The composition of common buckwheat (Fagopyrum esculentum Moench) seed milling fractions depends upon the relative abundance of various seed tissues in each. Fancy (light) flour contains mainly central endosperm, while the bran milling fraction has seed coat and some embryo tissues. Phytate, found in protein bodies of embryo and aleurone cells, is the major storage form of phosphorus, potassium, magnesium and some microelements in seeds. Phytic acid (35-38 g kg(-1)) and minerals are concentrated in bran, a milling fraction with high concentrations of phytate-rich tissues. Polyphenolics, including condensed tannins (proanthocyanidins), are also concentrated in bran (11-15 g kg(-1)). Rutin is concentrated in the hull of common buckwheat (0.8-4.4 g kg(-1)). Rutin concentration is low (0.2-0.3 g kg(-1)) in groats of common buckwheat but higher (0.7-0.8 g kg(-1)) in bran containing hull fragments. Rutin is 300-fold more concentrated (81 g kg(-1)) in groats of tartary buckwheat (Fagopyrum tataricum (L) Gaertn) than in groats of common buckwheat. Only small amounts of quercetin were detected. Bran is a concentrated source of phytic acid and tannins, a consideration in consumption of large amounts of buckwheat bran for nutritional or medicinal purposes. (C) 2001 Society of Chemical Industry.