Meat

Question 1

Meat is associated with the acronym “ZIP”. what 3 nutrients does ZIP refer to?

Answer 1

Zinc, iron, protein

Question 2

What form of iron is found in animal meat, and why is it beneficial?

Answer 2

Heme-iron, as they are more easily absorbed than non heme iron found in plants

Question 3

Meat is rich in which vitamin and mineral?

Answer 3

Vitamin B12, zinc

Question 4

[Animal to meat: processing]
When moving animals from farm to slaughterhouse, meat animals will experience stress. What kind of challenging stimuli may these animals face? [5]

Answer 4

• Handling –> increased human contact
• long transportation hours
• change in environment
• food and water deprivation
• changes in social structure –> separating animals from their groups and mixing them with others

Question 5

[Animal to meat: processing]

Since animals face stress when moving from farm to slaughterhouse, what are some detrimental effects to meat quality? [2]

Answer 5

1. Injured / bruised portions (may fight) on the carcass, leading to loss in carcass weight and yield
2. Glycogen depletion affecting meat quality (colour, cooking losses, tenderness)

• stress = glycogen depletion ; may be due to increased physical activity where animals fight with each other etc

Question 6

[Animal to meat: processing]

List the 5 main steps when an animal is turned into meat (processing steps).

Answer 6

1. Stunning
2. Sticking
3. Overhead rail system
4. Dressing and cutting of carcass
5. Refrigeration, transport and storage of meat

Question 7

[Processing step 1 : stunning]
What is meant by stunning?

Answer 7

Immobilization of the animal to facilitate cutting of blood vessels (sticking). Some form of restraint is often needed.

Question 8

[Processing step 1 : stunning]

What are the 3 aims of stunning?

Answer 8

1. Immobilize the animals to facilitate the next step (sticking)
2. Improve safety operations (for workers, if not the animal will keep kicking the worker)
3. Prevent animals from feeling pain or distress during exsanguination (draining blood).

Question 9

[Processing step 1 : stunning]

What are the 3 methods to stun an animal?

Answer 9

1. Mechanical instrument (captive bolt pistol, percussion stunner etc)
2. Electrical current passed through the brain
3. Using anaesthesia (CO2 gas)

Question 10

[Processing step 2 : sticking]

What is sticking?

Answer 10

To cut an animal’s neck using a very sharp knife to sever the major blood vessels in its neck and chest that supply the brain, and allowing the animal to bleed to death (exsanguination)

–> ensures rapid blood loss and death (humane killing, short and quick death)

Question 11

[Processing step 3 : Overhead rail system]

What does the overhead rail system involve?

Answer 11

It involves hanging of the animal by its hind legs starting from the time it has been exsanguinated for slaughter

Question 12

[Processing step 3 : Overhead rail system]

What are the main purposes of the overhead rail system [2] ?

Answer 12

1. More effective draining of blood vessels
2. Reduces cross contamination (carcass will not touch the dirty ground with all the shit and dirty stuff etc)

Question 13

[Processing step 3 : Overhead rail system]

What are the 2 advantages of a overhead rail system?

Answer 13

1. Effective use of manpower -> each worker carries out a specific task along the line
   - workers can focus on specific tasks such as cutting, trimming, or inspecting, without the need to constantly handle or move carcasses manually.
2. Reduces contamination (reduce contact of carcasses with surfaces)

Question 14

[Processing step 4 : Dressing and cutting]

What is meant by carcass dressing and what does it involve [6]?

Answer 14

Process of preparing an animal carcass for further processing and consumption.

Involves:
- removal of head, feet, hide (hair/skin), excess fat

• evisceration (removing internal organs) – edible and inedible
• trimming/splitting carcass into 2 halves (for cattle and pigs)
• washing / cleaning of carcass
• chill carcass prior for storage / processing
• prepare primal/wholesale cuts after chilling

Question 15

[Processing step 4 : Dressing and cutting]
What is the main purpose of dressing?

Answer 15

To prevent microbial contamination so as to reduce risks from pathogens, therefore prolonging the shelf life of meat.

Question 16

[Processing step 4 : Dressing and cutting]
Before processing, in a healthy animal, the carcass tissues and insides of body cavities are NOT microbiologically sterile. True or False?

Answer 16

False, they are microbiologically sterile due to the presence of their immune system

Question 17

[Processing step 5 : Refrigeration, Transport, Storage of meat]

Why is meat a particularly favorable substrate to microbes? What other issue does meat face?

Answer 17

meat is rich in proteins, lipids and water.

