Comparative metabolism of genistin by human and rat gut microflora: detection and identification of the end-products of metabolism

1. Biotransformations by gut microflora play a pivotal role in determining the biological activity of isoflavones that occur in soya-based foods predominantly as β -glycosyl conjugates. Microflora prepared from rat caecae and human faeces were used to investigate the metabolic fate of genistein β -glycosides extracted from soya flour. The end-products of such metabolism were determined by parallel incubations of microflora with [2',3',5',6'-3H] and [4-14C]-labelled genistein. 2. Quantitative analysis by LC-MS/MS indicated very rapid and complete degradation of genistin, which was associated with a transient increase in genistein. Qualitative studies indicated that the malonyl and acetyl glycosides of genistein were also degraded by the microflora. 3. Incubation of caecal and faecal microflora with [3H] and [14C]genistein yielded similar radiolabelled metabolites, which were identified by radio-LC-MSn as the intermediates dihydrogenistein and 6'-hydroxy-O-desmethylangolensin and end-product 4-hydroxyphenyl...