By

Dr.Atcharaporn Khoomtong

Content

Introduction

Fish muscle

Fundamentals of Freezing and Thawing of fishes and seafood

Quality-related changes in frozen fish muscle

The length of storage time for fish

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Know about fish

Pelagic fish are fish that live in surface / center, not at the bottom, generally consisting of small-sized fish such as anchovies, mackerel, and other screens.

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Know about fish (Cont’)

Demersal fish, such as cod, haddock and pollock, and flatfishes live near or at the bottom of the seas. They feed mostly on other fish and organisms.

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Fish muscle

Major composition

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Let you know about TMAO

TMAO is formed by biosynthesis in certain zooplankton species.

These organisms possess an enzyme (TMA mono-oxygenase) which oxidizes TMA to TMAO.

TMA is commonly found in marine plants as are many other methylated amines (monomethylamine and dimethylamine).

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Structure of fish muscle Fish muscle is composed

of striated muscle fibers arranged in a parallel, longitudinal shape.

Fish has muscle cells running in parallel and connected to sheaths of connective tissue (myocommata), which are anchored to the skeleton and the skin. The bundles of parallel muscle cells are called myotomes

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Post mortem changes in fish muscle

Directly after death of the fish, a series of biochemical reactions starts, which is importance for the quality and shelf life of products. It’s depend on

The type of fish species,

The physiological condition of the fish,

The environmental influences (for example water temperature, salinity) the living fish

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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

bio

chem

ical

rea

ctio

ns

Source from, Huss (1995)

Freezing and Thawing of fishes

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Fundamentals of Freezing of fishes

General Freezing temperature

Use temperature < 32 F (0° C)

Change in water from liquid to solid.

General Freezing theory lower temperature. Will reduce spoilage. Water is unavailable for microorganisms

and chemical reactions.

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FREEZING/SUPERFREEZING OF FISH

Freezing is the process by which temperatures of fish or seafood are reduced to -20oC

Super freezing is the process by which temperatures of fish are mechanically reduced to -40oC

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Freezing point depression

In fish muscle the freezing point is depressed below that of pure water because of small solutes present in the muscle water.

The freezing point is often referred to as ‘the equilibrium freezing point’

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In pre-rigor muscle, the cell fluids are associated to intra-cellular proteins and the diffusivity from inside to outside the cell is therefore limited resulting in the formation of the intracellular ice crystals independent of freezing rate.

If very slow freezing rates are used the muscle can go into rigor mortis during the freezing process, and ice crystal formation will then be extra-cellular

Ice crystal formation in pre- and post-rigor muscle

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(Love, 1970).

Thawing is the process of changing the state of a product from frozen to unfrozen.

It involves transferring “heat” to a frozen product to melt the ice that was formed within the flesh during the freezing process.

Like freezing, thawing should be carried out as quickly as possible to maintain the quality of the product.

Fundamentals of Thawing of fishes

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If the thawing process is carried out correctly there should be little effect on the quality of the product.

The final quality of thawed seafood will depend not only on the thawing process but also on factors such as frozen storage conditions and the length of time that it has been frozen, packaging, product form and product type.

Fundamentals of Thawing of fishes

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Over Thawing

The flesh may soften & discolor

Loss of flavor

Lower yield

Possible growth of bacteria

Possible increase in enzyme spoilage

Under Thawing

Fish may be difficult or dangerous to fillet

Poor filleting will result in a lower yield

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Quality-related changes

in frozen fish muscle

A mistake that many people make

when freezing fish and other seafood products is to assume that, once it has been frozen, it will not change.

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The quality of frozen fish or seafood is directly related to the quality of the starting material.

If the seafood you freeze is of poor quality, theseafood you thaw will be of poor quality or evenpoorer.

Care should be taken to ensure that only high-quality fish are considered for freezing.

Fish species

Temperature and Handling before slaughter

Slaughter stress

Temperature of the pre-rigor storage

Freezing rate

Frozen storage temperature and time

Thawing procedure

Prevention against oxidation (light,oxygen)

(Sørensen et al., 1995)23

Factors that effected on Quality-related changes in frozen fish muscle

Affecting protein changes in fish muscle

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Changes in lipids and fatty acids

Enzymatic breakdown of TMAO(Autolytic changes)

Dehydration and the effect of inorganic salts

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(Love, 1970)

Summarize of Protein denaturation

Changes in lipids and fatty acids

Oxidation of unsaturatedfatty acids or triglycerides in fish results in the formation of free radicalsproduced through decomposition of lipid hydroperoxides via a free-radical mechanism.

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Off flavors

andordors

Mackie, 1993

Enzymatic breakdown of TMAO(Autolytic changes)

Fishes, like cod, hake (Merluccius spp.) or Alaska pollack (Theragra chalcogramma), contain the enzyme trimethylamine oxide demethylase (TMAOase), which catalyses the cleavage of trimethylamine oxide (TMAO) into dimethylamine (DMA) and formaldehyde (FA).

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Changes in functional properties caused by protein changes

The main changes are reported to occur in myosin light-chain, but actin and actinin also degrade during frozen storage.

Some of the changes reported are increases in ß-sheet at the expense of -helix structure. As the main part of muscle water is located within the myofibrillar structure, changes in this typically result in reduced WHC.

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Reasons for Quality Loss in Frozen Fishery Products during Storage

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Source from, Huss (1995)

The length of storage time for fish in a freezer depends

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Fish species

On storage temperature,

Temperature fluctuations in the freezer,

Method of packaging and packaging materials,

Moisture and fat content of the fish and

The condition of the fish at the time of freezing.

Conclusion

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The quality of fishery products is influenced by both intrinsic and extrinsic factors. Species, size, sex, composition, toxins, contamination with pollutants, and cultivation conditions are the factors responsible for changes in intrinsic quality.

The biochemical characteristics of fish muscle such as low collagen, comparatively higher contents of unsaturated lipids as well as soluble nitrogen compounds influence autolysis, rapid microbial proliferation, and spoilage.

Low-temperature processing, including freezing, is probably the most widely used method to slow safety and quality deterioration of aquatic foods.

References

Aubourg, S.P. and Medina, I. (1999). Journal of the Science of Food and Agriculture, 79(13):1943-1948.

Cappeln, G., Nielsen, J., and Jessen, F. (1999). Journal of the Science of Food andAgriculture, 79(8): 1099-1104.

Huss, H.H.(1995).Quality and quality changes in fresh fish.FAO Fisheries Technical paper 348. Rome,Italy.195 p.

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…..ETC…….

THANK YOU FOR YOUR ATTENTION

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