Red Meat and Meat products Flashcards
What is “red meat” and where is it sourced?
mammalian skeletal muscle to be consumed as food
from cows, pigs, mutton, rabbit, etc (usually young animals
Composition of meat will depend on what factors? (6)
species breed age sex nutrition muscle condition (activity)
Compare carcass and lean meat:
lean meat is carcass with fat removed
lean meat is higher in protein, lower fat
The major beef producing countries are;
the major pork producing countries are:
Overall, the most common meat is:
beef: USA, Brazil
pork: China, Europe
PORK
what gives meat its characteristic color?
high concentration of Mb in muscle
What is the FA profile of the triglycerides in meat?
SFA: 40-46%
MUFAs: 45-50% (especially OLEIC)
PUFAs: 5-12%
What are the 2 classes of lipids in mammals?
Structural (cholesterol + PL)
storage (TG)
What are the skeletal muscle proteins, and their proportions?
sarcoplasmic (soluble) - 25-30%
myofibrillar (salt soluble muscle proteins) - 50-60%
stromal (conn tissue): 10-20%
What is the content of the structural lipids in meat?
cholesterol: 0.7-0.9%
PL: 0.1-0.5%
Most of the sarcoplasmic proteins are ____, which are needed for what 2 metabolic processes? What are other enzymes/functions?
enzymes; glycolysis, glycogenlysis
creatine kinase, deaminases, proteinases, Mb
In comparison to fish lipids, meat has less ____, which makes it less prone to:
PUFAs; less prone to oxidative rancidity
In resting muscle, ___ and ____ act as a complex and prevent ___ binding to actin.
troponin; tropomyosin
myosin heads
The major myofibrillar proteins are:
actin myosin troponin tropomyosin nebulin titin
Are myofibrillar proteins solubilized in the body? What form do they take?
NO: muscle is only 0.15M NaCl (0.3 is needed to solubilize)
in complex filament structures
The most abundant SP is ____, (20%) which is required for _____ .
G3P dehydrogenase
glycolysis
What is the largest protein? Where is it found and what role does it play?
titin
connects z line to m line (attach thick filaments to z line)
gives “elasticity” - centers thick filaments, and lets muscle spring back after contraction
Which proteins are most affected in the conversion of muscle to meat?
myofibrillar
What are the units of muscle?
sarcomeres
What are the most abundant myofibrillar proteins?
actin/myosin (40%)
titin
What causes the light/dark regions in sarcomeres.?
ANISOTROPIC bands - thick filament (myosin) regions
ISOTROPIC bands - thin filament (actin) regions
What is the z line?
the end of a sarcomere unit, where actin is linked
What are the regions of the myosin chains? Which one overlaps and binds to actin?
head, neck , tail
head
What is the middle of the H zone called?
M line (middle of myosin)
muscle contraction depends on the presence of ____ in the ____.
Ca
sarcoplasm
____ is a large protein that plays a role during sarcomere formation. What is it associated to?
Nebulin
associated with actin to regulate length
Descibe the steps of muscle contraction (6)
- nervous signal
- Ca release from SR -> sarcoplasm
- Ca bind to troponin -> tropomyosin is moved
- myosin can now bind -> actomyosin
- using ATP -> power stroke (repeated)
- causes muscle to shorten (contraction
More stromal proteins are needed in mammals vs fish because:
need to support weight on land
How does muscle relaxation occur? )(5)
- nerve impulse ends
- Ca returned to SR by CaATPase
- troponin/tropomyosin returns to position
- myosin blocked, no more contraction
- titin helps muscle spring back
The roles of stromal proteins:
provide high tensile strength
attach muscle to bone to allow for movement
The 3 main mammal stromal proteins:
collagen
elastin
desmosine
What distinguished the types of collagens? What is the predominant type in meat?
polypeptide chain sequences in tropocollagen
Type 1 has 2 a1(I), and 1 a2(I); Type 3 has 3 a1(III)
Type 1 is most common
What is the common sequence of AA in collagen? What AA is it especially high in?
Gly-Pro-X
Gly-X-HydroxyPro
high in glycine, hydroxyproline
What is the main unit of collagen? Describe its structure
tropocollagen triple helix (3 polypeptide chains)
What can be used as an estimate of collagen content?
hydroxyproline content: specific AA to collagen (makes up about 1/6 of it)
____ is usually associated with collagen, and has higher ____, making is important for what body structures?
Elastin
elasticity
arteries, ligaments
What causes the tougher meat as animals age?
collagen forms more cross-links
True/False: meat contains beta-carotene
True. Also contains vitamin A
Meat is not a good source of vitamins ___ and ____
vitamin C, vitamin K
What makes the links between elastin and gives it the elasticity?
