Abstract
The leavening ability of bakers' yeast cells grown in several media containing NaCl was evaluated in several types of dough. Three types of growth media were used : YPG medium containing 5% glucose, 1% peptone, 0.5% yeast extract, 0.1% KH2PO4 and 0.1% MgSO4·7H2O (pH 5.6); YPS medium containing 2% sucrose, 4% peptone, 2% yeast extract, 0.2% KH2PO4 and 0.1% MgSO4.7H2O (pH 5.6); and MO medium containing 1% urea, 0.2% KH2PO4, and 5% total sugar as cane molasses (pH 5.6). The addition of 3% NaCl to each of these growth media clearly suppressed the growth of the yeast cells, irrespective of the types of media; the cell yield was decreased by 15-60% in the stationary phase. When we analyzed the leavening ability of these cells that had been exposed to salt stress, the cells showed higher leavening ability than those grown in the absence of NaCl, irrespective of the types of growth media and dough. The increase ratio of leavening ability in the presence of NaCl was highest at 45% when we used the YPS or YPG medium containing 3% NaCl and dough supplemented with 5% glucose. However, the increase was at a much lower level (2-7%) in sugar-less dough, irrespective of the types of growth media. Since the leavening ability of yeast is well known to be primarily limited by the rate of sugar uptake, the high leavening ability of bakers' yeast grown in the presence of NaCl may be due to an increase in sugar-uptake rate. The presence of NaCl in each growth medium also enhanced the leavening ability of various Saccharomyces yeast strains.
