Direct Antioxidant Activity of Purified Glucoerucin, the Dietary Secondary Metabolite Contained in Rocket (Eruca sativa Mill.) Seeds and Sprouts JESSICA BARILLARI, †,‡ DONATELLA CANISTRO, ‡ MORENO PAOLINI, ‡ FIAMMETTA FERRONI, § GIAN FRANCO PEDULLI, § RENATO IORI,* ,† AND LUCA VALGIMIGLI* ,§ Consiglio per la Ricerca e la Sperimentazione in Agricoltura (C.R.A.), Istituto Sperimentale per le Colture Industriali, Via di Corticella 133, I-40129 Bologna, Italy, Department of Pharmacology, Biochemical Toxicology Unit, University of Bologna, Via Irnerio 48, 40126 Bologna, Italy, and Department of Organic Chemistry “A. Mangini”, University of Bologna, Via San Giacomo 11, I-40126, Bologna, Italy Rocket (Eruca sativa Mill. or Eruca vesicaria L.) is widely distributed all over the world and is usually consumed fresh (leafs or sprouts) for its typical spicy taste. Nevertheless, it is mentioned in traditional pharmacopoeia and ancient literature for several therapeutic properties, and it does contain a number of health promoting agents including carotenoids, vitamin C, fibers, flavonoids, and glucosinolates (GLs). The latter phytochemicals have recently gained attention as being the precursors of isothiocyanates (ITCs), which are released by myrosinase hydrolysis during cutting, chewing, or processing of the vegetable. ITCs are recognized as potent inducers of phase II enzymes (e.g., glutathione transferases, NAD(P)H:quinone reductase, epoxide hydrolase, etc.), which are important in the detoxification of electrophiles and protection against oxidative stress. The major GL found in rocket seeds is glucoerucin, GER (108 ( 5 µmol g -1 d.w.) that represents 95% of total GLs. The content is largely conserved in sprouts (79% of total GLs), and GER is still present to some extent in adult leaves. Unlike other GLs (e.g., glucoraphanin, the bio-precursor of sulforaphane), GER possesses good direct as well as indirect antioxidant activity. GER (and its metabolite erucin, ERN) effectively decomposes hydrogen peroxide and alkyl hydroperoxides with second-order rate constants of k 2 ) 6.9 ( 0.1 × 10 -2 M -1 s -1 and 4.5 ( 0.2 × 10 -3 M -1 s - , respectively, in water at 37 °C, thereby acting as a peroxide-scavenging preventive antioxidant. Interestingly, upon removal of H 2 O 2 or hydroperoxides, ERN is converted into sulforaphane, the most effective inducer of phase II enzymes among ITCs. On the other hand, ERN (and conceivably GER), like other ITCs, does not possess any chain-breaking antioxidant activity, being unable to protect styrene from its thermally (37 °C) initiated autoxidation in the presence of AMVN. The mechanism and relevance of the antioxidant activity of GER and ERN are discussed. KEYWORDS: Antioxidant; rocket; Eruca sativa (Mill.); Eruca vesicaria (L.); glucosinolate; isothiocyanate; glucoerucin; erucin INTRODUCTION Rocket comprises a number of species of the Brassicaceae (Cruciferae) family belonging to the Eruca (Miller) and Diplotaxis (DC.) genera. Eruca satiVa (Mill.) or Eruca Vesicaria (L.) has its origin in the Mediterranean region (1) but is widely distributed all over the world (2). It is mostly harvested from the wild or cultivated as an edible vegetable for the distinct spicy flavor of young leaves. Rocket seeds are also used for the production of oil and for appreciated pungent taste sprouts. Mentions of its medical use can be found throughout ancient literature. Rocket was believed to have aphrodisiac properties; such a virtue is mentioned by Virgil, and in the first century AD, Lucius Columella affirms “excitet ut Veneri tardos eruca maritos”, translated as “the rocket excites as the lovers embrace the lazy husbands” (De Re Rustica, X: 108). Both Dioscorides (3) and Galen (4) recommended eating seeds for increasing semen production; for these properties, rocket was forbidden in gardens of monasteries (5), despite the fact that both the Bible (Second Kings 4:39-40) and Pliny (Historia Naturalis) had * To whom correspondence should be addressed. E-mail: (L.V.) luca.valgimigli@unibo.it; (R.I.) r.iori@isci.it. † Istituto Sperimentale per le Colture Industriali. ‡ Biochemical Toxicology Unit, University of Bologna. § Department of Organic Chemistry “A. Mangini”, University of Bologna. J. Agric. Food Chem. 2005, 53, 2475-2482 2475 10.1021/jf047945a CCC: $30.25 © 2005 American Chemical Society Published on Web 03/08/2005