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food tech > lec 10 animal tissue foods: meat and fish > Flashcards

lec 10 animal tissue foods: meat and fish Flashcards

1
Q

what types of meat are there?

A

Red meat: Lamb/Mutton, pork, beef, game
White meat: Fowl

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2
Q

what pros are there with meat?

A
  • High satiety (Foods that induce high satiety are those that effectively reduce hunger and decrease the desire to eat, leading to a longer-lasting feeling of fullness and satisfaction.)
  • B-vitamins
  • Readily digestible proteins containing all essential amino acids
  • Low allergenicity
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3
Q

what cons are there with meat?

A
  • Environmental issues
  • Feed conversion/Water consumption
  • Animal welfare
  • Health drawbacks with red meat and meat products?
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4
Q

What is meat?

A
  • Skeletal muscle with fat and connective tissue.
  • Other parts are also used as food directly or part of meat products
  • Heart, lungs, liver, kidneys, thymus, tongue etc
  • By-products are also utilized
  • Blood, fat tissue, connective tissue and bone marrow
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5
Q

describe Muscle cells (muscle fibres)

A
  • Elongated cells with multiple nuclei (upto 100)
  • 10-15 μm diameter, 1-50 mm long
  • Fully formed at birth and grow with age
  • Unable to divide and increase in number
  • Upon muscle damage, new muscle-like cells can be produced
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6
Q

what are The muscle fibre built up of?

A

by myofibrils

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7
Q

what is a Sarcomer?

A

Smallest contractile unit of the muscle
* Contracts when the muscle is working

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8
Q

explain how Muscle contraction works?

A

when muscle relaxed -> thick filament (myosin) is bound to P and ADP

Nerve impulse – myosin binds
to actin: P released –> myosin bound to actin and ADP

Release of P induces “rowing movement” by twisting of the myosin head. Filament moves
approx. 10 nm. –> myosin - actin

ATP binds to myosin – complex
with actin dissociates –> myosin - ATP

ATP is hydrolysed and cycle is
repeated–> myosin- P and ADP

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9
Q

how much Energy (ATP) is obtained trough oxidation of glycogen (or fat)?

A
  • complete metabolism: 36 ATP/glucose unit
  • lack of oxygen – anaerobic glycolysis: 2 ATP/glucose unit and also lactate
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10
Q

what are the three protein groups?

A

Sacroplasmic (water soluble)
Myofibrillar(salt soluble)
Stromal (connective tissue)(neither water or salt soluble)

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11
Q

what happens post mortem when blood is removed?

A
  • Stops oxygen supply to the muscle
  • Anaerobic metabolism -> lactate -> pH decrease
  • Respiration stops
  • Glycolysis inhibited at pH 5.5
  • Glycogen is depleted
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12
Q

what happens when No more ATP is generated?

A
  • actin-myosin complex can not dissociate -> rigor mortis
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13
Q

What is rigor mortis and when is it released?

A
  • rigor mortis is released after approx. 48h due to cleavage of the actin at the z-line
  • Rigor mortis causes contraction of the muscles
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14
Q

why are carcasses stored hanging?

A

for stretching of muscles

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15
Q

how is Tenderizing of muscle done?

A
  • low pH -> gradual denaturation of myofibrillar proteins-> increased susceptibility to proteolytic enzymes
  • low pH -> activation of proteolytic enzymes
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16
Q

how is the Creation of flavour accomplished?

A
  • ATP -> ADP ->inosin ->hypoxanthine
  • optimal hypoxanthine concentration: 1-2 μmol/g
  • amino acids and peptides
  • other substances: NH3 , acetone, acetic aldehyde, diacetyl, H2 S etc.
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17
Q

give a sumamry of the post mortem processes

A

Slaughter ->Blood circulation and oxygen supply stops-> Respiration stops->

  • ATP-levels decrease->rigor mortis-> hypoxanthine is accumulated

-glycogen ->lactate –> pH decrease–> activation of proteolytic enzymes–> degradation of proteins

18
Q

what happens to the quality if glycolysis is Too rapid Post mortem?

A

rapid decrease in pH while T is high
* Occurs in animals stressed at slaughter
* Rapid denaturation of sarcoplasmic proteins –>water holding
capacity decreases.
* Light colour, loose texture, watery on surface.
* PSE meat - (”Pale, Soft and Exudative meat”)
* Especially relevant for pork
* Important with proper handling of animals!

19
Q

what happens to the quality if Glycogen depots are empty Post mortem?

A

insufficient decrease in pH (target pH=5.5)
* Animal is exhausted before slaughter
* Insufficient energy in muscle
* Insufficient lactic acid is produced
* Meat gets dark and water-holding increases
* Looks dry on the surface
* DFD meat – (”Dark, firm and dry meat”)

20
Q

Cooling after slaughter is crucial for
meat quality, how long should this go on for?

A
  • Normally up to 24h before the end temperature is reached (7°C)
  • pH decreases from lactic acid production
21
Q

what happens If cooling is too rapid?

