Formation of nanoemulsions stabilized by model food-grade emulsifiers using high-pressure homogenization: Factors affecting particle size

Nanoemulsions are finding increasing utilization in the food and beverage industries for certain applications because of their unique physicochemical and functional properties: high encapsulation efficiency; low turbidity; high bioavailability; high physical stability. In this study, we examined the impact of system composition and homogenization conditions on the formation of nanoemulsions using a high-pressure homogenizer (microfluidizer). The mean particle diameter decreased with increasing homogenization pressure and number of passes, with a linear log–log relationship between mean particle diameter and homogenization pressure. The minimum droplet diameter that could be produced after 6 passes at 14 kbar depended strongly on emulsifier type and concentration: SDS < Tween 20 < β-lactoglobulin < sodium caseinate. Small-molecule surfactants formed smaller droplets than proteins, which was attributed to their ability to rapidly adsorb to the droplet surfaces during homogenization. The impact of phase viscosity was examined by using different octadecane-to-corn oil ratios in the oil phase and different glycerol-to-water ratios in the aqueous phase. The minimum droplet size achievable decreased as the ratio of disperse phase to continuous phase viscosities (ηD/ηC) decreased for SDS-stabilized emulsions, but was relatively independent of ηD/ηC for β-lactoglobulin-stabilized emulsions. At low viscosity ratios, much smaller mean droplet diameters could be achieved for SDS (d ∼ 60 nm) than for β-lactoglobulin (d ∼ 150 nm). The information reported in this study will facilitate the rational design of food-grade nanoemulsions using high-pressure homogenization methods.