Postmortem Changes in Muscles

Vocabulary practice flashcards covering postmortem muscle biochemistry, pH decline, temperature effects, rigor mortis phases, and enzymatic aging mechanisms.

Homeostasis

The physiological state in which all organs and systems interact to maintain a narrow, stable internal environment (controlling oxygen concentration, pH, temperature, and energy supply) so biological functions can operate efficiently.

Exsanguination

The removal of blood during slaughter that marks the onset of postmortem muscle changes, causing a rapid drop in blood pressure and triggering compensatory circulatory responses that divert remaining blood flow to vital organs.

Postmortem Anaerobic Metabolism

The emergency metabolic pathway that takes over after oxygen depletion halts the TCA cycle and electron transport chain, generating limited ATP and accumulating lactic acid via glycolysis until muscle glycogen stores are exhausted.

Creatine Phosphate (CP)

A high-energy phosphate reserve within muscle tissue used to rapidly regenerate ATP during early postmortem metabolism before cellular energy reserves completely deplete.

Postmortem Muscle pH Decline Curves

Graphical profiles depicting postmortem pH changes across conditions, comparing normal decline in cattle and pigs against rapid lactic acid buildup in pale, soft, exudative (PSE) pork and minimal pH drop in dark, firm, dry (DFD) beef and pork.

Normal Postmortem pH Decline

The typical postmortem acid accumulation profile where muscle pH drops gradually from approximately $7.0$ to $5.7$ within $6\text{ to }8\text{ h}$, ultimately reaching an ultimate pH of approximately $5.5$ within $24\text{ h}$.

Postmortem Carcass Temperature Transient

A brief increase in carcass internal temperature immediately following exsanguination caused by ongoing anaerobic metabolic heat production prior to effective chilling.

Rigor Mortis

Literally 'stiffness of death,' a postmortem condition characterized by the formation of permanent, irreversible actomyosin cross-bridges across muscle fibers following the depletion of ATP.

Delay Phase of Rigor Mortis

The initial postmortem interval immediately after bleeding during which muscle remains extensible and relaxed because adequate levels of ATP and creatine phosphate are still present.

Onset Phase of Rigor Mortis

The postmortem phase occurring as creatine phosphate and ATP stores become depleted, causing muscle extensibility to drop and isometric tension to begin climbing.

Completion Phase of Rigor Mortis

The postmortem phase occurring within approximately $24\text{ h}$ where ATP is completely exhausted, maximal isometric tension is achieved, and muscle loses all extensibility.

Isometric Tension Development Curve

A diagram mapping postmortem muscle tension over time, charting the initial delay phase, the steep rise during rigor onset, peak isometric tension at rigor completion, and the subsequent tension decrease during rigor resolution.

Rigor Cross-Bridge Binding Ratio

The comparative proportion of actomyosin cross-bridges formed, reaching $100\%$ of available binding sites during rigor mortis compared to only $20\%$ during normal physiological contraction in living muscle.

Species Rigor Delay Times

The species-dependent duration before the onset of rigor mortis: $6\text{ to }12\text{ hours}$ for beef and lamb, $1/4\text{ to }3\text{ hours}$ for pork, less than $1\text{ hour}$ for turkey and fish, and less than $1/2\text{ hour}$ for chicken.

Resolution of Rigor

The postmortem reduction in muscle tension and progressive tenderization over time, which occurs through enzymatic degradation of structural proteins while actomyosin cross-bridge bonds remain unbroken.

Z-Disk Postmortem Degradation Micrographs

Transmission electron microscopy documenting structural breakdown in bovine longissimus muscle stored at $2\,^\circ\text{C}$, showing intact Z-disks at $1\text{ hour}$, apparent breakdown at $24\text{ hours}$, extensive myofibril breaks at $48\text{ hours}$, and complete lateral breaks after $8\text{ days}$.

Titin and Nebulin Sarcomere Organization

A sarcomeric model detailing large structural proteins: nebulin aligns the thin actin filaments along the Z-disk, while titin anchors the thick myosin filaments to the Z-disk to provide passive elasticity and structural centering.

Calpain System

A major endogenous proteolytic system active during meat aging that includes two calcium-dependent proteases—$\mu\text{-calpain}$ (activated by micromolar $\text{Ca}^{2+}$) and $\text{m-calpain}$ (activated by millimolar $\text{Ca}^{2+}$)—alongside their regulatory inhibitor.

Calpastatin

A specific endogenous inhibitor protein that limits and regulates the proteolytic activity of $\mu\text{-calpain}$ and $\text{m-calpain}$ in skeletal muscle.

Desmin Degradation

The postmortem proteolysis of intermediate filaments that link adjacent myofibrils laterally, the breakdown of which causes disruption of transverse cross-linking and myofibril fragmentation.

Titin and Nebulin Degradation

The postmortem proteolytic breakdown of massive longitudinal cytoskeletal proteins, leading to a loss of passive resting elasticity and fragmentation of myofibrils.

Troponin-T Degradation

The proteolytic breakdown and disappearance of a key regulatory component of thin filaments during postmortem aging, frequently monitored as an indicator of muscle tenderization.

Actin and Myosin Postmortem Stability

The characteristic biochemical resilience of the primary contractile proteins, which show no detectable proteolytic degradation even after $56\text{ days}$ of postmortem aging.

Postmortem Polypeptide Degradation Products

Novel low-molecular-weight peptide fragments (specifically $95{,}000\text{ Da}$ and $28{,}000\text{ to }32{,}000\text{ Da}$) that appear on polyacrylamide gel electrophoresis as structural myofibrillar proteins are proteolyzed during aging.