Effects of morphology and extraction procedures on the chemical, thermal and dielectric properties of ulvan polysaccharides

This study presents the first comparative analysis of ulvan polysaccharides extracted from two morphologically distinct Ulva species native to the Peruvian coast: Ulvan papenfussii (blade-like) and Ulvan nematoidea (filamentous). Ulvans were extracted under two different conditions (pH 7 and pH 13) to investigate the combined influence of species-specific morphology and extraction methods on their physicochemical and molecular properties. Regardless of species or extraction conditions, all ulvan samples exhibited complex, multimodal molecular weight distributions, most notably in U. nematoidea. Extraction at pH 7 produced ulvans with higher sulfate contents, with U. nematoidea displaying the highest levels. Structural and chemical characterization via FTIR revealed distinct differences in sulfate positioning and uronic acid content between the species. Thermal analysis (DSC) indicated higher glass transition temperatures in U. nematoidea, likely due to its elevated sulfate content. Dielectric relaxation spectroscopy demonstrated that both taxonomic origin and extraction conditions significantly influence ulvan molecular dynamics. These findings, interpreted through Havriliak-Negami and Vogel-Fulcher-Tammann-Hesse modeling, underscore the importance of algal morphology and processing conditions in shaping the structure–property relationships of ulvans. The results offer new insights into tailoring ulvans for applications as functional bio-based polymers.