Separation and identification of thermoduric bacteria strains in medium/high temperature Daqu and the analysis of the flavor metabolites

Objective: With the medium / high temperature Daqu bacteria through cultivation as examples,separation of thermoduric bacteria and the analysis of the flavor metabolites. Method: Isolated via enrichment culture and dilution coating,the morphological observation and 16 S r DNA sequence analysis,growth characteristics analysis,the solid and liquid fermentation products were analyzed through headspace solid- phase microextraction and gas chromatography- mass spectrometry technology. Result: The thermoduric bacteria strain NR2 was isolated and it was Bacillus licheniformis,the bacteria culture began to enter the logarithmic phase from the 4 h of cultivation and reached the stable phase after 24 h of cultivation,the liquid state fermentation flavor substances,such as 2,3-diacetyl,3- hydroxy-2- butanone and 2,3- butanediol,with 3- hydroxy-2- butanone being the main metabolites. In addition,there were more species of solid state fermentation metabolites that liquid ones.The contents of pyrazine compounds,such as 2,3,5- methyl pyrazine and 2,3,5,6- tetramethyl pyrazine increased.Conclusion: The formation of liquor and highly- flavored liquor flavor substances was closely related to the metabolic characteristics of the thermoduric bacteria.