Dielectric Properties of Blackberries as Related to Microwave Drying Control

Abstract

AbstractThe dielectric properties of blackberry samples with a 20.0–80.0 % w.b (web basis) moisture content were determined with a network analyzer and an open-ended coaxial-line probe over a frequency range from 5 to 3000 MHz and a temperature range from 20 to 100 °C. The results showed that the dielectric constant decreased with increasing temperature but increased with increasing moisture content; however, the loss factor increased with increasing temperature and moisture content. The dielectric constant and the loss factor decreased with increasing frequency. The penetration depth decreased with increasing temperature, frequency and moisture content. A large penetration depth at 915 MHz may provide practical large-scale dielectric drying for blackberries. The dielectric constants and loss factors for blackberry by combining the above mathematical model and temperature and moisture of the sample in the microwave drying process were used to analyze and control blackberry drying technology.