Ultrasound-assisted enzymatic extraction, characteristics, and biological activities of Benincasa hispida peel polysaccharides and their metal complexes

As an abundant agricultural by-product, Benincasa hispida (BH) peels hold untapped potential as a polysaccharide source, yet their composition, functional properties, and modification strategies remain underinvestigated. In contrast, research on polysaccharide-metal complexes lacks systematic comparisons of metal ion-specific effects. In this study, an acidic polysaccharide (UE-BHPP-2) was obtained via an ultrasound-assisted enzymatic extraction (UE) method, enhanced yields by 316.57 % over traditional heat reflux extraction. Polysaccharide complexes with zinc (UE-BHPP-2-Zn), iron (UE-BHPP-2-Fe), and selenium (UE-BHPP-2-Se) were prepared, with metal contents of 12.09 ± 1.95, 92.30 ± 5.04, and 0.94 ± 0.04 mg/g, respectively. The results showed that the complexes exhibit metal-specific antioxidant and hypoglycemic activities. At a concentration of 5 mg/mL, the ⋅OH scavenging activity and α-amylase inhibitory activity of the UE-BHPP-2-Zn complex were increased by 17.0 % and 2.83 %, respectively, compared with those of UE-BHPP-2. Furthermore, the complexes demonstrated good potential for trace element delivery in simulated digestion. This study confirms that metal ion complexation serves as a highly efficient strategy for polysaccharide functionalization, thereby offering a novel approach to the development of bifunctional materials that integrate dual properties of biological activity and trace element supplementation capacity.