Physico-chemical characteristics of nitrosomyoglobin: Water-extractability and stability toward an oxidizing agent of myoglobin derivatives

To clarify the mechanism of the insolubilization of nitrosomyoglobin (NOMb) formed in meat during curing, the extractability of myoglobin (Mb) derivatives with water coexisting with NOMb in cured meat was compared, and the effects of an oxidizing agent on heme pigments were investigated. Cured meat was prepared by adding nitrite, sodium chloride and sodium ascorbate to porcine skeletal muscle. In spite of the low extractability of NOMb from the cured meat, the other Mb derivatives were significantly more extractable with water. On adding potassium ferricyanide at 1 %, most of the heme pigments in the cured meat were oxidized to metmyoglobin (MetMb). NOMb formed during curing could not be extracted with water, even after being oxidized to MetMb with ferricyanide. NOMb thus appears to react strongly with endogenous muscle components, especially myofibrils, in cured meat. NOMb and oxymyoglobin (MbO₂) were prepared as model solutions and to both ferricyanide (0-0.5 %) was added. One reaction mixture was incubated at pH 5.5 and the other, at pH 7.0, followed by measurement of absorption spectra. Under the experimental conditions used, Mb was completely nitrosated, but the oxygenation of Mb did not proceed to 100 %. In a 90 % MbO₂ solution at each pH, all MbO₂ was oxidized to MetMb by 0.5 % ferricyanide. This treatment failed to oxidize NOMb completely. These results clearly show that NOMb is more stable toward oxidizing agents than MbO₂.