Screening Of Maotai-flavor Strains And Study On Aroma Characteristics Of Fermentation And Metabolism

The liquor style of Maotai-flavor liquor is "colorless(yellowish)transparent,Maotai-flavor full-bodied,elegant and delicate,and lasting in an empty glass",etc.Its style derives from fermentation and the complex microbial metabolism involved in the fermentation process.Therefore,it is very important to study and explore the microorganisms that contribute to or regulate the flavor of soy sauce.Microbial fermentation produces aroma mainly by fermentation and metabolism of functional strains to produce flavor compounds,certain flavor compound structure naturally forms certain flavor structure.In order to reveal the origin and fermentation mechanism of Maotai-flavor,this study took Maotai-flavor Daqu as the source of bacteria.To separate and identify the deodorant producing microorganisms in Daqu for the production of Maotai-flavor liquor from 1 ? 7 rounds.The characteristics and mechanism of perfuming-producing bacteria were studied by simulating solid-state fermentation and liquid fermentation.The main research results are as follows:(1)From 1 ? 7 rounds of Maotai-flavor Daqu,three strains of bacteria with distinct Maotai-flavor production under the conditions of solid and liquid fermentation were obtained.The strain Numbers were MTQ21,MTQ23 and MTQ45.The three strains were identified as bacillus licheniformis by morphological observation and molecular biology.By optimizing the liquid fermentation temperature conditions,the optimal liquid fermentation conditions were finally determined,that is,the bran extract juice was used as the fermentation medium,and the fermentation temperature was 37 ??50 ??55 ??60 ??65 ?,150 r/min shaking table for 10 d production of soy sauce is the most appropriate.(2)In the fermentation medium of bran extract juice,the three strains all had the highest metabolic secretase activity when the fermentation temperature was 60 ?.Metabolic enzyme activity was 58.15 U/m L for MTQ21 and 10.04 U/m L for amylase.The enzyme activity of MTQ45 was 56.81 U/m L,and that of amylase was 17.74U/m L.The enzyme activity of MTQ23 strain was 70.92 U/m L,and that of amylase was 14.72 U/m L.In the process of fermentation,the p H value of fermentation broth changed from neutral to weak acid to alkaline to neutral to acid.The flavor of fermentation broth was also enhanced with the increase of fermentation temperature,and the aroma lasted for a long time.(3)In the nutrient broth fermentation medium,the metabolic enzyme activity of the strain was very low,and the optimal temperature for protease production was65 ?.The protease activity of MTQ21 was 8.37 U/m L.The protease activity of MTQ23 strain was 7.25 U/m L.The protease activity of MTQ48 strain was 6.89 U/m L.The optimum temperature for amylase activity was 55 ?,and the activity of amylase in MTQ21 was 5.77 U/m L.The activity of amylase of MTQ23 was 1.83 U/m L.The activity of amylase of MTQ45 was 4.52 U/m L.During the whole process of fermentation,the p H of fermentation liquid changed from neutral before fermentation to alkaline at the end of fermentation,and the p H was weak at the end of fermentation.(4)In the liquid fermentation process with bran extract as the fermentation substrate,92 volatile substances were detected in the fermentation products of strain MTQ21,116 volatile substances in the fermentation products of strain MTQ23,112 in the qualitative and 4 in the unqualitative;79 volatile substances in the fermentation products of strain MTQ45,78 in the qualitative and 1 in the unqualitative.The relative contents of pyrazines,ketones and phenols are higher than 10%,which are the main dominant components in the fermentation process of functional bacteria.Volatile substances such as 2,3,5,6-tetramethylpyrazine,3-hydroxy-2-butanone,guaiacol and4-vinyl guaiacol are the main characteristic substances.(5)In the liquid fermentation process with nutrient broth as the fermentation substrate,101 volatile substances were detected in the fermentation products of strain MTQ21,among which 94 were qualitative and 7 were unqualitative.A total of 101 volatile substances were detected in the fermentation products of MTQ23 strain,95 ofwhich were qualitative and 6 of which were unqualitative.A total of 103 volatile substances were detected in the fermentation products of strain MTQ45,of which 100 were qualitative and 3 were unqualitative.In the whole fermentation process,the relative contents of pyrazines,phenols and unknown compounds are relatively high,which are the dominant components of MTQ21.However,MTQ23 and MTQ45 bacteria were divided into pyrazines in the early stage and during fermentation.In the late stage of fermentation,the dominant group of MTQ23 was divided into phenols.The dominant components of MTQ45 fermentation are unknown class compounds and aromatic compounds.Among them,the relative contents of benzaldehyde,2,5-dimethylpyrazine,Oxazolidine,2-phenyl-and other volatile substances are higher than other volatile substances,which are the main characteristic substances in the liquid fermentation process of functional bacteria.