ABSTRACT
Microwave (MW) and radio frequency (RF) drying can be attributed to dielectric drying. MW/RF waves are parts of the electromagnetic spectrum. The dielectric energy absorption in foods primarily involves two mechanisms: dipolar relaxation and ionic conduction (Figure 3.1). These interactions are carried out under the electric eld of RF and MW. Water in food is often the primary component responsible for dielectric heating/drying. Owing to their dipolar nature, water molecules attempt to follow the electric eld as they rotate at very high frequencies. Such rotations of the water molecules produce heat, which is expressed as the dipolar relaxation. Ions, such as those present in salty food, migrate under the inuence of the electric eld, thereby generating heat. This is the second major mechanism of heating using MW and RF energy (ionic conduction).1,2 Both the dielectric constant and the dielectric loss factor can measure the ability of the material to interact with the electric eld of MW/RFs. The capacitance meter has been used to estimate the dielectric properties, but now vector network analyzer (VNA) and the open-ended coaxial-line probe are used for easy and effective measurement of dielectric properties. As dielectric-related new technologies are developing, MW/RF drying is becoming increasingly popular in food processing industries.
