Determination of Total Soy Isoflavones in Dietary Supplements, Supplement Ingredients, and Soy Foods by High-Performance Liquid Chromatography with Ultraviolet Detection: Collaborative Study

Abstract

An interlaboratory study was conducted to evaluate a method for determining total soy isoflavones in dietary supplements, dietary supplement ingredients, and soy foods. Isoflavones were extracted using aqueous acetonitrile containing a small amount of dimethylsulfoxide (DMSO) and all 12 of the naturally occuring isoflavones in soy were determined by high-performance liquid chromatography (HPLC) with UV detection using apigenin as an internal standard. Fifteen samples (6 pairs of blind duplicates plus 3 additional samples) of soy isoflavone ingredients, soy isoflavone dietary supplements, soy flour, and soy protein products were successfully analyzed by 13 collaborating laboratories in 6 countries. For repeatability, the relative standard deviations (RSDr) ranged from 1.07 for samples containing over 400 mg/g total isoflavones to 3.31 for samples containing 0.87 mg/g total isoflavones, and for reproducibility the RSDR values ranged from 2.29 for samples containing over 400 mg/g total isoflavones to 9.36 for samples containing 0.87 mg/g total isoflavones. HorRat values ranged from 1.00 to 1.62 for all samples containing at least 0.8 mg/g total isoflavones. One sample, containing very low total isoflavones (<0.05 mg/g), gave RSDR values of 175 and a HorRat value of 17.6. This sample was deemed to be below the usable range of the method. The method provides accurate and precise results for analysis of soy isoflavones in dietary supplements and soy foods.

Effect of Cooking on Isoflavones, Phenolic Acids, and Antioxidant Activity in Sprouts of Prosoy Soybean (Glycine max)

“…Extraction and HPLC analysis of isoflavones. Isoflavones were extracted and analyzed using AOAC method 2008.03 (Collison 2008), using apigenin as an internal standard. The same Agilent technology chromatography system as used for phenolic acids analysis was used for analysis of isoflavone analysis.…”

“…The results of isoflavone profile analysis is presented in Table 5. The results were expressed in 2 ways similar to our previous study (Xu and Chang, 2008a): (1) Individual isoflavone contents of diadzin (Din), genistin (Gin), glycitin (Gly), diadzein (Dein), genistein (Gein), and glycitein (Glein) were calculated based on calibration curve, while malonyldiadzin (MDin), malonylgenistin (MGin), malonylglycitin (MGly), acetyldiadzin (ADin), acetylgenistin (AGin), and acetylglycitin (AGly) were calculated using response factors as described by AOAC method 2008.03 (Collison 2008). (2) Subtotal isoflavone contents of aglycones (aglycone equivalents) for each of the 3 types of isoflavones were calculated by converting the malonylglucosides, acetylglucosides, and β-glucosides weight into the aglycone weight using the respective molecular weight factors prior to summation.…”

Optimization of isoflavones extraction from soybeans using full factorial design

“…The isoflavone standards such as genistein, daidzein, glycitein, genistin, daidzin, and glycitin were provided by United States Pharmacopeia and all the standards were stored a −20°C for further experimental purposes. Working standard solutions were prepared in 40% (v/v) acetonitrile and stored at −20°C (Collison, ).…”

Pressurized water extraction of isoflavones by experimental design from soybean flour and Soybean Protein Isolate

“…This calculation permits to compare ASE extraction method with previously reported method. All isoflavone quantities are expressed in aglycon equivalent to take into account the molec ular mass differencies between malonyl, glucoside and aglycon forms (Collison, 2008).…”

“…Isoflavone extraction is generally carried out for analytical pur poses with aqueous acetonitrile (Eldridge, 1982;Song, Barua, Buseman, & Murphy, 1998) which could also be mixed with DMSO, (Collison, 2008) or extracted with aqueous alcohol (Klump, Allred, MacDonald, & Ballam, 2001 ). Mixing techniques such as stirred extraction, shaking, vortexing, sonication, stirring, soxhlet and pressurized extraction have been compared in the literature (Luthria, Biswas, & Natarajan, 2007).…”