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FST2106 -- Post harvest food processing > Meat > Flashcards

Meat Flashcards

1
Q

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

A

Zinc, iron, protein

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2
Q

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

A

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

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3
Q

Meat is rich in which vitamin and mineral?

A

Vitamin B12, zinc

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4
Q

[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]

A
  • 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
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5
Q

[Animal to meat: processing]

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

A
  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
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6
Q

[Animal to meat: processing]

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

A
  1. Stunning
  2. Sticking
  3. Overhead rail system
  4. Dressing and cutting of carcass
  5. Refrigeration, transport and storage of meat
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7
Q

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

A

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

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8
Q

[Processing step 1 : stunning]

What are the 3 aims of stunning?

A
  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).
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9
Q

[Processing step 1 : stunning]

What are the 3 methods to stun an animal?

A
  1. Mechanical instrument (captive bolt pistol, percussion stunner etc)
  2. Electrical current passed through the brain
  3. Using anaesthesia (CO2 gas)
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10
Q

[Processing step 2 : sticking]

What is sticking?

A

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)

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11
Q

[Processing step 3 : Overhead rail system]

What does the overhead rail system involve?

A

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

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12
Q

[Processing step 3 : Overhead rail system]

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

A
  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)
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13
Q

[Processing step 3 : Overhead rail system]

What are the 2 advantages of a overhead rail system?

A
  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)
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14
Q

[Processing step 4 : Dressing and cutting]

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

A

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
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15
Q

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

A

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

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16
Q

[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?

A

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

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17
Q

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

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

A

meat is rich in proteins, lipids and water.

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

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18
Q

[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]?

A

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)
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19
Q

[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]?

A
  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.
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20
Q

[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]

A
  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.
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21
Q

[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?

A

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

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22
Q

[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]?

A

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.

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23
Q

[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?

A

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

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24
Q

[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?

A

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

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25
Q

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

Storage of meat : should you thaw and refreeze meat? Why?

A

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

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26
Q

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

A

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

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27
Q

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

A
  1. Actin (thin fiber)
  2. Myosin (thick fiber)
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28
Q

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

A

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

29
Q

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?

A
  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.

<br></br>

  1. 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

<br></br>

  1. 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
30
Q

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

A
  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.
31
Q

[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.

A

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.

32
Q

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

A

Rigor mortis, which is the stiffening of the muscle.

33
Q

[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.

A
  • 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 andanaerobic 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.

34
Q

What is meant by “delay phase” ?

what are some factors that can affect it? [6]
(not as important)

A

Delay phase : time difference in between death of animal and onset of rigor state

Factors
- age
- health
- size of carcass (smaller size, shorter delay)
<br></br>
- 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)
<br></br>
- temperature of environment

35
Q

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

A

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
36
Q

What is meant by the resolution of rigor mortis?

A

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
37
Q

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

A

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

38
Q

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

What is the calpain system responsible for?

A

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
39
Q

At what pH does the calpain system show maximal activity?

A

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

40
Q

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

A

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)

41
Q

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

A

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)

Entrapped water : binded to hydrophilic sites of myofibrillar proteins

42
Q

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

A

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.

43
Q

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

A

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

44
Q

what does PSE meat stand for?
How does PSE meat arise and what are the characteristics of PSE meat?

  • texture
  • WBC (water-binding capacity)
A

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
45
Q

what does DFD meat stand for?
How does DFD meat arise and what are the characteristics of DFD meat?

  • texture
  • WBC (water-binding capacity)
A

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
46
Q

what is the hemoprotein that mainly determines meat colour?

A

Myoglobin

47
Q

What is meant by dark meat and white meat?

A

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

48
Q

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

A

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

49
Q

State the structure of myoglobin

A

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.

50
Q

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.

A

Fe2+, no ligand : purple (deoxymyoglobin)

Fe2+, O2 : red (oxymyoglobin)

Fe2+, CO : cherry red (carboxymyoglobin)

Fe3+, H2O : brown (metmyoglobin)

51
Q

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

A

(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)

52
Q

What are the 3 purposes of meat curing?

A
  1. Preservation
  2. Flavour enhancement
  3. Colour development
53
Q

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

A

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

54
Q

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

A

NaNO3 (nitrate) –> NaNO2 (nitrite) –> HONO (nitrous acid) –> NO (nitric oxide)

nitrate to nitrite is by bacteria action, NO2 to HONO under acidic conditions

55
Q

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

A

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.

56
Q

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

A

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

57
Q

Where is collagen mainly found?

A

Connective tissue and in tendons that connects muscle to bone

58
Q

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

A

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

Tropocollagen

59
Q

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

A

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

60
Q

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

A

True, higher collagen concentration means that meat is tougher

61
Q

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

A
  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.
62
Q

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

A

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

63
Q

What qualities of meat does fat affect and how so?

A
  1. Juiciness – fat increases WBC, has a lubricating effect and stimulates salivary flow during mastication, which gives rise to perception of juiciness
  2. Tenderness
64
Q

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

A
  1. Bulk Density theory
  2. Lubrication theory
  3. Insurance theory
  4. Strain theory
65
Q

What does the bulk density theory state ?

A

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.

66
Q

What does the lubrication theory state ?

A
  • 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
67
Q

What does the insurance theory state ?

A

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)

68
Q
A

FST2106 -- Post harvest food processing (4 decks)

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