A spectroscopic response factor-based toluidine blue assay towards a universal assay protocol for sulfated polysaccharides: Application to fucoidan content in crude extract

Sulfated polysaccharides (SPS) have attracted a lot of interest because of their diverse pharmacological functions. Numerous scientific studies have shown that SPS exhibit better biological activity than those that are not sulfated, such as immunomodulatory, anti-viral, and antioxidant activities. A crucial step to a better understanding of the mechanism of action and health effects is the production of high purity SPS. This calls for the development of selective assay techniques that can identify SPS preferentially without being influenced by other substances or the co-extracted polysaccharides. A universal modified toluidine blue (TB) assay was developed in this study to detect SPS. The assay procedures were conducted using different SPS standards including fucoidans from different biogenic sources, in addition to heparin and dextran sulfate. Spectroscopic response factor was calculated for each SPS which showed very good correlation (R2 = 0.998) with the corresponding sulfation degree. The proposed method was applied for determination of SPS content of crude fucoidan product using five different SPS standards. The method was cross validated by conducting ANOVA test to the obtained % recovery revealing that there is no significant difference between the results obtained by identical reference standard and four nonidentical natural SPS standards. This is the first report of a selective universal assay of SPS that enables the selective determination of SPS using a nonidentical reference standard.