Isoflavones in human breast milk and other biological fluids

We established a method for using HPLC and diode-array ultraviolet scanning to quantitate soy isoflavonoids in foods and in human plasma, urine, and b reast milk. The analytes occurring as glycoside conjugates were hydrolyzed enzymatically before HPLC analysis if extracted from biological matrices or were subjected to direct HPLC analysis after extraction from foods. We mon itored the isoflavones daidzein, genistein, glycitein, formononetin, and bi ochanin-A and their mammalian metabolites equol and O-desmethylangolensin i n human plasma, urine, and breast milk. Analytes were identified by absorba nce patterns, fluorometric and electrochemical detection, and comparison wi th internal and external standards. In addition, we identified analytes by using gas chromatography-mass spectrometry after trimethylsilylation. The H PLC method was also used to measure concentrations of isoflavones and their glucoside conjugates in various soy-based infant formulas. Total isoflavon e concentrations varied between 155 and 281 mg/kg. After one woman received a moderate challenge with 20 g roasted soybeans (equivalent to 37 mg isofl avones), we detected mean total isoflavone concentrations of approximate to 2.0 mu mol/L in plasma, 0.2 mu mol/L in breast milk, and 3.0 mu mol/h in u rine. According to our measurements, with adjustment for body weight, isofl avonoid exposure is 4-6 times higher in infants fed soy-based formula than in adults eating a diet rich in soyfoods (approximate to 30 g/d). Implicati ons of the presented results for the potential cancer-preventing activity o f isoflavones by exposing newborn infants to these phytochemicals are discu ssed.