## 3 Results and Discussion
### Volatile Compounds
#### 3.1.1 'Salad' Rocket  
A total of 57 volatile compounds were identified or tentatively identified in the headspace of _E. sativa_ leaf samples. Nineteen compounds are newly reported for this species, some of which make up relatively large portions of the total volatile compounds' bouquet (Table 2). Compounds with the greatest relative abundances were (_Z_)-3-hexen-1-ol (**31**, 40.9%), (_E_)-2-hexenal (**44**, 14.3%), hexanal (**43**, 8.6%), erucin (**23**, 7.2%), and 1-isothiocyanato-4-methylpentane (**16**, 5%; Figure 2). These observations are broadly in agreement with previous studies of'salad' rocket [3; 12]. Despite its high relative abundance, (_Z_)-3-hexen-1-ol produced only a weak, green, radishy aroma (Table 3) in rocket leaves. (_E_)-2-Hexenal by comparison was 2.9-fold less abundant in relative terms but produced a slightly stronger aroma, described by assessors as green, and apple-like. Hexanal (**43**) produced a pungent, green, grassy aroma of relatively high intensity, which has not been previously described in rocket to our knowledge. 2-Isopropyl-3-methoxypyrazine (**102**) by comparison was of low relative abundance in the rocket headspace (0.3%; Table 2) but was found to have one of the strongest aromas in rocket (rotten, potato-like, vegetative; Table 3). 1-Isothiocyanato-4-methylpentane had a weak aroma and was given a tentative new description of'musty', as no previous studies have reported an odour for this compound. The ITC erucin (**23**) is known for its anticarcinic properties, but its aroma was only recently described [12]. In agreement with a previous report, this compound produced a radishy aroma of weak intensity. Interestingly, the compound previously associated with characteristic \"rocket-like\" aroma (sativin, **20**) [12] was relatively weak-smelling. In this study, the compound was found to have a burnt, rubbery, and soil-like aroma. This suggests that sativin is not the main driver of pungency or aroma in'salad' rocket. Other compounds such as ethyl vinyl ketone (**65**; [41]), hexanal, 3-butteny ITC (**11**) [48; 54], and several unknown compounds (see final paragraph in this section) all had descriptions of pungency at higher intensities than sativin (Table 3). It may also be likely that no single compound is responsible for this attribute of rocket aroma but rather several. Pentyl ITC (**15**, 0.6%) not previously identified in'salad' rocket produced a strong odour, which was characterised as cabbage-like, green, and rotten (Table 3, Figure 2). As will be discussed in Section 3.2, we have tentatively identified pentyl GSL (Table 1) as a significant and previously unreported component of the GSL profile of'salad' rocket, which gives rise to this ITC compound. Other compounds not previously identified in'salad' rocket included 2-phenylethanol, 4-heptenal and 2-sec-butyl-3-methoxypyrazine. 2-Phenylethanol (**37**, 0.2%) was noted to impart a floral aroma at a medium-weak intensity (Table 3). This compound is derived from phenylalanine and has been found to contribute to aroma and flavour in many foods, such as tomatoes [66]. 4-Heptenal (**45**) occurred in rocket leaves with a relative abundance of 0.1% (Table 2). Despite this low amount in terms of the overall volatile profile, the compound was perceived at a medium intensity by the assessors (Table 3) and described as grassy and green. This compound has been variously described as mushroom-like [50], fatty and fishy [67], and potatoey [68]. The variation in these descriptions may be associated with the isomerisation of the compound, which could not be resolved in this study. 2-_sec_-Butyl-3-methoxypyrazine (**106**, 0.2%) has been reported in several Brasicales species, such as white mustard, rapeseed [60], and horseradish [25], but not in _E. sativa_ (Figure 2). It has been variously described as having a pea-like, musty, green, and bell pepper-like aroma. Assessors described the compound as earthy, similar to rotten potatoes, and vegetable-like.