Studies on the post-mortem fragmentation of myofibrils

Area of Science:

• Muscle physiology
• Biochemistry
• Post-mortem meat science

Background:

• Muscle contraction and relaxation are complex processes involving myofibril structure.
• Understanding post-mortem muscle changes is crucial for meat quality.
• Calcium ions play a significant role in muscle function and degradation.

Purpose of the Study:

• To investigate the relationship between myofibril fragmentation and tension during post-mortem muscle contraction.
• To determine the influence of calcium ion concentration and pH on myofibril fragmentation rate.
• To differentiate in vitro myofibril fragmentation from calcium-activated factor (CAF) induced degradation.

Main Methods:

• Measurement of myofibril fragmentation extent and sarcomere length during post-mortem contraction.
• Analysis of myofibril fragmentation rate across varying calcium ion concentrations and pH.
• Incubation of myofibrils with calcium chloride and assessment of protein release using SDS-polyacrylamide gel electrophoresis.
• Comparison of fragmentation patterns with CAF treatment.

Main Results:

• Myofibril fragmentation closely correlated with tension development, peaking at sarcomere lengths of 2.0-2.2 µm.
• Fragmentation rate was dependent on calcium ion concentration (10⁻⁵ to 2x10⁻² M) with a minimum at pH 6.5.
• In vitro fragmentation released specific Z-line components (54,000 and 76,000 daltons) and minimal alpha-actinin, distinct from CAF effects.
• Iodoacetate did not inhibit fragmentation of isolated myofibrils, suggesting a non-CAF mechanism.

Conclusions:

• In vitro myofibril fragmentation during mechanical homogenization is mechanistically distinct from CAF-induced proteolysis.
• Calcium ions play a role in the in vitro fragmentation of post-mortem muscle myofibrils.
• The identified protein fragments suggest specific Z-line involvement in calcium-mediated in vitro fragmentation.