Optical properties of oil-in-water emulsions containing titanium dioxide particles

The influence of titanium dioxide particles (d32=0.62 μm, φ=0–0.3 wt%) on the spectral reflectance and tristimulus color coordinates (L, a, b) of n-hexadecane oil-in-water emulsions (d32=0.29 μm, φ=0.25–20 wt%) was measured in the absence and presence of a red dye. There was a steep decrease in the spectral reflectance and ‘lightness’ of emulsions at droplet concentrations below 3 wt% and in titanium dioxide suspensions at particle concentrations below 0.1 wt%. In the absence of dye, dilute emulsions (φ<3 wt%) could be produced with approximately the same color (L, a, b) as concentrated emulsions by adding 0.1 wt% titanium dioxide. In the presence of dye, a higher concentration (>0.3 wt%) of titanium dioxide was required to match the color of dilute emulsions to concentrated ones. There was reasonable agreement between the measured optical properties of emulsions containing titanium dioxide and those predicted by light scattering theory. These results have important consequences for optimizing the appearance of emulsion-based products with reduced droplet concentrations, e.g. low-fat foods.