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Food Chemistry 1 > P5. Muscle to meat > Flashcards

P5. Muscle to meat Flashcards

1
Q

sarcoplasmic proteins comprise ____-____% of total muscle protein
- are located where?
- all designed to generate what?

A
  • 25-30%
  • located in cytoplasmic fluid (sarcoplasm of muscle)
  • generate E to the muscle
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2
Q

sarcoplasmic proteins are largely restricted to what? why?

A
  • to the cellular fluid bathing the myofibrils
  • because of packing constraints imposed by organization of myofibrillar proteins
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3
Q

sarcoplasmic proteins include (4)

A
  1. enzymes associated with glycolysis and glycogenolysis
  2. ancillary enzymes such as creatine kinase and AMP deaminase
  3. proteinases
  4. oxygen storage protein myoglobin
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4
Q

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

A
  • glycolytic enzymes
  • glyceraldehyde phosphate dehydrogenase (oxidation of GAP to 1,3biphosphoglycerate = first energy yielding step in glycolysis)
  • 20%
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5
Q
  • phosphorylase B = abundant in which type of myofibers? why?
  • myoglobin = abundant in which type of myofibers? why?
A
  • 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
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6
Q

greatest quantities of myoglobin in which animal muscle? why?

A
  • in whale muscle (up to 70% of total sarcoplasmic protein fraction) bc large supply of oxygen is required during prolonged deep-sea dives
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7
Q

where is creatine kinase found? (2)

A
  • sarcoplasm
  • as a component of M-line of myofibril
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8
Q

what reaction does creatine kinase catalyze?
- uses what?
- reversible?
- produces a _____ ______ _________?

A
  • creatine to creatine phosphate
  • uses ATP –> converts to ADP
  • reversible
  • high-energy compound
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9
Q

why is creatine kinase useful when intensive energy demands are placed on muscle?
- only consumed when?

A

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

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10
Q

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?

A
  1. oxidative phosphorylation
  2. glycolysis
  3. creatine kinase
  4. 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
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11
Q

the AMP formed by reaction catalyzed by adenylate kinase is _____________ to what? (catalyzed by what?) using ______ and producing ______

A
  • deaminated to inosine monophosphate (IMP)
  • catalyzed by AMP deaminase
  • H2O –> NH3
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12
Q

Inosine monophosphate (IMP) is further degraded to what? which causes what?

A
  • hypoxanthine
  • bitter flavor to meat
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13
Q

which proteinase are of particular interest in relation to conversion of muscle to meat?
- 3 main types (activated by what concentrations of what?)

A
  • 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+
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14
Q

what do calpains break down during postmortem conversion of muscle to meat? (3)

A

(particular proteins of myofibril)
1. titin
2. nebulin
3. TnT

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15
Q

strong connective tissue proteins efficiently transmit what? to produce what?

A

transmit mechanical force of contraction from muscle fibers to produce movements of bones to which they are attached

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16
Q

what are the 2 main stromal proteins? %?
- constitute ________ tissues

A
  • collagen (90%)
  • elastin (10%
  • connective tissues
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17
Q

collagen refers to a family of at least __ different __________ proteins found in connective tissues throughout body including (6 + 3)
- collagen analogy

A
  • 27 extracellular proteins
  • bone, tendon, cartilage, blood vessels, skin, teeth
    + endomysium, perimysium and epimysium of muscle
  • collagen = rope anchoring tissue to bone
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18
Q

what is the basic unit of collagen?
- consists of what? –> identical or different?

A
  • tropocollagen
  • 3 polypeptide chains –> may be identical or differ slightly in aa sequence, depending on type of collagen –> all alpha chains!
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19
Q

what is the dominant type of collagen in meat?
- characteristic about its polypeptide chains?

A
  • Type 1 collagen
  • 2 polypeptide chains of identical sequence + 2 chain of another sequence
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20
Q

each individual collagen polypeptide chain consists of approximately _______ aa residues
- mostly contains (5) aa
- doesn’t contain what? –> consquence?

A
  • 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
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21
Q

1 repeating sequence of most collagen chains?
- presence of ______ at every 3rd position, coupled with abundance in _______ results in what?

