The oxidative stability of oil-in-water (O/W) emulsions is highly dependent on the type of emulsifier. The purpose of this work was to investigate the specific role of the adsorbed emulsifiers on lipid oxidation of O/W emulsions. Emulsions of similar droplet size distribution stabilized by minimum amounts of proteins or surfactants were oxidized at 25 °C in the presence of equimolar iron-EDTA complex. The pH and the amount of emulsifier in the aqueous phase were also varied to investigate the role of the droplet charge and the emulsifier in the aqueous phase. Oxygen uptake, conjugated dienes (CD), and volatile compound formation demonstrated that the protein-stabilized interfaces are less efficient at protecting emulsified lipids against oxidation than surfactant-stabilized interfaces. The antioxidant effect of unadsorbed proteins was also confirmed.
Proteins often stabilize food emulsions and are also able to promote or delay lipid oxidation in complex systems. The purpose of this work was to investigate the relationship between metal ion availability and oxidative stability of oil-in-water emulsions stabilized by bovine serum albumin (BSA) or sodium caseinate (NaCas). Emulsions with similar and stable droplet size distributions were prepared with stripped sunflower oil (30 vol %) and protein solutions (20 g L(-)(1); pH = 6.5). In the absence of the water-soluble metal chelator EDTA, oxygen uptake, conjugated dienes, and volatile compounds developed faster in NaCas-stabilized emulsions than in those prepared with BSA. This effect is attributed to the chelating properties of NaCas and to electrostatic interactions that attract some metal ions at the interface where they could initiate lipid oxidation. When EDTA (100 muM) was present, oxidation was delayed to a greater extent in emulsions made with NaCas than in BSA stabilized emulsions. These conditions probably enabled NaCas to exert free-radical-scavenging activity.
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