Correlation between in vitro starch digestibility and starch structure/physicochemical properties in rice

Natural resistant starch (RS) in rice provides human health benefits, and its concentration in rice is influenced by the structure and physicochemical properties of starch. The native starch structures and physicochemical properties of three rice varieties, QR, BR58, and BR50, and their relationships to in vitro digestibility were studied. The starch granules in all three varieties were irregular or polyhedral in shape. There were a few oval granules and a few pinhole structures in QR, no oval granules but a higher number of pinholes in BR58, and no oval granules and pinholes in BR50. QR is a low-amylose (13.8 %), low-RS (0.2 %) variety. BR58 is a low-amylose (15.3 %), high-RS (6.5 %) variety. BR50 is a high-amylose (26.7 %), high-RS (8.3 %) variety. All three starches exhibited typical A-type diffraction patterns. Starch molecular weight, chain length distribution, starch branching degree, pasting capabilities, and thermal properties differed considerably between the rice starches. The RS contents of the rice starch varieties were positively correlated with AAC, Mw/Mn, Mz/Mn, peak 3, B, PTime, and Tp and negatively correlated with Mn, peak 2, DB, PV, and BD, according to Pearson's correlation analysis. These findings may be helpful for the breeding and development of high-RS rice varieties.