Interfacial Phenomena in the Evaluation of Antioxidants: Bulk Oils vs Emulsions

Antioxidants have been difficult to evaluate in oils and food emulsions due in part to the complex interfacial phenomena involved. Lipophilic and hydrophilic antioxidants were evaluated with corn oil stripped of natural tocopherols in bulk and in emulsion systems. Oxidation was followed by determining formation of hydroperoxides and hexanal. The lipophilic antioxidants alpha-tocopherol and ascorbyl palmitate were more effective in an oil-in-water emulsion system than in bulk oil, while the opposite trend was found for the hydrophilic antioxidants Trolox and ascorbic acid. The oil-insoluble ascorbic acid was a particularly efficient antioxidant in suspension in the bulk oil system. Mixtures of alpha-tocopherol and ascorbic acid were more active in bulk oil, while mixtures of alpha-tocopherol and ascorbyl palmitate were more efficient in emulsion systems. Differences observed in the efficiency of antioxidants may be explained by their affinities toward the air-oil interfaces in bulk oil and the oil-water interfaces in emulsions