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.