![•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.](https://image.slidesharecdn.com/3-221029112813-9d816e18/85/3-1-Postmortem-changes-1-pdf-22-320.jpg)
3.1 Postmortem changes - 1.pdf
- 1. POST-MORTEM CHANGES IN FISH (Sensory changes, Rigor Mortis and Autolysis)
- 2. Learning objectives • Examine the post harvest changes in fish – Postmortem changes • Intrinsic – Rigor mortis – Autolysis • Extrinsic
- 3. 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 • Biochemical characteristics that influence autolysis, rapid microbial proliferation and spoilage are – Low glycogen – High unsaturated lipids – Soluble nitrogen compds – 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
- 4. 4 Sensory changes Post-mortem changes PUTRID FRESH FLAT SWEET/STALE Microbial spoilage Lipid oxidation AUTOLYSIS Catch-bleeding-gutting Blood circulation stops Glycogen Lactic acid ATP falls pH falls Rigor mortis Enzymes activated Resolution of rigor and autolysis Microorganisms Spoilage
- 5. Postmortem changes • Live fish muscle is relaxed and elastic • Immediately after death, rigor mortis sets in – 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. The fish remains rigid for a period which can vary from an hour or so to three days, depending on a number of factors described later, and then the muscles soften again. – occurs due to changes in the physiology of muscles when aerobic respiration ceases
- 6. • Fish muscle has a low glycogen reserve and trimethylamine oxide is efficient at buffering against acidity so that the ultimate pH at the end of rigor is pH 6.4-6.8 – Trimethyl amine oxide (40-120mg/kg fresh), reduced after death by bacteria to “fishy” smelling trimethylamine (high in sea fish) – Fish muscle autolysis is low due to • Low proteinases; cathepsin have low pH optimum at 4.3 – Not active at fish muscle pH 6-7 • Seasonal changes such as spawning, feeding cycle, degree of struggle during capture, etc. affect the post-mortem condition of the fish. • The pH of the flesh influences fish quality, for example, frozen fish defects include “gaping”, brown discoloration, and shrinkage which results in “drip” formation and toughening – Gaping is separation of muscle bundles in fish fillets giving them a ragged appearance
- 7. PRE-RIGOR MORTIS • Live 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 • Low glycogen in muscles contributes to small pH drop – pH 6.2 is maintained (fresh: pH 6.0-6.5) – 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 were allowed to interact and bond together • but the bonding is prevented by the presence of substances that keep the muscle pliable • Fish exhausted by lengthy struggle (stress prior slaughter) give meat poor texture and a low keeping quality – Rigor mortis duration is shortened • pH remains high • Muscle type makes maturation time shorter • Factors highly favorable for rapid spoilage are; – Structure of muscle – Tendency to generate alkaline pH rxn in muscle – High probability of microbial infection during fishing and dressing
- 8. RIGOR-MORTIS • Rigor mortis is shorter in cold-blooded (hours-a day) animals • Duration of rigor mortis depends on species, tempt, and condition of fish when caught – Stiffness is delayed when caught and put on ice immediately and stay chilled • However freshness is extended, as bacterial spoilage only occur after rigor mortis has passed • Flesh that goes thru rigor mortis (stiff to relaxed muscle) has better texture and flavor • Water-holding capacity of proteins is increased – Makes flesh juicier • Freezing immediately after catch without chilling to allow rigor mortis results in tough texture • Cooking fish prior to rigor mortis also result in tough texture
- 9. 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, 18-22 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
- 10. Onset and duration of rigor mortis in various fish species Species Condition Temperature °C Time from death to onset of rigor (hours) Time from death to end of rigor (hours) Cod (Gadus morhua) Stressed 0 2-8 20-65 Stressed 10-12 1 20-30 Stressed 30 0.5 1-2 Unstressed 0 14-15 72-96 Grouper (Epinephelus malabaricus) Unstressed 2 2 18 Blue Tilapia (Areochromis aureus) Stressed 0 1 Unstressed 0 6 Tilapia (Tilapia mossanibica) small 60g Unstressed 0-2 2-9 26.5 Grenadier (Macrourus whitson) Stressed 0 <1 35-55 Anchovy (Engraulis anchoita) Stressed 0 20-30 18 Plaice (Pleuronectes platessa) Stressed 0 7-11 54-55 Coalfish (Pollachius virens) Stressed 0 18 110 Redfish (Sebastes spp.) Stressed 0 22 120 Japanese flounder (Paralichthys olivaceus) 0 3 >72 5 12 >72 10 6 72 15 6 48 20 6 24 Carp (Cyprinus carpio) 0 8 10 60 20 16 Stressed 0 1 Unstressed 0 6
- 11. 11 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 Influences of rigor mortis on fish
- 12. 12 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 b a Shrinkage of the fillets
- 13. • Rigor mortis – is a process not completely understood but thought to be related to the activation of one or more of the naturally-occurring muscle enzymes • digesting away certain components of the rigor mortis complex • 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.
