Fermentation method outweighs geographic origin in shaping kefir's in vitro anti-obesity potential and probiotic properties

Kefir is a traditional fermented dairy product containing diverse microbial consortia with potential health benefits. However, systematic comparisons of fermentation methods and grain origins on kefir's functional properties remain limited. This study selected kefir grains from eight geographic regions worldwide and prepared kefir fermented milk using both kefir grain fermentation (KGF) and back-slopping fermentation (BSF) methods. The in vitro anti-obesity potential and probiotic characteristics were evaluated, and multidimensional analysis was employed to elucidate the influence of different fermentation methods and regional sources on functional properties. Results demonstrated that the fermentation method exerted a stronger influence than geographic origin. KGF generally yielded kefir with higher antioxidant capacity, stronger antimicrobial activity, and safer probiotic profiles, whereas BSF favored lactic acid bacteria proliferation and triglyceride reduction. These findings emphasize that changes in fermentation strategy reshape the microbial community structure, thereby influencing the functional quality and probiotic properties of kefir. Consequently, KGF is recommended as the optimal strategy for producing kefir with enhanced health-promoting properties and superior safety. • Fermentation method dominated kefir functionality, surpassing grain geographic origin. • KGF enhanced probiotic safety and anti-obesity activity compared with BSF. • KGF supernatants showed stronger antioxidant and pathogen inhibition capacities. • BSF favored LAB growth and triglyceride reduction but lacked E. cloacae inhibition. • TOPSIS scoring confirmed KGF as superior for health-promoting kefir production.