Structure of gum arabic in aqueous solution

Gum arabic, a natural polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees, is a commonly used food hydrocolloid. The complex chemical structure of the gum has been widely studied revealing a multifraction material consisting mainly of a highly branched polysaccharide and a protein-polysaccharide complex (GAGP) as a minor component. This work investigates its mesoscopic structure in aqueous solution by small-angle X-ray and neutron scattering combined with cryotransmission electrons microscopy. Scattering measurements reveal an intricate shape composed of many spheroidal aggregates assigned to the polysaccharide with a small amount of larger coils. A scattering peak is observed at moderate to high concentrations, the spacing of which exhibits a c(-1/3) power law relation to polymer concentration (c). Upon addition of salt, this peak disappears, indicating its electrostatic nature. The large coils contribute a q(-2) power law at the low scattering vector (q) range. However, at low concentration in which the interaggregate peak is not observed, a q(-1) power law at the low q range indicates the possible existence of a fraction with a locally extended conformation. (c) 2006 Wiley Periodicals, Inc.