## 2 Results
### Identification of Volatiles
#### 2.1.3 Aldehydes and Alcohols  
All the analyzed cauliflower and broccoli cultivars contained high percentage levels of aldehydes. In broccoli, the dominating aldehydes were hexenal, 2-hexenal (more than 10% in all samples), 2,4-heptadienal and benzaldehyde. According to [29], those aldehydes contribute the \"green\" type aromas to the final broccoli fragrance. In the cauliflower cultivars, the content of aldehydes was even higher than in broccoli, with 2_4_-heptadienal, 2-hexenal, hexanal, benzaldehyde, propanal and nonanal being dominant (found in the highest percentage levels). The presented profile of aldehydes in cauliflower was quite similar to that in broccoli. A marked decline in the diversity and percentage contents of aldehydes was observed in all kohlrabi varieties. In all of the analyzed cultivars, the level of aldehydes was below 5%. The magnitudes of the aldehyde peaks on the chromatograms were also relatively small. In comparison with cauliflower and broccoli, which contain respectively 22 and 16 different aldehydes, seven aldehydes were identified in kohlrabi after GC\(\times\)GC analysis, seemingly to be a very small number. The most abundant aldehyde in all varieties was 2-butenal, with a flower-type odor [29]. In Brussels sprouts, the aldehyde percentage content was low; however, their peak areas and diversity were relatively high. Fifteen different aldehydes were identified by GC\(\times\)GC, with the ratios of all aldehydes being similar and with benzaldehyde being the most abundant. Twelve different alcohols were also present in the Brussels sprouts chromatograms and their percentage contents were significantly higher than those of the aldehydes (upper 20%). Only seven different aldehydes were identified in the kohlrabi samples, at less than 5% in all samples. Despite the small amounts of aldehydes, which are mostly important for \"green\", \"sweet\" and \"nice\" aromas, the intensity of \"raw kohlrabi\" and \"green\" odors detected by the panelists was relatively high. Alcohols were present in trace amounts, so they were disregarded in the percentage calculations. In cooked broccoli and cauliflower, the number of aldehydes was noticeably lower in the cooked vegetables, compared to raw varieties. In contrast, the number of aldehydes in the kohlrabi was significantly greater in the cooked vegetables. The percentage contents of different aldehydes in cooked kohlrabi varied between cultivars. In Brussels sprouts, the levels of the lipoxygenase (LOX) pathway products decreased in all cooked cultivars.  
Figure 4 shows the peak areas of the main groups of volatile compounds investigated in the analyzed vegetables, both raw and cooked. Total peak areas were used to indicate the differences between particular vegetables, so it can be seen that aldehydes are dominant in broccoli and cauliflower, whereas in kohlrabi, sulfides constitute the most abundant fraction. Additionally, the dominance of nitriles and isothiyanates in raw Brussels sprouts is easily noted. The error bars indicate differences caused by different cultivars taken for comparison, therefore they are in some instances relatively high.  
Similarly, the main fractions of the examined cooked vegetables can be compared, indicating an overall decrease in the amounts of volatiles caused by cooking, with some exceptions discussed above.