Reducing starch digestibility using a domestic rice cooking method: Structural changes in starch during cooking

In this study, a domestic cooking process based on two soaking stages was designed to reduce starch digestibility in japonica, indica, and waxy rice. Compared with the control rice prepared via a conventional method, each cooked rice prepared under optimal conditions (treated rice) exhibited lower protein and lipid content, similar starch levels but with a higher amylose ratio, and greater sensory acceptability. In vitro digestion assessments indicated that each treated rice had less rapidly digested starch (RDS) and more slowly digestible starch (SDS) and resistant starch (RS) than the control rice. The in vivo trial showed that compared with the corresponding control rice, the glycemic index (GI) of treated indica and waxy rice decreased by 9.11 % and 9.02 %, respectively. Scanning electron microscopy reported an increased presence of pores within the treated rice grains. Fourier-transform infrared spectroscopy and X-ray diffraction results revealed that each treated rice exhibited a higher short-range order and larger relative crystallinity than the corresponding control rice. The decrease in the starch digestibility and GI values of rice might be attributable to the enhancement of short-range order and relative crystallinity of starch caused by soaking.