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Methionine is the Methyl Group Donor for Sulfite‐Associated Methanethiol Formation in Isolated Soy Proteins
Author(s) -
Lei Q.,
Boatright W.L.
Publication year - 2006
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1750-3841.2006.00197.x
Subject(s) - methanethiol , sulfite , chemistry , methionine , sodium sulfite , sulfur , sulfite reductase , sodium bisulfite , sodium , methyl group , soy protein , organic chemistry , biochemistry , group (periodic table) , amino acid , enzyme , reductase
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‐ 13 C 1 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 34 S‐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.