The Effect Of Bovine Serum Albumin On The Foam Properties Of Tweens Surfactants

Foam is an important disperse system used widely in life and industrial fields. Controlling the foam formation and stability are significant. A great deal of efforts has been spent in studying the character of foam films and exploring the certain correlation between interfacial properties and foam stability. The character of the adsorbed layer strongly influences the stability and physical properties of the resulting foams. The interactions of Tween surfactants and proteins have drawn much attention, due to the nontoxicity, easy accessibility, emulsification, solubilization of Tweens and other advantages. In this thesis, Tween20, Tween40and BSA are chosen as the main object for this study. The foam properties are investigated on a Foamscan (TECLIS-IT Concept, France) and the foamability, the liquid in the foam, foam stability, bubble size and distribution have been measured and analyzed. The optimal ratio of Tween20to BSA is determined for the most stable foams. Fluorescence and circular dichroism (CD) methods have been used to investigate the interactions between Tween20/Tween40and BSA.In the first section, the foam type, the factors that affect the foamability and foam stability, research methods, measured parameters and foam application are summarized. The properties of Tweens surfactants and BSA have been introduced. The recent developments and significance of this study about interaction between surfactant and protein are discussed.In the second section, the apparatus, measurement methods and data analysis of Foamscan and surface dilational rheometer are illustrated in detail. The principle and measuring condition of fluorescence and circular dichroism spectrum are stated.In the third section, the foam properties of Tween20and BSA have been investigated, and the surface properties and interaction of Tween20and BSA are studied via surface tension, dilational rheology, fluorescence and circular dichroism spectrum. The foam results show that, the foamability of Tween20, BSA and their mixtures in buffer solution increases gradually with increasing the solutes concentration respectively and the foamability of the single Tween20system is better than that of single BSA system. And the diameter of bubbles of all systems gradually becomes larger with time, and the bubbles with the irregular shape of single BSA system are bigger than those of the Tween20systems in which the shape of bubble gradually changes from a sphere to polyhedron with time. The maximum of the liquid volume in the foams generated from Tween20and the mixed systems is about20ml, while that of the single BSA system is only8ml. The t1/2values of Tween20and mixed systems first increase and then decrease with an increase of the Tween20concentration, while the t1/2values of BSA system increase gradually and almost come to a constant. And the maximum value of the t1/2of mixed systems in which the maximum t1/2appears at low Tween20concentration is larger than that of the single systems. Surface tension and dilational rheological measurements indicate that, Tween20and BSA molecules compete to adsorb at the air-water surface and no complex is formed. And the absolute modulus and surface dilational elasticity increase with increasing oscillational frequencies, while the viscous component decreases slightly. And the absolute modulus and surface dilational elasticity pass through a maximum value and then decrease with increasing Tween20concentration, while the viscous component passes through a minimum. And surface dilational elasticity is much bigger than viscous component, indicating the adsorbed layer is. elastic. And the mixed system of0.01g-L"1Tween20and0.01g-L-1BSA has the largest absolute modulus and surface dilational elasticity value, just according with the optimal system of the corresponding foam stability (The chosen concentrations of all systems in the dilational rheological experiments are100times less than that of relevant systems in the foaming experiments, keeping the same ratio of Tween20and BSA). The fluorescence spectrum measurements show the micropolarity of Tween20solution is decreased in the presence of BSA. Tween20molecules mainly interact with tryptophan residues of BSA and the BSA fluorescence is quenched. CD spectrum indicates the interaction of Tween40and BSA does not change the second structure of BSA. The interaction between BSA and Tween20by hydrophobic and weak electrostatic force and the formation of particular gel-like network with higher surface dilational elasticity will enhance the foam stability. In the fourth section, the foam properties, the aggregation behaviors at air-water surface, fluorescence and circular dichroism spectrum of Tween40and BSA systems have been investigated. The foam properties reveal that the single Tween40system has better foamability but faster drainage and unstable foams, while single BSA system has weaker foamability but lower drainage rate and more stable foams. When BSA and Tween40are used to generate foam, it is essential to control the relative quantities of the two species. An optimal ratio has been established for most stable foam. The optimal system is consisted of2.0g-L-1Tween40and0.05g-L-1BSA. Surface tension results show that BSA molecules at surface are gradually displaced by Tween40molecules due to competition in the adsorbed layer, and Tween40-BSA complexes have been formed. Surface dilational rheological behavior displays the absolute modulus and surface dilational elasticity gradually increase with increasing Tween40concentration. And the adsorbed films are elastic. The addition of BSA reduces the absolute modulus and surface dilational elasticity, while it improves the foam stability. The fluorescence spectrum results show that micropolarity of Tween40is decreased in the presence of BSA. Tween40molecules interact mainly with the tryptophan residues of BSA molecules, increasing hydrophobicity of the area surrounding those residues. Tween40has a static quenching effect on BSA fluorescence and shifts the maximum peak position to short wavelength. CD spectrum demonstrates Tween40does not change the second structure of BSA. For foam systems, the connected network increases the surface dilational elasticity and subsequently improves the foam stability. For surface rheology systems (the Tween40concentration is low), the formation of Tween40-BSA complex in the bulk will relatively reduce the surface concentration, resulting in the instability of the adsorbed...