Elucidation of the Chemical Structure of Preformed Cooked Cured-Meat Pigment by Electron Paramagnetic Resonance Spectroscopy

Abstract

The preparation of cooked cured-meat pigment (CCMP) has previously been reported from our laboratories, but the exact chemical nature of this pigment has remained elusive. Electron paramagnetic resonance (EPR) spectroscopy was employed to help provide the answers sought. EPR spectra of CCMP in an acetone glass revealed that the molecule is paramagnetic and exists as a pentacoordinate mononitrosylheme complex. A well-resolved triplet in the g3 region of the spectrum was due to hyperfine splitting of the 14N nuclei of NO with an unpaired electron. In a pyridine glass, EPR spectra suggest that there was participation of a pyridine molecule with the nitrosylheme complex. Such spectra are typical of a hexacoordinate species and are similar to those of NO complexes of Fe(II) myoglobin and hemoglobin. Additionally, a loss in resolution of the hyperfine structure in the g3 region was apparent. EPR spectra of cooked nitrite-cured and CCMP-treated meat, in situ, were similar and were identical to that of the preformed CCMP in acetone. Thus, the pigment formed in thermally processed nitrite-cured meat is identical to that of CCMP prepared outside the meat matrix and then applied to meat as part of a nitrite-free multicomponent curing system. Keywords: Electron paramagnetic resonance spectroscopy; cooked cured-meat pigment; nitrite; myoglobin; hemoglobin