Wheat gluten hydrolysates and their fractions improve multiple stress tolerance and ethanol fermentation performances of yeast during very high-gravity fermentation

Transcriptome profiling unravels improved ethanol production and acetic acid tolerance in yeast by preculture of wheat gluten hydrolysates

The effects of wheat gluten hydrolysates (WGH) preculture on yeast acetic acid tolerance and fermentation performances were investigated. Results showed that WGH preculture significantly increased yeast growth and viability under acetic acid stress. Particularly, the WGH fraction precipitated with 90 % (v/v) gradient ethanol (WGH-C) preculture significantly improved yeast cell membrane integrity and H+-ATPase activity, thereby decreasing the intracellular accumulation of ROS and acetic acid. Meanwhile, WGH-C preculture promoted the ethanol production efficiency, shortening the fermentation lag time by 12 h and increasing the ethanol yield by 37.46 %. These improvements were attributed to that WGH-C preculture regulated intracellular amino acid composition and transport protein related gene expression of yeast. Transcriptome profiling demonstrated that the cell wall and plasma membrane structures were remodeled, reducing the oxidative stress induced by acetic acid. Furthermore, regulation of energy metabolism and transporter activity are prime mechanisms in improving acetic acid tolerance and fermentation efficiency of yeast.

Revealing the Cryoprotective Mechanism of Wheat Bran Antifreeze Arabinoxylan on Yeast Viability by Metabolite Profiling and Comparative Transcriptome Analysis

To elucidate the cryoprotective mechanism of wheat bran antifreeze arabinoxylan (AX) on yeast cells, this study investigated its effects on the physiological, metabolic, and genetic stability of yeast subjected to cyclic freeze-thaw cycles. Antifreeze AX inhibited ice crystal growth and interacted with cells to form an external barrier, which preserved cell membrane integrity, inhibited reactive oxygen species accumulation, and reduced oxidative damage. Metabolome analysis revealed that AX regulated key metabolic pathways, enhancing cell activity and maintaining homeostasis. Transcriptome analysis demonstrated that AX promoted DNA repair and maintained genetic stability. By synergistically inhibiting ice crystal growth, forming physical barriers and regulating metabolic and genetic pathways, antifreeze AX improved yeast cell viability and activity during freeze-thaw cycles, thereby maintaining cellular homeostasis under freezing stress. This study could provide a theoretical basis for the practical application of antifreeze AX as an efficient cryoprotectant in yeast cell cryopreservation.

Soy protein hydrolysates induce menaquinone-7 biosynthesis by enhancing the biofilm formation of Bacillus subtilis natto

Menaquinone-7 (MK-7) is a form of vitamin K2 with health-beneficial effects. A novel fermentation strategy based on combining soy protein hydrolysates (SPHs) with biofilm-based fermentation was investigated to enhance menaquinone-7 (MK-7) biosynthesis by Bacillus subtilis natto. Results showed the SPHs increased MK-7 yield by 199.4% in two-stage aeration fermentation as compared to the SP-based medium in submerged fermentation, which was related to the formation of robust biofilm with wrinkles and the enhancement of cell viability. Moreover, there was a significant correlation between key genes related to MK-7 and biofilm synthesis, and the quorum sensing (QS) related genes, Spo0A and SinR, were downregulated by 0.64-fold and 0.39-fold respectively, which promoted biofilm matrix synthesis. Meanwhile, SPHs also enhanced the MK-7 precursor, isoprene side chain, supply, and MK-7 assembly efficiency. Improved fermentation performances of bacterial cells during fermentation were attributed to abundant oligopeptides (Mw < 1 kDa) and moderate amino acids, particularly Arg, Asp, and Phe in SPHs. All these results revealed that SPHs were a potential and superior nitrogen source for MK-7 production by Bacillus subtilis natto.

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.

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.

