# Zinc Protoporphyrin-Rich Pork Liver Homogenates as Coloring Ingredients in Nitrite-Free Liver [PERSON]
## 3 Results
### Porphyrin Content before and after Sterilization Treatment  
Table 3 shows the changes in pate porphyrins (i.e., heme, ZnPP, and PPIX) after preparation and just before sterilization, and 24 h after thermal treatment. Before sterilization, the highest heme content was found in the positive control, followed by the 16% ZnPP-H and 16% ZnPP-H/A formulations and the negative control pates. The lowest heme content was observed in the 60% ZnPP-P/A formulation, which, in turn, was similar to that in the 60% ZnPP-P and 40% ZnPP-P/A formulations. In terms of ZnPP, the lowest content was observed in the positive and negative controls, whereas the highest content was observed in the 60% ZnPP-P/A formulation, followed by the 60% ZnPP-P, 40% ZnPP-P, and 40% ZnPP-P/A formulations. Thus, the addition levels and composition of ZnPP-rich ingredients determined the presence of ZnPP. Notably, ZnPP was more concentrated in ZnPP-P than in ZnPP-H. This is because ZnPP remains insoluble after 24 h of incubation at pH 4.8 and only approximately 1% of the ZnPP content in ZnPP-H is present in the soluble fraction after centrifugation at 5520\(\times\)\(g\) for 20 min at 4 \({}^{\circ}\)C [15]. The precursor of ZnPP is PPIX [27]. Thus, the amount of PPIX was expected to depend on ZnPP. In agreement with this, the lowest PPIX content was found in the controls, and the highest was found in the 60% ZnPP-P and 60% ZnPP-P/A formulations. Additionally, a non-significant tendency towards a high ZnPP content and low heme content was observed in the pate formulations with antioxidants when compared with that of their counterparts without antioxidants.  
Figure 1: Photographs of canned pork liver pátes after sterilization treatment and storage for 24 h at room temperature. The páte formulations include the following: Pos. Control, positive control with nitrites; Neg. Control, negative control without nitrites; 16% ZnPP-H, complete replacement of water and 16% of the liver with whole autolyzed homogenate rich in Zn-protoporphyrin (ZnPP-H); 40% ZnPP-P and 60% ZnPP-P, replacement of 40% and 60% of the liver, respectively, with pellet rich in Zn protoporphyrin (ZnPP-P), which was obtained after centrifugation (5520\(\times\)\(g\), 20 min) of the whole autolyzed homogenate. All ZnPP-H and ZnPP-P páte formulations in which the antioxidants sodium ascorbate andtocopherol were added (i.e., 16% ZnPP-H/A, 40% ZnPP-P/A, and 60% ZnPP-H/A) are also shown.  
Examining the effect of sterilization revealed that thermal treatment mainly decreased the heme and ZnPP contents but did not affect the PPIX content (Table 3). However, the porphyrin content of the sterilized gates showed trends similar to those before the thermal treatment (Table 3). Thus, the heme content was high in the controls, and the inclusion of ZnPP-rich ingredients resulted in a decrease in the heme content. Simultaneously, the inclusion of ZnPP-rich ingredients increased the ZnPP content. Heme protein degradation by thermal treatment has been reported [28; 29]. However, heme degradation was significant only in the presence of ZnPP-rich ingredients. In contrast, ZnPP degradation upon sterilization was only significant in the 40% and 60% ZnPP-P/A formulations.