Effects of continuous and cyclic dry heat treatment on the structure, thermal properties, and digestibility of buckwheat (Fagopyrum esculentum) starch

Abstract Dry heat treatment (DHT) is a physical modification technique that offers environmental advantages and low operational costs. In this study, buckwheat starch was modified under continuous conditions for 3–15 h (DHT-C) and cyclic conditions with five cycles (DHT-R) at 130 °C. Native and modified starches were characterized for morphological, structural, pasting, and in vitro digestibility properties. Starches modified with four and five cycles exhibited reduced gelatinization enthalpy, and SEM (scanning electron microscopy) revealed more pronounced surface depressions. Thermal stability increased with treatment time, but excessive exposure reduced both stability (179 mPa.s for continuous sample over 15 h and 56 mPa.s for the modified sample with 5 cycles) and peak viscosity. X-ray diffraction revealed a Type A pattern, with higher relative crystallinity in DHT-C and DHT-R samples (15,75% for native sample and 20,57% for the modified sample with 5 cycles). The primary molecular structure remained unaffected. Modification increased rapidly digestible starch and decreased resistant starch in DHT C15 (67,77% and 20,54%, respectively) and DHT-R. These findings provide new insights into the technological functionality and digestibility of buckwheat starch following physical modification.