水分对淀粉微波加热过程的介电增强作用及结晶结构的影响

淀粉类食品在热加工过程中会出现水分的迁移和流失，而水在食品体系中具有突出的介电响应特性，因此水分变化显著影响淀粉类食品的微波加工品质，易于出现微波烘焙面包质构瘪塌、微波蒸制馒头硬心等现象。为实现含水淀粉类食品的高品质微波化控制，在传质传热模型研究的基础上，针对水分在淀粉体系中介电增强作用的诱因，国内外学者提出了靶向活化假说、热搅动假说、以及多重极化弛豫假说。我们认为糊化过程中水与淀粉的水合过程使得水在淀粉中的分布和流动性改变，造成不同状态水的介电响应改变，改变了淀粉的介电极化机制，引发微波加热中后期产生热失控，导致质构劣化。本研究以传统淀粉类食品的水分活度为标准，旨在从极化、吸波角度揭示微波场下水分对淀粉的介电增强作用是否取决于水状态的差异，是否取决于水合淀粉极化机制及吸波性能的改变；同时，还将揭示由此引发的结晶结构变化。本研究将为微波加工淀粉类食品的品质提高以及工业化控制提供理论依据。

The issue of moisture migration and loss within starchy foods often appears during thermal processing. Due to the dominant role of water in the dielectric response of food system, the microwave processing quality of starchy foods, therefore, would be significantly affected by moisture changes. For instance, microwave-baking bread trends to present a deflated collapse, and microwave-steamed buns seem to have a hard centre. In order to achieve a high-level control upon the microwave processing of starchy foods, scholars respectively proposed hypotheses of targeted activation, thermal disturbance and multi-polarization relaxation, to explain the incentives of dielectric enhancement influenced by moisture. We are convinced that changes of water distribution and fluidity during gelatinization would result in the distinct dielectric response of different states of water. Thus, dielectric polarization of starch is strengthened, which could lead to a thermal runaway in the late microwave heating with a deterioration of texture. In this study, we investigate the starch with different water activity to reveal the reason of the dielectric enhancement in starch on the level of polarization and microwave absorbing, e.g., whether it is due to the distinction of water states or changes of polarization and microwave absorbing properties within hydrated starch. The consequent changes of crystal structure are also studied. This research will provide a theoretical basis for improving the quality of starchy foods during microwave processing and for their industrial control.