Microwave heating in food processing

Microwave (MW) heating belongs to the so-called nonconventional thermal processing technologies that have been developed or are still under investigation with the main aim of overcoming some typical problems associated with conventional thermal technologies. These problems include cost and environmental aspects, but first, the thermal impact on food quality, particularly in terms of loss of nutritional quality. In fact, irrespective of the main purpose of the heating process (preservation, development of taste and flavor, changes in structure to obtain a specific texture), a certain level of thermal damage will occur. Food technologists and engineers have, then, been working in the direction of minimizing as most as possible such thermal impact following a concept of total food quality, which cannot consider only the compulsory safety prerequisite but also the nutritional and sensorial quality of the final product. This chapter provides an overview of the basic mechanisms of MW heating, with a focus on its possible applications in the food sector (pasteurization and sterilization, baking and cooking, heating and tempering, freezing, drying, and extraction), underlining, for each application, the main limits of conventional thermal technologies and the potential advantages of MW treatment, together with its drawbacks. Moreover, to overcome typical limits related to MW application, especially nonuniform temperature distribution, the concept of hybrid/combination approach, also called MW-assisted food processing technologies, will be described. These technologies integrate the advantages of MW energy with unconventional processes (e.g., ultrasonication, ohmic heating, electron irradiation, freezing, osmotic dehydration, infrared heating, and vacuum processing) to enhance product quality and process efficiency and reduce time and operational costs of conventional processes (e.g., drying, extraction, baking, pasteurization/sterilization, tempering) (Verma, Mahanti, Thakur, Chakraborty, & Srivastav, 2020, p. 25). This chapter represents, with permission, an update of the work by Spigno (2016, p. 137).