Analysis of soy isoflavones in foods and biological fluids: An overview

Abstract

Soy isoflavones are phytoestrogens mainly present in soybean and soybean products. Isoflavones have been reported to possess physiological activities such as inhibition of cancer cell proliferation, reduction of cardiovascular risk, prevention of osteoporosis and alleviation of postmenopausal syndrome. This paper gives an overview of soy isoflavone analysis in foods and biological fluids. Extraction of isoflavones is often carried out by polar solvents such as methanol, ethanol, acetone or acetonitrile, or in combination with acid-containing water. The separation, identification and quantification of isoflavones are usually conducted by gas chromatography coupled with flame ionization detector or mass spectrometer (GC/FID or GC/MS), high-performance liquid chromatography with UV or mass spectrometer (HPLC/UV or HPLC/MS) and immunoassay. GC methods provide high sensitivity and adequate separation of only few soy isoflavones; however, a time-consuming derivatization step is needed before analysis. HPLC with a gradient solvent system with or without acid has been applied to analyze soy isoflavones, but most HPLC methods failed to separate all 12 isoflavones in a single run or the separation time is lengthy. Nevertheless, an appropriate choice of mobile phase and gradient condition in a C18 column with UV detection could provide a simultaneous separation of 12 soy isoflavones within short time. For immunoassay, it is convenient, fast, highly sensitive and can analyze a large number of samples at the same time. Yet, the drawback is that only a few soy isoflavones can be determined.