Ultrasonic effect on physicochemical and functional properties of α-lactalbumin

Ultrasound is the sound whose frequency is too high for humans to hear which is within the frequency range of 20 Hz-20 kHz, and the frequency of ultrasound is above 20 kHz. The aim of this study was to observe the effect of ultrasound and sonication on alpha-lactalbumin (alpha-LA) with a view to improving its physicochemical and functional properties. In this work both low-intensity ultrasound (500 kHz bath) and the high-intensity ultrasound (20 kHz probe and 40 kHz bath) were used. Ten per cent wt (g g(-1) dry matter) protein model suspensions of alpha-lactalbumin (alpha-LA) were treated with ultrasound probe (20 kHz for 15 and 30 min) and ultrasound baths (40 kHz and 500 kHz for 15 and 30 min). Changes in pH values, electrical conductivity, solubility measurements, foaming properties, as well as theological and freezing-thawing properties have been examined. The protein fractions of alpha-lactalbumin were analyzed before and after ultrasound treatment by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The result showed that pH did not change significantly upon ultrasound however conductivities increased significantly after 20 kHz sonication. Electrical conductivity decreased significantly for ultrasound treatments in baths at 40 kHz and 500 kHz for all samples. Solubility increased significantly for all samples at 20 kHz. Foam capacities and foam stabilities were improved after ultrasound treatments for both 20 kHz and 40 kHz treatments. Foaming properties were not improved for protein model suspensions for 500 kHz treatments. The molecular weight of the protein decreased significantly after ultrasound treatments both using a 20 kHz probe and 40 kHz bath. The flow behaviour of alpha-lactalbumin was observed to be shear-thickening after all treatments. Apparent viscosity data calculated with power law equation (R-2 = 0.983-0.999) have not been changed significantly after all treatments. A remarkable decrease of initial freezing point was obtained after 20 kHz treatments. (C) 2009 Elsevier Ltd. All rights reserved.