Abstract: To investigate the effects of the molecular size and functional groups of polysaccharides on their iron chelation capacity, low-methoxyl pectin was subjected to combined enzymatic hydrolysis and sulfation modification. The modification conditions were optimized based on the release rate of iron under simulated gastrointestinal conditions. The physicochemical properties of pectin-iron complexes were characterized by evaluating hygroscopicity, molecular mass, and monosaccharide composition. Results demonstrated that enzymatic treatment and sulfation modification significantly enhanced the iron content, successfully producing a sulfated pectin-iron complex with iron content of (24.17 ± 0.18)%. This complex exhibited excellent iron release performance during in vitro digestion, achieving a maximum release rate of (96.06 ± 0.04)%. The iron complex exhibited strong hygroscopicity. Chromatographic analysis indicated the complex was primarily composed of galacturonic acid (GalA), glucose (Glu), galactose (Gal), arabinose (Ara), and rhamnose (Rha). Following chelation, the molar ratio of GalA was significantly reduced, while the weight-average molecular mass increased from 36.77 to 95.05 kDa. Furthermore, sulfation modification enhanced the antioxidant activity of pectin, but significantly reduced that of its iron complex (P < 0.05). In conclusion, this study provides a theoretical foundation and technical reference for developing polysaccharide-based iron supplements.

Key words: low-methoxyl pectin; enzymatic hydrolysis; sulfation modification; iron complex