Study On Metabolic Mechanism Of Cider Characteristic Aroma By Saccharomyces Cerevisiae

China is the world's largest apple production base,but the single deep processing products has seriously restricted the deep development of apple planting industry and processing industry in China.Cider is the second largest fruit wine in the world,and apple brewing can drive the diversified development of apple industry,but the lack of aroma seriously restricts the development of cider.Therefore,it is necessary to carry out the research on the metabolic mechanism of the key aroma via Saccharomyces cerevisiae.Changes in volatile component and enzymes are monitored to determine key aroma metabolic mechanism,then the metabolic mechanism could make the better control of aroma in apple cider formation.In this study,S.cerevisiae CICC 31084 was used as the fermentation strain;the simulation system with/without amino acids and apple juice were prepared as fermentation systems.The growth of yeast,changes in the content of glucose,amino acid,pyruvic acid,key aroma(isoamyl alcohol,phenylethyl alcohol,isoamyl acetate,phenylethyl acetate,ethyl caprylat,octanoic acid,etc.)and changes in the activity of key enzymes were determined respectively during fermentation.Then correlation analysis was performed on key enzyme activities and aroma compounds,and path analysis was ferformed on substances which were producted during fermentation.The main results are as follows:1.During the fermentation process,amino acids and glucose decreased gradually,and the content stable in the late fermentation stage;pyruvic acid gradually accumulated and reached the maximum value,then began to be consumed and the content gradually decreased.In simulated juice system with addition of different amino acids and apple juice,the addition of amino acids significantly accelerated the consumption rate of glucose by S.cerevisiae cells,increased the production of pyruvic acid,and made the maximum time of pyruvic acid appear earlier.2.In the simulated juice system,which only included glucose(without amino acids),aroma compounds accumulated during the fermentation process,and the maximum contents were less than 0.5 mg/L.After adding amino acids to the simulated juice system,the content of aroma compounds were increased in simulated juice system with addition of different amino acids and apple juice,especially the content of alcohols and esters corresponding to amino acids were increased obviously: the addition of leucine improved the productions of isoamyl alcohol and isoamyl acetate;the addition of phenylalanine improved the amount of phenylethyl alcohol and phenylethyl acetate produced.In the addition of phenylalanine simulated juice system,the content of the key esters in descending order was phenylethyl acetate,ethyl caprylate,ethyl hexanoate and isoamyl acetate.In the addition of leucine simulated juice system,the content of key esters from high to low was isoamyl acetate,ethyl caprylate,ethyl hexanoate,phenylethyl acetate.While in apple juice system with addition of phenylalanine and leucine,the content of phenylethyl acetate and isoamyl acetate was significantly higher than that of the other two esters.And the content of key esters from high to low was phenylethyl acetate,isoamyl acetate,ethyl caprylate and ethyl hexanoate.3.In the simulated juice system,which only included glucose(without amino acids),it could be observed that the key enzymes(hexokinase,6-phosphofructokinase and pyruvate kinase)activities of the glycolysis process significantly increased with glucose by rapid consumption during fermentation.And there were significant positive correlations between hexokinase(HK),6-phosphofructokinase(PFK-1)and pyruvate kinase(PK)(p < 0.05);but there were no obvious correlations between the activities of the key glycolytic enzymes,pyruvate decarboxylase(PDC)and alcohol dehydrogenase(ADH)(p > 0.05).After the amino acid was added to the system,the activities of transaminase and PK were significantly increased,and the content of acetyl-CoA was also significantly increased.In the simulated system of leucine addition,PK was significantly associated with acetyl-CoA;In the simulated system of phenylalanine addition,PK was significantly associated with phenylalanine aminotransferase(PAL).4.In the simulated juice system without amino acid,PK activity was significantly positively correlated to the formation of pyruvic acid,esters and alcohols,but no significantly relation to acids during fermentation process;ADH activity was significantly negatively correlated with the formation of ethyl caprylate.In the simulated juice system with addition of leucine,leucine aminotransferase(LTR)was significantly associated with pyruvic acid,isoamyl acetate,and ethyl hexanoate;PK had a significant positive correlation with glucose,leucine,octanoic acid,alcohols,and esters;acetyl-CoA had a significant correlation with leucine,octanoic acid,isoamyl alcohol,phenylethyl alcohol,and ethyl caprate.In the simulated juice system with addition of phenylalanine,PAL had a significant positive correlation with pyruvic acid,hexanoic acid,phenylethyl alcohol and most esters;PK had a significant positive correlation with glucose,phenylalanine,acid,alcohols and esters;acetyl-CoA had a significant positive correlation with pyruvate only.5.Through the path analysis of simulated juice system and apple juice,it was found that the path coefficient of glucose and pyruvic acid was higer than the path coefficient of leucine and pyruvic acid,phenylalanine and pyruvic acid.It showed that glucose had great influences on production of pyruvic acid.Due to the existence of reversible reaction,the path coefficients of amino acids and its corresponding alcohols were not high.The path coefficients of alcohols and its corresponding esters is large,so there were big influences on alcohols and its corresponding esters.