Analysis and formation mechanism of Key aroma compounds with ammonia-like off-flavors in Jiang-flavored high-temperature daqu: Substances composition and main microorganisms

Ammonia odor is a notable off-flavor in Jiang-flavored high-temperature Daqu, impacting its quality, but the substances composition and formation of this odor are still unknown. In this study, molecular sensory science was employed to identify the key flavor compounds responsible for the ammonia odor in Daqu, while microbiomic analysis, correlation analysis, and functional gene prediction were conducted to investigate the mechanisms of their formation. Trimethylamine was identified as the predominant component contributing to the ammonia odor characteristic of Daqu. Subsequent microbial community analysis revealed that Bacillus, Kroppenstedtia, Thermoascus, and Thermomyces were the dominant microorganisms differentiating ammonia-flavored Daqu (AFDQ) from non-ammonia-flavored Daqu (NFDQ). Moreover, significant variations in the amino acid metabolic pathways of the bacterial community functional genes between these two Daqu types further influenced the development of the ammonia flavor. Concurrently, the research findings were applied to the Daqu production process for the identification of AFDQ. A support vector machine (SVM) discrimination model was developed based on trimethylamine and total volatile basic nitrogen levels, demonstrating robust performance in distinguishing AFDQ from NFDQ. These findings provide new insights into the flavor formation mechanisms of ammonia-flavored Daqu and offer a scientific basis for its quality control and optimization.