# Potential Aroma Chemical Fingerprint of Oxidised Coffee Note by HS-SPME-GC-MS and Machine Learning
## 4 Conclusions  
Twenty-five target components of the coffee volatilome were identified as markers of coffee oxidation because they showed the same behaviour and statistical significance in all samples studied, regardless of packaging and blending. Together, they play a synergistic role in the detection of oxidised coffee and can be considered the fingerprint of the oxidised note. Four volatiles associated with ageing increased in all the packages studied: acetic and propionic acids (_pungent, sour, rancid_), 1-H-pyrrole-2-carboxaldehyde (_musty_), and 5-(hydroxymethyl)-dihydro-2(3H)-furanone, while the other 21 decreased in oxidised coffees. The literature survey suggests several compounds as markers for the decrease in aroma quality of R&G coffee during storage, but they are not standardised. However, most of the proposed markers and indices seem to be more closely related to coffee aroma freshness, in particular: 2 and 3-methylbutanal (_malty_), 2-propanol (_ethereal pungent, earthly_), 2,3-butan and pentandione (_buttery, pungent_), dimethyl sulphide (cabbagelike), DMDS (_sulphur, cabbage_), MeSH (_sulphur, cabbage_), 2-FFT (_roasty, coffeelike_), and the ratios of 2-methylfuran/2-butanone, 2-methylfuran/2,3-butanedione, and MeSH/hexanal, the decrease of which was associated with coffee staling, or DMDS/MeSH, which increased with storage. The composition of the volatilome also depends on the packaging and blend. A comparison of these results with those in the literature shows that some markers are in common and present in lower amounts in oxidised coffees; these include 2,3-butanedione; 2,3-pentandione; 2-furfurylthiol; acetic acid (_pungent, sour_) and furaneal (_sweet, candy_); and the indices 2-methylfuran/2-butanone and 2-butanone/2-methylfuran. Conversely, other components seem to be specific to the packaging and/or blend, including 2-methylfuran, 2-methylbutanal, 2-acetylfuran, 2,5-dimethylfuran (_meaty_), and 2-methyl-2-cyclopenten-1-one. These data provide information on the oxidised note and show that artificial intelligence can be used successfully to instrumentally define the change in the quality of the coffee aroma over time. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods11244083/s1](https://www.mdpi.com/article/10.3390/foods11244083/s1)]([https://www.mdpi.com/article/10.3390/foods11244083/s1](https://www.mdpi.com/article/10.3390/foods11244083/s1)), Supplementary Table S1: List of volatile substances that have so far been associated in the literature with the deterioration of the aroma of roasted coffee. Supplementary Table S2: Volatiles identified with their experimental and literature retention indices (Its), target ion (Ti), and qualifier ions (Qis) and their mass spectral similarity index (SI). M, B, P, and I are the different packagings/blends for which the CV% of the coffee profiling, presented in conditional format, is reported (in yellow, CV% \(<-20\), and in red, CV% > 20). * Volatiles confirmed by reference standard. Supplementary Figure S1: CV% graph visualization of the standardized responses of the chromatographic profiles together with the CV% cut-off > 20 (orange range). Conceptualization, E.L., G.S., C.B., M.R.R., G.R. and G.P. ; data curation, G.S., E.B. and E.L.; formal analysis, G.S., E.B., G.R. and F.T. ; funding acquisition, C.B., G.P. and E.L.; investigation, G.S., E.B. and E.L.; methodology, G.S., E.B., M.R.R., G.R. and E.L.; supervision, E.L., M.R.R. and G.P. ; writing--original, G.S., E.B. and E.L.; writing--review and editing, G.S., E.B., M.R.R., G.R., F.T., E.L. and C.B. All authors have read and agreed to the published version of the manuscript. The authors declare that this study was supported by Lavazza S.p.A. by funding a PhD XXXV cycle from the University of Turin. The funder had the following involvement with the study: sharing study design, collection and providing samples, sensory analysis, revision, and editing of this article.