Effect of repeated heat-moisture treatments on the structural characteristics of nanocrystals from waxy maize starch

The effect of repeated heat-moisture treatment (RHMT) on the structural characteristics of waxy maize starch nanocrystals was investigated. Compared with native waxy maize starch (WMS), waxy maize starch nanocrystals (WMSNs) changed the crystalline pattern from A-type to B-type, and displayed the lower crystallinity (RC), molecular order (MO), enthalpy (∆H) and double-helix (DH) content, indicating a reduction in the long- and short-range orders of starch molecules. Single heat-moisture treatment significantly increased values, including RC, MO, α (power law exponent obtained by SAXS), ∆H, DH, and the melting temperatures (To, Tp and Tc), while repeated heat-moisture treatment further increased values of these parameters except ∆H, indicating the reinforcement of the long- and short-range orders of WMSNs. In addition, repeated heat-moisture treatment also caused a gradual conversion from B-type to “A + B”-type (Cb, Cc to Ca polymorphs in sequence) and finally to A-type crystallites. •A method to modify the properties of nanocrystals from waxy maize starch was established.•The crystalline packing shifted from B- to C-type (Cb, Cc to Ca in sequence), finally to A-type.•The crystallinity, double-helix content, and compactness of nanocrystals increased