Flavor compounds regulation in rice-flavor Baijiu by Bacillus velezensis: a genetic and functional analysis

Hong Ren, Ren Huang, Y Q Xie, Qinghua Chen, Feng Chen, Runhua Huang, Y Y Liang, Haiyan Lu, Jianwei Zheng, Guidong Huang, Xianfeng Zhong

To achieve targeted enhancement of the flavor complexity of rice-flavor Baijiu, this study evaluated the impact of fortified fermentation with four saccharification-promoting Bacillus velezensis strains on the volatile profile of fermented grains (Jiupei), and further dissected the genetic basis of the key strains. The volatile composition of Jiupei was analyzed using headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS) coupled with multivariate statistical analysis to assess the effect of B. velezensis bioaugmentation on flavor. All four fortified fermentation groups upregulated the contents of 304 volatile compounds, including 78 terpenoids and 62 esters. Using |lg FC| ≥ 1 and p < 0.05 as screening criteria, 68 significantly differential metabolites were identified, such as β -cubebene, ethyl 2-methyl-2-butenoate, and benzyl benzoate. Among the compounds with relative odor activity values (rOAV) ≥ 1, strains FUBL1 and FUBL3 significantly increased the level of 4-vinylguaiacol, and FUBL3 specifically elevated the content of farnesylacetaldehyde; together, these flavor substances constructed a rich Baijiu flavor profile. Comparative whole-genome analysis revealed that FUBL1 and FUBL3 harbor a complete methylerythritol phosphate (MEP) pathway for terpenoid biosynthesis as well as key genes for ester precursor synthesis. Notably, FUBL3 uniquely possesses a citronellol/citronellal dehydrogenase gene ( atuB ) and a flavin prenyltransferase gene ( ubiX ), which likely correlates strongly with its greater terpenoid diversity. In summary, this study elucidates the mechanism by which B. velezensis regulates the formation of the characteristic flavor of rice-flavor Baijiu from the perspectives of flavor component profiling and genomics, providing a theoretical basis for the mining of functional microbial resources and their precise manipulation in Baijiu brewing.