Fermentation by lactic acid bacteria enhances the flavor, bioactivity, and metabolic profile of guava juice

Four strains of lactic acid bacteria (LAB) isolated from diverse sources were used to ferment guava juice, revealing strain-specific characteristics. Systematic analysis revealed LAB fermentation significantly altered physicochemical properties, bioactive compounds, and metabolic profiles. Lactobacillus plantarum strains notably increased organic acids, polyphenols and flavonoids while reducing sugars in fermented guava juice (FGJ), enhancing its antioxidant capacity and α-glucosidase inhibitory activity. Sensory evaluation and flavoromics analysis identified 55 distinct volatile metabolites that collectively improved juice flavor profiles through increased beneficial flavor compounds (acetoin and acetophenone), and decreased off-flavor substances (caryophyllene and humulene). Non-targeted metabolomics revealed 289 significantly altered metabolites primarily enriched in amino acid metabolism (e.g., DL-glutamate and indolelactic acid) and lipid oxidation pathways (e.g., 6-hydroxyhexanoic acid and dihydroxyacetone), which correlated with both flavor enhancement and antioxidant accumulation. These results demonstrated LAB reshaped guava juice metabolism at both volatile and non-volatile levels, as well as established a theoretical foundation for developing FGJ as a novel functional beverage with health-promoting properties.