Effects of acidity, temperature and emulsifier concentration on the distribution of caffeic acid in stripped corn and olive oil in water emulsions

We evaluated the effects of oil type, oil to water ratio, emulsifier concentration, acidity, and temperature on the distribution of caffeic acid, CA, in emulsions composed of stripped olive and corn oils, acidic water, and Tween 20. CA mainly distributes between the water and interfacial regions because it is sparingly soluble in oils, as demonstrated by auxiliary partitioning experiments in the absence of an emulsifier. The distributions of CA were determined in the intact emulsions from values of the partition constant between the water-interfacial region, P_W^I, determined under different experimental conditions. At any given pH, CA is mostly located in the interfacial region of the emulsion,  %CA_I > 50 % at the lowest emulsifier volume fraction, Φ_I = 0.005, and its percentage increasing upon increasing Φ_I with  %CA_I > 90 % at Φ_I = 0.04. At any given Φ_I,  %CA_I decreases substantially with increasing pH because of the ionization of the CA. Our results indicate that the main parameters affecting the distribution of CA are Φ_I and the acidity, while the nature of the oil, the oil to water ratio and temperature have only minor effects. Results should aid the understanding of how environmental conditions affect the distribution of phenolic acids in emulsions.