Ultrasonic preparation of stable flax seed oil emulsions in dairy systems – Physicochemical characterization

This study reports the incorporation of 7–21% of flax seed oil in pasteurized homogenized skim milk (PHSM) using high intensity ultrasound (US) at 20 kHz between 1 and 8 min and at varying power levels. A minimum process time of 3 min at an applied acoustic power of 176 W was sufficient to produce emulsion droplets (7% oil) with an average mean volume diameter of 0.64 μm and they were stable at least 9 days at 4 ± 2 °C. The mechanical, cavitational and cavitation-after-effects of US are responsible for the production of smaller sized emulsion droplets and process-induced modifications of milk proteins. A very small proportion (less than 20%) of partially denatured whey proteins provided stability to the emulsion droplets. The emulsion droplets also showed a surface potential of about −30 mV due to the adsorbed proteins, which provided further stability to the emulsion droplets due to electrostatic repulsion. In order to see if other high shear techniques can generate stable emulsions, experiments were carried out using Ultraturrax (UT) at similar energy densities to that of US. UT did not produce stable emulsions until 20 min of processing suggesting the superiority of US emulsification process.