1. 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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2. 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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3. 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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4. 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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5. 9
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
biochemicalreactions
Source from, Huss (1995)
Freezing and Thawing of fishes
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6. 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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7. 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).

8.  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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9. 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

10. 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.

11. 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.

12.  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

13. 25
(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

14. 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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15. 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.

16. 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…….

17. THANK YOU FOR YOUR ATTENTION
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