Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2002
Publication Date: 3/26/2002
Citation: Interpretive Summary: This study was undertaken to determine if a technique called LC/MS/MS could detect compounds known as isoflavones, or phytoestrogens, in the urine of animals that ate soy protein. His method was found to be excellent for such studies and we were able to identify some new molecules never before reported to occur in rat urine. This has application for our studies in infants, because it is much easier and safer to obtain urine form infants than blood. Thus, using these techniques will allow us to study the metabolism of soy phytoestrogens in infants.
Technical Abstract: Isoflavone phytoestrogens found in soybeans are the most widely studied phytochemicals in human diets and soy infant formulas. The health benefits of the isoflavones daidzein and genistein have been reported, and concerns about potential adverse effects have also been raised. However, the results of direct analysis of isoflavones and their metabolites in biological fluids after consumption of soy-containing diets are scarce. This study describes an LC/MS/MS method for the analysis of isoflavones and their metabolites in the urine of female rats fed diets made with soy protein isolate. Five isoflavones (daidzein, genistein, glycitein, dihydrodaidzein, and O-desmethylangolensin) were identified by comparison with authentic standards. Seventeen conjugates of isoflavones were characterized in the urine, the most unusual being genistein 5-glucuronide and four glucuronide conjugates of reductive metabolites of daidzein. The application of LC/MS/MS to analyze isoflavone metabolites is simple and sensitive, and appears to be an excellent method for determining the bioavailability and metabolism of food phytochemistry.