Isolation of a mutant showing freeze-tolerance after pre-fermentation in bakers' yeast and its application to freeze bread dough
2003
Shiomi, N. (Kobe Coll., Nishinomiya, Hyogo (Japan)) | Yasuda, T.
Since pre-fermentation of Saccharomyces cerevisiae cells in fresh medium for 1 hour is considered as a good model of the first-fermentation in bread making, the freeze-tolerance of S. cerevisiae cells after the pre-fermentation was studied. We have found that S. cerevisiae cells after the pre-fermentation showed lower freeze-tolerance than the cells grown to stationary phase. Moreover, among heat-resistant mutants, we isolated a mutant that maintained freeze-tolerance after the pre-fermentation, because a positive correlation between heat shock tolerance and freeze-tolerance was found in S. cerevisiae cells after the pre-fermentation. When the freeze-tolerant mutant was used in frozen dough, the frozen dough expanded better than the one using the parent strain. The effects of cultivation conditions and freezing temperature of S. cerevisiae cells were also investigated to increase freeze-tolerance of the mutant cells. The pre-fermentation in the medium containing the no carbon source is the most effective to enhance survival ratio of the cells during the storage at -35 deg C. By use of the freeze-tolerant cells, the size of the bread baked from frozen dough, which stored for 7 days at -35 deg C, was almost the same as that of the one baked from unfrozen dough.
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