The effect of nitrogen source on yeast metabolism and H2S formation

The impacts of aspartic acid and glutamine used as nitrogen supplements for alcoholic fermentations conducted by Saccharomyces were studied. Synthetic grape juice media and commercially prepared grape juices were supplemented with diammonium phosphate, aspartic acid, or glutamine to increase yeast-assimilable nitrogen concentrations to 250 mg N/L prior to fermentation. Two yeast strains, UCD522 and EC1118, were inoculated at 10⁵ CFU/mL and fermentations were monitored for soluble solids, hydrogen sulfide (H₂S), and residual amino acids. In general, unsupplemented media/juices fermented slower than supplemented ones, produced more H₂S, and contained lower concentrations of amino acids after fermentation. Among the supplemented treatments, fermentation rates, H₂S production, and amino acid utilization varied depending on the nitrogen source and yeast strain. Those fermentations supplemented with aspartic acid were generally slower and sometimes did not achieve dryness. In contrast, glutamine additions yielded fermentation rates and H₂S production equivalent or better than other supplemented treatments. Based on these results, the use of glutamine appears promising as an alternative nitrogen supplement for wine production.