Hétérogénéité des membranes lipidiques et propriétés mécaniques : des bicouches modèles aux membranes des globules gras du lait

Abstract : The milk fat globules are enveloped by a biological membrane, called MFGM, of highly complex composition and structure. Investigation of this membrane, in situ in milk, using confocal microscopy suggested that polar lipids with high transition temperature (Tm) form domains in gel or liquid-ordered phase, dispersed in a continuous fluid phase. From this observation, the aim of this project was to understand how the composition and organization of dairy polar lipids can modulate the elastic properties of the MFGM, in order to better control stability of the fat globules in the dairy industry. The mechanical heterogeneity created by the coexistence of phases was then characterized by AFM force spectroscopy using lipid bilayers models at low (TTm).In order to closely analyze the factors that direct membrane elasticity, force spectroscopy measurements were undertaken on curved liposome membranes, in combination with structural characterization by TEM and SAXS. We showed, in particular, that heterogeneity in acyl chain length and unsaturation made gel-phase milk sphingomyelin membranes less rigid than expected, although more rigid than a fluid phase membrane. This approach was finally applied to native milk fat globules, where mechanical heterogeneity was visible. However, elasticity values were somewhat different from those calculated on model systems, probably because of the presence of membrane proteins.
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Oumaima Et Thakafy. Hétérogénéité des membranes lipidiques et propriétés mécaniques : des bicouches modèles aux membranes des globules gras du lait. Alimentation et Nutrition. Agrocampus Ouest, 2017. Français. 〈NNT : 2017NSARB299〉. 〈tel-01814738〉

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