Development of Gamma-Aminobutyric Acid (GABA)-Rich and Probiotic-Fermented Soymilk Using Lactiplantibacillus plantarum W12 as a Starter Culture

Research background. Fermented soymilk has emerged as a potential functional food due to its nutritional and health-promoting properties. Enhancing its functionality by enriching it with gamma-aminobutyric acid (GABA), a neurotransmitter with various health benefits, is an area of active research. This study aims to develop a novel GABA-enriched fermented soymilk using a newly isolated Lactiplantibacillus plantarum strain with both probiotic and GABA-producing capabilities. Experimental approach. Five L. plantarum strains isolated from Vietnamese soybean whey were screened for GABA production and probiotic characteristics. Strain W12, which exhibited superior performance, was selected for optimisation. Response surface methodology with a central composite design was used to optimise monosodium glutamate (MSG) and sucrose amounts for maximal GABA yield. A time-course study was then conducted to monitor bacterial growth, pH changes, organic acid production, and GABA accumulation during fermentation under the optimised conditions. Results and conclusions. L. plantarum W12 demonstrated exceptional probiotic traits: 97.1 % survival at pH=2.5, 96.5 % survival in bile salts/pancreatin, 97.3 % pepsin tolerance, 96.7 % auto-aggregation and 85.4 % hydrophobicity in chloroform. Initial GABA production reached (9.1±0.4) mM. Response surface optimisation predicted a maximum GABA concentration of 34.2 mM at 1.564 mg/mL MSG and 10.93 % sucrose, which was experimentally validated at (34.5±1.0) mM (15 h, 45 °C). Lactic acid was the predominant organic acid produced ((182.4±8.0) mg/g at 18 h), with viable cell counts exceeding 7.9 log CFU/mL, meeting probiotic thresholds. Novelty and scientific contribution. This study presents the first comprehensive characterisation of L. plantarum W12, a strain combining exceptional GABA biosynthesis with robust probiotic properties. The systematic response surface methodology (RSM) optimisation framework and detailed metabolic profiling provide reproducible protocols for developing multifunctional fermented soy beverages with applications in neurological and gastrointestinal health promotion.