Ultrasound-assisted freezing of fruits and vegetables: Design, development, and applications

Abstract

The application of power ultrasound to facilitate the freezing of fruits and vegetables is a relatively new concept. Sound waves cause cavitation and a sponge effect, both of which impact the freezing rate and properties of the frozen products. The application of ultrasound in the freezing process helps to inactivate enzymes and microbes and enhances the ice crystal nucleation process. The advantages of ultrasound-assisted freezing over conventional freezing include high freezing rate, faster crystallization, uniform distribution of ice crystals, better microstructure, and good product quality. However, very little is known about the fundamental thermodynamics, moisture diffusion and heat transfer in the ultrasound-assisted freezing process. The design of appropriate transducer systems and freezers to suit the needs of fruits and vegetables has not yet been undertaken. It appears that there is an urgent need to investigate the effect of the ultrasound-assisted freezing process on the physicochemical properties of frozen fruits and vegetables. In this context, this chapter presents a comprehensive review of the literature covering recent advances in structure and working principles of common and ultrasound-assisted freezers, along with the impact of the fast and slow freezing processes on the characteristics of frozen fruits and vegetables. The mathematical modeling and quantification aspects of the freezing and thawing process have also been reviewed. The structure–function aspects of power ultrasound, including the associated transducers and design aspects of different ultrasound-assisted freezing systems, have been reviewed in considerable detail. The urgent need for scaling up of equipment and process of ultrasound-assisted freezing from laboratory to industrial scale has been highlighted.