Chapter 3

Fish Processing Methods: Orientation

Dr. Bindu. J.
Fish Processing Division
ICAR-Central Institute of Fisheries Technology

Introduction

Research on food processing have attracted more due to huge demand in supply of healthy and
safe food products. Health, nutrition and convenience are the major factors driving the global food
industry in this era. Fish products have attracted considerable attention as a source of high amounts of
important nutritional Components like high-quality protein, essential vitamins, minerals and healthful
polyunsaturated fatty acids to the human diet. As a result of this the fresh fish and seafood's rank third
among the food categories with the fastest overall growth worldwide, next to drinkable yogurt (18 %)
and fresh soup (18 %). Consumption of both freshwater and seawater fish is expected to increase in
the future. As fish is highly nutritious, it is also highly susceptible to spoilage, due to intrinsic and
extrinsic factors. Proper processing and packaging help in maintaining the eating quality of fish for
extended period. Worldwide, an array of processing and packaging methods are followed. This ranges
from a simple chilled or ice storage, salted and drying to most recent and advanced high pressure and
electromagnetic field applications, which attracts opportunities from both small scale and industrial level
entrepreneurs. Fish products in live, fresh chilled, whole cleaned, fillets steaks, battered and breaded
products, variety of dried products, smoked fish, fish sausage and traditional products are the range of
low-cost processing methods which can be readily adopted by small-scale fishers. The processing
methods like canning or heat processing, freezing, vacuum and modified atmosphere packaging,
analogue products, high pressure processing, pulsed light processing, irradiation, electromagnetic field
etc are the processing methods which requires higher investments can be adopted by large scale
entrepreneurs, apart from the above-mentioned processing methods.

Benefits of Processing
▪ Converts raw food into edible, usable and palatable form
▪ Helps in preservation and storage of perishable and semi-perishable agricultural
commodities
▪ Helps in avoiding glut in the market and reduces post-harvest losses and make the produce
available during off-season
▪ Generates employment
▪ Development of ready-to-consume convenient products which saves time for cooking
▪ Helps in improving palatability and organoleptic quality of the produce by value addition and
helps in inhibiting anti-nutritional factors
▪ Helps in easing marketing and distribution tasks
▪ Enables transportation of delicate perishable foods across long distances
▪ Makes foods safe for consumption by controlling pathogenic microorganisms
▪ Modern food processing also improves the quality of living by way of healthy foods developed
for special people who are allergic to certain ingredients, diabetic etc., who cannot consume
some common food elements
▪ Food processing can also bring nutritional and food security
▪ Provides potential for export to fetch foreign exchange

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Aim of Preservation/ Processing
Based on the perishability and the extent of preservation required, foods may be classified as:
1. Perishable foods: Those that deteriorate readily (Seafood, meat, fruits and vegetables) unless
special methods of preservation are employed.
2. Semi-perishable foods: Those that contain natural inhibitors of spoilage (root vegetables) or
those that have received some type of mild treatment which creates greater tolerance to the
environmental conditions and abuses during distribution and handling (such as pickled meat and
vegetables).
3. Non-perishable foods (shelf-stable): Those that are non-perishable at room temperature
(cereal grains, sugar, nuts). Some have been made shelf stable by suitable means (canning) or
processed to reduce their moisture content (dried fish and shellfishes, raisins). Food
preservation in the broad sense, refers to all the measures taken against any kind of spoilage in
food.

Live Fishery Products

There is a great demand for live fish and shellfishes, the world over. These products fetch
maximum price compared to all the other forms of value-added products as it maintains the freshness.
The candidate species for live transportation include high value species, cultured grouper, red snapper,
seabreams, seabass, red tilapia, reef fish, air breathing fishes, shrimp, crabs, lobster, clams, oyster
and mussels. These are normally transported in air cargo maintained at low temperature in order to
lessen the metabolic activities of the animals.

