The conversion of muscle to meat (Naomi)

Question 1

Provide the factors effecting “Eating” quality

Answer 1

1. Tenderness
2. Flavour
3. Juiciness
4. Colour

Question 2

Name the physiological phases of post-mortem death

Answer 2

1. Palor mortis
2. Algor mortis
3. Rigor mortis
4. Livor mortis

Question 3

Define Palor mortis

Answer 3

Paleness of skin of face and body after onset of death

Question 4

Define Algor mortis

Answer 4

Heat loss of body post-mortem

Question 5

Define Rigor mortis

Answer 5

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.

Question 6

Define Livor mortis

Answer 6

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

Question 7

Provide the steps of normal conversion of muscle to meat

Answer 7

1. Circulatory failure
2. Glucose depleted, and lactic acid accumulates
3. [H+]-ion concentration increases
4. Muscle pH decreases
5. Proteolytic enzymes released
6. Rigor mortis – actomyosin
7. Normal pHu = prerequisite for good keepability (low microbial counts), tenderness and desirable colour

Question 8

What must not be destroyed during stunning and why?

Answer 8

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.

Question 9

Define Exsanguination

Answer 9

The removal of blood from the body of a slaughtered animal

Question 10

Define “Blood splash”

Answer 10

Small dark areas observed in muscle (meat) where capillaries have ruptured due to over-filling with blood.

Question 11

Whay causes Blood splash

Answer 11

Emotional stress that causes greater vasodilatation together with electrical stunning methods (pigs) may cause this phenomenon.

Question 12

Provide the steps of what happens after slaughter

Answer 12

1. Blood circulation stops
2. Muscle exhausts oxygen supply
3. Muscle can no longer use oxygen to generate ATP
4. Anaerobic glycolysis
5. The breakdown of glycogen →enough energy to contract the muscles→also produces lactic acid.
6. Formation of lactic acid
7. No blood flow to carry the lactic acid away
8. Lactic acid builds up in the muscle tissue
9. Lactic acid fall in pH 6.8 - 7.3 to about 5.4 - 5.8
10. Lactic acid build-up releases calcium
11. Causes muscle contraction
    » Glycogen supplies depleted
    » ATP regeneration stops
    » Actin and myosin remain locked in a permanent
    contraction called rigor mortis

Question 13

What is the meaning of the Latin Rigor mortis

Answer 13

stiffness of death

Question 14

Describe the delay phase of rigor mortis

Answer 14

1. muscle is still extensible
2. still ATP available to bind with Mg2+
3. helps disconnect the actin/myosin cross-bridges
4. allows muscles to relax

Question 15

Describe the onset phase of rigor mortis

Answer 15

1. Creatine phosphate is depleted during this phase
2. CP inhibits the phosphorylation of ADP into ATP
3. causes a sharp decrease in ATP production
4. the signal of the start of the onset phase of rigor

Question 16

What happens when muscles begin the process of rigor mortis?

Answer 16

Permanent cross bridges are formed at pH values of 5.7–5.8

Question 17

What happens when meat is cooked when muscles are still in rigor mortis?

Answer 17

The meat will be extremely tough

Question 18

When is Rigor mortis completed?

Answer 18

When creatine phosphate and other sources of rephosphorylation are depleted.

Question 19

Describe “aging” or “ripening” after slaughter

Answer 19

1. achieved by storing meat until muscles recover some extensibility
2. become more tender through partial enzymatic breakdown of the muscle fibres.
3. “Aging” also leads to improvement of flavour

Question 20

Describe the occurrence of Pale Soft Exudative meat
(PSE)

Answer 20

1. When animals are stressed immediately prior to slaughter
2. Preslaughter anaerobic glycolysis breaks down pyruvate to lactic acid
3. Lactic acid is broken down to a more stable lactate and hydrogen ions that causes in decrease in pH
4. 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.
5. 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

Question 21

Why is PSE meat exudative?

Answer 21

Because the meat loses its water holding capacity

Question 22

Why is PSE meat pale?

Answer 22

Because light is reflected by denatured sarcoplasmic proteins

Question 23

What can help decrease the occurrence of PSE meat in a highly stressed animal immediately pre-slaughter?

Answer 23

Rapid post-mortem cooling

Question 24

Why does aging help increase meat tenderness?

Answer 24

Aging allows enzymes in muscle cells to break down overlapping proteins

Question 25

Describe the occurrence of dark firm and dry meat (DFD)

Answer 25

1. Long-term stress before slaughter
2. Glycogen depletes post-slaughter
3. less lactic acid is formed after slaughter; pH stays above pH 6
4. Abnormal muscle condition - remains dark purplish red on exposure to air instead of a bright
5. Myosin and actin are far removed from isoelectric point
6. Binds water
7. Spoils quickly

Question 26

Define WBC

Answer 26

Water binding capacity (WBC) - the ability of meat to bind its own water

Question 27

What is the isoelectric point of meat proteins?

Answer 27

Between pH 5.0 and 5.1

Question 28

Describe the effect of pH on WBC

Answer 28

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

Question 29

What is the cause of softness in PSE pork?

Answer 29

1. Exudate-filled spaces between muscle fibre bundles contribute to the soft texture
2. Detachment of myosin molecule heads may contribute to the softness of PSE pork

Question 30

What is the cause of the pale colour in PSE pork?

Answer 30

1. Myofibril A-bands are strongly birefringent (they can rotate polarized light)
2. Birefringence is inversely proportional to pH peaking around the isoelectric point
3. As pH declines post-mortem, the back scattering of light is increased
4. The rapid decline in post-mortem pH also cause denatured myoglobin - converting pink myoglobin to pale brown metmyoglobin - causing an increase in paleness.

Question 31

Explain the colour change of meat under normal conditions

Answer 31

1. The color of muscle in living animal is bright red due to abundance of oxygen.
2. Post-mortem there is shortage of oxygen and color becomes dark purplish red.
3. Fresh meat when cut has dark red color but on exposure to atmospheric air within few minutes changes to brighter red color.
4. This happens due to oxygenation of myoglobin.

Question 32

What causes cold shortening?

Answer 32

When lamb (to a lesser extent beef) is chilled too rapidly after slaughter

Question 33

What can be done to prevent cold shortening?

Answer 33

Cold shortening does not take place when the carcass is cooled slowly - temperature must not fall below 10°C before the onset of rigor

Question 34

Denaturation will cause:

Answer 34

i) Loss of protein solubility
ii) Loss of water holding capacity
iii) Loss in intensity of muscle`s pigment coloration.