Batch and continuous lab ultrasonic emulsification processes were investigated using Tween 80 (low molecular weight surfactant) or pea protein isolate (PPI; high molecular weight biopolymer) as emulsifiers. The process parameters of processing volume, residence time and ultrasonic amplitude (i.e. acoustic power), as well as emulsion formulations, emulsifier type and concentration, were studied for the effect upon emulsion droplet size. Emulsions prepared with ultrasound yielded submicron droplets, ～150 nm, with Tween 80 and PPI, utilising both processing methodologies. Inverse power laws were obtained correlating emulsion droplet size (d_(3,2)) with respect to energy density (Ev), highlighting the efficiency of the continuous over batch processing. This efficiency is ascribed to the smaller processing volumes, associated with the continuous ultrasonic emulsification configuration. Longer processing times were required for PPI to achieve submicron droplets (< 200 nm) in comparison to Tween 80 as greater times are necessary for interfacial adsorption and surface stabilisation, as shown by interfacial tension measurements.
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