Simultaneous utilization of ammonia, free amino acids and peptides during fermentative growth ofSaccharomyces cerevisiae

The efficiency of nitrogen use by yeast is one of the key determinants of the successful completion of alcoholic fermentations. In this work the growth of Saccharomyces cerevisiae S288c in a synthetic medium containing ammonia and free amino acids, supplemented with yeast hydrolysate, was studied. Experiments with 15NH4Cl and 15N-labelled yeast hydrolysate were carried out to gain insight into which of these three classes of assimilable nitrogen sources yeast cells prefer. Co-consumption of all three sources was observed; approximately 40% of the total nitrogen in the yeast protein fraction originated from yeast hydrolysate, while free amino acids and ammonia contributed 40 and 20%, respectively. The results indicate that several amino acids are more readily obtained from peptides, most likely when the uptake of their free forms is competitively inhibited and/or repressed. During the second half of each fermentation, a decrease in the incorporation of yeast hydrolysate-derived nitrogen was observed. These results highlight the nutritional role of peptides in various yeast fermentations. Copyright © 2016 The Institute of Brewing & Distilling