Search

Abstract Very high-gravity (VHG) worts (24 °P) supplemented with wheat gluten hydrolysates (WGH) and their ultrafiltration fractions (Mw > 1 kDa and <1 kDa fractions) were used to evaluate their effects on physiological activity and ethanol fermentation of brewer's yeast. The results demonstrated that WGH and their ultrafiltration fractions supplementations could obviously improve the biomass and viability of yeast, and further enhance the sugar utilization and ethanol production under VHG fermentation. Supplementation with Mw < 1 kDa fraction exhibited the maximum biomass (6.90 g/L dry cell), sugar utilization (79.79%) and ethanol concentration (11.88%, v/v) during VHG fermentation. Meanwhile, the addition of Mw < 1 kDa fraction significantly decreased the plasma membrane permeability and intracellular reactive oxygen species (ROS) accumulation, and increased the mitochondrial membrane potential in cells during VHG fermentation. Moreover, Mw < 1 kDa fraction supplementation caused the highest accumulations of intracellular trehalose and glycerol, which were 12.10% and 31.22% higher than the control, respectively. These results illustrated that WGH (especially Mw < 1 kDa fraction) addition was an economic and efficient method to improve physiological activity and ethanol fermentation of brewer's yeast in VHG worts. Highlights • WGH and their ultrafiltration fractions were obtained as nitrogen sources of yeast. • WGH supplementation changed nitrogen metabolism of yeast during VHG fermentation. • Biomass and ethanol production were increased by WGH addition under VHG condition. • Physiological activity of yeast was improved by WGH addition under VHG condition. • Trehalose and glycerol in yeast accumulated by WGH addition under VHG condition. [ABSTRACT FROM AUTHOR]

Wheat gluten hydrolysates (WGH) were used to examine their adsorption–desorption kinetics and thermodynamics characteristics on six macroporous resins, and their effects on the stress tolerance in brewer’s yeast. Results showed that the pseudo second-order kinetics, Langmuir and Freundlich model could illuminate the adsorption mechanism, and the adsorption process was physical, spontaneous and exothermic. The 40% ethanol fraction separated by XAD-16 resin improved significantly the ethanol tolerance and the viability of brewer’s yeast, while the 0% ethanol fraction separated by XAD-16 resin increased obviously the osmotic stress tolerance and the viability of brewer’s yeast. Results from scanning electron microscopy showed that both these WGH fractions could increase budding rate and maintain normal morphology of yeast cells under various environmental stress. Thus, WGH separated by macroporous resin could be used in high gravity brewing to enhance the ethanol and osmotic stress tolerance in brewer’s yeast. [ABSTRACT FROM AUTHOR]

Abstract: Lys and Leu were generally considered as the key amino acids for brewer's yeast during beer brewing. In the present study, peptide Lys–Leu and a free amino acid (FAA) mixture of Lys and Leu (Lys + Leu) were supplemented in 24 °P wort to examine their effects on physiological activity and fermentation performance of brewer's yeast during very high‐gravity (VHG) wort fermentation. Results showed that although both peptide Lys–Leu and their FAA mixture supplementations could increase the growth and viability, intracellular trehalose and glycerol content, wort fermentability, and ethanol content for brewer's yeast during VHG wort fermentation, and peptide was better than their FAA mixture at promoting growth and fermentation for brewer's yeast when the same dose was kept. Moreover, peptide Lys–Leu supplementation significantly increased the assimilation of Asp, but decreased the assimilation of Gly, Ala, Val, (Cys)2, Ile, Leu, Tyr, Phe, Lys, Arg, and Pro. However, the FAA mixture supplementation only promoted the assimilation of Lys and Leu, while reduced the absorption of total amino acids to a greater extent. Thus, the peptide Lys–Leu was more effective than their FAA mixture on the improvement of physiological activity, fermentation performance, and nitrogen metabolism of brewer's yeast during VHG wort fermentation. [ABSTRACT FROM AUTHOR]

Summary: Wheat gluten hydrolysates (WGH) were fractionated through ultrafiltration membrane with molecular weight (Mw) cut‐off of 3 kDa and ethanol precipitation, respectively. WGH and their fractions were used to examine their effects on the growth and fermentation performances of brewer's yeast under high gravity fermentation. Results showed that WGH and their fractions exhibited significant differences in biomass accumulation, viability, ethanol yield, free amino nitrogen and sugar consumptions under high gravity fermentation. Compared to WGH, the fractions with Mw < 3 kDa and the supernatant of WGH treated with ethanol precipitation showed better fermentation performance for brewer's yeast. The relatively lower molecular weight and the higher levels of Leu, Lys, His and Arg in these two fractions might be responsible for their bioactivity for brewer's yeast. Thus, both ultrafiltration and ethanol precipitation could be used as efficient methods for enriching peptides with significant growth‐ and fermentation‐promoting activity for brewer's yeast under high gravity fermentation. [ABSTRACT FROM AUTHOR]