Chapter 20 - Recent Developments in Microwave Heating

Abstract

There has been a significant increase in the number of household microwave ovens in recent years. Nowadays, the microwave oven is widely used for the reheating of prepared foods in the food service sector. Microwave heating has also found applications in the food industry, including the tempering of frozen foods, precooking of bacon, pasteurization of packaged foods, and the final drying of pasta products. Microwave food processes offer a lot of advantages such as less start up time, faster heating, high energy efficiency, space savings, precise process control, selective heating, and foods with high nutritional quality. There are differences in the mechanisms of microwave heating and conventional heating. These differences may be beneficial or detrimental depending on different processes. For example, short processing time is desired in terms of less nutritive loss in microwave processed foods, but undesired in baked products since biochemical reactions may not be completed during this short period of time. Nonuniform heating, lack of color and flavor development, soggy surface, high moisture loss, and firm texture are the common problems observed in foods processed in microwave oven. Recently, new formulations are being developed in order to reduce these problems, and combination heating technologies have been used especially for baked products. Many recent techniques have been introduced to literature related to microwave heating. One of them is a 915MHz, single-mode microwave system, which is effective in the sterilization of nonhomogeneous food and may be used for other packaged nonhomogeneous foods, such as chicken meat in trays of gravy and salmon in pouches of sauce. This chapter will provide a general review about improvements achieved in the field of microwave heating in recent years. Dielectric properties of foods are important in understanding microwave heating characteristics of foods. Therefore, the work presented here first concentrates on the recent studies in dielectric properties of various foods. Then, advances in the fundamental understanding of microwave heating through heat and mass transfer modeling will be described. Finally, advances in microwave food processes and product formulations will be discussed.