Chilled Fishery Products

Chilling is an effective method of maintaining the freshness of fish products. This normally
involves keeping fishes in melting ice or slurry ice to maintain the fish temperature around 1- 4 ºC,
which delays the enzymatic action and microbial activity, thereby extending the shelf life of the
products. Traditionally, chilling is carried out using melting ice, either flake ice or crushed block ice. Of
late, slurry ice has been introduced for chilling. A wide range of fish and shellfish products varying from
whole, headless, peeled gutted, headless gutted fish, fillets, steaks, loins, cubes can be preserved by
chilling. Shelf life of fishes from different environment has been studied by the Division extensively.
Shelf life of 12-15 days has been achieved for seerfish and black pomfret. Indian Mackerel and Indian
oil sardine had very short shelf life in ice (3-7 days), due torancidity and belly bursting. Tilapia from
freshwater and brackishwater showed significant difference in shelf life when stored in ice. The former
kept longer (14-15 days) than latter (8-10 days).

Frozen Fishery Products

Freezing is an age old practice to retain the quality and freshness of fishery products for a long
time. This involves the conversion of water present in fishery products to ice i.e., a phase change from
liquid to solid phase takes place in freezing. This retards the microbial and enzymatic action by reducing
the water available for their action. This involves exposing fish products to very low temperature (<-
350C) to enable freezing of free water and maintained at -180C till it is consumed. Plate freezing, air
blast freezing, cryogenic freezing and individual quick freezing are the methods adopted by the industry
to preserve food products.

Canning

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 Canning is a method of food preservation in which preservation is achieved by the destruction
of micro-organisms by the application of heat of food packed in a sealed container. Since the canned
foods are sufficiently cooked products and free from micro-organisms, they offer consumer safety
besides being ready to consume. Canning has the unique distinction of being an invention in the field
of food processing/ preservation whereas all other methods can be considered as adaptation of natural
processes or their modifications. Because of their very long shelf life and ready to consume feature
canned products have become very popular and a variety of food stuffs, both plant and animal origin
and their combinations are produced and distributed.
However, the fish canning industry in India is declining due to the high cost of cans. Recent
innovations like polymer coated Tin Free Steel (TFS) cans provide a cheaper alternative. Studies
conducted at CIFT showed that polyester-coated TFS cans are used for processing ready to serve fish
products, which can be stored at room temperature for long periods. The industry can utilize these cans
for processing ready to eat fish and shell fish products for both domestic and export markets. This will
help in reviving the canning industry in India.
Unit Operations in a canning process are:
1. Selection and preparation of raw material.
2. Pre-cooking / blanching
3. Filling in to containers.
4. Addition of liquid medium
5. Exhausting
6. Seaming
7. Heat Processing / Retorting
8. Cooling
9. Drying, warehousing, labelling and casing

Dried and Salted Fishery Products

Drying is probably one of the oldest methods of food preservation. It consists of removal of water
to a final desired concentration, which in turn reduces the water activity of the product, thereby assuring
microbial stability and extended shelf-life of the product. In some cases, common table salt (Sodium
chloride) is also used to prolong the shelf life of fish. Salt absorbs much of the water in the food and
makes it difficult for micro-organisms to survive.

Smoked Fishery Products

Smoking is one of the most widely used traditional fish processing methods employed in many
countries to preserve fish. The preservation effect of the smoke is a result of drying of the product
during the smoking as well as due to smoke particle absorption into the flesh. The smoke particles,
mainly phenolic compounds, carbonyl and organic acids, being absorbed by the product, inhibit
bacterial growth on the surface of the product. The smoke particles also have a positive effect on the
taste and colour of the product and in many instances, smoking is normally practiced to improve these
sensory characteristics.

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 Hot and liquid smoked fish chunks and masmin chunks

