|
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.
|