Identification of Genistein, an Anticarcinogenic Compound, in the Edible Tubers of the American Groundnut (Apios americana Medikus)

Abstract

American groundnut (Apios americana Medikus) is a nitrogenfixing legume that produces edible tubers and seeds. Even though studies have been conducted on the quality of tuber storage compounds, very little is known about compounds that could have beneficial effects on human and animal health. The objective of this study was to investigate the presence of genistein in the tubers. The nodC gene of Rhizobium fredii Scholla and Elkan USDA191 that had been fused with β‐galactosidase was used to detect the presence of genistein in A. americana tubers. The flavonoids from A. americana tubers were purified by C₁₈ reversed‐phase HPLC. The HPLC profile revealed nine UV absorbing peaks. Among them, Peaks 6 and 8 activated the nodC‐lacZ gene fusion about two fold, while the bulk of the inducing activity was associated with Peak 9. The compound in Peak 9 and authentic genistein standard had identical retention times. When A. americana tuber flavonoids were spiked with an authentic genistein standard, Peak 9 coeluted with genistein. In addition, a peak at m/z 271, corresponding to the protonated genistein, was found when the HPLC Peak 9 was analyzed by electrostaticspray mass spectrometry. The results of this present investigation indicate that A. americana tubers contain the isoflavone genistein. The discovery of genistein in A. americana tubers should rekindle interest in this legume as a food crop since genistein has been shown to reduce the incidence of various forms of cancer.