Enhanced Gamma-aminobutyric Acid Production in a Fermented Cereal-Legume Blend Using Lactiplantibacillus plantarum FUTM-PM1: Process Optimization by Response Surface Methodology

Over time, the role of food has expanded beyond basic nutrition to become a powerful means of enhancing human health through additional functions. The presence of bioactive compounds, such as gamma-aminobutyric acid (GABA), in food makes it a functional system that actively influences physiological processes and supports human health. The controlled fermentation of staple foods by GABA-producing lactic acid bacteria (LAB) represents a promising and underexplored strategy to enhance the functional value of staple foods. The aim of this study was to isolate, screen, and characterise GABA-producing LAB from a pearl millet-soybean blend, and to optimize fermentation conditions (temperature, pH, and fermentation time) using the highest GABA-producing isolate as a starter inoculum, for an improved yield in the development of pearl millet-soybean blend GABA-enriched functional food. In this research, lactic acid bacteria capable of producing GABA were isolated from a traditional fermented cereal-legume blend. Screening using thin-layer chromatography (TLC) and a quantitative colorimetric assay (630 nm, R² = 0.99) identified the isolate with the highest GABA production (275.53 mg/L in MRS-MSG medium), and this isolate was subsequently confirmed as Lactiplantibacillus plantarum through 16S rRNA gene sequencing, and phylogenetic analysis. The fermentation of a cereal-legume blend with Lactiplantibacillus plantarum FUTM-PM1 was optimized using Response Surface Methodology (RSM) for enhanced metabolic activity and glutamate decarboxylase function, which resulted in an improved GABA yield of 373.79 mg/L. The results obtained from this research demonstrate the potential of indigenous L. plantarum as an effective starter inoculum for controlled fermentation, providing a viable strategy for naturally GABA-enriched functional food development.