Quantification of zinc–porphyrin in dry-cured ham products by spectroscopic methods: Comparison of absorption, fluorescence and X-ray fluorescence spectroscopy

Abstract

Zinc–protoporphyrin (Zn–pp), which has been identified as the major pigment in certain dry-cured meat products, was extracted with acetone/water (75%) and isolated from the following meat products: Parma ham, Iberian ham and dry-cured ham with added nitrite. The quantification of Zn–pp by electron absorption, fluorescence and X-ray fluorescence (XRF) spectroscopy was compared (concentration range used [Zn–pp] = 0.8–9.7 μM). All three hams were found to contain Zn–pp, and the results show no significant difference among the content of Zn–pp quantified by fluorescence, absorbance and X-ray fluorescence spectroscopy for Parma ham and Iberian ham. All three methods can be used for quantification of Zn–pp in acetone/water extracts of different ham types if the content is higher than 1.0 ppm. For dry-cured ham with added nitrite, XRF was not applicable due to the low content of Zn–pp (<0.1 ppm). In addition, XRF spectroscopy provides further information regarding other trace elements and can therefore be advantageous in this aspect. This study also focused on XRF determination of Fe in the extracts and as no detectable Fe was found in the three types of ham extracts investigated (limit of detection; Fe ⩽ 1.8 ppm), it allows the conclusion that iron containing pigments, e.g., heme, do not contribute to the noticeable red colour observed in some of the extracts.