- 14. AUTOLYSIS • Major processes occur during autolysis include – degradation of ATP- related compounds in a more-or-less predictable manner.
- 15. • Glycogen or fat is oxidized or "burned" by the tissue enzymes in a series of reactions to produce CO2, H2O and adenosine triphosphate (ATP). • Under anaerobic conditions, ATP may be synthesized by two other important pathways from creatine phosphate or from arginine phosphate. • •Normal pathway for the production of muscle energy (ATP) in most living teleost fish (bony finfish).
- 16. • Respiration takes place in two stages: – an anaerobic and an aerobic stage. • latter depends on the continued presence of oxygen (O2) which is only available from the circulatory system. • Most crustaceans are capable of respiring outside the aquatic environment by absorption of atmospheric oxygen for limited periods. • Note – Aerobic energy is restricted to vertebrate muscle (teleost fish) while the anaerobic is characteristic of some invertebrates such as the cephalopods (squid and octopus).
- 17. • ATP production ceases when the creatine or arginine phosphates are depleted. • Octopine is the end-product from the anaerobic metabolism of cephalopods and is not acidic (unlike lactate), – thus any changes in post mortem pH not related to the lactic acid prodn from glycogen. • Note – For most teleost fish, glycolysis is the only possible pathway for the production of energy once the heart stops beating.
- 18. • ATP is produced in glycolysis, – but only 2 moles for each mole of glucose oxidized as compared to 36 moles ATP produced for each mole of glucose if the glycolytic end products are oxidized aerobically in the mitochondrion in the living animal. • 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.
- 19. • 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).
- 20. • When intracellular Ca+2 levels are 1 µM, Ca+2 - activated ATP-ase reduces the amount of free muscle ATP which results in the interaction between the major contractile proteins, actin and myosin – (autolysis) – results in the shortening of the muscle, making it stiff and inextensible. • A fish in rigor mortis cannot normally be filleted or processed due to stiffness of carcass – Thus cannot be manipulated and is often contorted, making machine-handling impossible.
- 21. • Degradation of ATP to form – adenosine diphosphate (ADP), – adenosine monophosphate (AMP), – inosine monophosphate (IMP), – inosine (Ino)- • is a nucleoside when hypoxanthine is attached to a ribose ring (also known as a ribofuranose) via a β- N9-glycosidic – and hypoxanthine (Hx). • The degradation of ATP catabolites proceeds in the same manner with most fish – but the speed of each individual reaction (from one catabolite to another) greatly varies from one species to another • and often progresses coincidentally with the perceived level of spoilage.
- 22. •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.
- 23. • 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.
- 24. • 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.
- 25. • Figures indicate the catabolic pathway for the degradation of ATP through to inosine which is entirely due to autolytic enzymes. • Enzymes include: – ATP-ase; – myokinase; – AMP deaminase; – IMP phosphohydrolase; – nucleoside phosphorylase; – inosine nucleosidase; – xanthine oxidase.
- 26. Hx determination in certain species • Hx determination would likely not be useful for such species as swordfish and redfish.
- 27. POST-RIGOR MORTIS: • Spoilage of fish and seafood is caused by microbial, oxidative and enzymic spoilage which elicits deleterious changes in odour, flavour and texture. • Type and rate of spoilage is multifactorial. Some influences on early spoilage are: – A pH greater than 7 is optimum for bacterial and enzymic activity, for example, fish which have struggled for prolonged periods during netting operations will have a low glycogen content. – Evisceration, e.g. small pelagics are not gutted, hence proteolytic enzymes along with microorganisms rapidly invade the fish’s tissues. – Oily fish are susceptible to oxidative rancidity. – Cold water species of fish, which have a microflora of psychrophilic bacteria, are predisposed to earlier spoilage under chill conditions.
- 28. 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 proteins, peptides 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
- 29. CONCLUSION • Issue – Post – harvest physical handling (is important) • accelerates the autolytic changes in chilled fish. – Systems for conveying fish and for discharge from the vessels must be designed • so as to avoid physical damage to the delicate tissues. – Iced fish should never be stored in boxes deeper than 30 cm and that fish boxes are not permitted to "nest" one on top of the other • in order to minimize autolysis and extend rigor