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Heme proteins and oxidation in fresh
and processed meats
M. P. Richards, University of Wisconsin-Madison, USA
Abstract: This chapter describes mechanisms of heme protein-mediated
discoloration and rancidity development in raw muscle as well as processed
meat products. Protein crystallography and site-directed mutagenesis efforts
have improved our understanding of the mechanisms involved. Steric
displacement of bound ligands, weak anchoring of the heme propionates to
the globin, and larger channels for solvent entry into the heme crevice
explain why certain heme proteins are more reactive than others. The
interplay between pH, O
2
partial pressure, light, metals, and other factors
that promote pigment and lipid oxidation are described. Muscle-based
products that are particularly vulnerable to oxidation are noted. Strategies to
inhibit discoloration and off-flavor formation mediated by heme proteins are
also covered briefly.
Keywords: rancidity, discoloration, blood, hemoglobin, myoglobin, quality
deterioration.
4.1 Introduction
The main heme proteins in muscle tissue are hemoglobin (Hb) and myoglobin
(Mb). Heme proteins dictate the appearance (e.g., color) of muscle foods. In
addition, Hb and Mb have the capacity to promote lipid oxidation during storage
which leads to off-odors and off-flavors. Hemoglobin is located within
erythrocytes (e.g., red blood cells). Myoglobin is located within muscle cells
(e.g., myocytes). Bleeding is often believed to remove hemoglobin from the
muscle; however substantial quantities of blood remain in the muscle after
bleeding (Porter et al., 1992, Warriss, 1977). The primary function of Hb in the
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