Effect of single-, dual-, and triple-retrogradation treatments on in vitro digestibility and structural characteristics of waxy wheat starch

• DR treatment increases the yield of SDS in waxy wheat starch.
• DR treatment decreases ΔH and Tc – To of waxy wheat starch.
• DR treatment alters crystalline type of waxy wheat starch from A-type to B-type.
• DR treatment decreases relative crystallinity of waxy wheat starch.
• DR treatment can change the morphology of waxy wheat starch.

The effects of single-retrogradation (SR), dual-retrogradation (DR) and triple-retrogradation (TR) treatments on in vitro digestibility and structural characteristics of waxy wheat starch were investigated. The yield of slowly digestible starch in a DR-treated starch with retrogradation time interval of 48 h reached a maximum of 44.41%. The gelatinization temperature range and gelatinization enthalpy of DR-treated starch samples were the lowest. Moreover, compared with native starch, X-ray diffraction patterns of treated starches were altered from A-type to B-type and relative crystallinity was significantly decreased, which was responsible for the interaction between amylose–amylose and/or amylose–amylopectin chains that may generate more imperfect structures. Scanning electron micrographs revealed that compared with SR-treated and TR-treated starches, the surface of DR-treated starch with a retrogradation time interval of 48 h exhibited a net-like structure with numerous cavities. These results suggest that structural changes of waxy wheat starch by cycled retrogradation treatment significantly affect digestibility, and DR treatment can be used for preparing SDS product.