Ultrasonic spectroscopy study of relaxation and scattering in whey protein solutions

✍ Scribed by Bryant, Cory M; McClements, D Julian

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 134 KB
• Volume: 79
• Category: Article
• ISSN: 0022-5142
• DOI: 10.1002/(sici)1097-0010(199909)79:12<1754::aid-jsfa438>3.0.co;2-d

✦ Synopsis

Ultrasonic attenuation spectroscopy was used to investigate the in¯uence 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 ÐCO 2 H 6 ÐCO 2 À H and ÐNH 2 H 6 ÐNH 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 À8 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.