Meat’s lipid content makes it sensitive to oxidation —> lipid peroxidation

Question 18

[Processing step 5 : Refrigeration, Transport, Storage of meat]

What are the main cateogories of strategies and the strategies could be employed to extend the very short shelf life of meat [5]?

Answer 18

Chemical and biological means

1. Reducing temperature to slow/inhibit growth of MOs
2. Heating to destroy MOs and enzymes
3. Reduce water content by drying / osmotic control – binds water to salt so it becomes unavailable to other organisms
4. Use of chemicals to inhibit growth
5. More advanced technologies (e.g. ionising radiation)

Question 19

[Processing step 5 : Refrigeration, Transport, Storage of meat]

What are the purposes of hanging dressed carcasses in small cold rooms to pre-cool them before refrigeration [3]?

Answer 19

1. reduce the rate of biochemical reactions (by enzymes / microbes), ensuring microbiological quality and meat quality (freshness)
2. Reduce moisture loss : Rapid cooling can help to minimize moisture loss, which can occur if carcasses are left at higher temperatures for an extended period. (Water evaporate at high temp)
3. Uniform Cooling: Hanging carcasses allows for more uniform cooling, as air can circulate around the carcass, ensuring that all parts of the meat are cooled evenly. This helps to prevent the growth of bacteria that thrive in warm or unevenly cooled areas.

Question 20

[Processing step 5 : Refrigeration, Transport, Storage of meat]

Why can’t the temperature in the room for primary cooling of carcasses be too low? [3]

Answer 20

1. Freezer burn : It may cause the meat to freeze, and cause damage to the surface of the meat
2. meat quality : If the temperature is too low, rapid contraction of muscle fibers can result in tough and less tender meat.
3. Energy efficiency : Operating at extremely low temperatures requires more energy, which can increase operating costs and energy consumption.

Question 21

[Processing step 5 : Refrigeration, Transport, Storage of meat]

The ideal relative humidity in the room is about 90%. Why can’t the RH be too high / low?

Answer 21

High RH : more moisture in the air –> condensation of water on carcass can cause microbial growth

Low RH : Cause the evaporation of water from meat into surroundings, causing meat to dry out

Question 22

[Processing step 5 : Refrigeration, Transport, Storage of meat]

The ideal air speed in the primary cooling room is 0.5m/s. What is the purpose of adding a fan in the cooling room if there is already air-conditioning [2]?

Answer 22

Ensures efficient circulation of cool air around all the carcasses.

Can also cause heat to be removed faster from carcasses, beneficial in reducing the time required for pre-cooling, which can help to improve efficiency in meat processing operations.

Question 23

[Processing step 5 : Refrigeration, Transport, Storage of meat]

The ideal air speed in the primary cooling room is 0.5m/s. What is the problem if the air speed is too high?

Answer 23

It can dry out the carcass too much, affecting meat quality and texture

Question 24

[Processing step 5 : Refrigeration, Transport, Storage of meat]

The vehicles for transporting meat and carcasses should be done by non-refrigerated vehicles. True or False?

Answer 24

False, vehicles should be refrigerated in order to preserve the wholesomeness of meat (maintain cold chain)

Question 25

[Processing step 5 : Refrigeration, Transport, Storage of meat] Storage of meat : should you thaw and refreeze meat? Why?

Answer 25

No, as bacteria will start to multiply once meat is thawed, and refreezing it could lead to spoilage and food poisoning

Question 26

What are the 5 levels of organisation in skeletal muscle?(not v impt)

Answer 26

Skeletal muscle (biggest) > Muscle fascicle > Muscle fiber > myofibril > sacromere (smallest)

Question 27

What are the 2 main contractile proteins in the sacromere? Which is the thin and thick fibre?

Answer 27

1. Actin (thin fiber) 2. Myosin (thick fiber)

Question 28

What are the states of the actin and myosin during muscle relaxation and rigor mortis? (are they bonded to each other or..?) Keywords: - actin - myosin - tropomyosin - troponin

Answer 28

Muscle relaxation : Ca2+ is not present, actin is binded by tropomyosin ("chain") and troponin ("lock"), and actin and myosin are not bounded to each other During rigor mortis : Myosin head is unable to decouple from the binding pockets in actin filament due to the lack of ATP, thus is stuck as the actin-myosin complex

Question 29

In the conversion of muscle to meat, what are the 3 main stages and how is the texture and water holding capacity (WHC) of the meat like in each stage?