Current developments and challenges of green technologies for the valorization of liquid, solid, and gaseous wastes from sugarcane ethanol production

The sugarcane industry is one of the largest in the world and processes huge volumes of biomass, especially for ethanol and sugar production. These processes also generate several environmentally harmful solid, liquid, and gaseous wastes. Part of these wastes is reused, but with low-added value technologies, while a large unused fraction continues to impact the environment. In this review, the classic waste reuse routes are outlined, and promising green and circular technologies that can positively impact this sector are discussed. To remain competitive and reduce its environmental impact, the sugarcane industry must embrace technologies for bagasse fractionation and pyrolysis, microalgae cultivation for both CO₂ recovery and vinasse treatment, CO₂ chemical fixation, energy generation through the anaerobic digestion of vinasse, and genetically improved fermentation yeast strains. Considering the technological maturity, the anaerobic digestion of vinasse emerges as an important solution in the short term. However, the greatest environmental opportunity is to use the pure CO₂ from fermentation. The other opportunities still require continued research to reach technological maturity. Intensifying the processes, the exploration of driving-change technologies, and the integration of wastes through biorefinery processes can lead to a more sustainable sugarcane processing industry.

Wheat gluten hydrolysates promotes fermentation performance of brewer's yeast in very high gravity worts

The effects of wheat gluten hydrolysates (WGH) and their ethanol elution fractions obtained on XAD-16 resin on physiological activity and fermentation performance of brewer's yeast during very-high-gravity (VHG) worts fermentation were investigated. The results showed that the addition of WGH and their elution fractions in VHG worts significantly enhanced yeast biomass and viability, and further increased the fermentability, ethanol yield and productivity of yeast. Supplementation with 40% ethanol fraction exhibited the highest biomass (6.9 g/L dry cell), cell viability, fermentability (82.05%), ethanol titer (12.19%, v/v) and ethanol productivity during VHG worts fermentation. In addition, 40% ethanol fraction supplementation also caused the most consumption of amino acid and the highest accumulation of intracellular glycerol and trehalose, 15.39% of increase in cell-membrane integrity, 39.61% of enhancement in mitochondrial membrane potential (MMP), and 18.94% of reduction in intracellular reactive oxygen species (ROS) level in yeast under VHG conditions. Therefore, WGH supplementation was an efficient method to improve fermentation performance of brewer's yeast during VHG worts.

Improvement of ethanol production in fed-batch fermentation using a mixture of sugarcane juice and molasse under very high-gravity conditions

Ethanol fermentation in very high gravity (VHG) saves energy consumption for ethanol distillation. As the technology offers high ethanol yield and low waste generation and it can be operated at low cost, it could be more efficient at an industrial scale than other ethanol production methods. This work studied ethanol production using a fed-batch bioreactor with a working volume of 1.5 L. The main objective of this research was evaluate the effects of temperature, sugar concentration, and cellular concentration using a Central Composite Design (CCD). Experimental conditions were selected using the surface response technique obtained from the CCD, and the results were validated to test the reproducibility. The following operating conditions were selected: temperature of 27.0 °C, sugar concentration 300.0 g/L, and cell concentration 15.0% (v/v). Under these conditions, after 30 h of fermentation the ethanol concentration, productivity and yield were 135.0 g/L, 4.42 g/(L·h) and 90.0%, respectively. All sugar was completely consumed.

Reduction of Fermentation-Associated Stresses by Straw-Based Soluble Saccharides for Enhancing Ethanol Production

In this study, the effect of soluble polysaccharides (SPs) derived from agricultural waste, rice straw, on fermentation-associated stresses (temperature and concentrations of glucose and ethanol) was investigated to achieve high-performance ethanol production. The increase in temperature and concentrations of glucose and ethanol significantly inhibited Saccharomyces cerevisiae growth and lowered ethanol fermentation efficiency. Flow cytometric assays indicated that SPs could alleviate membrane permeability damage caused by fermentation-associated stresses. Atomic force microscopy and transmission electron microscopy revealed that fermentation-associated stresses induced cell surface shrinkage, causing a decrease in the cell size, whereas SPs stimulated the formation of extracellular matrices (EMs), which made the cell surface smooth and the cell morphology regular. Cells with EMs induced by SPs could efficiently produce ethanol under severe stresses. As a result, the titer of ethanol in the fermentation with SPs was 1.40-fold (from 26.40 to 36.98 g/L) higher than that in the fermentation without SPs, suggesting the stress-alleviating effect of SPs on ethanol production.