Microwave heating technology has obvious advantages in high processing efficiency, great energy utilization, and easy controllability, which has been applied in the agricultural and food product processing (Ekezie, Sun, Han, & Cheng, 2017). These advantages may be attributed to the rapid generation of microwave volumetric heating from the violent frication of polar molecules and collision of ions in dielectric material (Guo, Sun, Cheng, & Zhong, 2017). However, non-uniformity of microwave heating, as the unexpected occurrence of uneven temperature and moisture distribution inside material, is concerned research issue in the complication and importance (Li, 2016), which causes the uncontrollable quality of final product and limits the extension of optimization technology (Dinani, Hasic, Auer, & Kulozik, 2020). Existing researches investigated the non-uniformity formation and evolution of microwave heating in the processing parameters, the geometry size (Zhou, Wang, & Yang, 2022) and dielectric properties of material processed (Chen, Tao, Wang, Ye, & Li, 2020). The formation mechanism of non-uniformity of microwave heating is involved in i) different strength of electric field distribution (Zhao, Li, Li, & Gao, 2021) related to geometry size and arrangement patters of the magnetrons in microwave cavity (Altin, Skipnes, Skåra, & Erdogdu, 2022) and the interaction of microwave impinging with the material (Zhou & Li, 2019); ii) the thermal and dielectric properties of the material determining the absorption and distribution of microwave energy (Shen et al., 2022). Already researches noticed the resonant modes within cavity and dissipation inside material processed to explain the non-uniformity of temperature distribution under microwave heating (Yang et al., 2022). Some strategies have been developed, such as the movement of material including rotation and linear motion in microwave cavity, to mitigate the non-uniformity of temperature distribution inside material (Ye et al., 2021). Furtherly, multi-physical field simulation analysis may be introduced to elucidate the heating uniformity considering microwave energy dissipation and heat transfer, which quantitatively characterized the microwave heating uniformity inside material to control the temperature distribution (Palazoglu & Miran, 2019; Shen et al., 2020).

In views of processing purpose, the uniformity of microwave heating has respect to the component properties and quality objectives of material processed. Berry fruit, selected as a typical food material for the research of microwave heating, has thermal sensitive components (anthocyanins, flavonoids, etc.), high moisture content (higher than 90%, w.b.) and strong binding force of water molecules with hydrophilic components (pectin, dietary fiber, etc.). These may represent general properties of common fruits and vegetables for the research of the quality evaluation and technology optimization. Microwave heating has been applied in the processing of berry fruit such as dried berry, powder, and snack. However, the non-uniformity of temperature distribution in berry processed under microwave heating via drying, puffing, extracting, may badly affects the quality stability in the degradation of anthocyanins, unacceptable color due to excessively high temperature spots. To our knowledge, no systematic research was done to investigate the formation and evolution of non-uniformity of temperature distribution inside berry puree under microwave heating from the interaction of microwave dissipation intervening material. To investigate thoroughly and deeply the heating uniformity inside berry puree under microwave heating from electromagnetic-wave dissipation to heat and mass transfer, research objectives were developed as follows.

1. To investigate the microwave dissipation inside berry puree under microwave heating;

2. To analyze the distribution of microwave electric field inside berry puree loaded in a rectangular container;

3. To elucidate the temperature uniformity inside berry puree considering heat and mass transfer under microwave heating.