Muscle to Meat Flashcards
Post-mortem changes in meat
Exanguination leads to collapse of circulation
No oxygen is available
Energy comes from CP and anaerobic glycolysis - production of lactic acid
What is rigor mortis
Muscle stiffening and loss of extensibility after ATP is exhausted
What causes rigor mortis
ATP is depleted so myosin heads irreversibly bind to actin
Phases of rigor mortis
Delay phase
Onset phase
Completion phase
Resolution phase
Delay phase
Muscle gets energy from CP and anaerobic glycolysis
Causes lactic acid build up - lowers pH of meat
Onset phase
ATP is exhausted and extensibility reduces
Completion phase
Irreversible binding of actinomyosin bonds
Resolution phase
Proteolytic enzyme action
Pre-slaughter factors affecting rigor mortis
Stress depletes muscle glycogen stor
Leads to early rigor and high muscle pH
Post-slaughter factors affecting rigor mortis
Excessive chilling causes severe shortening - tough meat
Electrical stimulation can accelerate rigor without excessive shortening
Other factors affecting rigor
Fibre type composition - Determines ATP production/consumption
Fast muscle is prone to PSE - more glycogen
When does resolution occur
After a variable period of time
How does resolution occur
Two endogenous proteases:
Calpains
Cathepsins
What inhibits calpains?
Calpastatins
What inhibits cathepsins?
Cystastatin
What happens during ageing?
Proteins are broken down into amino acids and fats then into aromatic fatty acids (glutamic acid, inosinic acid)
Risks of prolonged ageing
Rancidity due to fat oxidation
What is tenderness
Eating/physical quality
Expressed in terms of:
Shear force
Myofibrillar fragmentation index (MFI)
Taste/eating quality assessment
What influences tenderness?
Age - older animals have more collagenous tissue
White meat is less tender than red
Amount of shortening during rigor
What is cold shortening?
When muscle cools below 10 degrees BEFORE rigor mortis starts
Due to excessive release of Ca from SR in presence of ATP
Prevention of cold shortening
Keep beef/lamb >10 degrees for first 10h
Keep pork >10 degrees for first 3h
Electrical stimulation
Within 1 hr of slaughter
Causes muscle contraction
Accelerates pH fall
Depletes ATP
Induces early rigor
Prevents cold shortening
Improves meat tenderness
Fractures sarcomeres and activates proteases
How do you suspend bovine carcasses?
By obturator foramen to stretch premium muscles (longissimus dorsi)
Makes meat more tender
Methods of improving tenderness
suspend cattle from obturator foramen
Needle/blade tenderisation
Papain from papaya
Bromelin from pineapple
Ficin from pigs
Marination
Electrical stimulation
How does pattern of acidification affect meat quality?
Rapid acidification = PSE
Slow acidification = DFD
Affected by pre-slaughter handling of animals
What is PSE?
Pale Soft Exudative Meat
Abnormally pale
High drip loss
Lower water holding capacity
Tough
Caused by rapid acidification
What is DFD?
Dark Firm and Dry meat
Abnormally dark
Rapid spoilage
Tender
High water holding capacity
Caused by slow acidification
What is water holding capacity?
pH of meat influences extent muscle proteins are changed
Most proteins lose change between pH 5.1-5.5
(In this range muscle release water)
Isoelectric point is 5.2
What causes the bright red colour
Oxidation of myoglobin to oxymyoglobin (Blooming)
Why does DFD not turn bright red
High water holding capacity so reduced oxygen penetration
No oxygenation of myoglobin
What causes paleness in PSE?
Enhanced protein denaturation
Increase in conversion to metmyoglobin
How do you assess colour of meat?
Minolta colour meter
Which is more succulent?
DFD
How can you improve succulence
Increase fat content
What is boar taint?
Unpleasant urine-like odour of uncastrated boars caused by sex steroids deposited in IM fat
Prevention of boar taint
Castrate males
Slaughter younger
slatted floors to reduce faecal contamination
Avoid overcrowding
How is carcass quality assessed?
Weight
Conformation
Fatness
