Meat Composition and Processing
Meat: Composition and Characteristics
Connective Tissue Proteins
Collagen:
- The main representative of connective tissue, also found in skin and bones.
- Contains glycine (30%), proline, and hydroxyproline (25%), conferring rigidity and strength.
- Its basic unit is tropocollagen, a helical structure consisting of 3 chains.
- Features a crystal structure, which might be related to rigidity and resistance to mastication. These features increase with the animal’s age due to an increased number of links.
- Easily denatured by heat. The critical temperature is 64°C (beef) and 30-45°C (fish).
- Prolonged heating solubilizes the gelatin.
- Trypsin and chymotrypsin do not affect natural collagen.
- It is attacked by pepsin and bacterial collagenase.
Elastin:
- A ball-type molecule with numerous links between chains. Yellow in color.
- During cooking in water, it swells and stretches but does not dissolve.
- Resistant to agents that break hydrogen bonds.
- Not attacked by trypsin, chymotrypsin, or pepsin.
- Attacked by papain and pancreatic elastases.
Sarcoplasmic Proteins
The main sarcoplasmic protein is myoglobin:
- The pigment of red meat.
- A conjugated protein formed by globin (a globular protein) and heme.
- The water molecule can be replaced by oxygen or NO.
- It has a high affinity for O2. In the muscle, it acts as a reserve.
Changes During Processing
In sausages, nitrites form nitrous acid, which decomposes and generates NO. When using nitrates, the process is slower. The use of these additives is questioned due to the possible formation of carcinogenic substances.
Postmortem Changes in Muscle
- O2 stops reaching the muscle.
- Aerobic reactions cease.
- Anaerobic glycolysis occurs.
- Lactic acid is generated.
- The amount of ATP decreases.
- The actin-myosin complex becomes permanent.
Rigor Mortis (Cadaveric Rigidity)
Specifications: pH 5.6-5.8, low water-holding capacity, dry, hard texture.
The intensity of change and the time it is reached depend on the species, slaughter method, nutritional status, and storage temperature.
Meat Handling and Quality
Slow Cooling: A rapid drop in pH to lower values (5) causes denaturation. Water is removed, giving a fibrous and dry texture.
Cooling Before Rigor Mortis: This process occurs during thawing or consumption. Hardening is very rapid and marked, and the muscle contracts.
Recommendation
- Gradual cooling, so that rigor is reached between 14 and 19°C.
- To freeze, it should be done after rigor, and thawing should not be very fast.
- Meat in a state of rigor should not be cooked.
Meat Maturation (Tenderization)
Corresponds to the softening of the flesh after some time has passed since Rigor Mortis was reached.
The mechanism is not the rupture but the separation of the actomyosin complex from the actin filaments of the Z line.
The changes are caused by ionic or enzymatic action.
The enzymes, cathepsins, are those of the flesh itself. They are found in lysosomes and are released due to the decrease in pH.
The time of disappearance of rigor depends on the species and storage temperature.