Zinc-protoporphyrin IX promoting activity in pork muscle

Zn-protoporphyrin IX (ZPP) is a major red pigment in dried hams made without nitrates. In this study, an assay procedure was developed for the measurement of ZPP-promoting activity in meat extracts. The method, adapted from assays already in use with other matrices, is based on the incubation of the meat extract with zinc and protoporphyrin IX (the reaction substrates) and recording of the resulting fluorescence at 590 nm, i.e. the emission wavelength of ZPP. When used to test pork samples, the assay procedure, whose relative standard deviation was <6%, revealed an average activity of 1.7 (enzyme activity units/g dried meat) with large inter-sample variation (CV=66%). Several substances, amongst those typically used in the meat industry, were tested for their effects on the assay performance, showing that sodium chloride and, to a lesser extent, sodium ascorbate significantly (P<0.05) enhance ZPP formation, whereas nitrate and glucose have no effect. It is concluded that fresh meat contains a ZPP-promoting activity, likely a zinc-chelatase enzyme, whose behaviour fits the chemical conditions occurring in hams undergoing the dry-curing process.