Abstract: In order to explore the effect of co-fermentation with Monascus and Aspergillus oryzae on the quality of soybean paste, the volatile flavor components in soybean pastes produced using pure and mixed cultures of A. oryzae (Piniang M003) and Monascus (PM001) were determined by headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and comparatively analyzed by principal component analysis (PCA), and Illumina MiSeq sequencing technology was used to analyze the changes in the microbial community structure during the mixed culture fermentation process. Meanwhile, the correlation between the major microorganisms and the major flavor substances was analyzed. The results showed that the composition and content of flavor substances and the composition and relative abundance of microbial communities in the soybean paste produced by co-fermentation were significantly better than those in the soybean paste fermented with A. oryzae monoculture. The major flavor substances in soybean paste were significantly positively correlated with dominant genera such as Aspergillus, Bacillus, Monascus and Leuconostoc. The flavor quality of the soybean paste produced with a mixed culture of A. oryzae and Monascus in a ratio of 3:1 (m/m) was best. The results of the study showed that the mixed culture fermentation with Monascus and A. oryzae could significantly improve the flavor quality of soybean paste, which will be informative for the improvement of the flavor quality of soybean paste.

Key words: Monascus; co-fermentation; soybean paste; volatile flavor components; microbial community structure