Insights into the multi-scale structure and digestibility of heat-moisture treated rice starch

- HMT transformed part of RDS into SDS and RS for rice starch.
- HMT induced concomitant structural disorganization and molecular rearrangement.
- Higher moisture content led to greater change in starch digestibility and structure.
- More ordered structure and greater dc thickness led to higher enzymatic resistance.

The digestibility and structural changes of rice starch induced by heat-moisture treatment (HMT) were investigated, and the relationships among the moisture content-starch structure-starch digestibility were revealed. HMT could simultaneously disorder and reassemble the rice starch molecules across multi-scale lengths and convert some fractions of rapidly-digestible starch (RDS) into slowly-digestible starch (SDS) and resistant starch (RS). In particular, the HMT rice starch with less than 30% moisture content showed a higher SDS + RS content (25.0%). During HMT, SDS and RS were preferably formed by the degraded starch molecules with Mw between 4 × 105 and 4 × 106 g/mol, single helices and amylose-lipids complexes that were formed by degraded starch chains with higher thermal stability and crystalline lamellae with greater thicknesses. Thus, our research suggests a potential approach using HMT to control the digestion of starch products with desired digestibility.