Muscle to meat

Question 1

Describe the immediate source of ATP in skeletal muscle energy metabolism

Answer 1

Oxidative phosphorylation of ADP in mitochondria
Sources: muscle glycogen, blood glucose, fatty acids
Produces 36 ATP per glucose molecule

Question 2

Describe the intermediate source of ATP in skeletal muscle energy metabolism

Answer 2

Direct phosphorylation of ADP to ATP by creatine phosphate (CP)
Rapid conversion
Gives 1 ATP per CP molecule
Conc of CP is 5 times that of ATP at rest

Question 3

Describe the ultimate source of ATP in skeletal muscle energy metabolism

Answer 3

Anaerobic glycolysis => little ATP but can be made rapidly in absence of oxygen
Fuel source = glucose from muscle glycogen
Leads to rapid lactic acid build up => fatigue and post-mortem pH (effects meat quality)
Gives 2 ATP per glucose molecule + lactic acid

Question 4

What is are the biochemical/physical changes that occur post-mortem?

Answer 4

Exsanguination (bleeding)
Circulatory failure
PM glycolysis
PM heat production and dissipation
Rigor mortis
Loss of structural integrity
Change in appearance
Enzymatic degradation (muscles relax)

Question 5

What are the 4 stages of rigor mortis?

Answer 5

delay
onset
completion
resolution

Question 6

Why does rigor mortis occur?

Answer 6

all energy stores exhausted so no movement of myosin heads => muscles remain contracted

Question 7

What pre-slaughter factors affect rigor mortis?

Answer 7

Physical stress/Disease depletes muscle glycogen store => limited glycosis leads to early rigor mortis and high muscle pH

Question 8

What post-slaughter factor affects rigor-mortis?

Answer 8

excessive chilling rate => severe shortening => tough meat

Question 9

What fibre type is prone to PSE (pale, soft and exudative)

Answer 9

fast muscle

Question 10

What proteases are involved in the resolution of rigor mortis?

Answer 10

Calpains (inhibited by calpastatins)
Cathepsins (inhibited by cystatin)

Question 11

What is the effect of more of the protease calpastatin on meat and which breeds are affected?

Answer 11

More calpastatin => more inhibition of calpains => less/slower resolution of rigor mortis => tougher meat

Brahman Cattle, Callipyge sheep

Question 12

Describe how flavour develops during conditioning/ageing of meat

Answer 12

Proteins are broken down into AAs and fats => into aromatic fatty acids that adds to the meaty flavour
Increased glutamic acid => adds to flavour
Inosinic acid convets to hypoxanthine (a flavour component)
Prolonged ageing risks fat oxidation causing rancid odour
High concs of CaCl for tenderisation causes bitterness

Question 13

What are the components of tenderness?

Answer 13

Shear force
Myofibrillar fragmentation index (MFI)
Taste

Question 14

What are the factors affecting tenderness?

Answer 14

White muscle (fast) less tender than red (slow)
Amount of shortening during rigor mortis (cold shortening)
Correlation between MFI, shear force and tenderness

Question 15

Describe the effect of rapid chilling and cold shortening of meat

Answer 15

Rapid chilling reduces microbial growth, evaporation and drip loss
CS occurs when muscle cools below 10C before rigor mortis:
- due to excessive Ca ion release from SR in presence of ATP
- shorten up to 1/3 original length
- tough on cooking

Question 16

How can cold shortening be prevented?

Answer 16

beef and lamb: not below 10C in first 10hrs
Pork: not below 10C in first 3hrs

Question 17

What are the benefits of electrical stimulation in beef and lamb?

Answer 17

prevents cold shortening
improves meat tenderness
Improves colour and texture

Question 18

Why is electrical stimulation not used in pig carcasses?

Answer 18

can induce PSE

Question 19

How does electrical stimulation improve meat tenderness?

Answer 19

via sarcomere fractures and activation of proteases, lysosomal cathepsins and calpains

Question 20

Describe the process of electrical stimulation of meat

Answer 20

applied after exsanguination
causes muscle contraction, acceleration pH fall, depletes ATP and induces early rigor mortis

Question 21

Describe how the hanging of bovine carcasses can improve tenderness of the meat

Answer 21

Suspended through obturator foramen (instead of achilles tendon) stretched the muscles more (tenderstretch)

Question 22

Describe the process of a tendercut

Answer 22

sawing the vertebral column at the 12th/13th rib junction and/or the ischium at the rump junction

Question 23

Describe methods to improve tenderness of meat

Answer 23

electrical stimulation
tenderstretch
tendercut
needle/blade tenderisation
papain, bromelin, ficin (plant based enzymes)
Marination
Hot boning and stretching
Ultrasonic wave, shockwaves, hydrostatic pressure and hydrodynamic pressure

Question 24

What post-mortem physical and sensory characteristics are used to assess the eating quality of meat?

Answer 24

Dark cutting beef (DCB) or dark firm dry pork (DFD)
Pale soft exudative pork (PSE)
Water holding capacity
colour and paleness
succulence
boar taint

Question 25

What causes pale soft exudative meat?

Answer 25

rapid acidification of meat

Question 26

What causes dark firm dry meat?

