39B-23

J. LIU¹, K. Chang¹, and T. Cai. (1) Food & Nutrition, North Dakota State University, IACC 370, North Dakota State University, Fargo, ND 58105

Isoflavone concentration in soybeans is affected by several factors and this leads to different, even contradictory reports on the concentration of isoflavone. Different extraction and analytical procedures contribute to the differences in isoflavone content. The major constituents in the extract at 80°C were daidzin, glycitin and genistin, whereas the major constituents in the extract obtained at room temperature were malonylated glycosides. Therefore, hot extraction changes the distribution pattern of isoflavone. But no detailed information was reported on this aspect. Our objective was to evaluate the extent and the trend of isoflavone conversion under different extraction conditions. Samples of ground soybeans were extracted with food grade ethanol. Different ethanol concentrations (60, 70 and 80%), extraction temperature (22, 60 and 80 °C), and extraction time (2, 4 and 6 h) were used. All twelve isoflavones were quantified by HPLC on a Brownlee Aquapore C8 reversed-phase column according to the procedure established in our laboratory. Our results shown there was no obvious chenge in aglycone isoflavones following with the increase of extraction time, ethanol concentration and extraction temperature. The glycoside isoflavones concentration increased with the increase of extraction temperature (P<0.05), extraction time (P<0.05). Malonylglycoside isoflavones concentration decreased at 80 °C following the increase of extraction time (P<0.05), but there was no difference at 60 °C and 22 °C. Acetylglycoside isoflavones showed the same trend of change with malonylglycosides at both 80 °C and 60 °C. The major constituents in the extract at 80°C were glycosides, whereas the major constituents in the extract obtained at 22°C and 60°C were malonylated glycosides. The results suggest that although the hot extraction procedure causes deesterification of malonylglycosides and acetylglycosides, thus changes the distribution pattern of isoflavones, but the changes are is not obvious until the temperature is quite high, such as 80°C.