Lipid-oxidation-induced carboxymyoglobin oxidation

We evaluated the usefulness of the ratio A₅₀₃/M₅₈₁ as a browning index (BI) for estimating brown color formation in solutions containing oxymyoglobin (OxyMb) and carboxymyoglobin (COMb). In split-chamber cuvette analyses with different proportions of metmyoglobin (MetMb), COMb and OxyMb, BI was highly correlated (r = 0.93-0.94) with direct estimation of MetMb. Moreover, A₅₀₃/A₅₈₁ was not influenced by different COMb-OxyMb proportions. Second, we investigated 4-hydroxy-2-nonenal (HNE)-induced spectral changes in OxyMb and COMb solutions. At pH 7.4 and 37°C, BI was greater in HNE-treated OxyMb and COMb samples than in aldehyde-free controls (P < 0.05). However, at pH 5.6 and 4°C, HNE-induced browning was more pronounced in COMb than in OxyMb. These results indicated that COMb is susceptible to lipid-oxidation-induced browning in a pH- and temperature-dependent manner.