The effect of pH and aging on mitochondrial reduction of bovine myoglobin's affinity for oxygen.

In skeletal muscles, mitochondria have been shown to decrease the oxygen affinity of myoglobin. In this study, we investigated whether the mitochondrial function of decreasing myoglobin affinity for oxygen persists and operates at the final pH of postmortem bovine skeletal muscle. The oxygen affinity and myoglobin consumption in the presence of mitochondria obtained from fresh and wet-aged beef were evaluated and compared at pH 5.1, 5.6, and 5.7. The results showed that mitochondria obtained from fresh beef preserved myoglobin oxygen consumption and affinity interference, whereas those obtained from wet-aged beef did not. Oxygen consumption and affinity interference were mostly absent at pH 5.1 and were higher at pH 5.7 than those at pH 5.6. Our findings suggest that mitochondria contribute both to an increase in the oxygen affinity of myoglobin in aged meat and a decrease in the oxygen affinity of myoglobin in high-pH meat, such as dark-cutting beef.

A method for extracting carboxy-myoglobin from beef.

The present study was conducted to devise a method for the effective extraction of carboxy-myoglobin (COMb) from beef without carbon monoxide dissociation. The ratio of COMb to myoglobin was computed at absorptions of wavelengths 541 and 551 nm, which characterize COMb and the isosbestic point between COMb and deoxy-myoglobin, respectively. The COMb extraction rate was found to vary with temperature, pH and oxygen conditions. The decrease observed in this rate was inversely proportional to the rise in extraction temperature. The COMb extraction rate was also affected by pH, and the stability of COMb in the extract solution was the highest at pH 8.0-9.0. Moreover, the presence of oxygen was found to disturb COMb extraction. According to these results, nearly all COMb could be extracted from carbon-monoxide-treated beef under stirring conditions in pH 8.5 deoxidized buffer, at 1°C, and under N2 flow with the improved extraction method in this study (98.1 ± 2.7%). The decrement of COMb in the extract was accelerated by light, and the COMb was stable for 20 min in the dark, at 1°C. The extraction conditions for COMb described above should allow the accurate evaluation of COMb in meat tissue.

Effect of nitrate on residual nitrite decomposition rate in cooked cured pork.

The effects of nitrate on the color stability of cooked cured pork were examined. Nitrate inhibited the nitrite decrement and discoloration in the cooked cured ham. Nitrate reduction and nitrite accumulation were observed in the uncooked sausage models, but were not detected in the sausage models cooked at 75°C. The kinetics of nitrite degradation was subsequently examined at various concentrations of nitric acid at constant acidity. The degradation rate of nitrite was clearly found to decrease with nitric acid content. Thus, nitrate does not appear to serve as a donor of nitrite, but rather inhibits nitrite reduction in cooked meat products, with consequent prolongation of color stability.