Studies On Breeding And Application Of Cold Sensitive Baker's Yeast

This paper focused on the breeding, application and genetic analysis of cold- sensitive baker yeast. A cold-sensitive strain Css- 14 was obtained by UV irradiation mutagenesis with Al 3-18 as the original strain. The double-layer plate with YPG medium as the lower part and soft dye agar as the upper part was used as screening plate for cold-sensitive strains of S.cerevisiae. The nystatin treatment at 100C in the presence of antimycin A would be effective on raising the ratio of cold-sensitive strains. A cold-sensitive baker yeast, S. cerevisiae F6-2, was obtained by protoplast fusion, which was carried out between a cold-sensitive haploid of S.cerevisiae Css-14 and a diploid of baker yeast Y-3. The fermentation ability of S. cerevisiae F6-2 at 300C was superior to the yeast Y-3 and was substantially zero at 40C after 6 days fermentation. Heredic characteristic was tested stable after 15 generations. A frozen-tolerant baker yeast S.cerevisiae X-003 was isolated by alcohol-resistance test. The survival ratio of S. cerevisiae X-003 is more than 80% after 3 weeks frozen. The quality of frozen-dough bread prepared by the yeasts F6-2 and X-003 was superior compared with 5 commercial baker yeasts. Genetic analysis of cold-sensitive diploid showed that gene recombination ratio of hybridization was 50% and the genes of cold- sensitive and mating type were not linked to each other.