α-Glucosidase inhibitory assay（5 mM PNPG，37℃， 30 min）
10 μL of α-glucosidase, 10 μL of 0.1 mg/mL Up, Up-3, Up-4, and Up-5, 80 μL of PBS buffer (0.02 mol/L, pH 6.8) and 10 μL of 5 mM PNPG were mixed in a 96-well plate, and then the mixture was incubated at 37℃ for 30 min. The presence of the product, p-nitrophenol (PNP) was monitored by measuring absorbance at 405 nm in a plate reader. Acarbose was used as a positive control. Reactions without inhibitor were also performed in parallel serving as controls. The PNP concentration was determined from a standard curve. The relative activity was expressed as a percentage of the PNP formation in the presence of acarbose or polysaccharides compared with that of the control reactions. Subsequently, the α-glucosidase inhibitory activity of acarbose, Up-3 and Up-4 at different concentrations (0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 1.0, and 2.0 mg/mL) were determined according to the method described above to calculate the IC50 value.
来源文献：Zhong QW, Zhou TS, Qiu WH, Wang YK, Xu QL, Ke SZ, Wang SJ, Jin WH, Chen JW, Zhang HW, Wei B, Wang H. Characterization and hypoglycemic effects of sulfated polysaccharides derived from brown seaweed Undaria pinnatifida. Food Chem. 2021 Mar 30;341(Pt 1):128148. doi: 10.1016/j.foodchem.2020.128148. Epub 2020 Sep 22. PMID: 33038776.
