Biogenic Amines Control in Bacterial-Type Douchi Using Bacillus velezensis A1: Strain Screening, Process Optimization, and Industrial Validation.

The study focused on biogenic amines (BAs) in fermented products, particularly douchi. Three strains showing high protease activity (> 90.00 U/mL) and low BA levels (< 40 mg/kg) were isolated from naturally fermented douchi: A1 Bacillus velezensis, A2 B. glycinifermentans, and A3 B. subtilis. A1, with the lowest total biogenic amine (TBA) levels, was selected as the representative strain. The optimal fermentation conditions (8% inoculum, 37°C temperature, 3 days duration) reduced TBA to levels well below the FDA standard (< 1000 mg/kg). Compared to the natural fermentation (NF), it was verified that the TBA of douchi was lowered to 10.51 ± 0.21 mg/kg after optimized fermentation, approximately reduced 10.80-fold. Spermine levels decreased by 43.17-fold, followed by tyramine and phenethylamine. Further, apply them to large-scale cultivation (scaled up by 100-fold) in actual production during colony-enhanced fermentation (CEF). The physicochemical properties and BA levels were monitored to assess the correlation. The findings showed that the douchi of CEF had up to 0.94% amino acid nitrogen (≥ 0.25% EN) and 0.72% total acid (≤ 2.5% EN). The TBA level was only 38.27 ± 0.13 mg/kg, significantly lower than NF (94.94 ± 2.59 mg/kg). This study proposed BA-reducing methods through strain screening and process optimization, particularly achieving large-scale verification from the laboratory to the factory. This approach significantly reduced the TBA levels in bacteria-type douchi, offering a crucial reference for the industrial-scale safe production of fermented soybean products. PRACTICAL APPLICATIONS: This research offers industrial-level guidance for douchi production. By utilizing Bacillus velezensis A1 and optimizing the process, the TBA can be reduced by a factor of 2.5 while maintaining product quality (T/GZSX 014-2018). This approach provides a collection of directly applicable safety production technology models for fermented soybean product enterprises, thereby assisting the industry in improving product safety and addressing health consumption demands.