Ultrasonic spectroscopy study of relaxation and scattering in whey protein solutions

• Published in: Journal of the science of food and agriculture Vol. 79; no. 12; pp. 1754 - 1760
• Main Authors: Bryant, C.M, McClements, D.J
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.09.1999; Wiley; Published for the Society of Chemical Industry by Elsevier Applied Science
• Subjects: aggregation; Animal, plant, fungal and microbial proteins, edible seaweeds and food yeasts; binding; Biological and medical sciences; chemical reactions; Food additives; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Methods of analysis, processing and quality control, regulation, standards; molecular relaxation; protein; scattering; solutions; spectral analysis; spectroscopy; ultrasonic attenuation spectroscopy; ultrasonics; ultrasound; whey; whey protein; Conditioner; Ultrasonic spectrometry; Dairy plant by product; Food additive; Experimental study; Molecular relaxation; Sound scattering; Analytical method; Wave scattering; pH; Molecular aggregation; Aqueous solution; Whey protein; Physicochemical properties
• ISSN: 0022-5142; 1097-0010
• DOI: 10.1002/(SICI)1097-0010(199909)79:12<1754::AID-JSFA438>3.0.CO;2-D

Ultrasonic attenuation spectroscopy was used to investigate the influence of pH on fast chemical reactions and aggregation of whey proteins in aqueous solution. Ultrasonic attenuation spectra (1-100 MHz) of 2.5 wt% aqueous solutions containing either 'native' or 'alkali-denatured' proteins were measured as a function of pH (2-12). Peaks in the attenuation occurred at pH 2.8 and 11.6 due to proton transfer equilibria, ie -CO(2)H in equilibrium with -CO(2)- + H(+) and -NH(2) +H(+) in equilibrium with NH(3)+ respectively. Attenuation at other pH values was attributed to a hydration relaxation mechanism. Relaxation times for the equilibria were of the order of 10(-8) s. There was an additional attenuation peak at the isoelectric point of the proteins (pH 5) for solutions containing 'alkali-denatured' protein, which was due to scattering of ultrasound by aggregated proteins. The particle size distribution of the aggregates could be determined using ultrasonic scattering theory to analyse the attenuation spectra. Ultrasonic spectroscopy is an extremely valuable tool for probing the molecular characteristics of proteins in solution.