Effects Of Cellar Sealing Method On The Quality Difference Of Different Layers Of Jiupei In The Brewing Of Luzhou-flavor Liquor

In the production of strong-flavor baijiu(SFB),there are obvious differences in the quality of the liquor produced by the Jiupei in the cellar.The main manifestation is that with the increase of the depth of the cellar,the quality of the Jiupei gradually improves.This problem seriously limits the increase of high-quality SFB production,but the reason for this phenomenon is not clear,and the relevant mechanism needs to be analyzed urgently.In the traditional brewing process of SFB,yellow mud is often used to seal the cellar.Since the yellow mud directly contacts the Jiupei,it will directly affect the quality of the liquor produced by the Jiupei.However,there is no report on the effect of cellar sealing on the quality difference of Jiupei at different layers in SFB brewing.This paper takes Luzhou-flavor liquor,a typical representative of SFB,as the research object.Based on high-throughput sequencing and metabolomics,the flavor substances,microorganisms and metabolites that led to the difference in the quality of Jiupei in different layers were analyzed.The effect of cellar sealing on the quality difference of Jiupei in different layers was explored,and an improved cellar sealing method was proposed based on the research results.1.There are differences in the content of flavor substances and metabolites of Jiupei in different layers of the mud sealed cellars.The total amount of flavor substances,esters and four major esters in the raw liquor showed an increasing trend with the depth of the cellar,and the acid content of the raw liquor from the bottom Jiupei was also significantly higher than that of the other three layers(P<0.05).Ethyl hexanoate,ethyl hexanoate,ethyl lactate and other ester substances are the key flavor substances that lead to the difference in the quality of the raw liquor with different layers.A total of 1051 metabolites of Jiupei were identified,mainly including organic acids and derivatives,lipids and lipid-like molecules and organoheterocyclic compounds,etc.With the depth of the cellar,the contents of amino acids,peptides,and analogues showed an increasing trend.However,the content of acid substances in the surface Jiupei is higher than other layers of fermented wine.2.There are differences in the microbial community structure and physicochemical factors of different layers of Jiupei in the mud sealed cellars,and the oxygen content is the key factor leading to the difference in liquor quality of different layers of Jiupei.The Prevotella in the surface Jiupei seriously affected the determination of acid-producing microorganisms such as Lactobacillus,which decreased from 95.92% to 41.02%.The relative abundances of Aspergillus and Thermomyces increased with the depth of the cellar,while the relative abundances of Candida and Pichia showed an decreasing trend.There were 5differential bacterial genera and 11 differential fungal genera between surface Jiupei and bottom Jiupei.The oxygen content of the surface Jiupei was significantly higher than that of the bottom Jiupei at the 7th day of fermentation(P<0.05).After the fermentation,the reducing sugar content of the bottom Jiupei was higher,the p H of the surface Jiupei was higher,and the starch content and acidity had no significant difference.The content of caproic acid,butyric acid and acetic acid in bottom Jiupei was significantly higher than that in surface Jiupei(P<0.05).Oxygen content is a key factor leading to differences in microbial community structure and flavor substances.In the early stage of fermentation,due to the different sensitivities of different microorganisms to oxygen,different levels of oxygen will cause differences in microbial growth and metabolism.There was a significant negative correlation between oxygen content and 13 flavor substances which caused the difference of raw liquor.In the later stage of fermentation,yellow water is deposited at the bottom of the pit,and when the concentration of yellow water reaches 50%,the growth of most microorganisms will be inhibited,and the production of flavor substances is mainly affected by yellow water and the metabolites produced by microorganisms in the early stage of fermentation.3.The anaerobic micropressure sealed cellars makes the content of flavor substances in different layers of raw liquor,the microbial community structure and metabolites of Jiupei more uniform.The oxygen content in the surface Jiupei was significantly higher than that in the bottom Jiupei when fermented for 7 d in the anaerobic micropressure sealed cellars(P<0.05),but the difference was lower than that in the mud sealed cellars.There was no significant difference in starch content,reducing sugar content,p H and acidity.With the increase of the depth of the cellar,the content of caproic acid and butyric acid in the Jiupei showed an increasing trend,but the content of acetic acid did not change significantly.The microbial community structure of Jiupei in the anaerobic micropressure sealed cellars had no obvious change with the depth of the cellar.Lactobacillus dominated the bacteria,Aspergillus21.68% and Thermomyces 23.45% were the most abundant.With the increase of the depth of the cellar,the total amount of metabolites and the content of acid substances in the Jiupei showed an increasing trend,and there was no significant difference in the contents of amino acids,peptides,and analogues,carbohydrates and carbohydrate conjugates.The metabolites of Jiupei in anaerobic micropressure sealed cellars were more uniform in type and content.The contents of esters,acids and alcohols in the raw liquor of different layers of the anaerobic micropressure sealed cellars had no significant change.There are 14 different flavor substances in the raw liquor from the surface Jiupei and bottom Jiupei,excluding the four major acids and four major esters,and most substances have no significant relationship with oxygen.To sum up,this paper takes Luzhou-flavor liquor as the research object,and reveals that oxygen is the key factor that causes the difference in liquor quality of different layers of Jiupei caused by cellar sealing.An anaerobic micropressure sealed cellars method with better sealing performance was introduced.The research results provide a reference for the improvement of the production process of Luzhou-flavor liquor,and provide a certain theoretical support for improving the yield of high-quality SFB.