## 1 Introduction  
Crops of the Brassicaceae family are grown all over the world, and they form an important part of many different cuisines and cultures [1]. Some species are noted for their distinctive, and often very strong, tastes and flavours. _Armencia rusciana_ (horseradishh), _Eruca sativa_ ('salad' rocket), _Eutrema japonicum_ (wasabi), and _Nasturtium officinal_ (watercress) are four such examples, which are noted for their pungent, peppery, and aromatic organoleptic properties [2; 3; 4]. Horseradishh and wasabi produce large roots that are grated and used as a comment in many cultures across the world, most notably in Eastern Europe and the United Kingdom (horseradishh) and Japan (wasabi; [5]). Horseradish is a vegetative perennial that grows widely in temperate regions [6], whereas wasabi can only be grown in a very few locations, owing to its sensitivity to temperature change and root oxygen availability [7]. Wasabi is traditionally cultivated in damp river valleys of Japan, although commercial operations have been established elsewhere, such as in the UK. Salad rocket originates from the Middle East and has spread throughout the Mediterranean basin [8]. It has become naturalised on every inhabited continent and is considered an invasive weed in some regions. Watercress has similarly become naturalised (for example in North America) and grows in shallow rivers and streams. It can be cultivated commercially on large scales using artificial growing 'pools' flooded with stream water. Its leaves and shoots are a popular salad and sandwich garnish, and they can also be made into soups [9]. It is widely accepted that the distinctive aroma and flavour traits are produced by glucosinolate (GSL) hydrolysis products (GHPs [10]). GSLs are sulphur-containing secondary metabolites produced by Brassicales plants in response to biotic and abiotic stress [11]. Myrosinase enzymes are responsible for the hydrolysis of GSLs in water to form a plethora of GHPs, the conformation of which can be determined by the presence of enzyme cofactors, pH level, metallic ion concentration, and the precursor GSLs side-chain structure [8]. These products include: isothiaryantes (ITCs), nitriles, epithionitriles, indoles, oxazolidine-2-thiones, and other diverse products that result from tautomeric rearrangements (Figure 1). Previous work has reported olfactory data for each of these crops; however, data are generally very scarce. Only five studies of _E. sativa_ volatile compounds have been published in the last twenty years [3; 12; 13; 14; 15]. Very little information regarding wasabi root volatile composition and aroma is available outside of Japanese language journals [7; 16]. Similarly, very little information is available for watercress, with only four papers published in the last 40 years [17; 18; 19; 20]. Harseradish is the most well characterised of these four species, but still, only six studies of note have been published in the last 50 years [6; 21; 22; 23; 24; 25]. There is also an 'elephant in the room' regarding previous reports of GHPs present in aroma profiles of these Brassicaceae vegetables. Many of the reported GHP compounds are derived from GSL precursors that are not regularly reported as part of the profile for each respective species. In _E. sativa_, for example, GHPs such as methyl ITC, 3-butenyl ITC, 1-isothiocyanato-4-methylpentane, and 5-(methylsulfonyl)pentanenitrile have all been previously reported [13]. The GSL precursors to these compounds (glucocapparin, GCP; gluconapin, GNP; 4-methylpentyl GSL, 4 MP; and glucoberteroin, GBT; respectively) have never been reliably or consistently reported as being part of the GSL profile in this species [26; 27]. This begs the question whether these identifications are correct or  
Figure 1: The glucosinolate–myrosinase reaction and hydrolysis products. Abbreviations: ESM1, epithiospecific modifier protein 1; TFP, thiocyanate forming protein; NSP, nitrile specifier forming protein; ESP, epithiospecific protein.