Biochemical Properties of Pork Muscle in Relation to Curing. Part II

SUMMARY— The stimulation in the presence of methylene blue of the enzymic production of nitric oxide from added nitrite by pork muscle minces under anaerobic conditions and the partial suppression by nitrite of the aerobic respiration of the minces suggested that the respiratory system is involved in nitrite reduction. Using mitochondrial preparations from pork skeletal muscle, it was shown that under anaerobic conditions the mitochondria can utilize nitrite with formation of nitric oxide. Ferrocytochrome c has been located as the immediate substrate involved, the mediating enzyme being cytochrome oxidase, suggesting that under anaerobic conditions nitrite can replace oxygen as the terminal point of the respiratory chain. In the absence of a reducing agent nitrite oxidizes myoglobin in vitro to the met‐form. The reduction of metmyoglobin by pork muscle minces was erratic and reduction by mitochondria has not been observed. Mitochondria can, however, readily reduce nitric oxide metmyoglobin and this observation suggests a possible mechanism for the formation of nitric oxide myoglobin during curing. Observations on mature curing brines from Wiltshire bacon factories indicated that, although active in utilization of nitrite and nitrate, they do not produce nitric oxide. The tissue enzymes, therefore, appear to be the sole agents for producing nitric oxide and thus cured meat color.