Quantitative Determination of Isoflavones in Soy Based Nutritional Supplements by High-Performance Liquid Chromatography

An increasing number of nutritional supplements contain phytoestrogens, in particular isoflavones, which potentially alleviate climacteric complaints. Intention of the present study was the qualitative and quantitative determination of isoflavones in soy based nutritional supplements in order to compare the actual content with the labeling of these products. For the analysis high-performance liquid chromatography (HPLC) with photo diode array (PDA) detection was used. The amount of isoflavones was determined via external calibration functions. Our analyses revealed certain variations in the isoflavone content of soy based nutritional supplements, with regard to the individual and the total amount. Furthermore, the total amount of isoflavones per serving unit in some products was higher than declared on the labeling, although only the major isoflavones were taken into account. This study shows that there is the necessity to clearly specify the isoflavone composition on the labeling and - due to safety aspects - to standardize and control the isoflavone content.