Modulating the interfacial concentration of gallates to improve the oxidative stability of fish oil-in-water emulsions

Distributions of a homologous series of gallic acid (GA) derivatives of increasing lipophilicity were determined in stripped fish oil-in-water emulsions. The distribution was determined by employing a kinetic method based on the reaction between the hydrophobic 4-hexadecylbenzenediazonium ions (16-ArN₂⁺) and the antioxidants (AOs), that allows to determine the partition constants between the oil-interfacial, P_O^I, and water-interfacial, P_W^I, regions of the emulsion. Results showed that the antioxidant activity of gallic acid and its derivatives was positively correlated with the percentage of AO at the interface. The percentage of butyl, octyl and dodecyl gallates in the interfacial region is similar but much higher than that of the other derivatives, showing the highest AO efficiency. When increasing the surfactant fraction, the percentage of all compounds at the interface increased but the emulsion stability decreased due to the dilution of AO at the interface region. Both butyl and octyl gallates were found the most suitable AOs to carry out fish oil-in-water emulsions protection. For maximum effectiveness, butyl and octyl gallate should be used with the lowest emulsifier volume fraction necessary to physically stabilize emulsions.