Processing of nanoemulsions
Laura Lee & Ian Norton, University of Birmingham
The purpose of this work was to compare the production of oil-in-water nanoemulsions using a Microfluidizer and a high pressure valve homogeniser (HPH) for food emulsions. This work systematically compares the variables that control the energy dissipation rate and final droplet size of the emulsion, namely: operating pressure, residence time (passes) in the high turbulence zone, emulsifier type and continuous and dispersed phase viscosities.
At viscosity ratio 50, equivalent to sunflower oil in water, both devices produced droplet sizes of approximately 110 – 130 nm. An increase in viscosity ratio to 100 showed an increase in droplet size for the HPH, however the droplet size in the Microfluidizer was unaffected by viscosity and therefore elongational flow is hypothesised to be present. Decreasing the viscosity ratio from 10 – 0.1 led to an overall decrease in d3,2 for both machines, with no observed minimum.
Studies on emulsifier type used in the formulation showed that the final droplet size is controlled by the emulsifier used. The anionic emulsifier, SDS, has shown that it can reduce the coalescence in the HPH and this has been explained to be from the electrostatic stabilisation of droplets. Other emulsifiers tested were Tween 20 and sodium caseinate.
This is the first attempt at comparing these two processes and this work provides a better understanding of the nano-emulsion formation in both the HPH and Microfluidizer with emphasis on the droplet break-up mechanisms present.