Abstract
Coffee is a beverage widely consumed in the world. The coffee species most commercialized worldwide are Arabica (Coffea arabica) and Robusta (Coffea canephora). Roasted coffee beans are the most used, but coffee leaves are also consumed as infusion in several countries for traditional medicinal purposes. They contain several interesting phenolic antioxidant compounds mainly belonging to chlorogenic acids (CGAs). In the present work, a liquid chromatography-electrochemical detection (LC-EC) method was developed for the determination of three main chlorogenic acid isomers, namely 3-, 4-, and 5-caffeoylquinic acids (CQA), in coffee leaves aqueous extracts. Samples from eight coffee species, namely; Coffea arabica, Coffea canephora, Coffea liberica, Coffea humilis, Coffea mannii, Coffea charrieriana, Coffea anthonyi, and Coffea liberica var. liberica, were grown and collected in tropical greenhouses. Linearity of the calibration graphs was observed in the range from the limit of quantification to 1.0 × 10−5 M, with R2 equal to 99.9% in all cases. High sensitivity was achieved with a limit of detection of 1.0 × 10−8 M for 3-CQA and 5-CQA (i.e., 3.5 µg/L) and 2.0 × 10−8 M for 4-CQA (i.e., 7.1 µg/L). The chromatographic profile of the samples harvested for each Coffea species was studied comparatively. Obtained raw data were pretreated for baseline variations and shifts in retention times between the chromatographic profiles. Principal Component Analysis (PCA) was applied to the pretreated data. According to the results, three clusters of Coffea species were found. In the water sample extracts, 5-CQA appeared to be the major isomer, and some species contained a very low amount of CQAs. Fluctuations were observed depending on the Coffea species and harvesting period. Significant differences between January and July were noticed regarding CQAs content. The species with the best CQAs/caffeine ratio was identified. The LC-EC data were validated by liquid chromatography-high resolution mass spectrometry (LC-HRMS).
Highlights
Coffee trees belong to the genus Coffea in the Rubiaceae family
The genus Coffea L. comprises more than 100 species, of which only two species, that is, Coffea arabica and Coffea canephora, are commercially cultivated on a large scale [1]
Interesting ethno-pharmacological uses and biological activities, which can partly be related to the presence of high amounts of chlorogenic acids (CGAs), have been described for coffee leaves [3,4,8,9]
Summary
Coffee trees belong to the genus Coffea in the Rubiaceae family. If the chemical composition of green coffee beans is well-known, less attention has been paid to the phytochemistry content of coffee leaves [2,3,4,5,6,7]. Interesting ethno-pharmacological uses and biological activities, which can partly be related to the presence of high amounts of chlorogenic acids (CGAs), have been described for coffee leaves [3,4,8,9]. Coffee leaves of Coffea arabica have been found to contain a total phenolic compound content at a concentration of 17.4 and 13.9% for young and mature leaves, respectively [10]. Total chlorogenic acids content in coffee beans accounts for 5–10% of dry matter basis (dmb), which is a much larger amount than caffeine
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