Application of Protein Hydrolysates from Defatted Walnut Meal in High-Gravity Brewing to Improve Fermentation Performance of Lager Yeast

Assess different fermentation characteristics of 54 lager yeasts based on group classification

Saccharomyces pastorianus, hybrids of Saccharomyces cerevisiae and Saccharomyces eubayanus, were generally regarded as authentic lager beer yeasts. In recent years, with more new findings of other Saccharomyces genus hybrids, yeasts used in lager beer brewing have been proved much more complicated than previous cognition. In this study, we analyzed the different fermentation characteristics of 54 yeast strains used for lager brewing in normal and very high gravity brewing based on group classification. The difference between Group Ⅰ and Group Ⅱ lager yeasts were more striking in very high gravity brewing. However, during our research progress, we realized that some yeasts used in this study were actually hybrids of S. cerevisiae and Saccharomyces kudriavzevii. Features of these hybrids could be beneficial to very high gravity brewing. We further discussed about the mechanism behind their outstanding characteristics and the reason why group classification methods of lager beer yeasts had limitations. Hybridization in yeasts is constantly getting richer. Lager yeasts could have more possibilities based on better understandings of their genetic background and roles of other Saccharomyces genus hybrids. Their heterosis shed light on innovation in brewing and other diverse fermentation industries.

Plant-derived antioxidant dipeptides provide lager yeast with osmotic stress tolerance for very high gravity fermentation

Osmotic stress in the yeast limits productivity in industrial beer production under very high gravity brewing. This study focused on assessing the protective impacts of eleven plant-derived antioxidant dipeptides (PADs) on the osmotic stress tolerance of lager yeast. The results showed that PADs provided yeast with stress tolerance under osmotic stress. PADs supplementation enhanced cell membrane integrity and reduced oxidative damage. PADs upregulated the expression of SOD2, PEX11 and CTT1 genes under osmotic stress. Moreover, the volatile compounds contents and antioxidant activities of beers were improved by PADs, suggesting favorable quality characteristics. Especially, Phe-Cys and Leu-His could increase the DPPH radical scavenging activity of beer by 41.92% and 18.78% respectively, compared with control. Therefore, PADs are industrially scalable enhancers to improve the ability of yeast to resist osmotic stress and beer quality during very high gravity brewing.

Walnut Protein: A Rising Source of High-Quality Protein and Its Updated Comprehensive Review

Recently, plant protein as a necessary nutrient source for human beings, a common ingredient of traditional processed food, and an important element of new functional food has gained prominence due to the increasing demand for healthy food. Walnut protein (WP) is obtained from walnut kernels and walnut oil-pressing waste and has better nutritional, functional, and essential amino acids in comparison with other vegetable and grain proteins. WP can be conveniently obtained by various extraction techniques, including alkali-soluble acid precipitation, salting-out, and ultrasonic-assisted extraction, among others. The functional properties of WP can be modified for desired purposes by using some novel methods, including free radical oxidation, enzymatic modification, high hydrostatic pressure, etc. Moreover, walnut peptides play an important biological role both in vitro and in vivo. The main activities of the walnut peptides are antihypertensive, antioxidant, learning improvement, and anticancer, among others. Furthermore, WP could be applied in the development of functional foods or dietary supplements, such as delivery systems and food additives, among others. This review summarizes recent knowledge on the nutritional, functional, and bioactive peptide aspects of WP and possible future products, providing a theoretical reference for the utilization and development of oil crop waste.

Screening and transcriptomic analysis of the ethanol-tolerant mutant Saccharomyces cerevisiae YN81 for high-gravity brewing

Ethanol stress is one of the major limiting factors for high-gravity brewing. Breeding of yeast strain with high ethanol tolerance, and revealing the ethanol tolerance mechanism of Saccharomyces cerevisiae is of great significance to the production of high-gravity beer. In this study, the mutant YN81 was obtained by ultraviolet-diethyl sulfate (UV-DES) cooperative mutagenesis from parental strain CS31 used in high-gravity craft beer brewing. The ethanol tolerance experiment results showed that cell growth and viability of YN81 were significantly greater than that of CS31 under ethanol stress. The ethanol tolerance mechanisms of YN81 were studied through observation of cell morphology, intracellular trehalose content, and transcriptomic analysis. Results from scanning electron microscope (SEM) showed alcohol toxicity caused significant changes in the cell morphology of CS31, while the cell morphology of YN81 changed slightly, indicating the cell morphology of CS31 got worse (the formation of hole and cell wrinkle). In addition, compared with ethanol-free stress, the trehalose content of YN81 and CS31 increased dramatically under ethanol stress, but there was no significant difference between YN81 and CS31, whether with or without ethanol stress. GO functional annotation analysis showed that under alcohol stress, the number of membrane-associated genes in YN81 was higher than that without alcohol stress, as well as CS31, while membrane-associated genes in YN81 were expressed more than CS31 under alcohol stress. KEGG functional enrichment analysis showed unsaturated fatty acid synthesis pathways and amino acid metabolic pathways were involved in ethanol tolerance of YN81. The mutant YN81 and its ethanol tolerance mechanism provide an optimal strain and theoretical basis for high-gravity craft beer brewing.

