Fe(II), Cu(II) and Zn(II) chelating activity of buckwheat and buckwheat groats tannin fractions
2007
Karamac, M.,Polish Academy of Sciences, Olsztyn (Poland). Inst. of Animal Reproduction and Food Research, Div. of Food Science
Phenolic compounds were extracted from buckwheat and buckwheat groats into 80 percent acetone (v/v). The crude extracts were separated with Sephadex LH-20 column chromatography into low molecular weight phenolic compounds and tannin fractions. The tannin fractions were characterized by colour reaction with vanillin/HCl reagent, ability for protein precipitation as well as SE-HPLC method. Chelation of Cu(II) and Zn(II) by tannin fractions was determined by reaction with tetramethylmurexide (TMM) whereas Fe(II) chelation was investigated by forming complexes with ferrozine. The tannin fractions obtained from buckwheat and buckwheat groats gave similar results in vanillin test, A500/mg was 1.04. Also results obtained using precipitation method were comparable. SE-HPLC chromatograms showed that in tannin fraction of buckwheat groats polymers with molecular weight greater or qual tannic acid were present. On the chromatogram of buckwheat tannins peaks were shifted to lower molecular weight compounds. Tannins of buckwheat were stronger chelators of all metal ions tested (Fe(II), Cu(II) and Zn(II)) than tannins of buckwheat groats. Ions of copper were chelated the most effectively, 1 mg of buckwheat and buckwheat groats tannin fractions added per assay bound 86.0 and 72.9 percent of Cu(II), respectively. Buckwheat tannins used in the test at a level of 2.5 mg/assay bound approximately twice more Fe(II) than the same addition of buckwheat groats tannins. Zn(II) was chelated to the lowest extent, 17.2 percent was bound by buckwheat tannins and 13.5 percent by buckwheat groats tannins (5 mg of tannin/assay)
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