Purification And Identification Of Peptides With Growth-and Fermentation-promoting Activity Of Brewer's Yeast From Wheat Gluten Protein

Very high gravity brewing has become a common practice in modern breweries due to its high productivity,substantial economic savings and potential improvements on beer stability.However,the negative effects of high gravity brewing would result in the modification of physiological activity and the decrease in fermentation performance for brewer's yeast.Thus,it is of importance for brewers to improve physiological activity and fermentation performance of brewer's yeast by nutrient supplements during high gravity fermentation.It is reported that the protein hydrolysates can effectively promote growth and fermentation performance of brewer's yeast.To the best of our knowledge,there were no detailed investigations on the purification and identification of peptides with significant growth-and fermentation-promoting activity from wheat gluten protein.Therefore,this dissertation aimed to purify and identify the active peptides with significant growth-and fermentation-promoting activity from wheat gluten protein.The main research contents and results are as follows:(1)Six kinds of media with different nitrogen compositions were used to examine their effects on the growth and fermentation performances of brewer's yeast under very high gravity fermentation(20 °P).Results showed that both the nitrogen composition and level had significant impacts on yeast.Media supplemented with wheat gluten hydrolysates(WGH)induced the increase of the original FAN level,growth and fermentation performances of brewer's yeast,and the diversity of nitrogen sourch,which indicated that WGH was an effective nitrogen source for yeast growth and fermentation.And the appropriate adding amount of YNB was 0.43(w/v).(2)WGH and their fractions were used to examine their effects on the growth and fermentation performances of brewer's yeast under very high gravity fermentation(20 °P).Results showed that WGH and their fractions exhibited significant differences in growth and fermentation performances of brewer's yeast.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 very high gravity fermentation.And the fractions with Mw less than 3 kDa and the supernatant of WGH treated with ethanol precipitation(WGH-80%S)showed better fermentation performance for brewer's yeast.(3)WGH-80%S was fractionated through D-101 resin and Sephadex G-15,respectively.WGH-80%S and their fractions were used to examine their effects on the growth and fermentation performances of brewer's yeast under very high gravity fermentation.The result showed that the fractions D1 and G2 had better significant growth-and fermentation-promoting activity for brewer's yeast.Medium supplemented with D1 induced the increases of biomass by 5.98% and the apparent attention by 4.23%,while medium supplemented with G2 induced the increases of biomass by 12.50% and the apparent attention by 21.38%.(4)The structure of components of D1 and G2 were then identified by ultra performance liquid chromatography mass spectrometry(UPLC-ESI-MS/MS),and the composition of free amino acids and total amino acids were determined.Result showed that the D1 and G2 components are mainly in the form of peptides,accounting for 73.03% and 63.27%,respectively.According to the spectrum analysis results,the small molecule peptides which mainly promote the growth and fermentation of brewer's yeast might be L(I)D and AL(I)D in D1,while AQP?ENG?SSR?L(I)R?L(I)M?L(I)PPY and PPY might be contributed to growthand fermentation-promoting activity in G2.