A new method for the quantification of polysaccharide structural domain: Rapid quantification of Rhamnogalacturonan-II by colorimetry

Abstract

Polysaccharides are important pharmacodynamically active components in traditional Chinese medicines and based on the type of monosaccharides and glycosidic linkages, they can be divided into different structural domains. Rhamnogalacturonan II (RG-II) is among the most complex and conserved structural domain within polysaccharides and possesses significant pharmacological effects. Nevertheless, there is no suitable method for quantifying homogeneous polysaccharides that contain the RG-II structural domain. In this study, a colorimetric method was developed to rapidly quantify this particular polysaccharide, utilizing the principle that the unique monosaccharides (Kdo and Dha) in RG-II were derivatized and reacted with thiobarbituric acid (TBA) to produce a pink substance with a maximum absorption wavelength at 548 nm. The method demonstrates excellent specificity, linearity, stability, reproducibility, accuracy, and sensitivity. It also features the advantages of simple operation, low instrument requirements, low cost, and time efficiency. The critical application of this method in polysaccharide quality control lies in comparing the contents of RG-II in polysaccharide samples from different sources. This method also serves as a potential tool for screening RG-II-rich traditional Chinese medicines and foods, simplifying the structural characterization of RG-II-type polysaccharides and study the quantity-effect relationship of these polysaccharides.