Abstract
Autoxidation and photooxidation of nitrosylmyoglobin, MbFe(II)NO, the pigment of nitrite-cured meat, was investigated in aqueous solution saturated with gas mixtures containing varying levels of CO 2 (0%, 20% and 90%) in the presence of either 1.5 or 10% O 2 and balanced with N 2 in order to mimic modified atmosphere (MA) packaging of meat products. Quantum yields for photooxidation at 1.5% O 2 for monochromatic UV-light (366 nm) were slightly higher than for visible light (436 nm) in agreement with previous findings, while the quantum yields showed no dependence on the CO 2 levels. Autoxidation of MbFe(II)NO was evaluated by global analysis of spectral data applying a kinetic model with two consecutive reaction steps, and the second rate constant was significantly reduced at the highest CO 2 level investigated, while the rate constant of the initial reaction step was found independent of the CO 2 levels. The varying dependence observed for autoxidation and photooxidation of MbFe(II)NO in relation to CO 2 level confirms the differing reaction mechanisms for the two types of MbFe(II)NO degradation. Photooxidation of nitrite-cured meat products packed in MA is accordingly expected to be independent of the presence of varying CO 2 levels, while thermal oxidation (autoxidation) of MbFe(II)NO is reduced at elevated levels of CO 2, which may be of some relevance during product storage and retail display.
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