Meat Quality: Composition, Muscle Tissue, and Rigor Mortis

Posted on Mar 22, 2025 in Human Biology

Meat Composition and Muscle Tissue Properties

1. Meat Composition: Water, Protein, and Fat

In cattle, meat composition typically consists of:

  • Protein: 20-22%
  • Water: 70-73%
  • Lipids (Fat): 4-8%

Intramuscular fat is characterized by a high proportion of unsaturated fatty acids.

2. Four Types of Tissue

The four primary types of tissue are:

  • Epithelial: Skin
  • Connective: Blood and bone connective tissue
  • Nervous
  • Muscular:
    • Smooth or involuntary (bowel and stomach)
    • Striated involuntary or cardiac (heart)
    • Voluntary or striated skeletal (pulp)

3. Definition of Meat

Meat is defined as the skeletal muscle of a mature animal used as food for human consumption.

4. Muscle Fiber Changes During Prerigor

During prerigor, ATP levels remain relatively constant, while creatine phosphate levels decrease.

5. Characteristics of Rigor Mortis

Rigor mortis is characterized by the irreversible interaction of actin and myosin, leading to stiffness and tension in the muscles.

6. Differences Between Red and White Muscle Fibers

  • Red Meat Fibers: High myoglobin content, many mitochondria, and energy obtained primarily through aerobic respiration.
  • White Meat Fibers: Lower myoglobin content, fewer mitochondria, and energy obtained primarily through glycolysis and creatine phosphate.

7. PSE (Pale, Soft, Exudative) Meat

PSE meat is associated with stress before slaughter, which stimulates glycolysis. This causes a rapid drop in pH to levels as low as 5.3.

8. Factors Preventing Final pH Achievement

Factors that prevent meat from reaching its final pH include antemortem stress and feeding patterns.

9. Structures of the Muscle Fiber

Key structures of the muscle fiber include the sarcolemma, myofibrils, mitochondria, endoplasmic reticulum, sarcoplasm, terminal cisternae, and transverse tubules.

10. Sarcoplasmic Reticulum

The sarcoplasmic reticulum is a membrane system surrounding the myofibrils. Its primary function is to serve as a storage reservoir for calcium ions (Ca++).

11. Sarcomere Structures

A sarcomere is composed of the following structures:

  • Z Line: Divides the sarcomere.
  • A Band: Contains thick filaments (anisotropic, shifts polarized light).
  • I Band: Contains thin filaments (isotropic, does not shift polarized light).
  • H Band

12. Membrane Potential vs. Action Potential

  • Membrane Potential: Difference in ion concentration across the cell membrane, maintained by ATP hydrolysis.
  • Action Potential: Electrical impulses that propagate along the cell membrane.

13. Muscle Contraction Process

The contraction process begins with an electrical impulse and involves the following steps (requires 3 ATP per myosin head):

  1. Electrical impulse.
  2. Na+ ion influx (action potentials) in the sarcolemma.
  3. Release of Ca++ from the sarcoplasmic reticulum.
  4. Calcium binds to troponin, causing a conformational change. Tropomyosin moves, exposing myosin-binding sites on actin filaments.
  5. ATP is broken down into ADP + Pi. Myosin heads bind to active sites on actin, forming cross-bridges.
  6. Pi and ADP are released, causing a conformational change in myosin.
  7. Myosin bends, pulling actin filaments toward the center of the sarcomere.
  8. A new ATP molecule binds to the actin-myosin complex, causing myosin to detach from actin.

The process begins in the brain and involves the sarcoplasmic reticulum, terminal cisternae, transverse tubules (triad), sarcomeres, and nerve terminals.

14. Muscle Fiber Conditions During Contraction and Relaxation

  • Contraction: Increased concentration of Ca++ ions, inhibition of (TnI-ATP-Mg), and ATP consumption (3 per head).

15. Channels suspend pelvic and achilles heel

[Information missing]

16. Prerigor and Postrigor Changes in ATP

  • Prerigor: ATP remains constant, creatine phosphate decreases.
  • Postrigor: ATP decreases, IMP (inosinic acid) forms.

17. Implications of Stress Before Slaughter

Stress before slaughter can lead to:

  • PSE (Pale, Soft, Exudative) Meat: Caused by stress-induced anaerobic glycolysis and lactic acid formation, resulting in a low pH (below 6).
  • DFD (Dark, Firm, Dry) Meat: Caused by long-term stress leading to glycogen depletion before slaughter, resulting in a high pH and increased water retention capacity. This reduces oxygen diffusion and light absorption on the meat surface.