Profiling urinary isoflavone metabolites after the consumption of either fermented or unfermented soy products in humans

Abstract

Soy isoflavones are reported to have many health benefits including anticarcinogenic and estrogenic activity. The primary soy isoflavones are geneistein and daidzein and their respective beta-glycosides genistin and daidzin. In soybeans and unfermented soy foods the isoflavones are present primarily as beta-glucosides, in fermented soy products (e.g. tempeh, miso, soy paste) the isoflavones are present as aglycones. To date there is controversy whether soy isoflavones in the aglycone form are more bioavailable than isoflavone glycosides. To date, few studies address the bioavailability of soy isoflavones from unfermented and fermented soy foods. The following study describes LC/MS/MS methodology for comparing the kinetics of the urinary excretion of soy isoflavones and their metabolites in humans after the consumption of fermented soy paste or unfermented soy flour. Mass spectra indicate that the majority of isoflavone metabolites (genistein, daidzein, O-desmethylangolensin, equol, dihydrogenistein, dihydrodaidzein) are present as glucuronide coujugates. Additional conjugates identified include sulfate conjugates (e.g. sulfoglucuronides of isoflavones). LC/MS spectra demonstrate difference in the kinetics profiles for the excretion of isoflavone metabolites and demonstrate the strength of this approach for these types of studies. This work is supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD). (KRF-2005-214-F00053)