. 2020 Jan 18;25(2):408. doi: 10.3390/molecules25020408

Table 1.

Relative concentration (µg g⁻¹ based on the relative quantitation using internal standard, of volatile organic compounds detected acid by HS-SPME-GC-MS in the different onion samples in the absence and presence of ascorbic acid. Data are the mean of three determinations. Retention Indices (RI_cal): Non-isothermal Kovats retention indices from temperature-programming, using the definition of Van den Dool and Kratz, 1963 [19]. Retention Indices (RI_ref): Non-isothermal Kovats retention indices from temperature-programming from Chemistry WebBook. Not dectected (n.d.). traces (tr). For each compound, different letters (a, b, c) indicate significant differences at p < 0.05 by Fisher’s Least Significant Difference (LSD) test.

Compound	RI_ref	RI_cal	Identification Ions		Dry Onion (µg g⁻¹)		Dry Onion with Ascorbic Acid (µg g⁻¹)
Compound	RI_ref	RI_cal	Identification Ions		Flakes	Rings	Flakes	Rings
monosulfides				Σ	0.32	0.09	0.25	0.09
monosulfides				Σ	0.32	0.09	0.25	0.09
dimethyl sulfide	729	729	62, 47, 35		0.07 ^b	0.03 ^a	0.06 ^b	0.03 ^a
allyl propyl sulfide	1137	1113	116, 87, 73		0.20 ^b	0.04 ^a	0.16 ^b	0.04 ^a
1-propenyl propyl sulfide	-	1138	41, 116, 74		0.05 ^b	0.02 ^a	0.03 ^a	0.02 ^a
disulfides				Σ	76.76	32.89	75.04	41.74
disulfides				Σ	76.76	32.89	75.04	41.74
dimethyl disulfide	1105	1081	94, 79, 45		0.14 ^b	0.03 ^a	0.11 ^b	0.02 ^a
methyl propyl disulfide	1263	1244	80, 122, 43		2.56 ^b	0.51 ^a	2.34 ^b	0.73 ^a
methyl cis-1-propenyl disulfide	1298	1278	73, 120, 45		2.09 ^b	0.20 ^a	1.60 ^b	0.42 ^a
methyl allyl disulfide	1322	1293	41, 120, 45		0.05 ^b	0.02 ^a	0.05 ^b	0.04 ^a,b
methyl trans-1-propenyl disulfide	1322	1302	73, 120, 45		2.81 ^c	0.29 ^a	2.47 ^c	0.80 ^b
isopropyl propyl disulfide	-	1331	150, 43, 108		0.04 ^b	0.01 ^a	0.03 ^b	0.01 ^a
dipropyl disulfide	1413	1391	150, 43, 108		49.34 ^b	28.53 ^a	49.77 ^b	33.35 ^a
propyl cis-1-propenyl disulfide	1450	1427	148, 106, 41		6.69 ^b	0.61 ^a	6.05 ^b	1.38 ^a
allyl isopropyl disulfide	-	1443	57, 148, 106		0.46 ^c	0.14 ^a	0.47 ^c	0.25 ^b
propyl trans-1-propenyl disulfide	1473	1452	148, 106, 41		11.30 ^b	1.53 ^a	10.87 ^b	3.34 ^a
allyl cis-1-propenyl disulfide	1464	1480	146, 41, 105		0.05 ^b	0.01 ^a	0.04 ^b	0.02 ^a
allyl trans-1-propenyl disulfide	1533	1500	146, 41, 105		0.08 ^b	0.03 ^a	0.08 ^b	0.04 ^a
1-(1-(methylthio)propyl)-2-propyl disulfide	-	1876	89, 61, 73		0.15 ^ab	0.07 ^a	0.19 ^b	0.18 ^b
methyl 1-(propylthio)propyl disulfide	-	1985	117, 75, 41		0.44 ^a	0.65 ^b	0.48 ^a	0.82 ^c
1-(cis-1-propenylthio)propyl propyl disulfide	-	2075	115, 81, 73		0.19 ^b	0.09 ^a	0.20 ^b	0.14 ^a,b
1-(trans-1-propenylthio)propyl propyl disulfide	-	2080	115, 81, 73		0.37 ^b	0.17 ^a	0.29 ^a,b	0.20 ^a
trisulfides				Σ	41.08	5.30	41.69	11.21
trisulfides				Σ	41.08	5.30	41.69	11.21
dimethyl trisulfide	1403	1399	126, 111, 79		6.01 ^c	0.49 ^a	7.16 ^c	1.97 ^b