Answer 29

1. Pre-rigor stage - Meat is soft and pliable as [ATP] is maintained through breakdown of creatine phosphate and anaerboic glycolysis to produce lactic acid. Since actin and myosin kept apart in relaxed muscle, WHC is high.
2. Rigor mortis - meat is tough and stiff, as ATP falls to 0 due to depletion of glycogen stores. Thus, there will be no ATP left to cause dissociation of actomyosin complex. furthermore, Ca2+ released from sarcoplasmic reticulum causes troponin to fall off, exposing active sites on actin and more actomyosin complexes are formed irreversibly → muscle stays in contracted state, expelling water fro myofibrils → stiff and tough texture
3. Resolution of rigor mortis (meat ageing) : proteins in muscles are degraded due to activation of endogenous enzymes (Calpain system which is activated by ca2+, breaks down cytoskeletal proteins and intermediate filaments) → denaturation of proteins → more tender texture

Question 30

State the 5 steps of the sliding filament theory of muscle action. (steps that occur during muscle contraction)

Answer 30

1. As ATP levels fall, Ca2+ is released from the sarcoplasmic reticulum. Ca2+ binds to troponin, causing the tropomyosin chain surrounding actin to fall off and exposing active sites on actin. For myosin head, ADP and P is attached to it before muscle contraction. 2. Myosin head forms a cross-bridge with actin, forming an actin-myosin complex. 3. During the power stroke,the myosin head bends, ADP and P released from myosin. 4. A new molecule of ATP attaches to myosin head, causing cross-bridge to detach. 5. ATP hydrolyses back to ADP and phosphate, returns the myosin to the "cocked" position.

Question 31

[Muscle to meat] The post-mortem pH of meat is 5.3 to 5.5, compared to the initial physiological pH of meat at 7.2 to 7.4. Explain this decrease in pH.

Answer 31

Upon exsanguination, blood circulation stops. **Oxygen supply to muscle** tissues decreases and anaerobic conditions prevail. This leads glycogen being converted into lactic acid through anaerobic glycolysis, causing decrease in pH.

Question 32

[Muscle to meat] What is the most important change that occurs in post-mortem muscle?

Answer 32

Rigor mortis, which is the stiffening of the muscle.

Question 33

[Muscle to meat] Right after exsanguination, there is a pre-rigor stage before approaching rigor mortis. What are the characteristics of the meat in pre-rigor stage? - water-holding capacity - texture and quality Explain.

Answer 33

- water-holding capacity : high - texture and quality : soft, tender In pre-rigor stage, [ATP] remains relatively constant as muscles try to maintain ATP levels from creatine phosphate and**anaerobic glycolysis** of glycogen (main source of energy) - (transfer of phosphate group from CP to ADP to form ATP) Thus, the presence of ATP keeps actin and myosin apart, meat is soft. Since the proteins are in relaxed and unbounded state, can hold onto water more effectively, WHC is high.

Question 34

What is meant by "delay phase" ? what are some factors that can affect it? [6] (not as important)

Answer 34

Delay phase : time difference in between death of animal and onset of rigor state **Factors** - age - health - size of carcass (smaller size, shorter delay)
- amount of fat cover -pH and glycogen level: more stressed animal, glycogen depletion, less glycogen for anaerobic glycolysis and thus shorter delay phase (faster onset of rigor)
- temperature of environment

Question 35

How does temperature affect the delay phase and onset of rigor mortis?

Answer 35

Lower temperature --> slow rate of biochemical reactions --> longer delay phase and slower onset of rigor mortis - that's why we want to keep the meat refrigerated, so it is more tender and if you overcook your meat at too high temp, it is very tough

Question 36

What is meant by the resolution of rigor mortis?

Answer 36

Resolution of rigor mortis during aging is the process where muscles undergoes a series of changes and observe a remarkable improvement in tenderness - occurs after onset of rigor mortis, where muscles start to relax again after 72h

Question 37

During the resolution of rigor mortis where meat becomes more tender, what is it mainly due to? Name the group of compounds involved

Answer 37

Degradation of muscle fibers (made of proteins) due to the activation of endogenous proteolytic enzymes. Enzymes involved : calpain system,activated by Ca2+ which is released as muscle remains in contracted state - Degrades cytoskeletal proteins and intermediate filaments

Question 38

What is the calpain system and what are they activated by? What is the calpain system responsible for?

Answer 38

The calpain system is a system of endogenous proteolytic enzymes which are activated by calcium ions - The calpain system is responsible for proteolysis of cytoskeletal proteins (titin and nebulin) and intermediate filaments (desmin) - minimal effects on myosin and actin

Question 39

At what pH does the calpain system show maximal activity?

