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This study aimed to investigate the role of the yeast cell wall and membrane in enhancing osmotic tolerance by antioxidant dipeptides (ADs) including Ala-His (AH), Thr-Tyr (TY), and Phe-Cys (FC). Results revealed that ADs could improve the integrity of the cell wall by restructuring polysaccharide structures. Specifically, FC significantly ( p < 0.05) reduced the leakage of nucleic acid and protein by 2.86% and 5.36%, respectively, compared to the control. In addition, membrane lipid composition played a crucial role in enhancing yeast tolerance by ADs, including the increase of cell membrane integrity and the decrease of permeability by regulating the ratio of unsaturated fatty acids. The up-regulation of gene expression associated with the cell wall integrity pathway ( RLM1 , SLT2 , MNN9 , FKS1 , and CHS3 ) and fatty acid biosynthesis ( ACC1 , HFA1 , OLE1 , ERG1 , and FAA1 ) further confirmed the positive impact of ADs on yeast tolerance against osmotic stress.

Although high gravity brewing technology has been widely used for beer industries due to its economic benefits, yeast cells are subjected to multiple environmental stresses throughout the fermentation process. Eleven bioactive dipeptides (LH, HH, AY, LY, IY, AH, PW, TY, HL, VY, FC) were selected to evaluate their effects on cell proliferation, cell membrane defense system, antioxidant defense system and intracellular protective agents of lager yeast against ethanol-oxidation cross-stress. Results showed that the multiple stresses tolerance and fermentation performance of lager yeast were enhanced by bioactive dipeptides. Cell membrane integrity was improved by bioactive dipeptides through altering the structure of macromolecular compounds of the cell membrane. Intracellular reactive oxygen species (ROS) accumulation was significantly decreased by bioactive dipeptides, especially for FC, decreasing by 33.1%, compared with the control. The decrease of ROS was closely related to the increase of mitochondrial membrane potential, intracellular antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and glycerol level. In addition, bioactive dipeptides could regulate the expression of key genes (GPD1, OLE1, SOD2, PEX11, CTT1, HSP12) to enhance the multilevel defense systems under ethanol-oxidation cross-stress. Therefore, bioactive dipeptides should be potentially efficient and feasible bioactive ingredients to improve the multiple stresses tolerance of lager yeast during high gravity fermentation., Competing Interests: Declarations of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

High concentrations of ethanol could cause intracellular oxidative stress in yeast, which can lead to ethanol-oxidation cross-stress. Antioxidant dipeptides are effective in maintaining cell viability and stress tolerance under ethanol-oxidation cross-stress. In this study, we sought to elucidate how antioxidant dipeptides affect the yeast cell wall and membrane defense systems to enhance stress tolerance. Results showed that antioxidant dipeptide supplementation reduced cell leakage of nucleic acids and proteins by changing cell wall components under ethanol-oxidation cross-stress. Antioxidant dipeptides positively modulated the cell wall integrity pathway and up-regulated the expression of key genes. Antioxidant dipeptides also improved the cell membrane integrity by increasing the proportion of unsaturated fatty acids and regulating the expression of key fatty acid synthesis genes. Moreover, the addition of antioxidant dipeptides significantly ( p < 0.05) increased the content of ergosterol. Ala-His (AH) supplementation caused the highest content of ergosterol, with an increase of 23.68 ± 0.01% compared to the control, followed by Phe-Cys (FC) and Thr-Tyr (TY). These results revealed that the improvement of the cell wall and membrane functions of antioxidant dipeptides was responsible for enhancing the ethanol-oxidation cross-stress tolerance of yeast.

