Catheptic Activity, Textural Properties and Surface Ultrastructure of Post‐mortem Beef Muscle

Catheptic enzyme release was studied in beef psoas muscle as a function of post‐mortem aging. Textural qualities (tensile and shear) and fiber surface ultrastructure were examined. A crude (12‐fold purification) catheptic fraction was prepared that exhibited the expected pH and temperature optima and was activated by dithiothreitol, EDTA and Triton X‐100. When beef muscle was fractionated according to its solubility characteristics the susceptibility to proteolysis decreased: water soluble > salt soluble > insoluble. During post‐mortem aging proteolytic activity decreased slightly at rigor, increased to day 6 and subsequently decreased. Shear force, breaking strength, ATP, break elongation and elasticity all dropped during the first 4 days, but the latter two parameters increased thereafter. The major alteration in fiber appearance through 2 days was shortening. Later, however, transverse striations became depressed and beginning at day 5 and continuing through the 2‐wk period extensive fiber breakage occurred. The possibility that cathepsins play a role in these post‐mortem events is considered.