Meat revision Flashcards
1
Q
muscle types
A
skeletal - main one looked at
smooth
cardiac
2
Q
Structure of skeletal muscle
A
- endomysium
- perimysium
- epimysium
3
Q
Endomysium
A
connective tissue surrounding and holding myofibril
4
Q
Perimysium
A
large sheet of connective tissue surrounding primary muscle fibres held in a fibre bundle
5
Q
Epimysium
A
outer layer of connective tissue surround and holding the fibre bundles to produce a whole muscle
6
Q
Sarcolemma
A
sheath that surrounds each fibre and underneath the connective tissue of the endomysium
7
Q
White skeletal muscle
A
- High myofibrils low sarcoplasm
- Few mitochondria
- Good at anaerobic reactions
- Contract and tire quickly
8
Q
White skeletal muscle example
A
birds and poultry
9
Q
Red skeletal muscle
A
- Low myofibrils high sarcoplasm
- High mitochondria
- Contract slowly and last long
10
Q
Red skeletal muscle example
A
legs of mammals
11
Q
myofibrils
A
contractile unit
12
Q
myofibrils location
A
surrounded and imbedded in the sarcoplasm
13
Q
myofibrils composition
A
myofilaments
- thick filaments
- thin filaments
14
Q
thick filaments
A
protein myosin
15
Q
thin filaments
A
contractile protein actin, regulatory protein tropotomyosin and troponin, cytoskeletal protein nebulin
16
Q
Arrangement of myofilament in sarcomere
A
A band: thick and thin filament overlap H zone: Thick filament M Line: dark line in centre of H zone due to bulge of myosin I band: think filament Z disc: connected to thin filaments
17
Q
ACtin filaments
A
form the thin filament in myofibrillar
18
Q
Myosin filament
A
protruding heads are functionally active sites of thick filaments during contraction
19
Q
troponin
A
interacting with thin actin filaments
20
Q
actomyosin
A
When F-actin and myosin bind together to form contraction of muscle.
21
Q
sacroplasmic reticulum
A
contains sources of Ca2+ needed for contraction of muscle fibres
22
Q
muscle contraction
A
- Electrical nervous impulse depolarises muscle cell (sarcolemma)
- Stimulus is transmitted to interior of muscle
- Ca2+ released for SR
- Ca2+ binds to Troponin C causes a conformational change in troponin
- Results in movement of tropomyosin along F-actin into F-actin grove.
- Myosin heads bind to actin monomer to form crossbridges
- Crossbridges convert chemical energy to mechanical
- Polarity of thin filaments and the heads to thick filaments reverses half way between Z lines, therefore drawn towards each other.
23
Q
Muscle relaxation
A
high atp will reverse contraction conditions
24
Q
connective tissues
- type and location
A
collagen: endomysium
elastin: epimysium and perimysium
25
collagen composiition
glycoproteins
26
collagen structure
intermolecular crosslinknig of collagen fibres
27
effects of crosslinking and why occurs?
influenced by age of animal and how much muscle has been used
responsible for insolubility of collagen fibres therefore tougher meat
28
collagen and collagen lilnk relationship on tenderness
amount of collagen has no effect of tenderness
| no.links makes less soluble therefore reduced tenderness
29
elastin: nutritive vvalue to meat
none - cannot be broken down by enzymes and solubilized by cooking
30
postmortum changes in muscle
1. Oxygen supply ceases: aerobic pathway to produce enery stops and anaerobic pathway begins. Produces lactic acid for ATP (postmortem glycolysis)
2. Glucose supply from liver ceases: muscles must use their own energy sources (glycogen)
3. Metabolic by products are not removed: Lactic acid build up declines pH
4. Heat is not removed: Heat in deep parts of the body can no longer be carried away by circulatory system for dissapation. Rise in muscle temperature due to energy production.
31
how does postmortem glycolysis stop
glycogen conversion to lactic acid stops when pH is low enough to inactivate glycolytis enzymes
around pH5.4-5.6
32
How does lactic acid effect meat quality?
Denaturation of muscle protein occurs due to low pH.This leads to loss of protein solubility, water, reduction if water binding capacity and colouration.
33
When does rigor mortis occur?
When energy is depleted postmoterm (not ATP)
34
What happens in rigor mortis?
Stiffening of muscles as relaxation of muscles requires ATP. Therefore actin and mysoin are stuck bound together.
35
Phases of rigor mortis
Onset rigor motoris is formation of actomyosin crossbridges due to falling ATP levels. Occurs in two stages
1) delay phase: occurs slowly
2) fast phase: onset proceeds rapidly
3) completion phase: muscle becomes relatively inextensible when ATP is no longer formed from ADP
This is an irreversible muscle contraction
36
Physcial changes in rigor mortis
1. Loss of elasticity of muscle
2. Loss of extensibility of muscle
3. Shortening of muscles
4. Tension developed
5. Loss of water holding capcity (WHC)
37
What is WHC
water holding capacity
38
Whay does WHC reduce in rigor mortis
Due to disapperance of ATP and consequent formation of actomyosin crossbriges.
