Meat past exams and possible exam questions

Question 1

Effect of preslaughter stress on pigs and its affect on tenderness/quality of pork

Answer 1

acute preslaughter stress can lead to PSE - mainly affects pigs
PSE is pale, soft, exudative
- dry and poor textured meat once cooked
- increase in lactic acid ->low pH athigh temp -> denaturation of muscle -> lack of water binding (poor WHC) -> increase light scattering -> pale colour
- lowered processing yields, increases water loss and reduced juciness

Question 2

Effect of preslaughter stress on beef cattle and its affect on tenderness/quality of beef

Answer 2

chronic preslaughter stress can lead to DFD - occurs mostly in red fibres e.g. beef
DFD is dark, firm, dry
- dry and sticky
- poor flavouring and processing characteristics
- increased spoilage potential and shorter shelf life
- low/no glycogen levels - > decreases lactic acid and meat not acidified properly -> high pH -> proteins don’t denature -> high WHC -> decreases light scattering -> darker
firm because fibres packed tightly
dry because water bound tightly

Question 3

The effect of WHC on meat structure?

Answer 3

5% of water in muscles bound directly to hydrophilic groups on meat protein
95% of water in muscle is stored between the thick myosin filaments and thin actin filaments
therefore increase WHC -> swollen ->juicy and soft meat

Question 4

Why does pH in muscle decrease with time?

?

Answer 4

as glycogen supply is used up ->accumulation of lactic acid (cant be removed) -> decreases in pH

Question 5

What is the ultimate pH

Answer 5

pH is >6 while temperature is >35 degrees
pH is <6 before temperature gets to 12 degree
ultimate pH is around 5.5-6?

Question 6

What is cold shortening?

Answer 6

the shortening of muscle sarcomeres
occurs when slow pH drop and fast temp drop
meat is chilled before RM and before glycogen is converted to LA -> big contraction not follwed by relaxation -> shortened sarcomeres -> results in tougher meat

Question 7

Why electrical stimulation is used to overcome cold shortening

Answer 7

• application of an electrical current to carcasses of meat animals one hour after slaughter
• can match level of ES to chilling
• stimulates the contraction/relaxation cycle of muscles and depletion of ATP -> tender meat

Question 8

Differences in vacuum packaging and modified atmosphere packaging

Answer 8

vacuum packaging

• removes all O2 from plastic bag then meat is sealed in bag impermeable to gas, anaerobic conditions
• great for storage and transport but not for presentation

Modified atmosphere packaging
- higher co2 and O2 in bag than in air
- enhanced O2 concentration encourges penetration of O2 further into meat
- CO2 inhibits undesirable microbial growth
concern is the increase shelf life can enable pathogenic bacteria to unsafe growth

Question 9

Differences in PSE and DFD

Answer 9

PSE
 - pale soft exudative
 - dry and poor texture
 - acute stress
 - aminly in white fibre e.g. pig
DFD
 - dry firm dark
 - dry, stick , poor flavouring and processing characteristics
 - chronic stress
 - mainly in red fibre e.g. cattle

Question 10

Why does collagen make meat tougher?

Answer 10

as the amount of connective tissue in muscle (in which collage is a principle component) affects texture and tenderness
- lack of collagen/crosslinks -> poor texture -> tougher meat

Question 11

What are the three pigments that colour meat?

How are they interrelated

Answer 11

myoglobin 
- purple
 - heme iron
 - reduced state (fe2+)
oxymyoglobin
 - red
 - oxygenated form of myoglobin 
 - reduced state (fe2+)
metmyoglobin 
- brown
 - oxidized form of myoglobin 
 - oxidised state(fe3+)

Question 12

What is thaw rigor?

What is it’s effect on tenderness?

Answer 12

• severe type of rigor mortis that developed when muscle that was frozen pre rigor is thawed
• developed by sever contraction produced by sudden release of Ca2+ ions into sarcoplasm -> releases large amounts of meat juice (poor WHC) -> tougher meat

Question 13

Describe the three main post mortem stages involved in conversion of muscle to meat
- acidification

Answer 13

• denatures proteins and myofibrillar proteins reach isotonic point -> negatively affects WHC (by exudating moisture from cut surface ->drip loss) and colour (increased light scattering -> pale and opaque)

Question 14

Describe the three main post mortem stages involved in conversion of muscle to meat
- development of rigor

Answer 14

development of RM - the temperature at which muscles go into rigor affect tenderness
e.g. if high temp -> heat shortening -> denaturation in proteolytic calpain enzymes -> tough meat

Question 15

Describe the three main post mortem stages involved in conversion of muscle to meat
- resolution of rigor/ tenderisation

Answer 15

• when muscles soften

- affected by sarcomere length, temperature, pH, ageing time, marinating and injecting, diet

Question 16

What is the post slaughter tenderisation process for meat called ageing or conditioning? how is it done?

