Proteolysis involvement in zinc-protoporphyrin IX formation during Parma ham maturation

•Mechanism of formation of red pigments in Parma ham during maturation•Zinc-protoporphyrin-IX increases throughout the Parma ham maturation period.•Proteolytic degradation of myoglobin is essential for heme transmetallation.

During maturation of Parma ham a continuing increase in concentration of glycerol, choline, and free amino acids, as followed for 15 months by high resolution 1H NMR of ham extracts, indicates activity of lipolytic and proteolytic enzymes. Proteolysis was shown to be mediated by endogenous cathepsins with detectable activity even at the latest stage of maturation. The concentration of red proteinous pigments containing zinc-protoporphyrin-IX (Zn-PP), as measured by fluorescence spectroscopy, increased throughout the whole maturation period concomitant with formation of low molecular weight peptides. EPR spectroscopy showed that the concentration of the high-spin iron(III) species metmyoglobin present at early stages of production, decreased during maturation to form a EPR-silent pigment suggested to be labile, partly proteolyzed iron(II) myoglobin gradually loosing iron forming non-heme colloidal ferric hydroxide. Proteolytic degradation of myoglobin and precipitation of inorganic iron(III) in the meat matrix are essential for the metal exchange to form Zn-PP and non-heme iron(III) species.