Desmosine
After the animal is killed, ____ process will exceed ___ processes, and ____ is no longer maintained.
catabolic; anabolic
homeostasis
How are ATP levels maintained in the live animal muscle? What is it dependent on?
cellular respiration
requires blood flow to keep providing O2 and substrates, and remove CO2 and end products
Meat is especially high in the minerals ___ and ____
K and P
What are the further breakdown products of AMP and their relevance?
AMP -> adenosine and IMP -> inosine -> hypoxyxanthine -> xanthin -> uric acid
high IMP is good, meat still fresh
hypoxyxanthine and xanthine will taste bitter, poor quality meat
True/False: ATP production ceases after blood flow stops.
False: will still continue for some time after death
How will the muscle continue making ATP after death? (4)
- use some remaining O2 bound to Mb (only last 5 min)
- use Cr-P and creatine kinase -> regenerate ATP from ADP
- combine 2 ADPs using adenylate kinase -> ATP + AMP
- eventually, must use muscle glycogen for ANAEROBIC GLYCOLYSIS
In the anaerobic glycolytic pathway, for every 2 mol ATP produced, 1 mol ____ will be made. What effect does this have?
lactic acid pH decline (eventually deactivates enzymes, no more glycolysis)
The 3 phases of muscle conversion to meat:
delay -> rigor -> resolution
Describe the delay phase. How long does it last?
ATP levels stay high (regenerated fast enough), cells still function adequately. No stiffening.
about 12 hrs
Around what pH does glycolysis cease?
5.4-5.5
The delay phase ends once: ____
What causes the next phase?
pH falls to 5.4-5.5, glycolysis ceases: no more ATP
No ATP -> Ca can’t be returned to SR, so muscle stays permanently contracted (rigor)
Rigor mortis occurs because: (2)
- no ATP to pump Ca back to SR
2. no ATP to detach myosin heads
True/False: in the resolution phase, the actomyosin will be dissociated, allowing muscles to relax again.
False; remains locked, but proteases break down muscle myofibril structures -> fragmented, so more tender
How can rigor phase affect the texture of meat? Is this change permanent?
shortening of sarcomeres -> tougher
No, muscle will be softened again in resolution phase
Are there major changes in connective tissue during the resolution tenderization?
Some, but much slower, less extensive. (mostly myofibril breakdown that has tenderizing effect)
What are the proteases active during the resolution phase? (3) What proteins do each target?
Calpains - MOST active - myofibrillar proteins
Cathepsins - troponin/collagen, also some actomyosin
Proteosomes - conn tissue and myofibrillar, actomyosin
The proteases largely target the _____ of the myofibrils.
z-line
Tenderization time is different depending on the ____. It can be increase by:
animal increasing temperature (2x speed for every 10C increase)
Why are calpains most active of the proteases?
Ca activated, and large amount of Ca in Sarcoplasm
Which protease functions best at low pH?
cathepsins
How do calpains and proteosomes function together?
proteosomes cannot break down intact myofibrils directly
calpains first start breakdown, and proteosomes can target the fragments
ideally, the final pH decline of meat should reach:
What is too high, and too low?
- 6
- 2 too low
- 8 too high
What are the steps to slaughter?
stunning (concussion, electric, CO2)
exsanguination (bleed out)
*except: halal and kosher, bleed out directly
What happens if pH declines too much (final pH is very low)? What causes it?
PSE (pale, soft, exudative) meat
proteins rapidly denatured, lose water binding capacity -> dry texture, because water is exuded
denatured proteins appear pale
occurs if meat not chilled after slaughter, glycogen used very rapidly
How would PSE and DFD meats be problematic?
PSE is mushy and dry texture, even after cooking (though pale color will be lost)
DFD has a dark color that consumers find unappealing
How is the dead animal converted to a meat carcass?
remove head/feet/tail/skin/etc
eviscerate/gut
wash, weigh, chill
What happens if the pH decline is not enough (final pH too high?) What could cause this?
DFD (dark firm dry) meat
myosin and other proteins not denatured, since pH is not low enough
myosin will retain water better, and proteins appear darker (dry surface, dark color)
caused by lack of GLYCOGEN - animal struggle during slaughter and used it up
What happens if the meat is cut from the carcass immediately after slaughter and chilled?
ATP and muscle processes continue,
MgATPase is SLOWED due to cold temp, so Ca will build up in sarcoplasm
as Ca builds up the muscle will contract. No bone to hold it in place -> shortens and becomes tougher (COLD-SHORTENING)
will need longer resolution phase
After death, what will happen to color of meat? What reverts it back to original, and what happens with prolonged time?
no oxygen -> deoxyMb (purple)
expose to O2 -> becomes MbO2 (red)
too long -> oxidized to MetMb (brown)
What is thaw rigor? What are the effects?
meat is frozen before rigor-> form intracellular ice crystals -> disrupt SR -> Ca floods out, cause contraction of muscle
cause short, tough meat
What are the water types in meat?
Bound - attached to proteins, innermost layer
Immobilized - less organized, may be expelled
Free - can participate in rxn, held very weakly
