Ultrasound processing has  been used by the industry as processing aids in food production. Ultrasound applications are based on 3 different methods:

 

• Direct application to the product

• Coupling with the device

• Submergence in an ultrasonic bath

 

Listed below are some of the common applications of ultrasound processing.

 

Food preservation:

 

Food preservation is essential to ensure that food products have a long shelf life. Food deterioration is contributed by both microorganisms (biological spoilage) and presence of enzymes (chemical spoilage) in food and as a result, the ability to eliminate microorganisms or enzymes is the primary concern of food manufacturers. Currently, thermal processing is the most popular method applied to inactivate microorganisms present on food. However, thermal methods can also result in the destruction of heat labile compounds such as polyphenols, polyunsaturated fatty acids (PUFA) and flavour compounds. Thus, it may alter certain nutritional or sensorial properties of the food product.

 

Inactivation of microbes:

 

During ultrasound processing, longitudinal waves are formed when sonic waves interact with the liquid medium creating series of compressions and rarefactions. The regions of pressure changes cause cavitation and gas bubbles are formed in the medium. Gas bubbles present start to expand due to diffusion of gases into the bubbles till a point where by the ultrasound energy provided is unable to retain the vapour pressure and condensation occurs causing the bubbles to collapse violently and create shock waves. The shock waves can result in high temperatures and pressure. This high pressure is the main bactericidal effect in the processing. However, as the hot spots are localized, the effective area is not very large. In addition, heat and high pressure have been used together with ultrasound, which are known as thermosonication and manosonication, respectively, to improve efficiency in terms of processing time and energy consumption.

 

Inactivation of enzymes:

 

Ultrasound processing has also been used to inactivate enzymes responsible for certain physicochemical changes occurring in various foods that can result in nutritional and sensorial changes. Manothermosonication (MTS), a combination of heat and high pressure with ultrasound processing has been shown to incite similar inactivation mechanism as heat treatment in peroxidase.