Exam 3 Flashcards
Post Mortem Aging
widely used practice occurs to some degree by default in all meat products
essentially is the controlled rotting of meat products to increase tenderness
protease enzymes (calpain) are released in muscle & degrade protein structure *A specific process (no mush)
amount of degradation influences tenderness & other eating quality characteristics (can be controlled to a degree)
Aging process length
28 days 95% key response of aging process complete (typically)
Tensor Fasciae Latae
tri-tip
not a lot of difference between quality grades regarding tenderness
should buy cheaper meat if selling for fundraising purposes, no need to buy prime if the tenderness difference is neglible
marbling and aging
higher marbling means a quicker aging response
Aging Definition
a naturally occurring process by which meat is held under controlled temperatures for a period of time. This allows enzymatic activity (calpain) to degrade complex proteins changing flavor and tenderness
meat kept above freezing (28 degrees F for meat)
Dry aging
hold the meat under refrigeration
no packaging
dry surface of meat
pro: easy, excellent flavor development (oxidation of fats)
con: surface dehydration, significant trim loss, need larger store space for inventory
Wet aging
hold meat under refrigeration
vacuum packaging
wet surface
pro: no yield loss, easy to transport
con: limited flavor development, need vacuum packaging system
*no difference in tenderness between wet and dry only flavor
Dry vs wet aged fabrication
meat price (cost is the most expensive thing in a meat plant
wet aged beef is cheaper (less loss)
dry aged beef is more expensive (less product) considered a luxury item
Physical tenderization
mimicking enzymatic aging
method of suspension: tenderstretch, tendercut
electrical stimulation: physical destruction, prevents cold shortening
hydrodyne: uses explosives to send shock waves through water (not very practical)
blade needle or pin tenderization
Blade/Needle tenderization
also known as needling, cubbing can be included: done by costco
cuts through the muscle fibers and connective tissue
usually done on low grade meat
most effective means of breaking down connective tissue
very commonly used for food service cuts: especially sirloin
food safety concerns: transferring pathogens from the surface of the meat to the interior of the muscle
needle tenderized meat needs to be cooked to a greater degree of doneness
Seasoned and marinated
application of various seasonings and coatings/breading to meat products
fajita marinades, rosemary seasoned rack of lamb, pork carnitas
usually incorporated into enhanced products that need added value, flavor improvement, and or tenderness improvement
Batter and Breading
application of seasonings and coating/breading to meat products
utilizes advanced milling techniques
adds significant value (cheap weight) to products
adds significant caloric content
adds convenience and flavor
General Composition of meat
water: 70-75%
proteins: 20-25%
lipids: 1-6% (IM fat)
carbohydrates: 1% (glycogen: postmortem pH changes)
inorganic constituents: 1% (iron, vitamin B)
Muscle Proteins
three major groups based on solubility:
sarcoplasmic proteins: 25-30% (cytoplasm of meat, determines meat color)
myofibrillar proteins 50-60%
stromal proteins 10-20% (connective tissue)
Sarcoplasmic Proteins
25-30%
water-soluble
enzymes and myoglobin (color)
Myofibrillar Proteins
50-60%
salt soluble
actin and myosin
Stromal proteins
10-20%
insoluble, requires stong acid/alkali
collagen and elastin (connective tissue)
Muscle function
muscle comprises 30-40% of an animals body mass: the largest organ mass in the body of vertebrates
primary functions:
movement: locomotion, digestion, breathing, vision, circulation
support: tonic contraction
maintenance of body temp: metabolic activity produces heat
dietary protein source: muscle foods
Basic muscle types
Skeletal: voluntary
cardiac: involuntary
smooth: involuntary
Skeletal muscle
voluntary
in meat science, a basic knowledge of the structure and function of skeletal muscle is required to understand the basis for differences in meat quality and various functional processing of meat
Levels of Muscle organization (5)
1) skeletal muscle: surrounded by epimysium
2) muscle bundle: surrounded by perimysium
3) muscle cells (fiber): surrounded by endomysium
4) myofibril: surrounded by sarcoplasmic reticulum (not a connective tissue)
5) sarcomere: the contractile unit
Muscle design
collection of individual cells: muscle fibers encased “harnessed by a highly organized network of connective tissue (provides structural integrity)
Connective Tissue is subdivided into “sheaths” that encase:
the entire muscle (perimysium)
bundles of muscle fibers, blood vessels, neurons, fat cells (perimysium)
individual muscle fibers (endomysium)
IM fat location
intramuscular fat is located on the perimysium
marbling in meat consist of groups of IM fat cells deposited in the perimysium in close proximity to blood vessels
Connective tissue in muscle
2% collagen
0.1% elastin
Collagen Characteristics
the structural unit of collagen is tropcollagen
tropocollagen molecule is a triple helix consisting of three polypeptide chains (glycine-proline-hydroxyproline)
repeating tripeptide
Structure of collagen
repeating tripeptide: glycine-proline-hydroxyproline
as collagen matures it forms stable crosslinks which increases its tensile strength
therefore as the animal matures more crosslinks are formed and meat gets tougher
differences among muscles in collagen content
increasing hydroxyproline (collagen) content
psoas major (tenderloin): least amount most tender
longissimus dorsi (ribe eye)
rectus femoris
triceps brachii
superdigital flexor (shank): greatest amount least tender
Elastin
rubbery protein (connective tissue) that is abundant in structures that require the ability to stretch (ligaments, arteries & veins, abdominal wall, lungs, skin)
contains two unique amino acids: Desmosine and Isodesmosine which from cross-links
is very resistant to extremist in alkalinity, acidity, and heat: very stable protein (more so than collagen)
elastin fibers are capable of stretching to several times their original length but quickly resume their original length when tension is released
Muscle cell=?
