Antioxidant activity of phenolic compounds in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose

The aim of this work was to study the evolution of oxidation and the efficiency of phenolic antioxidants in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose (Cas‐Lac) or stabilized by Tween‐20 (T‐20). Two groups of phenolic antioxidants which are structurally similar were tested, i.e. (1) α‐tocopherol and its water‐soluble analogue, Trolox; and (2) gallic acid and its ester derivatives propyl gallate and dodecyl gallate. Emulsion samples were oxidized at 40 °C and the progress of oxidation was followed through quantitation of oxidized triacylglycerol monomers, dimers and oligomers. Results showed that Cas‐Lac emulsions were more stable to oxidation than T‐20 emulsions. In both types of emulsions, the most protective antioxidants were the compounds of lower polarity, namely, α‐tocopherol and dodecyl gallate. It was also found that substantial amounts of α‐tocopherol coexisted with significant polymerization, which was indicative of the heterogeneity of oxidation, i.e. differences of oxidation rate in oil droplets.