Metabolite-Pool Networks and Biological–Non-Enzymatic Synergy in Volatile Flavor Formation by Lactic Acid Bacteria in Fermented Foods: A Review

Volatile flavor compounds (VFCs) are major determinants of sensory quality in fermented foods. In lactic acid bacteria (LAB)-containing systems, their formation reflects precursor metabolism, strain-specific metabolic capacity, environmental and community regulation, and non-enzymatic chemistry. This review develops an integrated precursor–pool–flux framework for LAB-associated VFC formation. Carbohydrate/citrate-, protein/amino-acid-, and lipid-related routes provide the principal precursor inputs, which intersect to different extents at three functional metabolite pools centered on α-keto acids, acetyl-CoA-related metabolites, and C4–C5 TCA intermediates. These pools are treated as operational convergence and redistribution nodes rather than new biochemical classifications. Genetic capacity, intracellular regulation, cultivation conditions, and interspecies interactions modify precursor supply and flux partitioning, thereby altering quantitative VFC output. Biological–non-enzymatic coupling is considered where processing changes precursor accessibility, fermentation-derived substrates undergo subsequent chemical transformation, or biological and chemical reactions proceed concurrently. Comprehensive volatile profiling defines the resulting chemical phenotype, whereas molecular sensory and flavoromics identify aroma-active endpoints. This framework provides a mechanistic basis for interpreting LAB-associated VFC formation and guiding strain and process selection toward targeted aroma regulation.