Meat Proteins Flashcards
Where is bovine meat from?
Cattle
Where is ovine meat from?
Lamb and mutton
What is the nutritional value of meat?
- High biological value (composition close to human proteins)
- Source of essential amino acids
- Sounds of vitamins
- High in saturated fats
What are the health concerns surrounding eating meat?
- Cardiovascular disease
- Cancer (nitrites involved in producing cured meats may be carcinogenic)
- Food safety (salmonella)
- Spread of bacteria that are resistant to antibiotics from animal to human
What are the environmental concerns surrounding eating meat?
Agricultural sustainability (lots of energy is lost in the production of animals from plants = inefficient) Environment protection and animal welfare (animal exploitation)
How does protein and fat content vary between animals?
With age, breed and the cut of meat
When is the slaughter point of an animal?
When there is optimum protein content and intermediate fat content
What are the three meat protein classifications?
- Stromal proteins (connective tissue)
- Myofibrillar proteins
- Sarcoplasmic proteins
What three layers are found in stromal proteins and what are they?
- Epimysium = covers the muscle
- Perimysium = covers fascicles (bundles of muscle fibres)
- Endomysium = covers muscle fibres
What three components make up connective tissue?
Collagen
Elastin
Reticulin
How does collagen appear is meat?
White / transparent
What property of meat does collagen affect?
Tenderness - the older the meat the less tender it is
Does collagen degrade to form gelatin?
Yes - between 65 and 80 degrees
What is the structure of collagen?
Triple helix
What is powdered collagen used for?
Useful gels
- Sausage casing
- Contact lenses
- Pharmaceuticals
What is gelatin?
The end product of the thermal degradation of collagen
How does elastin appear in meat?
Yellow
Is elastin degraded to form gelatin?
No
What components make up myofibrillar proteins?
Myosin Actin Troponin Tropomyosin Desmin
What are the properties of myosin?
Long
Filamentous
Charged = polar
High affinity for calcium and magnesium
What is the structure of myosin?
2 subunits
- Light meromyosin = LMM
- Heavy meromyosin = HMM
How is desmin affected with ageing?
Ageing increases water holding capacity
What is the structure of actin?
Globular G actin molecules link to form filamentous F actin
What molecule is troponin and tropomyosin associated with?
Filamentous F actin
What are most sarcoplasmic proteins?
Enzymes and pigments
What are the properties of sarcoplasmic proteins?
Small, water soluble proteins
What are calpains?
Enzymes which contribute to tenderization and flavouring
What is haemoglobin?
A pigment which is responsible for colour variations in meat
What is myoglobin?
A conjugated protein which contains and heme group with an attached histidine-iron protein
What determines the colour of meat?
The oxidation state of iron within myoglobin and the attached ligands
When is meat purple/blue?
When myoglobin is in the form deoxymyoglobin
- Fe II
- No ligands
When is meat red?
When myoglobin is in the form oxymyoglobin
- Fe II
- Oxygen
When is meat brown?
When myoglobin is in the form metmyoglobin
- Fe III
- No ligands
What are the main stages in the process of turning muscle to meat?
- Animal slaughtered
- Acidification
- Onset of rigor mortis
- Resolution of rigor mortis
- Conditioning
What happens when an animal is slaughtered?
O2 levels fall
Supply of O2 to muscles stop
Respiration stops
What happens during acidification?
- ATP is generated from glycogen = anaerobic glycolysis
- Lactic acid accumulates and the muscle acidifies (pH 7.2 to 5.5) = muscle proteins denature
- Loss of biological activity = water holding capacity, solubility
- Meat changes from dark to pale
What occurs during onset rigor mortis?
- Glycolysis is inhibited and ATP levels fall
- Actin and myosin form actomyosin (myosin cannot be released due to lack of ATP)
- Muscle extensibility is lost
What happens during the resolution of rigor mortis?
- Tenderization starts
- Muscles soften as myofibrils become fragmented
What does the rate of tenderization depend on?
Species
Temperature
Age
What happens during conditioning?
- Continuation of tenderization
- Myofibrils weaken
- Calpains provide flavouring
What is PSE meat and when is it produced?
Pale soft exudative
Produced when the animal is under short term stress and there is a very low pH when the animal is slaughtered
What is DFD meat and when is it produced?
Dark firm dry
Produced when the animal is under long term stress and there is a very high pH when the animal is slaughtered
