Muscle to meat Flashcards by Leah Stevenart

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

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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

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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

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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)

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What are the 4 stages of rigor mortis?

delay
onset
completion
resolution

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Why does rigor mortis occur?

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

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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

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What post-slaughter factor affects rigor-mortis?

excessive chilling rate => severe shortening => tough meat

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

fast muscle

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What proteases are involved in the resolution of rigor mortis?

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

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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

Brahman Cattle, Callipyge sheep

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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

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What are the components of tenderness?

Shear force
Myofibrillar fragmentation index (MFI)
Taste

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What are the factors affecting tenderness?

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

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Describe the effect of rapid chilling and 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

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How can cold shortening be prevented?

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

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

prevents cold shortening
improves meat tenderness
Improves colour and texture

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Why is electrical stimulation not used in pig carcasses?

can induce PSE

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How does electrical stimulation improve meat tenderness?

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

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Describe the process of electrical stimulation of meat

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

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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)

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Describe the process of a tendercut

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

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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

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

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 lower pH causes a lower water-holding capacity

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

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