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Three peptides (LL, LML, and LLL) were used to examine their influences on the osmotic stress tolerance and cell wall properties of brewer's yeast. Results suggested that peptide supplementation improved the osmotic stress tolerance of yeast through enhancing the integrity and stability of the cell wall. Transmission electron micrographs showed that the thickness of yeast cell wall was increased by peptide addition under osmotic stress. Additionally, quantitative analysis of cell wall polysaccharide components in the LL and LLL groups revealed that they had 27.34% and 24.41% higher chitin levels, 25.73% and 22.59% higher mannan levels, and 17.86% and 21.35% higher β-1,3-glucan levels, respectively, than the control. Furthermore, peptide supplementation could positively modulate the cell wall integrity pathway and up-regulate the expressions of cell wall remodeling-related genes, including FKS1, FKS2, KRE6, MNN9, and CRH1. Thus, these results demonstrated that peptides improved the osmotic stress tolerance of yeast via remodeling the yeast cell wall and reinforcing the structure of the cell wall. Key points: • Peptide supplementation improved yeast osmotic stress tolerance via cell wall remodeling. • Peptide supplementation enhanced cell wall thickness and stability under osmotic stress. • Peptide supplementation positively modulated the CWI pathway under osmotic stress. [ABSTRACT FROM AUTHOR]

The influences of three wheat gluten peptides (WGP-LL, WGP-LML, and WGP-LLL) on the osmotic stress tolerance and membrane lipid component in brewer's yeast were investigated. The results demonstrated that the growth and survival of yeast under osmotic stress were enhanced by WGP supplementation. The addition of WGP upregulated the expressions of OLE1 (encoded the delta-9 fatty acid desaturase) and ERG1 (encoded squalene epoxidase) genes under osmotic stress. At the same time, WGP addition enhanced palmitoleic acid (C16:1) content, unsaturated fatty acids/saturated fatty acids ratio, and the amount of ergosterol in yeast cells under osmotic stress. Furthermore, yeast cells in WGP-LL and WGP-LLL groups were more resistant to osmotic stress. WGP-LL and WGP-LLL addition caused 25.08% and 27.02% increase in membrane fluidity, 22.36% and 29.54% reduction in membrane permeability, 18.38% and 14.26% rise in membrane integrity in yeast cells, respectively. In addition, scanning electron microscopy analysis revealed that the addition of WGP was capable of maintaining yeast cell morphology and reducing cell membrane damage under osmotic stress. Thus, alteration of membrane lipid component by WGP was an effective approach for increasing the growth and survival of yeast cells under osmotic stress. Key points: •WGP addition enhanced cell growth and survival of yeast under osmotic stress. •WGP addition increased unsaturated fatty acids and ergosterol contents in yeast. •WGP supplementation improved membrane homeostasis in yeast at osmotic stress. [ABSTRACT FROM AUTHOR]

Wheat gluten hydrolysates (WGH) and KCl were used to examine their effects on fermentation performances and physiological characteristics of brewer's yeast during very high gravity (VHG) fermentation. Results showed that all supplementations exhibited a notable promotion in yeast growth, glucose utilization, ethanol production, and physiological characteristics. Combination supplementation of 0.3% WGH and 0.5% KCl showed the best promotion effect with 6.38%, 9.41% and 8.68% of increases in biomass, glucose utilization and ethanol production, respectively. Moreover, combination addition of WGH and KCl also enhanced significantly membrane integrity and mitochondrial functionality of brewer's yeast. Amino acid compositions of WGH and intracellular metabolites analysis indicated that active nitrogen metabolism and high levels of stress resistant substances might be responsible for the improvement of growth and fermentation performances in brewer's yeast by nutrient supplementation. • WGH and KCl supplementations promoted cell growth and fermentation of yeast. • WGH and KCl addition improved membrane integrity and mitochondrial functionality. • Combination of 0.3% WGH and 0.5% KCl showed the best bioactivity for yeast. • Active nitrogen metabolism and stress resistant substances were related to activity. [ABSTRACT FROM AUTHOR]