Battered and Breaded Products

The most prominent among the group of value-added products is the battered and breaded
products processed out of a variety of fish and shellfish. Battered and breaded products offer a
‘convenience’ food widely valued by the consumer. These are products, which receive a coat or two
each of a batter followed by coating with breadcrumbs, thus increasing the bulk and reducing the cost
element. The pick-up of coating can be increased by adjusting the consistency of the batter or by
repeating the coating process. By convention, such products should have a minimum fish component
of 50%. Coated products viz., fish fingers, squid rings, cuttlefish balls, fish balls and prawn burgers form
one of the major fish and shellfish-based items of trade by the ASEAN countries (Chang et al., 1996).
The production of battered and breaded fish products involves several stages. The method
varies with the type of products and pickup desired. In most cases it involves seven steps. They are
portioning/forming, pre-dusting, battering, breading, pre-frying, freezing and, packaging and cold
storage. The first commercially successful coated product is ‘fish finger; or ‘fish stick’. Later several
other products particularly the coated fish fillet, fish portions, fish cakes, fish medallions, fish nuggets,
breaded oysters and scallops, crab balls, fish balls, coated shrimp products, coated squid rings etc.
became prominent in most of the developed countries with the advent of the fast-food trade. The
present-day production of coated seafood items involves fully automated batter and breading lines
which start from portioning and end with appropriate packaging of the product. A variety of battered
and breaded products can be prepared from shrimp, squid, clams, fish fillets, minced meat from low-
cost fish etc. A brief profile of some important battered and breaded products is given below.

Fish finger or Fish portion

Fish fingers, or portions or sticks are regular sized portions cut from rectangular frozen blocks
of fish flesh. They are normally coated with batter, and then crumbed before being flash fried and
frozen. They may be packed in retail or catering - size packs. The typical British fish finger normally
weighs about 1 oz. (28 g) of which up to about 50% of the total weight may be batter and crumbs. Food
Advisory Committee of the UK government has recommended a minimum fish content of 55% for
battered and 60% for the fingers coated with breadcrumbs.
Shrimp products

Battered and breaded shrimp can be prepared from wild as well as from farmed shrimp in
different styles and forms. The most important among them are butterfly, round tail-on, peeled and
deveined (PD), nobashi (stretched shrimp) etc. The products from farmed shrimp have indicated longer
shelf life, 16-18 months compared to those from wild variety 12-14 months at –20 ºC

Fish fillets

The brined fillets are battered and breaded. Fillets from freshwater fish are also used for the
production of coated products. The only problem noticed in this case is the presence of fin bones; its
complete removal is still a major hurdle.

Squid products

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 Squid rings and stuffed squid are the popular coated products processed out of squid. Cleaned
squid tubes are cut in the form of rings of uniform size, cooked in boiling brine (3%) for 1-2 minutes
followed by cooling, breading and battering. The coated rings are flash-fried, cooled, frozen and
packed. Stuffed squid is generally processed out of small size animals. The cleaned tubes are filled
with a stuffing mixture prepared using cooked squid tentacles, potato, fried onion, spices etc. It is then
battered, breaded and flash-fried.

Clam and other related products

Meat shucked out from depurated live clams after boiling is blanched in boiling brine, cooled,
battered, breaded, flash-fried and packed. Other bivalves such as oyster, mussels etc. can also be
converted into coated products by the same method.

Fish cutlet

Cooked fish mince is mixed with cooked potato, fried onion, spices and other optional
ingredients. This mass is then formed into the desired shape, each weighing approximately 30g. The
formed cutlets are battered and breaded.

Fish balls

Fish balls are generally prepared from mince of low-cost fish. Balls can be prepared by different
ways. The simplest method is by mixing the fish mince with starch, salt and spices. This mix is then
made into balls, cooked in boiling 1 % brine. The cooked balls are then battered and breaded.

Crab claw balls

Swimming legs of crab may be used for this purpose. Crab claws are severed from the body,
washed in chilled portable water and the shell removed using a cracker. The leg meat is then removed
and mixed with 2 % starch-based binder. This is then stuffed on the exposed end of the claw.
Alternatively, the body meat mixed with the binder also can be used for stuffing. The stuffed claw is
then frozen, battered and breaded and flash fried. The coated products are packed in thermoformed
containers with built in cavities.
Fish Mince and Mince Based Products

Mechanically deboned fish meat is termed as fish mince. Fish mince is more susceptible to
quality deterioration than the intact muscle tissue since mincing operation cause disruption of tissue
and exposure of flesh to air, which accelerates lipid oxidation and autolysis. The quality of the mince is
dependent on the species, season, handling and processing methods. Also, low bone content in the
mince (01-0.4%) is desirable for better functional and sensory properties. Depending on the type of raw
material, fish mince can have a frozen storage life up to 6 months without any appreciable quality
deterioration. Generally minced fish is frozen as 1-2 kg blocks at -40 0C in plate freezers and stored in
cold store at -18 0 C.

