Comparison of Two Methods Detecting Lysozyme Adsorption to Oil-water Interface in the Presence of Surfactants

Purpose To compare the formation of the adsorbed lysozyme layer at the oil-water interface with two different methods and to scrutinize the possibilities of avoiding film-formation by addition of model surfactants. Methods Surface tension measurements were carried out using pendant drop (KRÜSS, Germany). An aqueous droplet of 70 mL was formed with a needle (diameter 1.83 mm) in a glass cuvette containing the oil-phase. Film formation was evaluated by withdrawal of the aqueous phase after 10 minutes emersion in the oil phase. Rheological properties were measured by use of a TA AR-G2 rheometer equipped with a double wall ring (DWR) geometry. The system consists of a ring and a Delrin® trough with a circular channel (interfacial areal=1882.6 mm²). Oscillatory shear measurements were conducted at constant frequency of 0.1 Hz, temperature of 25°C and the strain was set to 1%. Results The adsorption of lysozyme to the oil-water interface results in the formation of a flexible protein film. This formation can be prevented by addition of surfactants, in a manner that is dependent on the concentration and the type of surfactant. According to the rheological method the more hydrophilic surfactants are more effective in hindering lysozyme adsorption to oil-water interfaces whereas the hydrophobic surfactants seem to be more effective according to the surface tension measurements. According to the rheological method the larger surfactants are more persistent in preventing film formation whereas the smaller eventually give place for the lysozyme on the interface. Conclusion The two methods can be used to detect the interfacial adsorption of lysozyme and can be used to evaluate the performance of model surfactants in hindering film formation. This will aid in processing of any delivery systems for proteins where the protein will be introduced to oil-water interfaces that could affect the stability of the protein.