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

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.