Reactions of green and black teas with Cu(II)

Electron paramagnetic resonance (EPR) measurements of the products of reactions between Cu(II) and samples of green and black teas showed spectral components from at least six different Cu(II) complexes with both tea types. Several of these complexes were common to both teas in spite of major differ...

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Bibliographic Details
Published in:Food & function 2012-04, Vol.3 (4), p.399-409
Main Authors: Goodman, B A, Ferreira Severino, J, Pirker, K F
Format: Article
Language:English
Subjects:
Amino acids
Beverages
Camellia sinensis - chemistry
Copper
Copper - chemistry
E.S.R
Electron Spin Resonance Spectroscopy
Free radicals
gallic acid
Hydrogen-Ion Concentration
Oxidation
pH effects
Plant Extracts - chemistry
Polyphenols
Polyphenols - chemistry
Tea
Tea - chemistry
theanine
Transition metals
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Summary:Electron paramagnetic resonance (EPR) measurements of the products of reactions between Cu(II) and samples of green and black teas showed spectral components from at least six different Cu(II) complexes with both tea types. Several of these complexes were common to both teas in spite of major differences in their polyphenol compositions. The pH range observed for complex formation, and the total signal intensity in the pH range 4-8, were greatly different from those for the reactions of Cu(II) with (-)-epigallocatechin gallate and gallic acid, the main polyphenols responsible for the free radical signals observed during oxidation of these beverages. Components with spectral parameters similar to those of Cu(II) complexes with theanine, the major amino acid in tea, may contribute to two of the spectra recorded under acidic conditions. However, the initial complexes formed at the lowest pH values investigated are still unidentified. EPR spectra with parameters consistent with Cu(II) polyphenol complexes were only observed under alkaline conditions, thus suggesting that components of tea other than polyphenols might be more important in reactions with copper, and possibly other transition metals, in solutions under physiological conditions.
ISSN:2042-6496
2042-650X
DOI:10.1039/c1fo10086f