Surimi

Surimi is stabilized myofibrillar protein obtained from mechanically deboned flesh that is washed
with water and blended with cryoprotectants. Washing not only removes fat and undesirable matters
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such as blood, pigments and odoriferous substances but also increases the concentration of myofibrillar
protein, the content of which improves the gel strength and elasticity of the product. This property can
be made use of in developing a variety of fabricated products like shellfish analogues. India produces
about 40.000 MT of surimi per annum ,70% of which comes from thread fin bream.

Kneaded products

Several kneaded products like kamaboko, chikuwa, hampen, fish ham and sausage are
processed using surimi incorporating other ingredients. The ingredients used in most of these
preparations are identical; however, the classification is principally based on the manufacturing process
involved. The ingredients employed other than surimi include salt, monosodium glutamate, sugar,
starch, egg white, polyphosphate and water. The method of processing all these products involves
grinding together of the various ingredients to a fine paste and some sort of heat treatment at some
stage.

Fiberized products

Fiberized products are in great demand among the surimi based imitation shellfish products.
The ingredients used in the formulation of fibreized products includes, besides surimi, salt, starch, egg
white, shellfish flavour, flavour enhancers and water. All the ingredients are thoroughly mixed and
ground to a paste. The paste is extruded in sheet on the conveyor belt and is heat treated using gas
and steam for partial setting. A strip cutter subdivides the cooled sheet into strings and is passed
through a rope corner. The rope is coloured and shaped. The final product is formed by steam cooking
the coloured and shaped material.

Fish sausage

Fish sausages are surimi or fish mince mixed with additives, stuffed in suitable casings and heat
processed. The surimi or fish mince is mixed with salt (3-4%), sugar (2-3%), sodium glutamate (0.3%)
starch and soy protein in a silent cutter and stuffed in casings by an automatic screw stuffer. The stuffed
sausage is heated in hot water at 85-90°C for 40-60 min. After heating, it is cooled slowly to avoid
shrinking of the tube and then stored at refrigerated temperature. The production of fish sausage in
India is rather insignificant, although market potential for this product is good. Sausages prepared from
rohu mince treated with potassium sorbate had a shelf life of 16 days at refrigerated temperatures.

Emerging technologies for value addition of fish

Retort pouch processing:

As in canning, retort pouch food is sterilized after packing, but the sterilizing procedure differs.
The pouches are processed in an over pressure retort. The time and temperature will be standardized
depending on the product. With the availability of retort pouches, it can function as an excellent import
substitute for metallic cans. Besides, cost reduction retort pouch packages have unique advantages
like boil in bag facility, ease of opening, reduced weight and do not require refrigeration for storage.
Processed food products can be kept for long periods at ambient temperature. The energy saving is
more in processing in flexible pouches compared to cans. On a comparison of total costs, including
energy, warehousing and shipping, the pouch looks even more favourable. There is 30 to 40%
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reduction in processing time compared to cans, solids fill is greater per unit, empty warehousing is 85%
smaller and weight of the empty package is substantially smaller.

Extrusion:

In order to improve the utilization of underutilized fisheries resources, there is a need to minimize
the post-harvest losses, develop innovative processing technologies and utilize processing waste for
industrial and human use. One such technology, which will be suitable for utilization of low value fish
or by catch, is extrusion technology. Use of fish mince with cereals for extrusion process will enable
production of shelf-stable products at ambient temperature. Extrusion cooking is used in the
manufacture of food products such as ready-to-eat breakfast cereals, expanded snacks, pasta, fat-
bread, soup and drink bases. The raw material in the form of powder at ambient temperature is fed into
extruder at a known feeding rate. The material first gets compacted and then softens and gelatinizes
and/or melts to form a plasticized material, which flows downstream into extruder channel. Basically,
an extruder is a pump, heat exchanger and bio-reactor that simultaneously transfer, mixes, heats,
shears, stretches, shapes and transforms chemically and physically at elevated pressure and
temperature in a short time. At times, the extrusion cooking process is also referred as High
Temperature Short Time process. In extrusion process gelatinization of starch and denaturation of
protein ingredient is achieved by combined effect of temperature and mechanical shear. The
conversion of raw starch to cook and digestible materials by the application of heat and moisture is
called gelatinization. During extrusion the conditions that prevail are high temperature, high shear rate
and low moisture available for starch may lead to breakdown of starch molecules to dextrins.

