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.