1
Q
Fibre types inmuscle
A
aerobic (red/pink) - strong cytochrome oxidase activity
type I and type IIa
anaerobic (white) - weak cytoochrone oxidase activity
type IIb
2
Q
Type I
A
slow twitch aerobic low glycogen content high lipid content low glycolytic enzymes high myoglobin contnet
3
Q
Type IIa
A
high glycogen content
medium glycolytic acitivity
varibale ATPase activity
medium myoglobin conent
4
Q
type IIb
A
medium glycogen content
high glycolytic enzyme activity
strong ATPase activity
low myoglobin content
5
Q
PSE meat occurs when
A
- acute stress around time of slaughter by stimulating rate of acidification of muscles immediate post mortem.
- Anaerobic glycolysis causes lactic acid and thus a LOW pH -> muscle protein to denature ->reduction of amount of water they bind (Poor WHC) - > high light scattering
- mainly effects pigs (also found in other white fibre animals)
6
Q
PSE quality
A
pale, soft exudative
dry and poor texture after cooking
- exudate leads to weightloss and therefore reduced yield in fresh and process products
7
Q
PSE appearance
A
- due to high light scattering ->light reflects of water -> less absorbed -> pale
8
Q
DFD meat occurs when
A
- chronic pre-slaughter stress - no glycogen left before death
therefore –> less lactic acid formed and meat does not acidify normally-> high pH-> proteins do not denature–> high WHC –> low light scattering–> high absorbed–> dark - mainly effects beef (red fibres)
9
Q
DFD quality
A
- dark firm dry
- poor flavour and processing characteristics(slow uneven formation of cured meat pigments) and high spoilage potential so has shorter shelf life
- firm due to tightly packed fibres
- dry due to tightly bound water
10
Q
stunning
A
rendering animal unconscious (prevents animal feeling any pain or distress during exsanguination)
Mechanically - Captive bolt pistol, Percussion stunner, Free bullet
Non mechanically – electric current and immersion in aesthetic gas
11
Q
exsanguination is
A
cutting of major arteries to the brain = bleeding to death
12
Q
phases in stunning
A
- Tonic phase – immediate collapse, stopping rhythmic breathing
- Clonic phase – involuntary kicking for 15-45sec, can recover if no killed immediately
13
Q
slaughter methods
A
- stunning
- Sticking - cutting major blood vessels in neck or thorax so that animal bleeds to death (important to sever both carotid and jugular) – death 15-20sec after, never cut throat of pig
- Pithing – use of long flexible rod in adult cattle to destroy parts of brain and spinal cord that control movement so that reflex muscular contractions do not occur subsequently
14
Q
What factors effect the rate at which a carcass looses heat?
A
- Size of the carcass
- Level of subcutaneous fat
- Air circulation
15
Q
What does rate of cooling effect in the muscles?
A
- rates of pH fall through the production of lactic acid
- the disappearance of CP and ATP
- speed of onset of RM
Rapid chilling can reduce PSE in pork
16
Q
What occurs when there is a slow pH drop + fast temp drop in carcass?
A
cold shortening
17
Q
Cold shortening
A
- Slow pH drop and fast temp drop
- If meat is rapidly chilled before RM and before glycogen is converted to lactic acid there is a super contraction. The contraction is not followed by relaxation and so results in shorter sarcomeres and thus tougher meat
- mainly red muscles due to potential reduced ability to sequester calcium
18
Q
What occurs when there is a quick pH drop + high temp in carcass?
A
heat shortening
19
Q
Heat shortening
A
Occurs if pH ultimate level is reached while the the temp is still high
muscles are stimulated & allowed to contract & shorten at high temperatures without subsequent relaxation, meat may become tougher if enter RM in this state
20
Q
What is the optimum window for pH and carcass temp?
A
- pH should not fall < 6 when temp is >35°C
- pH should be < 6 before the temp falls to 12°C
21
Q
What effect does electric stimulation have on meat?
