A novel titration methodology for elucidation of the structure of preformed cooked cured-meat pigment by visible spectroscopy

The chemical structure of preformed cooked cured-meat pigment (CCMP), which is believed to be the pigment of thermally-processed nitrite-cured meat, was investigated by a novel titration methodology. Electronic spectra of reduced haemin and its nitrosyl derivative were recorded in the visible region in an aqueousor a dimethyl sulphoxide-medium. Changes in the electronic spectrum of reduced haemin upon gradual addition of aliquots of a saturated solution of nitric oxide (NO) revealed that only one molecule of NO ligates itself to the iron of the porphyrin molecule. A similar conclusion was reached from the infrared studies of CCMP, which revealed the presence of only one NO stretching band. Thus, preformed CCMP is irrefutably a mononitrosyl, not a dinitrosyl, derivative of reduced haemin. This conclusion is further supported by an independent electron paramagnetic resonance study of CCMP, which showed that the pigment was a pentacoordinated paramagnetic complex.