Physicochemical properties of common buckwheat starch

Abstract: In order to understand the physicochemical characters of common buckwheat starch, 12 varieties of common buckwheat were planted in the research farm of the Yan'an Institute of Agricultural Sciences and the granule morphology, solubility, transparencies, gelatinization and viscosities of their starch granules were investigated in this study. The starch granules' shapes and sizes were examined by Scanning Electron Microscope (SEM). The starch granule diameters, amylase contents, solubility and transparencies were found to significantly differ among the different test varieties（P<0.05）. The starch granules of the test varieties had irregular polygonous and global shapes and the granules of the varieties with the former shapes were larger and numbered more than their ones with the latter shapes. The granule diameters of the test varieties ranged within 0.38-25.78 μm. The starch granules of Ning D07-1, Wuqi Honghuaqiao-2, Pingxuan 01-036, Dingbian Tianqiao and D07-2 were polygonous with clear-cut edges and the starch granules of Qingyang Honghuaqiao, Zhidan Honghuaqiao and Dingbian Tiaoqiao were global and smooth at high percentages. The starch granules of the varieties presented similar two-peak size distributions of which the first peak appeared at the granule diameter of 1 μm and the second peak appeared at the granule diameter of 15 μm and the former peaks were higher than the latter ones. Ning D07-3 had the highest amlyose content of 43.06% and Ning D07-2 had the lowest amlyose content of 36.63%, and the other varieties had amlyose contents that ranged between 36.82%-42.22%. The amlyose content of Ning D07-3 and Pingxuan 01-036 were significantly higher than those of the other varieties and the amlyose contents of Wuqi Honghuaqiao-1 and Ning D07-2 were significantly lower than those of the other varieties. The starch solubility of the varieties increased with increased temperatures and that significantly differed; and at 80 and 90℃, the starch solubility of Menggu 20, Wuqi Honghuaqiao-1, and Dingbian Tianqiao were significantly lower than those of Ning D07-1, Wuqi Honghuaqiao-2 and Qingyang Honghuaqiao. The starch paste transparencies of the varieties significantly differed, with Wuqi Honghuaqiao-2 presenting the highest transparency of 8.65%, and Menggu 20 presenting the lowest transparency of 7.37%. The starch paste retrogradation of the varieties tended to increase slowly at first and then quickly with time, with the starch paste retrogradation of Zhidan Honghuaqiao, Xinong 9976,Wuqi Honghuaqiao-1, NingD07-2 and Xinong 9978 standing higher and the starch paste retrogradation of Ning D07-1, Wuqi Honghuaqiao-2, Qingyang Honghuaqiao, Menggu20 and Pingxuan 01-36 standing lower. The initial starch pasting temperatures and peak viscosities of the test varieties ranged between 62.80-72.60℃ and 126.58-141.00 RU, respectively. The starch trough viscosities, final viscosities, breakdowns, setbacks and peak viscosity times of the test varieties significantly differed. The highest viscosity was 118.00 RU, and the lowest breakdowns and setbacks were 13.00 RU and 57.33 RU respectively. The longest peak viscosity time was 5.80 min, and the most stable starch pastes appeared in Dingbian Tianqiao. These results indicated that the test varieties had significantly different starch characters and thus, while the varieties were used to process buckwheat starch or flour, their different starch characters should be taken into account.