Microwave-assisted extraction of an acidic polysaccharide from Ribes nigrum L.: Structural characteristics and biological activities

Microwave-assisted extraction of the polysaccharide from blackcurrant (Ribes nigrum L.) fruits (MBP) was optimized using response surface methodology (RSM). The yield of MBP was 10.59 % (w/w) under the optimal conditions of power (414 W), liquid to material ratio (31/1 mL/g), and the time (41 min). After purification using D4006 macroporous resin and Sepharose-6B column chromatography, a water-soluble acidic heteropolysaccharide (PMBP) was obtained with a molecular weight of 1.99 × 106 g/mol. PMBP was thermally stable and exhibited excellent rheological properties. Fourier transform infrared spectroscopy, gas chromatography and nuclear magnetic resonance analysis confirmed the presence of α-, β-pyranose and six main glycosidic linkages in PMBP. Scanning electron microscopy, atomic force microscopy, and X-ray diffraction studies demonstrated that PMBP was amorphous aggregates with irregular shape, porous, and smooth surface. Bioactivity assays revealed the notable antioxidant and hypoglycemic activities of PMBP. Moreover, PMBP was kinetically characterized as a competitive inhibitor for α-amylase and α-glucosidase.