Ultrasonic spectrometry study of the influence of temperature on whey protein aggregation

Ultrasonic attenuation spectroscopy was used to investigate the influence of pre-treatment temperature on the formation of pH-induced particulate aggregates in aqueous native and alkaline-denatured whey protein solutions. Ultrasonic attenuation spectra (1–150 MHz) of 2.5 wt.% whey protein solutions were measured over a pH range of 2–12 using whey solutions, which were previously heated at temperatures ranging from 30 to 90°C. There was a large temperature dependent increase in attenuation around the isoelectric point of the proteins (pH 3–5.5), which was caused by scattering of ultrasound by increased protein aggregation. A maximum in attenuation was observed at 80°C. The particle size distribution and concentration of the aggregates was determined using ultrasonic scattering theory. A loss of large particles (10 μm) was detected upon heating. Ultrasonic spectroscopy was shown to be a valuable tool for studying aggregation of proteins in solution.