Ultrasound Processing of Fluid Foods

This chapter outlines the effects of ultrasound on inactivation of both microorganisms and enzymes in liquid foods along with quality and nutritional changes which may arise. Although ultrasound is generally regarded as an effective bactericidal agent, there have been reports of its use to enhance biocidal activity. The ability of ultrasound to stimulate biological activities has received very little attention; however, it is generally believed that the stimulatory impact detected is mainly due to increased cell membrane permeability and higher nutrient transfer rates. For the sterilization of liquid foods, much higher acoustic energies are employed and the approaches can be classified as sonication alone, manosonication (pressure and ultrasound), thermosonication (heat and ultrasound), or monothermosonication (heat, pressure, and ultrasound). Such approaches have been reported to be effective against several pathogenic and spoilage microorganisms for a range of liquid foods, including fruit juices, milk, smoothies, and liquid whole egg, with minimal changes in physicochemical characteristics. Power ultrasound has also been investigated for enzyme inactivation in fruit juices as well as dairy products. Although the potential of power ultrasound has been investigated for many food applications, challenges remain prior to widespread adoption of the technology. One of the difficulties is the nonstandardized reporting of methodology and control parameters. For application of power ultrasound on an industrial scale, it is essential to have energy-efficient processors and design considerations and materials which mirror current trends in food processing.