Aroma fingerprinting in green and roasted beans and ground coffee by Proton PTR-ToF-MS

The research is based on the utilization of the PTR-TOF-MS headspace analysis to distinguish, by VOCs, different matrices in coffee beans. Two species, Coffea arabica and Coffea canephora, contribute to the total production; the commercial value of the coffee depends on the species (Coffea arabica generally being considered of highest quality) and on geographical origin, including not only the pedoclimatic conditions, but also the processing systems (dry or wet). Green beans, medium roasted beans and the related ground coffee of both C. arabica and C. canephora, coming respectively from 7 and 5 different geographical zones of Africa, America and Asia, were comparatively evaluated. By a PLS-DA analysis the green beans samples resulted sharply separated from the roasted beans and from the ground coffees, with a quantitative and qualitative increase of VOCs. The main protonated masses discriminating C. arabica from C. canephora were, in the green beans, m/z = 33.033 (tentatively identified as methanol), 49.010 (TI: methanethiol), 81.069 (TI: terpene fragment), 95.086 (TI: terpene fragment), 101.060 (TI: pentanedione) and, in the class of roasted beans, m/z = 69.033 (TI: furan), 85.028 (TI: furanone), 97.028 (TI: furfural), 111.045 (TI: acetilfuran), 141.055 (TI: furfurilacetate). In the arabica group, roasted beans and ground coffee resulted very well distinguished, without regard of the country of production. The different Indian samples (two canephora and one arabica) were correctly classified. The separation between the two subgroups roasted beans and ground coffee was determined by quantitative differences of the same protonated masses, as m/z = 43.054 (TI: alkyl fragment), 61.028 (TI: acetic acid), 85.028 (TI: furanone), 148.076 (TI: furfurilpyrrole). These results show that by the PTR-TOF-MS headspace VOCs analysis it is possible to check the correct attribution of the roasted beans and ground coffees to the right category (arabica or canephora), without regard of geographical origin of production