GABA-enriched dairy functional food fermented by acid-resistant <i>Lactiplantibacillus plantarum </i>LH46<i> </i>isolated from human milk

<jats:p>Background: Microbiota-derived γ-aminobutyric acid (GABA) and other neuroactive metabolites produced by lactic acid bacteria (LAB) have attracted increasing attention due to their potential application in functional foods containing bioactive GABA. Human breast milk represents a valuable source of beneficial LAB with promising probiotic and technological properties. Objective: This study aimed to isolate GABA-producing, acid-resistant LAB from human breast milk and evaluate their suitability as starter cultures for the production of GABA-enriched fermented dairy functional foods. Methods: LAB strains isolated from human breast milk were screened for acid resistance and GABA production. The selected strain was used as a single starter culture for skimmed-milk fermentation, with and without monosodium glutamate (MSG) supplementation. Fermentation performance was evaluated by measuring pH, titratable acidity, viscosity, syneresis, texture, and sensory characteristics of the fermented dairy product. GABA concentration was quantified using high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Results: Among the LAB isolates, a strain of Lactiplantibacillus plantarum LH46 was obtained, which demonstrated high GABA-producing capacity and acid resistance. This strain efficiently fermented milk as a single starter and accumulated up to 0.28 g/L GABA without the addition of MSG and up to 3.57 g/L GABA with MSG supplementation on the first day of refrigerated storage. The resulting fermented dairy product exhibited a firm texture, high viscosity, low syneresis, pH 4.60, titratable acidity of 153 °Th, and favorable sensory properties. Conclusion: This study demonstrated that the Lactiplantibacillus plantarum LH46 strain isolated from human breast milk is a promising monoculture starter for the production of GABA-enriched functional yoghurt. A 300 mL portion of the resulting fermented dairy product provides a measurable amount of naturally produced GABA while maintaining favorable technological, physicochemical, and sensory properties. The high proteolytic activity of the strain may support GABA synthesis without the addition of MSG by providing glutamate released from milk caseins as a substrate. In addition, activation of the GAD system not only promotes GABA biosynthesis but also ensures the maintenance of intracellular pH homeostasis and enhances bacterial viability under acidic conditions through a proton-suppression mechanism. The combination of these properties makes L. plantarum LH46 a promising starter culture for the development of GABA-enriched functional dairy products. Novelty: Application of human-milk-derived Lactiplantibacillus plantarum LH46 as a single-strain starter culture capable of both milk fermentation and GABA production, including GABA production without supplementation with an external glutamate precursor.  Keywords: Human breast milk microbiome, Lactiplantibacillus plantarum, proteօlitic activity, milk fermentation, GABA-enriched functional dairy food, sensory properties.</jats:p>