Lipid oxidation in corn oil-in-water emulsions stabilized by casein, whey protein isolate, and soy protein isolate

Proteins can be used to produce cationic oil-in-water emulsion droplets at pH 3.0 that have high oxidative stability. This research investigated differences in the physical properties and oxidative stability of corn oil-in-water emulsions stabilized by casein, whey protein isolate (WPI), or soy protein isolate (SPI) at pH 3.0. Emulsions were prepared with 5% corn oil and 0.2-1.5% protein. Physically stable, monomodal emulsions were prepared with 1.5% casein, 1.0 or 1.5% SPI, and greater than or equal to 0.5% WPI. The oxidative stability of the different protein-stabilized emulsions was in the order of casein > WPI > SPI as determined by monitoring both lipid hydroperoxide and headspace hexanal formation. The degree of positive charge on the protein-stabilized emulsion droplets was not the only factor involved in the inhibition of lipid oxidation because the charge of the emulsion droplets (WPI > casein greater than or equal to SPI) did not parallel oxidative stability. Other potential reasons for differences in oxidative stability of the protein-stabilized emulsions include differences in interfacial film thickness, protein chelating properties, and differences in free radical scavenging amino acids. This research shows that differences can be seen in the oxidative stability of protein-stabilized emulsions; however, further research is needed to determine the mechanisms for these differences.