MYOFIBER
myofibers are long and cylindrical in shape
length ranges from a few mm up to several cm
diameter ranges from 10 to more than 100 microns
multinucleated: nuclei located at the periphery just beneath the sarcolema
designed to shorten resulting in movement
sarcolema
cell membrane
sarcoplasm
cytoplasm of the muscle cell (water, proteins, lysosomes, glycogen granules, lipid droplets, ribosomes)
nuclei
muscle cells are multinucleated, elliptical nuclei are located near cell periphery
myofibrils
contractile machinery of cell, comprised of contractile units called sarcomeres
sarcoplasmic reticulum and T-tubules
highly developed endoplasmic reticulum unique to muscle cells
membrane-bound around the myofibril
sits just under the endomysium
stores Ca in the relaxed muscle
transverse T-tubules: invaginations of the sarcolemma that form a “communication channel” into the interior of a muscle fiber
structure and banding features of Myofibrils
muscle cells (fibers) are packed with smaller rod-like organelles called myofibrils
myofibrils occupt over 80% of cell volume
myofibrils show distinct alternating light (I) and dark (A) bands
I band
light band containing just thin filament
(actin, troponin, tropomyosin, titin, nebulin)
A band
dark band containing an overlap of thin and thick filaments
(actin, myosin, M line)
Z line
a dense thin line that bisects the I band
z filaments composed of alpha-actinin
anchor the thin filaments on each side of the Z line
a key primary structural element of myofibril
the area for one Z line to another is referred to as the sarcomere
Z lines form the lateral boundaries for repeating contractile units
H zone
light zone with the A band
region in which there is no overlap of thick and thin filaments: just thick filament
psuedo H zone
dark region bisecting the H zone where the M line holds the thick filaments together
M line
very thin dark line withing the pseudo H zone
M line holds the thick filaments in position
Muscle contraction
involves shortening of the sarcomeres
thick and thin filaments slide across one another bringing Z lines closer together
Contractile proteins in Myofibril
mysoin (thick filament)
actin (thin filament)
Regulatory proteins in myofibril
troponin (thin f)
tropomysoin (thin F)
Structural/Cytoskeletal proteins in myofibril
alpha-actinin (z line, integral protein)
titin (z line to m line)
nebulin (parallels thin f)
myomesin (m line)
desmin (peripheral to z line)
Contractile Proteins: Myosin
thick myofibril
70-80% of the myofibrillar protein
thick filament
burns ATP for muscle contraction
myosin head moves back and forth to perform muscle contraction
Contractile Proteins: Actinin
thin myofilament
20-25% of the myofibrillar protein
thin filament
arranged like a twisted pearl necklace (f-protein)
myosin head attaches to the actinin at the myosin binding site
Thin filaments
composed of superhelix of F-actin (polymerized form of G actin)
include regulatory proteins Troponin (T,I,C) and tropomyosin
Thin filament regulatory proteins
regulate contraction and the speed of contraction
troponin (T,I,C)
tropomyosin
tropomyosin
(thin filament)
thin protein that lays around the actin proteins
covers the myosin-binding site of actin
troponin
(thin filament)
bound to tropomyosin and has three subunits
Troponin T: bound to tropomyosin
Troponin C: binds to Ca
Troponin I: inhibitory sub-unit that prevents interaction between actin and myosin
Ca binding to troponin C
when Ca is present it will bind to troponin C then tropomyosin will slide away from the myosin binding site on the actin molecules, allowing formation of actomyosin bonds
titin
largest protein ever discovered
extends from z line to m line
attaches thick filaments to Z line
molecular spring
maintains passive muscle tension
relaxation
keeps sarcomere in alignment
nebulin
originates at the z line and extends along the thin filament
though to provide a template for building and maintaining
F-actin & may be involved in connecting thin filament to Z line
is there muscle contraction after death>?
