Formative Mechanism Of Saccharifying Enzymes Profile In Xiaoqu And Its Effects On Baijiu Fermentation

Jiuqu is the important saccharifying and fermenting agent,and determines the saccharification,ethanol and flavor compounds metabolism in the baijiu fermentation.However,the profile and formative mechanism of saccharifying enzymes in Jiuqu and their effects on the baijiu fermentation remains unclear.It is important to reveal the formative mechanism of saccharifying enzymes and their effects on baijiu fermentation,for improving the quality and function of Jiuqu by adjusting the preparations,improving the baijiu fermentation and estabolishing the scientific and reasonable evaluation system of Jiuqu.Xiaoqu is a typical Jiuqu generally used in baijiu fermentation,and has a strong saccharifying and fermenting agent with a short production cycle.Therefore,this study selected Guangdong Bingqu and its mechanical moldy bran(Sanqu)as the objects,and applied the theory and methods of systems biology to reveal the profile and formative mechanism of saccharifying enzymes in Xiaoqu and their effects on baijiu fermentation.The main results were as follows:(1)Multiple omics analysis(high-throughput amplicons sequencing and metaproteomics analysis)were applied to reveal the profile of saccharifying enzymes and microbiota in Xiaoqu.We identified 59 carbohydrate hydrolases in Xiaoqu,including 15 auxiliary activities(AAs),11 carbohydrate esterases(CEs),21 glycoside hydrolases(GHs)and 12 glycosyltransferases(GTs).The profile of saccharifying enzymes in Xiaoqu was mainly composed of 21 glycoside hydrolases.Especially,?-amylase and glucoamylase were the most important enzymes related to starch hydrolysis,and their relative abundance were 0.11% and 0.27%.These saccharifying enzymes were affiliated to Rhizopus,Aspergillus and Rhizomucor,and their relative abundance were 17.4%,8.3% and 0.05% in situ system.(2)We revealed the formative mechanism of saccharifying enzymes,from the enzyme-producing characteristics and its driven factors in the preparations of different Qus.Traditional Bingqu was squeezed to bricks,and its saccharifying activity(409.0±66.0 U/g DW)was significantly higher than that of mechanical Sanqu(in diffused shape)(224.5±105 U/g DW)(P < 0.05).We found eight glycoside hydrolases(GHs)were differently expressed between two Qus(P < 0.05 & fold change < 0.83 or > 1.20).Especially,the relative abundance of ?-amylase and glucoamylase in Bingqu were significantly higher than that of Sanqu.Moreover,glucoamylase in Bingqu(0.27%)was 1.35-fold higher than that in Sanqu(0.20%),whereas,?-amylase was not expressed in Sanqu.Furthermore,we found that the volumetric weight of Qu was positively asscociated with the expression of saccharifying enzymes(R~2 > 0.60),and volumetric weight of Bingqu(0.78±0.03 g/cm~3)was significantly higher that of Sanqu(0.62±0.04 g/cm~3)(P < 0.05).In addition,as volumetric weight of Qu increased 2.4-fold,moisture and acidity of Qu decreased 1.1-and 2.0-fold,whereas,the biomass of saccharifying microbes and the saccharifying activity increased 1.2-and 3.5-fold in a simulative system under laboratory.(3)We applied source tracking analysis to trace the saccharifying enzymes in baijiu fermentation,and revealed the contributions of Xiaoqu on saccharifying enzymes.Furthermore,we assessed the effects of saccharifying enzymes from Xiaoqu on alcoholic fermentation,and indicated an efficient mode of saccharifying enzymes in baijiu fermentation.Forty-six carbohydrate hydrolases were identified in the baijiu fermentation,and its profile of saccharifying enzymes was mainly composed of 25 glycoside hydrolases(GHs)in this baijiu fermentation.Among them,16 glycoside hydrolases were provided by Xiaoqu,and covered 64% of the total saccharifying enzymes in this baijiu fermentation.Furthermore,?-amylase and glucoamylase from Xiaoqu were positively associated with alcoholic fermentation in the baijiu fermentation(R~2 > 0.60).Moreover,compared to the fermentation driven by the single glucoamylase,ethanol yield increased 1.2-fold in the fermentation driven by the enzyme mixture(?-amylase and glucoamylase in a ratio of 1:6,wt/wt).(4)We revealed the effects of saccharifying enzymes from Xiaoqu on the formation of fermentable sugars and microbial metabolism,from the sugars profile in baijiu fermentation.The sugars profile was composed of glucose,D-galactose,arabinose,maltose and cellobiose in the baijiu fermentation.The formation of sugars profile was associated with the saccharifying enzymes from Xiaoqu(including ?-amylase,glucoamylase and so on).Furthermore,the utilization of glucose and maltose was asscociated with microbial succession in this baijiu fermentation(R~2 > 0.60).Moreover,compared to the fermentation selected the single glucose as substrate,the interations and metabolism of the community members were enhanced in the fermentaion selected the sugars mixture(glucose and maltose in a ratio of 9:1,wt/wt)as substrate.As a result,the biomas of Saccharomyces cerevisiae and Lactobacillus fermentum synergetically increased 1.2-fold,whereas,ethanol yield increased 1.8-fold.In total,this study revealed the profile and formative mechanism of saccharifying enzymes in Xiaoqu and their effects on baijiu fermentation.It provided a theoretical guidance to improve the quality and function of Xiaoqu by adjusting the preparation of Xiaoqu or combining matuered Qus to attain the optimized profile of saccharifying enzymes.Meanwhile,it also provided the theoretical foundation to develop the quality evaluation of Jiuqu based on its omic profiles.