Ž . Effect of high-pressure treatment on rheology of oil-in-water emulsions prepared with hen egg yolk M. Anton a,  , N. Chapleau b , V. Beaumal a , S. Delepine b , ´ M. de Lamballerie-Anton b Abstract This study evaluated the potentiality of high-pressure treatment to stabilise microbiologically emulsions made with yolk without Ž . Ž causing destabilisation and gelation. The effects of two levels of treatment 200 or 500 MPa on the properties oil droplet size, . interfacial protein concentration and composition , the rheology, and the microbiology of yolk emulsions prepared at two pH Ž . values 3.0 and 7.0 were determined. Our results showed that, oil droplet size, interfacial protein concentration and composition were not altered by the high-pressure treatments. The rheological study demonstrated that high-pressure treatment induced a significant increase of viscosity in emulsions prepared at pH 7.0, whereas no obvious thickening was noticed in emulsions prepared at pH 3.0. Furthermore, as the protein concentration increased, the effect of high-pressure was more pronounced. Microbial analysis revealed that high-pressure treatment allowed an efficient reduction of the microbial charge of emulsions and that this effect was better at acidic pH than at neutral pH. Consequently, high-pressure treatment could be used to stabilise yolk emulsions in acidic conditions. Keywords: Yolk emulsions; High-pressure; Oil water interface; Rheology; Stabilisation Industrial rele  ance: High pressure treatment of heat sensitive products such as egg yolk emulsion at acidic pH leads to suitable reduction of the total microbial flora and thus stabilizing the product without sacrifices of physicochemical properties. The initiation of flocculation at neutral pH indicates the potential of the pH-pressure processing matrix for product development and optimization. 1. Introduction Hen egg yolk is an essential ingredient in a wide range of food emulsions, due to its excellent emulsify- ing properties and its satisfying organoleptic character-  istics. All yolk constituents low-density lipoproteins Ž . Ž . LDL , high-density lipoproteins HDL , phosvitin and  livetin have the capacity to adsorb at the oil  water Ž interface Shenton, 1979; Kiosseoglou & Sherman, 1983a; Chung & Ferrier, 1992; Anton, 1998; Anton & . Gandemer, 1999 . During adsorption, yolk constituents tend to form a strong film at the oil  water interface. It has been demonstrated that adsorbed lipids coming from lipoproteins do not play a major role in the Ž stability of yolk emulsions Mizutani & Nakamura, 1984, 1985; Bringe, Howard & Clark, 1996; Le Denmat, . Anton & Beaumal, 2000 . Conversely, adsorbed pro-