yes
Motor Neuron & Synapse
happens at the neuro muscular junction
Sequence of events in muscle contraction
1) a signal (action potential) reaches the motor end plate (neuromuscular junction)
2) Acetyl Choline (ACH) released into the synaptic cleft, sarcolemma is depolarized (Na flux into fiber)
3) AP transmitted via T-tubules to sarcoplasmic reticulum
4) Ca released from the sarcoplasmic reticulum terminal cisternae into the sarcoplasm
5) calcium binds to troponin C
6) tropomyosin shifts exposing myosin binding site
7) myosin ATPase activated & ATP hydrolyzed
8) Actin myosin cross bridge formed
9) conformational change “power stroke”
10) ATP binds, releasing and repositioning myosin head
Arrival of Action Potential and Release of Acetylcholine
the signal is passed onto the sarcolemma
ACH binds to receptors on sarcolemma causing the resting potential to change: Na flux into myofiber, K leaves myofiber
sarcolemma deplorizes
action potential passes in both directions along the sarcolemma
the depolarization causes the sarcoplasmic reticulum to release Ca into the cytosol
Ca binding to troponin C
tropomyosin shifts exposing myosin binding site
myosin ATPase activated & ATP is hydrolyzed into ADP and Pi (myosin ready to bind)
The ATPase activity of myosin
ATP is bound to the myosin head in the resting state
ATPase hydrolyzes the ATP into ADP and Pi (still attached to the myosin head) and cocks the myosin Head
the myosin head then attaches to the exposed myosin binding site on Actin (weak bond)
Pi leaves the myosin head causing the power stroke
ADP is then released causing a strong myosin-actin bond
ATP reattaches to the myosin head
releases myosin head from the myosin-actin binding site
Shortening of Sarcomere during contraction
I band disappears as sarcomere shortens and thick and thin filaments slide over each other due to myosin-actin binding
Sequence of events during muscle relaxation
1) cholinesterase released, acetylcholine breakdown
2 sarcolemma & T tubules re-polarized
3) SR pump activated & Ca returned to SR terminal cisternae
4) actin-myosin cross-bridge formation terminated
5) return of tropomyosin to myosin binding site
6) Mg complex formed with ATP
7) passive sliding of filaments (revealing I bands)
8) sarcomeres return to resting state
Muscle fiber types
(myosin heavy chain isoforms)
Type I
Type IIA
Type IIX or Type IID
Type IIB (cattle do not have)
each typer differ by metabolism and job they perform
most muscles contain all four fiber types
Type I
high myoglobin content: rely on aerobic respiration (more ATP)
muscle will be red (dark)
slow contraction speed (slow twitch, endurance activities)
small diameter
Very OXIDATIVE metabolism: require lots of oxygen, greater concentration of capillaries
very little glycolytic activity and glycogen
-chicken thighs
produce less force
greater lipid content (IM fat as energy source)
very resistant to fatigue: posture, flight muscles in birds, masseter in bovine
Type IIA
moderate myoglobin content
moderate contraction speed: can contract quickly
small fiber diameter
moderate lipid content
moderate fatigue resistant
oxidative metabolism: Very little glycogen content or glycolytic metabolism
have larger blood supply network than type IIB
normal everyday muscle contraction
normal everyday horse used for riding pleasure
can take advantage of both aerobic and anaerobic metabolism pathways: often called fast oxidative glycolytic (FOG) fibers)
Type IIX(D)
low myoglobin content
moderate fiber diameter
moderate contraction speed
very little fatigue resistance
very little oxidative metabolism
moderate glycogen content and glycolytic activity
low lipid content
once thought to be a transitional fiber type
now considered the 4th fiber type
athletes that combine both strength and endurance like a race horse
Type IIB
low myoglobin content: low IM fat, pale in color
large fiber diameter
very little fatigue resistance
fast contraction speed (fast twitch)
very little oxidative metabolism: rely on ANAEROBIC respiration (rely on glucose not fat)
high glycogen content and glycolytic metabolism
very little lipid content
short burst of activity: powerlifters, sprinters
contract quickly fatigue quickly
produce more force with each contraction
lower concentration of capillaries
-chicken breast
Muscle fibers two extremes
Type I: slow twitch, oxidative metabolism, aerobic respiration, high myoglobin, red (dark), lots of mitochondria, lots of capillaries, high lipid content, low glycogen level
Type IIB: fast twitch, glycolytic metabolism, anaerobic respiration, low myoglobin content, white (pale), low mitochondria, low capillaries, low lipid content, high glycogen level
Sources of ATP for muscle contraction and relaxation
direct phosphorylation: the phosphagen (creatine) system
anaerobic glycolysis: short term ATP demand
oxidative phosphorylation: long term ATP demand
Pre-harvest energy metabolism
aerobic metabolism
glycolysis through oxidative phosphorylation
exsanguination
interrupts the supply of oxygen to the muscles
muscles attempt to maintain homeostasis during early postmortem (PM) period
shits energy metabolism from aerobic (TCA cycle) to anaerobic (glycolysis) pathways
