Physicochemical Properties and Immunomodulatory Activity of Exopolysaccharide Produced by Lactic Acid Bacteria in Fermented Mung Bean Porridge

To develop high-activity functional mung bean products, this study utilized mung beans as the raw material, and employed a high-viscosity lactic acid bacterial strain: Lactobacillus fermentum GBJ to prepare fermented mung bean porridge. The exopolysaccharides (EPS) present in the soup were extracted using a water-extraction and alcohol-precipitation method. The molecular weight, monosaccharide composition, functional groups, apparent morphology and thermodynamic stability of EPS were subsequently analyzed. Furthermore, RAW264.7 macrophages were employed as a model to investigate the immunomodulatory activity of EPS. The results indicated that the yield of EPS was 851 mg/L, with an average molecular weight of 1.25×10⁶ Da. The composition primarily included fucose, rhamnose, arabinose, galactose, glucose, xylose, galacturonic acid and glucuronic acid with a molar ratio of 0.33:3.16:33.43:21.00:16.45:9.27:15.31:1.05. Infrared spectroscopy, SEM, and thermogravimetric analysis revealed that EPS exhibited typical infrared absorption peaks of polysaccharides and possessed a sheet-like structure with good thermal stability. Immunomodulatory activity analysis demonstrated that EPS significantly promoted the proliferation and neutral red phagocytic capacity of RAW264.7 cells, as well as increased the secretion of NO, reactive oxygen species and cytokines in macrophages within a concentration range of 50~400 μg/mL. At a concentration of 200 μg/mL, the secretion levels of TNF-α, IL-1β, IL-6, and IL-10 in RAW264.7 cells reached their peak values, which were 2.00-fold, 1.69-fold, 1.20-fold, and 1.62-fold that of the control group, respectively. Furthermore, EPS was found to elevate the proportion of macrophage cells in the G2/M phase of the cell cycle while attenuating apoptosis and upregulating the mRNA expression levels of cytokines. These findings indicated that EPS isolated from fermented mung bean porridge could effectively enhance the immunological activity of RAW 264.7 cells. These studies may provide valuable data support for developing high-activity functional mung bean products.