Amylose content and molecular-order stability synergistically affect the digestion rate of indica rice starches.

This work concerns the multi-scale structures and digestion behaviors of indica rice starches with apparent amylose contents (AACs) of ca. 14%-24%. A higher AAC not always allowed a lower digestion rate (k), different from previous findings that starches containing more amylose normally show slowed digestion. Here, the proportion of stable molecular orders (melting temperature above ca. 73 °C) and AAC synergistically governed starch digestion rate. With a similar AAC, a higher amount of stable orders (Rh/l, ratio of enthalpy of stable orders to that of the rest) led to a lower k. Also, with a similar Rh/l, a larger AAC caused a lower k. Consistently, JPZ starch had almost the highest AAC and Rh/l, showing the lowest k. Regarding this, amylose and stable orders played roles in increasing the bulk density of starch structure matrices, and eventually slow the diffusion, absorption and catalysis events of digestion enzymes within the matrices.