A
causes all muscles to contract which uses up glycogen and therefore enhances aerobic glycolysis giving a rapid fall in pH -> enzymes active -> tender meat
22
Q
What effect does carcass suspension have on meat
A
carcass suspension can result in more tender meat
- hang carcass by hind legs -> weight of carcass puts muscle into tension ->stretches them as pass into rigor -> increases sarcomere length -> tender meat, although forequarter part of carcass only supported by muscle
- hang carcass from pelvis suspension - > stretches/tenderizes muscles outside of hip although may toughen other areas and form different shape -> takes up more space in chillers
23
Q
Meat packaging function
A
- protect meat from contamination
- inhibits microbial growth
- reduces/eliminates evaporative weight loss and surface drying
- may enhance meat appearance
- delay spoilage and prolong shelf life (due to higher conc. Co2 (inhibits undesirable microbial growth) and O2 (encouraged penetration of O2 into meat for great distance from surface) in packaging than in air)
24
Q
Meat packaging - gas permeable plastic film (over wrapping)
A
allow O2 from air to penetrate easily and react with myoglobin to give oxymyoglobin – 1-2 days before oxidation to metMb becomes problem
25
meat packaging - vaccum packing
oxygen removed before sealing in impermeable bag, anaerobic condition, ideal for storing and transporting but not display
26
What are the three most common pigments found in meat?
Myoglobin (Mb) - purple
Oxymyoglobin (MbO) - red
Metmyoglobin (metMb) - brown
27
What changes occur in the muscle between slaughter and consumption?
- acidification
- development of rigor
- tenderisation
28
What are the two main characteristics affected by acidification and why?
- colour – increased light scattering -> goes pale and opaque
- WHC – exudation of moisture from cut surfaces -> drip loss
Both because of protein denaturation and myofrillar proteins reaching isoelectric point
29
Development of rigor
- Effected by temp - If enters rigor at high temp –> less tender meat due to heat shortening and denaturation in proteolytic calpain enzymes
- accelerated development – (cold shortening and carcass handling)can enable fast chilling without meat toughening
- early development – (electrical stimulation) –> muscle goes into rigor in relaxed state - > tender
30
factors affetcing tenderisation
- sarcomere length (can't be changed after rigor)
- temperature that muscles go into rigor (optimal window)
- ageing time (changes in connective tissue components of meat & weakening of myofibrils) - tenderisation faster at higher temp (post rigor) & different species.
- temperature post rigor- keeping meat at higher temperature post rigor promotes tenderisation through increased Calpain activity.
- ph of muscle- low pH will denature calpains reducing activity -> less tenderisation occurs.
- marinating and injecting (salt solutions with acids- break muscle structure down possibly by encouraging the action of collagenases and cathepsins that work at low pH).
- diet: feeding cattle vit D 3: imp for calcium & phosphorous met- higher calcium ass. with high calpain activity ('frees' it)
- poor slaughtering handling: PSE,DFD, carcass damage
31
proteolytic enzymes involved in tenderisation
1. Calpains (thought to be most imp) -> , activated by calcium ions, max activity in neutral to alkaline conditions
2. Cathespins (occurs in lyososomes) -> max activity in mildy acidic conditions, Only degrade actin and myosin below pH 5
- normal role is breakdown & recycling of proteins
- In meat they give tenderisation
32
Pre rigor interventions to increase tenderness
reduce stress
| Vit D in diet
33
What are the 5 major components of meat quality?
