Effects of heat-moisture treatment after citric acid esterification on structural properties and digestibility of wheat starch, A- and B-type starch granules.

In this study, wheat starch, A- and B-type starch granules were firstly treated with citric acid (CT) and then subjected to heat-moisture treatment (HMT). The maximum thermo-stable resistant starch (RS) contents reached 71.52%, 71.27%, 71.58% for CT-HMT wheat starch, A- and B-type starch granules, respectively. The hydrolysis kinetic parameters (C∞ and k) reduced after CT-HMT. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results revealed that the endothermic and crystalline peaks of CT-HMT starch samples disappeared. Scanning electron microscopy (SEM) results showed that more collapses and destructiveness appeared on the surfaces of CT-HMT starch granules. The esterification reaction became stronger during HMT according to Fourier transform-infrared (FT-IR) spectroscopy analysis, which was consistent with the results of degree of substitution. Raman spectroscopy presented similar structural properties results with XRD and FT-IR. These results suggest that CT prior to HMT is a useful method for preparing high amount of thermally stable RS.