RECENT TRENDS IN DRYING AND DEHYDRATION OF FISHERY PRODUCTS

Abstract

Dried and dehydrated fish and fishery products are important source of protein in many parts of the globe including Asia and Africa. Natural sun-drying is mostly used for traditional drying of fish. Traditional sun-drying is accompanied by many problems associated with raw material quality, insect infestation, hygiene and sanitation, pesticide abuse, packaging and storage. Most often, the physical, nutritive and organoleptic qualities of many traditional sun-dried products are unsatisfactory for human consumption. Globally, traditional dried fish contaminated by both insects and insecticides comprises about 30-45% of the total dried products that is considered to be unfit for human consumption. To overcome these problems, particularly to reduce such huge post-harvest loss and improve food safety situation, many improvements have been practiced in recent years. Improvement in traditional fish drying includes good handling of raw material, use of improved drying devices, hygienic processing, packaging and storage, salt application and use of solar drying techniques. On the other hand, various innovations in mechanical/instrumental drying technology have also been suggested to improve the product quality and keep the taste, texture and flavor of original raw materials. Here, the methods and principles of drying and dehydration of aquatic products, constraints facing, along with various emerging smart drying methods and techniques and their effects on quality of final products are highlighted.

Full text

1
RECENT TRENDS IN DRYING AND DEHYDRATION OF FISHERY PRODUCTS
A K M Nowsad Alam, Professor, Department of Fisheries Technology, Bangladesh Agricultural
University, Mymensingh 2202, Bangladesh, E-mail:nowsad12@yahoo.com
Abstract
Dried and dehydrated fish and fishery products are important source of protein in many parts of the
globe including Asia and Africa. Natural sun-drying is mostly used for traditional drying of fish.
Traditional sun-drying is accompanied by many problems associated with raw material quality,
insect infestation, hygiene and sanitation, pesticide abuse, packaging and storage. Most often, the
physical, nutritive and organoleptic qualities of many traditional sun-dried products are un-
satisfactory for human consumption. Globally, traditional dried fish contaminated by both insects
and insecticides comprises about 30-45% of the total dried products that is considered to be unfit for
human consumption. To overcome these problems, particularly to reduce such huge post-harvest
loss and improve food safety situation, many improvements have been practiced in recent years.
Improvement in traditional fish drying includes good handling of raw material, use of improved
drying devices, hygienic processing, packaging and storage, salt application and use of solar drying
techniques. On the other hand, various innovations in mechanical/instrumental drying technology
have also been suggested to improve the product quality and keep the taste, texture and flavor of
original raw materials. Here, the methods and principles of drying and dehydration of aquatic
products, constraints facing, along with various emerging smart drying methods and techniques and
their effects on quality of final products are highlighted.
Introduction
Drying is a popular method of processing and preservation of fish. Dried fishery products are
important source of protein in many parts of the globe. Dried products are unique in flavor, aroma,
taste and texture, relished by great diversity of people from ethnic community to new generation
people. Drying and dehydration process can be divided into thermal and non-thermal drying.
Thermal drying uses heat to remove air that includes natural sun drying to application of many
advanced thermal appliances and methods. Non-thermal technologies include ultrasounds, high
pressure processing, pulsed electric fields, etc. which are able to inactivate microorganisms at near-
ambient temperatures, avoid thermal degradation of food components and preserve sensory and

