Aerobic fermentation of ethanol by a mutant strain NF 1-1 of sake yeast Kyokai no.7

Abstract

To obtain higher productivity under aerobic fermentation, we screened for mutant strains of Sake yeast Kyokai no. 7 (K-7). A high concentration of ethanol producing mutant was isolated from 18 strains of non-foaming mutants. The NF 1-1 strain was placed in some media containing molasses and/or tomato extract, and the effect of culture conditions was studied. By shaking the culture at 30°C, a concentration of ethanol of 125.3 g/L with a productivity of 3.0 g/L·h, which was 1.1 times higher than that of the K-7 used, and a fermentation efficiency of 81.7% were obtained in a tomato extract medium that initially contained 30%(w/v) sugar. NF 1-1 showed lower ethanol tolerance, but higher heat tolerance and osmotic stress than its parent strain. The NF 1-1 strain was used in tomato wine brewing test on a fermentor for 20 h. As compared with the K-7 strain, the NF 1-1 strain produced a low concentration of succinic acid and malic acid, but the concentration of ethanol (7.6%) was higher than that of the K-7 used (6.7%) in a tomato juice that initially had 10%(w/v) sucrose added. The taste of the wine fermented by NF 1-1 was milder than its parent strain.