Muscle to meat Flashcards
What are the steps involved in skeletal muscle contraction & relaxation?
Describe the immediate source of ATP in skeletal muscle energy metabolism
Oxidative phosphorylation of ADP in mitochondria
At moderate muscular activity, most ATP supplied this way
Fuel sources: muscle glycogen, blood glucose & fatty acids
Gives 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
Rapid conversion
ATP supply lasts several seconds.
Gives 1 ATP per CP molecule
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 & post-mortem pH (effects meat quality)
Gives 2 ATP per glucose molecule + lactic acid
Define exsanguination
Bleeding
Why does rigor mortis occur?
What happens to muscles during enzymatic degradation post mortem?
Muscles relax
What are the biochemical/physical changes that occur post-mortem?
Define rigor mortis
Muscle stiffening & loss of extensibility after death
What marks the conversion of muscle to meat?
The onset of rigor mortis, from <1h to several hours
What are the 4 phases of rigor mortis?
- Delay (remaining ATP used by muscles –> twitch)
- Onset
- Completion (100% actin-myosin bond formation (all muscles contracted))
- Resolution (enzymes come into action)
Lactic acid levels keep increasing & thus pH decreases
What pre-slaughter factors affect rigor mortis?
Physical stress/Disease depletes muscle glycogen store => limited glycolysis leads to early rigor mortis & high muscle pH
What post-slaughter factors affect rigor mortis?
Excessive chilling rate => severe shortening => tough meat
How does fibre type affect rigor mortis?
Fibre type composition determines rate of ATP production, consumption & pH fall
Fast muscle prone to PSE (pale, soft & exudative)–> reduces meat quality
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
e.g. Brahman cattle & Callipyge sheep
What are the recommended conditioning times (days) for pork, lamb & beef?
Describe how flavour develops during conditioning/ageing of meat.
Proteins broken down into amino acids & fats => aromatic fatty acids that add to meaty flavour
Increased glutamic acid => enhance flavour
Inosinic acid converts to hypoxanthine (flavour component)
Prolonged ageing risks fat oxidation causing rancid odour
High concs of CaCl for tenderisation causes bitterness
What is used to detect flavour components in conditioned meat?
Electronic noses
How can mould growth during ageing be prevented?
Using UV rays
What are the components of tenderness?
Shear force
Myofibrillar fragmentation index (MFI)
Taste
What factors affect tenderness?
White muscle less tender than red
Amount of shortening during rigor mortis (cold shortening)
Correlation between MFI, shear force & tenderness
What is cold shortening?
Rapid chilling reduces microbial growth, evaporation & drip loss but risks cold shortening
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 & lamb: not below 10C in first 10hrs
Pork: not below 10C in first 3hrs
What are the benefits of electrical stimulation in beef & lamb?
prevents cold shortening
improves meat tenderness
Improves colour and texture
Why is electrical stimulation not used in pig carcasses?
can induce PSE
What is electrical stimulation?
Application, after exsanguination, of electrical current within 1h of slaughter
Low (up to 100v) or
high (100-500) voltage (AC)
Causes muscle contraction, accelerates pH fall, depletes ATP & induces early rigor
Describe how the hanging of bovine carcasses can improve tenderness of the meat.
Suspended through obturator foramen (instead of achilles tendon) stretches expensive muscles more to improve tenderness (tenderstretch) but takes up more space in chiller
What is tendercut?
Alternative method to tenderstretch
Offers advantage in carcass handling because leg is still hung by Achilles tendon
Applies tension on muscles by breaking vertebrae & pelvic bones in hot carcass
Involves sawing vertebral column at 12th/13th rib junction &/or ischium at rump junction
Name the methods used 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 & 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 is the rate of acidification of meat affected by?
Preslaughter handling of animals
What causes pale soft exudative meat?
Rapid acidification of meat
Meat considered PSE if it has pH <6 after 45 min
What causes dark firm dry meat?
Slow acidification of meat
Meat considered DFD if it has pH >6.4 after 45 min
How does the water holding capacity differ between PSE & DFD meat?
What are the key steps leading to PSE meat?
- Acute stress before slaughter → rapid initial acidification
- Low pH at high carcass temperature → protein denaturation
- Proteins reach their isoelectric point → reducing water-holding capacity
- Water is expelled → muscle fibres separate, creating large extracellular spaces (ECS)
- Myofilament lattice shrinks → increasing light scattering
- Meat appears pale, soft & exudes fluid upon cutting
What are the key steps leading to DFD meat?
