Radio Frequency Energy Regulates the Multi-Scale Structure, Digestive and Physicochemical Properties of Rice Starch

Radio frequency (RF) heating as an emerging technology was applied to regulate the structural, digestive and physicochemical properties of rice starch. In vitro digestibility results showed that RF treatment enhanced the resistant starch content and reduced the rapidly digestible starch content of rice starch, resulting in higher resistant to enzyme hydrolysis. Microstructure analysis indicated that RF treatment caused the granular surface erosions and morphology changes with increasing treatment time. RF treatment did not alter the A-type crystal form of starch, but disrupted the relative crystallinity, short-range molecular order, and lamellar structure in different degrees. Moreover, the DSC results suggested that starch orders with a higher thermal stability formed after RF treatment, thereby reducing the accessibility of starch granules to the enzyme. Furthermore, rapid viscosity analysis revealed that RF treatment significantly reduced the peak viscosity and breakdown of indica and japonica rice starch, while increased them in waxy rice starch. The rheological properties of rice starch were also changed after RF treatment. This work provides a theoretical basis for the application of RF technology in starch modification.