Properties of Tilapia Carboxy- and Oxyhemoglobin at Postmortem pH

Hemoglobin plays an important role in the color and oxidative stability of seafoods. A recent practice in the seafood industry is to stabilize muscle color by the application of gases containing carbon monoxide. The goal of this study was to examine and compare the properties of tilapia hemoglobin complexed to either O2 (Oxy-Hb) or CO (CO-Hb) at pH 6.5, which reflects the tilapia muscle postmortem pH. CO-Hb was significantly (p < 0.01) more stable against autoxidation compared to Oxy-Hb when kept at 4 and −30 °C for 23 days. Almost no loss of CO was detected for both temperatures according to the UV−vis spectra of Hb. This stabilization was also believed to play a role in increased protein structure stabilization (p < 0.001) since less protein aggregation was seen for CO-Hb. The higher protein stabilization for Hb was linked to the heme group, which was maintained in its reduced state longer for CO-Hb vs Oxy-Hb and was likely less exposed to solvent. CO-Hb had significantly (p < 0.01) less peroxidase activity than Oxy-Hb and thus reactivity with H2O2. The pro-oxidative activity of CO-Hb was significantly (p < 0.01) reduced in a linoleic acid micelle system compared to that of Oxy-Hb, while smaller differences in activity were seen in a washed cod and tilapia muscle model system. Keywords: Hemoglobin; tilapia; CO (carbon monoxide); O2 (oxygen); autoxidation; stability; peroxidase; pro-oxidative; lipid oxidation