Surface properties of hen egg yolk low-density lipoproteins spread at the air-water interface

Hen egg yolk is largely used as food ingredient notably because of its exceptional emulsifying properties. Low-density lipoproteins (LDL) are the main egg yolk constituent. LDL and particularly apoLDL are thought to control largely emulsifying properties of egg yolk-based products. Nevertheless, few studies have concerned the interfacial behaviour of these lipoproteins at the oil-water interface and nothing has been published about the air-water interface. Controversies still remain about LDL adsorption mechanism at the oil-water interface even if a widely spread theory suggests their breaking at the interface, allowing then their constituents to spread. The Langmuir film balance and atomic force microscopy (AFM) were used in this study in the aim to characterise LDL surface behaviour in dynamic conditions at the air-water interface. The understanding of LDL adsorption mechanism and surface organisation at the air-water interface should provide useful information about LDL behaviour at the oil-water interface. LDL and lipids extracted from LDL-neutral lipids, phospholipids and total lipids (mixture of the two previous species)-were spread at the air-water interface to clarify the role of each constituent in the lipoprotein film. Results clearly show that LDL are disrupted at the interface to release notably neutral lipids from the lipoprotein core, enabling then their spreading. Each lipid class has been identified on the LDL film isotherm and seems to behave independently and individually at the interface within the lipoprotein film. (C) 2003 Elsevier B.V. All rights reserved.