engleski

Physical properties of ultrasound treated whey protein suspensions with and without hydrocolloids addition

Ultrasound is a method of transferring energy of sound and vibrations into liquid medium. The frequencies usually used in food processing are in a range from 20 kHz to 2 MHz. The aim of this research was to investigate the effect of ultrasound treatment on the physical properties of several model systems prepared by mixing adequate amount of whey protein isolates (9.5 % w/w) with guar gum or methyl cellulose (0.5 %w/w), as well as with sucrose (10 % w/w) or milk powder (5 % w/w). Ultrasound treatments were performed with 30 kHz frequency probe set for 5 and 10 minutes. Before and after treatments foaming, emulsifying and rheological properties as well as freezing and thawing temperatures were determined. The results obtained have shown that ultrasound treatment of WPI suspensions as well as suspensions with guar gum or MC addition had no positive effect on the foaming properties. In the contrary, addition of sucrose or milk powder in WPI suspensions significantly increased foam volume and improved foam stability. Ultrasound treatment effected a decrease of emulsion activity and emulsion stability indices of all investigated model systems. The results of rheological properties determination have shown that all investigated model systems exhibit dilatant non-Newtonian properties. Viscosity of suspensions depended on their chemical composition (hydrocolloids, sucrose, proteins) and duration of ultrasound treatment. The results have shown a significant increase of viscosity after 5 minutes of treatment, but after 10 minutes the lowering of viscosity has happened. Ultrasound treatments, both, after 5 and 10 minutes, caused the lowering of initial freezing as well as thawing temperatures of all samples. The degree of this decrease was proportional to the time of US duration and chemical composition of suspensions.

ultrasound; whey protein isolate; hydrocolloids; physical properties

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