Sequential Extraction and In Vitro 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 in vitro. 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 Lactobacillus casei, 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.