Abstract
SUMMARY: A green pigment was produced when yellowfin (and other) tuna myoglobins, trimethylamine oxide (TMAO), and cysteine were heated together in 0.1 M phosphate buffer pH 5.7. The green product could not be produced with mammalian myoglobins, which contain no cysteine residues. The roles of myoglobin, cysteine, and TMAO in the production of off‐color (green) cooked tuna were investigated. Denaturation of myoglobin, apparently exposing a sulfhydryl group, was necessary for the greening reaction to occur. TMAO acted as a mild oxidizing agent to promote the formation of a disulfide bond between cysteine and the sulfhydryl group on the denatured myoglobin. TMAO could be replaced by oxygen (air), but cysteine appeared to be specific for the reaction. The green color could be reversed by sodium sulfite, but not by other reducing agents tested.
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