Analysis On The Quality Difference Between The Surface And The Core Of Luzhou-flavor Daqu

Liquor is not only a traditional unique fermented beverage in China,with a long history and unique national cultural connotation,but also plays one of the important industries of the national economy.There is a saying that "Qu is the bone of liquor" and "Qu determines the type of liquor" in liquor brewing.Daqu prepared from wheat and as raw materials plays an important role in the production process of Luzhou-flavor liquor and is an important guarantee of liquor quality and yield.In the process of fermentation and post-ripening of Daqu,the surface and the core of Daqu show different appearance characteristics.The quality of Daqu can be judged by the sensory characteristics of the surface and the core in production practice,but little is known about the difference between their quality and ripening changes after fermentation.In our study,based on the medium temperature Daqu of Luzhou-flavor liquor,the main physical and chemical indexes,enzyme activities,material quality indexes and microbial community evolution of the surface and the core were analyzed.The genetic diversity microbial communities and the differences among important microbial genera were compared in the surface and the core of Daqu.The main results are as follows:1.Determination and analysis of the physical and chemical indexes of the surface and the core in the process of Daqu fermentation.The temperature content increased at first and then decreased,moisture and starch contents decreased by about 26%,and starch content decreased from 69.32% on day 0 to 18% on day 90.The acidity content increased at first and then decreased and then increased.On the day 90,the acidity of the surface and the core were 0.058 mmol/g and 0.148 mmol/g,respectively.Amino acid nitrogen and protein contents showed an increasing trend,in which the protein content increased from 12.56%to 14.10%;reducing sugar decreased at first and then increased;the core of Daqu was in the core position,the temperature,moisture,amino acid nitrogen and protein contents were higher,and the acidity of the surface was nearly 3 times that of the core,while the content of reducing sugar and starch were higher in the surface.2.Determination and analysis of the enzyme activities of the surface and the core in the process of Daqu fermentation.The liquefied enzyme activity and esterifying enzyme activity increased at first and then decreased.The liquefied enzyme activity of the core reach a higher level of 0.61 U/g on the day 6,while the highest level was 1.45 U/g in the surface on the day 9.The glucoamylase activity increased at first and then decreased to570U/g on day 90 in the core,while the glucoamylase activity increased continuously,from 368U/g on day 0 to 1058U/g on day 90 in the surface.The fermentation enzyme activity of the surface increased at first,then decreased,then slightly increased and then decreased,the highest level was 2.25U/g(on day 6),and the fermentation enzyme activity reach a higher level was 2.18U/g in the core(on day 3);the cellulase activity of the core was higher than that of the surface from the 0 to 9 day,and the cellulase activity of the surface increased at first and then decreased slightly,while that of the core increased rapidly;the cellulase activity increased and then decreased at 15-90 days,the surface(0.94U/g)was higher than that of the core(0.48 U/g).3.Determination and analysis of the quality traits of the surface and the core in the process of Daqu fermentation.The content of amylose and amylopectin and the yield of type A and B starch showed a decreased trend,and the amylose content of the surfae and the core consumed 6.63% and 8.29%,respectively.The content of amylopectin decreased slightly on the 0-15 days,and decreased rapidly on the 15-90 days,while the surface could consume more amylopectin.On the 0-3 days,the structure of most starch granules were intact,but from 6 to 90 days,the starch granules gradually became rough and incomplete,and the starch granules were destroyed greatly in the core.On the 9th day,the glutenin band could not be detected,and the glutenin concentration of the core was lower,and the free amino acid content of the core was higher.The order of the first five amino acids with high content of 17 free amino acids in Daqu was glutamic acid > proline > phenylalanine >serine > valine.The content of rhamnose decreased continuously in the surface,and the content of rhamnose decreased at first and then increased in the core.The arabinose content increased at first and then decreased in the core,the arabinose content increased continuously in the surface.The glucose content decreased,4.71mg/g and 4.44mg/g decreased respectively on day 6 from 5.32 mg/g on day 0.The xylose content of the core decreased,but the xylose content of the surface decreased at first and then increased slightly.The fructose content increased at first and then decreased,sucrose content increased.The contents of rhamnose,arabinose,glucose,xylose and sucrose were higher in the core,while fructose was higher in the surface.The content of flavonoids increased at first and then decreased slowly,and the content of flavonoids in the core was about 5 times that of the surface.The content of cellulose decreased at first and then increased,while that of the core was higher.4.16 S r DNA high-throughput sequencing technique was used to analyze the microbial community structure of bacteria during the fermentation of Daqu.There were differences in community structure and dominant microorganisms between the surface and the core.A total of 13 phylums and 267 genera of bacteria were detected.Lactobacillus,Weissella,Pediococcus,Erwinia and Methylobacterium were the dominant genera in the surface,while Bacillus,Staphylococcus,Thermoactinomyces and Undibacterium were the dominant genera in the core.The bacterial community succession of the surface and the core has high similarity,and the bacterial community was more diversification in the core.5.The ITS high-throughput sequencing technique was used to analyze the microbial community structure of fungus in the fermentation of Daqu.4 phyla and 71 genera of fungi were detected.Among them,Hyphopichia,Emericella,Wickerhaomyces,Dipodascus and Pichia were the dominant genera in the surface,while Aspergillus,Thermoacscus,Theromyces,Candida and Clavispora were the dominant genera in the core.On the other hand,there were obvious differences between the fungal community succession of the surface and the core,and the fungal community was more diversification in the surface.6.Acording to the results of redundancy analysis,13 factors such as temperature,starch,acidity,glucoamylase,cellulase,amylose affected the distribution in the surface and23 factors such as amino acid nitrogen,reducing sugar,starch,protein,liquefied enzyme activity,glucoamylase activity and fermentation enzyme activity affected the distribution of bacteria in the core.It showed that the diversity of bacterial community was more inclined to the core.The temperature,acidity,esterifying enzyme activity,glucoamylase activity,fermentation enzyme activity and other 14 factors affected the distribution of fungus in the surface,while the temperature,moisture,glucoamylase activity,cellulose activity,amylopectin and other 11 factors affected the distribution of fungus in the core.It showed that the diversity of fungal community was more inclined to the surface.In addition,there were the main factors affecting the distribution of bacteria: moisture,starch,acidity,amino acid nitrogen,glucoamylase activity,esterifying enzyme activity and cellulase activity.While temperature,acidity,glucoamylase activity and cellulase activity were the main factors affecting the distribution of fungus.