prevents the recycling of metabolic by-products leading to the accumulation of lactate
Post mortem metabolism
anaerobic glycolysis
just glycolysis with the accumulation of lactic acid in the muscles
Normal Glycogen Metabolism and muscle pH decline
in normal animals, glycogen represents about 1% of muscle weight reduced to about 0.1% by PM glycolysis
PM glycolysis (no Oxygen) produces lactic acid & because there is no opportunity to recycle the LA it accumulates in the muscles (lactate & H+)
the accumulation of H+ ions causes muscle pH to decline from an initial value of about 7-7.2 to an ultimate pH value of 5.4-5.5 (24 hours)
rate and extent of pH decline differ among animals due to:
differences in muscle glycogen load at harvest (related to genetic effects and pre-harvest conditions)
carcass chill rate
Rigor Mortis
stiffness of death
when creatine phosphate and glycogen stores have been exhausted, the muscle slowly depletes ATP, and permanent actomyosin cross-bridges (rigor bonds) are formed: accompanied by loss of extensibility and muscle shortening
three phases of rigor mortis
dealy phase: muscle remains extensible and elastic (ATP still being used)
onset phase: muscle begins to lose extensibility
completion phase: ATP is depleted, muscle is inextensible
Time course of rigor
time required for rigor onset is affected by chill rate, initial glycogen level in muscle and glycolytic capacity of muscle
can be regulated by temp or electrical stimulation
cattle 6-12h
sheep 6-12h
swine 1/4-3h
rigor shortening and associated toughness of meat
sarcomeres shorten as muscle goes into rigor: meat gets tougher
peak toughness is at 40% shortening
degree of sarcomere shortening is temp dependent
chilling muscles to temps less than 15 degree C while ATP is still present, results in “cold-shortening” (pork is less susceptible than beef or lamb)
15-20 degrees C is the optimal rigor temperature: minimal sarcomere shortening
pre-rigor electrical stimulation of beef and lamb
pre-rigor electrical stimulation depletes ATP supplies before muscle goes into rigor preventing cold shortening
Differences in sarcomere length among several beef muscles
muscles doffer in chill rate and degree of tension exerted on myofibrils during the onset of rigor
shortest: glutes medius (deep in muscle takes longer to chill)
longest: psoas major (outside muscle quick to chill
Contractile state and tenderness
sarcomere shortening between 20&40% of resting length increases meat toughness
postmortem changes in meat toughness
rigor mortis leads to increased toughnees with peak toughness around 24 hours post harvesting
enzymatic degradation takes over as the resolution to rigor mortis making meat more tender
changes during post mortem aging that improve tenderness
1) actin-myosin interactions (rigor bonds) are weakened (24-36 hours postmortem) non-enzymatic change resulting in slight improvement in tenderness
2) enzymatic degredation of key structural proteins (postmortem proteolysis) during early PM period (calpain system)
3) perimysium and endomysium are weakened during extended aging periods (>10 days)
Postmortem Proteolysis
Calpain Protease System
endogenous enzymes dependent on Ca for activity, most active at pH 7
calpains degrade proteins directly attached to, closely associated with, or near the Z-lines
Calpain Protease System inhibitor
calpastatin
a regulatory protein
controls actions of calpain (inhibition)
increased calpastatin=decreased tenderness
calpastatin levels decrease over time
high calpastatin activity slows the rate of tenderization during post mortem aging
proteolytic effect of calpains
degradation of key structural proteins increases meat tenderness
calpains:
degrade intermediate filaments that link myofibrils together (desmin)
sever the connection of myofilaments to the Z-line (titin and nebulin)
cause alpha-actinin to be released from z-line, but alpha-actinin is not degraded
degrade costameres (linkage of myofibrils to sarcolemma) vinculin and dystrophin, myofilaments breakaway from the z-line
*actin and myosin bonds aren’t influenced by the calpain system
factors that increase calpastatin activity
breed/genotype & sex: bos indicus influence in cattle, callipyge gene in sheep, intact males (testosterone)
preharvest stress: epinephrine
growth modifiers: beta agonists
cattle breed effects on the rate of PM aging
bos indicus breeds have increased calpastatin activity
calpastatin activity in muscles of normal vs callipyge sheep
calipyge gene= much higher calpastatin activity (muscle mass larger)
effects of beta-agonists supplementation on PM tenderization
slow PM tenderization
you get 20-30 pounds more muscle with these products but calpastatin levels are much higher: age meat for longer to overcome tenderness issue
Changes in connective tissue with post mortem aging
degradation of connective tissue is associated with tenderization effects observed with extended aging periods
connective tissue is not affected about 10 days post mortem but weakens thereafter
Degredation of Collagen and Proteoglycans during PM aging
enzymes that may have a role: Matrix Metalloproteinases,
Lysosomal enzymes, Calpains?
