Effect Of Soy Active Peptides On The Proliferation And Metabolism Of Yeast And Beer Brewing

This dissertation prepared soy protein hydrolysates with different molecularcharacteristics using controlled enzymatic hydrolysis technology, and in-depth researched theeffect of soy peptides on the growth and fermentation performance of yeast, order to probeinto the effectiveness of soy peptides in improving the fermentation performance of yeast,making up the defects of high-accessories brewing and lifting the restrictions of high gravitybrewing. Results can be concluded as follows:(1)4commercial proteases (Alcalase、Protamex、Flavorzyme、Papain) were used tohydrolysis soy protein isolated, and the hydrolysates with different DH are applied in yeastgrowth experiment. According to the proliferation and activity of yeast, the optimalhydrolysis time was determined: for Alcalase is6h, Protamex9h, Flavorzyme6h, Papain9h.Hydrolysates from different enzymes and peptides with different molecular weight werecompared. Results indicated that hydrolysate prepared with Protamex for9h showed thestrongest growth promoting activity, and the active peptides mainly concentrated under3kDa.(2) Effect of selected soy peptides on the fermentation performance of yeast was studiedby adding it to the culture medium, and the interaction of soy peptides and yeast cells wasinvestigated by fluorescence labeling. Results showed that soy peptides can improved theethonal tolerability, osmotic tolerability, real attenuation and ethanol production ability byattracting to cell membranes, so that to improve the environment of cell metabolism.(3) The effects of different nitrogen source (peptone, yeast extract and soy peptides) onhigh-accessories beer production were compared. Results indicated that soy peptides wasmore efficient than peptone and yeast extract, which could make the apparent fermentationdegree and ethanol production increased by10.4%and7.2%respectively, and improve thefoam stability of finished product beer without affecting its abiological stability.(4) The effects of soy peptides on the fermentation characters of yeast and beer flavorunder high gravity brewing were studied. Results showed that the addition of soy peptidesimproved the activities of glycolytic key enzymes (hexokinase, phosphfructokinase andpyruvate) at each stage of fermentation, so that the utilization efficiency of glucose, maltose and maltotriose by yeast was promoted, and the apparent fermentation degree and ethanolproduction were increased by7.84%and10%respectively, fermentation period was shortenedby4d. Meanwhile, the addition of soy peptides made the alcohol increased and ethyl acetatedecreased，bringing about more harmonious taste.