Conversion of muscle to Meat

Question 1

What is the role of calcium in muscle contraction?

Answer 1

Calcium is needed for contraction and calcium needs to be removed to relax

Question 2

What is the difference in ATP production in aerobic glycolysis vs anaerobic glycolysis?

Answer 2

If oxygen is present, 36 ATP are produced, if there is no oxygen, only 2 ATP are produced for each sugar molecule and there is lactic acid accumulation.

Question 2

Describe the mechanism of contraction, including the “conformational change”

Answer 2

The myosin head attaches to the thin filament in the presencec of Ca, this happens because the presence of Ca changes the structure of the thin filament, exposing the site where myosin can attach. Thanks to ATP the 2 filaments can separate and the whole process can start again

Question 3

Why does the pH drop in the muscle post mortem?

Answer 3

Because there is an accumulation of lactic acid, so we go from neutral pH to 6-6.5

Question 3

What is a normal pH decline in meat post mortem? Provide pH values (initial and final) and well as timeframes

Answer 3

from pH 7 to 5.6-5.7 in 6-8 h and pHu of 5.3-5.7 in 24 h

Question 4

Why does rigor mortis happen?

Answer 4

Because there is no ATP and actin and myosin bridges become permanent

Question 5

Provide pH decline and timeframe in PSE meat

Answer 5

5.3-5.5 in 1 h

Question 6

Why is PSE meat pale?

Answer 6

denaturation of myoglobin

Question 7

Why does the pH drops quickly in PSE meat?

Answer 7

They are genetically prone to stress, they overheat, at slaughter they go into oxygen debt, go into anaerobic respiration, resulting in more lactic acid produced quickly

Question 8

Why is PSE meat soft and exudative?

Answer 8

Because the pH goes down to acidic levels and this leads to decreased water holding capacity, there is modre drip and the meat is tough

Question 9

Why does the pH not decrease in DFD meat?

Answer 9

Because due to stress there is no glycogen available to do anerobic respiration, so lactic acid cannot be produced

Question 9

Provide ultimate pH in DFD meat

Answer 9

6.5-6.8

Question 10

Why is DFD meat dark?

Answer 10

Because there is reduced oxygen penetration as a result oxygen consuming reactions that occurr at a higher level in DFD meat, resulting in a shallow red layer and the purple layer is closer to the surface

Question 11

Why is DFD meat firm and dry?

Answer 11

Due to higher WHC, meat might also be more tender

Question 12

What are the 4 intrinsic factors affecting postmortem glycolysis?

Answer 12

Species, breed, muscle location and type of muscle fibre (while/red)

Question 13

What are the differences between red and white muscle fibres?

Answer 13

Contraction speed is slow in red and high in white, myoglobin is high in red and low in white, metabolism is oxidative in red and glycolytic in white, glycogen content is low in red and high in white

Question 14

What is the main extrinsic factor affecting postmortem glycolysis?

Answer 14

Temperature

Question 15

What is the relationship between temperature and rate of postmortem glycolysis?

Answer 15

Rate is rapid at in vivo temperatures and it decreases with decreasing temperatures, however from 15 down to 0 it increases because Ca is released, stimulating contraction, so more ATP is needed

Question 16

When does cold shortening occur?

Answer 16

Muscles should enter rigor in a relaxed state. When muscle enters rigor mortis in a contracted state, we have cold shortening. To avoid it, muscle temperature should be above 12C when pH 6 is reached (and the muscle enters rigor). The muscle cell’s ATP can be depleted quickly to speed up rigor using ES

Question 17

What is the “10-10 rule”?

Answer 17

to avoid cold shortening, the meat should be kept above 10C for 10 hours after slaughter

Question 18

Why is electrical stimulation used?

Answer 18

to decrease muscle pH < 6 so muscle is not susceptible to cold shortening (onset of rigor has taken place) and rapid refrigeration is possible. It accelerates pH decline and the onset of rigor using electricity. It also disrupts muscle structure and makes meat more tender

Question 19

Which 5 factors affect the efficacy of electrical stimulation?

Answer 19

Voltage used, duration, mode of application, time after death, type of muscle