Muscle to meat Flashcards
Describe the immediate source of ATP in skeletal muscle energy metabolism
Oxidative phosphorylation of ADP in mitochondria
Sources: muscle glycogen, blood glucose, fatty acids
Produces 36 ATP per glucose molecule
Describe the intermediate source of ATP in skeletal muscle energy metabolism
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
Describe the ultimate source of ATP in skeletal muscle energy metabolism
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
What is are the biochemical/physical changes that occur post-mortem?
Exsanguination (bleeding)
Circulatory failure
PM glycolysis
PM heat production and dissipation
Rigor mortis
Loss of structural integrity
Change in appearance
Enzymatic degradation (muscles relax)
What are the 4 stages of rigor mortis?
delay
onset
completion
resolution
Why does rigor mortis occur?
all energy stores exhausted so no movement of myosin heads => muscles remain contracted
What pre-slaughter factors affect rigor mortis?
Physical stress/Disease depletes muscle glycogen store => limited glycosis leads to early rigor mortis and high muscle pH
What post-slaughter factor affects rigor-mortis?
excessive chilling rate => severe shortening => tough meat
What fibre type is prone to PSE (pale, soft and exudative)
fast muscle
What proteases are involved in the resolution of rigor mortis?
Calpains (inhibited by calpastatins)
Cathepsins (inhibited by cystatin)
What is the effect of more of the protease calpastatin on meat and which breeds are affected?
More calpastatin => more inhibition of calpains => less/slower resolution of rigor mortis => tougher meat
Describe how flavour develops during conditioning/ageing of meat
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
What are the components of tenderness?
Shear force
Myofibrillar fragmentation index (MFI)
Taste
What are the factors affecting tenderness?
White muscle less tender than red
Amount of shortening during rigor mortis (cold shortening)
Correlation between MFI, shear force and tenderness
Describe cold shortening of meat
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
How can cold shortening be prevented?
beef and lamb: not below 10C in first 10hrs
Pork: not below 10C in first 3hrs
What are the benefits of electrical stimulation in beef and lamb?
prevents cold shortening
improves meat tenderness
Improves colour and texture
Why is electrical stimulation not used in pig carcasses?
can induce PSE
How does electrical stimulation improve meat tenderness?
via sarcomere fractures and activation of proteases, lysosomal cathepsins and calpains
Describe the process of electrical stimulation of meat
applied after exsanguination
causes muscle contraction, acceleration pH fall, depletes ATP and induces early rigor mortis
Describe how the hanging of bovine carcasses can improve tenderness of the meat
Suspended through obturator foramen (instead of achilles tendon) stretched the muscles more (tenderstretch)
Describe the process of a tendercut
sawing the vertebral column at the 12th/13th rib junction and/or the ischium at the rump junction
Describe methods to improve tenderness of meat
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
What are the physical/eating properties of meat quality?
Dark cutting beef (DCB) or dark firm dry pork (DFD)
Pale soft exudative pork (PSE)
Water holding capacity
colour and paleness
succulence
boar taint
What causes pale soft exudative meat?
rapid acidification of meat
What causes dark firm dry meat?
slow acidification of meat
What affects the rate of acidfication of meat?
preslaughter handling
describe the features of PSE meat
pale
high drip loss
may be tougher
reduced juiciness and shrinkage on cooking
describe the features of DFD meat
dark
rapid spoilage (due to high water content)
more tender
less weight loss and shrinkage on cooking
How does the fibre type effect PSE
Fast fibres are prone to PSE
Slow fibres are resistant to PSE
Why are slow fibres resistant to PSE
contain large amounts of mitochondria and myoglobin, are darker and have high oxidative phosphorylation capacities
Smaller for better oxygen diffusion
(opposite for fast fibres)
What breeds are susceptible to PSE and why?
Breeds with halothane positive gene (mutation in ryanodine receptor gene) => uncontrolled calcium release => rapid glycolysis
e.g. pietrain
What is water holding capacity?
the ability of meat and meat products to retain its own or added water during processing, storage, cooking, transport etc.
How does pH affect water holding capacity?
pH influences the extent muscle proteins are charged which is necessary to attract and hold the dissociated form of water
What is the isoelectric point pH of meat
5.2
when +ve and -ve charges are equal
Describe the pH and WHC of PSE and DPD meat
DPD meat has higher pH so higher WHC
PSE has lower pH and WHC
Why is WHC important?
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
Why does meat hold more extracellular water than muscle?
more extrcellula spaces are created due to enzyme degradation
What methods are used to measure WHC?
no external force
applying external force
thermal force
Describe measuring WHC with no external force
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
Describe measuring WHC using external force
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
Describe measuring WHC using thermal forvce
Cooking loss - meat heated and water loss measured
Which are the best methods to use for measuring WHC?
centrifugation and protein solubility reliable but expensive
cooking loss, grau hamm and capillary methods less acceptable
rapid filter paper cheap and reliable
Describe colour in meat
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
What causes paleness in PSE pork?
increased light scattering due to released water
enhanced protein denaturation
increased conversion to pale brown metmyoglobin
How do pH and colour relate?
paleness is inversely proportional to pH
PSE meat has low pH => paler
Why does meat go brown eventually?
prolonged exposure to oxygen converts myoglobin to metmyoglobin which is brown
What is boar taint?
unpleasant urine-like odour of entire boards and a minority of pigs
What causes boar taint?
sex steroids (e.g., androstenone) deposited in intramuscular fat
microbial breakdown of tryptophan in gut to skatole and indole => deposited in adipose tissues
How can boar taint be prevented?
castration
immunocastration
avoiding overcrowding
slatted floors to reduce faecal contamination
early slaughter of males
development of genetic markers for low boar taint pigs
How can bones be found in bone less meat and how an this be prevented?
processing errors and mechanical factors
detection methods like x-ray and ultrasound to identify bone fragments
preventative measures (training and regular quality checks)
What are the factors assessed in meat quality?
compositional quality (e.g., lean/non-lean)
physical properties
eating qualities
what the factors assessed in carcass quality?
conformation
fatness
weight
what are the systems of meat classification?
beef carcass classification (BCC) scheme
lamb carcass classificaiton
pig classification
What are the scales for fatness and conformation in the beef classification grid?
Conformation: E, U+, U-, R, O+, -, P+, P-
Fatness: 1, 2, 3, 4L, 4H, 5L, 5H
What are the scales for fatness and conformation in the sheep classification grid?
Fatness: 1, 2, 3L, 3H, 4L, 4H, 5
Conformation: E, U, R, O, P
How are pig carcasses classified?
weight, age and P2 backfat
What is P2 backfat in pig carcass classification
estimate of lean meat %
fat thickness over M. longissimus taken by optical probe