Answer 16

natural process of tenderisation when meat is stored post rigor
done in two processes
rapid phase (more important)
 - changes to myofibrillar component
 - attaches thin filament to Z disc
 - increases water soluble N compounds
slower phase
 - structural weakening of intramuscular connective tissue

Question 17

post slaughter tenderisation process for meat called ageing or conditioning - 3 chemical/physcial changes that occur?

Answer 17

• proteins of myofibril denature and weaken
• changes in connective tissue components of meat
• increase pH and WHC

Question 18

post slaughter tenderisation process for meat called ageing or conditioning - enzymes involved?

Answer 18

calpains
- activated by calcium ions
- max activty in neutral - alkaline conditions
cathespins
- in lyosomes
- max activity if slightly acidic conditions
- degrades troponin T and collagen crosslinks etc

Question 19

What are the differences in the proteins that make up thick and thin filaments of muscle microfibril?

Answer 19

thick - myosin
- 2 heads, neck and tail (fromed by two long strands wound together)
- forms crossbridges with heads
thin - actin
- globular molecules
- forms thin filaments with troponin and tropomyosin

both bind ATP but in different spots

Question 20

Why is transport of animal to abattoir important for meat quality?

Answer 20

• selected, weighed and drafted on farm
• loaded (different animal groups from different pens)
• transported via road
  risks
• loading and unloading animals - difficult and stressful
• food and water deprivation
• animals fighting or other mishap injuries - can cause bruising, hemorraging, broken bones
• if animal dies - total loss of yield and eonomic

Question 21

stresses involved in getting animals to slaughter

Answer 21

• removal from home environment
• loading and unloading
• long journey
• unfamilliar surroundings
• physical stresses - temperature, vibrations, speed, crowding, hunder, thirst, fatigue
• psychological stresses - mixing with unfamiliar animals in unfamiliar environment

Question 22

5 major components of meat quality

Answer 22

yield and composition - determines how much there is to sell - higher yield -> more product-? more profit
appearance and technical characteristics ->appearance only criteria before buying
palatability - tenderness and juiciness interrelated, aroma and flavour interrelated
wholesomeness - safe to eat and beneficial to health
ethical quality - animal meat - sympathetic to animal welfare and environmentally friendly

Question 23

conflicting problems with meat quality

Answer 23

• juiciness is linked to intramuscular fat (unhealthy)
• lean pigs linked to soft fat (healthier but not as supportitive
• nitrite in production of cured meats – gives attractive colour, inhibits growth of pathogenic bacteria but is implicated in development of some cancers

Question 24

Genes affecting pork quality

Answer 24

the halothane gene
- susceptible pigs exhibit - extended and rigid limbs, raised bodys temps -> malignant hyperthermia -> fall in pH -> PSE
the rendement napole gene
- increases glycogen content -> converted to lactic acid after slaughter -> decreases pH -> breakdown proteins -> increase drip loss and cook loss -> pale meat (similar characteristics to PSE)

Question 25

Why wouldn’t electrically stimulate a pig

Answer 25

pigs have special fibre composition -> if electrically stimulate -> pH rapidly fall and produce PSE

Question 26

Carcass suspension effect on meat

Answer 26

• tenderises
• hang by hind legs
  
  • weight of carcass puts muscles into tentison -> stretches muscles as pass into rigor -> increase sarcomere length -> tender meat
    although forequarter part of carcass is only support by muscle
• hang by pelvis suspension
  
  • stretches muscles outside of hip -> increase sarcomeres -> tender
    however while tenderise some parts of pig, can toughen others
    also takes up more room

Question 27

Electrical stimulation effect on meat

Answer 27

• tenderises
• causes muscles to use up glycogen and CP -> enhances aerobic glycolysis -> rapid fall of pH -> enzymes activated -> early developmetn of rigor (while in relaxed state) -> tender meat

Question 28

Heat shortening

Answer 28

opposite of cold shortening
- quick temp fall and slow pH fall
- occurs if ultimate pH is reached while temp is still high
muscles contracts -> denatures of calpain -> sarcomeres shorten -> tougher meat

Question 29

What does rate of cooling effect in the muscles

Answer 29

• pH fall
• disapearance of CP and ATP
• speed of onset RM
• aerobic rates of glycolysis

Question 30

Stunning

Answer 30

mechanically - captive bolt pistol, percussion stunner, free bullet

non-mechanical - electric current, immersion in aesthetic gas

phases in stunning
tonic - immediate collapse and stop of rhythmic breathing
clonic - involuntary kciking for 15-25 sec

Question 31

Fibres types

Answer 31

- type I
aerobic - red
slow twitch
low glycogen content
high lipid content
low ATPase 
low glycolytic enzymes
 - type IIa
aerobic - pink 
fast twitch
high glycogen content
medium glycolytic enzymes
variable ATPase
 - type IIb
anaerobic - white
fast twitch
med glycogen content
high glycolytic enzymes
high ATPase
low myoglobin