A

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

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22
Q

which side chain points toward the center of the triple helical coiled-coil collagen?

A

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

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23
Q

how is the triple helix of collagen stabilized? (3)

A
  1. each chain is slightly staggered –> enables H-bonding btw N-H of glycine and C=O of adjacent X residue
  2. further stabilized by H-bonds involving hydroxyl group of hydroxyproline residues
  3. covalent crosslinks btw tropocollagen molecules stabilize and strengthen striated collagen fibrils in muscle
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24
Q

in live animals, number of covalent crosslinks increase/decrease over time, contributing to what?

A
  • increase
  • contributing to increased toughness of meat from older animals
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25
Q

how are elastin fibers formed?

A

via extensive crosslinking of elastin monomers (tropoelastin molecules) initiated by enzyme lysyl oxidase

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26
Q

how to elastin differ form collagen?
- elastin fibers found in tissues requiring what? (2 ex)

A

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

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27
Q

does collagen have a considerable role in determinant of meat texture?

A

no! content it less than 10% total collagen content
- toughness of meat always due to collagen

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28
Q

2 types of crosslinks in elastin fibers? explain/give characteristics

A
  • 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
29
Q

how long is the conversion of muscle to meat? why?

A

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

30
Q

what is the specific function of muscle?

A

convert chemical energy into mechanical energy
- immediate source of that chemical energy is ATP

31
Q

levels of ATP are maintained by various _________ pathways, which depend upon what to where to deliver (2) and removed (2)

A
  • metabolic pathways
  • circulation of blood to muscle tissue to deliver oxygen and energy substrates and remove carbon dioxide and metabolic end producs
32
Q

with the cessation of blood flow that occurs at slaughter, 3 reserve mechanisms are still available to muscle:

A
  1. initially, myofibers utilize the oxygen bound to myoglobin to support aerobic metabolism, but these reserves of oxygen are rapidly depleted (5min)
  2. creatine phosphate serves as a rapidly accessible reservoir of high-energy phosphate for regeneration of ATP through the action of enzyme creatine kinase
  3. adenylate kinase also contributes to generation of ATP at this point
33
Q

what happens when 3 initial sources of ATP synthesis are exhausted after slaughter?
- efficient?

A

anaerobic glycolysis utilizing glycogen reserves stored in the muscle becomes dominant metabolic pathway for generation of ATP
- much less efficient

34
Q

consequences of anaerobic glycolysis?

A
  • 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
35
Q

what are ATP levels like in the delay phase?

A
  • 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
36
Q

why does the delay phase occur? –> hence, muscle remains ?

A
  • bc muscle cells still function adequately as long as ATP levels remain high –> hence muscle remains pliable and undergoes lengthening when subjected to strength
37
Q

how low does delay phase last? depending on what? (4)

A

up to 12 hours
- depending on species, animal genetics, antemortem nutritional status, management of animal prior to slaughter (frightened animal)

38
Q

when does delay phase end?

A

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

39
Q

depletion of ATP reduces what? –> what happens to the muscle (resting vs contraction)

A
  • 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
40
Q

what causes muscle cramps during prolonged exercise?

A

when anaerobic glycolysis cannot keep up with muscle’s ATP demand –> myosin cannot dissociate from actin = muscle cannot relax

41
Q

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 _______

A
  • increase
  • locked
  • lack of ATP
42
Q

decrease in ATP –> consequence in terms of rigor and extensibility

A

increase in rigor development as measured by decrease in extensibility (increase in resistance of muscle to lengthen when stretched)
- may be some sarcomere shortening

43
Q

what are the 3 phases of conversion of muscle to meat?
- at what phase can muscle be treated as meat?

A
  1. delay phase
  2. rigor phase
  3. aging/rigor resolution phase
    - phase 3!
44
Q

what occurs during the resolution phase?
- consequences on muscle extensibility and tenderness?

A

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)

45
Q

length of resolution phase:
- pork
- lamb
- beef

A
  • pork and lamp: few days
  • beef: up to 2 weeks
46
Q

at what pH range are calpains most active?
- regulated by (3)

A
  • neutral pH range
  • by calcium, phospholipids and calpastatin (widely distributed calpain-specific protein inhibitor)
47
Q

which 2 isoforms of calpains are ubiquitously expressed in tissues? –> tend to be concentrated where?
- 3rd one: specifically where? binds to what?

