Improving storage stability and antioxidant activity of yogurt using novel Exopolysaccharide-producing Lactobacillus fermentum SN4-1

To improve the storage stability and antioxidant activity of yogurt, an exopolysaccharide (EPS)-producing strain, Lactobacillus fermentum SN4-1, was isolated from traditional Qinghai yak yogurt, and the EPS biosynthetic pathway was analyzed via whole-genome sequencing. A novel EPS (EPS-2) from SN4-1 was purified by anion-exchange chromatography and characterized by HPLC, HPGPC, and FT-IR. SN4-1 was combined with a commercial starter, and its effects on yogurt quality during cold storage were evaluated. Results showed that EPS-2 mainly consisted of mannose, glucose, and galactose (molar ratio 5.93:1.19:1) with an average molecular weight of 40.3 kDa. SN4-1 contained an EPS gene cluster ( eps-2 ) and multiple probiotic-related genes. During cold storage, the EPS content in yogurt with SN4-1 peaked at 144.21 mg kg -1 on day 5. Accordingly, the yogurt exhibited higher hardness, adhesiveness, cohesiveness, and viscosity, with adhesiveness increasing by 198.81%. Its water-holding capacity was 10.35% higher than that of the control on day 15. Moreover, the yogurt demonstrated strong radical scavenging capacities (DPPH 89.49%, ·OH 76.32%, O 2 - 63.23%, ABTS ∙+ 90.14%). These findings highlight the potential of SN4-1 in developing stable, clean-label probiotic yogurt.