what is Seafood spoilage ?
Physical or biochemical deterioration of breakdown of tissue makes the fish unfit for
human consumption
Fish is highly perishable. Why?
All the food commodities are perishable. But fish is highly perishable. Because High moisture
• Low glycogen reservoir leads to postmortem pH near neutral favors the
Microbial growth
• Low connective tissue makes the major protein more susceptible to proteolytic
degradation
• Highly unsaturated fatty acids more prone to oxidation
• High content of non protein nitrogenous compounds
What are all the causes of seafood spoilage and intrinsic characteristics of fish
that supports the causes?
Note: Other animals’ meat have post mortem pH in acid range, compared
to fish muscle and high connective tissue content delay the degradation of
protein by endogenous proteases as well as secreted from bacterial origin.
Fish preservation
To prevent spoilage of fish, some form of preservation is necessary.
What is preservation?
Preservation means keeping the fish, after it has landed, in a condition whole some
and fit for human consumption for a period ranging from days to months depending
upon type of preservation.
What are all the fish preservation methods available?
Some of the preservation methods commonly employed in fish preservation are
listed below
• Chilling
• Freezing
• MAP
• Curing (drying, salting and smoking)
• Canning and Retort pouch packaging
• Marinating
• Boiling
• Fermentation
• Irradiation
• Freeze-drying
1.5. Fish preservation methods and principles
At present different methods are used to preserve the fish and fishery
products based on the desirable end product properties. Most commonly
used fish preservation methods are; chilling, freezing, curing (drying, salting
and smoking), canningatmospheric packaging, retort pouch packaging are also used for
preserving fish.
Chilling
Preservation by chilling is mainly due to the lowering of the temperature of
the fish as low as possible (near to 0oC) to delay both biochemical and
microbiological processes. With the lowering temperature the lag period of
microorganisms will be extended, resulting in delayed growth. The lower
the fish temperature, the low will be the activity of enzymes and
microorganisms.
1.5.2. Freezing
In freezing along with the effect of low temperature, mechanical rupture of
bacterial cells during ice formation, freezing out of the major fraction of
water in substrate also contributes to the death of microorganisms, thus by
extending shelf life. The lower the fish temperature, the low will be the
activity of enzymes and microorganisms. The oxidative rancidity problem is
controlled by glazing the product before freezing.
1.5.3. MAP (Modified Atmospheric Packaging)
The preservation in MAP is by retarding the growth of microorganisms by
changing the gaseous composition of the environment, thus by creating
unfavorable conditions for microbial growth (mainly due to the effect of
carbon dioxide on microorganisms) and by avoiding the lipid oxidation.
1.5.5. Canning and Retort pouch packaging
The preservative effect in both the cases is mainly by subjecting the
products in hermetically sealed containers / pouches, to high temperatures
in order to bring the commercial sterility, where most of the microorganisms
cannot survive, except highly heat stable spore formers. In this method the
products are heated to high temperatures (121oC) for certain time with the
intention of achieving commercial sterility to avoid the risk of pathogens
and toxins, mainly Clostridium botulinum, which is a high heat resistant
spore forming and toxin producing bacteria occurs in canned foods.
1.5.6. Marinating
The marinades are preserved by keeping them in acid medium (acetic acid
and propionic acid) containing salt at a pH 4.5. At a pH 4.5 or below most
of the spoilage causing and all food poisoning bacterial growth is arrested,
resulting in a product with a characteristic flavor and an extended but
limited shelf life. Acetic acid controls the pH and selectively allows the autolytic reactions to take place. The salt (sodium chloride) causes the
removal of water and coagulates the protein. It also controls the hydrolytic
action and allows it to proceed within desired limits. However some
bacteria and enzymes will remain active and cause spoilage, which can be
slow down by storing at low temperatures (below 10oC). The amounts of
acid and salt required can be reduced when the product is kept chilled until
eaten.
1.5.7. Boiling
The action of boiling fish in water at normal temperatures and pressures
denatures (cooks) the proteins and enzymes and kills many of the bacteria
present on the fish. The normal spoilage that occurs in a dead fish is thus
stopped or drastically reduced. Often salt is added before, during or after
processing; high levels of salt in the final product will help to extend the
shelf life.
1.5.8. Fermentation
The fermentation processes are those in which organic catalysts (enzymes
or ferments) break down complex organic molecules to simpler ones. Many
of the processes used in fish preservation aim at keeping the fish flesh as
near as possible to its original condition. With fermentation, however, we
are considering methods by which the wet protein is broken down to
simpler substances which are themselves stable at normal temperatures. In
some of the processes we shall be considering, breakdown is only partial
and is controlled by the addition of salt; thus the process is designed to
produce a particular flavour as well as to preserve the product.
1.5.9.Irradiation
Food irradiation is the process for the treatment of food products to
enhance their shelf life and to improve microbial safety. Electromagnetic
radiations, namely gamma, and X-rays having short wavelength (< 300 µm)
and higher energy than visible light can significantly penetrate the material
including foods causing ionization of atoms and molecules by removing
electrons from their outer shell. The inactivation of living cells (microbial
cells) by irradiation is essentially due to scission of single or double strands
of DNA, which is essentially caused by the OH radical formed by radiolysis
of water. In addition to DNA damage, ionizing radiation has also been
shown to cause damage to the membrane and other structures causing
sub-lethal injury Freeze-drying
Freeze drying is a dehydration process typically used to preserve a
perishable material or make the material more convenient for transport.
Freeze-drying works by freezing the material and then reducing the
surrounding pressure to allow the frozen water in the material to sublimate
directly from the solid phase to the gas phase (i.e., it does not transit
through the liquid state) under vacuum. Freeze-drying benefits heatsensitive products by dehydrating in the frozen state without intermediate
thaw. Freeze-drying of meat yields a product of excellent stability, which on
rehydration closely resembles fresh meat. Adequate control of processing
conditions contributes to satisfactory rehydration, with substantial retention
of nutrient, colour, flavour, and texture characteristics
1.5.11.Hurdle technology
Hurdle technology (also called combined methods, combined processes,
combination preservation, combination techniques or barrier technology)
advocates the deliberate combination of existing and novel preservation
techniques in order to establish a series of preservative factors (hurdles)
that any microorganisms should not be able to overcome.
Summary
Fish is rich source of good quality protein and health promoting
polyunsaturated fatty acids. Due to low connective tissue, near neutral pH,
highly unsaturated fatty acids, fish is more prone to bacterial, enzymatic
and oxidative spoilage. In general thermal (low or high), non-thermal and
combination of various preservative methods employed in fish preservation.
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