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The objectives of this study were to determine the contents of
isoflavone glucosides (daidzin, genistin) and their aglycones
(daidzein, genistein) in commercial soybean and related bean
products by HPLC; and to investigate the effects of processing
conditions on changes in the isoflavones content of black
soybean milk, yuba and chaw-tofu. The contents of isoflavones
(daidzin, genistin, daidzein and genistein) in black soybean
were higher than those in soybean. The contents of
isoflavones in soy sprouts were also higher than those in
soybean. The contents of isoflavone glucosides (daidzin,
genistin) in unfermented soybean products followed the order
of yuba (3196 mg/g dry wt) > hard bean curd (2164mg/g dry wt)>
tofu (1971 mg/g dry wt)> soy sprout (1487 mg/g dry wt)>
soymilk (851 mg/g dry wt). The contents of isoflavone
aglycones (daidzein, genistein) in unfermented soybean
products followed the order of yuba (410mg/g dry wt) ≒ soy
sprout (401 mg/g dry wt)≒ tofu (377mg/g dry wt)> hard bean
curd (175 mg/g dry wt)> soymilk. The contents of daidzein and
genistein in fermented soy products followed the order of
soybean paste (935 mg/g dry wt)≒chaw-tofu (855 mg/g dry wt)>
toshi (653 mg/g dry wt)> sufu (302 mg/g dry wt)> miso (267 mg/
g dry wt)> soy sauce (18 mg/g dry wt). The levels of daidzein
and genistein in fermented soybean products were higher than
those in unfermented products, except soy sauce. When black
soybeans were soaked in water at 30 and 50℃ for various
periods of time, the contents of daidzein and genistein
increased with an increase of the soaking time while daidzin
and genistin decreased. There was no significant difference
(p<0.05) in the contents of isoflavones in black soybean under
soaking at 30℃ for 12h and at 50℃ for 2h. The amounts of
isoflavones in black soybean changed markedly under soaking at
20-60℃ for 8h. The content of isoflavone glycosides and
their aglycones in black soybean ranged from 226~227and 360~547
mg/g dry wt, respectively, under soaking at 50℃ for 8h. The
change in the contents of isoflavones in black soybean during
soaking might be related to its b-glucosidases activity. The
effect of soaking temperature in b-glucosidases activity of
black soybean was in the order of 50> 40> 60> 30> 20℃. No
significant difference (p>0.05) was found in the sensory
evaluation of black soy milk, prepared under different soaking
conditions, which contained different amounts of daaidzein and
genistein. The contents of daidzein and genistein in Yuba (B)
prepared by soaking soybeans at 50℃for 6 h was 389 and 505
mg/g dry wt, respectively. The contents of these two
compounds in Yuba (B) were about 2.5 times those in Yuba (A)
that prepared by soaking soybeans at 30℃for 12 h. Yuba (B)
contained higher ash but lower protein and fat content than did
Yuba (A). The contents of daidzein and genistein in chaw-tofu
increased during the fermentation period while the contents of
daidzin and genistin decreased. In addition, 9-25% of the
contents of isoflavones in chaw-tofu were removed after frying
treatment. The effects of isoflavone aglycones on DNA damage in
mammals cells, human blood lymphocyte, human promyelocytic
leukemia (HL-60) cells and Chinese hamster ovary (CHO) were
investigated by means of single cell gel electrophoresis
(Comet assay). Moreover, the effects of UV and H2O2 mediated
DNA damage in human lymphocyte were also investigated. After
incubation with cells for 30 min, daidzein induced DNA damage in
CHO and HL-60 cells only at a higher concentration of 40 mg/ml
but did not induce DNA damage in human lymphocyte at the same
concentration. DNA damage in CHO and HL-60 cells increased
significantly(p<0.05) under treatment with genistein at a
concentration of 5 mg/ml, especially the HL-60 cells. The
mean values of tail DNA % increased to 28.65 in HL-60 cells.
DNA damage in human blood lymphocyte exhibited a significant
increase only at a concentration greater than 40 mg/ml, and the
mean values of tail DNA % increased to 21.89. Genistein caused
greater DNA damage than did daidzein in these three kinds of
cells at a concentration of 0-40 mg/ml. In addition,
genistein caused more DNA damage in CHO and HL-60 cells than
in human lymphocytes. The reason might be that genistein can
inhibit topoisomerase and then induce protein-linked DNA damage.
UV-C induced DNA damage in human blood lymphocyte was inhibited
by daidzein and genistein in a concentration dependent
manner(0-40 mg/ml). When the cells were preincubated with
daidzein or genistein (40 mg/ml) before expose to UV-C for 5
min, the mean values of tail DNA % values decreased from 69.19
to 21.69 and 34.66, respectively, compared to the control
group. No protective effect was found when cells did not
undergo preincubation with daidzein and genistein before
exposure to UV-C. The protective effects of these two compounds
on UV-C mediated DNA damage might be due to the absorption of
UV-C or induction antioxidant enzymes in cells by these two
compounds. Furthermore, daidzein and genistein exhibited no
protective effect on H2O2 induced DNA damage in human blood
lymphocytes. In conclusion, the protective effects of
daidzein and genistein on DNA damage induced by UV light
irradiation were greater than those of by H2O2.
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