2
nutritional quality of food products (Pereira and Vicente, 2010). Non-thermal drying still has limited
application in commercial fish processing.
Traditional sun drying is associated with many constraints like slow process, dependency on climate,
insect infestation, rodent and bird attack, storage and marketing problems and so on. In order to
overcome these constraints, particularly, to shorten drying time and improve quality of products,
many energy-efficient and environment-friendly thermal drying technologies have been developed
and practiced in different countries now a days (Wang et al., 2011). A few of the improved
technologies are controlled mechanical heating, hot air oven drying, heat pump drying, freeze drying,
microwave drying, radio frequency drying, infrared drying, electro-hydrodynamic drying, etc., as
well as, hybrid drying methods combining two or more of such drying techniques.
Drying removes water from fish or products, shrinks muscle tissues to form a characteristic rigid but
elastic texture, reduces water activity and thus inhibits enzyme activity and microbial growth. In both
traditional and advanced fish drying, salts are often added for rapid removal of water, that imparts
additional texture formation and aroma development. Salt application may prevent spoilage of fish
and repeal insect attack in traditional processing.
The methods and principles of drying and dehydration of aquatic products, constraints facing, along
with various emerging advanced drying methods and techniques, with emphasis on high-quality smart
drying and their effects on quality of final products are discussed in this chapter.
Traditional Drying: Principle, Practices and Constraints
Principle of Sun-Drying
Traditional sun-drying is a low cost and easy method, where any fish can be dried under the sun
everywhere. It is generally carried out in the open air, from seashore or riverbank to roof-top of the
house, using the energy of the sun to evaporate the moisture and natural air flow to carry away the
vapor coming out from the fish body (Fig. 1). Winter is the best season for natural drying, while low
humidity facilitates evaporation. During initial stage of drying, evaporated vapor makes the
surrounding environment humid that hinders drying process. So, strong air flow is required to carry
away the vapor rapidly. In good quality sun-dried fish products, moisture content should be reduced
to less than 15-16%, with water activity reduced to <0.60, since most of the microbiological
(bacteria and mold) and enzymatic activities are slowed down or stopped at this water activity level
(Nowsad, 2007). In traditional practice, however, water content is difficult to reduce to 15-16%,
rather it seems to remain at around 18-20%. In commercial processing in sea-shore based drying
yards, water content is often higher, where partial salting is done and consumers prefer an

3
intermediate moisture product. Water content is higher when salt is used in salted-dehydrated
products (20-25% salt). But in many countries salted product is not relished. To increase the
storage life of unsalted products, pesticides are used. Moisture content of unsalted traditional dried
fish often ranges between 18-20%, while those of semi-salted and salted dried fish ranges within 20-
25% and 30-35%, respectively (Nowsad, 2007). Salt accelerates the drying process by rapid removal
of water from the body and makes the product stable at room temperature with long shelf life. During
drying, substantial shrinkage and other irreversible changes take place. Therefore, traditional sun-
dried fish cannot be reconstituted.
Fig. 1. Process of sun-drying of fish (adapted from Nowsad, 2007)
During sun drying evaporation of water from fish is accomplished through two distinct phases
(Clucas and Ward, 1996). In the initial phase, the surface of fish is wet. Here the rate of evaporation
depends on the conditions of the air surrounding the fish, like relative humidity of air, air velocity,
air temperature and surface area of fish. In the final phase, all the surface moisture is carried away
from the body. So, here drying of fish mainly depends on the rate at which moisture is brought to the
surface from the anterior core of tissues. The rate of moisture flow from the tissue to the surface
depends on the constituent nature, thickness, temperature and water content of the fish.
Water activity (aw) influences quality of dried products substantially. Water activity is the ratio of
partial pressure of water vapor in equilibrium with a substance to the saturation partial pressure of
pure water vapor at the same temperature, and expressed as-
aw = Pv/Psat
Here, aw = water activity; Pv = partial pressure of water vapor in fish tissue; Psat = saturation partial
pressure of pure water vapor.
The water activity of any matter in the world ranges between 1.0 to 0.0. The water activity of pure
water is the highest, i.e., 1.0. When water molecules are bound physically or chemically within
muscle tissue, the water activity of the fish drops. In salted product, addition of salt acts to bind
water molecules. Some humectants such as sugar, glycerol, saltpeter, etc. that are commonly added
to muscle foods have the effect of lowering the water activity of the food. Drying of fish
Fish
Wind action
Moisture
Sunlight
Humidity

