. 2020 Mar 5;25(5):1166. doi: 10.3390/molecules25051166

Table 1.

Volatile compounds detected in espresso coffees (EC) samples by headspace solid-phase microextraction (HS-SPME)/gas chromatography–mass spectrometry (GC-MS).

Compound	KI ¹	ID ²	Compound	KI ¹	ID ²
ALDEHYDES			ESTERS
2-methylpropanal	827	B	methyl acetate	838	B
2-methylbutanal	919	B	ethyl acetate	898	B
3-methylbutanal	921	A	propanoic acid, 3-methyl-, methyl ester	1008	C
furfural	1472	B	methyl isovalerate	1020	C
benzaldehyde	1527	A	butyl butanoate	1229	C
5-methyl-2-furfural	1580	B	prenyl acetate	1256	C
2-methylbenzaldehyde	1596	C	furfuryl formate *	1504	B
2-methyl-3-(2-furyl)acrolein	1682	C	2-oxobutyl acetate	1533	C
1H-pyrrole-2-carboxaldehyde	2034	A	2-furfuryl-propanoate	1602	B
KETONES			PYRAZINES
2-butanone	906	B	pyrazine	1210	B
2-pentanone	979	B	2-methyllpyrazine *	1266	B
2,3-butandione	982	B	2,5-dimethylpyrazine *	1320	B
2,3-pentanedione	1063	B	2,6-dimethylpyrazine *	1325	B
3-penten-2-one	1127	B	2-ethylpirazine *	1334	B
2,3-hexanedione	1134	B	2,3-dimethylpyrazine *	1345	B
1-(furan-2-yl)ethanone *	1512	B	2-ethyl-6-methylpyrazine *	1385	B
1-(furan-2-yl)butan-2-one	1604	B	2-ethyl-5-methylpyrazine *	1390	B
1-(1-methylpyrrol-2-yl)ethanone	1659	B	2,3,5-trimethylpyrazine	1404	A
1-(1-methylpyrrol-2-yl)ethanone	1659	B	2-ethyl-3-methylpyrazine	1419	C
furfural acetone derivative	1910	C	2,6-diethylpyrazine *	1433	B
furfural acetone derivative	1910	C	3-ethyl-2,5-dimethylpyrazine *	1441	B
TERPENES			SULFUR COMPOUNDS
β-linalool	1550	B	dimetilsulfide	1070	B
p-menthene monoterpenoid derivative	1650	C	2-(methylsulfanylmethyl)furan (furfuryl methyl sulfide)	1490	B
p-menthene monoterpenoid derivative 2	1694	C
PYRROLES			PHENOLIC COMPOUNDS
1-methyl-1H-pyrrole	1141	B	2-methoxyphenol (guaiacol)	1867	B
1H-pyrrole derivative *	1801	C	2-methoxy-4-methylphenol	1871	B
1-furfurylpyrrole	1837	B	4-ethylguaiacol	2034	B
2-acetyl-1H-pyrrole	1979	B	2-methylphenol (o-cresol)	2092	B
1-methyl-1H-pyrrole-2-carbaldehyde derivative *	2107	C	3-methylphenol (m-cresol)	2171	B
1-methyl-1H-pyrrole-2-carbaldehyde derivative *	2107	C	p-vinylguaiacol (2-methoxy-4-vinylvinylphenol)	2193	B
FURANS			OTHERS
2-methylfuran	879	B	unknown 1	1459	-
2,5-dimethylfuran	956	B	benzyl alcohol	1880	C
Vinylfuran	1074	B	2-furanmethanol	1667	B
2-(methoxymethyl)furan	1243	B	2-furanmethanolacetate (furfuryl alcohol acetate)	1542	B
2-butylfuran derivative	1524	C	unknown 2 *	2030	-
furan,2,2′-methylenbis	1614	B	unknown 3 *	2038	-
			furfurylammine derivative	2236	C
difurfuryl ether (2,2′-[oxybis(methylene)]) bisfuran	1992	C	unknown 4	2253	-
difurfuryl ether (2,2′-[oxybis(methylene)]) bisfuran	1992	C	indole	2386	B
			3-methylindole	2450	B
PYRIDINES
Pyridine	1181	B
4(H)-pyridine, n-acetyl	1724	B

¹ Kovats Index (KI) experimentally determined for the SUPELCO^®-Wax capillary column using homologous series of C8-C30 alkanes; ² Identification (ID). Reliability of identification proposal is indicated by: (A) mass spectrum, retention time, and KI according to standards; (B) mass spectrum and retention index comparing literature data [1,12,15,16,17,18,19,20,21,22]; (C) mass spectrum compared with NIST 11 mass spectral database (pubchem.ncbi). * Key odorants selected by partial least squares discriminant analysis (PLS-DA) (VIP threshold > 1).