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The objects of this research were to investigate the effects of
different roasting degrees on the antioxidant properties of
water extracts from Cassia tora L. (WECT), and the antioxidant
properties of anthraquinones and anthrone, and the effects of
WECT on oxidative damage to deoxyribose, DNA and DNA base in
vitro.The antioxidant properties of WECT prepared under
different degrees of roasting were investigated. The water
extracts of unroasted Cassia tora L. (WEUCT) showed 94 %
inhibition of peroxidation of linoleic acid at a dose of 0.2 mg/
ml, which was higher than that of a-tocopherol (82%). Water
extracts prepared from Cassia tora L. roasted at 175 ℃for 5 min
and at 200℃for 5 min exhibited 83% and 82%, respectively,
inhibition of linoleic acid peroxidation. This result indicated
that the antioxidant activities of WECT decreased with longer
roasting time or higher roasting temperature. The IC50 of WEUCT
in liposome oxidation induced by Fenton reaction was 0.41 mg/ml,
which was higher than that of a-tocopherol (IC50=0.55 mg/ml).
WEUCT also exhibited good antioxidant activity in enzymatic and
nonezymatic microsome oxidative systems. The water extracts of
roasted Cassia tora L. increased with the degree of browning and
produced chemiluminescence when compared with the unroasted
sample. However, the total polyphenolic compounds of WECT
decreased after the roasting process finished. In conclusion,
the decreased in the antioxidant activity of water extracts from
roasted Cassia tora L. might have been due to the degradation of
Maillard reaction products and the decreased of polyphenolic
compounds.Anthraquinones are the major compounds found in Cassia
tora L. The antioxidant properties of anthraquinones (AQs) and
anthrone were evaluated using different model systems. The
antioxidant activity of these compounds (200 ppm) on the
inhibition of peroxidation of linoleic acid were found to follow
the order BHA (96%)≒anthrone (95%)≒alizarin (93%) > aloe-
emodin (78%) > rhein (71%) > emodin (36%) > anthraquinone (8%).
Chrysophanol accelerated the peroxidation of linoleic acid.
Anthrone and alizarin exhibited a reducing power, but the other
AQs did not show any reducing power. AQs and anthrone exhibited
a weak chelating ability on iron(II). Alizarin completely
scavenged hydrogen peroxide at a concentration of 0.2 mg/ml. At
a concentration of 0.25 mg/ml, anthrone, aloe-emodin and emodin
exhibited 26.2, 16.6 and 41.8% scavenging effects, respectively,
on hydroxyl radicals produced by the Fenton reaction. However,
anthraquinone, alizarin, chrysophanol and rhein accelerated the
production of hydroxyl radicals at the same concentration.
These results suggested that the antioxidant mechanism for
emodin and aloe-emodin is most likely due to scavenge free
radicals. The strong antioxidant activities showed by anthrone
and alizarin could be due to their reducing power and scavenging
effects on reactive oxygens. The prooxidant activity exhibited
by chrysophanol might be due to enhanced the production of free
radicals. The effects of WECT on oxidative damage to
deoxyribose, DNA and DNA base in vitro were investigated. WECT
alone caused a slight strand-breaking of DNA. In the presence
of Fe3+/H2O2, WECT accelerated the strand-breaking of DNA under
the concentration of 2 mg/ml, but it decreased with an
increasing concentration of WECT. WECT inhibited oxidative
damage to DNA induced by Fe2+/H2O2, perhaps due to scavenge
reactive oxygen species. WECT accelerated the oxidation of
deoxyribose induced by Fe3+-EDTA/H2O2 under a concentration of
0.2 mg/ml, but inhibited the oxidation of deoxyribose induced by
Fe3+-EDTA/H2O2/ascorbic acid. WECT also caused the oxidation of
2*-deoxyguanosine (2*-dG) to form 8-OH-2*-dG induced by Fe3+-
EDTA /H2O2. The prooxidant action of WECT on the oxidation of
2*-dG was in the order of unroasted > roasted at 150℃ > roasted
at 200℃> roasted at 250℃. The decrease in prooxidant activity
of roasted sample might be due to the reduction of its
anthraquinone glycoside content after roasting. WECT exhibited
either prooxidant or antioxidant property in the model system
that was dependent on the ability of reducing metal ions,
scavenging hydroxyl radical and chelating ferrous ion.
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