On the nature of the haematin-protein bonding in cooked meat

Evaluation of induced color changes in chicken breast meat during simulation of pink color defect

The objective of the study was to establish a pink threshold and simulate the pink defect in cooked chicken breast meat with treatment combinations that would induce significant changes in the color of raw and cooked meat. The subjective pink threshold used in judging pink discoloration was established at a* = 3.8. Samples of three color groups (normal, lighter than normal, and darker than normal) of boneless, skinless chicken breast muscles were selected based on instrumental color values. The in situ changes were induced using sodium chloride, sodium tripolyphosphate, sodium erythorbate, and sodium nitrite at two levels: present and not present. Fillets in all treatments were subjected to individual injections, followed by tumbling, cooking, and chilling. Samples were analyzed for color [lightness (L*), red/green axis (a*), yellow/blue axis (b*)] and reflectance spectra. Simulation of the pink defect was achieved in eight of the 16 treatment combinations when sodium nitrite was present and in an additional two treatment combinations when it was absent. Pinking in cooked samples was affected (P < 0.05) by L* of raw meat color. Results confirmed that it was possible to simulate the undesired pinking in cooked chicken white meat when in situ conditions were induced by sodium chloride, sodium tripolyphosphate, and sodium nitrite. The continuation of the simulation study can aid in developing alternative processing methods to eliminate potential pink defects.

Biochemical changes in an intermediate moisture cecina-like meat during storage

Biochemical and microbiological changes in two cecina-like products were evaluated during storage. Two products were prepared, one by salting and the other by infusion in a salt-glycerol solution. The samples were vacuum packed and tested monthly for pH, colour, haematin complex, soluble nitrogen and microbiological spoilage. Proteolysis and increase in pH showed a high correlation for both samples. Temperature-dependent changes in colour and concentration of haematin complex during storage were also found in both samples. The activation energy for haematin transformation was found to be around 1 kcal/mol. Based on the low activation energy for haematin complex degradation (around 1 kcal/mol) for both samples, this process may be regarded as a low energy biochemical process.

A note on the nature of the haematin pigments present in freeze dried and cooked beef

Analysis of the reflectance spectra of beef samples treated to contain all the haemoproteins in one pigment form indicated that little or no change in the haematin environment occurs on freeze drying fresh, oxymyoglobin-rich meat or cooked meat. Dehydration of metmyoglobin in meat results in the water molecule at the sixth coordination site being replaced by a protein-bound ligand. On rehydration, this ligand may be replaced by water to reform metmyoglobin, but the degree of conversion depends on the rate of rehydration. The spectral similarity between cooked and freeze dried, oxidised meat indicates that the haematin environments are similar. It is suggested that in these meats the predominant pigments are di-imidazole complexes.

Pigeon (Columba L.) meat iron solubility and availability for absorption in rats

1. The distribution of iron in 59Fe-labelled pigeon (Columba L.) leg and breast muscle and liver were determined by gel filtration. While the insoluble Fe was between 14 and 25% of the total Fe from the tissues, the haem-Fe represented 79.1% (breast) to 45% (liver) of the total Fe and ferritin was between 5.5% (breast) and 26.5% (liver) of the total Fe. 2. The tissue haem-Fe concentration was found to be lower than that determined by gel filtration using the method of Schricker et al. (1982) for non-haem-Fe and obtaining haem-Fe by difference. 3. A simulated in vitro digestion procedure showed significantly (P less than 0.01) reduced 59Fe solubility from 59Fe-labelled pigeon meat after cooking at 90 degrees for 30 min. 4. 59Fe absorption from whole pigeon meat and soluble extract was significantly reduced by cooking when given to Fe-replete rats. Cooking liver, however, slightly improved 59Fe absorption in Fe-replete rats. 5. 59Fe absorption from the separated pigeon-meat fractions (haemoproteins, ferritin and haemosiderin) was variable but considerably lower than that from whole meat. 6. The relative distribution of Fe compounds in meat, the processing conditions they are subjected to and the protein content and composition may all influence the absorption of meat-Fe to some degree.