Effects Of Assimilable Nitrogen On The Fermentation Characteristics Of Saccharomyces Cerevisiae

Nitrogen is an important nutrient in alcoholic fermentation because it affects both fermentation kinetics and the formation of yeast metabolites.Synthetic grape must have proven ideal for this present study of effects of nitrogen levels on the growth and fermentation characteristics of Saccharomyces cerevisiae.Based on this,effect of diammonium phosphate(DAP)and selected amino acids(phenylalanine,isoleucine,leucine,threonine,tyrosine,valine)addition to synthetic grape must on the growth and fermentation characteristics of Saccharomyces cerevisiae were investigated.The influences of phenylalanine supplementations during Icewine fermentation on its volatile acidity production were also studied.The new findings of this study would be beneficial to winemaking for the addition of nitrogen source.The main results are as followed:(1)Moderate nitrogen concentration(200 mg N/L)significantly promoted the cell growth and was favored by wine fermentation.Five strains of Saccharomyces cerevisiae(VL1,LFN524,LFA711,LFP529 and LFE1219)were used to discuss the effects of growth and fermentative behavior under different nitrogen concentration(100,200 and 400 mg N/L).Results showed that moderate nitrogen concentration(200 mg N/L)could increase cell growth rate,biomass,and consumption rates of reducing sugar,in particular for strains of LFA711,LFE1219 and VL1 when compared with high nitrogen concentration(400 mg N/L).Moreover,for strains LFN524 and LFP529,higher specific growth rate and biomass were achieved under 400 mg N/L nitrogen concentration.In addition,decreased specific growth rate and biomass were observed under low nitrogen concentration(100 mg N/L),also along with obvious sluggish fermentation.Different strains in this study also showed their demand for assimilable nitrogen,and ordered as LFP529>LFN524>LFA711> LFE1219>VL1> LFP529.(2)Appropriate supplementation of diammonium phosphate to synthetic grape must significantly promoted the cell growth and shorten the fermentation period.Different levels of diammonium phosphate addition prior to alcoholic fermentation at concentration of 50,100,200 mg N/L,was to evaluate their influence on the growth and fermentation characteristics of wine yeasts(VL1,LFA711 and LFE1219).Results showed that diammonium phosphate supplementations(50 mg N/L)significantly improved cell growth rate,biomass,and consumption rates of reducing sugar,as well as yeast assimilable nitrogen.Compared with the control with 50 mg N/L diammonium phosphate addition,the fermentation period of three strains could be shortened about 48 hours.Consumption rates of assimilable nitrogen of VL1,LFA711 and LFE1219 was 85%,82% and 80%,which was significantly higher than other groups(100,200 mg N/L).(3)Exogenous addition of phenylalanine and leucine before alcoholic fermentation were beneficial to fermentation proceed.Under the nitrogen level of 50 mg N/L,six single amino acids(phenylalanine,isoleucine,leucine,threonine,tyrosine,valine)was supplemented to evaluate their influence on the growth and fermentation characteristics of wine yeasts(LFA711 and LFE1219).Compared with the control,supplementation of phenylalanine in LFA711,LFE1219 significantly reduced the volatile acidity content,reaching at 15.1% and 27.4%,respectively.The fermentation period could be significantly shortened by leucine addition,reducing about 24 h and 72 for LFA711 and LFE1219 when compared with the control.Also threonine and isoleucine supplementation of synthetic grape must,colud extend the fermentation period of LFA711,LFE1219 about 72 h and 48 h.The addition of tyrosine to synthetic grape must,led to a higher consumption rates of assimilable nitrogen.(4)Moderate addition of phenylalanine could significantly reduce the content of volatile acidity in Icewine.Phenylalanine with two nitrogen levels(100,300 mg N/L)was supplemented to evaluate their influence on the fermentation characteristics of wine yeasts(LFA711 and LFE1219).Compared with the control(100 mg N/L diammonium phosphate),supplementation of phenylalanine(75 mg N/L phenylalanine,25 mg N/L diammonium phosphate)could significantly reduce the volatile acidity content in LFA711(18.1%)and LFE1219(25.6%).And malic acid,tartaric acid,citric acid and succinic acid of LFA711 reduced 23.5%,44.5%,56.7% and 50.2%,when adding 75 mg N/L phenylalanine.