Irradiation

Irradiation is a physical treatment that consists of exposing foods to the direct action of electronic,
electromagnetic rays to assure the innocuity of foods and to prolong the shelf life. Irradiation of food
can control insect infestation, reduce the numbers of pathogenic or spoilage microorganisms, and delay
or eliminate natural biological processes such as ripening, germination, or sprouting in fresh food. Like
all preservation methods, irradiation should supplement rather than replace good food hygiene,
handling, and preparation practices.
Three types of ionizing radiation are used in commercial radiation to process products such as foods
and medical and pharmaceutical devices (International Atomic Energy Agency (IAEA), radiation from
high-energy gamma rays, X-rays, and accelerated electrons.
• Gamma rays, which are produced by radioactive substances (called radioisotopes). The
approved sources of gamma rays for food irradiation are the radionuclides cobalt-60 (60Co; the
most common) and cesium-137 (137Cs). They contain energy levels of 1.17 and 1.33 MeV (60Co)
and 0.662 MeV (137Cs).
• Electron beams, which are produced in accelerators, such as in a linear accelerator (linac) or a
Van de Graaff generator at nearly the speed of light. Maximum quantum energy is not to exceed
10 MeV.
• X-rays or decelerating rays, which can be likewise produced in accelerators. Maximum quantum
energy of the electrons is not to exceed 5 MeV

Different forms of irradiation treatment are raduarization (for shelf-life extension), radicidation (for
elimination of target pathogens) and radappertization (for sterilization). Radiation processing is widely
used for medical product sterilization and food irradiation. Moreover, the use of irradiation has become
a standard treatment to sterilize packages in aseptic processing of foods and pharmaceuticals.

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Irradiation produces some chemical changes, which, although lethal to foodborne bacteria, do not affect
the nutritional quality of the food but lead to the production of small amounts of radiolytic products.
Gamma irradiation has been considered as an interesting method of preservation to extend the shelf
life of fish and also to reduce qualitatively and quantitatively the microbial population in fish and fish
products. Irradiation doses of 2–7 kGy can reduce important food pathogens such as Salmonella,
Listeria, and Vibrio spp., as well as many fish-specific spoilers such as Pseudomonaceaeand
Enterobacteriaceae that can be significantly decreased in number.

Microwave processing:

The applications of microwave heating on fish processing include drying, pasteurization,

sterilization, thawing, tempering, baking etc. Microwaves are electromagnetic waves whose frequency
varies within 300 MHz to 300 GHz. Microwave heating is caused by the ability of the materials to absorb
microwave energy and convert it into heat. Microwave heating of food materials mainly occurs due to
dipolar and ionic mechanisms. Water content in the food material causes dielectric heating due to the
dipolar nature of water. When an oscillating electric field is incident on the water molecules, the
permanently polarized dipolar molecules try to realign in the direction of the electric field. At high
frequency electric field, this realignment occurs at a million times per second and causes internal friction
of molecules resulting in the volumetric heating of the material. Microwave heating also occur due to
the oscillatory migration of ions in the food which generates heat in the presence of a high frequency
oscillating electric field. Studies showed that chemical changes involved during different microwave
cooking practices of skipjack tuna and will retain omega-3 fatty acids compared to frying/canning.
Microwave blanching can be carried out for color retention and enzyme inactivation which is carried out
by immersing food materials in hot water, steam or boiling solutions containing acids or salts.
Microwave drying is used to remove moisture from fish and fishery products. Microwave drying has
advantage of fast drying rates and improving the quality of product. In microwave drying, due to
volumetric heating, the vapors are generated inside and an internal pressure gradient is developed
which forces the water outside. Thus, shrinkage of food materials is prevented in microwave drying.
One of the disadvantages of microwave drying is that excessive temperature along the corner or edges
of food products results in scorching and production of off-flavors especially during final stages of
drying. Microwave combined with other drying methods such as air drying or infrared or vacuum drying
or freeze drying gave better drying characteristics compared to their respective drying methods or
microwave drying alone.

