Glucosinolate types and concentrations in seedlings of different Brassica species used for food

Summary

Brassicaceous food crops contain in their tissues different quantities of the glucoside allelochemicals known as glucosinolates (Bellostas et al., 2004; Sørensen, 1990). These compounds are alkyl-N-hydroximine sulphate esters with a β-D-thioglucopyranoside group attached to the hydroximine carbon in Z-configuration relative to the sulphate group (Ettlinger and Kjær, 1968; Kjær, 1960). Glucosinolates are biosynthetically derived from amino acids (Hill et al., 2003) and they occur in all plants of the order Capparales and in some other plants (Bjerg and Sørensen, 1987; Kjær, 1960; Rodman, 1978). These compounds co-occur with myrosinase isoenzymes (Thioglucosidase; EC 3.2.1.147), which catalyze the hydrolysis of the β-D-thioglucopyranoside bond releasing an aglucone that forms a variety of biologically active products with structures defined by the type of glucosinolate and the reaction conditions (Bjergegaard et al., 1994; Buskov et al., 2000a; Buskov et al., 2000b; Buskov et al., 2000c; Palmieri et al., 1998). These breakdown products are chemically very reactive and they have for a long time been related to the pungent odour and flavour typical for Brassicaceous plants. These compounds show a various range of biological activities that goes from antinutritional (Bjerg et al., 1989; Hansen et al., 1997), to fungicidal, nematicidal and bactericidal (Brown and Morra, 1997; Buskov et al., 2002; Kirkegaard and Sarwar, 1998). In the last years, interest in their anticarcinogenic properties has increased and research has mainly focused on the effect of the isothiocyanates present in sprouts of certain Brassica food crops, especially broccoli (Zhang et al., 1992; Zhang, 2004). These isothiocyanates have been related to the increase in the activity of the Phase 2 enzymes, which is related to detoxification of xenobiotica and protection against cancer (Bonnesen et al., 1999). They have also been related to an increased antioxidative metabolism by induction of the scavenging of oxygen radicals, which may contribute to a decreased risk of coronary diseases (Wu et al., 2004).
Given the biological effects of Brassica crops used for food, it was considered of interest to investigate the glucosinolate profile during early development of the Brassica plant in order to be able to determine the stages at which the desired biologically active compounds are present. It would also allow determining the presence of other potentially active compounds as well as to allow better understanding the metabolic changes occurring during germination and early growth.
Five B. oleracea used for food (white cabbage, red cabbage, broccoli, cauliflower and savoy cabbage) and two B. napus (a low and a high-glucosinolate rapeseeds) were used in the present experiments. The content of glucosinolates in seeds, seedlings and the individual parts of grown plants was followed from germination to one-month growth. Samples were taken at one, two, three, four, seven, 14, 21 and 28 days and plants were separated into cotyledons, leaves, epicotyle and roots. Glucosinolates were isolated and their concentration determined by HPLC following standard procedures developed at our laboratory.