The underlying starch structures of rice grains with different digestibilities but similarly high amylose contents.

Six rice cultivars with similarly high amylose contents but significant differences in resistant starch (RS) contents were employed to investigate factors affecting rice starch digestibility. Results of scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction analyses revealed that the enzymolysis resistance and high gelatinization temperature (GT) of the starch granules were the main reasons for the different starch digestibilities. Furthermore, starch fine structure analysis showed that RS content has a positive correlation with intermediate chain amylopectin (DP 13-24) content and a negative correlation with short chain amylopectin (DP 6-12) content. Moreover, under normal cooking conditions, some starch granules within the endosperm do not gelatinize completely due to the high GT of the starch, leading to a lower starch digestibility. Overall, this work provides useful information for understanding the effects of starch fine structure as well as GT on starch digestibility.