4
substantially reduce the water activity in the tissue because of removal of water. It is found that
lowering of water activity below 0.9 is sufficient to prevent the growth of the dangerous toxin
forming pathogenic bacteria (Doe, 2002). At water activity < 0.75, the halophilic bacteria can only
survive, whereas at water activities below < 0.63 molds fail to germinate and grow. Water activity
for adequate dried fish should be <0.60.
Traditional Fish Drying Practice
Commercial fish drying yard receives daily deliveries of fish from nearby landing centers. The
quality of fish destined for sun drying is not often up to the mark, because the fishing boats
generally carry an insufficient quantity of ice or no ice. Upon arrival at the yard, the fish is kept on
bamboo mat and mixed with salt. The ratio of fish and salt and mixing time vary according to the
quality of fish. If the quality is severely deteriorated, salt concentration is higher. But a higher salt
content may reduce the price of dried fish. Therefore, a balance between the salt content used and
the extent of deterioration is maintained to maximize the profit. Generally, 5-7% salt is sprinkled
over the unwashed fish. In case of salted dehydrated product up to 25% salt is used. Mixing time for
partial salting varies from 2-5 hours, while for salted-dehydration it may be up to several days. Salt
hardens the fish and makes handling, washing and spreading on rack easier.
Partially salt-treated fish is sorted for different species and size according to the demand in the
market. The fish are then washed in bamboo baskets. After washing, the fish is spread over the
elevated racks for drying. Longer sized fish like ribbon fish, sharks, etc. are tied up at the caudal end
in pairs, while a pair of Bombay duck are joined together with the extended jaws and hung-up in
bamboo bars. Larger and thicker species like Indian mackerel, tuna, tassel fish, Indian salmon, etc.
receive pretreatments like gutting and splitting the lateral muscle, partial salting and then fixing
circular rings at the trunk region to widen drying surface, shaping like a spindle or torpedo. During
foggy or cloudy days when sunshine is scarce, unsalted fish are reported to have been dipped into
pesticide solution before spreading on rack or sprayed with pesticides on the rack while drying, to
repeal blow flies or kill maggots (FAO, 1981).
The fish are left hanging on bamboo bars or kept on the elevated racks until dry. For uniform drying,
fish are turned in both the racks and hanging bars at short intervals. Generally, small fish spread in
thin layer on the elevated rack takes a shorter time to dry. Larger and thicker fish take longer time.
In winter, when the relative humidity is less in the air (60-65%), 2-3 days are sufficient for drying
small fishes. Average duration of drying during sunny days in the drying season for different fishes
are – jewfish: 2-3 days; ribbonfish: 3-4 days; Bombay duck: 2-3 days, Indian mackerel and salmon:
4-5 days. However, the duration varies if it rains or the sky is foggy or cloudy.

5
Traditional Storage of Dried Fish
In commercial scale open store-house, elevated platform inside the house (18 inches from the floor),
made with bamboo or wood, is used where dried fish in plastic gunny sacs are kept piled.
Sometimes, large circular basket (height: 8-10 feet: diameter: 6-8 feet) made of weaving bamboo
splits is also used to keep dried fish. It is reported that granular pesticides like DDT, Basudin, etc.
are spread in layers in the storage sacs or bamboo baskets to repeal storage beetle infestation (FAO,
1981, Bala & Mondol, 2001). Product stored in such a way is checked for quality in every 2 month.
If any infestation (beetles, mites or others) is found, stored product is again sun-dried for 1-2 days
and restored with additional pesticides. With such periodic checking, dried fish can be stored for 6-8
months.
Dried Fish Infestation by Insects
Infestation of traditional sun-dried fish by insects is a great problem. Two major infestations damage
the products (Nowsad, 2007):
i. larvae (maggots) of several species of blowfly (Diptera spp.) infest during the early stages of
drying; and
ii. beetle (both larvae and adults) and mite infest during storage and marketing of products.
Because of ignorance and negligence during prolonged storage, the extent of damage caused by
beetle infestation is much higher than blowfly infestation caused during processing, although
comparatively greater attention is paid during processing.
The life cycles of all these insects involve four developmental stages, the egg, larva, pupa and adult.
The adult female, after mating, lay eggs on or inside the fish. The eggs hatch into small larvae that
feed vigorously and develop rapidly. In all cases, damages in dried fish are caused by the larval
stage.
i. Blowfly infestation
Adult blowflies are attracted to the fish both visually, by the large quantity of mostly spoiled fish
spread out to dry, and chemically, by the odors or volatile compounds released from the fish (Clucas,
2003). Larger fish are at most risk from gravid female blowflies during the raw material preparation
and early stages of sun drying when the moisture content is high. Moist condition makes the larvae
able to feed upon the flesh and survive. Therefore, small fish which dry quickly are not usually
attacked by the blowfly larvae unless the weather conditions, like heavy fog or cloud, prevent them
from drying.

