Determination of Major Isoflavones in Soy Drinks by Solid-Phase Micro Extraction Coupled to Liquid Chromatography

Abstract

A simple method for determination of major isoflavones (daidzein, genestein, genistin) and equol, a daidzein metabolite, has been developed using solid-phase micro extraction coupled to liquid chromatography with diode array UV detection. All the aspects influencing adsorption (fibre coating, extraction time, temperature, pH and salt addition) and desorption of the analytes (desorption and injection time and minimize carryover) were carefully investigated. The limits of detection obtained using a polydimethylsiloxane /divinylbenzene fiber coating were in the range 4 (genistein) to 38 (genistin) nM. The method proved to be useful for determination of analytes in soy-based products. Daidzein, genistein, and genistin were found in all samples (three soy milks and two blended rice/soy beverages) at concentrations ranging from 0.8 ± 0.2 (daidzein) to 180.4 ± 12.1 (genistin) μM, while glycitein and equol were found in three and in one of the drinks at levels between 1.7 ± 0.1 and 5.0 ± 0.2 μM and at 2.7 ± 0.2 μM, respectively. The procedure was used to define the binding constants of isoflavones with serum albumin bovine that were found from 2.5 × 104 (daidzein) to 2.9 × 105 (genistein) L mol−1. The method proposed restricts the use of organic solvents and can be used widely in most laboratories with standard equipment. In addition, it is suitable for easily studying the isoflavone interaction with the main constituents in plants, e.g., proteins and lipids, to evaluate their bioavailability and to clarify the controversial question on benefits for or damage to human health resulting from soy intak

Solid-phase microextraction and on-fiber derivatization for assessment of mammalian and vegetable milks with emphasis on the content of major phytoestrogens

“…The presence of daidzein in all selected samples was expected, as well as that of equol and enterodiol in ruminant milks. Their estimates agreed with previously reported data 9,18 . The high sensitivity of the method permitted the determination of glycitein for the first time in cow and soy-rice milk.…”

“…SPME of the target analytes was performed using recently optimized 18 conditions, i.e. 20 min at room temperature directly exposing a 65 μm PDMS-DVB fiber to a 0.2% formic acid - 30% NaCl solution under constant magnetic stirring.…”

“…Recently, solid-phase microextraction (SPME) coupled with LC-UV/DAD, has been successfully used for the extraction and analysis of some major isoflavones from bovine milk and soy derived products 18,19 . The advantages of the SPME approach are well established, i.e.…”

Analysis of Isoflavones in Foods

“…SPME is rapid, solventless, and readily adaptable for automation extraction technique. In isoflavone extraction, this technique has been employed by Aresta and others () for the determination of daidzein, genistein, glycitein, genistin, and equol in soy drinks. To optimize the extraction, the authors evaluated the variables that affected both adsorption and desorption of the analytes.…”

Determination of Isoflavones in Soybean Flour by Matrix Solid-Phase Dispersion Extraction and Liquid Chromatography with UV-Diode Array Detection

“…The most used methods for isoflavone determination are liquid-liquid (LLE) and solid-phase extraction (SPE) [14]. Recently, solid-phase microextraction (SPME) has also been proposed for the determination of some major isoflavones in soy drinks [21]. A simple, low-cost, and relatively quick alternative to the above approaches is matrix solid-phase dispersion (MSPD).…”