The effects of glucose, sucrose and maltose supplementations on the fermentation performance and stress tolerance of lager yeast (Saccharomyces pastorianus) during high gravity (18°P) and very high gravity (24°P) fermentations were studied. Results showed that throughout 18°P wort fermentation, fermentation performance of lager yeast was significantly improved by glucose or sucrose supplementation, compared with maltose supplementation, especially for sucrose supplementation increasing wort fermentability and ethanol production by 6% and 8%, respectively. However, in the later stage of 24°P wort fermentation, fermentation performance of lager yeast was dramatically improved by maltose supplementation, which increased wort fermentability and ethanol production by 14% and 10%, respectively, compared with sucrose supplementation. Furthermore, higher HSP12 expression level and more intracellular trehalose accumulation in yeast cells were observed by maltose supplementation with increase of the wort gravity from 18°P to 24°P, indicating higher stress response of yeast cells. The excretion of Gly and Ala, and the absorption of Pro in the later stage of fermentation were promoted by maltose supplementation. In addition, with increase of the wort gravity from 18°P to 24°P, higher alcohols level was decreased with maltose supplementation, while esters formation was increased significantly with glucose supplementation. This study suggested that the choice of optimal fermentable sugars maintaining better fermentation performance of lager yeast should be based on not only strain specificity, but also wort gravity., (Copyright © 2016 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Four kinds of worts with different nitrogen compositions were used to examine their effects on fermentation performance of brewer's yeast. The absorption pattern of peptides with different molecular weights (Mw) in yeast cells during wort fermentation was also investigated. Results showed that both the nitrogen composition and level had significant impacts on the yeast biomass accumulation, ethanol production, and free amino nitrogen and sugars consumption rates. Worts supplemented with wheat gluten hydrolysates increased 11.5% of the biomass, 5.9% of fermentability, and 0.6% of ethanol content and decreased 25.6% of residual sugar content during wort fermentation. Moreover, yeast cells assimilated peptides with various Mw differently during fermentation. Peptides with Mw below 1 kDa decreased quickly, and the rate of assimilation was more than 50% at the end of fermentation, while those with Mw above 10 kDa almost could not be assimilated by yeast. All these results further indicated that the level and composition of wort nitrogen had significant impacts on the growth and fermentation performances of brewer's yeast, and peptides with Mw below 1 kDa were one of preferred nitrogen sources for brewer's yeast.

The aim of this work was to further investigate the glycolysis performance of lager and ale brewer's yeasts under different fermentation temperature using a combined analysis of metabolic flux, glycolytic enzyme activities, and flux control. The results indicated that the fluxes through glycolytic pathway decreased with the change of the fermentation temperature from 15 °C to 10 °C, which resulted in the prolonged fermentation times. The maximum activities (V (max)) of hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK) at key nodes of glycolytic pathway decreased with decreasing fermentation temperature, which was estimated to have different control extent (22-84 %) on the glycolytic fluxes in exponential or flocculent phase. Moreover, the decrease of V (max) of PFK or PK displayed the crucial role in down-regulation of flux in flocculent phase. In addition, the metabolic state of ale strain was more sensitive to the variation of temperature than that of lager strain. The results of the metabolic flux and nodes control analysis in brewer's yeasts under different fermentation temperature may provide an alternative approach to regulate glycolytic flux by changing V (max) and improve the production efficiency and beer quality.

Soy protein isolate was hydrolysed with Alcalase, Papain, Flavorzyme and Protemax, respectively, and further fractioned by ultrafiltration. The resulting soy protein hydrolysates ( SPH) and their ultrafiltration fractions were used to examine their effects on the growth and fermentation performances of brewer's yeast. Results showed that degree of hydrolysis, molecular weight distribution and amino acid composition of SPH significantly affected the growth, viability and fermentation performance of brewer's yeast. The SPH prepared from different proteolytic enzymes exhibited distinct growth- and fermentation-promoting activity for brewer's yeast. The SPH treated with Protemax for 9 h and with the molecular weight below 3 kDa showed the highest growth-promoting activity and induced more rapidly reducing sugar consumption and higher ethanol production. The relatively lower molecular weight and the hydrophilic and electropositive amino acid residues ( Lys, His, Arg and Ile) in SPH might be responsible for its functionality, promoting the growth and fermentation of brewer's yeast. [ABSTRACT FROM AUTHOR]

Yeast plays a crucial role in jujube wine fermentation. In this study, the effects of five commercial yeasts on the physicochemical parameters, color, antioxidant properties, phenolic profiles and flavor components of jujube wine were evaluated. The results showed the alcohol content of five wine samples ranged from 12.62% to 13.15%. The colors of the five fermented jujube wine samples were bright yellow-green. Jujube wine samples fermented by BV818 had the best color quality. The total contents of phenolic profiles and free amino acids in wine fermented by BV818 (76.01 mg/L and 110.33 mg/L, respectively) and SY (80.99 mg/L and 121.54 mg/L, respectively) yeasts were significantly higher than those of the other three jujube wine. The free amino acids of wine samples mainly were sweet, and the BV818-fermented wine had the highest content at 56.47%. There were twenty-seven shared aroma substances were found in five samples. The types of volatiles in wine fermented by BV818 and SY were both forty-four, but the former had lower contents of higher alcohols. Sensory score of jujube wine fermented by BV818 was better. Therefore, BV818 was the most suitable yeast for fermenting jujube wine. This study provides a theoretical basis for producing jujube wine. • The quality of jujube wine fermented by different yeasts is significantly different. • BV818 showed the best physiological features for fermenting jujube wine. • The main volatile substances in jujube wine are alcohols and esters. [ABSTRACT FROM AUTHOR]