Rheological behaviour of emulsions of avocado and watermelon oils during storage

Rheological properties of emulsions made out of avocado pulp and watermelon seed oils with whey protein concentrate were determined during different storage periods. The oils, as well as the emulsions behaved like non-Newtonian liquids, having shear-thinning characteristics. Both oils showed moderate shear-thinning characteristics as the flow behaviour indices were between 0.86 and 0.88. The shear-rate/shear-stress data could be adequately fitted (r = 0.997–0.999) to a common rheological equation, e.g. the power-law model. Avocado pulp oil was markedly more viscous than was watermelon seed oil which was also evident from the higher apparent viscosity and consistency index values.The rheological parameters during storage did not significantly change flow parameters, e.g. flow behaviour and consistency indices and apparent viscosity. The values of different droplet sizes and their distribution patterns, as evident from phase contrast microscopy, were considered almost unimodal (i.e., between 2 and 10 μm). Such a narrow range of variations in the particle diameters may not markedly influence particle behaviour. Cream and serum separation of emulsions were not noticed during storage, indicating that the stability of these two emulsions was not affected during storage for up to 2 months at room temperature.