Synbiotic formulation of fermented yak milk by Lacticaseibacillus paracasei YT805 and inulin and its efficacy on gut microbiota modulation

This study developed a synbiotic fermented yak milk (F3) by integrating Lacticaseibacillus paracasei YT805 with inulin and evaluated its physicochemical, textural, and functional properties compared to probiotic (F2; L. paracasei YT805 without inulin) and control (F1; commercial starter culture only) fermented milks. Results demonstrated that F3 exhibited significantly higher water-holding capacity (55.17% vs. 49.14% in F1) and total solids (33.19% vs. 26.95% in F1) on day 0. Microstructural and circular dichroism analyses revealed a denser, homogeneous protein network in F3, characterized by reduced surface hydrophobicity (43.35% vs. 69.11% in F1) and increased β-sheet content (40.12% vs. 18.35% in F1). Texture profiles indicated improved elasticity (4.79 N vs. 0.93 N in F1) and chewiness (3.33 N vs. 0.96 N in F1), alongside reduced hardness. After 21 days of storage at 4°C, F3 retained 6.17×10 8 CFU/mL lactic acid bacteria, with L. paracasei YT805 viability maintained at 4.33×10 7 CFU/mL. Inulin content decreased by 27.22% during storage but remained sufficient to support YT805 activity. Volatile compound diversity increased in F2 and F3, notably with elevated esters, ketones, and terpenes, while sulfur-containing off-flavor compounds decreased. In vitro fermentation of F3 significantly altered gut microbiota composition, enriching Acidaminococcus , Megasphaera , Megamonas , and Parabacteroides —genera linked to short-chain fatty acids (SCFAs) production. Correspondingly, SCFAs levels (acetic, propionic, butyric acids) increased by 25 - 90%, highlighting F3’s ability to enhance gut health. These findings demonstrate that synbiotic fermented yak milk, combining YT805 and inulin, is a promising functional food for modulating gut microbiota while maintaining desirable sensory and physicochemical qualities. • Developed synbiotic fermented yak milk (F3) with L. paracasei YT805 and inulin. • F3 enhanced protein network stability and volatile flavor diversity. • F3 maintained LAB ≥10 7 CFU/mL and inulin content after 21-day storage at 4°C. • F3 modulated gut microbiota, enriching SCFA-producing genera, elevating SCFA levels. • F3 validated as a gut health-promoting food and stable dairy product.