Stability and degradation of chlorogenic acids in green and roasted coffee beans during long-term storage

In this study, the stability of chlorogenic acids during long-term coffee storage was investigated. Two time series including green coffee beans over a four-year period under ambient storage conditions and roasted coffee over a two year period with added historical samples with up to 28 year storage periods were investigated. Our investigations cover both Arabica and Robusta coffee as well as a selection of different origins. For six key chlorogenic acids absolute quantities were determined by LC-MS methods using authentic reference materials. For an additional ten chlorogenic acids relative quantities are reported and half-life times for the derivatives determined. The main chemical pathways responsible for degradation were studied including hydrolysis of chlorogenic acids and oxidation to yield novel chlorogenic acid quinone derivatives characterized by high resolution tandem mass spectrometry. For all samples a surprising stability of the compounds was observed if compared to other coffee constituents. Stability was mainly depending on the matrix with roasted coffee displaying increased chlorogenic acid storage stability if compared to green coffee beans.