Abstract
The effect of non-ionizing microwave radiation on starch is due to a gelatinization temperature range that changes starch structure and properties. However, the changes in starch upon microwave heating are observable throughout the heating process. We compared the effects on starch heating by microwaves to the effects by rapid and regular conventional heating. Our results show that microwave heating promotes the rapid rearrangement of starch molecules at low temperatures; starch showed a stable dielectric response and a high dielectric constant. Microwave heating changed the Cole-Cole curve and the polarization of starch suspension at low temperatures. A marked transition at 2.45 GHz resulted in a double-polarization phenomenon. At temperatures below gelatinization, microwave-induced dielectric rearrangement and changes in the polarization characteristics of starch suspensions reduced the absorption properties; at temperatures above gelatinization, these characteristics became consistent with conventional heating. Throughout the heating process, microwaves change the electrical response and polarization characteristics of the starch at low temperatures, but on the macro level, there is no enhancement of the material’s microwave absorption properties. In contrast, with the warming process, the starch exhibited a “blocking effect”, and the absorption properties of the starch quickly returned to the level observed in conductive heating after gelatinization.
Highlights
Microwave radiation is non-ionizing and changes the structural characteristics of materials during processing
We evaluated the difference between microwave heating and traditional heating and established a microwave heating (MW) model based on rapid conduction heating (RCV) temperature
We studied the gelatinization of rice starch heated by microwave heating, comparing the time-temperature profiles for MW and Rapid conventional heating (RCV) up to 85 °C
Summary
Microwave radiation is non-ionizing and changes the structural characteristics of materials during processing. To promote the understanding and application of the physical effects of this process, Muzimbaranda[1] et al and Lewandowicz[2] et al reported on the interaction between microwave radiation and starch These reports confirmed that microwave heating causes a rearrangement of intramolecular structures during gelatinization, altering the water absorption capacity, solubility, swelling ability, gelatinization characteristics, dehydration shrinkage behavior and rheological properties of starch[3,4,5]. Polymer matrix materials dispersed in water undergo different degrees of adsorption, binding and release upon heating; as a result, the material’s molecular polarization behavior changes and a power shift occurs in the dielectric response spectrum[17]. Researchers have used the Cole-Cole model to study the structural effects of high-field treatment on a single material, no study has yet applied this method to liquid mixed materials, especially for the study of liquid dispersions of food macromolecules
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