P5. Muscle to meat Flashcards
sarcoplasmic proteins comprise ____-____% of total muscle protein
- are located where?
- all designed to generate what?
- 25-30%
- located in cytoplasmic fluid (sarcoplasm of muscle)
- generate E to the muscle
sarcoplasmic proteins are largely restricted to what? why?
- to the cellular fluid bathing the myofibrils
- because of packing constraints imposed by organization of myofibrillar proteins
sarcoplasmic proteins include (4)
- enzymes associated with glycolysis and glycogenolysis
- ancillary enzymes such as creatine kinase and AMP deaminase
- proteinases
- oxygen storage protein myoglobin
what type of enzymes make up over half of total sarcoplasmic protein content?
- what is the most abundant of this type of enzyme? how much % of total sarcoplasmic protein fraction
- glycolytic enzymes
- glyceraldehyde phosphate dehydrogenase (oxidation of GAP to 1,3biphosphoglycerate = first energy yielding step in glycolysis)
- 20%
- phosphorylase B = abundant in which type of myofibers? why?
- myoglobin = abundant in which type of myofibers? why?
- phosphorylase B = type IIb (fast-white (flying bird or running) –> bc these myofibers rely heavily on glycogenolysis for energy requirements
- myoglobin –> Type 1 (slow-red, walking) bc they derive a greater share of their energy from oxidative metabolism
greatest quantities of myoglobin in which animal muscle? why?
- in whale muscle (up to 70% of total sarcoplasmic protein fraction) bc large supply of oxygen is required during prolonged deep-sea dives
where is creatine kinase found? (2)
- sarcoplasm
- as a component of M-line of myofibril
what reaction does creatine kinase catalyze?
- uses what?
- reversible?
- produces a _____ ______ _________?
- creatine to creatine phosphate
- uses ATP –> converts to ADP
- reversible
- high-energy compound
why is creatine kinase useful when intensive energy demands are placed on muscle?
- only consumed when?
cell would rapidly be depleted of ATP before glycolytic and oxidative reactions could replace it –> creatine kinase quickly replaces ATP by catalyzing reverse reaction: adding phosphate from creatine phosphate to ADP
- only consumed when channel of Ca2+ doesnt meet demand
how are ATP levels restored after high energy demands/how is ADP converted back to ATP? (4)
- these reactions are especially significant ___________
they can be stored in what?
- oxidative phosphorylation
- glycolysis
- creatine kinase
- 2 ADP –> ATP + AMP catalyzed by adenylate kinase (enzyme present in sarcoplasmic protein fraction) –> when creatine kinase doesn’t produce ATP fast enough
- postmortem
- some of excess high-energy capacity that is in form of ATP is stored in creatine phosphate
the AMP formed by reaction catalyzed by adenylate kinase is _____________ to what? (catalyzed by what?) using ______ and producing ______
- deaminated to inosine monophosphate (IMP)
- catalyzed by AMP deaminase
- H2O –> NH3
Inosine monophosphate (IMP) is further degraded to what? which causes what?
- hypoxanthine
- bitter flavor to meat
which proteinase are of particular interest in relation to conversion of muscle to meat?
- 3 main types (activated by what concentrations of what?)
- calpains = calcium dependent proteinase
1. u-calpain: activated by micromolar (um) concentrations of Ca2+
2. m-calpain: activated by millimolar (mm) concentrations of Ca2+
3. calpain 3 (also called p94): activated by submicromolar (nanomolar) concentrations of Ca2+
what do calpains break down during postmortem conversion of muscle to meat? (3)
(particular proteins of myofibril)
1. titin
2. nebulin
3. TnT
strong connective tissue proteins efficiently transmit what? to produce what?
transmit mechanical force of contraction from muscle fibers to produce movements of bones to which they are attached
what are the 2 main stromal proteins? %?
- constitute ________ tissues
- collagen (90%)
- elastin (10%
- connective tissues
collagen refers to a family of at least __ different __________ proteins found in connective tissues throughout body including (6 + 3)
- collagen analogy
- 27 extracellular proteins
- bone, tendon, cartilage, blood vessels, skin, teeth
+ endomysium, perimysium and epimysium of muscle - collagen = rope anchoring tissue to bone
what is the basic unit of collagen?
