Sequential Extraction and <i>In Vitro</i> Bioactivities of Polysaccharides Fraction from Mung Bean Meal Byproduct

Mung bean meal (MBM) is a byproduct of vermicelli production that is usually discarded as waste but has been shown to be a valuable source of functional food ingredients. This study focused on extracting polysaccharides from MBM, analyzing the structures of the two fractions, and assessing their biological activities <i>in vitro</i>. Crude polysaccharides were sequentially extracted and partially purified from mung bean powder using hot water, alkaline solution, amylase hydrolysis, and three-phase partitioning (TPP) to obtain a water-extracted polysaccharide (MBM-P1) and an alkaline-extracted polysaccharide (MBM-P2). Two mung bean meal polysaccharides were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR) analyses. The results revealed that MBM-P1 and MBM-P2 differed in their monosaccharide compositions and molecular weights. MBM-P1 was composed of rhamnose (67.80 ± 1.00%), galactose (24.79 ± 0.52%), and arabinose (7.41 ± 1.19%), with molecular weights of 7.89 ± 0.25 and 6.74 ± 0.22 kDa, while MBM-P2 contained galactose (80.99 ± 1.81%), rhamnose (13.72 ± 1.40%), and arabinose (5.29 ± 0.46%), with molecular weights of 93.92 ± 5.73 and 19.03 ± 1.20 kDa. MBM-P1 and MBM-P2 exhibited crystalline and semicrystalline structures, respectively. ¹H NMR analysis indicated that both polysaccharides contained β-configurations. TGA analysis indicated that MBM-P1 possessed a higher structural thermal stability compared to MBM-P2. Moreover, MBM-P1 exhibited notable antioxidant activity, while MBM-P2 effectively promoted the proliferation of <i>Lactobacillus casei</i>, highlighting distinct functional properties of the two polysaccharide fractions. Furthermore, MBM-P1 exhibited dual effects on NO production in RAW 264.7 cells, while MBM-P2 induced only an increase in NO levels, suggesting differential immunomodulatory activities between the two polysaccharide preparations. Overall, the results of this study suggest that MBM-P1 and MBM-P2 from an agro-industrial byproduct have potential as natural functional additives for use in food and pharmaceutical industries.