Effect of phenolic antioxidants on the dispersion state and chemical stability of olive oil O/W emulsions

The effect of gallic acid, catechin and quercetin on physical and chemical stability of olive oil-in-water emulsions was investigated. These molecules, characterised by different polarity and antioxidant activity, showed different interface activity and efficiency in delaying lipid oxidation. Gallic acid contributed positively to stabilise the colloidal properties of the systems toward physical instability whilst showed a low activity towards secondary oxidation. Catechin showed an interfacial localisation which was reflected in the enhancement of primary oxidation and in the inhibition of secondary oxidation. Quercetin poorly partitioned in the aqueous phase and was proven not to slow down the bimolecular phase of auto-oxidation.Results confirmed that polarity is not the only parameter to determine efficiency of antioxidants in emulsions but other variables, such as its antioxidant activity in terms of capacity and rapidity in donating an hydrogen atom, can affect its protective role towards lipids auto-oxidation in emulsions.