Fermentation characteristics and safety evaluation of high-yield gamma-aminobutyric acid-producing Lactobacillus brevis D17 on hydrolyzed oat milk

Abstract:

[Background] It is of great significance to evaluate the fermentation characteristics and safety of Lactobacillus brevis D17, a high gamma-aminobutyric acid (GABA)-producing bacterium from fermented grains for the production of Chinese liquor. [Objective] To investigate the fermentation characteristics and evaluate the safety of L.brevis D17, laying a foundation for further assessment of probiotic properties. [Methods] The MRS medium and hydrolyzed oat milk were used to study the fermentation characteristics of strain D17. The whole genome sequence of D17 was compared with the virulence factor database (VFDB) and the comprehensive antibiotic resistance database (CARD) to assess the presence of virulence genes and antibiotic resistance genes. The antibiotic susceptibility profile of L.brevis D17 was established by antibiotic susceptibility tests. The toxicological test in mice was carried out to assess the in vivo safety of L.brevis D17. [Results] L.brevis D17 showcased good fermentation performance on oat milk, with the lactate production reaching 82.5% of that in the MRS medium. Moreover, it produced 480 mg/L GABA from the glutamate in oat milk. Additionally, L.brevis D17 improved the flavor profile of oat milk. L.brevis D17 did not carry virulence genes or antibiotic resistance genes. Despite inherent antibiotic resistance, D17 strain had no risk of resistance transfer. L.brevis D17 colonized the mouse intestine without causing any disease or death. Moreover, it exerted positive effects on serum indicators and gut microbiota in mice. [Conclusion] L.brevis D17 showcased strong potential for fermentation of plant-derived substrates and was confirmed to be safe, demonstrating significant probiotic properties.