Ohmic heating:

Ohmic heating is an emerging technology with large number of actual and future applications.
Ohmic heating technology is considered a major advance in the continuous processing of particulate
food products. Ohmic heating is direct resistance heating by the flow of an electrical current through
foods, so that heating is by internal heat generation. Ohmic heating is defined as a process wherein
electric current is passed through materials with the primary purpose of heating the object. During ohmic
heating, heating occurs in the form of internal energy transformation (from electric to thermal) within
the material. Therefore, it can be explained as an internal thermal energy generation technology and it
enables the material to heat at extremely rapid rates from a few seconds to a few minutes. Ohmic
heating have a large number of actual and potential future applications, including its use in blanching,
evaporation, dehydration, fermentation, extraction, sterilization, pasteurization and heating of foods.
The microbial inactivation due to ohmic heating can be explained by the presence of electric field. The
additional effect of ohmic treatment may be its low frequency (usually 50e60 Hz), which allows cell

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walls to build up charges and form pores. As a main consequence of this effect, the D value observed
for the microbial inactivation under ohmic heating is reduced when compared to traditional heating
methods. More research is needed to completely understand all effects produced by ohmic heating to
food products, effects of applied electric field, the applied electric frequency during ohmic heating over
different microorganisms and foods, cold spot determination etc.

Accelerated Freeze Drying

Accelerated freeze-drying is now being increasingly used for the preservation of high value food
products. The product has the advantages like absence of shrinkage, quick re-hydration upto 95%,
minimum heat induced damage etc. In India this technique is now applied for processing shrimp, squid
rings etc. The possibilities for various ready-to-eat products based on fish and shellfish employing this
technique are immense. In this, there is a speeding of the freeze-drying process, as a result of
modification in the heating mechanism. Food is arranged in single layers between metal sheets or grids
held in a tray. This is kept between the heating plates. When the required pressure and temperature is
attained in the chamber, fluid contained within the hollow plates is heated to temperature of 60 to 100
C. The heat is conducted through the metal mesh, and trays to the product while allowing the water
vapour to escape through the mesh channels to the side of the heating plates from where it is removed.
Otherwise, the pressure at the food surface would increase and the ice will melt. When the ice is melted
from the surface the pressure is applied to the plates using a hydraulic mechanism so that the mesh
will be pressed against the surface of the fish giving more direct heat contact to the product. At the
same time the temperature of the heating material is reduced since, after sublimation the surface
temperature of the fish will be the same as that of heating plates (Balachandran, 2001). This method
appeared to reduce the freeze-drying time appreciably from 10-12 hours to 6-7 hours, depending on
the thickness of the food, temperature and pressure, and hence it is termed as accelerated freeze
drying.

Infrared and Radiofrequency Processing Technologies:

Electromagnetic radiation is a form of energy that is transmitted through the space at an

enormous velocity (speed of light). The heat generation in material exposed to EMR could be due to
vibrational movement (as in case IR) or rotational movement (as in case of RF and MW) of molecules.
Application of EMR heating is gaining popularity in food processing because of its definite advantages
over the conventional processes. Faster and efficient heat transfer, low processing cost, uniform
product heating and better organoleptic and nutritional value in the processed material are some of the
important features of EMR processing. In conventional heating system like hot air heating, the heat is
applied at the surface which is carried inwards through conduction mode of heating. In case of
EMR/dielectric heating, the waves can penetrate the material to be absorbed by inner layers. The quick
energy absorption causes rapid heat and mass transfer leading to reduced processing time and better
product quality.

