Microwave assisted thermal sterilization and pasteurization systems, as emerging thermal processing technologies, use circulation water to reduce edge heating of the food packages in the microwave heating sections. Yet, the influence of the circulation water on microwave heating efficiency for food is unknown. This research studied the dielectric properties of purified water from a reverse osmosis unit and tap water over microwave frequencies of 150–2500 MHz at 23–120 °C and evaluated microwave loses in the circulation water. The values of the dielectric constant of purified and tap water decreased (P < 0.05) with increasing temperature and slightly decreased with increasing frequency. The value of the loss factor of purified water also decreased with temperature (P < 0.05) but increased with frequency. The trend was more complicated for the loss factor of tap water. The penetration depth of 915 MHz microwave power in purified water was 399 and 457 mm at 90 and 120 °C, respectively, it was reduced to 161 and 136 mm in tap water. The microwave power loss in the 18–30 mm deep purified water, depending on the thickness of the food packages, was 4–7%, compared to 11–20% in tap water. Thus, using purified circulation water in microwave assisted thermal sterilization (MATS) and pasteurization systems (MAPS) can significantly improve the efficiency of microwave heating of packaged foods.

Industrial relevance

The information from this research are highly relevant to industrial operations of microwave-assisted thermal sterilization and pasteurization systems of pre-packaged foods. The dielectric property data will contribute to the literature related to the physical properties of water in microwave heating.

中文翻译：

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与微波辅助热巴氏杀菌和包装食品灭菌相关的水的介电特性

微波辅助热杀菌和巴氏杀菌系统作为新兴的热处理技术，在微波加热部分使用循环水减少食品包装的边缘加热。然而，循环水对食品微波加热效率的影响尚不清楚。本研究在 150-2500 MHz 的微波频率下，在 23-120 °C 下研究了来自反渗透装置的纯净水和自来水的介电特性，并评估了循环水中的微波损失。纯净水和自来水的介电常数 随温度升高而降低（P < 0.05），随频率升高略有降低。纯化水的损失系数值也随温度的升高而降低（P < 0.05) 但随着频率的增加而增加。自来水损失系数的趋势更为复杂。915 MHz 微波功率在 90 °C 和 120 °C 纯净水中的穿透深度分别为 399 和 457 mm，而在自来水中则降至 161 和 136 mm。18-30 毫米深度纯净水中的微波功率损失（取决于食品包装的厚度）为 4-7%，而在自来水中为 11-20%。因此，在微波辅助热灭菌 (MATS) 和巴氏杀菌系统 (MAPS) 中使用净化循环水可以显着提高包装食品的微波加热效率。

工业相关性

这项研究的信息与预包装食品的微波辅助热灭菌和巴氏杀菌系统的工业操作高度相关。介电特性数据将有助于与微波加热中水的物理特性相关的文献。