lec 10 animal tissue foods: meat and fish

Question 1

what types of meat are there?

Answer 1

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

Question 2

what pros are there with meat?

Answer 2

• 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

Question 3

what cons are there with meat?

Answer 3

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

Question 4

What is meat?

Answer 4

• 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

Question 5

describe Muscle cells (muscle fibres)

Answer 5

• 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

Question 6

what are The muscle fibre built up of?

Answer 6

by myofibrils

Question 7

what is a Sarcomer?

Answer 7

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

Question 8

explain how Muscle contraction works?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

what are the three protein groups?

Answer 10

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

Question 11

what happens post mortem when blood is removed?

Answer 11

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

Question 12

what happens when No more ATP is generated?

Answer 12

• actin-myosin complex can not dissociate -> rigor mortis

Question 13

What is rigor mortis and when is it released?

Answer 13

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

Question 14

why are carcasses stored hanging?

Answer 14

for stretching of muscles

Question 15

how is Tenderizing of muscle done?

Answer 15

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

Question 16

how is the Creation of flavour accomplished?

Answer 16

• 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.

Question 17

give a sumamry of the post mortem processes

Answer 17

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

Question 18

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

Answer 18

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!

Question 19

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

Answer 19

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”)

Question 20

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

Answer 20

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

Question 21

what happens If cooling is too rapid?

Answer 21

• 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

Question 22

what are Fat depots in meat?

Answer 22

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

Question 23

what are the Connective tissue proteins in meat?

Answer 23

Collagen and elastin

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

Question 24

where are Extracellular proteins generated from

Answer 24

fibroblasts

Question 25

why does the connective tissue proteins Strength increase with age?

Answer 25

cross-lniking of proteins

Question 26

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

Answer 26

partial hydrolysis --> weakens the network

Question 27

what happens at the different temperatures while Cooking meat?

Answer 27

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

Question 28

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

Answer 28

expand and gelatinize

Question 29

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

Answer 29

contraction

Question 30

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

Answer 30

* 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

Question 31

how is Emulsification done in emulsion sausages?

Answer 31

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

Question 32

why does Addition of salt increases protein solubility?

Answer 32

water holding capacity increases

Question 33

Why do we eat fish?

Answer 33

* 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

Question 34

what is the Myotome

Answer 34

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

Question 35

what happens After catch of fish?

Answer 35

* 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

Question 36

what is present in In salt water fish?

Answer 36

* 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

Question 37

what can bacteria convert trimethylaminoxide to after catch of fish?

Answer 37

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

Question 38

what are the Fish processing steps?

Answer 38

* salting * drying * smoking * fermentation * freezing (today the most important)

Question 39

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

Answer 39

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

Question 40

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

Answer 40

* 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

Question 41

what are some Chemical and biological contaminants in fish?

Answer 41

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)