Dye affinity chromatography for fast and simple purification of fucoidan from marine brown algae
Fucoidan is a sulfated polysaccharide with promising pharmacological applications. Due to its medicinal properties, there is a demand for a separation technique that yields a high purification grade. Here, we present a novel purification tool for recovering fucoidan from the marine brown macroalgae Fucus vesiculosus. The developed method is based on amino-derivatized Sepabeads® EC-EA. The beads were modified with toluidine blue (TB), a thiazine derivative, to exploit the strong donor acceptor interactions between the cationic dye and the anionic polysaccharide. The adsorption kinetics and the binding capacity of the resin were analyzed. A Sips model was used to approximate the adsorption isotherm, resulting in a maximum capacity of 127.7 mg fucoidan per g adsorbent. Investigation of the effect of adsorption step's pH on purity and chemical structure was performed by TB and Fourier transform infra-red spectroscopy assays. Results showed that adsorption at pH 1 and 6 had negligible effects on fucoidan's chemical structure. However, purity was actually improved by 1.55- and 1.69-fold at pH 1 and 6, respectively, with an average yield of 5 g/100 g dried algae powder. In contrast, only a 1.46-fold increment was observed in fucoidan purified by the traditional method at pH 2, with a yield of 7.5 g/100 g dried algae powder. Furthermore, fucoidan purified by this method at pH 6 complies with, or even exceeds the quality of the commercially available (>95% pure) fucoidan (Sigma-Aldrich®) with respect to molecular weight and sulfur content. Therefore, dye affinity chromatography provides more advantages than the classically used techniques for fucoidan purification.