Lactic Acid Bacteria-Derived γ-Aminobutyric Acid: From Targeted Screening and Biosynthesis to Functional Food Applications and Health Benefits

γ-Aminobutyric acid (GABA) is a non-proteinogenic amino acid that acts as a major signaling molecule across the nervous, cardiovascular, and immune systems. While GABA has historically been produced via chemical synthesis or plant extraction, microbial fermentation using lactic acid bacteria (LAB) provides a safe, sustainable, and food-grade alternative. This review details the recent progress of LAB-derived GABA, covering the workflow from strain selection to functional food applications. We discuss how modern screening methods combine high-throughput phenotypic testing with genomic mining of the gad operon to efficiently identify high-yielding strains. The biochemical mechanisms of the GABA shunt are also explained, alongside recent CRISPR-based metabolic engineering efforts designed to bypass natural yield limits. Furthermore, we address practical industrial challenges—such as the poor proteolytic ability of key producers like Levilactobacillus brevis—and evaluate viable solutions, including symbiotic co-cultures and optimized downstream purification steps. The review then summarizes the specific health benefits of dietary LAB-derived GABA, focusing on its ability to relieve anxiety via the microbiota-gut–brain axis, control blood pressure, and regulate immunity. Finally, we analyze the current regulatory and sensory hurdles, highlighting how integrating multi-omics data can help establish LAB-derived GABA as a reliable ingredient for functional foods and personalized nutrition.