Oxygen consumption rate of permeabilized cells and isolated mitochondria from pork M. masseter and liver examined fresh and after freeze-thawing at different pH values.

Unlabelled: The oxygen consumption rate (OCR) of 2 types of permeabilized tissues and their corresponding isolated mitochondria from porcine M. masseter and liver, resulting in 4 systems, was studied at different pH values (5.0 to 7.1) using fresh samples and samples frozen directly in liquid nitrogen (N₂) or air-frozen at -20°C. A protocol with the additive sequence rotenone-succinate-ADP (adenosine diphosphate)-cytochrome c-FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone) was used to study respiration changes. The OCR of liver respiring on succinate (OCR(S)) was higher than that of muscle tissue. pH had a larger effect on OCR(S) than freeze-thawing. Low pH was associated with reduced OCR(S). The OCR(S) of isolated muscle mitochondria appeared to be an underestimated relative to the OCR(S) of permeabilized muscle cells. Increasing pH, following prior subjection to pH 5.0, showed partial reversibility of the OCR(S). The freeze-thaw cycle increased the OCR(S) when muscle systems were frozen and examined above pH 6.0; this effect was less apparent for liver tissue. A response to cytochrome c addition, indicating a defective outer mitochondrial membrane, was observed for all 4 systems. The response was, however, lowest for permeabilized cells. The ADP/FCCP additive pair indicated partial coupling for isolated liver and muscle mitochondria. These additives gave weak responses for the permeabilized liver cells while the OCR seemed to be inhibited for permeabilized muscle fibers when ADP/FCCP was added.

Practical Application: The mitochondrial state is believed to be important for myoglobin reduction, development of flavor, and possibly other meat qualities. By monitoring the oxygen consumption in mitochondria and meat we can better understand and control such processes following freezing and thawing.