Chemical structure and inhibition on α-glucosidase of polysaccharides from corn silk by fractional precipitation

Aimed to explore different corn silk polysaccharide (CSP) fractions derived by ethanol precipitation on the physicochemical properties and biological activities, four fractions (CSP20, CSP40, CSP60, and CSP80) were obtained. CSPs consisted of mannose, galactose, arabinose, rhamnose, xylose, and glucose with different ratios, and exhibited different total sugar content, uronic acid content, protein content, and total phenols content. All fractions also showed different physical properties, such as molecular weight, intrinsic viscosity, particle size, and microstructure. Besides, CSP80 exhibited stronger antioxidant activity and alpha-glucosidase inhibitory activity than the other three fractions. Enzyme kinetic analysis suggested that CSP80 inhibited alpha-glucosidase by mixed type and reversible mechanisms, respectively. Fluorescence intensity measurements confirmed that the secondary structure of alpha-glucosidase was changed by the binding of CSP80. Isothermal titration calorimetry (ITC) results illustrated that the binding of CSP80 to alpha-glucosidase complex was spontaneous driven by enthalpy and hydrogen bonds played a major role in the binding.