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4) Food Commodities > 4. Red Meats and Meat Products > Flashcards

4. Red Meats and Meat Products Flashcards

1
Q

what does red meat refer to?

A

mammalian skeletal muscle consumed as food

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2
Q

what is the color of red meat from?

A

high concentration of myoglobin in muscle

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3
Q

what are factors affecting composition of red meat?

A

species, breed, sex, age, nutritional status, muscle condition of live animal (related to animal’s level of activity)

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4
Q

what are the 3 main skeletal muscle proteins?

A

sarcoplasmis
myofibrillar
stromal

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5
Q

what are examples of enzymes that are sarcoplasmic proteins?

A
  • enzymes of glycolysis and glycogenolysis
  • creatine kinase, AMP deaminase
  • proteinases
  • O2 storage protein: myoglobin
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6
Q

what type of muscle protein is myoglobin?

A

sarcoplasmic

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7
Q

describe the solubility of sarcoplasmic proteins

A

h2o soluble

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8
Q

what is the most abundant sarcoplasmic protein?

what type of enzyme is this?

A

glyceraldehyde-3-phsophate dehydrogenase (glycolytic enzyme)

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9
Q

what constitutes the largest fraction of muscle protein?

A

myofibrillar proteins (50-60%)

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10
Q

describe the solubility of myofirbillar proteins

A

soluble in dilute salt solutions

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11
Q

what is the function of myofibrillar proteins?

A

regulates, supports and performs mechanical work of contraction

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12
Q

what kind of structure are myofibrillar proteins assembled into?

A

quaternary structural filaments

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13
Q

what are the major myofibrillar proteins?

A 
myosin
actin
troponin complex
tropomyosin
titin
nebulin
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14
Q

what is the function of nebulin?

A

regulates length of thin filaments during assembly of sarcomeres

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15
Q

what is the function of titin?

A

large protein responsible for elasticity of muscles

connects the Z line to the M line in the sarcomere

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16
Q

in the sarcomere of muscle fibers, describe the dark and light bands

A

dark

  • A bands
  • anisotropic
  • brighter at center (region is called H-zone)

light

  • I bands
  • isotropic
  • narrower and darker at center (region is called Z-disc
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17
Q

what are z-discs? where are they found?

A

the dark region at center of I band

they are the border of each sarcomere

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18
Q

what is the H zone?

A

bright region in middle of A bands

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19
Q

describe the steps involved in the troponin, myosin and actin complex

A
  1. when actin and tropomyosin is complexed, actin can’t bind to myosin
  2. sarcoplasmic reticulae (SR) releases Ca2+ ions into the cytoplasm to facilitate binding of myosin and actin
  3. tropomyosin and troponin bound to actin act as a complex block binding of actin to myosin
  4. troponin binds with Ca2+ –> releases tropomyosin from actin –> allows myosin to bind
  5. when all cross bridges in a sarcomere move at the same time, the sarcomere contracts
  6. when all cross bridges in a sarcomere move at the same time, the sarcomere contracts
  7. reabsorbs free Ca2+ ions –> enables ATP to bind to myosin cross bridge to disconnect the brridge from the actin
  8. actin fibers change back to previous position –> sarcomere relaxes
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20
Q

what is another name for stromal proteins?

A

connective tissue

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21
Q

what are characteristics of stomal proteins?

A
  • insoluble in H2O and dilute salt solutions

- high tensile strength protein molecules

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22
Q

what is the function of stromal proteins

A

transmits contractions from muscle fibers to cause movements of the bones or tissues to which they are attached

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23
Q

what are the 3 main connective tissue proteins?

A

collagen
elastin
desmosine

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24
Q

what do collagen CT proteins include?

A 
blood vessels
bone
cartilage
skin
teeth
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25
Q

what is the basic unit of collagen?

A

tropocollagen

26
Q

what is tropocollagen made out of?

A

3 similar polypeptide chains coiled around a common axis

27
Q

what is the AA sequence in tropocollagen?

A

Gly-Pro-X or Gly-X-HOPro

gly = glycine
pro = proline
HOpro = hydroxyproline
X = another AA
28
Q

what is the composition of collagen CT proteins?

A

glycine = 1/3 of AA content of collagen

hydroproline: 1/6 of collagen content

29
Q

what is the dominant collagen in meat?

A

type 1 collagen

30
Q

what is the composition of type 1 collagen?

A

2 polypeptide chains of identical sequence: alpha 1 (I) and alpha 2 (I)

31
Q

what is the structure of type III collagen?

A
  • has 3 identical chains: alpha 1 (III)

- 3 bonds are stabilized by intra and intermolecular bonds

32
Q

why does toughness of meat increase in older animals?

A

when covalent crosslinks of collagen increase over time

33
Q

what role does elastin have in meat texture?

A

minor role

34
Q

why are elastin fibers found in tissues such as artery walls and ligaments?

A

elastic fibers return to their original shape even after being stretched

35
Q

what is responsible for elastic properties of elastin?