39
Intrinsic factors affecting rigor mortis
infleunces amount of glycogen reserves
| muslce fibre type, type of muscle and species of animals
40
extrinsic factors affecting rigor mortis
Pre-slaughter stress (feat), holding temeperature of carcass (heat speeds up rigor mortis)
41
what effects meat textute
Fibre size: large bundles are less tender
| Connective tissue: More perimysium around each bundle makes meat less tender
42
How does stress of animal effect tenderness?
stress causes physiological adjustments. Hormones are released and can adjust metabolism. Increased metabolic adjustment leads to increased contraction and thus increased rate of blood flow in muscles - tougher meat when stress
43
PSE
Pale, soft, exudative muscle
44
When does PSE occur
Occurs when stress leads to a rise in lactic acid and temperatures, as well as decrease energy
Results - muscle become more paler and soft due to water loss
45
DFD
Dark, firm, dry muscle
46
When does DFD occur
Occurs in muscle when stress depletes glycogen stores before slaughter, leading to a high pH which minimizes colour changes and thus darker meat
47
WHat is cold shortening
Shortening or contraction of the muscle sacromere due to chilling of meat too early
48
Effect of cold shortening on meat texture
Lower temperatures lead to release of Ca2+ and induces muscle contraction. Ca2+ return pump into SR is ineffective due to low temperatures
- Creates tougher meat
49
What is thaw rigor
Severe type of rigor mortis that develops when muscle that was frozen in thawed.
50
Effect of thaw rigor on meat
Occurs in severe contraction by sudden release of Ca2+. Ice crystals disable SR Ca2+ pump therefore destroys the muscles ability to maintain low Ca2+ in sarcoplasm. Releases meat juices and toughens
51
pH of 6
less tender meat
52
Effect of pH on meat colour of PSE
pH<5.5 shrinks fibres and scatters more light
| Therefore PSE is paler and lower WHC.
53
Effect of pH on meat colour of DFD
makes swollen fibres and thus scatters less light
| Leads to dry meat (due to good WHC) and dark meat
54
What is ageing of meat
Holding of unprocessed meat above the freezing point in a cold room
Increases tenderness and improvement in aroma and flavour
55
Chemical changes to the meat
1. Slight rise in pH
2. Increase WHC
3. Decrease fluid loss from heat-treated meat
4. Proteins of myofibrils denature when temperatures are below 0 or low pH
Increases tenderness
56
Proteolytic enzyme system in meat
Calpains: (calcium-activated water soluble enzymes) start protein degreadation during rigor mortis (become inhibited at pH 5.5). Degrade myofibrillar proteins and cytoskeletal proteins
Cathepsins: becomes activated a low pH's and continue proteolysis. Hydrolyse myofibrillar and isolated proteins.
57
What is carcass hanging and why use it?
Suspended by a hook passed through Achilles tendon. Helps muscle to stretch and thus leads to minimum actomyosin complexed being formed. Pveventions of shortening
58
What is electrical stimulation and its effects?
Application of an alternating electrical current. Causes strong contraction of the muscle. Accelerates postmortem glycolysis and increases rate to rigor mortis. Also improves colour and tenderness of some muscles.
59
Effects of too much electrical stimulation
If pH is achieved at temperatures above 35 degrees due to rapid pH decline then heat shortening occurs.
60
effects of too little electrical stimulation
f pH 6 is not reached before 12 degrees then cold shortening occurs.
61
hot boning
Removal of warm meat from skeleton to allow partial cooling of carcuss
62
Physcial changes during cooking of meat
```
Phase 1 (40-50C): Sharp increase in toughness due to thermal denaturation of myofibrillar proteins which shrink and form gel
Phase 2 (60-70C): Sharp increase due to further denaturation of myosin. More fluid released.
Phase 30 (>80C): heating of meat is prolonger period leads to increase in tenderness due to partial hydrolysis.
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63
Where is water usually found in muscles
5% - bound directly to hydrophilic groups on meat proteins
| 95% - present in myofibrils in the spaces between thick myosin filaments and thin actin/tropomyosin filaments
64
effects of WHC on meat
When larger amount of water is bound to network, muscle is swollen and meat is softer and juicier. Decreased crosslinks results in swelling
65
Effects of ultimate pH on WHC
At isoelectric point of myofibrillar protein: total charge is highest, therefore electrostatic interactions are highest. Thus crosslinks are greatest and swelling is minimum.
At pH below isoelectric point: Increased +ve charge leads to repulsion of water. Swelling increases as water is attracted by capillary action.
At pH above isoelectric point: more -ve charge therefore repulsion and swelling increased as water is attracted by capillary action.
66
Effects of salt on WHC
WHC increased at all pH's as it shifts isoelectric point.
67
Effect of cooking on WHC
40-50C: shrinkage of muscle fibres, no effect on WHC as water is retains within the endomysial sheath.
60-70C: endomysial and perimysial collagen fibres shrink, reduced WHC
68
Three forms of poor WHC
weep: in uncooked meat that has not been frozen
drip: in thawed uncooked meat
shrink: in cooked meats
69
Effects of myoglobin on colour (3 forms)
Myoglobin: Haem iron is reduced state. Water molecule is attached to Fe2+, purplish red form
Oxymyoglobin: Haem iron in reduced state, however has been oxygenated therefore oxygen molecule is attached to Fe2+, red colour
Metmyoglobin: Oxidised state of haem iron, Fe3+
70
Effect of cooking on colour
Due to chemical changes in myoglobin. Myoglobin in denatured which results in insolubilization and precipitation of proteins within myofibrils. Results in light-scattering and a dull appearance. Haem iron is more susceptible to oxidation therefore becomes greyish-brown colour (metmyoglobin
71
Effects of packaging on meat colour
vacuum packaging: retains deoxymyoglobin as no oxygen is present therefore purple colour.
Opened vacuum packaging: all deoxymyoglobin is transformed to oxymyoglobin therefore cherry red.
72
What is meat curing and why use it?
For preservation and affects flavour, colour and tenderness due to addition of curing agents
