Dynamic measurement of dielectric properties of food snack pellets during microwave expansion

The in situ dielectric properties of a starch-based food pellet have been measured during microwave expansion. A dual-mode cylindrical cavity allowed simultaneous microwave heating and dielectric measurements of a single pellet inside a quartz tube, ensuring uniform heating during microwave processing. The cavity included additional measurement devices to correlate the dielectric properties with the main parameters of the expansion process, such as temperature, expansion time, pellet volume and absorbed power. A commercially available snack food pellet was Used as the test material for expansion experiments. Results indicated that dielectric constant (epsilon') and loss factor (epsilon") increased during heating, reaching a threshold value of epsilon' = 12.5 and epsilon" = 5.2, around a temperature of 115 degrees C when the material expanded and the dielectric properties dropped abruptly due to the loss of water content and the increase in size. This measurement procedure may provide useful material science information to improve the overall design of starch-based food pellets processed by microwaves. (C) 2017 Elsevier Ltd. All rights reserved.