Protein kinases Elm1 and Sak1 of Saccharomyces cerevisiae exerted different functions under high-glucose and heat shock stresses

Phosphorylation catalyzed by protein kinases is the most common and important regulatory pathway in the adaptive physiological responses to the changes in nutrition and environment of yeast. This study focused on the functions of Elm1, Sak1, and Tos3, which are three upstream protein kinases of Snf1 in Saccharomyces cerevisiae, in response to high-glucose and heat shock stresses. Results suggested that changing the gene dosage of ELM1/SAK1/TOS3 had different effects under high-glucose and heat shock stresses. ELM1 and SAK1 overexpressions could enhance the tolerance of S. cerevisiae to high-glucose and heat shock stresses, respectively. Nevertheless, the overexpression of TOS3 decreased the tolerance to high-glucose stress, and a native level of Tos3 was important for the normal adaptation to heat shock condition. The overexpression of ELM1 increased the accumulation of trehalose and ergosterol and altered the composition of fatty acids with altered gene expressions involved in the metabolism of three metabolites. Enhanced resistance to heat shock stress in SAK1 overexpression might be related to the enhanced accumulation of trehalose and ergosterol and upregulated transcription of genes related to the metabolism of trehalose and ergosterol. Furthermore, Elm1 might regulate the metabolism of trehalose, ergosterol, and fatty acids in a Snf1-independent form under high-glucose stress. A Snf1-independent pathway might be involved in the regulation of trehalose metabolism by Sak1 under heat shock condition. However, Sak1 and Snf1 may have an indirect relationship in the regulation of ergosterol synthesis. KEY POINTS: • Altering the gene dosage of ELM1/SAK1/TOS3 had different effects on stress responses • Elm1 regulated high-glucose response in a Snf1-independent manner • Sak1 and Snf1 had an indirect relationship in the regulation of heat shock response.

An overview of walnuts application as a plant-based

The plant-based refers to plant-based raw materials or products that are available as the source of protein and fat. Utilization and development of walnuts as a plant-based, resulting in a high-quality protein-rich walnut plant-based product: walnut protein powder and walnut peptides. Progress in research on the application of walnuts as a plant-based has been advanced, solving the problem of wasted resources and environmental pollution caused by the fact that walnut residue, a product of walnuts after oil extraction, is often thrown away as waste, or becomes animal feed or compost. This paper reviews and summarizes the research and reports on walnut plant-based at home and abroad, focusing on the application of walnut plant-based in the preparation process (enzymatic and fermentation methods) and the biological activity of the walnut protein and walnut peptide, to provide a theoretical basis for the further processing of walnuts as a walnut plant-based. It can make full use of walnut resources and play its nutritional and health care value, develop and build a series of walnut plant-based products, improve the competitiveness of walnut peptide products, turn them into treasure, and provide more powerful guidance for the development of food and medicine health industry in Yunnan.

Recycling and Conversion of Yeasts into Organic Nitrogen Sources for Wine Fermentation: Effects on Molecular and Sensory Attributes

Organic nitrogen plays a significant role in the fermentation performance and production of esters and higher alcohols. This study assessed the use of yeast protein hydrolysate (YPH) as a nitrogen source for grape must fermentation. In this study, we prepared an enzymatic protein hydrolysate using yeasts recovered from a previous fermentation of wine. Three treatments were performed. DAP supplementation was used as a control, while two YPH treatments were used. Low (LDH) and high degrees of hydrolysis (HDH), 3.5% and 10%, respectively, were chosen. Gas chromatography and principal component analysis indicated a significant positive influence of YPH-supplementations on the production of esters and higher alcohols. Significantly high concentrations of 3-methyl-1-penthanol, isoamyl alcohol, isobutanol, and 2-phenylethanol were observed. Significant odorant activity was obtained for 3-methyl-1-pentanol and ethyl-2-hexenoate. The use of YPH as nitrogen supplementation is justified as a recycling yeasts technique by the increase in volatile compounds.

Enhanced multi-stress tolerance and glucose utilization of Saccharomyces cerevisiae by overexpression of the SNF1 gene and varied beta isoform of Snf1 dominates in stresses

Background

The Saccharomyces cerevisiae Snf1 complex is a member of the AMP-activated protein kinase family and plays an important role in response to environmental stress. The α catalytic subunit Snf1 regulates the activity of the protein kinase, while the β regulatory subunits Sip1/Sip2/Gal83 specify substrate preferences and stress response capacities of Snf1. In this study, we aim to investigate the effects of SNF1 overexpression on the cell tolerance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses and to explore the valid Snf1 form in the light of β subunits in these stresses.

Results

The results suggest that overexpression of SNF1 is effective to improve cell resistance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses, which might be related to the changed accumulation of fatty acids and amino acids and altered expression levels of genes involved in glucose transport and glycolysis. However, different form of β regulatory subunits dominated in stresses with regard to cell tolerance and glucose utilization. The Sip1 isoform was more necessary to the growth and glucose consumption in ethanol stress. The glucose uptake largely depended on the Sip2 isoform in high sugar and ethanol stresses. The Gal83 isoform only contributed inferior effect on the growth in ethanol stress. Therefore, redundancy and synergistic effect of β subunits might occur in high glucose, ethanol, and heat stresses, but each subunit showed specificity under various stresses.

Conclusions

This study enriches the understanding of the function of Snf1 protein kinase and provides an insight to breed multi-stress tolerant yeast strains.

Bioactive Peptides from Walnut Residue Protein

Walnut residue is a kind of high-quality plant protein resource. The bioactive peptide prepared from walnut residue has excellent health care functions such as antioxidation and antihypertensive activity, but at present, walnut residue is often regarded as waste or low value feed, fertilizer and other materials. The uneconomical use of walnut residue has hindered the development of the walnut industry to some extent. Effective utilization of walnut residue protein to develop bioactive peptides and other products is of great significance to realize the comprehensive utilization of walnut residue, improve the added value of by-products, and change the current low utilization rate of walnut residue. In this paper, the preparation, purification and structure identification of walnut protein bioactive peptides are reviewed, and different functional walnut active peptides (WBPs) are introduced. The potential effects of these bioactivities on human health and their different uses in food, medicine and other industries are discussed. The purpose is to provide reference information for the effective utilization of walnut residue resources and the development of walnut industry.