Characterization of Chlorogenic Acids in Coffee by Flow-Through Chronopotentiometry

Abstract

In this study, flow-through chronopotentiometry (FTCP) has been developed as an electroanalytical method for characterization (identification and quantification) of chlorogenic acids (CGAs) in coffees. The characterization of CGAs in coffee was based on the electrochemical behavior of the main chlorogenic acid (CGAs) isomers presented in coffee (caffeoylquinic acids (CQAs), dicaffeoylquinic acids (diCQAs), and feruloylquinic acids (FQAs)) and the spiking of CGAs standards in coffee samples. The FTCP study has shown that electrochemical properties of CGAs strongly depend on their chemical structure and electronic properties, particularly on the presence of electron-donating −OH, −CH═CH− and −OCH3 groups and strong electron-withdrawing ester (−COOR) group presented in their structure. The FTCP measurements of coffee samples show that their electrochemical behavior is very similar to that of CGAs. Therefore, FTCP can be used for characterization of CGAs and determination of their content in coffees. 5-O-Caffeoylquinic acid (5-CQA), prevailed CGAs in coffees, was used as a standard for quantification of total CGA content in coffee. The linear calibration curve of 5-CQA was observed within the concentration range of 5 to 100 μmol L−1 with the limit of detection 5.7·10−7 mol L−1. The total CGA content of coffees has been expressed in 5-CGA equivalents per 100 g of coffee. It was shown that FTCP is a very sensitive, precise, and acurate method for determination of total CGA content in coffee. It should be noted that in presented investigation, FTCP was for the first time used for the study of electrochemical properties of polyphenolic antioxidants (including CGAs) and their characterization in some of the food samples.