High-purity ulvan from Ulva ohnoi: green extraction and physicochemical insights into a biomedical polysaccharide

Ulvan is a sulfated heteropolysaccharide and the main component of the seaweed Ulva ohnoi. Its chemical structure is similar to that of fucoidan, chondroitin sulfate, and hyaluronic acid, which are used as drugs and in the development of drug delivery systems. This study aimed to develop an environmentally friendly method for extracting ulvan from Ulva ohnoi. The structure, morphology, and physical–chemical properties of ulvan were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), elemental analysis, X-ray fluorescence (XRF), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), hydrogen-1 nuclear magnetic resonance (1H NMR) and X-ray diffraction (XRD). Analysis of the results revealed a fibrous, semi-crystalline structure with regular pores, a yield greater than 25%, and a degree of purity greater than 94%. A search for chemical compounds revealed low protein and high sulfur content, mineral salts, and the absence of heavy metals. The results demonstrate that electromagnetic-assisted aqueous extraction (EAAE) efficiently obtained ulvan with a high degree of purity and potential for biomedical application.