Effect of Copper on Fatty Acid Profiles in Non- and Semifermented Teas Analyzed by LC-MS-Based Nontargeted Screening

J Agric Food Chem. 2015 Sep 30;63(38):8519-26. doi: 10.1021/acs.jafc.5b02792. Epub 2015 Sep 15.

Abstract

Unsaturated fatty acids are well-known precursors of aroma compounds, which are considered important for green tea quality. Due to the known copper-induced oxidation of unsaturated fatty acids and the broad variability of the amount of copper present in tea infusions, this paper investigates the influence of copper, added at a nontoxic concentration (300 μM) to non- and semifermented teas, on the degradation of fatty acids and fatty acid hydroperoxides thereof. The abundance of fatty acids in green and oolong tea was determined by means of a nontargeted approach applying high-resolution MS/MS. As a result, most of the fatty acids in green and oolong tea were already oxidized prior to copper addition. Addition of 300 μM CuSO4 to the oolong tea sample resulted in a decrease of 13-hydroperoxy-9Z,11E-octadecadienoic acid, an important flavor precursor, from 0.12 ± 0.02 to 0.05 ± 0.01 μM (p = 0.035), and other oxidized fatty acids decreased as well. However, copper-induced degradation of oxidized fatty acids was less pronounced in green tea compared to oolong tea, most likely due to the formation of copper complexes with low-molecular-weight compounds as evidenced by electron paramagnetic resonance spectroscopy.

Keywords: copper; epigallocatechin-3-gallate; fatty acid; nontargeted screening; polyphenol; tea.

MeSH terms

  • Chromatography, High Pressure Liquid / methods
  • Copper / chemistry*
  • Fatty Acids / chemistry*
  • Fermentation
  • Flavoring Agents / chemistry
  • Oxidation-Reduction
  • Tandem Mass Spectrometry / methods
  • Tea / chemistry*

Substances

  • Fatty Acids
  • Flavoring Agents
  • Tea
  • Copper