- consists of what? –> identical or different?
- tropocollagen
- 3 polypeptide chains –> may be identical or differ slightly in aa sequence, depending on type of collagen –> all alpha chains!
what is the dominant type of collagen in meat?
- characteristic about its polypeptide chains?
- Type 1 collagen
- 2 polypeptide chains of identical sequence + 2 chain of another sequence
each individual collagen polypeptide chain consists of approximately _______ aa residues
- mostly contains (5) aa
- doesn’t contain what? –> consquence?
- 1000
- 33% glycine, 12% proline, 11% alanine, 10% hydroxyproline, 1% hydroxylysine + small amounts of polar and charged aa
- tryptophan is virtually absent from collagen –> used as criterion of purity for collagen preparations
1 repeating sequence of most collagen chains?
- presence of ______ at every 3rd position, coupled with abundance in _______ results in what?
Gly - X - Y
- X is often proline and Y is often hydroxyproline or hydroxylysine
- glycine, abundance in proline at X position –> results in highly extended polypeptide a-chain which forms a shallow, left handed helix –> triple helix = coil-coil = 3000 aa
which side chain points toward the center of the triple helical coiled-coil collagen?
side chain of every third residue points towards very tightly packed center of the coiled-coil
- glycine = aa with smallest possible side chain (H) = only aa that could be accommodated in interior of such structure
how is the triple helix of collagen stabilized? (3)
- each chain is slightly staggered –> enables H-bonding btw N-H of glycine and C=O of adjacent X residue
- further stabilized by H-bonds involving hydroxyl group of hydroxyproline residues
- covalent crosslinks btw tropocollagen molecules stabilize and strengthen striated collagen fibrils in muscle
in live animals, number of covalent crosslinks increase/decrease over time, contributing to what?
- increase
- contributing to increased toughness of meat from older animals
how are elastin fibers formed?
via extensive crosslinking of elastin monomers (tropoelastin molecules) initiated by enzyme lysyl oxidase
how to elastin differ form collagen?
- elastin fibers found in tissues requiring what? (2 ex)
differs in its elasticity! elastin fibers return to their original shape after being stretched to several times their og size
- thus, elastin fibers are found in tissues requiring elasticity: wall of arteries + elastic ligaments
does collagen have a considerable role in determinant of meat texture?
no! content it less than 10% total collagen content
- toughness of meat always due to collagen
2 types of crosslinks in elastin fibers? explain/give characteristics
- lysinonorlysine crosslinks –> cross linking between allysine (aldehyde = reactive), which is formed by oxidation of a lysine residue by lysyl oxidase and an adjacent unmodified lysine residue
- desmosine crosslinks: where desmosine is uniquely found in elastin
how long is the conversion of muscle to meat? why?
2 days to 2 weeks
- bc muscle is still a living organ for some time after death of the animal and strives to continue to function
what is the specific function of muscle?
convert chemical energy into mechanical energy
- immediate source of that chemical energy is ATP
levels of ATP are maintained by various _________ pathways, which depend upon what to where to deliver (2) and removed (2)
- metabolic pathways
- circulation of blood to muscle tissue to deliver oxygen and energy substrates and remove carbon dioxide and metabolic end producs
with the cessation of blood flow that occurs at slaughter, 3 reserve mechanisms are still available to muscle:
- initially, myofibers utilize the oxygen bound to myoglobin to support aerobic metabolism, but these reserves of oxygen are rapidly depleted (5min)
- creatine phosphate serves as a rapidly accessible reservoir of high-energy phosphate for regeneration of ATP through the action of enzyme creatine kinase
- adenylate kinase also contributes to generation of ATP at this point
what happens when 3 initial sources of ATP synthesis are exhausted after slaughter?
- efficient?
anaerobic glycolysis utilizing glycogen reserves stored in the muscle becomes dominant metabolic pathway for generation of ATP
- much less efficient
consequences of anaerobic glycolysis?
