Protease activity and the ultrastructure of broiler chicken PSE (pale, soft, exudative) meat

The biological cause of broiler PSE meat seems to be an excessive release of Ca2+, promoted by a genetic mutation of ryanodine receptors located in the sarcoplasmic reticulum of skeletal muscle cells. Excessive Ca2+, associated with protein denaturation in meat, enhances protease activity and influences the functional properties of PSE meat. Twenty-four-hour post-mortem Pectoralis major m. samples exhibited lower values for pH, water-holding capacity, and shear force than did control samples, in contrast to colour (L∗) and cooking loss values. Protease activity, measured as myofibril fragmentation index, presented higher values in PSE meat than in control samples. Ultrastructural examination revealed shrinking and depolymerisation of myofilaments and Z-lines disorganisation within the sarcomere in PSE meat. Intense calpain activity was also observed, indicating that the process may initiate at the filaments, because of protein denaturation, and spread through Z-lines, resulting in the collapse of the sarcomere structure.