- Chronic stress before slaughter → reduced glycogen levels
- High ultimate pH → proteins don’t denature
- Proteins hold more water → increasing water-holding capacity
- Muscle fibers remain tightly packed → creating small extracellular spaces (ECS)
- No myofilament lattice shrinkage → reducing light scattering
- Meat appears dark, firm & retains moisture longer
describe the features of PSE meat.
pale
high drip loss
may be tougher
reduced juiciness & shrinkage on cooking
describe the features of DFD meat.
dark
rapid spoilage (due to high water content)
more tender
less weight loss & 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 & myoglobin, are darker & 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
‘Halothane gene testing’ is employed to weed out +ve animals
What is water holding capacity?
Ability of meat & meat products to retain its own or added water during processing, storage, cooking, transport etc
How does pH affect water holding capacity?
pH influences extent muscle proteins are charged which is necessary to attract & hold dissociated form of water
Most proteins in meat lose their charge between pH 5.1 - 5.5, which is close to ultimate pH of meat. In this range muscle releases water
What is the isoelectric point pH of meat?
5.2
when +ve & -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 & WHC
Why is WHC important?
Contributes to texture, colour & flavour
Affects amount of product that can be sold
weight losses during processing, storage, transit, display & cooking if poor WHC
- So industry likes DFD meat more
Excessive fluid loss makes raw product unsightly & cooked product is dry
Affects quantity & quality of further processed products
Why does meat hold more extracellular water than muscle?
More extracellular 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 on piece of muscle which has been cut for 15 min, 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 force.
Cooking loss - meat chops heated in sealed bag for 1h at 80C & water loss measured
Which are the best methods to use for measuring WHC?
Depends on availability of equipment, urgency for results & purpose
Centrifugation & protein solubility reliable but expensive
Cooking loss, grau hamm & capillary methods less acceptable
Rapid filter paper cheap & reliable
Describe colour in meat.
Redness in presence of oxygen (blooming) due to myoglobin
More myoglobin in slow muscle
DFD pork & DCB with high WHC makes meat turgid & 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
How does myoglobin influence meat colour?
Myoglobin is chief muscle pigment. Its state determines meat colour:
Oxymyoglobin (O₂ exposure) → Bright red
Deoxymyoglobin (low O₂) → Purplish-red
Metmyoglobin (oxidation) → Brown
How do oxygen and nitric oxide affect meat colour?
Oxygen → Converts myoglobin to oxymyoglobin (bright red), but prolonged exposure leads to metmyoglobin (brown)
Nitric oxide (NO) → Binds to myoglobin, forming NO-myoglobin (bright pink). If metmyoglobin is already present, NO can’t restore pink colour
What is used in industry to give meat a brighter colour?
Nitric oxide
What are the main factors influencing meat juiciness?
Fat content & moisture retention in cooked meat
Lean carcasses tend to be less juicy
Higher fat content improves perceived tenderness & succulence
How do different meat types vary in juiciness?
DFD pork & dark cutting beef (DCB) retain moisture & are juicier
PSE pork has lower juiciness due to excessive water loss
What is boar taint?
Unpleasant urine-like odour of entire boars & 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 & 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 is androstenone metabolised in pigs?
- Synthesised in testis → enters plasma
2a. Travels to salivary glands → acts as a sex pheromone
2b.Undergoes liver degradation → excreted in bile or enters enterohepatic circulation
2c. Fat deposition of androstenone leads to boar taint
Why is androstenone a problem in meat quality?
It is hydrophobic, allowing fat deposition in deep muscles
Difficult to detect using standard methods
Contributes to boar taint
How is skatole metabolised in pigs?
- Synthesised in intestine from tryptophan
- Travels through plasma to liver
- Undergoes Phase I & Phase II metabolism in liver
- Excretion via kidney OR
If not fully metabolised, it deposits as fat skatole → causing boar taint
Why do males have higher skatole levels than females?
Females have better liver degradation of skatole, reducing fat accumulation
Males are more prone to boar taint due to reduced skatole breakdown
How can bones be found in boneless meat and how can this be prevented?
Processing errors & mechanical factors
Detection methods like x-ray & ultrasonic scanning to identify bone fragments
preventative measures (training & 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 (extremely poor to excellent)
fatness (low to very high (average best))
weight
what are the systems of meat classification?
beef carcass classification (BCC) scheme
lamb carcass classification
pig classification
What are the scales for fatness and conformation in the beef classification grid?
Conformation: E, U+, U-, R, O+, O-, P+, P-
Fatness: 1, 2, 3, 4L, 4H, 5L, 5H
Farmers pay depends on this classification
How is carcass quality graded in USDA beef?
More focused on marbling (intramuscular fat)
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 (lean meat %)
What is P2 backfat in pig carcass classification?
Estimate of lean meat %
fat thickness over M. longissimus taken by optical probe
What is the AutoFom Ultrasound scanner?
Automatic carcass grading system
Provides accurate information on amount & distribution of muscle, fat & bone
