To produce a freeze resistant yeast capable of providing a high-quality frozen bread dough by raising the activity of a delta-9-fatty acid desaturase in a baker's yeast cell and increasing the ratio of an unsaturated fatty acid content occupying the total fatty acid content of the cell.
An AH4-40 strain belonging to Saccharomyces cerevisiae and having freeze resistance is subjected to a mutation treatment with ethyl methanesulfonate to select a strain (AHM77) manifesting the same separation of the freeze sensitivity and phenotype of growth inhibition at 37°C. A fragment of a chromosomal DNA of the AH4-40 strain is then transduced thereinto to prepare a gene library derived from the AH4-40 chromosomal DNA. The screening of a freeze resistant reverse gene is carried out by using the reversion of the growth inhibition at 37°C as an index to transduce the resultant freeze resistant OLEI gene into the AHM77 strain. Thereby, the activity of a delta-9- fatty acid desaturase in a cell is raised to afford a freeze resistant baker's yeast AHM77REP strain having the ratio of the unsaturated fatty acid content occupying the total fatty acid content in the baker's yeast cell increased to ≥80%.
NIO NORIKI
MIWA TETSUYA
SEGURO KATSUYA
