Comparative analysis of the physicochemical and functional properties and in vitro hypoglycemic activities of Phlebopus portentosus polysaccharides extracted sequentially with hot water and alkali

Phlebopus portentosus (Berk. & Broome) polysaccharides have been extensively investigated, however, limited attention has been paid to the residues remaining after water extraction. In this study, P. portentosus polysaccharides (PBPs), including the water-extracted polysaccharides (HPBP) and the residue-derived alkali-extracted polysaccharides (APBP), were comparatively analyzed to elucidate differences in their physicochemical and functional properties, as well as their in vitro hypoglycemic activities. Both HPBP and APBP exhibited high glucose content (>85%) and similar characteristic infrared absorption peaks of polysaccharides. APBP had a higher molecular weight (4.15 × 10 4 kDa) than HPBP and displayed a thicker and smoother sheet-like network structure. APBP showed higher water-holding capacity (3.90 g water/g), oil-holding capacity (26.57 g oil/g), and emulsion stability (55.58%) than HPBP (3.40 g water/g, 21.34 g oil/g, and 49.83%, respectively). Rheological analysis indicated that APBP exhibited more pronounced elastic behavior than HPBP under the tested conditions. Moreover, APBP had a more pronounced effect than HPBP on the rheological properties of potato starch (PS), with higher apparent viscosity and greater changes in the dynamic rheological parameters of the PS system. Furthermore, under in vitro conditions, APBP showed higher α-glucosidase inhibitory activity and glucose adsorption capacity than HPBP, which may be associated with differences in molecular weight and apparent viscosity. This comparative and exploratory study suggests the potential value of alkali-extracted polysaccharides from water-extraction residues and may provide useful information for the comprehensive utilization of P. portentosus resources, although the potential structure–function relationships require further clarification.