Study Of Wheat Gluten Protein Hydrolysates As The Nitrogen Source Of Brew’s Yeast

In this study, the wheat gluten protein was used as a new source of supplementary nitrog en in beer preparation, in addition, the mechanisms of the effects of wheat gluten hydrolysates on the growth and fermentation of yeast were also investigated. Which would provide a theoretical basis for utilization of the wheat gluten protein hydrolysate in beer industry.Firstly, neutral protease was used to hydrolyzed the wheat gluten protein, the basis enzymatic hydrolysis conditions were determined by single factor experiments. The results showed that the basis enzymatic hydrolysis conditions were reaction temperature 50℃, p H 6.5, the substrate concentration 10% and neutral protease 2460 U/g(E/S = 1.0%). Degree of hydrolysate of the prepared hydrolysates were 3.2%, 5.5%, 6.5%, 7.4%, 8.7%, 8.9% and 9.1% respectively. The peptide molecular weight distribution analysis showed that the content of larger molecular weight peptides(>3 k Da) was decreased with the increase of hydrolysis degree. and the content of lower molecular weight peptides(<3 k Da) was increased with the increase of hydrolysis degree.Secondly, the effects of wheat gluten protein hydrolysates on the growth of yeast and its mechanism, were studied the wheat gluten hydrolysate were added into corn syrup. The results showed that wheat gluten hydrolysate can be as an effective nitrogen material for yeast growth and proliferation; and the yeast reached the best proliferation when DH of wheat gluten hydrolysates was 8.7%; The molecular weight of peptides which could be effectively used by beer yeast was below 3 k Da; and the free amino acid composition of lower molecular weight peptides was beneficial for the improvement of yeast proliferation.Thirdly, the effects of different DH wheat gluten protein hydrolysates on yeast fermentation performance in high auxiliary materials beer were studied, different DH wheat gluten protein hydrolysates were added to the mixture of 12 ° P wort and 12 ° P corn syrup(1:1). The results showed that wheat gluten protein hydrolysates could promote the fermentation of beer yeast by improving sugar consumption and alcohol production rate, and the greater the degree of hydrolysis, the more obvious role was reached, compared with WD, the final alcohol and fermentation degree of WGH7 were increased 9.7% and 8.7% respectively. The impact of hydrolysates on yeast fermentation performance was associated with its high content of free amino nitrogen(FAN), and the utilization amount of FAN in the five groups fermented liquid were 97.8 mg/L, 123.8 mg/L, 149.3mg/L and 155.2mg/L. Respectively, hydrolysates could increase the contents of higher alcohols and ethyl acetate of beer which can improve beer flavor; on the other hand, they could promote the formation of organic acids, which was not conducive to beer flavor. Hydrolysates could improve the beer foam properties, and WGH1(DH3.2%) has the best foam performance, Lundin fraction displaying that protein proportion of group B in its fermentation was 23.39%. The lower DH of hydrolysates, the greater the turbidity of beer was reached, and the smaller the viscosity of beer, but the impacts of DH on the total acid and the color difference were not significant(P> 0.05).Fourthly, the effects of different molecular weight wheat gluten protein hydrolysates on yeast fermentation performance in high gravity brewing were studied, Different molecular weight wheat gluten protein hydrolysates were added to the 18 ° P wort. The results showed that low molecular weight <3 k Da hydrolysates could significantly improve the performance of yeast fermentation(P<0.05), and the degree of fermentation increased 8.1% when compared with HWD. The utilization amount of FAN in the five groups fermented liquid were 111.4 mg/L, 128.3 mg/L, 147.1 mg/L, 179.3 mg/L and 218.0 mg/L. Respectively different molecular weight hydrolysates affected the flavor of beer complexly. The contents of alcohol and ethyl acetate were increased and the content of organic acids in beer was also increased. High molecular weight hydrolysates >10 k Da can significantly increased the turbidity of beer(P<0.05), and had an impact on the viscosity of beer.Finally, the mechanism of wheat gluten protein hydrolyzate promoting the brewer’s yeast fermentation was studied. The results showed that this promoting effect was related with the improve ment of yeast osmotic tolerance and alcohol tolerance. 0.3% peptides with low molecular weight <3 k Da can upgrade yeast’s osmotic tolerance to 45% and alcohol tolerance to 20%, Which may be related to the peptides could protect the yeast cell morphology and membrane permeability.