Dielectric and microwave-absorbing behavior of hydrated wheat starch-gluten systems in relation to water mobility

Microwave heating has become popular in wheat-based food processing owing to its environmental friendliness, high-efficiency and low energy consumption. Water plays an important role in microwave food processing as it is a highly dielectric material that can react with many food components while being dynamic in complex food systems and affecting the overall dielectric response. In this study, hydrated systems of wheat starch, gluten (GLU) and starch-GLU mixtures (CBF) with different moisture contents were prepared and the variation patterns of their water mobility, dielectric properties and microwave absorption properties were measured. The results of low-field nuclear magnetic resonance (LF-NMR) analysis showed that water mobility was strongly influenced by moisture content and interactions between starch or GLU and water-restricted dynamic migration. In CBF, interactions between starch and water predominated under a reduced effect of GLU. As the water content increased, the complex permittivity showed an upward tendency, and the coupling capability of the hydrated systems with microwave was best at 35% moisture content. And the dielectric response and absorption characteristics of the hydrated systems fluctuated in a non-additive manner due to the interplay between moisture and the system components. Moreover, the correlation analysis was confirmed that the relationship between dielectric response behavior and water mobility, as higher water mobility more strongly influenced the augmentation of the dielectric characteristics and dominated changes in the locations of the microwave absorption peak and reflection loss value. These findings provide a possibility to manipulate the dielectric response changes of wheat-based materials under a microwave field through regulating the water mobility, thereby laying a theoretical basis to improve the utilization of microwave for wheat-based food production.