Mechanistic insights into LuxS/AI-2 quorum sensing-regulated biofilm formation and its impact on the texture and flavor of kefir.

Abstract

Kefir is a biofilm-based fermented dairy product whose unique flavor and texture are closely associated with the complex microbial community within kefir grains. However, the regulatory mechanisms underlying biofilm formation in kefir and its impact on product quality remain unclear. This study systematically investigated the dynamics of biofilm formation, core microbiota, and key metabolites in both traditional and backslopped kefir. Traditional kefir exhibited more stable metabolic activity and higher biofilm content, with biofilm levels significantly positively correlated with lactic acid bacteria (LAB) biomass (r = 0.58, p < 0.05), yeast biomass (r = 0.54, p < 0.05), and lactic acid concentration (r = 0.70, p < 0.05). Subsequent co-culture experiments revealed that yeast metabolites promoted LAB growth, and that lactic acid levels modulated yeast-LAB interactions. Critically, both the acidic environment and yeast interaction enhanced biofilm formation by regulating the LuxS/AI-2 quorum sensing (QS) system, as evidenced by increased expression of key QS genes and autoinducer-2 activity. Co-fermentation with high-biofilm-forming LAB significantly improved the physicochemical properties of fermented milk, increasing water-holding capacity by 1.2-fold, viscosity by 1.6-fold, and total volatile flavor compounds by 1.3-fold, while enriching fruity and buttery aroma profiles. This study elucidates the molecular mechanism by which acidic conditions and microbial interactions regulate biofilm formation via the QS system in kefir, and provides a novel strategy for improving fermented food quality through biofilm modulation.