| As one of the main starters for the fermentation of Huangjiu,raw wheat Qu(koji)is an important raw material for the two-sided fermentation process of Huangjiu.Raw wheat Qu(block Qu)is produced by solid-state fermentation with wheat as raw material.Its special block structure and T-shaped arrangement make the changes of physical and chemical factors(temperature,moisture,oxygen content,etc.)in the fermentation process affect the succession of microbial community.There are problems such as poor working environment,low efficiency,and seasonal restrictions in the traditional raw wheat Qu production process,so it's imperative to the modernization of raw wheat Qu production.At present,there are few studies on the succession of the microbial community structure of raw wheat Qu and its correlation between the dynamic changes of environmental factors,which severely restricts the development of modern production of raw wheat Qu.Analyzing the driving forces of the community succession of raw wheat Qu is of great significance of promoting the modern production of Huangjiu raw wheat Qu and the improvement to the quality of Huangjiu.The main work and results are as follows:(1)Analysis on succession law of community structure of manual raw wheat Qu.A total of 1,435 bacterial genera and 257 fungal genera were detected in manual raw wheat Qu,including Bacillus,Pantoea,Saccharopolyspora,Staphylococcus and Weissella,which is the main bacterial genera of manual Qu(sum of relative abundance >88.2%).The Saccharopolyspora in center is significantly more than surface;the fungi are mainly composed of Alternaria,Aspergillus,Cryptococcus,Emericella,Epicoccum(sum of relative abundance >92.6%),the relative abundance of Aspergillus on surface is higher than center while Thermomyces acts the opposite.According to the cluster analysis of microbial communities,the manual Qu fermentation process can be divided into three stages: 0 d-6 d,6 d-19 d,19 d-60 d.(2)Analysis on succession law of community structure of mechanical raw wheat Qu.A total of 367 fungal genera and 1671 bacterial genera were detected in the mechanical raw wheat Qu.The main fungi are Aspergillus,Alternaria,Epicoccus and other 6 genera(sum of relative abundance > 83.0%),while Rhizopus is more inside;The main bacteria are Bacillus,Pantoea,Saccharopolyspora,Staphylococcus and other 12 genera(sum of relative abundance >84.1%).The content of Saccharopolyspora inside is significantly higher than outside.According to the cluster analysis of the community structure,The fermentation process of mechanical Qu can be divided into three stages: 0 d-10 d,10 d-19 d,and 19 d-60 d.(3)Analysis of driving forces of raw wheat Qu.The analysis of the correlation between the succession of community structure and the dynamic changes of environmental factors showed that the initial stage of manual Qu fermentation was significantly related to temperature and water content,the middle stage was related to oxygen significantly,and there was no significant correlation between the later stage and environmental factors;the mechanical Qu was affected mostly by water content in the initial stage of fermentation.It has a greater impact with oxygen,and is basically stable in the mid-term.In the later period,the fungal community is affected by the combined effect of temperature and water content.The bacterial community is significantly related to oxygen.Redundant analysis showed that during the whole fermentation process of manual and mechanical wheat Qu,the glucoamylase activity is positively correlated with Erwina,Pantoea,Fusarium,Alternaria,Kocuria,Staphylococcus,Bacillus and Candida,while the liquefaction enzyme activity is related to Pseudomonas,Mortierella,Pichia,Rhizomucor and Thermomyces.(4)Verification of driving forces of raw wheat Qu.Enzyme activity was used as an indicator to verify the temperature of fermentation stage I,the initial amount of water added,and the thickness of the lumps.The results showed that the increase in temperature contributed to the increase in the relative abundance of Saccharopolyspora,Kosakonia and Rhizomucor.It has the highest glucoamylase activity at 50?,and the liquefaction enzyme activity decreases with the increase of temperature;the initial water addition mainly affects the community structure of Aspergillus,Saccharopolyspora,and Pantoea,but it has the highest glucoamylase activity and higher liquefaction enzyme activity at 19% water addition.When the thickness is above 7.5 cm,it is helpful for the growth of Aspergillus,and when the thickness is below 7.0cm,there are more bacteria genus,and the enzyme activity is positively related to the thickness.(5)Optimization of key technology of raw wheat Qu and liquor making the evaluation of optimized Qu.The measurement and analysis of the microbial community structure and enzyme activity of raw wheat Qu fermented under different temperatures,water additions,and thicknesses show that the influence on the community structure is thickness > temperature >water addition.Enzyme activity is significantly affected by temperature and thickness.Based on the single-factor verification results,the response surface optimization experiment was carried out.The optimized Qu was made with the optimal conditions of 51.5?,19% initial water addition,and thickness of 7.75 cm,and the wine-making performance of the optimized Qu was verified.The results show that the optimized Qu has the advantages of faster fermentation speed,lower residual sugar,and lower acidity.The comparison results of typical flavor substances show that the total amount of organic acids in the Huangjiu made by optimized Qu is lower,and the main aroma substances are not significantly different from the control groups.However,the content of diethyl succinate,phenol and 4-vinylguaiacol is high,while the content of hexanol,propanol and ethyl caproate is lower significantly.This study took the raw wheat Qu as the research object,and used high-throughput sequencing methods to study the community succession of the manual and mechanical raw wheat Qu during fermentation,and clarified the main environmental factors driving the succession of the microbial community of raw wheat Qu.The key environmental factors of the making process were analyzed and the key process was optimized.Finally,the application evaluation of optimized Qu,manual Qu,and mechanical Qu was evaluated. |
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