Identification of markers of thermal processing ("roasting") in aqueous extracts of Coffea arabica L. seeds through NMR fingerprinting and chemometrics.

Roasting of Coffea arabica L. seeds gives rise to chemical reactions that produce more than 800 compounds, some being responsible for the desired organoleptic properties for which the beverage called "coffee" is known. In the industry, the "roasting profile", i.e. the times and temperatures applied, is key to influence the composition of roasted coffee beans and the flavour of the beverage made from them. The impact of roasting on the chemical composition of coffee has been the subject of numerous studies, including by NMR spectroscopy. However, the roasting equipment and profiles applied in these studies are often far from real industrial conditions. In this work, the effect of two critical technological parameters of the roasting process namely the "development time" (the period of time after the "first crack", a characteristic noise due to seed disruption) and the final roasting temperature on coffee extracts were investigated. Seeds were roasted at pilot scale according to 13 industrial roasting profiles and extracted in D2 O. The extracts were analysed by 1 H NMR experiments. The NMR spectra were compared using (i) quantitative analysis of main signals by successive orders of magnitude and (ii) chemometric tools (PCA, PLS and S-OPLS). This allowed to identify compounds which may serve as markers of roasting and showed that changes in chemical composition can be detected even for slight change in final temperature (~1°C) or in total roasting time (~ 25 s).