TY - JOUR
T1 - Methionine is the methyl group donor for sulfite-associated methanethiol formation in isolated soy proteins
AU - Lei, Q.
AU - Boatright, W. L.
PY - 2006/11
Y1 - 2006/11
N2 - 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.
AB - 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.
KW - Isolated soy proteins
KW - Methanethiol
KW - Methionine
KW - Methyl group donor
KW - Sulfite
UR - http://www.scopus.com/inward/record.url?scp=33845381567&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33845381567&partnerID=8YFLogxK
U2 - 10.1111/j.1750-3841.2006.00197.x
DO - 10.1111/j.1750-3841.2006.00197.x
M3 - Article
AN - SCOPUS:33845381567
SN - 0022-1147
VL - 71
SP - C527-C531
JO - Journal of Food Science
JF - Journal of Food Science
IS - 9
ER -