Determination of isoflavones in soy and selected foods containing soy by extraction, saponification, and liquid chromatography: collaborative study

J AOAC Int. Nov-Dec 2001;84(6):1865-83.


Isoflavones are biologically active compounds occurring naturally in a variety of plants, with relatively high levels found in soybeans. Twelve laboratories participated in a collaborative study to determine the aglycon isoflavone content of 8 test samples of soy and foods containing soy. The analytical method for the determination of isoflavones incorporates a mild saponification step that reduces the number of analytes measured and permits quantitation versus commercially available, stable reference standards. Test samples were extracted at 65 degrees C with methanol-water (80 + 20), saponified with dilute sodium hydroxide solution, and analyzed by reversed-phase liquid chromatography with UV detection at 260 nm. Isoflavone results were reported as microg/aglycon/g or microg aglycon equivalents/g. The 8 test samples included 2 blind duplicates and 4 single test samples with total isoflavone concentrations ranging from approximately 50 to 3000 microg/g. Test samples of soy ingredients and products made with soy were distributed to collaborators with appropriate reference standards. Collaborators were asked to analyze test samples in duplicate on 2 separate days. The data were analyzed for individual isoflavone components, subtotals of daidzin-daidzein, glycitin-glycitein, and genistin-genistein, and total isoflavones. The relative standard deviation (RSD) for repeatability was 1.8-7.1%, and the RSD for reproducibility was 3.2-16.1% for total isoflavone values of 47-3099 microg/g.

MeSH terms

  • Chromatography, Liquid / methods*
  • Chromatography, Liquid / standards
  • Chromatography, Liquid / statistics & numerical data
  • Food Analysis / methods*
  • Food Analysis / standards
  • Food Analysis / statistics & numerical data
  • Genistein / analysis
  • Genistein / chemistry
  • Glucosides / analysis
  • Glucosides / chemistry
  • Isoflavones / analysis*
  • Isoflavones / chemistry
  • Isoflavones / standards
  • Laboratories
  • Molecular Structure
  • Reference Standards
  • Soybeans / chemistry*


  • Glucosides
  • Isoflavones
  • daidzin
  • daidzein
  • glycitein
  • Genistein
  • glycitin