title: Competitive solubilization of cholesterol and phytosterols in nonionic microemulsions studied by pulse gradient spin-echo NMR.
abstract: The actual mechanism of cholesterol reduction by phytosterols is yet to be explored. One hypothesis states that cholesterol and phytosterols compete on the solubilization locus within gastric bile salt micelles. In this study competitive solubilization within microemulsions as vehicles for dietary intake of cholesterol and phytosterols was studied by pulse gradient spin-echo nuclear magnetic resonance. The loaded microemulsions undergo phase transitions as a function of dilution, the type of solubilized sterol, and the weight ratio of the cosolubilized sterols. Microemulsions containing 10-20 wt% of aqueous phase, show similar diffusivity of the oil and aqueous phases in all examined systems (excluding PS-loaded one) reflecting the minor influence of these solubilizates on the structure of the inner and the outer phases. The closeness of these structures enables the mobility of water molecules between them. Upon further dilution (>20 wt% aqueous phase), significant differences in decrease rate of the oil and increase of the water phases mobilities (occurring upon inversion), were detected within the studied systems. It was concluded that the solubilized sterols influence the structural transitions based on their location within the structures and their competitive solubilization. The phytosterols solubilized mostly in the continuous oil phase and between the surfactant tails. Cholesterol is solubilized in the vicinity of the surfactant headgroups and affects the surface curvature. In mixtures of cholesterol and phytosterols, structural changes are dictated mostly by the presence of the cholesterol.
authors.affiliation: Casali Institute of Applied Chemistry, The Institute of Chemistry, Givat Ram Campus, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Shoshana
authors.initials: S
authors.lastname: Rozner
authors.forename: Abraham
authors.initials: A
authors.lastname: Aserin
authors.forename: Nissim
authors.initials: N
authors.lastname: Garti
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D004655:Emulsions; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D044367:Phase Transition; D010840:Phytosterols / Q000737:chemistry*; D012995:Solubility
chemical_list: D004655:Emulsions; D008823:Micelles; D010840:Phytosterols; D002784:Cholesterol