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Characterization of chlorogenic acids in coffee by differential pulse voltammetry

Chlorogenic acids (CGAs) are one of the most important dietary polyphenols in human diet and the coffee is the major source of CGAs. The most abundant CGAs in the coffee are caffeoylquinic acids (CQAs) and the dominant is 5-O-caffeoylquinic acid (5-CQA). In this study, the characterization of CGAs in different coffee samples was performed by differential pulse voltammetry (DPV) and 5-CQA was used as a standard. The effect of concentration of 5-CQA on the DPV responses was investigated. Calibration curve has shown linearity in the concentration range 5-50 μmol L-1 (LOD=1.2·10-6 mol L-1, LOQ=4.0·10-6 mol L-1). Coffee extracts (green beans, roasted beans, ground coffee, instant coffee) were diluted in 0.1 mol L-1 PBS pH 7 in order to perform DP voltammogram. All DPVs of coffees were characterized by the presence of two anodic peaks, peak 1 between 0.187-0.200 V and peak 2 between 0.430-0.444 V. In order to identify the profile of CGAs in the coffee samples, the spiking was performed with standard solutions of CQAs, diCQAs and FQAs. The total CGAs content in coffee samples was calculated from the summarised peak current (Ip) values of peak 1 and peak 2 by using calibration curve of 5-CQA as a standard. The total CGAs content was expressed as mg 5-CQA equivalents per 100 g of coffee (mg 5-CQAE/ 100 g coffee). The CGAs content decreases as follow: green coffee, ground coffee, instant coffee, roasted beans. This indicated that the roasting process and the coffee processing have an influence on the loss of CGAs. DPV results are in the very good agreement with the results obtained by HPLC method. The DPV measurements of coffee samples have shown that electrochemical properties of coffee samples were very similar to that of investigated CGAs. Therefore, DPV has shown as very sensitive and selected method for the determination of total CGAs content of coffee samples.

chlorogenic acids; differential pulse voltammetry; coffee

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