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Molecular Structure and Some Physicochemical Properties of Buckwheat Starches

¹Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima, University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan. ²Present address: Nihon Starch Co. Ltd., 3-20 Nan-Ei, Kagoshima 891-0196, Japan. ³Food Technology Research Institute of Nagano Prefecture, 1-205 Kurita, Nagano 380-0921, Japan. ⁴Kirishima Corp., 4-28-1 Shimokawahigashi, Miyakonojo, Miyazaki 885-8588, Japan. ⁵Corresponding author. Phone/Fax: +81-99-285-8641. E-mail: takeda@chem.agri.kagoshima-u.ac.jp

The molecular structure and pasting properties of starches from eight buckwheat cultivars were examined. Rapid viscograms showed that buckwheat starches had similar pasting properties among cultivars. The actual amylose content was 16–18%, which was lower than the apparent amylose content (26–27%), due to the high iodine affinity (IA) of amylopectin (2.21–2.48 g/100 g). Amylopectins resembled each other in average chain-length (23–24) and chain-length distributions. The long-chains fraction (LC) was abundant (12–13% by weight) in all the amylopectins, which was consistent with high IA values. The amyloses were also similar among the cultivars in number-average DP 1,020–1,380 with 3.1–4.3 chains per molecule. The molar-based distribution indicated that all the amyloses comprised two molecular species differing in molecular size, although the weight-based distribution showed a single species. A comparison of molecular structures of buckwheat starches to cereal starches indicated buckwheat amylopectins had a larger amount of LC, and their distributions of amylose and short chains of amylopectin on molar basis were similar to those of wheat and barley starches.