methyl propyl trisulfide	1576	1553	154, 112, 43		6.56 ^c	0.88 ^a	6.45 ^c	1.92 ^b
dipropyl trisulfide	1713	1695	182, 43, 75		23.28 ^b	3.32 ^a	22.08 ^b	5.37 ^a
allyl propyl trisulfide	1797	1753	115, 180, 73		0.13 ^b	0.04 ^a	0.10 ^b	0.03 ^a
propyl trans-1-propenyl trisulfide	1770	1768	180, 74, 116		5.10 ^c	0.57 ^a	5.90 ^c	1.92 ^b
other S-compounds				Σ	6.08	2.45	9.09	4.83
other S-compounds				Σ	6.08	2.45	9.09	4.83
carbon disulfide	745	716	76, 44, 32		0.07 ^b	0.02 ^a	0.03 ^a	0.02 ^a
1-propanethiol	845	816	76, 47, 43		0.21 ^a	0.14 ^a	0.84 ^c	0.46 ^b
2,4-dimethylthiophene	1197	1199	112, 111, 97		0.42 ^b,c	0.16 ^a	0.46 ^c	0.26 ^a,b
3,4-dimethylthiophene	1253	1264	112, 111, 97		3.57 ^b	1.16 ^a	5.80 ^c	2.55 ^b
cis-3,5-diethyl-1,2,4-trithiolane	1775	1807	180, 74, 151		0.77 ^c	0.35 ^a	0.84 ^c	0.63 ^b
trans-3,5-diethyl-1,2,4-trithiolane	1795	1826	180, 74, 151		1.04 ^c	0.62 ^a	1.12 ^c	0.91 ^b
aldehydes				Σ	1.80	1.31	3.71	3.41
aldehydes				Σ	1.80	1.31	3.71	3.41
propanal	784	764	58, 29, 28		0.20 ^b	0.11 ^a	0.23 ^b	0.21 ^b
2-methyl propanal	800	788	72, 43, 41		0.03 ^a	0.03 ^a	0.03 ^a	0.03 ^a
2-methyl butanal	916	917	41, 86, 57		0.09 ^a	0.06 ^a	0.07 ^a	0.07 ^a
3-methyl butanal	914	921	44, 71, 45		0.36 ^c	0.31 ^b,c	0.21 ^a	0.23 ^a,b
pentanal	978	985	44, 86, 58		0.02 ^a	0.02 ^a	0.06 ^b	0.05 ^b
hexanal	1084	1088	56, 72, 82		0.30 ^b	0.23 ^a	0.47 ^c	0.31 ^b
2-methyl-2-butenal	1104	1106	84, 55, 39		0.05 ^a	0.03 ^a	0.04 ^a	0.04 ^a
2-methyl-2-pentenal	1185	1170	98, 41, 69		0.20 ^c	0.07 ^a	0.14 ^b	n.d.
heptanal	1186	1192	70, 86, 96		0.07 ^a	0.06 ^a	0.11 ^b	0.13 ^b
octanal	1296	1298	84, 100, 110		0.08 ^a	0.06 ^a	0.63 ^c	0.35 ^b
(Z)-2-heptenal	1339	1336	83, 112, 55		0.10 ^b,c	0.06 ^a	0.13 ^b,c	0.08 ^a,b
nonanal	1394	1402	98, 57, 114		tr	tr	tr	tr
furfural	1471	1470	96, 95, 39		n.d.	0.06 ^a	1.00 ^b	1.55 ^c
decanal	1515	1507	112, 82, 95		0.16 ^a	0.13 ^a	0.49 ^c	0.28 ^b
benzaldehyde	1529	1542	106, 105, 77		0.14 ^c	0.08 ^a	0.10 ^b	0.08 ^a
ketones				Σ	0.04	0.03	0.03	0.03
ketones				Σ	0.04	0.03	0.03	0.03
6-methyl-5-hepten-2-one	1338	1340	126, 69, 108		0.04 ^a	0.03 ^a	0.03 ^a	0.03 ^a
carboxylic acids				Σ	0.02	0.07	5.30	3.32
carboxylic acids				Σ	0.02	0.07	5.30	3.32
hexanoic acid	1838	1846	87, 60, 73		n.d.	n.d.	0.62 ^a	0.55 ^a
2-ethyl hexanoic acid	1950	1951	88, 73, 116		n.d.	n.d.	3.26 ^b	1.85 ^a
nonanoic acid	2173	2167	73, 158, 129		0.02 ^a	0.07 ^a	1.42 ^c	0.92 ^b
other compounds				Σ	1.16	0.65	1.10	0.79
other compounds				Σ	1.16	0.65	1.10	0.79
2-penthylfuran	1236	1235	138, 81, 82		0.05 ^a,b	0.02 ^a	0.07 ^b	0.05 ^a,b
1-octen-3-ol	1451	1444	57, 72, 99		0.27 ^b	0.20 ^a	0.22 ^a	0.32 ^a
isopropyl dodecanoate	1832	1835	200, 102, 183		0.27 ^b	0.17 ^a	0.29 ^b	0.19 ^a
2,2,4-trimethyl-1,3-pentanediol diisobutyrate	-	1885	71, 83, 111		0.57 ^b	0.26 ^a	0.52 ^b	0.23 ^a
Total VOCs content					127.26	42.79	136.21	65.42