A complex interplay between alginate/pectin and rice varieties in determining the starch digestibility of...

Non-starch polysaccharide (NSP) encapsulated rice flour is a novel type of rice analogue, while the influence of different NSPs and rice varieties on starch digestibility remains unknown. Therefore, three rice varieties with different structures were encapsulated by alginate or pectin, and their digestibility and textures were investigated with regards to the alterations of their multi-scale structures during digestion. An approximately 1.9 times difference of enzymatic binding rate constant and 10 % difference of the maximum starch digested percentage were found among different rice beads. Nanjing rice beads showed slower starch digestibility when encapsulated by alginate, while Panjin and Subei rice showed the opposite. Alginate encapsulated rice beads showed a harder texture than pectin encapsulated ones, although the texture also depended on rice varieties. Mechanistically, amylopectin chains with a peak DP around 15 from Nanjing rice were proposed to interact with alginate, thus reducing its digestibility. In comparison, the large pores formed in pectin encapsulated Panjin and Subei rice beads after cooking promoted the re-association of starch molecules into more ordered structure and thus reduced digestibility. These results suggest that careful selection of both NSP types and rice varieties is required to develop rice beads/analogues with desirable starch digestibility.