Comparison of the effects of three different phosphatidylcholines on casein-stabilized oil-in-water emulsions

Soy oil-in-water emulsions, stabilized by casein, but incorporating one of three different phosphatidylcholines (PC), namely egg-PC, di-palmitoyl phosphatidylcholine (DPPC) and di-oleyl phosphatidylcholine (DOPC), have been studied by photon correlation spectroscopy, light scattering, fast protein. liquid chromatography, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PACE). Egg-PC enhanced the stability of emulsions made with low casein concentration, and it competed for space with casein at the oil-water interface during the emulsification process, but no further displacement of protein was found. DPPC had little effect on emulsion stability nor did it show a detectable competition at the interface with casein during or after emulsification. DOPC, however, not only competed with casein at the interface during emulsification, it also removed casein from the interface during storage of the emulsion. The displacement of casein caused instability of the emulsions. Adding DOPC to emulsions also led to displacement of casein from the interface and caused instability of the emulsion, but the process was much slower and occurred to a smaller extent compared to emulsions prepared with DOPC. The different behavior of egg-PC, DPPC, and DOPC on the oil-water interface was in good agreement with their relative solubility in the oil phase as measured by spectrophotometry. All three lipids modified the hydrodynamic thickness of the adsorbed casein layer corresponding to their modification of the surface concentration of casein.