The main advantage of electromagnetic heating over conventional electric and gas oven-based
heating is its high thermal efficiency in converting the electrical energy to heat in the food. In ordinary
ovens, a major portion of the energy is lost in heating the air that surrounds the food, fairly a good
amount escapes through the vent, besides being lost through the conduction to the outside air. In
contrast, almost all the heat generated by electromagnetic radiations, which reaches the interior of the
oven, is produced inside the food material itself. According to the reports the energy efficiency of EMR

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based systems is 40-70%, as compared to approximately 7-14% in case of conventional electric and
gas ovens.

High pressure processing:

High pressure processing (HPP) is an emerging and innovative technology that has a great
potential for extending the shelf-life with minimal or no heat treatment. It is also effective in preserving
the organoleptic attributes of many foods. High pressure Processing is a non-thermal technology in
which the food product to be treated is placed in a pressure vessel capable of sustaining the required
pressure and the product is submerged in a liquid, which acts as the pressure transmitting medium.
Water, castor oil, silicone oil, sodium benzoate, ethanol or glycol may be used as the pressure
transmitting medium. The ability of the pressure transmitting fluid to protect the inner vessel surface
from corrosion, the specific HP system being used, the process temperature range and the viscosity of
the fluid under pressure are some of the factors involved in selecting the medium.

Ultrasound Processing:

Ultrasound refers to sound that is just above the range of human hearing, i.e., above frequency
of 20 kHz. Ultrasound when propagated through a biological structure induces compressions and
depressions of the medium particles imparting a high amount of energy to the material. The sound
ranges for food applications employed can be divided into two, namely, low energy, high frequency
diagnostic ultrasound and high energy low frequency power ultrasound. Low energy applications
involve the use of ultrasound in the frequency range of 5-10 MHz at intensities below 1 W/cm2.
Ultrasonic waves at this range are capable of causing physical, mechanical, or chemical changes in
the material leading to disrupting the physical integrity, acceleration of certain chemical reactions
through generation of immense pressure, shear, and temperature gradient in the medium. Ultrasonics
has been successfully used to inactivate Salmonella spp., Escherichia coli, Listeria monocytogenes,
Staphylcoccus aureus and other pathogens.

Bio preservation:

Bacteriocins are a heterogeneous group of antibacterial proteins that vary in spectrum of activity,
mode of action, molecular weight, genetic origin and biochemical properties. Various spices and
essential oils have preservative properties and have been used to extend the storage life of fish and
fishery products. Natural compounds such as essential oils, chitosan, nisin and lysozyme, bacteriocins
have been investigated to replace chemical preservatives and to obtain green label products.

Application of enzymes:

Enzymes have been used for the production of various cured and fermented fish products from
centuries. Because of their appreciable activity at moderate temperature, products and process have
emerged that utilizes enzymes in a deliberate and controlled fashion in the field of food processing.
Cold active enzymes including elastase, collagenase, chymotrypsin extracted from Atlantic cod were
used in various food processing applications. The other applications of cold active enzymes include
caviar production, extraction of carotenoprotein etc. Treatment with protease under mild treatment
conditions extending for a few hours can result in the recovery of the proteins from fish frame or shrimp
shell waste. The role of transglutaminase in surimi production is well established. The gel strength of
surimi can be improved by the application of extracellular microbial transglutaminase. Lipase extracted

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from Pseudomonas spp can be used to produce PUFA enriched cod liver oil. Enzymatic de-skinning of
fish fillets was done by partial denaturation of skin collagen using a gentle heat treatment followed by
immersion in enzyme solution for several hours at low temperature (0-10 oC). De-skinning of tuna,
Herrin, Squid were also carried out by using different enzyme technology.

Conclusion

Value can be added to fish and fishery products according to the requirements of different
markets. These products range from live fish and shellfish to ready to serve convenience products. In
general, value-added food products are raw or pre-processed commodities whose value has been
increased through the addition of ingredients or processes that make them more attractive to the buyer
and/or more readily usable by the consumer. It is a production/marketing strategy driven by customer
needs and perceptions. Technology developments in fish processing offer scope for innovation,
increase in productivity, increase in shelf life, improve food safety and reduce waste during processing
operations. A large number of value added and diversified products both for export and internal market
based on fish, shrimp, lobster, squid, cuttlefish, bivalves etc. have been identified.

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