Meat Processing Flashcards
Collagen
Most abundant protein in multicellular animals
Extra-cellular glycol-protein organised into fibres
High tensile strength
Stress and load bearing
Collagen structure
Triple helix
33% glycine
15-30% proline
Sugars are bound to amino acid residues
Collagen synthesis
Polypeptide synthesis Hydroxylation of lysine and proline (Needs vitamins C) Glycolysation Triple helix forms Secrete from cells in soluble form Mature into fibre bundles
Hydroxylation
Peptide chain formation
Glycosylated
Forming a triple helix
Hydroxylysine
Cross link
Collagen Degradation
When heated to 60 degrees collagen fibrils are degraded to constituent molecule
Forms sol in water
Most stable below 30 degrees
Myoglobin
Myoglobin is a haem protein
Absorbs oxygen from blood and stores in muscle
When muscle needs more O2 it released from myoglobin
Myoglobin and cooking
When myoglobin is heated it denatures
Changes texture and colour of muscle
Beef most tender if heated to 65 degrees
Purpose of curing meat
Store meat at ambient temperature
Curing meat process
Immersed in brine
24% NaCl
0.3% NaNO3
0.1% NaNO2
NaCl and curing meat
2-6% in final product
Increases water holding capacity of cells
Reducing water activity
Inhibit microbial growth
NaNo3 and curing meat
Added as additional preservative
When O2 is low it can transfer NO3 to NO2
NaNO2 and curing meat
Active curing agent
Strong oxidant
Inhibits microbial growth of anaerobic bacteria
How does NaNO2 inhibit microbial growth
Oxidises Deoxymyoglobin to make metmyoglobin
Metmyoglobin reacts with nitrite to nitrosyl myoglobin
Nitrite breaks down to produce NO
NO forms with nitrite which may react with non-haem protein to form nitroso derivatives (N-nitrosamines)
Cancer risk and cured meat
Concerned about N-nitrosamines
But have developed a way to minimise there formation.
Reduction of the use of nitrite and nitrate and start using increased amount of ascorbic acid
But risk of N-nitrosamines is less than anaerobic bacteria that could grow in meat
Salt Detection
Ion channel that allows Na+ ions to enter cell generate taste
ENaC
Salt taste
Na+
K+ and Li+
Enhances other tastes
Prevent sodium deficiency but too much has aversive taste
Muscle protein structure
Thick and thin filaments organised into repeating units called sarcomeres
Light and Dark Zones with ends that overlap
Light band - hexagonally arranged thin filaments
Dark zone contain only hexagonally arranged thick filaments
Muscle contraction
Electric stimulus from nerve fibre
Release Ca2+ into muscle
ATP bind to thick filament
Ca2+ binds to thin filament exposing a binding site
ATP hydrolysis -> Conformational change, pulls thin filament toward centre of sarcomere
ADP+Pi released
Muscle contracts
Repeats till no more Ca2+ or ATP can not be regenerated
ATP regeneration
Creatine phosphate
Glucose from glycogen
Aerobic respiration
Anaerobic respiration
Anaerobic respiration and death
Anaerobic respiration continuous after death till pH fall below 5.4
Post-Mortem Changes
Low temperature inhibits membrane pump that removes Ca2+
causing contraction as long as ATP is present and pH above 6
When Ca2+ is always present will continue until ATP not join
Once ATP is used muscle becomes locked (Rigor mortis)
Muscle is now shortened, hardened and difficult to chew
If can keep muscle extended then get a tender meat
How to extend muscle after death
Do not chill while ATP us present
Slow cooling reduce 15-20 degrees for 10 hours
This allows ATP to be used while Ca2+ pump is still active
But it is good conditions for micro-organisms to grow to needs to be good hygiene conditions
Lean muscle composition
75% water
21% protein
3% fat
Bound water and meat
Water molecules that are interacting directly with charge side chains on protein
Intermediate water and meat
Water molecules that are bound to bound water molecules
Free water and meat
Not interacting with protein or held via surface tension
Water in meat and colour
Excess free water - wet surface and cut muscle reflects light and looks pale
Isoelectric point of Meat
approximately 5.2
Amount of bound and intermediate water minimized at this pH and free water maximised
As pH increases or decreases around this point water holding capacity increases
Pale, Soft and exudative Meat
PSE
Excessive formation of lactic acid
Short term stress - adrenalin causes glycogen to release large amount of water
Caused by rough handling or washing before slaughter
Dark, firm and dry Meat
DFD
Depletion of glycogen stores before death So no glucose - pH above 6 Exhaustion Long transport before slaughter Prolonged stress
Hanging meat
Purpose to improve meat quality
Allow endogenous protease in cells to partially degrade muscle sarcomeres and collagen
Hanging method
Remove intestines and skin Store for 2 or more weeks Keep temp at 2-3 degrees - bacteria growth slow but enzymes still active Control humidity to 85% No oxygen in meat