36
Q

describe desmosine

A
  • type of stromal protein
  • cross link found in elastin
  • formed from 3 allysyl side chains and 1 lysyl side chain from the same or neighbouring polypeptide
  • responsible for elastic properties of elastin
37
Q

in skeletal muscles, which types of lipids have constant levels? which have variable levels?

A

structural lipids have constant levels

storage lipids or TGs have highly variable levels

38
Q

what type of structural lipids are found in skeletal muscle?

A

cholesterol

phospholipids

39
Q

in the live animal, process of the body operate to ensure ____

A

homeostasis

40
Q

after the animal dies, what biochemical changes cause conversion of muscle to meat?

A

when catabolism exceeds anabolism

41
Q

what is the primary function of muscle?

A

to convert biochemical energy into mechanical energy

42
Q

in pre-mortem animals, how are ATP levels maintained?

A

by various metabolic pathways that rely on blood circulation to muscle tissues which:

  1. produce O2 and energy
  2. remove Co2 and metabolic end products
43
Q

when an animal dies, how does muscle briefly sustain ATP synthesis?

A
  1. O2 bound to Mb sustains aerobic metabolism. Occurs for first 5 mins until O2 reserves are depleted
  2. creatine phosphate + ADP –> creatine + ATP
  3. adenylate kinase contributes to ATP generation by interconversions of adenine nucleotides
44
Q

describe how adenylate kinase contributes to ATP generation

A
  1. ADP + ADP –> ATP + AMP
  2. AMP produces adenosine and IMP
  3. inosine –> hyoxanthine –> xanthine –> uric acid
45
Q

what flavor does xanthine impart in meat?

when is this produced?

A

bitter flavor

46
Q

what does high IMP levels in meat represent?

what does low IMP mean?

A

high IMP = high meat freshness. This means that IMP has not been degraded into inosine, hyoxanthine, xanthine or uric acid yet

low IMP = low freshness

47
Q

what are steps of slaughtering?

A
  1. stunning
  2. exsanguination
  3. termination of nutrients and O2 supply to muscle
  4. loss of homeostasis (rise in carcass temp)
  5. use and depletion of MbO2
  6. use and depletion of glycogen and creatine-P
  7. lactic acid production and accumulation in muscle
  8. decline in muscle pH
48
Q

what are 3 main end results after slaughtering?

A
  1. pH effects
  2. cold shortening of meat
  3. thaw rigor
49
Q

what pH effects occur after slaughtering?

what two main effects does this cause?

A

lactic acid accumulates in muscle which decreases muscle pH and effects meat quality

main effects

  1. PSE: pale, soft exudative meats (when pH is too low)
  2. DFD: dark, firm, dry meats (when animal is put under too much stress before slaughtering, which depletes glycogen in muscle)
50
Q

how can pH decrease be beneficial after slaughtering?

A

because microbial growth is lower at lower pH

51
Q

after slaughtering, what is considered normal, high and low pH?

A

normal pH: 5.6
too high pH: 6.8
too low pH: 5.2

52
Q

when does cold shortening of meat occur?

A

after slaughtering, when flesh is excised and chilled before rigor

53
Q

what causes cold shortening of meat to occur?

A
  1. mgATPase has slower capacity to pump Ca2+ for the sarcoplasm into the reticulum
  2. Ca2+ builds up in sarcoplasm
  3. displacement of troponin and tropomyosin complex from actin permits cross bridge formation between myosin and actin
  4. shortens length of muscle which causes tough texture in meat
54
Q

what is the ultimate result of cold shortening of meat?

A

tough texture in meat

55
Q

what causes thaw rigor to occur?

A

when the muscle is frozen rapidly before rigor takes place

56
Q

what are the steps which cause thaw rigor?

A
  1. formation of intercellular ice crystals, which affects SR membrane and sarcolemma
  2. causes Ca2+ to flood the sarcoplasm
  3. displaces tropomyosin-troponin complex from actin
  4. enables cross bridges to form between myosin and actin
  5. shortens muscle length = tough texture
57
Q

what is the ultimate result of thaw rigor after slaughtering?

A

shortens muscle length, which causes tough texture

58
Q

A) what are the effects of natural and induced postmortem biochemical changes on meat quality that influence appeal and value to consumers?

B) what affects these quality attributes?

A

A) water holding capacity
color
tenderness

B) animal species, breed, genotype, nutritional status, pre-slaughter handling, postmortem biochemical changes (chilling, processing, storage)

59
Q

in post-mortem, what is the cause of the bright red color of fresh meats?

60
Q

in post-mortem, what causes the dark purplish red color?

A

depletion of O2 causes MbO2 to be converted to Mb

61
Q

what are the three categories of water holding capacity?

A
  1. bound: inner most layer of H2O is bound to proteins
  2. immobilized: middle layer is less organized and is expelled depending on force applied
  3. free: outermost layer is held by weak capillary forces

4) Food Commodities (6 decks)

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