Answer 26

slow acidification of meat

Question 27

What affects the rate of acidfication of meat?

Answer 27

preslaughter handling

Question 28

describe the features of PSE meat

Answer 28

pale high drip loss may be tougher reduced juiciness and shrinkage on cooking

Question 29

describe the features of DFD meat

Answer 29

dark rapid spoilage (due to high water content) more tender less weight loss and shrinkage on cooking

Question 30

How does the fibre type effect PSE

Answer 30

Fast fibres are prone to PSE Slow fibres are resistant to PSE

Question 31

Why are slow fibres resistant to PSE

Answer 31

contain large amounts of mitochondria and myoglobin, are darker and have high oxidative phosphorylation capacities Smaller for better oxygen diffusion (opposite for fast fibres)

Question 32

What breeds are susceptible to PSE and why?

Answer 32

Breeds with halothane positive gene (mutation in ryanodine receptor gene) => uncontrolled calcium release => rapid glycolysis e.g. pietrain

Question 33

What is water holding capacity?

Answer 33

the ability of meat and meat products to retain its own or added water during processing, storage, cooking, transport etc.

Question 34

How does pH affect water holding capacity?

Answer 34

pH influences the extent muscle proteins are charged which is necessary to attract and hold the dissociated form of water lower pH causes a lower water-holding capacity

Question 35

What is the isoelectric point pH of meat

Answer 35

5.2 when +ve and -ve charges are equal

Question 36

Describe the pH and WHC of PSE and DPD meat

Answer 36

DPD meat has higher pH so higher WHC PSE has lower pH and WHC

Question 37

Why is WHC important?

Answer 37

contributes to texture, colour and flavour affects amount of product that can be sold weight losses during processing, storage, transit, display and cooking if poor WHC excessive fluid loss makes raw product unsightly and cooked product is dry affects quantity and quality of further processed products

Question 38

Why does meat hold more extracellular water than muscle?

Answer 38

more extrcellula spaces are created due to enzyme degradation

Answer 39

.

Question 40

Describe measuring WHC with no external force

Answer 40

Drip loss - chop suspended in bag for 48h, drip calculated as % of chop weight rapid filter paper - small disc of filter paper applied for 2 sec, score or weigh filter paper

Question 41

Describe measuring WHC using external force

Answer 41

Grau Hamm filter paper method - meat is pressed onto filter paper, measure diameter of wet spot Centrifugation - releases held water, measured Capillary volumeter - meat pressed using capillary tube, water released is measured Protein solubility - muscle protein extracted in buffer

Question 42

Describe measuring WHC using thermal forvce

Answer 42

Cooking loss - meat heated and water loss measured

Question 43

Which are the best methods to use for measuring WHC?

Answer 43

centrifugation and protein solubility reliable but expensive cooking loss, grau hamm and capillary methods less acceptable rapid filter paper cheap and reliable

Question 44

Describe colour in meat

Answer 44

Redness in presence of oxygen due to myoglobin More myoglobin in slow muscle DFD pork and DCB with high WHC makes meat turgid and reduces oxygen penetration => not as red

Question 45

What causes paleness in PSE pork?

Answer 45

increased light scattering due to released water enhanced protein denaturation increased conversion to pale brown metmyoglobin

Question 46

How do pH and colour relate?

Answer 46

paleness is inversely proportional to pH PSE meat has low pH => paler

Question 47

Why does meat go brown eventually?

Answer 47

prolonged exposure to oxygen converts myoglobin to metmyoglobin which is brown

Question 48

What is boar taint?

Answer 48

unpleasant urine-like odour of entire boards and a minority of pigs

Question 49

What causes boar taint?

Answer 49

sex steroids (e.g., androstenone) deposited in intramuscular fat microbial breakdown of tryptophan in gut to skatole and indole => deposited in adipose tissues

Question 50

How can boar taint be prevented?

Answer 50

castration immunocastration avoiding overcrowding slatted floors to reduce faecal contamination early slaughter of males development of genetic markers for low boar taint pigs

Question 51

How can bones be found in bone less meat and how an this be prevented?

Answer 51

processing errors and mechanical factors detection methods like x-ray and ultrasound to identify bone fragments preventative measures (training and regular quality checks)

Question 52

What are the factors assessed in meat quality?

Answer 52

compositional quality (e.g., lean/non-lean) physical properties eating qualities

Question 53

what the factors assessed in carcass quality?

Answer 53

conformation fatness weight

Question 54

what are the systems of meat classification?

Answer 54

beef carcass classification (BCC) scheme lamb carcass classificaiton pig classification

Question 55

What are the scales for fatness and conformation in the beef classification grid?

Answer 55

Conformation: E, U+, U-, R, O+, -, P+, P- Fatness: 1, 2, 3, 4L, 4H, 5L, 5H

Question 56

What are the scales for fatness and conformation in the sheep classification grid?

Answer 56

Fatness: 1, 2, 3L, 3H, 4L, 4H, 5 Conformation: E, U, R, O, P

Question 57

How are pig carcasses classified?

Answer 57

weight, age and P2 backfat

Question 58

What is P2 backfat in pig carcass classification

Answer 58

estimate of lean meat % fat thickness over M. longissimus taken by optical probe