Extraction, structural characterisation, antioxidant, and hypoglycaemic activity of polysaccharides from <i>Floccularia luteovirens</i>

This study systematically optimised the extraction process of <i>Floccularia luteovirens</i> polysaccharides (FLVP), establishing the optimal conditions as: power 400 W, temperature 52 °C, time 51 min, solid-liquid ratio 32:1 mL/g, and Ethylenediaminetetraacetic acid (EDTA) concentration 1.1 mg/mL. Three homogeneous polysaccharide fractions were isolated and purified: FLVP-I (124.327 kDa), FLVP-II (25.439 kDa), and FLVP-III (17.871 kDa). All three possess pyranose ring structures, with FLVP-I and FLVP-III containing both <i>α</i>- and <i>β</i>-glycosidic bonds, while FLVP-II exclusively contains <i>α</i>-glycosidic bonds. In antioxidant assays, FLVP-I exhibited the strongest activity, showing IC₅₀ values of 0.27, 0.31, and 0.21 mg/mL against DPPH, ABTS+, and hydroxyl radicals, respectively, and restored the viability of H₂O₂-injured HepG2 cells to 87.42%. For hypoglycaemic activity, FLVP-II was most effective, with IC₅₀ values of 0.29 and 0.22 mg/mL against <i>α</i>-amylase and <i>α</i>-glucosidase, respectively, and significantly promoted glucose consumption (8.02 mM) and hepatic glycogen synthesis (7.62 μg/mg protein) in insulin-resistant cells.