Surface properties and bulk rheology of Sterculia apetala gum exudate dispersions

Exudate gums of Sterculia genus trees are known to have interesting thickening, emulsifying and stabilising properties. Surface tension measurements, dilatational surface viscoelastic properties and bulk rheology results support the idea that the gum exudate from Sterculia apetala is capable of adsorbing at surfaces and produces aqueous dispersions with enhanced viscosity and viscoelasticity. The rheological bulk characterization was performed as a function of gum concentration (0.5–3 w/v %) at 25 °C. Aqueous dispersions of S. apetala exudate gum exhibited flow properties at steady shear which changed from Newtonian to shear thinning in the concentration range studied. Furthermore, such dispersions showed gel-like viscoelastic behaviour above 2% w/v under small amplitude oscillatory shear measurements. Dynamic surface tension and surface viscoelastic properties were explored by means of the pendant drop method in the concentration range (0.1–3 w/v %) at 25 °C. The decrease in surface tension and the significant elasticity of the gum monolayer adsorbed suggest that S. apetala exudate gum may play the role of an emulsifier in O/W emulsions.