SUMMARY— Results in model Mb solutions were confirmed by tests on pork samples treated with the mentioned additives and heated. The content of nitric oxide chromogen (DNOMb) in the samples was determined according to Hornsey. It was found that optimum DNOMb formation required not less than 5 mols nitrite per mol Mb; this may be due partly to side reactions with cysteine and other components of meat. In the presence of sufficient sodium ascorbate (200 mols per mot Mb), 3 mols nitrite per mol Mb was optimum. A large excess of nitrite (500 mols per mol Mb) induced the formation of green pigments, and appreciably less DNOMb was found. Reheating meat containing denatured Mb with nitrite converted Mb to a red pigment, but the color intensity so obtained was 40–60% of that obtained with normal nitrite treatment before heating. Potassium nitrate did not influence the DNOMb formation. The higher the temperature to which meat is heated, the lower its DNOMb content. Exclusion of oxygen by means of carbon dioxide during the treatment of meat improved the final DNOMb content. Irradiation by light of meat containing DNOMb showed that the concentration of nitrite necessary for optimal DNOMb formation in the absence of ascorbate (5 mols nitrite to 1 mol Mb) also caused optimum stability to irradiation in air. Potassium nitrate did not affect this stability. The breakdown of DNOMb increased with the light intensity. In a carbon dioxide atmosphere the breakdown of DNOMb is much slower than in air and it is independent of the light intensity.

SUMMARY— The rate and extent of the formation of nitric oxide myoglobin (NOMb) were studied in aqueous model solutions containing 1–1.5 mg Mb per ml, to which various substances were added to study their effect. Conversion of Mb to NOMb was optimum when 1 mol sodium nitrite per mol Mb was present, provided that the solution contained optimum sodium ascorbate (200 mob). Results were the same with sodium erythorbate, ascorbic acid, and erythorbic acid. Cysteine also furthers the formation of NOMb; its optimum concentration was 100–200 mol per mol Mb, but even then the NOMb formation was appreciably lower than that found with ascorbate. The optimum nitrite concentration in the presence of cysteine was not less than 3 mols nitrite per mol Mb; this could be attributed to the chemical side reactions between nitrite and cysteine. Glutathion showed very little effect on the reaction between nitrite and Mb. The color intensity of NOMb was less in sodium chloride solution than in water. Sodium chloride also had an adverse effect on the formation of NOMb, but sodium nitrate and several sodium polyphosphates had no effect. Ferrous sulfate, on the other hand, accelerated the formation and produced a higher final concentration of nitric oxide myoglobin. Higher temperature and lower pH during the formation of NOMb both markedly accelerated its velocity, but the optimum quantities of NOMb formed were about the same. Investigations of the stability of NOMb in model solutions on exposure to light while in contact with air showed that the ratio between the concentrations of Mb, nitrite, and ascorbate and pH are the decisive factors, and that cysteine, glutathion, potassium nitrate, and polyphosphates had no effect in this respect.

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