Methionine is the methyl group donor for sulfite-associated methanethiol formation in isolated soy proteins

Q. Lei, W. L. Boatright

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Addition of 3.2 mM sodium sulfite resulted in a 5.1-time higher amount of methanethiol in aqueous slurries of isolated soy proteins (ISP) over the corresponding controls after being stirred for 60 min. Introduction of 4.0 mM methionine to the slurries induced a 2.7-time increase. However, when both sodium sulfite (3.2 mM) and methionine (4.0 mM) were added, a 25.7-time higher amount in methanethiol concentration was observed. Similar results were obtained when sodium sulfite and methionine were added to a partially purified protein fraction prepared from defatted soy flakes. Mass spectra of the methanethiol formed with addition of L-methionine-methyl-13C1 and unlabeled sulfite showed that the carbon-13 labeled methyl group was actually integrated into methanethiol. But no incorporation of isotopic sulfur was observed when 34S-labeled sodium sulfite was applied. The free methionine contents in commercial and lab-prepared ISP and in-process protein extracts ranged from 10.34 μg/g to 52.74 μg/g, which were not proportional to the indigenous methanethiol contents. Results from the current study showed that methionine is an important methyl group donor for methanethiol in ISP associated with sulfite as a reducing agent.

Original languageEnglish
Pages (from-to)C527-C531
JournalJournal of Food Science
Issue number9
StatePublished - Nov 2006


  • Isolated soy proteins
  • Methanethiol
  • Methionine
  • Methyl group donor
  • Sulfite

ASJC Scopus subject areas

  • Food Science


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