The variability of isoflavones in soy seeds and the possibility of obtaining extracts for over the counter tablet preparations that can be standardized

In the last decade over the counter (OTC) tablet preparations of isollavones extracted from soy had an increase in sales mainly because it was claimed that they can be of benefit in the treatment of some of the disorders caused by menopause. The results of the clinical trials and the safety of these soy isoflavones for therapeutic purposes continue to be controversial. However, the binding of the different isoflavones to the alpha- and beta-oestrogen receptors (ERs) is very well studied and some consensus exists. Objective: Because some clinical and/or in vivo and in vitro assays are made with the ingestion of crude soy seeds and others with prepared soy seed extracts, our objective in this work was to check the isoflavone HPLC/DAD profile for the seeds and investigate the possibility of obtaining an extract with the major bioactive isollavones for OTC tablet preparations that could be standardized. Design: The HPLC/DAD protocol followed was optimised in our lab some years ago and can be carried out with different kinds of crude drugs and extracts or medicines available in the marketplace that contain polyphenols as active components. Results: The results show that the main compounds in soy seeds, as described by other authors, are the malonyl derivatives of genistin, daidzin and glycitin, whereas the OTC tablet preparations of soy isoflavones contain mainly genistin, daidzin and glycitin (results already published). Conclusions: It is presumed that during the industrial preparation of the soy seed extracts for OTC tablet preparations, the malonyl derivatives are either not extracted or are hydrolysed to the respective glycosidic forms of the isoflavones genistin, daidzin and glycitin. Thus, it could be helpful to determine the bioactivity of these extracts once glycitin is transformed during the entero-hepatic cycle, initially into daidzein. Then in the estimation of equol-producers this amount can be added to the equol produced by the daidzin itself. Thus, for therapeutic purposes and if clinical trials produce a consensus, the '' therapeutic window '' could be determined from the amount of genistin, the more active compound, and the combined value of daidzin + glycitin. However, the different affinity shown by these isoflavones to the oestrogen receptors cannot be disregarded in the calculation of the therapeutic effect or of the safe dosage. (C) 2007 Elsevier B.V All rights reserved.