Determination of the adiabatic compressibility of bovine serum albumen in concentrated solution by a new ultrasonic method

New data are presented for the adiabatic compressibility of bovine serum albumen (BSA) over the temperature range 2–85°C and at pH 5, 6, 7 and 8. The relative impact of intrinsic and hydration contributions to the observed compressibility for BSA is estimated and shown to agree very well with general values for globular protein and with previous results for BSA. The compressibility manifests a maximum value in the regions where BSA is most stable, exhibiting a parabolic dependence on temperature with lowest values where it is least stable. These data are obtained with a novel technique that employs a commercial, low cost and automated pulse echo apparatus for the measurement of the speed of sound to an accuracy of 1 m s−1 and a precision of 0.1 m s−1. This requires the use of relatively high protein concentrations, typically of the order of 10 mg ml−1 upwards. The ultrasound data is analysed using a relation obtained from scattering theory that accounts for the multiple scattering of sound in concentrated systems. The technique has a data acquisition rate of 20 measurements per second and large quantities of high-quality data can be amassed, permitting the automatic scanning of the compressibility of a protein as a function of temperature for example. This makes it particularly appropriate for studying the behaviour of proteins and other large biomolecules in food.