Dielectric properties of tomatoes assisting in the development of microwave pasteurization and sterilization processes

Dielectric properties of tomatoes crucially affect their heating behaviors in an electromagnetic field and are essential for developing microwave pasteurization and sterilization processes for different tomato products. The open-ended coaxial probe technique was used to determine the dielectric properties of tomatoes over a frequency range of 300-3000 MHz for temperatures between 22 and 120 °C. Three tomato tissues, the pericarp tissue (including the skin), the locular tissue (including the seeds) and the placental tissue were studied separately. The effects of NaCl (0.2 g/100 g) and CaCl2 (0.055 g/100 g) on the dielectric properties of tomatoes were also investigated. The dielectric loss factors were significantly different among the three tomato tissues. However, no significant differences were found in their corresponding dielectric constants. The loss factors of the three tomato tissues decreased with increasing frequency and increased with salts added. Increasing temperature increased the loss factors of the three tomato tissues at 915 MHz, but initially decreased then increased their corresponding values at 2450 MHz. The differences in the loss factors of the three tomato tissues were mainly caused by the difference in ionic conductivity.