Environmental Influence on Isoflavones and Saponins in Soybeans and Their Role in Colon Cancer.

Author: Ruth S. MacDonald et al.
Publication: Journal of Nutrition 135: 1239-1242, 2005.

Soybeans contain many health-promoting components, including soy protein, isoflavones, saponins, fibre, trypsin inhibitors and fatty acids. Saponins are phytochemicals, which consist of aglycones of triterpenes or steroids. Saponins act as foaming or emulsifying agents because they have both hydrophobic and hydrophilic sides. The emulsifying activity of saponins is believed to lower blood cholesterol.

The aim of this study was to investigate the influence of soybean variety on the levels of isoflavones and saponins; and to investigate the relationship between colon tumorigenesis in mice and ingestion of isoflavones and saponins. Epidemiological studies show a relationship between colon cancer and diet but the specific components have not yet been identified.

To investigate the levels of isoflavones and saponins 16 soybean cultivars were grown in 5 different locations. Some cultivars produced significantly different levels of isoflavones and saponins based on location. It was also observed the isoflavones and saponin levels were positive correlated. Two distinct cultivars were found: cultivar PI437654 had the highest levels of saponins (about 4500 ppm) and isoflavones (about 2400 ppm) whereas elite cultivar Magellan had lower levels (about 2400 ppm saponins and 1200 ppm isoflavones).

Human colon cancer cells, which were incubated in vitro, were treated with the isoflavones genistein and daidzein, and with commercial soy extract rich in isoflavones (Novasoy). Genistein was most effective in reducing the cell growth of the human colon cancer cells. Daidzein and Novasoy also reduced cancer cell proliferation. Saponins from the group A also reduced colon cancer cell proliferation in vitro. Soy saponins dosed up to 3% are very well tolerated by rats had no negative effects on their growth. However the soy saponins are not absorbed by rats.