CHARACTERIZATION OF GUM FROM ACACIA-SENEGAL TREES OF DIFFERENT AGE AND LOCATION USING MULTIDETECTION GEL-PERMEATION CHROMATOGRAPHY

The chemical and physicochemical characteristics of eight authenticate d Acacia senegal gum samples from trees of varying age growing in Suda n have been investigated. The samples originated from the Kordofan reg ion in west Sudan which is the traditional source of the gum and from the new plantations established in the El Daley region in east Sudan. The monosaccharide compositions, protein and amino acid contents and o ptical rotation were found to be similar to values reported in the lit erature and there were no obvious trends observed with age or source o f the tree. The molecular mass distribution was determined by gel perm eation chromatography (GPC) using four different detection systems, na mely, UV absorbance, refractive index, photon correlation spectroscopy (PCS) and multiangle laser light scattering (MALLS). The weight avera ge molecular masses obtained by GPC agreed well with the values calcul ated from the intrinsic viscosity and varied for the individual sample s between 2x10(5) and 7.9x10(5). The highest values were obtained for samples from trees 15 years old. All samples were found to be polydisp erse (Mw/Mn = 1.3-1.8) and the GPC UV elution profiles demonstrated th e existence of three principal molecular mass components with molecula r masses of 14x10(6), 1.5-3.0x10(5) and 1.8x10(5). The radii of gyrati on, Rg, and hydrodynamic radii, Rh, obtained by GPC/MALLS and GPC/ PCS of all of the molecular species were found to be small relative to th eir molecular mass. The plot of log Rg against log molecular mass for each sample was linear with a slope of similar to 0.42 and the ratio o f Rg/Rh was consistently about 0.8 + /-0.2 nm. These findings were tak en as evidence of a highly branched globular structure consistent with the 'wattle blossom' model proposed for arabinogalactan protein compl exes generally. (C) 1998 Elsevier Science Ltd. All rights reserved.