Meat Processing

Question 1

Collagen

Answer 1

Most abundant protein in multicellular animals
Extra-cellular glycol-protein organised into fibres
High tensile strength
Stress and load bearing

Question 2

Collagen structure

Answer 2

Triple helix
33% glycine
15-30% proline
Sugars are bound to amino acid residues

Question 3

Collagen synthesis

Answer 3

Polypeptide synthesis
Hydroxylation of lysine and proline
(Needs vitamins C)
Glycolysation 
Triple helix forms
Secrete from cells in soluble form
Mature into fibre bundles

Question 4

Hydroxylation

Answer 4

Peptide chain formation

Question 5

Glycosylated

Answer 5

Forming a triple helix

Question 6

Hydroxylysine

Answer 6

Cross link

Question 7

Collagen Degradation

Answer 7

When heated to 60 degrees collagen fibrils are degraded to constituent molecule
Forms sol in water

Most stable below 30 degrees

Question 8

Myoglobin

Answer 8

Myoglobin is a haem protein
Absorbs oxygen from blood and stores in muscle
When muscle needs more O2 it released from myoglobin

Question 9

Myoglobin and cooking

Answer 9

When myoglobin is heated it denatures
Changes texture and colour of muscle
Beef most tender if heated to 65 degrees

Question 10

Purpose of curing meat

Answer 10

Store meat at ambient temperature

Question 11

Curing meat process

Answer 11

Immersed in brine
24% NaCl
0.3% NaNO3
0.1% NaNO2

Question 12

NaCl and curing meat

Answer 12

2-6% in final product
Increases water holding capacity of cells
Reducing water activity
Inhibit microbial growth

Question 13

NaNo3 and curing meat

Answer 13

Added as additional preservative

When O2 is low it can transfer NO3 to NO2

Question 14

NaNO2 and curing meat

Answer 14

Active curing agent
Strong oxidant
Inhibits microbial growth of anaerobic bacteria

Question 15

How does NaNO2 inhibit microbial growth

Answer 15

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)

Question 16

Cancer risk and cured meat

Answer 16

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

Question 17

Salt Detection

Answer 17

Ion channel that allows Na+ ions to enter cell generate taste
ENaC

Question 18

Salt taste

Answer 18

Na+
K+ and Li+
Enhances other tastes
Prevent sodium deficiency but too much has aversive taste

Question 19

Muscle protein structure

Answer 19

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

Question 20

Muscle contraction

Answer 20

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

Question 21

ATP regeneration

Answer 21

Creatine phosphate
Glucose from glycogen
Aerobic respiration
Anaerobic respiration

Question 22

Anaerobic respiration and death

Answer 22

Anaerobic respiration continuous after death till pH fall below 5.4

Question 23

Post-Mortem Changes

Answer 23

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

Question 24

How to extend muscle after death

Answer 24

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

Question 25

Lean muscle composition

Answer 25

75% water
21% protein
3% fat

Question 26

Bound water and meat

Answer 26

Water molecules that are interacting directly with charge side chains on protein

Question 27

Intermediate water and meat

Answer 27

Water molecules that are bound to bound water molecules

Question 28

Free water and meat

Answer 28

Not interacting with protein or held via surface tension

Question 29

Water in meat and colour

Answer 29

Excess free water - wet surface and cut muscle reflects light and looks pale

Question 30

Isoelectric point of Meat

Answer 30

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

Question 31

Pale, Soft and exudative Meat

PSE

Answer 31

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

Question 32

Dark, firm and dry Meat

DFD

Answer 32

Depletion of glycogen stores before death
So no glucose - pH above 6
Exhaustion
Long transport before slaughter
Prolonged stress

Question 33

Hanging meat

Answer 33

Purpose to improve meat quality

Allow endogenous protease in cells to partially degrade muscle sarcomeres and collagen

Question 34

Hanging method

Answer 34

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