Purification And Identification Of Active Peptides That Promote Yeast Growth And Metabolism

In the beer industry,the high gravity and high adjunct brewing are the main brewing technologies.Their application can reduce the cost and improve the economic profit,however,during the process of brewing production,the increase of wort concentration and the addition of adjunct cause some adverse effects,especially the high osmotic pressure and alcohol toxicity in the fermentation environment hindering the growth and metabolism of yeast.The nitrogen supplement can effectively improve the unfavorable situation.It is reported that the hydrolysate is one of the effective nitrogen sources,and small peptides from protein hydrolysates can facilitate yeast growth,but the effective active peptides have not yet been isolated and identified.Therefore,this paper aimed to study the influence of protein hydrolysates on the growth and metabolism of yeast,and further to separate and purify the bioactive peptides.At first,the optimal time of wheat gluten and soy isolated protein hydrolyzed by trypsin and compound proteinase,respectively,was analyzed,as well as the effect of adding of protein hydrolysates on the growth and metabolism of yeast.The results showed that the optimal enzymatic hydrolysis time of trypsin and complex protease were 24 h and 12 h,while the appropriate adding amount of wheat gluten protein hydrolysate and soy isolated protein hydrolysate were 1.0%and 0.1%,respectively.The investigation on the effect of hydrolysate on yeast found that the hydrolysate of soy isolated protein showed the better promotion effect.After fermentation,the yeast added with hydrolysate of soy isolated protein had the maximal net growth,followed by the yeast treated with the hydrolysate of wheat gluten protein and control group the least.The speed of sugar consumption was in order as following:soybean group>wheat group>control group,as the same trend in ethanol production and FAN utilization.Therefore,soy protein hydrolysates would be selected for subsequent experiments.The hydrolysate of soy isolated protein was separated by using the ultrafiltration membrane into the SP-II(molecular weight>3 kDa)and SP-I(molecular weight<3 kDa)two group.It was demonstrated that the biological activity of the component in SP-I was higher than SP-II.Then,SP-I was further purified by using D-101 resin,and gradient elution was applied in order to get each components.By comparison,it turned out that the polypeptide component eluted by the deionized water had the best biological activity.The molecular weight and structure of components in different eluted gradient was then identified by ultra performance liquid chromatography mass spectrometry(UPLC-ESI-MS/MS),and the distribution of free amino acids was determined.According to the spectrum analysis results,the small molecule peptides which mainly promote the growth and fermentation of brewer 's yeast might be LW?LLW?LLLW?LLLLW and LLLLLW(Leu-Leu-Leu-Leu-Leu-Trp).