Exopolysaccharides from lactic acid bacteria as functional components for synergistic synbiotic formulations

Exopolysaccharides (EPS) produced by lactic acid bacteria are extracellular or surface-associated polymers that contribute to stress tolerance, technological performance in fermented foods and potential biological functionality. In this study, an EPS-producing strain of technological relevance, Leuconostoc mesenteroides MBm99, isolated from fermented vegetables, was investigated. The EPS was isolated, purified and structurally characterized by one- and two-dimensional NMR spectroscopy together with chromatographic analyses, allowing the determination of its monosaccharide composition, glycosidic linkages and key structural features. The functional characterization was focused on evaluating the potential of the purified EPS as a component of synergistic synbiotic formulations. Growth assays with selected probiotic strains were performed to assess whether the EPS could selectively support bacterial proliferation under controlled anaerobic in vitro conditions. The ability of the EPS to enhance probiotic survival during simulated gastrointestinal transit was evaluated using the standardized INFOGEST 2.0 digestion protocol. A strain of Limosilactobacillus reuteri and a strain of Lacticaseibacillus paracasei, administered alone or in combination with the purified EPS, were compared to determine the protective effect of the polymer during gastrointestinal digestion. Additional experiments evaluated probiotic persistence in human fecal matrices following simulated digestion, in order to estimate a potential protective effect under conditions approximating the intestinal ecosystem. The impact of the EPS on intestinal barrier function was further investigated using differentiated Caco-2 cell monolayers. Transepithelial electrical resistance (TEER) was monitored at different time points following treatment with the EPS alone or in combination with the selected probiotic strains to evaluate their potential synergistic effects on epithelial barrier integrity. Overall, this study provides a comprehensive structural and functional characterization of an EPS produced by a technologically relevant Leuconostoc mesenteroides strain and supports its potential application as a functional ingredient for the development of next-generation synbiotic foods and dietary supplements.