Microwave-assisted extraction of polysaccharides from Moringa oleifera Lam. leaves: Characterization and hypoglycemic activity

Microwave-assisted extraction of Moringa oleifera Lam. leaf polysaccharides was investigated using a response surface methodology. The following conditions were found to generate an experimental yield of 2.96 ± 0.11%, which closely agreed with the predicted value of 2.89%: time 70 min, microwave power 700 W, temperature 70 °C and a liquid/solid ratio of 35 mL/g. After the MLPs were treated with graded precipitation of 40%, 60% and 80% (v/v) ethanol solution, the respective average molecular weight polysaccharide fractions, namely MLP-1 (9.68 × 103 kDa), MLP-2 (6.29 × 103 kDa) and MLP-3 (4.86 × 103 kDa), were obtained. These three fractions were composed of xylose, mannose, glucose, galactose and arabinose but with differing molar ratios. They had similar Fourier transform infrared spectroscopy but their surface morphology differed as determined by scanning electron microscopy. The Congo red assay indicated that the three fractions were not helical polysaccharides. The three polysaccharide fractions exhibited different rheological properties. MLP-1 exhibited pseudoplastic flow behaviors, while MLP-3 displayed near-Newtonian flow behaviors over the entire accessible frequency range. In addition, MLP-3 had stronger inhibitory effects on α-amylase and α-glucosidase than MLP-1 and MLP-2. The results suggest that MLP-3 has potential for the treatment of diabetes.