Fragmentation of myofibrils, limited proteolysis and water holding capacity of meat

Protein changes in ageing meat result in increased vulnerability of the myofibrils to fragmentation, caused possibly by limited proteolysis. It was investigated which groups of muscle proteases, if any, were involved and what was the relation between fragmentation and hydration of beef meat. In samples ranging in natural pH from 5.4 to 7.0 the least fragmentation after 3 days at 2 degrees C was at pH 6. This could suggest the role of both the cathepsins and neutral proteases. In samples aged in the presence of EDTA fragmentation was significantly lower than in the controls. This could indicate the role of Ca2+ activated neutral proteases, or support the hypothesis on the nonenzymatic mechanism involving Ca2+. The results of PAG electrophoresis could not have been due to the neutral proteases, as the 30,000 g X mol-1 component, resulting from the hydrolysis of troponin T, did not accumulate at pH 7 until the 9th day of ageing, but at pH 5.4 the intensity of this band increased markedly already after 3 days. There was no correlation between the fragmentation and the hydration of the aged meat after cooking. The addition of 0.001% of trypsin or 0.0005% of papain to minced meat did not cause after 9 days any increase in the contents of free amino acids and peptides or significant changes in the PAGE pattern as compared to those in the controls. However, the fragmentation and hydration of the raw meat was larger in the samples containing added enzymes. After cooking the hydration of the samples did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)