This study investigates the potential of novel heme-ligand complexes, derived from heme-iron isolated from porcine hemoglobin by enzymatic hydrolysis, to use as pigments for meat products. Five alternatives to sodium nitrite were identified as possible heme ligands and stabilizing agents of the red conformation of heme. The effects of 4-methylimidazole, methyl nicotinate, pyrrolidine, piperidine, pyrazine and sodium nitrite (as comparative benchmark) on the color of heme-iron extract and pure hemin standard were studied in solution. The ligand affinity and heme-ligand stability was assessed over time in solution by UV-Vis absorbance spectroscopy and CIELAB color space parameters. The CIE redness score a* was used as a single measurement to propose a predictive model based on the following parameters: heme source (heme-iron extract or hemin standard), heme-to-ligand molar ratio (1:20 to 1:300), and storage time (up to 32 days). The optimal concentration at which each ligand can be added to either heme source, as well as the stability of the red color of the formed heme-ligand complexes in-solution was determined. Heme-iron extract-derived samples showed increased redness and color stability as compared to their hemin counterparts. No ligand showed as much affinity for heme as sodium nitrite. As the most promising ligand candidates, methyl nicotinate and 4-methylimidazole started to show color changes at a 1:50 molar ratio, but higher amounts (1:100 and 1:300, respectively) were required to attain the maximum redness possible with the highest stability.
Keywords: Animal side-streams; Color stability; Heme; Ligands; Sodium nitrite.