Limited contribution of isoflavones to hepatocellular phase II enzyme-inducing activity of soybean (Glycine max) extracts

Soy flour was successively extracted with ethyl acetate, ethanol, and water and tested for quinone reductase (QR) induction in the Hepa 1c1c7 cell line. The ethanol extract was found to be the most potent, with a CD value (concentration required to double QR specific activity) of 460 μg/ml. Phase separation of the ethanol extract and a phospholipid removal procedure yielded a fraction that doubled QR at 80 μg/ml. Reverse phase medium pressure chromatography of the purified ethanol extract yielded 13 fractions. Constituents of selected fractions were identified using mass spectrometry and NMR analysis. Fractions 2, 8, and 10 contained 47% of the recovered mass and were the least active of the isolates. These three fractions contained isoflavone glycosides. The latest eluting fractions 11–13 were found to be the most potent, and contained the majority of recovered inducing units (IUs), a measure of potency.