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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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