Post-mortem changes in chicken muscle : some key biochemical processes involved in the conversion of muscle to meat

Abstract

The post mortem changes taking place in poultry muscular tissue and the resulting meat quality, until the moment of consumption of the meat by the consumer are described. Modern broiler chickens grow 'at the edge of what is metabolically possible'. This hypothesis is derived from the fact that muscle, and thus protein, accretion is accomplished through a dynamic equilibrium between synthesis and degradation. The cell reaches a certain maximum synthesis capacity. To grow beyond this maximum synthesis capacity the cell has to decrease it degradation. This in its turn is of great influence for meat aging.The chromatographic properties of a class of proteïnases, important for meat aging, called calpains as well as the development of a method for the quantification of the activity of these enzymes is described.Furthermore, a number of endogenous proteïnase and inhibitor activities, important for meat aging, was measured in four chicken selection lines differing in both growth rate and protein efficiency. Differences between lines were observed, the fastest growing lines showing the lowest proteolytic capacities of the calpain/calpastatin system while the slower growing animals showed higher proteolytic potentials in their breast muscles.The highly protein efficient line showed high proteïnase capacity of cathepsin H. Studies on the post mortem course of both the protein and the energy metabolism in the above mentioned selectionlines are described. The slowest growing lines showed the fastest post mortem meat tenderization while the faster growing lines showed slower tenderization, which was not yet completed within 48 hours post mortem. This suggests that increasing growth speed, which is aimed at by the poultry production industry, may at the end lead to meat aging problems and an unacceptable poultry meat quality, especially since the retail sector strives for shorter periods between slaughter and presentation to the customer, based on microbiological considerations.The development of methods to measure the post mortem proteolytic degradation of the cytoskeletal proteins titin, nebulin, desmin and vinculin using SDS-PAGE and 'Western blotting' are described. Possible candidate fragments of the different cytoskeletal proteins were identified to serve as markers for monitoring the course of meat aging.</p