Changes in Zn-porphyrin and proteinous pigments in italian dry-cured ham during processing and maturation.

Substitution of iron with zinc in myoglobin during maturation of Parma ham to yield zinc porphyrin extractable by 75% vol/vol acetone/water solution and detectable by fluorescence spectroscopy, was found to occur concomitant with protein modification in myoglobin. The content of zinc porphyrin increases throughout the whole processing and maturation of Parma ham, from I(fl) 0.1±0.06 for green ham to I(fl) 84.4±48.8 for fully matured Parma ham. In an aqueous extract of Parma ham with pH 6.0 protein alteration in myoglobin, as detected by size-exclusion chromatography, is initiated during the resting period following salting and seems to precede formation of zinc porphyrin. During maturation the results indicate that the modified myoglobin could undergo polymerization, and it is suggested that initial protein denaturation or degradation facilitates substitution of iron with zinc. The pigment polymerization may be a result of non-covalent protein association to zinc porphyrin in denatured or partly degraded myoglobin.