Determination of isoflavones in nutritional supplements by HPLC with coulometric electrode array detection

摘要

In the present study eleven soy and/or red clover based supplements were analyzed after acid hydrolysis or direct extraction with 70% aqueous etha-nol for their content of total isoflavone aglucones and free aglucones plus glucosides by high performance liquid chromatography in gradient elution mode coupled with coulometric electrode array detection.The ratio of the individual isoflavones and the conjugation pattern turned out to be highly variable in the investigated products.Whereas red clover based supplements contained isoflavones(mainly formononetin and bio-chanin A)exclusively in free form,soy containing preparations showed variable proportions of conjugated isoflavones.The total isoflavone aglucone content in products intended for direct consumption ranged from 12.0 to 45.6mg per capsule or tablet,whereas the content of free aglucones and glucosides was between 12.2 and 51.6mg per capsule or tablet.The experimentally determined isoflavone aglucone content was in agreement with or higher than the manufacturer's claim in 6 of the 11 investigated products.Expression of the isoflavone content as a sum of free aglucones and glucosides raised the number of matched claims to 8.