The effect of pH and salt on the stability and physicochemical properties of oil-in-water emulsions prepared with gum tragacanth

• The addition of NaCl does not significantly change the emulsion stability.
• Gum tragacanth-coated droplets are unstable near the isoelectric point.
• Confirmatory and complementary relationships between tests results were obtained.

The effect of pH (2.5, 4.0 and 5.4) and salt concentration (0.0, 0.5 and 1.0 wt%) on the physical stability of oil-in-water emulsions stabilized with gum tragacanth were investigated during 150 days of storage. Mean droplet diameter, zeta-potential, interfacial tension and steady-shear and dynamic rheological properties were determined to achieve more information about the likely stability mechanisms. The results showed that increasing salt concentration did not have a significant effect on emulsion stability. Emulsions were highly unstable at pH 2.5, with their emulsion-stability index declining almost three times more than that of other emulsions during the storage time. Based on the size distribution data, a direct correlation was not observed between droplet size distribution and emulsion stability. Rheological analysis revealed that pH 2.5 had the lowest apparent viscosity, storage modulus, energy of cohesion (EC) and a-value, and the highest tan δ and b-value.