Answer 39

Maximal activity at pH 7, thus at the ultimate pH of meat (~5.5), they are expected to show a lower activity

Question 40

What is an important factor that influences the autolysis and activation of calpains and ultimately the tenderness of meat?

Answer 40

**Rate of decline** of early post-mortem **pH** - if rate of decline is too fast, calpains will have significantly lower activity, reducing proteolysis of substrates (proteins in muscle fibers)

Question 41

Which 2 factors affect the water-holding capacity (relating to entrapped water) of meat during post-mortem?

Answer 41

1) Net charge of myofibrillar proteins (due to pH) ``` . ``` 2) Structure of muscle cells and components (myofibrils, cytoskeletal linkage, membrane permeability) ``` . ``` 3)amount of extraceullar space within muscle (more space, more WHC, less loss of entrapped water) ## Footnote Entrapped water : binded to hydrophilic sites of myofibrillar proteins

Question 42

What happens to the water holding capacity of meat as its pH decreases from 7.0 to 5.5 post-mortem?

Answer 42

Water holding capacity decreases As pH decreases, --NH2 groups gets protonated into -NH3+ while --COO- groups still remains as -- COO- (pKa is arnd 2+). Thus, isoelectric point is reached and strong ionic bonds are formed between oppositely charged groups. This brings filaments to approach each other and causing cross-sectional shrinkage of myofibril, causing water to be expelled.

Question 43

What are the pH of PSE meat and DFD meat as compared to normal meat?

Answer 43

PSE meat : lower pH than normal meat DFD meat : higher pH than normal meat

Question 44

what does PSE meat stand for? How does PSE meat arise and what are the characteristics of PSE meat? - texture - WBC (water-binding capacity)

Answer 44

Pale, soft, exudative meats Animals are **well-fed** before slaughter, thus there are **a lot of glycogen reserves** in the body. However during post mortem the pH declines rapidly to an abnormally low pH while muscle temperature is still high.(more glycogen, more H+, lower pH) - soft - low pH denatures proteins, lowering WBC, a lot of exudate

Question 45

what does DFD meat stand for? How does DFD meat arise and what are the characteristics of DFD meat? - texture - WBC (water-binding capacity)

Answer 45

Dark, firm, dry meat. When animals are exhausted before slaughter, resulting in adequate glycogen stores and ultimate higher pH. - firm : high pH : little denaturation of proteins - higher WBC : little denaturation, resulting in little to no exudate formed

Question 46

what is the hemoprotein that mainly determines meat colour?

Answer 46

Myoglobin

Question 47

What is meant by dark meat and white meat?

Answer 47

**Dark meat** Muscles more frequently used for movement (sustained source of energy for more movement), thus having a significantly higher amount of myoglobin (and collagen) - more myoglobin = more O2 carried for aerobic resp **White meat** Muscles less frequently used for movement(short bursts of energy), has less myoglobin (& collagen) and appears more white in colour - less myoglobin = less O2 = anaerobic resp for short bursts of activity

Question 48

what is the purpose of an absorbent pad placed in meat products?

Answer 48

To soak up the meat exudate, allowing for **removal of odours** and reducing **growth of spoilage MOs**

Question 49

State the structure of myoglobin

Answer 49

Myoglobin is made of **1 subunit of globin.** Within the globin group is a heme prosthetic group containing a central iron atom. The 4 planar / equatorial bonds are bonded to N atom of porphyrin ring. 5th (axial) coordinate bond to iron atom at the axial position is bonded to histidine, and the 6th (axial) coordinate bond is bonded to a ligand.

Question 50

State the various oxidation states of iron in the heme prosthetic group and ligands being able to bond to myoglobin, and the resulting colour of the meat. Name the compound too.

Answer 50

Fe2+, no ligand : purple (deoxymyoglobin) Fe2+, O2 : red (oxymyoglobin) Fe2+, CO : cherry red (carboxymyoglobin) Fe3+, H2O : brown (metmyoglobin)

Question 51

In a **fresh** packaged raw meat, what is the colour at the (i) surface of the meat (ii) deep inside the meat?

Answer 51

(i) surface of meat --> exposed to O2 --> high O2 envt thus meat is of a bright red colour (oxymyoglobin) (ii) deep inside meat --> less O2 --> low oxygen environment --> meat is purplish (deoxymyoglobin)

Question 52

What are the 3 purposes of meat curing?

