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In this study, five Fucus vesiculosus polysaccharides (FVPs; FVP-2, FVP-4, FVP-7, FVP-10, and FVP-13) were extracted by different pH, and their physicochemical characteristics and α -glucosidase inhibitory activity were investigated. Results showed that extraction pH significantly affected the chemical composition, molecular weight, zeta potential, structure characterization, and rheological property of FVPs. The viscosity consistency index of Fucus vesiculosus polysaccharides at high concentration (40 mg/mL) were ranked in decreasing order as FVP-10 > FVP-4 > FVP-7 > FVP-2 > FVP-13, which was strictly in accordance with the order of Mw. Among the five polysaccharides, FVP-13 showed the strongest α -glucosidase inhibitory activity, which might be related to its the lowest Mw and relatively higher xylose content. Fluorescence quenching analysis indicated that the interaction of FVPs and α -glucosidase was predominated by a dynamic mechanism. Thermodynamic analysis showed that the main driving forces for the interaction was hydrophobic interaction. Circular dichroism spectrum analysis found that FVPs could induce the secondary structure of α -glucosidase changes like the decrease of β -sheet content and the increase of β -turn and random coil content to inhibit α -glucosidase activity. These results suggested that extraction with high pH was an efficient method to obtain FVPs with strong α -glucosidase inhibition activity. • Five Fucus vesiculosus polysaccharides were obtained at different extraction pH. • FVP-13 showed the stronger α -glucosidase inhibitory activity. • The α -glucosidase inhibitory mechanism of polysaccharide was studied. • Hydrophobic interaction played a key role in the bonding of FVPs to α -glucosidase. [ABSTRACT FROM AUTHOR]