Structural and physicochemical properties of resistant starch under combined treatments of ultrasound, microwave, and enzyme

The structural characteristics and physicochemical properties of native corn starch (NCS) and resistant starch (RS) prepared by enzymatic hydrolysis (RS-E), microwave-enzymatic hydrolysis (RS-ME), ultrasound assisted enzymatic hydrolysis (RS-UE), and microwave-ultrasound assisted enzymatic hydrolysis (RS-MUE) were investigated. The results showed that the combined treatments of ultrasound, microwave, and enzyme resulted in increases in RS content, amylose content, and solubility with a decrease in swelling power. RS-MUE exhibited the lowest digestibility, with a 41.71 % RS content. Particle-size distribution and scanning electron microscopy analyses demonstrated that RS samples exhibited larger granule sizes and rougher surfaces with irregular shapes. The Fourier transform infrared spectroscopy and X-ray diffraction pattern analysis demonstrated that no new groups were created during the modification processes, the crystal structure of all RS samples changed from A to B + V, and the short-range order and relative crystallinity of RS-E, RS-ME, RS-UE, and RS-MUE increased. RS-MUE exhibited the highest molecular order R1047/1022 value (0.8769) and relative crystallinity (45.54 %). These results suggested that the new technology combining microwave, ultrasound, and enzyme for improving RS content is effective and has potential for application in the production of RS and low glycemic index foods.