Evaluation of different nitrogen sources on growth and fermentation performance for enhancing ethanol production by wine yeasts

Abstract

The utilization of grape juice from low oenological value grape varieties for bioethanol productionrepresent an alternative for diversification and value addition in viticulture. Optimizing VeryHigh Gravity (VHG) fermentation can significantly increase ethanol productivity while reducingwater and energy consumption. In this study, the impact of different nitrogen sources on growthand fermentative performance of locally selected yeast strains was investigated. Five yeast strainsof species Saccharomyces cerevisiae and Zygosaccharomyces rouxii were cultured in both syntheticculture media and natural grape juice supplemented with ammonium sulfate (NH), yeast extract(YE), Fermaid K (FERM), and urea (U) at varying concentrations. Due to the very low fermentationrate, the Z. rouxii strain was excluded from the selection. The results obtained in syntheticmedium showed that nitrogen sources that promoted growth (NH and YE) had minimal effects onfermentative performance and were highly dependent on the specific yeast strain. However, thecombination of urea and ammonium favored the rate of sugar consumption. When validated innatural grape juice, urea combined with ammonium (U + NH 300 + 75 mg/L) improved bothgrowth parameters and ethanol yield. Doubling the concentration (U + NH 600 + 150 mg/L)further enhanced sugar consumption and ethanol production while reducing unwanted byproducts.The combined use of urea and ammonium exhibited a synergistic effect, making it acost-effective nitrogen supplement for VHG fermentations.