Gelatinization and X-ray crystallography of buckwheat starch: Effect of microwave and annealing treatments

Abstract

Buckwheat, a non-glutinous pseudo-cereal having a long and traditional history as a food source in Asia, Europe, and the United States, has many beneficial health aspects. However it has suffered from declining production during the past few years. In order to prevent further decline of buckwheat production new products need to be developed for the consumer market and more research need to be carried to study the effect of different processing parameters on buckwheat characteristics. This study was carried out to investigate the effect of microwave heat-moisture and annealing processes on buckwheat starch that had been dried to three moisture levels: 30.3, 40.0, and 50.4 kg/100kg. Starch samples were analyzed using a differential scanning calorimeter, a colorimetric amylose leaching tests, and an x-ray diffractometer. Additional moisture levels in the starch treatment groups (15.2% and 25.8%) were produced for the x-ray diffraction tests. DSC data indicated that moisture levels had a significant effect on onset melting temperature, peak melting temperature and enthalpy of fusion. In addition, heat treatment and interaction of moisture with heat treatment both had a significant effect on amylose leaching results. Significant effect on starch was found mainly at the 50.4 kg/100 kg moisture level as compare to the 30.3 and 40.0 kg/100 kg moisture level. X-ray diffraction readings showed a stable D-space placement for all treatment groups. Intensity visibly increased with decreased moisture level and with heat treatment in case of 40.0% and 50.4% moisture level starches. Resistance to amylose leaching and melting at higher temperatures for higher moisture level buckwheat starch samples was attributed to increased networking among the amylose and amylopectin components in the buckwheat starch.