Dielectric properties during the heating process of savory and sweet coconut-/almond-based bread in the microwave region

For microwave-assisted heating, accurate knowledge of the dielectric properties (DPs) plays a key role for optimizing the heating process. In this paper, the DPs of four different bread dough formulations are presented from 300 MHz to 20 GHz. The base dough was prepared with almond powder, coconut powder, eggs, cashew nut powder, ghee butter, and cardamom. In addition, three more honey-sweetened formulations were prepared with honey, goat milk and cacao. The DPs were measured during the complete baking process, from room temperature up to 80°C. It is shown that in all cases, ε′ and ε″ decrease as frequency increases. In addition, a second-order Debye equation was extracted for all formulations showing two relaxation times (τ₁ and τ₂), which can be seen in the Cole–Cole plot. Moreover, it is shown that in all formulations, as temperature increases, ε′ and ε″ also increase, which is a typical trend for low moisture foods. Finally, the penetration depths are calculated for all formulations.

Practical Applications

The dielectric properties (DPs) of four different bread dough formulations are provided covering a wide band in the microwave range from 300 MHz to 20 GHz. DPs are useful for the development of microwave-assisted heating applications, where prior knowledge of the DPs permits the optimization of the heating process. In addition, penetration depth is necessary as this parameter allows to calculate the maximum depth that the microwave energy will heat up the sample.