lec 10 animal tissue foods: meat and fish Flashcards
what types of meat are there?
Red meat: Lamb/Mutton, pork, beef, game
White meat: Fowl
what pros are there with meat?
- 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
what cons are there with meat?
- Environmental issues
- Feed conversion/Water consumption
- Animal welfare
- Health drawbacks with red meat and meat products?
What is meat?
- 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
describe Muscle cells (muscle fibres)
- 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
what are The muscle fibre built up of?
by myofibrils
what is a Sarcomer?
Smallest contractile unit of the muscle
* Contracts when the muscle is working
explain how Muscle contraction works?
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
how much Energy (ATP) is obtained trough oxidation of glycogen (or fat)?
- complete metabolism: 36 ATP/glucose unit
- lack of oxygen – anaerobic glycolysis: 2 ATP/glucose unit and also lactate
what are the three protein groups?
Sacroplasmic (water soluble)
Myofibrillar(salt soluble)
Stromal (connective tissue)(neither water or salt soluble)
what happens post mortem when blood is removed?
- Stops oxygen supply to the muscle
- Anaerobic metabolism -> lactate -> pH decrease
- Respiration stops
- Glycolysis inhibited at pH 5.5
- Glycogen is depleted
what happens when No more ATP is generated?
- actin-myosin complex can not dissociate -> rigor mortis
What is rigor mortis and when is it released?
- rigor mortis is released after approx. 48h due to cleavage of the actin at the z-line
- Rigor mortis causes contraction of the muscles
why are carcasses stored hanging?
for stretching of muscles
how is Tenderizing of muscle done?
- low pH -> gradual denaturation of myofibrillar proteins-> increased susceptibility to proteolytic enzymes
- low pH -> activation of proteolytic enzymes
how is the Creation of flavour accomplished?
- 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.
give a sumamry of the post mortem processes
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
what happens to the quality if glycolysis is Too rapid Post mortem?
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!
what happens to the quality if Glycogen depots are empty Post mortem?
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”)
Cooling after slaughter is crucial for
meat quality, how long should this go on for?
- Normally up to 24h before the end temperature is reached (7°C)
- pH decreases from lactic acid production
what happens If cooling is too rapid?
- 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
what are Fat depots in meat?
- Subcutanious fat - triglycerides
- tallow – beef and mutton
- lard – pork
- Most prevalent fatty acids: palmitic, stearic and oleic acid
- inter muscular fat
- intra muscular fat
what are the Connective tissue proteins in meat?
Collagen and elastin
Supportive tissue in the muscle
Elastin (elastic) and collagen (tough) -> mesh-like network
where are Extracellular proteins generated from
fibroblasts
why does the connective tissue proteins Strength increase with age?
cross-lniking of proteins
Connective tissue-rich meat is typically heat treated for a long time, what happens then?
partial hydrolysis –> weakens the network
what happens at the different temperatures while Cooking meat?
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
what happens when Denaturation of actin and sarcoplasmic proteins (globular
proteins occur?
expand and gelatinize
what happens when Denaturation of collagen and myosin (fibrous proteins) occurs?
contraction
what is the difference in beef Tenderness Pre rigor and post rigor?
- 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
how is Emulsification done in emulsion sausages?
- Fat is emulsified in a continous phase of muscle tissue through grinding and mixing
- Proteins and supra-molecular protein structures act as emulsfiers
why does Addition of salt increases protein solubility?
water holding capacity
increases
Why do we eat fish?
- 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
what is the Myotome
Myotome consists of muscle cells (myomeres) in fish
* Size of muscel cells increases with age – number of cells does not increase
what happens After catch of fish?
- 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
what is present in In salt water fish?
- 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
what can bacteria convert trimethylaminoxide to after catch of fish?
trimethylamine
Trimethylamine has very low odor threshold: ~ 600 PPB (for comparison: ammonia ~ 110 000 PPB)
* Causes ”fishy” smell
what are the Fish processing steps?
- salting
- drying
- smoking
- fermentation
- freezing (today the most important)
why should Freezing be performed after rigor (24-48h on ice)?
to avoid muscles to be frozen in contracted (short) state-> avoid water loss upon thawing
* Rapid freezing and rapid thawing -> minimizing tissue damage
why is Fish tissue is more sensitive to heating than meat?
- 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
what are some Chemical and biological contaminants in fish?
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)
