Intrinsic sulfite content of isolated soy proteins

C. J. Stine, W. L. Boatright, G. Lu

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Commercial isolated soy proteins (ISP) contain 22 and 31 ppm sulfite as measured by the optimized Monier-Williams method (Sulfites in Foods, Official Methods of Analysis, 16th edn., AOAC, Washington, DC, 1995, Official Method 990.28). A method was developed to cryogenically trap and quantify the sulfur dioxide produced by this method using GC-MS. The same commercial ISP samples were found to contain 17 and 26 ppm sulfite, respectively, with GC-MS. ISP prepared in the laboratory contained 33 ppm sulfur dioxide, and defatted soybean flakes contained only a trace. Adding dithiothreitol after beginning the boiling step of the Monier-Williams assay had no significant effect on the sulfite content of a commercial ISP, whereas adding dithiothreitol prior to bringing the sample to a boil reduced the sulfite content from 17 to about 1 ppm.

Original languageEnglish
Pages (from-to)829-833
Number of pages5
JournalJAOCS, Journal of the American Oil Chemists' Society
Issue number9
StatePublished - Sep 2004

Bibliographical note

Funding Information:
This research was funded in part by USDA NRICGP grant #KY0-05018, by the Archer Daniels Midland Company, and by Kentucky Agricultural Experiment Station Project #KY 007029. It is published with the approval of the Director of the Kentucky Agricultural Experiment Station as Journal Article #04-07-058.


  • GC-MS
  • Methanethiol
  • Monier-williams assay
  • Soy protein
  • Sulfites

ASJC Scopus subject areas

  • Chemical Engineering (all)
  • Organic Chemistry


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