- for 2 molecules of ATP produced, 1 molecule of lactic acid is produced –> accumulates in muscle + lowers pH
- at pH 5.4-5.5, many glycolytic enzymes are deactivated –> no further glycolysis can take place
what are ATP levels like in the delay phase?
- level of ATP remains at >95% of initial level (5 mM) –> rate at which ATP is regenerated is nearly equal to rate at which it is consumed
why does the delay phase occur? –> hence, muscle remains ?
- bc muscle cells still function adequately as long as ATP levels remain high –> hence muscle remains pliable and undergoes lengthening when subjected to strength
how low does delay phase last? depending on what? (4)
up to 12 hours
- depending on species, animal genetics, antemortem nutritional status, management of animal prior to slaughter (frightened animal)
when does delay phase end?
when creatine phosphate has been depleted because anaerobic glycolysis alone cannot produce ATP fast enough to match the rate at which it is being hydrolyzed in the cell
depletion of ATP reduces what? –> what happens to the muscle (resting vs contraction)
- reduces ability of calcium pump protein to reduce sarcoplasmic Ca2+ concentration to the submicromolar range –> reduces ability to maintain muscle in the resting state
- upon contraction of muscle, there is insufficient ATP to dissociate myosin from actin –> muscle cannot relax –> results in onset of rigor mortis
what causes muscle cramps during prolonged exercise?
when anaerobic glycolysis cannot keep up with muscle’s ATP demand –> myosin cannot dissociate from actin = muscle cannot relax
as ATP levels continue to fall, there is a continuous decrease/increase in number of myosin cross-bridges with actin that are unlocked/locked bc of lack of _______
- increase
- locked
- lack of ATP
decrease in ATP –> consequence in terms of rigor and extensibility
increase in rigor development as measured by decrease in extensibility (increase in resistance of muscle to lengthen when stretched)
- may be some sarcomere shortening
what are the 3 phases of conversion of muscle to meat?
- at what phase can muscle be treated as meat?
- delay phase
- rigor phase
- aging/rigor resolution phase
- phase 3!
what occurs during the resolution phase?
- consequences on muscle extensibility and tenderness?
partial degradation of the structure of myofilament framework by endogenous proteolytic enzymes (destruction of sarcomere scaffold)
- some of muscle extensibility is gradually regained = increase in meat tenderness (bc cells are broken)
length of resolution phase:
- pork
- lamb
- beef
- pork and lamp: few days
- beef: up to 2 weeks
at what pH range are calpains most active?
- regulated by (3)
- neutral pH range
- by calcium, phospholipids and calpastatin (widely distributed calpain-specific protein inhibitor)
which 2 isoforms of calpains are ubiquitously expressed in tissues? –> tend to be concentrated where?
- 3rd one: specifically where? binds to what?
u-calpain and m-calpain
- in Z-discs –> to hold integrity
- calpain 3: specific to skeletal muscles –> binds specifically to titin but does not cut titin (but facilitates its degradation)
explain role/functioning of calpains:
1. how are they activated?
2. once activated, cause what?
3. results in what?
- calpains are activated as Ca2+ concentration in sarcoplasm increase postmortem (not pumped back)
- once activated, they cause rapid and complete loss of Z-disc owing to degradation of troponin-T, titin and nebulin + minor proteins
- actin, myosin and other proteins are then passively released from sarcomere and become substrates for other proteolytic enzymes
while calpains are ________-activated proteases, cathepsins are ________ proteases
- calcium-activated
- lysosomal proteases
which proteases are maximally active at acidic pHs in the resolution phase?
cathepsins
do calpains or cathepsins have a bigger role in postmortem tenderization?
- calpains!
- more proteolytic degradation mimicked in vitro
what are the 3 quality attributes of meat that strongly influence its appeal to consumers/its value?
