Functional characterization and application of autochthonous lactic acid bacteria from Chinese kefir for improved fermented milk quality.

Lactic acid bacteria (LAB) are essential for the quality and functionality of fermented dairy products. This study aimed to isolate and characterize LAB from traditional kefir grains collected from 5 regions in China and evaluate their potential as adjunct cultures in fermented milk production. A total of 80 LAB isolates were identified, representing 9 species within 6 genera, with Lactococcus lactis being the most prevalent. Based on curdling ability, acid production, viscosity, water-holding capacity, and sensory performance, 2 isolates, Lacticaseibacillus paracasei A35 and Lactococcus lactis E24, were selected for further investigation. These were combined with a commercial starter (PYS-010) at optimized ratios: 0.75 × 106 cfu/mL of Lacticaseibacillus paracasei A35, 1.75 × 106 cfu/mL of Lactococcus lactis E24, and 0.003% of basic culture. Fermentation kinetics, rheological properties, volatile profiles, textural attributes, and sensory quality were evaluated during fermentation and 21 d of refrigerated storage. The optimized formulation achieved rapid acidification, desirable gel structure, rich ester and alcohol content, and high sensory scores (83/100), outperforming control and other experimental groups. Instrumental analyses (electronic nose/tongue) corroborated sensory results, indicating balanced taste and complex aroma. Throughout storage, physicochemical and microbial properties remained stable. This study demonstrates that regionally sourced LAB can enhance the technological and sensory quality of fermented milk. The selected isolates show promise for use in tailored starter systems, supporting innovation in functional dairy development.