Answer 52

1. Preservation 2. Flavour enhancement 3. Colour development

Question 53

Name the 3 ingredients involved in meat curing and their purposes.

Answer 53

**1. Salt, NaCl** - flavour - antimicrobial activity and reduce lower water activity (preservation) **2. (table) sugar, sucrose** - modulates harshness of salt - nutrient source for flavour-producing bacteria **Sodium nitrate, NaNO3** - can be converted to sodium nitrite (NO2) via bacterial action and then reduced all the way to nitric oxide (NO), which binds to iron atom in heme group to eventually form light pink colour of cured meats. sodium nitrate: - contributes to cured meat flavour and colour - antimicrobial agent which inhibits growth of food poisoning bacteria (Clostridium Botulinum) - Indirect antioxidant, NO2 and NO (produced from nitrite) can act as ligands to bond to coordination site of iron, preventing binding of oxygen --> retarding development of rancidity

Question 54

How is nitric oxide, NO generated from sodium nitrate in cured meats?

Answer 54

NaNO3 (nitrate) --> NaNO2 (nitrite) --> HONO (nitrous acid) --> NO (nitric oxide) ## Footnote nitrate to nitrite is by bacteria action, NO2 to HONO under acidic conditions

Question 55

How does the pink colour of cured meat arise? (Where does the pink colour come from)

Answer 55

NO reacts with myoglobin to form dark red coloured pigment (nitrosomyoglobin). During the curing process at 60°C, pigment is converted ('fixed') into a more stable pigment, nitrosohemochrome, which is light pink in colour.

Question 56

What are some strategies to preserve the cured meat colour to increase appeal to consumers?

Answer 56

Pigments are sensitive to the presence of O2 and light Exclusion of O2 - vacuum packaging - Modified atmosphere packaging MAP with < 0.3% O2 - oxygen scavengers such as antioxidants (ascorbic acid etc) Exclusion of light - packaging that blocks out light - clear plastic packaging with colour agents and UV absorbers

Question 57

Where is collagen mainly found?

Answer 57

Connective tissue and in tendons that connects muscle to bone

Question 58

What is the structure of a collagen molecule? What is the name for it?

Answer 58

Triple helix structure (3 polypeptide chain with alpha helix conformation bonded tgt through intermolecular bond) Tropocollagen

Question 59

In mature animals, the collagen concentration increases, leading to a tougher structure. True or False?

Answer 59

False, when an animal ages, the collagen matures and forms cross-links intramolecularly (between different tropocollagen molecules), which are more resistant to physical breakdown.

Question 60

The concentration of collagen in different cuts of meat affects the tenderness of meats. True or False?

Answer 60

True, higher collagen concentration means that meat is tougher

Question 61

What are the 2 strategies in cooking that can breakdown collagen to give a tender texture?

Answer 61

1. Using slow moist heat to break down the collagen 2. Tenderisation of meat: use plant-derived proteases such as papain (papaya), bromelain (pineapple) to breakdown myofibrillar proteins and collagen in meat.

Question 62

In cooking, state how the breakdown of collagen leads to a more tender and juicy mouthfeel

Answer 62

When heated, collagen fibres denature at around 60-65 °C. Triple helix structure of collagen unwinds into random coils that are soluble in water, resulting in gelatin, which gives a juicy, tender mouthfeel

Question 63

What qualities of meat does fat affect and how so?

Answer 63

1. Juiciness -- fat increases WBC, has a lubricating effect and stimulates salivary flow during mastication, which gives rise to perception of juiciness 2. Tenderness

Question 64

What are the 4 theories that explain the role of fat in contributing to the tenderness and juiciness of meats?

Answer 64

1. Bulk Density theory 2. Lubrication theory 3. Insurance theory 4. Strain theory

Question 65

What does the bulk density theory state ?

Answer 65

Fat is less dense than heat-denatured protein in cooked meat. As fat content increases, overall density of meat decreases. Thus, within a given bite, when bulk density decreases, tenderness of the meat increases.

Question 66

What does the lubrication theory state ?

Answer 66

- As meat is cooked, triglycerides in fat melt and coat muscle fibres - As meat is chewed, salivation increases, meat is perceived as juicy. - Muscle fibres also slide more easily due to lubrication and resulting in increased perception of tenderness

Question 67

What does the insurance theory state ?

Answer 67

Fat acts as an insulator which provides **protection** against the denaturation of proteins. As meat is cooked, fat slows down heat transfer so protein denaturation is less severe and less moisture is lost during cooking --> more juicy. (proteins are responsible for binding water)