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Sulfite‐Radical Anions in Isolated Soy Proteins
Author(s) -
Lei Q.,
Boatright W.L.
Publication year - 2007
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.1750-3841.2007.00395.x
Subject(s) - methanethiol , chemistry , sulfite , sulfur , radical , methionine , potassium iodate , aqueous solution , iodate , inorganic chemistry , manganese , organic chemistry , photochemistry , biochemistry , amino acid , iodine
Aqueous mixtures of manganese and sulfite, at levels found in isolated soy proteins (ISP) and defatted soy flakes, spontaneously react in the presence of oxygen to produce methanethiol from the 1‐electron oxidation of methionine. The carbon and sulfur of methanethiol originate from the methyl‐carbon and sulfur of methionine. Similar aqueous mixtures of sulfite, manganese, and oxygen also produce sufficient levels of free radicals to degrade fluorescein. The degradation of methionine by free radicals generated in the sulfite, manganese, and oxygen reaction mixture is inhibited by the free radical spin trapping agent 5,5‐dimethyl‐1‐pyrroline N‐oxide. Processing ISP with either L‐cystine or potassium iodate reduces the free sulfite content of ISP and reduces the headspace methanethiol from aqueous ISP slurries to nondetectable levels. ISP processed without additives contained sufficient levels of free radicals to generate methanethiol from the oxidation of added methionine. There were no detectable levels of methanethiol produced when methionine was added to ISP processed with iodate.