Table 3.
Main volatile organic compounds detected by HS-SPME-GC×GC-TOF in the different onion samples. Data are the mean of three determinations. First dimension retention time in minute (1st D RT). Second dimension retention time in second (2nd D RT). Response of the two-dimensional peak (volume). Relative amount (%) calculations were based on the ratio between the peak volume of each compound and the sum of volumes of all selected compounds. Not detected (n.d.).
| Compound | 1st D RT (min) |
2nd D RT (s) |
Rings (volume) |
Flakes (volume) |
Rings (%) |
Flakes (%) |
|---|---|---|---|---|---|---|
| propyl mercaptan | 6.05 | 0.42 | 1,724,317 | 2,979,593 | 5.0 | 5.8 |
| allylthiol | 6.20 | 0.62 | 816,521 | n.d. | 2.4 | n.d. |
| 2-methyl-2-butenal | 8.65 | 1.04 | 677,649 | n.d. | 2.0 | n.d. |
| 2,4-dimethylthiophene | 12.85 | 1.06 | 562,705 | 787,731 | 1.6 | 1.5 |
| 3,4-dimethylthiophene | 13.80 | 1.24 | 1,170,022 | 6,773,463 | 3.4 | 13.2 |
| methyl propyl disulfide | 14.80 | 1.04 | 416,658 | 2,247,811 | 1.2 | 4.4 |
| methyl 1-propenyl disulfide | 15.15 | 1.28 | 149,034 | 1,541,084 | 0.4 | 3.0 |
| dimethyl trisulfide | 16.40 | 1.72 | 133,334 | 1,679,770 | 0.4 | 3.3 |
| dipropyl dilsulide | 21.60 | 0.94 | 11,529,581 | 14,500,819 | 33.4 | 28.3 |
| propenyl propyl disulfide | 21.95 | 1.10 | 1,365,546 | 3,030,564 | 4.0 | 5.9 |
| diethanol disulfide | 23.40 | 1.38 | 740,611 | 3,813,741 | 2.1 | 7.4 |
| unidentified sulfide mw 152 | 23.95 | 1.68 | 254,301 | 2,194,284 | 0.7 | 4.3 |
| decanal | 25.15 | 0.92 | 145,059 | 1,481,756 | 0.4 | 2.9 |
| dipropyl trisulfide | 29.50 | 1.08 | 8,135,894 | 5,312,160 | 23.6 | 10.4 |
| trans-3,5-diethyl-1,2,4-trithiolane | 29.90 | 1.62 | 1,341,744 | 220,925 | 3.9 | 0.4 |
| cis-3,5-diethyl-1,2,4-trithiolane | 30.15 | 1.64 | 2,565,177 | 912,354 | 7.4 | 1.8 |
| propenyl propyl trisulfide | 30.15 | 1.38 | 1,970,506 | 3,730,800 | 5.7 | 7.3 |
| 4,6-Diethyl-1,2,3,5-tetrathiolane | 38.40 | 2.22 | 809,467 | n.d. | 2.3 | n.d. |