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Phytochemistry. 2004 May;65(9):1273-81.
Heating decreases epithiospecifier protein activity and increases
sulforaphane formation in broccoli.
Matusheski NV, Juvik JA, Jeffery EH.
Department of Food Science and Human Nutrition, University of
Illinois, 499 Bevier Hall, 905 South Goodwin Avenue, Urbana, IL 61801,
USA.
Sulforaphane, an isothiocyanate from broccoli, is one of the most
potent food-derived anticarcinogens. This compound is not present in
the intact vegetable, rather it is formed from its glucosinolate
precursor, glucoraphanin, by the action of myrosinase, a
thioglucosidase enzyme, when broccoli tissue is crushed or chewed.
However, a number of studies have demonstrated that sulforaphane yield
from glucoraphanin is low, and that a non-bioactive nitrile analog,
sulforaphane nitrile, is the primary hydrolysis product when plant
tissue is crushed at room temperature. Recent evidence suggests that
in Arabidopsis, nitrile formation from glucosinolates is controlled by
a heat-sensitive protein, epithiospecifier protein (ESP), a
non-catalytic cofactor of myrosinase. Our objectives were to examine
the effects of heating broccoli florets and sprouts on sulforaphane
and sulforaphane nitrile formation, to determine if broccoli contains
ESP activity, then to correlate heat-dependent changes in ESP
activity, sulforaphane content and bioactivity, as measured by
induction of the phase II detoxification enzyme quinone reductase (QR)
in cell culture. Heating fresh broccoli florets or broccoli sprouts to
60 degrees C prior to homogenization simultaneously increased
sulforaphane formation and decreased sulforaphane nitrile formation. A
significant loss of ESP activity paralleled the decrease in
sulforaphane nitrile formation. Heating to 70 degrees C and above
decreased the formation of both products in broccoli florets, but not
in broccoli sprouts. The induction of QR in cultured mouse hepatoma
Hepa lclc7 cells paralleled increases in sulforaphane formation.PMID:
15184012