Modification of protein structure and functionality using high-intensity ultrasound

by 1976- Gu?zey, Demet

The objective of this study was to determine the effect of high intensity ultrasound on the adsorption kinetics of proteins. Protein solutions (3x10  M ) were treated with ultrasound at power intensity levels ranging from 5 to 35 Wcm and at temperatures ranging from 20 to 85 Æ C with treatment times ranging from 15 to 45 minutes. Also, the effect of pulsing versus continuous application on the ultrasound treatment was evaluated. Surface activity (adsorption and coverage) of proteins was investigated using a drop shape analysis tensiometer. The study consisted of three major parts. The results of the first part of this study showed that application of high intensity ultrasound increased the rate of adsorption of bovine serum albumin (BSA) at the air-water interface. The rate of adsorption increased as the sonication time increased. Ultrasound treatment increased the helical content as measured by CD and surface hydrophobicity measured using fluorescence spectroscopy. In the second part of the study, it was observed that the effect of ultrasound on the adsorption kinetics of BSA was related to the ultrasonic power level and temperature. CD data showed that thermal treatment caused a loss in helical content while ultrasound increased the helical content of BSA. When heat and ultrasound were applied together the loss in helical content of BSA was less pronounced than the loss caused by thermal treatment alone. In the third part of the study, ultrasound susceptibility of the food proteins, BSA, fatty acid free BSA, -lactoglobulin and lysozyme was investigated using drop shape analysis and CD. Lysozyme was the most sensitive protein studied followed by BSA, fatty acid free BSA and -lactoglobulin. The difference in the susceptibility of these proteins was attributed to the differences in their amino acid composition, molecular size and rigidity and secondary structure. The effect of ultrasound on the interfacial properties protein probably is due to the increased flexibility of protein molecules on small length scales. Dimerization of protein molecules with the newly exposed hydrophobic groups is another possible explanation. iii