A
  • Cold contraction
  • If cooling is to rapid (before ATP levels have decreased) muscles will shorten
  • Rigor mortis occurs i a shortened condition
  • If freezing -> stronger effect -> freeze contraction
  • Meat shrinkage up to 70%
  • Contracted muscles are hard to relax/tenderize-> tough and hard meat
22
Q

what are Fat depots in meat?

A
  • Subcutanious fat - triglycerides
  • tallow – beef and mutton
  • lard – pork
  • Most prevalent fatty acids: palmitic, stearic and oleic acid
  • inter muscular fat
  • intra muscular fat
23
Q

what are the Connective tissue proteins in meat?

A

Collagen and elastin

Supportive tissue in the muscle
Elastin (elastic) and collagen (tough) -> mesh-like network

24
Q

where are Extracellular proteins generated from

A

fibroblasts

25
Q

why does the connective tissue proteins Strength increase with age?

A

cross-lniking of proteins

26
Q

Connective tissue-rich meat is typically heat treated for a long time, what happens then?

A

partial hydrolysis –> weakens the network

27
Q

what happens at the different temperatures while Cooking meat?

A

40°C = myosin heads start denaturing, thickness of meat starts shrinking
50°C = sacroplasmic proteins start denaturing
60°C = the fiber part of the myosin starts denaturing, the muscle shrinks longitudinally, water is pressed out
60-65°C = Myoglobin denatures, colour change
65°C = collagen starts denaturing
80°C = actin starts denaturing

28
Q

what happens when Denaturation of actin and sarcoplasmic proteins (globular
proteins occur?

A

expand and gelatinize

29
Q

what happens when Denaturation of collagen and myosin (fibrous proteins) occurs?

A

contraction

30
Q

what is the difference in beef Tenderness Pre rigor and post rigor?

A
  • Pre rigor
    depends on: Animal (species, breed, age, sex, weight at slaughter etc.)
  • Amount of connective tissue
  • Animal stress
  • Intra-muscular fat (marbling)

Post rigor depends on
* Proteolytic enzymes
* hanging – 10-30 days at low T (1-3 ⁰C) and high humidity (~ 85%), drip (loss) = few %
* vaccuum – reduces drip, immersed in water and remaning blood
* electrostimulation – speed up glycolysis -> rapid decrease in pH
* Cooking – denaturation of proteins
* water loss
* toughening

31
Q

how is Emulsification done in emulsion sausages?

A
  • Fat is emulsified in a continous phase of muscle tissue through grinding and mixing
  • Proteins and supra-molecular protein structures act as emulsfiers
32
Q

why does Addition of salt increases protein solubility?

A

water holding capacity
increases

33
Q

Why do we eat fish?

A
  • Essential fatty acids, protein, vitamin A, D and B12, Se etc.
  • Fish fat is mainly unsaturated
  • omega-3 fatty acids (mainly in fatty fish e.g. salmon, heering, mackerel etc.)
  • An important natural resource in many countries
  • Controversies
  • Sustainable fishing
  • Feed conversion in fish farming
34
Q

what is the Myotome

A

Myotome consists of muscle cells (myomeres) in fish
* Size of muscel cells increases with age – number of cells does not increase

35
Q

what happens After catch of fish?

A
  • Asphyxiation and sometimes stunning
  • Post mortem changes similar to those of meat–> Low glycogen content in fish muscle -> pH decrease is less pronounced than in meat –> minimum pH 6-7
  • Fish needs to be kept cold after catch
    –>microbial spoilage
  • Especially important for fish from cold waters
36
Q

what is present in In salt water fish?

A
  • trimethylaminoxide is present
  • Upon heating and freezing: converts into:
    -dimethyl amine -> off-flavour
    • formaldehyde -> off-flavours and cross-linking of protein -> can reduce water-holding capacity
37
Q

what can bacteria convert trimethylaminoxide to after catch of fish?

A

trimethylamine
Trimethylamine has very low odor threshold: ~ 600 PPB (for comparison: ammonia ~ 110 000 PPB)
* Causes ”fishy” smell

38
Q

what are the Fish processing steps?

A
  • salting
  • drying
  • smoking
  • fermentation
  • freezing (today the most important)
39
Q

why should Freezing be performed after rigor (24-48h on ice)?

A

to avoid muscles to be frozen in contracted (short) state-> avoid water loss upon thawing
* Rapid freezing and rapid thawing -> minimizing tissue damage

40
Q

why is Fish tissue is more sensitive to heating than meat?

A
  • Less connective tissue with different composition than in meat
  • Fish collagen has higher solubility
  • Connective tissue softens rapidly and its proteins denature at 50-60°C
  • (Meat collagen approx. 65°C)
  • Myomeres are released -> ”layers” fall apart
  • Water-holding capacity rapidly decreases
41
Q

what are some Chemical and biological contaminants in fish?

A

Hg
* Chlorinated organic compunds (DDT, PCB etc.)
* Radioactive Cs
* Freshwater fish from the north of Europe
* From Chernobyl 1986
* Health risk is low if intake is limited
* Micobial toxins
* Parasites (nematodes, killed upon cooking)

42
Q
A

food tech (11 decks)

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