Oil-in-water emulsion properties and interfacial characteristics of hen egg yolk phosvitin

Phosvitin is an egg yolk protein, constituted by 50% of serines, which are all phosphorylated. This singularity makes of phosvitin one of the most safety natural iron binding molecules. When hen egg yolk is used as emulsifying agent, the adsorption of phosvitin could alter this iron binding property. Consequently, this work was performed to better understand emulsifying and interfacial properties of phosvitin in optimal metal binding conditions. We have studied sunflower oil-in-water emulsions of phosvitin at pH 5 and 6, and ionic strengths of 0.05 and 0.15 M. The oil droplet size, the stability against coalescence and flocculation, the composition of the interfacial protein film and the interfacial activity at model interfaces were analysed. Finally, the capacity of phosvitin to bind iron when it is anchored at the emulsion interface was investigated. Phosvitin showed satisfactory emulsifying capacity in conditions favouring iron fixation. In these conditions, emulsifying activity is sensitive to pH whereas flocculation is influenced by ionic strength. Coalescence destabilisation is not extended and the interfacial protein film has better characteristics at pH 5. Phosvitin was not efficient to reduce the oil-in-water interfacial tension, although at 0.1 mg/ml the interfacial tension was reduced from 31 mN/m to 15 mN/m. The high iron binding capacity of phosvitin in solution is kept by interfacial adsorbed phosvitin. Finally, to explain the poor adsorption efficiency coupled with the suitable emulsifying properties of phosvitin and the preservation of the iron binding capacity, it is likely that phosvitin is anchored at the interface only by a tiny terminal portion, presenting the rest of the molecule solvated on the aqueous phase. (c) 2005 Elsevier Ltd. All rights reserved.