Gum arabic, also known as acacia gum, is a natural exudate harvested from the stems and branches of Acacia trees (primarily Acacia senegal and A. seyal), valued as a complex glycoprotein-polysaccharide for its emulsifying and stabilizing properties.
Molecular Structure
Gum arabic comprises three main fractions: arabinogalactan (AG, ~90%, Mw ~300 kDa, <1% protein), arabinogalactan-protein (AGP, ~10%, Mw 300–2000 kDa, 10–20% protein), and glycoprotein (GP, ~1%, Mw >2000 kDa, high protein). The core is highly branched arabinogalactan with β-(1→3)-galactose backbones bearing β-(1→6)-linked galactose side chains substituted by α-L-arabinofuranose, L-rhamnose, and 4-O-methyl-D-glucuronic acid; hydroxyproline-rich proteins form polyproline II helices enabling interfacial adsorption.
Extraction and Properties
Tapping Acacia trees yields nodules manually collected, dried, and milled into powder (pH 4.5, density 1.35–1.49 g/mL, solubility 43–48% in water). AGP's amphiphilicity creates viscoelastic films at oil–water interfaces, preventing droplet coalescence via steric and electrostatic repulsion; solutions exhibit low viscosity (shear-thinning), high stability (pH 2–9, heat to 100 °C), emulsifying capacity (~30%), and an odorless glassy appearance.
Biomedical Applications
Hydroxyproline glycosylation enhances solubility and bioactivity; AGP modulates immunity, lowers cholesterol via bile acid binding, and supports gut health as a prebiotic, with clinical evidence for renal protection and anti-inflammatory effects in inflammatory bowel disease models.
