Evaluation of in vitro simulated digestion and fermentation characteristics of the crude exopolysaccharide from Levilactobacillus brevis M-14.

The present study employed an in vitro static digestion model to simulate the saliva-gastrointestinal digestion and fecal fermentation of exopolysaccharides (EPSs) extracted from Levilactobacillus brevis M-14, aiming to understand the dynamic changes in physicochemical properties, biological potential of EPS, as well as their impact on the human enteric microorganism. EPS was mainly composed of polysaccharides. The molecular weight (M_w) showed that EPS comprised two parts with a high M_w and a low M_w fraction of 42.81 × 10⁴ and 1.23 × 10⁴ Da, respectively. EPSs mainly consisted of mannose, rhamnose, galacturonic acid, glucose, and galactose in a molar ratio of 0.42∶0.13∶0.21∶0.13∶0.11. In the simulated digestion process, EPS was relatively stable. Furthermore, simulated digestion increased the antioxidant and hypoglycemic capacities of EPS. During the fermentation stage, the total carbohydrate contents of EPS decreased by 20.19%. The M_w of the two components of EPS decreased by 16.37% and 61.67%, respectively, and accompanied by the production of free monosaccharides. EPS had the potential to modulate the composition of gut microbiota, increasing the relative abundance of Enterococcus and Parabacteroides, while decreasing the relative abundance of Bacteroides. The pH decreased and total short-chain fatty acids contents increased, especially acetic acid and propionic acid. This research provided valuable insights into the potential application of EPS as a prebiotic agent.