- Yield and Gross Composition
- Appearance and Technological Characteristics
- Palatability
- Wholesomeness
- Ethical Quality
34
Meat quality - yield and composition
- determines how much there is to sell – quantity of sellable products
- higher yield – more product – greater profit
35
Meat quality - appearance and technical characteristics
- factors which affect the microstructure of the muscle PM affect both aspects of colour and WHC
- Appearance is only criteria consumer as to judge meat before purchase
36
Meat quality - Palatability
- Lack of succulence attributed to poor WHC or low levels intramuscular fat
- Humans perceive tenderness and juiciness as interrelated
e. g. - Juicy meat perceived as more tender
- Flavor and aroma are closely associated
37
Meat quality - wholesomeness
Meat should be safe to eat
- Free from parasites, microbiological pathogens and harzardous chemicals
- Do not want to be exposed to high levels or residues from vet medication, growth or promoting agents or pesticides
People prefer meat to be positively beneficial to their health
- Minerals
- High value protein
- Essential Fas – EPA and DHA
38
Meat quality - ethical quality
concern – meat should come from animals that have been , bred, reared, handled and slaughtered in ways that are sympathetic to animals welfare and in systems that are sustainable and environmentally friendly
39
Genes afftecting pork quality
The halothane gene – presence in pid as double recessive genotype – confers suspecptibility to anaesthetic gas halothane
- Susceptible pigs exhibit – characteristic response, extended and rigid limbs, develop raised body temp - >malignant hyperthermia -> pH fall ->PSE meat
The rendement napole (RN-) gene – lower pH, dominant gene
-Used to measure yield (measured by curing and cooking smaples under defined conditions)
-Negatively effects pork pH, WHC, colour, drip loss, cooking loss and processing yield - >increase glycogen content in muscles ->after slaughter converted to lactic acid -> lowers muscle pH ->breakdown in protein
40
What is involved in Organically produced meat
- Animals are reared without the use of growth promotors
- Limited use of antibiotics
- Only organically grown feed is used, cannot be derived from GMOs
- Also some regulations about good animal welfare
41
Why is transport of animal to abattoir important for meat quality?
1. Selected, weighed, drafted on farm
2. Groups of animals made up from different pens and different animal group
3. transport via road.
- Loading and unloading animals can be difficult and stressful. Animals can spend considerable time in transit. Animals can be held for various lengths of time before slaughter in a lairage or stockyard.
- Carcass quality equates to carcass yield (easy to relate to economic loss)
> total loss if animal dies during transport
> losses of variable sizes occurs if carcass is damaged though bruising, haemorrhage or broken bones from fighting or mishaps during transport
>Food and water deprivation
42
Stresses involved in getting animals to slaughter
1. removal from home environment
2. Loading and unloading on to vehicles
3. often long journeys
4. holding in unfamiliar surroundings
5. Potential exposure to physical stress
- Temperature
- vibrations
- crowding
- speed
- hunger, thirst, fatigue
6. Psychological stresses
- breakdown of social group
- mixing with unfamiliar animals
- new smells
- novel environments.
43
Why would you not electrically stimulate a pig carcass ?
Due to the special fibre composition in pigs- pH falls too rapidly and therefore produce PSE meat
44
Conflicting problems with meat quality
- juiciness and intramuscular fat (unhealthy)
- soft fat in very lean pigs
- addition of nitrites to pork products
- rapid carcass cooling for reducing of microorganisms
45
Diet will influence meat composition
- North America beef from grain fed animals considered better flavour than grass fed (UK is opposite)
- Japan – wagyu beef – high levels of marbeling – very tender and desirable flavour
feeding cattle vit D 3: important for calcium and phosphorous - higher calcium associated with high calpain activity ('frees' it) -> more tender meat
46
anaerobic glycolysis
glucose --ATP, NADH ->
pyruvate - lactate
- NADH -> acetyl coa ->TCA cycle
47
What is the most essential aspect of quality assurance schemes?
- Monitoring compliance with set standards and auditing them effectively
- traceability
48
sausages
- chopped lean meat and fat mixed with salt, spices and other ingrediatns filled into a casing (cleaned intestines of cattle, sheep, pigs)
- often made from reconstituted collagen derived from other parts of animals
types
- fresh – perishable unless refrigerated
- cooked
- dry – chorizo, salami – make by adding bacteria to develop characteristic flavours (held for long time of production)
49
cuts of beef and lamb
- type of cut explains variability
- beef cuts of importance – cube roll, striploin, tenderloin, sirloin butt (other bits go to sausages and hambugers, stirfry and slow cook options
- grill higher price/kg – capture value (dice, wet cook (min 2hr), stirfry (thin and marinated) before trim (trim is snags and burgers), mince (paulG and butcher)
50
tenderising with salt and acid
- Acid breaks down muscle structure and makes myofibrils swell and hold water better -> increases tenderness and juiciness
- Can give salty taste in too much
51
Tenderizing with enzymes
- Injected into blood stream in inactive form
| - Results in more tender meat
52
Thaw rigor
develops when frozen muscle is thawed -> releases meat juices and toughens meat as it occurs in a severe contraction by sudden release of Ca2+, ice crystals disable SR Ca pump and therefore destroys
FOOD2000
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