6
The adult blowflies usually lay their eggs
in the gills, oral cavity and underneath of
the fish. Eggs are also found to be laid in
the crevices between muscle bands and in
the abdominal or bony cavities in
beheaded or split fish. Hatched out larvae
or maggot immediately congregate in
feeding area of muscle and may make
deep burrow into the flesh. This causes
the fish to break up and make it more prone to subsequent infestations by other pests, especially
beetle. Blowfly larvae hatched from the eggs laid upon other food sources like other fish, debris and
rubbish around drying site may also crawl across onto the new fish to form new feeding zones (Fig.
2) (Clucas & Ward, 1996). The larvae continue to feed upon the flesh until the fish is fully dried or
they are pupated. To pupate, the larvae usually leave the fish, drop on the sand/soil and burrow into
the earth beneath the drying rack or mat. If the fish is dried very quickly, the larvae may either die
off or leave the fish for other moist food source. Therefore, the amount of damage caused by
blowfly larvae depends largely on the speed of drying. If fish is spread in the morning and sufficient
sunlight is available during the whole day, all eggs whatever laid will be died off within the day due
to insufficient moisture available to them. Partial salt treatment reduces the rate of blowfly
infestation, while no such infestation is visible in
salted-dehydrated products (20-25% salt).
Damage can be heavy where salt is not used and
drying condition is poor, as much as 25-30%
under very humid conditions in Bangladesh
(Nowsad, 2014).
ii. Beetle infestation
Heavy damage in dried fish is caused by storage
beetle infestations mainly at the end of drying,
during storage and marketing. Certain other
insects and mites, more often associated with
other stored products such as cereal grains and
flour, are also found on dried fish. Dermestes
beetle appears to be the major insect although other minor beetles like Necrobia spp. can also
Fig.2. Maggots of blowfly often form feeding pack on
wet fish
Fig.3. Adult Dermestes beetle

7
damage the product. The level of losses due to Dermestes beetle is directly related to the length of
storage. Losses are negligible for only a short storage up 2-4 weeks. However, up to 50% losses by
weight due to Dermestes attack have been recorded by many observers when unsalted dried fish is
stored for about 6 months (FAO, 1981).
Within 12 to 40 hours of copulation, female beetles (Fig. 3) lay oval-shaped eggs in the cracks of the
body wall or muscles of the drying or completely dried fish. Laid eggs are hatched into larvae within
1-3 days at 25 to 35oC temperature range. Beetle larvae differ from those of flies as they have a
distinct head, 3 pairs of legs and the body is more or less hairy. The larva of Dermestes beetle is
very hairy and at the posterior end of the body possesses two spines. The optimum temperature for
larval development lies between 30 and 35oC and on an average, it takes 20 days for the larvae to
pupate under favorable conditions. Under unfavorable conditions, however, larval period increases
and number of molding also increases. Cast (case of larval skin after molding) are commonly found
in infested fish. To pupate, the larvae burrow into the muscle tissue of dried fish. The larvae then
become shorter, thicker and quiescent, and finally mold to become pupae. At favorable conditions
with temperature of 27oC, the pupae are developed into adult within 6 days and then crawled away.
Improved Practice of Sun-Drying
Recently many improvements have been made in traditional practice to improve the dried fish
quality (FAO, 2021). Improved traditional fish drying may have the following steps, as also shown
in the flow chart (Fig.4):
o Purchase fresh fish in ice and keep in ice and salt until further processing.
o Sort out the fish, remove the spoiled or torn-belly one. Gut the bigger species like jewfish,
mackerel, tasselfish, pomfret, catfish, etc., remove gills and scales and finally wash with clean
water.
o Split the lateral muscles if the fish is thick (ribbon fish, jewfish, Indian mackerel, skipjack tuna,
Indian salmon, etc). Wash thoroughly with potable water, or if not found, with clean tube well
water. A 5-10 ppm chlorinated water may be used. Other effective sanitizer, like chlorine
dioxide (ClO2) at a concentration of 0.2-0.5 ppm can be used.
o Mix fish with 10-12 % clean salt, ice the salted fish (in polythene pouch) in ice box. Keep the
fish in ice and salt for 6-8 hours. This amount of salt and salting schedule will not make the
product salty, but improve the texture and flavour of the product. Besides, it will
prevent/reduce insect infestations during process and storage. Bombay duck should not be
salted, because of excessive drip may disrupt muscle structure and deteriorate texture.

