Interfacial properties and structural conformation of thermosonicated bovine serum albumin

Abstract

Aqueous Bovine Serum Albumin (BSA) solutions were treated with high-intensity ultrasound (20 W cm−2) for 15, 30 and 45 min at temperatures of up to 85 °C. The equilibrium and dynamic surface tension of native and ultrasonicated BSA at the air-solution interface was measured using drop shape analysis. The effect of ultrasound on the secondary structure of BSA was monitored by circular dichroism spectroscopy. Surface pressure of BSA at the air-solvent interface increased as a consequence of sonication treatment at 20 °C. Both the rate of surface pressure increase and the equilibrium surface pressure of sonicated BSA were significantly different than that of native BSA. Diffusion coefficients calculated from dynamic surface tension values using long-term and short-term solutions of the general adsorption model of Ward and Tordai increased upon application of ultrasound, e.g. Deff,shortterm≈5.2×10−9 m2/s for native BSA and Deff,shortterm≈2×10−8 m2/s for BSA solutions sonicated for 45 min. Deconvolution of circular dichroism spectra indicated a small but reproducible increase in helical content and a 22% decrease in unordered structure elements after 45 min of sonication. The increase in the rate of protein adsorption with ultrasonication was more pronounced at elevated temperatures. Above the denaturation temperature of the protein, both heat treatment and thermosonication were found to reduce helical content of BSA, e.g. from 61% for native protein to 31 and 40% for heat-treated and thermosonicated proteins at 85 °C, respectively. Results were attributed to an ultrasonically-induced modification of the molecular structure of BSA with increased intramolecular mobility and surface activity.