Chemical composition of an effective emulsifier subfraction of gum arabic

Gum arabic, which is principally a mixture of polysaccharides and arabinogalactan-proteins (AGPs), contains trace levels of lipids. This report explores the hypothesis that these lipids are attached to the gum arabic AGPs as glycosylphosphatidylinositol (GPI) lipids, or in some other way, and make a significant contribution to the emulsifying properties of gum arabic. Treatment of gum arabic with nitrous acid, which cleaves the GPI oligosaccharide, decreased the emulsion stabilizing capacity of gum arabic. Treatment with 50% aqueous HF at 0°C also resulted in diminished emulsion stabilizing properties of gum arabic, but this effect could not be unambiguously attributed to lipid cleavage because the HF also caused other structural changes, as indicated by a significant reduction in arabinose content. The subfraction of gum arabic components (≈ 1-3%) that adsorb at the surface of oil droplets has a higher abundance of GPI linker components and much higher relative lipid content than the whole gum.