Structural changes of waxy and normal maize starches modified by heat moisture treatment and their relationship with starch digestibility

In the present study, the variations in structure of waxy and normal maize starches modified by heat-moisture treatment (HMT) for different treating time (3 h and 9 h) were investigated. HMT caused the destruction of starch granules. The H-1 NMR confirmed that glycosidic bonds were broken during HMT. The C-13 NMR result suggested that HMT caused the transformation of starch granules from double and single helical components into amorphous components. Heat-moisture treated starches exhibited higher gelatinization temperature (To, Tp and Tc), narrower gelatinization temperature range (Tc-To) and lower gelatinization enthalpy (Delta H). HMT caused the rearrangement of starch molecules, degeneration of double helices and formation of new single helix. In addition, in vitro digestibility assessment indicated that the contents of rapidly digestible starch (RDS) and slowly digestible starch (SDS) were improved and resistant starch (RS) was reduced after HMT, which was related to the decrease of single and double helical components.