Abstract
Glycerol is the main compatible solute in yeast Saccharomyces cerevisiae. When faced with osmotic stress, for example during semi-solid state bread dough fermentation, yeast cells produce and accumulate glycerol in order to prevent dehydration by balancing the intracellular osmolarity with that of the environment. However, increased glycerol production also results in decreased CO2 production, which may reduce dough leavening. We investigated the effect of yeast glycerol production level on bread dough fermentation capacity of a commercial bakery strain and a laboratory strain. We find that Δgpd1 mutants that show decreased glycerol production show impaired dough fermentation. In contrast, overexpression of GPD1 in the laboratory strain results in increased fermentation rates in high-sugar dough and improved gas retention in the fermenting bread dough. Together, our results reveal the crucial role of glycerol production level by fermenting yeast cells in dough fermentation efficiency as well as gas retention in dough, thereby opening up new routes for the selection of improved commercial bakery yeasts.
Highlights
The common brewer’s and baker’s yeast Saccharomyces cerevisiae limits dehydration by balancing the intracellular level of osmolytes with the extracellular water activity
The first step of this conversion is catalyzed by NAD-dependent glycerol 3-phosphate dehydrogenase (Gpd), which is encoded as two isoforms by the genes GPD1 and GPD2 [7]
Our results demonstrate that glycerol production level in yeast cells is important for dough fermentation efficiency and level of gas retention in dough, and that the glycerol-3phosphate dehydrogenase Gpd1 plays a central role in glycerol synthesis during bread dough fermentation
Summary
The common brewer’s and baker’s yeast Saccharomyces cerevisiae limits dehydration by balancing the intracellular level of osmolytes with the extracellular water activity. In environments with lower water activity compared to the cytoplasm, cells divert part of the glycolytic flux towards the production of glycerol, while limiting glycerol catabolism and efflux and increasing glycerol uptake from the environment [1,2,3,4,5,6]. Glycerol is produced by reduction of the glycolytic intermediate dihydroxyacetone phosphate to glycerol 3-phosphate (G3P) followed by dephosphorylation of G3P to glycerol (Fig. 1). The first step of this conversion is catalyzed by NAD-dependent glycerol 3-phosphate dehydrogenase (Gpd), which is encoded as two isoforms by the genes GPD1 and GPD2 [7]. The expression of GPD1, which is required for growth at high osmolarity [8], is induced by PLOS ONE | DOI:10.1371/journal.pone.0119364 March 12, 2015
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