The effect of different pH values and temperatures on the denaturation of red and white myofibrils from pork and poultry as incubated at different concentrations of ATP

The susceptibility to denaturation of myofibrils from pork and chicken red and white muscles was investigated. The M. pectoralis (white muscle) and the M. pubio-ishio (red muscle) of 6 Arboracre chickens, and the M. semimembranosus (white muscle) and M. psoas major (red muscle) of 3 Yorkshire x Landrace x Duroc cross and 3 Yorkshire x Landrace hogs were used. The myofibrils were purified and incubated at 25°C or 40°C, at pH 6.5 or 5.4. To simulate the conditions of a live, early postmortem and a rigor muscle, ATP (0 mM, 0.68 mM, and 3.4 mM) was added to the incubation. Incubations were sampled after 0, 10, 20, and 60 minutes. Myosin denaturation was measured as a loss in soluble myosin. At pH 6.5, higher ATP concentrations resulted in increased loss of myosin solubility of myofibrils from pork and chicken red, and pork white muscle. Myosin solubility of chicken white myofibrils was not affected by ATP. In all myofibrils, except in those from white chicken muscles, pH 5.4 resulted in significantly more denaturation than pH 6.5. The results indicate that red pork and chicken, and white pork myofibrils are equally susceptible to myosin denaturation. Chicken white myofibrils were the least susceptible to denaturation. Compared to white muscle fibers, red muscle fibers enter rigor at a higher ultimate pH. Consequently, myosin denaturation, and PSE, is prevented. This may explain why chicken white muscle has, in the past, shown little susceptibility to PSE type meat.