Structural and Functional Properties of a Sulfated Polysaccharide Extracted from Mexican Red Algae

Sulfated polysaccharides from red algae are multifunctional hydrocolloids whose properties depend strongly on molecular structure, sulfate content, and chain conformation. In this study, a sulfated galactan extracted from Gracilaria vermiculophylla collected from a coastal region of northwestern Mexico was investigated to elucidate its structural and functional properties. The polysaccharide was extracted by enzymatic treatment and characterized by monosaccharide analysis, FTIR, 1D/2D NMR spectroscopy, and size-exclusion chromatography coupled with multi-angle light scattering and viscometry. The extracted polysaccharide exhibited high carbohydrate (97%) and sulfate (28%) contents, with galactose as the predominant monosaccharide. It showed a moderate molecular weight (Mw = 2.39 × 105 g/mol), a relatively narrow molar mass distribution (Mw/Mn = 1.23), a high intrinsic viscosity (420.9 mL/g), and an Rg/Rh ratio of 2.2, consistent with an expanded macromolecular conformation in solution. The sulfated polysaccharide also exhibited measurable antioxidant activity, particularly in the ABTS+ assay (IC50 = 31.8 ± 2.5 mg/mL) compared with the DPPH assay (IC50 = 51.1 ± 3.0 mg/mL), and showed Fe3+-responsive association, leading to the formation of microgel-like structures. These findings indicate that the sulfated galactan characterized in this study is a structurally complex and functionally active hydrocolloid with potential relevance for functional food systems and related biomaterial applications.