Microwave and radio frequency heating refers to the use of electromagnetic waves of certain frequencies to generate heat in a material.
Typically, microwave food processing uses the 2 frequencies of 2450 and 915 MHz. Of these two, the 2450 MHz frequency is used for home ovens, and both are used in industrial heating. It is worthwhile to note that outside of the United States, frequencies of 433.92, 896 and 2375 MHz are also used.
There is not much commercial use of these frequencies for food pasteurization or sterilization, although they are used in baking and other processes in the food industry.
Heating with microwave and radio frequency involves primarily 2 mechanisms-- dielectric and ionic. Water in the food is often the primary component responsible for dielectric heating.
Due to their dipolar nature, water molecules try to follow the electric field associated with electromagnetic radiation as it oscillates at the very high frequencies. Such oscillations of the water molecules produce heat.
The second major mechanism of heating with microwaves and radio frequency is through the oscillatory migration of ions in the food that generates heat under the influence of the oscillating electric field.
Microwave and radio frequency heating for pasteurization and sterilization are preferred to the conventional heating for the primary reason that they are rapid and therefore require less time to come up to the desired process temperature.
This is particularly true for solid and semi-solid foods that depend on the slow thermal diffusion process in conventional heating. They can approach the benefits of high temperature-short time processing whereby bacterial destruction is achieved, but thermal degradation of the desired components is reduced.
Microwave in food processing
