Analysis Of The Mechanism Of Isoamyl Alcohol Synthesis By Yeast Isolated From Fermented Grains

Higher alcohol is an important flavor substance in strong aroma Baijiu,and its content will affect the quality and comfort feeling after drinking.Isoamyl alcohol is the main higher alcohol in strong aroma Baijiu.An appropriate amount of isoamyl alcohol can make strong aroma Baijiu mellow,and increase the flavor of strong aroma Baijiu by forming isoamyl acetate with acetic acid;excessive isoamyl alcohol will make the Chinese Baijiu spicy and bitter.Therefore,analyzing the metabolic pathways of isoamyl alcohol synthesis by yeast isolated from fermented grains,and the factors affecting the synthesis and metabolism of isoamyl alcohol by yeast can be useful for analyzing the synthesis and accumulation mechanism of isoamyl alcohol during the strong aroma Baijiu fermentation,and it also can be useful for implementing the synthesis of isoamyl alcohol and provide a theoretical basis for precise control during the strong aroma Baijiu fermentation.This study focuses on the yeasts that contributed to the synthesis of isoamyl alcohol during the strong aroma Baijiu fermentation.The capability of isoamyl alcohol synthesis by yeasts isolated from fermented grains was about to be analyzed and compared,and metabolic pathways of isoamyl alcohol synthesis were revealed.On this basis,the factors affecting the synthesis and metabolism of isoamyl alcohol by yeast isolated from fermented grains were explored.The main findings are as follows:(1)Analysis of the capability and period of synthesis of isoamyl alcohol by different species yeasts.The capability from high to low of synthesizing isoamyl alcohol by the five yeast strains isolated from fermented grains was found to be Naumovozyma castellii JP3-1,Saccharomyces cerevisiae JP3,Pichia fermentans JP22,Pichia kudriavzevii JP1 and Naumovozyma dairenensis CBS421.Isoamyl alcohol was mainly synthesized during the logarithmic growth period,and it was also synthesized during stable growth period in N.castellii JP3-1,P.fermentans JP22 and N.dairenensis CBS421.(2)Analysis of the metabolic pathways of isoamyl alcohol by yeasts isolated from fermented grains.The genes related to isoamyl alcohol synthesis in the whole genome of Pichia fermentans were identified by Open reading frame protein sequence alignment and design primer of genes related to isoamyl alcohol synthesis in Pichia;on this basis,the corresponding precursors metabolisms proved that N.castellii JP3-1,S.cerevisiae JP3,P.fermentans JP22,P.kudriavzevii JP1 and N.dairenensis CBS421 can synthesize isoamyl alcohol through the amino acid anabolic pathway(Harris pathway)and amino acid catabolic pathway(Ehrlich pathway).The ability of t yeast synthesize isoamyl alcohol through two metabolic pathways were different.(3)Analysis of factors affecting the capability of synthesis isoamyl alcohol by yeast isolated from fermented grains.Regardless of the growth period,the Harris pathway was the main pathway for synthesizing isoamyl alcohol in S.cerevisiae JP3,N.castellii JP3-1 and N.dairenensis CBS421,while it was the Ehrlich pathway in case of P.kudriavzevii JP1.During the logarithmic growth phase,synthesis of isoamyl alcohol through Harris pathway and Ehrlich pathway was identical in P.fermentans JP22.But Harris pathway was the main pathway in stable growth phase for this strain.The oxygen content in the culture system had little effect on the synthesis of isoamyl alcohol by S.cerevisiae JP3,N.castellii JP3-1,P.fermentans JP22 and N.dairenensis CBS421,and Harris pathway was the main pathway for synthesizing isoamyl alcohol in S.cerevisiae JP3,N.castellii JP3-1,P.fermentans JP22 and N.dairenensis CBS421.The Harris pathway was the main pathway for synthesizing isoamyl alcohol in P.kudriavzevii JP1 under aerobic culture conditions,while the Ehrlich pathway was the main pathway for synthesizing isoamyl alcohol in case of static and anaerobic culture conditions.Some Lactobacillus and its metabolites can promote the ability of P.fermentans JP22 and N.castellii JP3-1 to synthesize isoamyl alcohol,Lactobacillus and its metabolites can attenuate the ability of N.dairenensis CBS421,P.kudriavzevii JP1 and S.cerevisiae JP3 to synthesize isoamyl alcohol.