Structural and physicochemical properties of native starches and non-digestible starch residues from Korean rice cultivars with different amylose contents

In this study, rice starches from four cultivars: Baegokchal (BOC), Ilmi (IM), Mimyeon (MM), and Dodamssal (DDS), were studied in terms of their physicochemical and structural features. Native starches (NS) from MM and DDS showed high amylose content and low rapidly digestible starch, as well as high slowly digestible starch and resistant starch (RS) ratios. To elucidate the characteristics of RS in rice, non-digestible starches (NDS) were isolated from NS from each cultivar. The starch crystallinity of BOC, IM, and MM showed an A-type X-ray diffractometry pattern; however, DDS granules displayed a C-type crystallinity pattern with a predominant B-type. DDS starch granules had a convex spherical shape, whereas BOC, IM, and MM starch granules had a polygonal shape. All starches from IM and BOC were hydrolyzed, with no NDS residues remaining. The NDS from MM and DDS, which are high-amylose cultivars, showed a lower molecular weight, longer average amylopectin chain length, and lower viscosity than NS. DDS had the lowest digestibility, highest RS content, and showed potential for use as a source of starch for weight loss and hypoglycemic effects owing to its low glycemic index. The low viscosity of DDS can potentially be exploited for its use as a daily dietary component through the development of suitable processing methods for products such as rice noodles.