| Baijiu is a unique distilled liquor in China,which is the precious material wealth of the Chinese nation.It has a long history of brewing and a dazzling culture.The production of Strong-flavor Baijiu is inseparable from the study of liquor-making microorganisms,among which the microorganisms in pit mud play a major role.However,due to the regional differences,water quality,technology and other factors,Strong-flavor Baijiu styles vary in different regions.Chenggu Strong-flavor Baijiu has a long history and has a unique style.As an important part of the brewing industry in Shaanxi province,It is welcomed by consumers and has great development potential and economic value.However,there is still no research on the microflora of its pit mud.The quantity and activity of caproic acid-producing strains in pit mud of Chenggu Baijiu,are the key factors to determine the quality or effectiveness of pit mud,which directly affected the quality of Strong-flavor Baijiu.Therefore,it is necessary to add suitable caproic acid-producing bacteria solution and compound microorganism from old pit mud to carry out purposefully fusion and mixed inoculation in order to improve the quality of pit mud,shorten the aging time of pit mud,stabilize the yield and quality of baijiu and expand the production.In this project,the pit mud of Chenggu baijiu in Shaanxi Province was used as the experimental object.The microbial diversity of pit mud was analyzed by high-throughput sequencing technology to reflect its community structure,reflected its community structure,and annotated the gene function,so as to study the microorganisms of pit mud on the whole;The growth characteristics of the selected caproic acid producing strain were tested to evaluate its applicability in baijiu production environment;The selected strains were applied to the fermentation of artificial solid pit mud,the physicochemical indexes and sensory identification of the pit mud were determined;and its quality was comprehensively evaluated.Artificial solid pit mud was used for fermentation test,and the quality of liquor samples was evaluated by physicochemical indexes and chromatographic analysis.It provides technical reference and scientific basis for stabilizing the quality of Chenggu Baijiu pit mud and expanding production.The main conclusions were as follows:1.The microbial diversity,community structure and gene function annotation of Chenggu Baijiu pit mud were analyzed by high-throughput sequencing technology.The results showed that there were 68 genera and other unclassified genera in bacterial composition and classification.The fungi were divided into 149 genera and other unclassified genera.The core genera were Debaryomyces(13.83%),Petrimonas(10.54%),Issatchenkia(17.12%),Bacillus(9.21%)and so on.The core genera were different from other baijiu producing areas,but it still had certain similarity in the classification of bacterial community composition compared with the same flavor baijiu.A total of 236,022 unigene were annotated in KEGG database.Carbohydrate metabolism was the main metabolic activity,including 15 carbohydrate metabolism pathways,and pyruvate metabolism was the main metabolic pathway;CAz Y and COG databases annotated 210 major carbohydrate-active enzymes and 23 functional categories respectively.The glycoside hydrolase and glycosyltransferase were the largest in the former,and the number of predicted proteins with function unknown was the largest in the latter.accounting for 74% of the total carbohydrate-active enzymes and 31% of the predicted protein sequence.This provides the material basis and reaction conditions for the further generation,transformation and metabolism of sugars.2.The bacteria producing caproic acid in pit mud were screened by copper sulfate colorimetry combined with gas chromatography.The results showed that the 8 strains screened had the ability to produce caproic acid,among which bacterial strain x6 had the highest yield of 83.1mg/100 m L.The growth characteristics of strain x6 showed that the strain could grow well in the range of 35-40? and p H 4.5-6,and had 10% ethanol tolerance and25% glucose tolerance.The antibiotic sensitivity was good,and it could adapt to the fermentation environment of Strong-flavor Baijiu,could be applied to the fermentation process and had a good application potential in the preparation of artificial pit mud.The strain was identified as Bacillus simplex by bacterial morphology,microscopic morphology,physiological and biochemical reaction and molecular biology.3.B.simplex x6 and pit mud solution were inoculated into artificial solid pit mud preparation according to different bacterial solution ratios 1?1(A),1?2(B),2?1(C),1?3(D),3?1(E)for pit mud fermentation.The physiochemical indexs and sensory identification of fermented pit mud were determined.The results showed that the addition of bacterial solution in each group had a significant impact on the moisture,p H,ammonia nitrogen,available phosphorus,available potassium and humus of artificial solid pit mud.All indexes accord with the dynamic changes of pit mud fermentation process.Combined with the sensory identification results,the pit mud cultured in group A had the best maturity after comprehensive evaluation.4.The brewing experiment of pit mud in group A and CK was conducted by using Strong-flavor Baijiu production process.After fermentation,the liquor was distilled and the quality of liquor was analyzed.The results showed that the contents of total acid and total ester in group A were 0.18 g / L and 0.46 g / L higher than those in CK group,respectively;Compared with CK group,the contents of n-propanol,isobutanol,n-butanol,isoamyl alcohol and n-hexanol decreased by 5.35 mg / ml,0.73 mg / 100 m L,7.31 mg / 100 m L,3.62 mg /100 ml and 0.81 mg / 100 ml respectively;Methanol and n-butanol increased by 0.37 mg /100 ml and 0.87 mg / 100 ml respectively compared with CK group;Acetaldehyde and acetal decreased by 0.3 mg / 100 ml and 0.87 mg / 100 ml respectively compared with CK group;The contents of ethyl caproate,ethyl acetate,ethyl butyrate and ethyl valerate increased by 31.06 mg / 100 m L,7.21 mg / 100 m L,2.54 mg / 100 ml and 1.03 mg / 100 ml respectively compared with CK group;The content of ethyl lactate was slightly lower than that of CK group by 3.47 mg / 100 ml,The ratio of ethyl caproate and ethyl lactate was in the range of 1?0.5-0.8,and the sum of ethyl acetate and ethyl lactate was greater than that of ethyl caproate.The main aroma of the baijiu was prominent,the flavor was harmonious,the typicality was strong and the quality was good,which was in line with the expected target. |
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