Quantification of isoflavones in coffee by using solid phase extraction (SPE) and highperformance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).

A new method for extracting isoflavones from espresso coffee (EC) was coupled with high-performance liquid chromatography- tandemmass spectrometry (MS/MS) for the first time to analyse five isoflavones, which included both a glycosilated form, genistin and the aglycons daidzein, genistein, formononetin and biochanin A. Isoflavones were extracted fromcoffee samples usingmethanol, stored in a freezer overnight to precipitate proteic or lipidic residues and purified on SPE C18 cartridges before highperformance liquid chromatography-MS/MS analysis. The recovery percentages obtained by spiking the matrix at concentrations of 10 and 100 μg l-1 with a standard mixture of isoflavones were in the range of 70 to 104%. The limits of detection and limits of quantification were in the range of 0.015-0.3 μg l-1 and 0.05-1 μg l-1, respectively. Once validated, the method was used to analyze the concentrations of isoflavones in six ECs and ten ground coffee samples. Only formononetin and biochanin A were found, and their respective concentrations ranged from 0.36 to 0.41 μg l-1 and from 0.58 to 3.26 μg l-1 in ECs and from 0.36 to 4.27 μgkg-1 and from 0.71 to 3.95 μgkg-1 in ground coffees. This method confirms the high specificity and selectivity of MS/MS systems for detecting bioactives in complex matrices such as coffee. [ABSTRACT FROM AUTHOR]