1. POST-MORTEM CHANGES IN FISH (Sensory changes, Rigor Mortis and Autolysis)

2. Post-harvest changes
Quality of harvested fish depends on these factors
Intrinsic
Species, size, sex, composition, spawning, presence of parasites, toxins, contaminants with pollutants and cultivation
Extrinsic
Location of catch, season, methods of actch (gill net, handline, longline, or trap, etc), on-board handling, hygienic conditions of f/vessel, processing and storage conditions

3. Sensory changes Post-mortem changes FRESH Microbial spoilage
Catch-bleeding-gutting
Post-mortem changes
FRESH
Blood circulation stops
Glycogen
Lactic acid
ATP falls
pH falls
AUTOLYSIS
Rigor mortis
Enzymes activated
(Ref 2. Quality and quality changes in fresh fish (chapter 5))
Overview of post mortem changes (autolysis, microbial activity and lipid oxidation) that influence sensory characteristics.
Onset, duration and resolution of rigor mortis is affected by
species /size /temperature /handling
physical condition of the fish
catching and killing methods
Michanism
Anaerobic pathway (Glycolysis) : 1 Glucose > ATP
Aerobic pathway : 1 Glucose > ATP
Resolution of rigor and autolysis
FLAT
Microbial spoilage
SWEET/STALE
Microorganisms
Lipid oxidation
PUTRID
Spoilage

4. Postmortem changes
1. Pre rigor - Live fish muscle is relaxed and elastic
2, In rigor -stiffening of fish muscle
- rigor in fish usually starts at the tail, and the muscles harden gradually along the body towards the head until the whole fish is quite stiff. Rigor remains for an hour to 3 days depending on number of factors.
3. Post- Rigor mortis - relaxed and elastic
but the freshness of fish starts deterioting

5. Biochemical changes in live fish and after death of fish
Cycles of chemical changes take place continuously in the muscle
these provide energy for the muscle while the fish is swimming, and also produce substances necessary for growth and replacement of worn-out tissue.
enzymes are compounds that bring about, and control, these changes
The enzymes in the flesh go on working even after the fish is dead
some of them act on those substances that normally keep the muscle pliable and lifelike.
During life, the muscle contract and become rigid if its two main protein components (Actin and myosin) were allowed to interact and bond together
but the bonding is prevented by the presence of oxygen that keep the muscle pliable
Death Fish: Immediately after the death of fish, stiffening of muscle occurs. The process of stiffening of fish muscle after death of fish is known as RIGOR MORTIS

6. HOW RIGOR OCCUR
1.Death of fish post mortem 2. Calcium released from the cell 3. Calcium activates ATPase 4. ATPase activates ATP to break down to ADP and further compunds 5. In the process of ATP breakdown to ADP, energy is released. 6. This chemical energy is converted to mechanical energy. 7. This mechanical energy pushes the two major protein in fish muscle (Actin and Myosin) to produce Actomyosin which results in the stiffening of fish known as RIGOR MORTIS.

7. Factor for on set of rigor mortis
Species:
Some species take longer than others to go into rigor, due to differences in their chemical composition.
E.g. Whiting go into rigor very quickly and may be completely stiff one hour after death, whereas redfish stored under the same conditions may take as long as 22 hours to develop full rigor.
Trawled codling, inches long, gutted and stored in ice, usually take 2-8 hours to go into rigor.
Condition:
The poorer the physical condition of a fish, that is the less well nourished it is before capture, the shorter will be the time it takes to go into rigor; this is because there is very little reserve of energy in the muscle to keep it pliable. Fish that are spent after spawning are an example.
Degree of exhaustion:
In the same way, fish that have struggled in the net for a long time before they are hauled aboard and gutted will have much less reserve of energy than those that entered the net just before hauling, and thus will go into rigor more quickly.
Size:
Small fish usually go into rigor faster than large fish of the same species.
Handling:
Manipulation of pre-rigor fish does not appear to affect the time of onset of rigor, but manipulation, or flexing, of the fish while in rigor can shorten the time they remain stiff.
Temperature:
The most important factor governing the time a fish takes to go into, and pass through, rigor because the temperature at which the fish is kept can be controlled.
The warmer the fish, the sooner it will go into rigor and pass through rigor.
E.g gutted cod kept at 32-35°F may take about 60 hours to pass through rigor, whereas the same fish kept at 87°F may take less than 2 hours.
Tempt difference between water and storage of fish
> difference – the shorter time of death to rigor mortis

