Effect of meat ultimate pH on rate of titin and nebulin degradation

The processes involved in the tenderisation of meat were studied on muscles with a range of ultimate pH values (5.4-7.0), produced by subcutaneous injection of various doses of adrenaline and exercise. The m. longissimus thoracicum et lumborum (LD) was removed from carcasses stored at 10 °C and held for 1, 3 or 6 days after slaughter, then frozen until tenderness assessment. The tenderness of meat cooked from the frozen state was determined as the force to shear samples of 10 mm × 10 mm cross-section using a MIRINZ tenderometer. The maximum toughness of 15 kgF occurred at an ultimate pH (pH(u)) of about 6.0, resulting in a curvilinear relationship between tenderness and pH(u) at 1 day post-slaughter. By 6 days post-slaughter, all meat had reached the same low shear value of approximately 3 kgF. SDS-PAGE patterns obtained from samples at 12, 24 and 48 hr post-slaughter showed increasing titin and nebulin degradation over time, with the slowest rate of degradation occurring at pH(u) values 6.0-6.3. Titin and nebulin are known to play an important role in the stabilisation of myofibril structure, and it is suggested that the curvilinear relationship results when pH-dependent titin and nebulin degradation occurs.