Factors affecting flavonoids absorption.

In experiments on rats, some of the factors affecting flavonoids absorption (solubility, glycosylation and nutritional status: fasted and not-fasted animals) were examined. Administration of quercetin with different solubilization degree showed no direct correlation between the quercetin absorption extent and solubility, i.e. despite 3 orders of difference in solubilization degree, the extent of absorption varied only about 4-fold. Absorption comparison of genistein and its glycoside genistin showed no difference in the extent of absorption; however, aglycone, in contrast to glycoside, was absorbed already from the rat stomach. Conjugation patterns (sulfation and glucuronization) of genistein metabolites demonstrated that the plasma of animals fasted prior to isoflavone administration contained significantly more sulfates and less glucuronides and mixed sulfates/glucuronides conjugates than the plasma of non-fasted animals.