Long-term kinetics of daidzein and its main metabolites in human equol-producers after soymilk intake: identification of equol-conjugates by UPLC-orbitrap-MS and influence of the number of transforming bacteria on plasma kinetics

The main aim of the study was to establish in vivo a correlation between equol (EQU) production and a number of intestinal bacteria able to perform the transformation. Thus, healthy female volunteers were selected for their ability to convert slowly (n=6, 10(5)-10(9) cells/g wet feces) or quickly (n=6, 10(10)-10(12) cells/g wet feces) daidzein (DAI) in EQU. After oral administration of 100mg DAI in soymilk, plasma (0-99h) and urine (0-96h) samples were collected. DAI and its metabolites were determined by LC-MS/MS and EQU -conjugates by UPLC-High Resolution-MS. Only for EQU a direct correlation was found between the number of transforming microorganisms and parameters such as t(max) and t(1/2) (p=0.027). Peak serum concentration time, C-max, AUC(0-72h) and t(1/2) for total EQU (n=12) were 36 +/- 10 h, 89 +/- 78 nM, 2.4 +/- 1.7 (mol x h/L) and 15.6 +/- 3.3 h, respectively. In plasma and urine EQU was found mainly as 7-O-glucuronide.