Brewing Technology, Suntory Ltd., 1-1-1, Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka 618, Japan. (1) Presented at the 60th Annual Meeting, Toronto, Canada, 1994. (2) Author to whom correspondence should be addressed. J. Am. Soc. Brew. Chem. 53(2):58-62, 1995. Accepted October 3, 1994.

Hydrogen sulfide (H(2)S) is produced by yeast during fermentation and is known as one of the young flavors of beer. The MET25 gene product [i.e., O-acetylhomoserine (OAH), O-acetylserine (OAS) sulfhydrylase], which utilizes H(2)S in the course of methionine synthesis, was assumed to play a key role in the production of excess H(2)S. We therefore attempted to diminish H(2)S production in brewing by controlling the MET25 gene expression. In the present study, the MET25 gene was brought under control of a constitutive promoter and was introduced into a brewing yeast strain. Resulting transformants showed a level of MET25 expression several times higher than that of the parental strain. In pilot-scale experiments, these transformants were confirmed to produce 10× less H(2)S than the parental strain did. This result was attributable to the decrease in H(2)S production by yeast cells at the early stage of fermentation. Control of the MET25 gene may be one way to shorten the maturation period. Keywords: Brewing, Hydrogen sulfide, MET25, Saccharomyces cerevisiae