Improvement of the Shochu Yeast (Saccharomyces cerevisiae MK 021) by Electrofusion Technique

Abstract

The electrofusion technique was applied to the breeding of shochu yeast. An auxotrophic strain(lys) obtained from Saccharomyces cerevisiae MK 021, a diploid strain used for shochu making, and an auxotrophic strain (ade) obtained from Saccharomyces cerevisiae Kyokai No.9, a diploid strain, used for sake making, were fused by the electrofusion technique.The optimal parameters for the fusion of Saccharomyces protoplasts were: 2 MHz AC frequency, 400 V/cm AC voltage, 6 kV/cm DC pulse voltage, 60 psec duration, and 2 pulses.Some of the fusants showed good growth and fermentation, and produced larger amounts of aroma components, when compared to the original strains. Spore segregation test was carried out to obtain more stable strains.Spores from a fusant strain, F-1 having the highest sporulation ability were isolated by micromanipulation, and their fermentation rate and formation of aroma components were investigated using rice or barley koji. Of the selected segregants, F-1-2, was found to show especially good growth and to produce much aroma components such as n-propyl alcohol, isobutyl alcohol, isoamyl alcohol and isoamyl acetate.