A

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)

48
Q

explain role/functioning of calpains:
1. how are they activated?
2. once activated, cause what?
3. results in what?

A
  1. calpains are activated as Ca2+ concentration in sarcoplasm increase postmortem (not pumped back)
  2. once activated, they cause rapid and complete loss of Z-disc owing to degradation of troponin-T, titin and nebulin + minor proteins
  3. actin, myosin and other proteins are then passively released from sarcomere and become substrates for other proteolytic enzymes
49
Q

while calpains are ________-activated proteases, cathepsins are ________ proteases

A
  • calcium-activated
  • lysosomal proteases
50
Q

which proteases are maximally active at acidic pHs in the resolution phase?

A

cathepsins

51
Q

do calpains or cathepsins have a bigger role in postmortem tenderization?

A
  • calpains!
  • more proteolytic degradation mimicked in vitro
52
Q

what are the 3 quality attributes of meat that strongly influence its appeal to consumers/its value?

A
  • water-holding capacity
  • color
  • tenderness
53
Q

water-holding capacity, color and tenderness of meat are governed by 6 things

A
  • animal species
  • breed
  • genotype
  • nutritional status
  • pre-slaughter handling
  • postmortem biochemical changes (chilling, processing, storage)
54
Q

postmortem metabolism leads to a increase/decrease in pH from physiological value ____ to ___-_____

A
  • decrease
  • 7.4 to 5.5-5.9
55
Q

why is the natural increase/reduction in pH during postmortem metabolism beneficial? (IMPORTANT)
vs detrimental (3 steps ish)

A
  • 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
56
Q

why is exudation of water from meat tissue bad for economic value of meat? (2)

A
  • 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
57
Q

effects of antemortem glycogen depletion on pH
- antemortem glycogen depletion result from (3)
- effect on pH? –> results in what?

A
  1. antemortem depletion of glycogen stores may result from pre-slaughter stressor (cold, damp weather), exercise or excessive fasting
  2. 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)
58
Q

2 phases of effect of heat on meat texture

A
  1. 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
  2. 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
59
Q

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

A
  • water –> forced out by shrinkage of endomysium –> some loss of fluid
  • shrinkage of perimysial fibers generates substantial force that expels fluid from myofibers
60
Q

with prolonged heating of the meat (especially over ___°C), tenderness gradually increases/decreases
- attributed to what (2) –> partially offsets what?

A
  • 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
61
Q

when fresh meat product like beef steak is heated –> what happens to the color? why?

A
  • initial lightening of the color occurs owing to precipitation of proteins within myofibers, which changes perception of color
62
Q

most of color changes observed upon heating of meat are bc of (3)

A
  • 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
63
Q

what color is
- Fe (II) bound to O2 (oxymyoglobin)
- Fe (II) in absence of O2 (deoxymyoglobin)
- Fe (III) (metmyoglobin)

A
  • Fe (II) bound to O2 (oxymyoglobin): bright to dark red
  • Fe (II) in absence of O2 (deoxymyoglobin): purple
  • Fe (III) (metmyoglobin): brown
64
Q

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?

A
  • heat
  • 50°C
  • Fe(III)
65
Q

is internal color a reliable indicator of internal temp from food safety perspective? Why?

A

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

66
Q

associate each correctly:
red, pink, brown
medium, well-done, rare
68, 60, 77

A
  • red = rare = 60
  • pink = medium = 68
  • brown = well-done = 77
67
Q

what is the end-point temp of safety level that ensures destruction of _________ _________?

A
  • 71°C
  • pathogenic microorganisms
68
Q

formation of particular flavors depend on 3 types of factors
- antemortem (3)
- postmortem (3)
- ?

A
  1. antemortem factors: species, breed, diet
  2. postmortem factors: types of cooking (wet, dry, conventional, microwave), cooking time, end-point cooking temp
  3. flavor compound formed via Maillard reaction pathway like pyridines, pyrazines, thiophenols, thiazoles
69
Q

cooking of meat results in production of _______ or _______ of flavor compounds

A

hundreds or thousands

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