A NEW METHODOLOGY FOR STUDYING PROTEIN ADSORPTION AT OIL-WATER INTERFACES

A new methodology has been developed for studying the adsorption behav ior of proteins at oil-water interfaces. This technique employs the ra diotracer method for monitoring adsorption of C-14-labeled proteins at the oil-water interface. The uniqueness of the new method lies in the formation of a 1000 Angstrom thick triglyceride oil film on the water surface. beta-casein was used to generate a standard curve for relati ng interfacial radioactivity (mu Ci/m(2)) to cpm at the oil-water inte rface. Adsorption isotherm of beta-casein was determined in the bulk p rotein concentration range 1.5 x 10(-5)-3.8 x 10(-3)% by weight of sol ution. The saturated monolayer coverage was found to be about 7.3 mg/m (2). This value was quite different from other values reported in the literature. Adsorption studies with another protein, lysozyme, at the oil-water interface also revealed a high surface concentration of 3.0 mg/m(2). The most significant difference between the adsorption of bet a-casein at the oil-water and air-water interfaces was the lack of an induction period for the development of interfacial pressure in the fo rmer. This difference may be attributed to the attractive dispersion i nteraction between protein molecules and the oil phase. (C) 1998 Acade mic Press.