Screening Of Brewing Microorganisms From Maotai-flavor Daqu And Studying On Fermentation Conditions

Maotai-flavor liquor is one of the major flavor liquors in China. Maotai-flavor Daqu played as saccharifying ferment in the brewing process, which is an important source for Maotai aroma and aroma precursors. Microorganisms have played an important role in Daqu. It help to learn the knowledge of brewing mechanism and understand the contributions of microorganisms on Maotai flavor formation by researched brewing microorganisms in Maotai-flavor Daqu. This paper aimed at the main microorganisms in Maotai-flavor Daqu, and screened out yeasts, moulds and bacteria by different indexes. In order to explor the fermentation conditions, the characteristic of fermentation products and its influence on the flavor of liquor, we used mixed bacteria which screened in Maotai-flavor Daqu to ferment in liquid-state. All these work could provide reference for the control of brewing technology. GC-MS was applied to analyze characteristic components in fermentation broth and flavor substances in Maotai-flavor liquor and vintage wine. The main conclusions of the study are as follows:According to the fermentation characteristics, MT-2 was screened out with better performance. The strain MT-2 identified as Wickerhamomyces anomalus by 26 S r DNA molecule identification, which has good function on production esters. According to the transparent circle and enzyme activity, a strain MJ-11 with excellent enzyme production capacity was screened out. The strain MJ-11 identified as Aspergillus oryzae by microscopic observation and 18 S r DNA molecule identification. According to the transparent circle and the crude enzyme activity, a better strain XJ-1 was screened out. The strain XJ-1 identified as Bacillus subtilis by 16 S r DNA molecule identification.These screened strains were used in liquid-state fermentation. We investigated the effect of alcohol content, total acid and total ester by mixed proportions of strains,temperature, inoculation volume, the ratio of material to water, p H, and time, respectively.The inoculation volume, p H and time were selected to optimize the fermentation conditions. The optimal liquid fermentation conditions were determined as inoculation volume 6%, p H 6.5 and fermentation time 7 d. The wine sample has a soft fermented aroma and ester aroma, which was comfortable.Methylene chloride was used to extract the flavor compounds in fermentation broth and these flavor compounds were analyzed by GC-MS. There are 38 kinds of compounds in MT-2 fermented liquor. Ethyl acetate, 2-Methyl-1-propanol, 3-methyl butanol, Acetic acid, Benzeneethanol, and Tryptophol were the characteristic fermentation products. There are 33 kinds of compounds in XJ-1 fermented liquor. 3-Hydroxy-2-butanone,2,3-Butanediol, 1,3-Butanediol, Tetramethyl-pyrazine, Guaiacol, and Palmitic acid were the characteristic fermentation products. The were 42 kinds of compounds in mixed culture fermented liquor, which including alcohols, acids, esters, carbonyl compounds and aromatic compounds,etc. Adding bacteria to mixed culture fermentation can increase flavor compounds in the fermentation system, which provide material basis for the Maotai flavor.Flavor compounds in different Maotai-flavor liquors were analyzed by HS-SPME-GC-MS. The results showed that there are 51 flavor compounds in these wines,including 9 kinds of alcohols, 3 kinds of acids, 25 kinds of esters, 1 nitrogenous compound,4 kinds of carbonyl compounds, and 9 kinds of alkane compounds. The analysis showed that different Maotai-flavor liquors have some differences in types and contents of flavor compounds.