Development of new analytical methods for the quantification of organic acids, chlorogenic acids and caffeine in espresso coffee by using solid-phase extraction (SPE) and high-performance liquid chromatography-diode array detector (HPLC-DAD)

Acidity is an important parameter in coffee, contributing to aroma and flavor, imparting fruity notes, and improving the gloss of the coffee, making the beverage more interesting. In this study, two analytical methods were proposed to quantify the content of nine organic acids, caffeine, phenolic acids, and four chlorogenic acids in espresso coffee using an HPLC-DAD instrument. In addition, a new solid-phase extraction (SPE) sample cleanup procedure for organic acids has been optimized. The newly developed analytical methods were characterized by satisfactory recovery levels of sample clean-up procedure (41.798.6%) and good resolution of all peaks in both chromatography separations. In addition, the investigated validation parameters implied good repeatability, sensitivity and linearity. These methods were applied to espresso samples with three different roasting degrees (light, medium, and dark) of the same coffee variety (100% Arabica) to study the effects of the roasting process on the content of caffeine, organic and chlorogenic acids. The caffeine content was relatively stable to heat. The concentration of chlorogenic acids decreased due to roasting while the total organic acid content increased, with the formation of acetic and lactic acids in medium and dark roasting. Therefore, these new approaches can be considered as reference methods for the determination of carboxylic acids in coffee.