Characterization of activity and microbial diversity of typical types of Daqu for traditional Chinese vinegar.

Daqu is a fermentation starter used in traditional Chinese vinegar production and determines the quality of the final vinegar products. In this study, the activity and microbial diversity of three typical types of Daqu were investigated using a nested PCR–denaturing gradient gel electrophoresis (DGGE) and plating technique. The bacterial DGGE profile and plate analysis indicated that the bacterial composition of Daqu was dominated by Bacillus sp., Pantoea sp., Saccharopolyspora sp., Enterobacter cloaceae and Cronobacter sakazakii, and lactic acid bacteria including Weissella sp., Pediococcus pentosaceus. DGGE analysis of fungal plates identified Aspergillus niger, Absidia corymbifera, Rhizopus sp. and Penicillium sp. as the predominant fungi involved in Daqu. However, DGGE results indicated that the bacterial microbiota of QC (Qing-Cha) and HX (Hong-Xin) were more complex than that of HR (Huai-Rang) Daqu. The total populations of microorganisms in QC were about 1 log CFU g−1 higher than in HR and HX Daqu. Moreover, the saccharifying power of QC was significantly higher than in HR and HX Daqu, and the liquefying power of QC was significantly higher than in HR, but slightly lower than in HX Daqu. Our results indicate that microbial diversity plays a crucial role in determining the activity of typical types of Daqu.