Contrasting starch digestion and physiochemical characteristics between japonica and indica rice varieties with comparable high-amylose content.

Abstract

Limited information is available on the starch digestion properties in high-amylose japonica rice. This study compared starch digestion properties and physiochemical characteristics-including texture profiles, starch and protein composition, and pasting properties-between the high-amylose japonica rice variety Youtangdao 3 (Y3) and the high-amylose indica variety Guangluai 4 (G4). Y3 exhibited a 36 % shorter active digestion duration, 24 % faster glucose production rate, and 21 % lower glucose production than G4. The faster starch digestion rate in Y3 was attributed to its lower cohesiveness, which was associated with its higher resistant starch content-driven by a higher amylose-to-amylopectin ratio and higher protein content, particularly albumin and glutelin. The lower glucose production in Y3 resulted from its lower total starch content-linked to higher protein content-and higher resistant starch content. This study clarifies varietal differences in starch digestion and related physiochemical traits between high-amylose japonica and indica rice. Additionally, this study highlights that a higher resistant starch content does not always correspond to slower starch digestion in rice.