Tender vs Tough muscle fibers
muscles involved with locomotion have more connective tissue, nerves, etc.. so, therefore, are tougher than muscles involved in support
Difference between muscles
different muscles in the meat animal have different functions
muscles of locomotion are less tender
muscle of attachment do very little work and are more tender:
often called middle meats, sold for a higher price, muscles found in the loin and rib
muscle specificity
actomyosin affect: sarcomere length, muscle fiber diameter
background affect: connective tissue
bulk density/lubrication affect: intramuscular fat
Connective tissue effects on meat tenderness
differences in connective tissue amount (collagen concentration)
muscle to muscle differences (locomotion>support)
genetic effects (dilution of connective tissues)
Effect of myostatin on tenderness
myostatin (myo=muscle, statin=stop)
a growth differentiation factor (GDF-8) that inhibits myogenesis
expression of myostatin=muscle growth stops
mutation or suppressed expression of myostatin gene=more muscle, less fat
animals have more muscle fibers
inactivated or unexpressed mysostatin= more tender beef, more muscle mass with the same amount of connective tissue, typically not done because animal becomes to big to handle
feeding concentrates to mature cattle increases collagen solubility
mature cows fed a high-energy diet synthesize new collagen with immature reducible crosslinks and greater solubility
total collagen amount is the same but increased proportion of newly synthesized more soluble collagen results in increased tenderness
muscle pH and water holding capacity (WHC)
WHC is the ability of meat to retain water which influences meat properties
isoelectric point: number of + and - charges is equal. lowest when pH nears the isoelectric pint of muscle proteins
in fresh meat, pH ranges from about 5.2-6.8, lower pH values associated with lower water holding capacity
types of water in muscle
bound water: held tightly by charged hydrophilic groups on muscle proteins
immobilized water: held by weaker attractive forces near charged particles
free water: held only by capillary forces, independent of charged proteins, amount of free water is pH dependent
animals differ in muscle glycogen content at slaughter
influences rate and extent of post mortem pH decline
muscle pH and its effect on muscle color and morphology
muscle color is hugely impacted by muscle pH
low pH: pale, soft, exudative meat
normal pH: normal color and texture
high pH: dark, firm, dry (dark cutters)
muscle characteristics of normal animal and dark-cutting animal
normal: glycogen at harvest 1%, glycogen at 24hr 0.1%, lactate production moderate, ultimate muscle pH 5.4-5.5
dark cutter> glycogen at harvest 0.3%, glycogen at 24 hr 0.1%, lactate production Low, ultimate muscle pH >6.2
dark cutting condition
DFD pork and dark-cutting beef
caused by depletion of muscle glycogen stores before harvest
physiological stress/fear & excitement: fright= epinephrine leading to glycogen loss
physical stress: mixing, handling, long-distance transit, illness, injury, etc
environmental stress: weather extremes, long-term restriction of dietary energy
*usually a result of the cumulative effects of one or more of these stressors
relationship between muscle pH and beef tenderness
beef toughness is greatest when muscle pH is between 5.8 and 6.2 caused by stress-induced epinephrine release
carcasses with this pH range are “border-line” dark cutters with a slightly dark “muddy” color of lean
Pale Soft and Exudative meat
caused by extreme rapid rate of pH decline: low muscle pH & high temp
low pH-high temp conditions cause denaturation of muscle proteins: resulting in excessive moisture loss (exudate), a pale muscle color, and soft lean
