17E-15

Proteins are used as emulsifiers to stabilize emulsion droplets against coalescence or flocculation. Ability of proteins to stabilize food emulsions may be improved by application of high-intensity ultrasound. However, the impact of solution pH on ultrasound-induced modification of interfacial activity food proteins has not yet been investigated

The objective of this study was to evaluate the effect of solution pH in combination with high-intensity ultrasonication on the adsorption kinetics of BSA.

BSA solutions were adjusted in pH to 2-12 using HCl and NaOH. Solutions were sonicated for 0, 15, 30, 45 and 60min. at an ultrasonic intensity of 20.6Wcm^-2. A drop shape tensiometer was used to measure the adsorption kinetics of BSA solutions at the air-water interface. Free sulfhydryl content was determined using a spectrophotometric assay.

High-intensity ultrasound generally enhanced surface activity i.e. surface tension decreased more rapidly with time after sonication regardless of pH value. Sonication of protein solutions at acidic pH enhanced surface activity of protein solutions more significantly than sonication of neutral or basic pH values. Sonication of BSA solutions at pH 4 for 45min. increased rate of adsorption by 18.5% more than sonication of BSA solution at pH 7 and equilibrium surface tension (i.e. surface tension after completion of adsorption) was significantly lower (45mN/m versus 55mN/m). Free sulfhydryl content generally decreased as a function of sonication time. However, free sulfhydryl content of acidic solutions was significantly higher than basic ones after sonication. BSA solutions that were sonicated for 60min. at pH 6 had 1.85x the amount of free sulfhydryl than at pH 8. Results were attributed to cavitation-induced formation of radicals which may alter BSA structure and functionality as a function of solution pH.

Results suggest that efficiency of high-intensity ultrasound to modify protein structure and functionality depends on solution pH and increases in acidic systems.