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Direct antioxidant activity of
purified glucoerucin, the dietary secondary metabolite contained in rocket (Eruca
sativa Mill.) seeds and sprouts.
J Agric Food Chem.
2005 Apr 6;53(7):2475-82
Barillari J, Canistro D, Paolini M, Ferroni F, Pedulli GF,
Iori R, Valgimigli
L.
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.
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 micromol 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 x 10(-)(2) M(-)(1) s(-)(1) and 4.5 +/- 0.2 x 10(-)(3) M(-)(1)
s(-) , respectively, in water at 37 degrees 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
degrees C) initiated autoxidation in the presence of AMVN. The mechanism and
relevance of the antioxidant activity of GER and ERN are discussed.
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