Effect of Microwave Treatment on the Physicochemical and Digestive Properties of Loquat Kernel Starch

To investigate the effect of microwave treatment on the physicochemical and digestive properties of loquat kernel starch, the changes of crystal structure, gelatinization characteristics, particle morphology, solubility, swelling force, transparency and digestibility of loquat kernel starch under different heating time and power of microwave treatment was studied by using the X-ray diffraction (XRD), rheometry, scanning electron microscopy (SEM), and Englyst methods. It was found that the difference in the heating time (90, 120, 150 s) and power of microwave treatment (150, 300, 450 W) revealed the different effect on the properties of loquat kernel starch. The crystal form of loquat kernel starch, which remained C type, was not affected by the microwave treatment. With the increase of microwave heating time and power, the gelatinization characteristics (peak viscosity, valley viscosity, final viscosity), solubility, and swelling power of loquat kernel starch gradually increased, and the surface morphology of loquat kernel starch was partly changed. The contents of fast digestible starch (RDS), slow digestible starch (SDS) and resistant starch (RS) of loquat kernel primary starch were 9.45%, 6.75%, and 83.8%, respectively. The contents of RDS increased to 12.03% and 13.45% with the increase of microwave heating time and power, respectively, whereas the content of SDS decreased to 2.93% and 2.03% under the same treatment, which indicated that the microwave treatment could considerably change the digestibility of loquat kernel starch. Microwave treatment could effectively change the structure and physicochemical properties of loquat kernel starch, and improve in vitro digestion rate of starch.