Resistant starch in high-amylose wheat flour partially withstands harsh thermal processing

The objective of this study was to investigate whether resistant starch (RS) in high-amylose wheat (HAW) flour could withstand harsh steaming and then oil-frying in a high-moisture food system. In-vitro starch digestibility analysis showed that the harsh thermal processing reduced the RS content in HAW flour from 53.7 % to 23.2 %. Scanning electron micrographs and confocal laser scanning microscopic images showed that the HAW starch granules remained as granular ghost-like shapes after harsh thermal processing. These ghost-like granules exhibited weak birefringence under a polarized-light microscope, indicating the presence of high-temperature-resistant crystalline structures. Thermal properties and X-ray diffraction results revealed that amylose-lipid complexes were present in HAW starch before harsh thermal processing, and that their crystalline structures formed after treatment. HAW flour exhibited a high pasting temperature and low overall pasting viscosity. These results suggest that the high-temperature-resistant crystalline structures and amylose-lipid complexes in HAW starch inhibited granule swelling during pasting and maintained ghost-like granular morphology after harsh thermal processing, ultimately contributing to the observed RS in HAW flour from the harsh-thermal treatment. This study could provide theoretical support to broaden the application of HAW flour in the food industry.