8. Onset and duration of rigor mortis in various fish species
Condition
Temperature °C
Time from death to onset of rigor (hours)
Time from death to end of rigor (hours)
Cod (Gadus morhua)
Stressed
2-8
20-65
10-12 1
20-30 30
0.5
1-2
Unstressed
14-15
72-96
Grouper (Epinephelus malabaricus) 2 18
Blue Tilapia (Areochromis aureus) 6
Tilapia (Tilapia mossanibica) small 60g
0-2
2-9
26.5
Grenadier (Macrourus whitson)
<1
35-55
Anchovy (Engraulis anchoita)
Plaice (Pleuronectes platessa)
7-11
54-55
Coalfish (Pollachius virens)
110
Redfish (Sebastes spp.) 22
120
Japanese flounder (Paralichthys olivaceus) 3
>72 5 12 10 72 15 48 20 24
Carp (Cyprinus carpio) 8 60 16

9. Influences of rigor mortis on fish
General influence of rigor on fish is that it makes the fish stiffen
Rigor mortis does not affect whole fish that is iced on board and during transportation to the factory.
This is because rigor mortis has passed during holding in ice on board and transportation to the factory.
Factors affecting Rigor Mortis
Method used for stunning and killing
Temperature
Stunning and killing hypothermia (the fish is killed in iced water) give the fastest onset of rigor, while a blow on the head gives a delay of up to 18 hours

10. Shrinkage of the fillets
The shape of the fillets becomes distorted and the surface of the flesh takes on a corrupted appearance
a-The fillet is cut off before rigor mortis => the length is reduced 24 %
b-The fillet is cut off after rigor mortis => the length is reduced a little bit a b

11. The softening of the muscle during resolution of rigor mortis (and eventually spoilage processes) is coincidental with the autolytic changes
rigor mortis occur simultaneously with autolysis
Autolysis is "self-digestion"
contributes to varying degrees to the overall quality loss in addition to microbially-mediated processes.

12. AUTOLYSIS Major processes occur during autolysis include
degradation of ATP-related compounds in a more-or-less predictable manner.

13. AUTOLYSIS
Immediately after death of fish, enzymes start to react and break down products. This is known as "Self Digestion" or Autolysis. Example: Protein → Simple amino acid Further breakdown of simple amino acid by bacteria to higher amino acids will result in the spoilage of fish.

14. the muscle enters rigor mortis.
After death, the anaerobic muscle cannot maintain its normal level of ATP, and when the intracellular level declines from 7-10 µmoles/g to 1.0 µmoles/g tissue,
the muscle enters rigor mortis.

15. Rigor mortis sets in when the muscle ATP level drops to 1.0 µmoles/g.
ATP is not only a source of high energy which is required for muscle contraction in the living animal
but also acts as a muscle plasticizer.
Muscle contraction is controlled by
calcium and an enzyme; ATP-ase (found in muscle cells).

16. Saito et al. (1959) were the first to observe rigor mortis process and to develop a formula for fish freshness based on these autolytic changes:
where [ATP], [ADP], [AMP], [IMP], [Ino] and [Hx] represent the relative concentrations of these compounds in fish muscle measured at various times during chilled storage.

17. The K or "freshness" index gives a relative freshness rating based primarily on the autolytic changes which take place during post mortem storage of the muscle.
Thus, the higher the K value, the lower the freshness level.

18. Note : It is now widely accepted
IMP (inosine monophosphate)
is responsible for the desirable fresh fish flavour which is only present in top quality seafood.
Hx (hypoxanthine)
is considered to have a direct effect on the perceived bitter off-flavour of spoiled fish
ATP loss is associated with rigor mortis.

19. Summary of Autolytic Changes in Chilled Fish
Enzyme(s)
Substrate
Changes Encountered
Prevention/Inhibition
glycolytic enzymes
glycogen
production of lactic acid, pH of tissue drops, loss of water-holding capacity in muscle
high temperature rigor may result in gaping
fish should be allowed to pass through rigor at temperatures as close to 0°C as practically possible
pre-rigor stress must be avoided
autolytic enzymes, involved in nucleotide breakdown
ATP    ADP    AMP    IMP
loss of fresh fish flavour, gradual production of  bitternes with Hx (later stages)
same as above
rough handling or crushing accelerates breakdown
cathepsins
proteins, peptides
softening of tissue making processing difficult or impossible
rough handling during storage and discharge
chymotrypsin, trypsin, carboxy-peptidases
autolysis of visceral cavity in pelagics (belly- bursting)
problem increased with freezing/thawing or long- term chill storage
calpain
myofibrillar proteins
softening, molt-induced softening in crustaceans
removal of calcium thus preventing activation?
collagenases
connective tissue
gaping" of fillets
softening
connective tissue degradation related to time and temperature of chilled storage
TMAO demethylase
TMAO
formaldehyde-induced toughening of frozen gadoid fish
store fish at temperature <= -30°C
physical abuse and freezing/thawing accelerate formaldehyde-induced toughening