Abstract :
[en] Fat in milk and cream is present as tiny droplets, which are enveloped by a thin membrane known as milk fat globule membrane (MFGM). This protective envelope appears as a complex assembly of proteins, lipids and other minor compounds. It originates from the plasma membrane of secretory cells of the mammary gland and contains cholesterol and cholesterol esters. MFGM has very important functional and nutritional properties, intervening in dairy technology as well as in the formulation of certain food products. Various studies on the surface properties of the MFGM have been carried out with a particular view to linking them to its techno-functional properties. While techniques for cholesterol reduction and milk fat fractionation have been developed or are under development, there does not appear to be any relevant scientific information on the effect of cholesterol removal on properties of the MFGM. The present work aimed to characterize the impact of MFGM fraction composition on the interfacial and techno-functional properties of MFGM, and to deepen the understanding regarding role of cholesterol. First, fractions of MFGM were extracted at different stages. Their chemical composition as well as their physicochemical properties were then characterized. Differences in composition were observed between the fractions, which affects the surface properties, both in adsorption kinetics, mechanical properties and rheological properties of the interfacial films. In an attempt to better understand specific interfacial properties of the various components of MFGM, their monolayers were characterized using a Langmuir film balance. Fractions of MFGM were separated into lipids (total and polar lipids) and defatted membrane. The interfacial properties of these components have been characterized at the air / water interface. The interfacial properties of MFGM and polar lipids were also characterized at the oil / water interface. By using the compression isotherm, the surface elasticity of the components of the MFGM were calculated. MFGM polar lipids have been found to have relatively high surface elasticity, confirming their potential to help stabilize food systems. Cholesterol was removed from MFGM using β-cyclodextrin (β CD) and methyl β-cyclodextrin (MβCD). The use of ß CD in dairy products is approved by many regulatory agencies around the world. A lower concentration of MβCD eliminated cholesterol more effectively from MFGM compared to ß CD. The properties of low-cholesterol MFGM were compared to the native MFGM. The lipid classes and fatty acid composition were found to be modified due to the removal of cholesterol, resulting in different surface properties of low- cholesterol MFGM. Emulsions were finally prepared using MFGM and low cholesterol MFGM. A relationship could be established between the values of equilibrium surface tension and the stability of emulsions vis-a-vis creaming. The lower the value of the equilibrium surface tension, the lesser is the creaming. Moreover, the stability of the emulsions obtained by whipping of the emulsions could be related to the elasticity modulus. The higher the elasticity modulus, the greater the stability of the whipped emulsions.
