Abstract
Ultrasonic processing is an emerging technology in food processing. When ultrasound passes through a liquid, bubble nuclei present in the liquid grow by bubble coalescence and rectified diffusion. When these bubbles reach a critical size range, they collapse under near-adiabatic conditions generating extreme conditions within the bubbles and in the surrounding liquid that include intense shear forces, turbulence and microstreaming effects. These ultrasound-induced physical effects are finding increasing use in food and dairy processing, in applications such as the enhancement of whey ultrafiltration, extraction of functional foods, reduction of product viscosity, homogenization of milk fat globules, crystallization of ice and lactose and the cutting of cheese blocks. After a brief introduction to the ultrasonic processing of food systems in general, this review presents a critical discussion of applications in dairy processing, together with the findings of some recent research on the use of ultrasound to modify the functionality of dairy protein ingredients.