The Fundamental Mechanism Research On The Effect Of Bile Salts Intervention On Tween Emulsion System

Bile salts are the main component of bile and are natural emulsifiers biosynthesized from cholesterol. They have many physiological functions, which include the promotion of digestion and absorption of lipids, regulation cholesterol metabolism, inflammation sterilization and thus to enhance immunity, and the protection of gallbladder. The function that can enhance esterase activity and then promote fat digestion and absorption is essential to human physiological and irreplaceable. We often need to add a certain amount of exogenous emulsifier in the food processing and production to ensure the quality of food and specific features. When through the stomach and then into the intestine, can these exogenous emulsifying system exist stable, will there be a synergistic interaction or interfacial adsorption layer replaced between exogenous emulsifiers and bile salts in the human body, will there be synergy when they are added together as direct food emulsifier, the discussion of these issues is the research background. The research on these issues will help further understanding the of mechanism of lipid digestion and adsorption, and will provide guiding significance of development food formulation and drugs which aid digestion.In this thesis, we used polysorbate(Tween) as emulsifier, preparing a stable emulsion first. We adopted optical microscopy, combined with rheometry, light scattering technology and fluorescence spectrum method to study the influence of bile salts on the emulsion stability and on the macro-structure of the interface, and further discuss the effect of solution environmental factors on the interaction. Then we further analysis the synergistic effect between the binary mixtures, revealing the interaction mechanism of bile salts-nonionic surfactant mixtures in the oil-water or air-water interface.(1) The study on the preparation and stability of Tween emulsionWe used the emulsion which is prepared in this chapter as an in vitro model to provide experimental basis for further study on the influence of bile salt on the emulsion stability. We used n-tetradecane as the oil phase, Tween20and60, respectively, as an emulsifier, adopted ultrasonic homogenizer to prepare emulsion. We determined the optimum ratio and the best emulsification method by measuring the particle size distribution and ζ, potential. The results showed that the best emulsion proportion is oil:3wt%, emulsifier:0.75wt%.(2) The influence of the involvement of bile salt on the Tween emulsion stabilityUsing the dynamic light scattering, rheological, and steady-state fluorescence spectroscopy, we examined the influence of bile salts on the emulsion interface properties, and combining with laser scanning confocal microscope, we investigated the change of micro-structure in the emulsion particle. The results showed that the concentration of bile salts has a great effect on the emulsion, when at low concentration, the droplet surface ζ potential values was decreased, but with the increasing concentration, the ζ potential value tends to be constant. This indicates that when at low concentration, bile salts may competed with the active substances Tween or inserted in the surface-active molecules to formation of mixed micelles by hydrophobic interaction. Moreover, we can see the higher stability at low bile salt concentration as well as the more negative electrophoretic mobility. And hydrophobic interactions is the major driving force. In addition, higher concentrations of sodium deoxycholate will cause the emulsion unstable. But the creaming stability mechanisms are different. The former mechanism may be:with the increasing concentration of sodium deoxycholate, Tween20will be displaced to form a precipitate or large droplets; latter mechanism may be due to the electrostatic repulsion and steric effect of sodium deoxycholate cause the particle repulsion to droplet flocculation, with the corresponding increasing of creaming layer. Results show that when at pH=2, the emulsion itself will be unstable, and there will be a creaming phenomenon when added sodium deoxycholate.(3) The study on the synergistic interaction and interface membrane micro-structure of bile salt-Tween binary mixturesUsing the conductivity and fluorescence probe, we studied the bile salt-Tween20interfacial properties, including the interface properties of the mixed film and synergistic interaction. It was found that there have synergy between mixtures, the main force is the hydrophobic interaction and hydrogen bonding interactions. For Tween20-sodium cholate mixed system, the molar ratio of a=0.7, the β interaction is maximum, the synergistic effect is the most obvious at this point; for Tween20-sodium deoxycholate mixed system, the molar ratio a=0.3,β value is maximum and the synergistic effect is the most obvious. Moreover, increasing the Tween-sodium deoxycholate molar ratio, the solution micro-polar and the aggregation number will be decreased. We infer that the hydrophobic force is the main driving force.