By

Ms.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

ch

em

ical re

acti

on

s

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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18

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, the

seafood you thaw will be of poor quality or even

poorer.

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)

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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 unsaturated

fatty acids or triglycerides

in fish results in the

formation of free radicals

produced through

decomposition of lipid

hydroperoxides via a free-

radical mechanism.

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Off

flavors

and

ordors

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 and

Agriculture, 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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