Isolation, purification, structural characterisation, and in vitro bioactivities of raspberry (Rubus idaeus L.) polysaccharides

This study explored the characterisation of polysaccharide fractions from raspberry (Rubus idaeus L.) and evaluated their biological activities in vitro. Raspberry polysaccharides (RAPs) were extracted using a complex enzymatic method and subsequently separated via a DEAE-Sepharose fast-flow column, resulting in two fractions: RAP-1 and RAP-3. Structural analysis revealed that RAP-1 consisted of rhamnose (5.00%), arabinose (28.80%), galactose (18.90%), glucose (26.60%), xylose (2.30%), mannose (4.20%), and galacturonic acid (14.10%), while RAP-3 comprised rhamnose (12.20%), arabinose (28.40%), galactose (16.90%), glucose (6.40%), xylose (2.80%), and galacturonic acid (33.40%). RAP-1 was identified as a neutral polysaccharide (molecular weight: 1.96 × 104 Da), whereas RAP-3 was an acidic polysaccharide (molecular weights: 7.66 × 104 Da and 3.05 × 104 Da). Tertiary structure analysis indicated that neither fraction exhibited a triple-helix structure. Antioxidant assays demonstrated that RAP-3 displayed superior antioxidant activity and hypoglycemic effects compared to RAP-1. Both fractions exhibited mixed inhibition types against α-glucosidase. These findings suggest that RAP-3 holds significant promise for applications in the pharmaceutical and functional food industries.