- water-holding capacity
- color
- tenderness
water-holding capacity, color and tenderness of meat are governed by 6 things
- animal species
- breed
- genotype
- nutritional status
- pre-slaughter handling
- postmortem biochemical changes (chilling, processing, storage)
postmortem metabolism leads to a increase/decrease in pH from physiological value ____ to ___-_____
- decrease
- 7.4 to 5.5-5.9
why is the natural increase/reduction in pH during postmortem metabolism beneficial? (IMPORTANT)
vs detrimental (3 steps ish)
- reduction in pH
- beneficial –> because it retards microbial growth and extends shelf-life
- detrimental –> because final pH of meat is close to isoelectric point of myosin (around 4.6) –> protein-protein interactions become favored at the expense of protein-water interactions = decrease in water holding capacity and some exudation of water from tissue
why is exudation of water from meat tissue bad for economic value of meat? (2)
- because meat is sold by weight
- because consumers consider fresh cuts of meat bathed in exuded water to be unappealing and to have lost their juiciness and tenderness
effects of antemortem glycogen depletion on pH
- antemortem glycogen depletion result from (3)
- effect on pH? –> results in what?
- antemortem depletion of glycogen stores may result from pre-slaughter stressor (cold, damp weather), exercise or excessive fasting
- following slaughter, lack of adequate glycogen reserves result in early termination of glycolysis –> final pH of meat remains relatively high (>6) –> resulting quality of meat is referred to as dark, firm and dry meat (DFD)
2 phases of effect of heat on meat texture
- sharp increase in toughness occurs over range of 40-50°C –> attributed to thermal denaturation of myofibrillar proteins actin and myosin –> shrink and form a gel within the myofiber that accounts for increased toughness
- further increase in temp = another sharp increase in toughness over range of around 65-75°C –> shrinkage of collagen fibers associated with perimysium that denature and are gradually converted to gelatin
effect of heat on meat quality:
- in phase 1: some of _______ previously associated with myofiber is apparently _______ out by shrinkage of the __________, accounting for some loss of _____ observed over this temp range
- in phase 2: shrinkage of _______ fibers generates a substantial force that expels large amount of _______ from the myofibers
- water –> forced out by shrinkage of endomysium –> some loss of fluid
- shrinkage of perimysial fibers generates substantial force that expels fluid from myofibers
with prolonged heating of the meat (especially over ___°C), tenderness gradually increases/decreases
- attributed to what (2) –> partially offsets what?
- 70°C –> tenderness increases (more time for hydrolysis!)
- to partial hydrolysis of heat-labile crosslinks btw collagen chains + (to a lesser extent) to peptide hydrolysis
- partially offsets initial heat induced toughening
when fresh meat product like beef steak is heated –> what happens to the color? why?
- initial lightening of the color occurs owing to precipitation of proteins within myofibers, which changes perception of color
most of color changes observed upon heating of meat are bc of (3)
- chemical changes/denaturation in myoglobin
- depend on chemical state of iron in its heme group –> oxidation of Fe(II) in its heme group to Fe(III)
- some browning also results from formation of Maillard reaction products
what color is
- Fe (II) bound to O2 (oxymyoglobin)
- Fe (II) in absence of O2 (deoxymyoglobin)
- Fe (III) (metmyoglobin)
- Fe (II) bound to O2 (oxymyoglobin): bright to dark red
- Fe (II) in absence of O2 (deoxymyoglobin): purple
- Fe (III) (metmyoglobin): brown
myoglobin is one of the most _____-stable of muscle proteins –> retains its structure and color properties to at least ___°C –> favorises which iron oxidation state?
- heat
- 50°C
- Fe(III)
is internal color a reliable indicator of internal temp from food safety perspective? Why?
no! premature browning in ground beef may occur as a result of greater sensitivity of meymyoglobin and oxymyoglobin to thermal denaturation as compared to deoxymyoglobin
associate each correctly:
red, pink, brown
medium, well-done, rare
68, 60, 77
- red = rare = 60
- pink = medium = 68
- brown = well-done = 77
what is the end-point temp of safety level that ensures destruction of _________ _________?
- 71°C
- pathogenic microorganisms
formation of particular flavors depend on 3 types of factors
- antemortem (3)
- postmortem (3)
- ?
- antemortem factors: species, breed, diet
- postmortem factors: types of cooking (wet, dry, conventional, microwave), cooking time, end-point cooking temp
- flavor compound formed via Maillard reaction pathway like pyridines, pyrazines, thiophenols, thiazoles
cooking of meat results in production of _______ or _______ of flavor compounds
hundreds or thousands
