Optimized production of a probiotic exopolysaccharide and its application as a natural stabilizer in fermented milk

Exopolysaccharides (EPS) produced by lactic acid bacteria have gained increasing attention as clean-label stabilizers for fermented dairy products. However, limited production efficiency and insufficient understanding of structure-function relationships restrict their wider application. In this study, an EPS (GS-EPS) from Lactobacillus gasseri was produced under optimized fermentation conditions using single-factor experiments combined with response surface methodology, achieving a yield of 4.49 g/L. Structural characterization revealed GS-EPS to be a heteropolysaccharide with a relatively low molecular weight (14.1 kD) and mixed glycosidic linkages (α- and β-glycosidic linkages). Incorporation of GS-EPS into fermented milk markedly improved the physicochemical and textural properties, including increased firmness, viscosity, and water-holding capacity, alongside reduced syneresis and delayed post-acidification during storage, with 0.4 g/L identified as the optimal concentration. Spectroscopic analyses (Raman and FT-IR) revealed that GS-EPS supplementation was associated with detectable changes in protein structural features in fermented milk. These structural signatures were consistent with the observed improvements in macroscopic quality attributes, suggesting that GS-EPS contributes to the modulation of gel structure formation. Overall, this study demonstrates that GS-EPS represents an effective clean-label stabilizer capable of improving the quality and storage stability of fermented milk, providing practical insights for the development of EPS-based functional dairy products. • The optimal GS-EPS production occurred at 36 h, 31°C, 2 g/L maltose, and 1 g/L yeast peptone. • The addition of 4% EPS significantly enhances the fermentation quality of fermented milk. • The incorporation of EPS remodels the gel network structure of proteins in fermented milk.