GEC (γ-Glutamyl-S-Ethenyl-Cysteine)
Like other Vicia species, the seed of the Narbon vetch contains several antinutritional factors. Levels of inhibitors of trypsin and chymotrypsin in Narbon beans are lower than those in peas, chick peas, vetches and lentils (Saini et al., 1988). However, they contain 10-30 g/kg of γ-glutamyl-S-ethenyl-cysteine (GEC), a toxic, sulphur-rich (11.6%) dipeptide not found in other vetch species (Francis et al., 1999). The GEC content is closely related to sulfur content in the seeds (Berger et al., 1999). GEC is an off-flavour precursor closely related to similar compounds in chives (Allium schoenoprasum) and onions (Allium cepa) (Enneking, 1995). The main consequence of GEC is that it makes raw Narbon beans unpalatable to animals and humans (Bryant et al., 2011; Sanchez-Vioque et al., 2011). Some cases of nephritis and damage to red blood cells in pigs and acute tubular nephrosis in broiler chickens might be due to GEC, but no toxicity has been shown in ruminants (Wali et al., 2005; Davies, 1987; Hadjipanayiotou, 2000; Jacques et al., 1994).
GEC can be readily destroyed by acid hydrolysis (Enneking, 1995). It might be possible to control GEC content in Narbon beans through the selection of genotypes that do not accumulate sulphur in seeds (Berger et al., 1999). For example, some subspecies such as Vicia narbonensis var. japonica contain less GEC (Berger et al., 2003). GEC content was shown to be higher in seeds of plants grown on soils rich in sulphur or on alkaline, saline or clayey soils (Berger et al., 1999).