Dual effects of microbiome-guided screened Bacillus amyloliquefaciens PB04 from moromi: Histamine reduction and volatile flavor promotion in moromi fermentation

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Histamine, the most prevalent and toxicologically relevant biogenic amine in moromi, poses a critical safety and quality challenge in soy sauce. In this study, a microbiome-guided targeted three-tier screening strategy integrating physicochemical profiling and microbiota analysis was implemented to isolate histamine-degrading strains from moromi. Twenty-two non-biogenic-amine-producing isolates were preliminarily obtained via the bromocresol purple single-layer plate (BCPSP). Following two-step verification combining amine oxidase activity test and high-performance liquid chromatography (HPLC), five potent strains were identified as two Calidifontibacillus erzurumensis strains, two Bacillus amyloliquefaciens strains, and one Priestia flexa strain, with histamine degradation rates of 18.56%, 26.11%, 16.10%, 57.77%, and 8.11%, respectively. All strains displayed reliable biosafety. Among them, Bacillus amyloliquefaciens PB04, owing to its outstanding tolerance to acid, high salt, and bile salts, was evaluated in moromi fermentation and significantly reduced histamine levels. Sensory evaluation showed inoculated samples exhibited superior aroma, taste, body, and overall acceptability, without color deterioration. PB04 inoculation elevated the number and total content of VFCs by 374.38%, with concentrations of furans, aldehydes, esters, acids, phenols, ketones, and alcohols increasing by 1,651.99%, 1,131.57%, 989.10%, 520.04%, 380.66%, 310.67%, and 172.10%, respectively. Odor activity value (OAV > 1)-based screening and variable importance in projection (VIP ≥ 1) analysis revealed 11 key odor compounds (KOCs) as representative VFC markers. Collectively, this study demonstrates that indigenous Bacillus amyloliquefaciens PB04 from moromi can achieve synchronous histamine control and flavor quality enhancement, and provides a promising microbial candidate and a practical framework for the safety control and quality upgrading of fermented products.