Analysis of a complex polysaccharide (gum arabic) by multi-angle laser light scattering coupled on-line to size exclusion chromatography and flow field flow fractionation

Abstract : The heterogeneous polysaccharide gum arabic has been characterized using size exclusion chromatography (SEC) and flow field flow fractionation (F4) coupled on-line to multi-angle laser light scattering (MALLS). Two distinct populations have been shown. About 80% of the material consist of highly branched arabinogalactan (AG) units. The rest is mainly composed of heterogeneous arabinogalactan–protein complex (AGP) of high molecular weight. The F4/MALLS method is shown to allow the complete analysis of gum arabic whereas SEC gave only partial information. From light-scattering-based radii of gyration (Rg) and F4-based hydrodynamic radii (Rh) we found that the ratio Rg/Rh is near 0.8 for AGP. This value is reasonably consistent with a globular conformation and gives further evidence in favour of the “wattle blossom model” proposed by Connolly et al.