Ultrasound assisted synthesis of stable oil in milk emulsion: Study of operating parameters and scale-up aspects

In the present work, application of ultrasound and stirring individually or in combination for improved emulsification of turmeric oil in skimmed milk has been investigated. The effect of different operating parameters/strategies such as addition of surfactant, sodium dodecyl sulfate (SDS), at different concentrations, quantity of oil phase, applied power, sonication time and duty cycle on the droplet size have been investigated. The stability of emulsion was analyzed in terms of the fraction of the emulsion that remains stable for a period of 28 days. Optimized set of major emulsification process variables has been used at higher emulsion volumes. The effectiveness of treatment approach was analyzed based on oil droplet size, energy density and the time required for the formation of stable emulsion. It was observed that the stable emulsion at 50 mL capacity with mean droplet diameter of about 235.4 nm was obtained with the surfactant concentration of 5 mg/mL, 11% of rated power (power density: 0.31 W/mL) and irradiation time of 5 min. The emulsion stability was higher in the case of ultrasound assisted approach as compared to the stirring. For the preparation of stable emulsion at 300 mL capacity, it was observed that the sequential approach, i.e., stirring followed by ultrasound, gave lower mean droplet diameter (232.6 nm) than the simultaneous approach, i.e., ultrasound and stirring together (257.9 nm). However, the study also revealed that the simultaneous approach required very less time (15 min) to synthesize stable emulsion as compared to the sequential approach (30 min stirring and 60 min ultrasound). It was successfully demonstrated that the ultrasound-assisted emulsification in the presence of SDS could be used for the preparation of stable turmeric oil-dairy emulsions, also providing insights into the role of SDS in increasing the stability of emulsions and of ultrasound in giving lower droplet sizes.