Non-additive response of starch systems in different hydration states: A study of microwave-absorbing properties

In the food industry, microwave-based curing and modification represent green, low-energy-consumption techniques for food processing, offering significant advantages. Water, a representative high-dielectric material, can react with many food components; however, few studies on microwave absorption to these components have been reported. In this study, commercially available potato starch and rice starch (the latter a representative cereal starch) were selected as the research materials. Based on vector network analysis of these materials, the bow coaxial probe and improved arch methods were used to study the dielectric properties and microwave reflection loss of the potato starch and rice starch systems, with different hydration levels, at 2.45 GHz. Their absorption behaviour was compared with the classical model to study the absorption properties of the starch systems under different hydration conditions. The results showed that at ambient temperature, potato starch and rice starch had similar dielectric responses, which both showed a steady rise with increasing water content. Therefore, because of their similar dielectric properties, the two systems behaved similarly in the microwave field. However, further experiments found that the microwave absorption properties of both starches differed significantly from that of water: starch-water systems with different compositions varied nonlinearly in their microwave absorption performance, consistently with the “true single layer of water” theory.