Abstract
The aim of this study was to observe the effect of ultrasound on particle size and molecular weight of whey proteins. In this work high-intensity ultrasound (20 kHz probe and 40 kHz bath) were used. 10 wt.% protein model suspensions of whey protein isolate (WPI) and whey protein concentrate (WPC-60) were treated with ultrasound probe (20 kHz for 15 and 30 min) and ultrasound bath (40 kHz for 15 and 30 min). The results of particle size distribution have shown that, after treatment with an ultrasonic probe of 20 kHz, ultrasound caused a decrease in particle size, narrowed their distribution, and significantly increased the specific free surface in all samples. After treatment with ultrasonic bath of 40 kHz, there was a significant reduction in the size of particles. After treatment with probe of 20 kHz there was a significant decrease in molecular weight and protein fractionation. Ultrasonic bath treatment with 40 kHz ultrasound also showed significant changes in the composition of the molecular weight of protein fractions. Prolonged treatment of WPI with ultrasonic bath of 40 kHz encourages the formation of aggregates of molecules.
1. Introduction
Ultrasound frequency can mainly be classified into two fields: high frequency low energy diagnostic ultrasound in the MHz range, and low frequency high-energy power ultrasound in kHz range. The high frequency ultrasound is usually used as an analytical technique for quality assurance, process control and non-destructive inspection, which has been applied to determine food properties, to measure flow rate, to inspect food packages, etc. (Floros and Liang, 1994; McClements, 1995; Mason et al., 1996; Mason, 1990).
4. Conclusions
In this study the effect of ultrasound treatment on particle size distribution and molecular weight were studied. Ultrasound caused significant changes in particle size and molecular weight of whey proteins. The results of particle size distribution have shown that, after treatment with an ultrasonic probe of 20 kHz, ultrasound caused a decrease in particle size, narrowed their distribution, and significantly increased the specific free surface in all samples. After treatment with ultrasonic bath of 40 kHz, there was a significant reduction in the size of particles, but not to the extent as treatment probe. Ultrasound-induced structural changes in proteins are associated with partial cleavage of intermolecular hydrophobic interactions, rather than peptide or disulphide bonds. After treatment with probe of 20 kHz there was a significant decrease in molecular weight and protein fractionation. Ultrasonic bath treatment with 40 kHz ultrasound also showed significant changes in the composition of the molecular weight of protein fractions. Prolonged treatment of WPI with ultrasonic bath of 40 kHz encourages the formation of aggregates of molecules.
