DIFFERENTIAL IMPORTANCE OF TREHALOSE IN STRESS RESISTANCE IN FERMENTING AND NONFERMENTING SACCHAROMYCES-CEREVISIAE CELLS

The trehalose content in laboratory and industrial baker's yeast is wi dely believed to be a major determinant of stress resistance. Fresh an d dried baker's yeast is cultured to obtain a trehalose content of mor e than 10% of the dry weight. Initiation of fermentation, e.g., during dough preparation, is associated with a rapid loss of stress resistan ce and a rapid mobilization of trehalose. Using specific Saccharomyces cerevisiae mutants affected in trehalose metabolism, we confirm the c orrelation between trehalose content and stress resistance but only in the absence of fermentation. We demonstrate that both phenomena can b e dissociated clearly once the cells initiate fermentation. This was a ccomplished both for cells with moderate trehalose levels grown under laboratory conditions and for cells with trehalose contents higher tha n 10% obtained under pilot-scale conditions. Retention of a high treha lose level during fermentation also does not prevent the loss of ferme ntation capacity during preparation of frozen doughs. Although higher trehalose levels are always correlated with higher stress resistance b efore the addition of fermentable sugar, our results show that the ini tiation of fermentation causes the disappearance of any other factor(s ) required for the maintenance of stress resistance, even in the prese nce of a high trehalose content.