Surface viscosity of glycosylated derivatives of beta-lactoglobulin at the air-water interface

Surface viscosities of beta-lactoglobulin (beta LG) and glycosylated derivatives of beta LG were determined at the air-water interface using a rotational viscometer. The surface viscosity of 0.1% solutions increased rapidly during the first few minutes and then decreased slightly. Surface viscosity and rate of development of surface viscosity were maximum near the isoelectric point of beta LG. Glycosylation of beta LG decreased its rate of development and maximum surface viscosity. Apparently, surface viscosity was affected by decreased electrostatic repulsions and increased hydrophilic interactions, protein conformational stability and the interfacial concentration of beta LG. The shearing action of the viscometer probably contributed to surface viscosity by increasing the rate of protein adsorption and desorption and increasing the entanglement of proteins at the air-water interface. This study increases our understanding of the protein structure-function relationships in foams and emulsions.