The conversion of muscle to meat (Naomi) Flashcards
Provide the factors effecting “Eating” quality
- Tenderness
- Flavour
- Juiciness
- Colour
Name the physiological phases of post-mortem death
- Palor mortis
- Algor mortis
- Rigor mortis
- Livor mortis
Define Palor mortis
Paleness of skin of face and body after onset of death
Define Algor mortis
Heat loss of body post-mortem
Define Rigor mortis
Stiffness of death. Small muscles stiffen first, followed by bigger muscles. Starts ca. 2 hours p.m. and ends at about 8h p.m. Rigor mortis ends due to decomposition of muscles and body.
Define Livor mortis
Final stage of death. Effects of gravity start to influence the body in that blood starts to collect in certain parts of body. This is also referred to as the lividity of the body
Provide the steps of normal conversion of muscle to meat
- Circulatory failure
- Glucose depleted, and lactic acid accumulates
- [H+]-ion concentration increases
- Muscle pH decreases
- Proteolytic enzymes released
- Rigor mortis – actomyosin
- Normal pHu = prerequisite for good keepability (low microbial counts), tenderness and desirable colour
What must not be destroyed during stunning and why?
Medulla oblongata must not be destroyed as this controls the heart and brain and therefore used after death to pump all blood out of carcass.
Define Exsanguination
The removal of blood from the body of a slaughtered animal
Define “Blood splash”
Small dark areas observed in muscle (meat) where capillaries have ruptured due to over-filling with blood.
Whay causes Blood splash
Emotional stress that causes greater vasodilatation together with electrical stunning methods (pigs) may cause this phenomenon.
Provide the steps of what happens after slaughter
- Blood circulation stops
- Muscle exhausts oxygen supply
- Muscle can no longer use oxygen to generate ATP
- Anaerobic glycolysis
- The breakdown of glycogen →enough energy to contract the muscles→also produces lactic acid.
- Formation of lactic acid
- No blood flow to carry the lactic acid away
- Lactic acid builds up in the muscle tissue
- Lactic acid fall in pH 6.8 - 7.3 to about 5.4 - 5.8
- Lactic acid build-up releases calcium
- Causes muscle contraction
» Glycogen supplies depleted
» ATP regeneration stops
» Actin and myosin remain locked in a permanent
contraction called rigor mortis
What is the meaning of the Latin Rigor mortis
stiffness of death
Describe the delay phase of rigor mortis
- muscle is still extensible
- still ATP available to bind with Mg2+
- helps disconnect the actin/myosin cross-bridges
- allows muscles to relax
Describe the onset phase of rigor mortis
- Creatine phosphate is depleted during this phase
- CP inhibits the phosphorylation of ADP into ATP
- causes a sharp decrease in ATP production
- the signal of the start of the onset phase of rigor
What happens when muscles begin the process of rigor mortis?
Permanent cross bridges are formed at pH values of 5.7–5.8
What happens when meat is cooked when muscles are still in rigor mortis?
The meat will be extremely tough
When is Rigor mortis completed?
When creatine phosphate and other sources of rephosphorylation are depleted.
Describe “aging” or “ripening” after slaughter
- achieved by storing meat until muscles recover some extensibility
- become more tender through partial enzymatic breakdown of the muscle fibres.
- “Aging” also leads to improvement of flavour
Describe the occurrence of Pale Soft Exudative meat
(PSE)
- When animals are stressed immediately prior to slaughter
- Preslaughter anaerobic glycolysis breaks down pyruvate to lactic acid
- Lactic acid is broken down to a more stable lactate and hydrogen ions that causes in decrease in pH
- At slaughter the normal process of glycogen being broken down to lactic acid and subsequently lactate further decreases the pH and creates a high acidic environment.
- It’s this high level of acidity that causes partial breakdown of muscle structure
6 This causes softness and exudation resulting in pale, soft and exudative meat
Why is PSE meat exudative?
Because the meat loses its water holding capacity
Why is PSE meat pale?
Because light is reflected by denatured sarcoplasmic proteins
What can help decrease the occurrence of PSE meat in a highly stressed animal immediately pre-slaughter?
Rapid post-mortem cooling
Why does aging help increase meat tenderness?
Aging allows enzymes in muscle cells to break down overlapping proteins
Describe the occurrence of dark firm and dry meat (DFD)
- Long-term stress before slaughter
- Glycogen depletes post-slaughter
- less lactic acid is formed after slaughter; pH stays above pH 6
- Abnormal muscle condition - remains dark purplish red on exposure to air instead of a bright
- Myosin and actin are far removed from isoelectric point
- Binds water
- Spoils quickly
Define WBC
Water binding capacity (WBC) - the ability of meat to bind its own water
What is the isoelectric point of meat proteins?
Between pH 5.0 and 5.1
Describe the effect of pH on WBC
1.Towards isoelectric point, thick and thin filaments in myofibrils move closer together and reduce the water space between them.
2. pH declines post mortem
3. Filaments move closer together as charged amino acid side chains causes attraction between the two filaments
4. Myofibrils shrink
5. Volume of sarcoplasm increases
6. Muscle fibres depleted of ATP
7. Membranes no longer confine cell water
8. Thus, as the pH of pork declines postmortem, its
water binding capacity decreases, and much of the water associated with muscle proteins is free to leave
the muscle fibre
What is the cause of softness in PSE pork?
- Exudate-filled spaces between muscle fibre bundles contribute to the soft texture
- Detachment of myosin molecule heads may contribute to the softness of PSE pork
What is the cause of the pale colour in PSE pork?
- Myofibril A-bands are strongly birefringent (they can rotate polarized light)
- Birefringence is inversely proportional to pH peaking around the isoelectric point
- As pH declines post-mortem, the back scattering of light is increased
- The rapid decline in post-mortem pH also cause denatured myoglobin - converting pink myoglobin to pale brown metmyoglobin - causing an increase in paleness.
Explain the colour change of meat under normal conditions
- The color of muscle in living animal is bright red due to abundance of oxygen.
- Post-mortem there is shortage of oxygen and color becomes dark purplish red.
- Fresh meat when cut has dark red color but on exposure to atmospheric air within few minutes changes to brighter red color.
- This happens due to oxygenation of myoglobin.
What causes cold shortening?
When lamb (to a lesser extent beef) is chilled too rapidly after slaughter
What can be done to prevent cold shortening?
Cold shortening does not take place when the carcass is cooled slowly - temperature must not fall below 10°C before the onset of rigor
Denaturation will cause:
i) Loss of protein solubility
ii) Loss of water holding capacity
iii) Loss in intensity of muscle`s pigment coloration.