8
o After salt treatment wash the fish by soaking for 1-2 minutes. Keep the washed fish on elevated
rack or perforated trays to let the surface water drain out completely.
o Do not use any pesticide. To protect fish from bacteria or mold contamination, sprinkle 0.2-
0.3% calcium propionate on the moist fish.
o To deter insects, soak fish in 0.2% turmeric solution (dissolve 0.2 g turmeric in water in a final
volume of 100 ml) or rub turmeric powder at 0.1% of the body weight inside the abdominal
and gill cavities and on the body surface.
o Spread fish on the elevated covered rack, box or ring tunnels or hanging on bamboo pole or
iron bars inside the box tunnel for drying.
o Allow fish to dry perfectly for 3-4 days depending on species, size, climatic conditions, etc.
Turn fish if necessary, for uniform drying in both sides. Check one by one for quality drying.
o After sunset, keep fish covered on the rack by polythene sheet to avoid dew.
o Do not keep dry fish exposed in baskets, keep in tightly covered container to avoid storage
beetle infestation. Trim out paired and unpaired fins and head and cut into consumer size if the
fish is large. Fill in thick polythene pouch (0.2 mm thickness) and seal immediately.
o Vacuum packaging is necessary to protect the product from beetle and mite infestations. If not
available, use electric sealer machine to seal in thick polythene pouch.
o Store the product in closed container in cool (3-5oC) and clean place.

9
Fig. 4. Process flow chart of improved traditional fish drying
Packaging of Sun-Dried Fish
Dried fish needs to be protected from insect attack. So, the prime and foremost duty is to keep it
covered from the rack until final consumer packaging. For immediate protection, dried fish can be
transferred to covered drum or plastic container instantly from the drying rack. Plastic drum with
airtight lid of any size can be used. Precaution should be made to ensure that no beetle, mites or
other small insects can enter the drum to lay eggs on dried fish.
Fresh
fish
Sort
Dress/gut/split
Wash
Salt
Wash/drain
Add calcium
propionate
Spread/hang on covered
tunnel/box on the rack
Check out spoiled/damaged product
Pack from the tunnel/rack
Trim, cut and final pack
Store in clean/cool
place (3-5
o
C)
Size
Thickness
Spoiled or torn-belly one
Bigger species
Potable water
Salted (2-3%) tube well water
10-12% clean salt, 6-8 hrs with ice
Soaking into freshwater for 1- 2 min
0.2-0.3%
3-5% with dry salt in salted fish
Covered by mosquito net
Vacuum packaging
Covered container

10
For consumer packaging, thick (0.2 mm thickness), high density polypropylene or polyvinylidene
chloride/alcohol packaging material can be used. Plastic material should be thick enough to prevent
perforation made by sharp edges of the cut pieces of dried products.
When the products are packaged completely air-tight by vacuuming inside of the bag or container,
this is called vacuum packaging. Vacuum packaging is done by machine. Modified atmosphere
packaging (MAP) is an advanced version of vacuum packaging, where the mixture of several gases
like carbon dioxide, oxygen and nitrogen are treated during packing to extend the shelf life of the
product. Packing of dried fish in special mixtures of gases by machine may extend the shelf life for
several months to years.
If the proportion of these gases is accurately controlled at the time of packing, this is called
“controlled atmosphere packaging (CAP). Generally, MAP or CAP is achieved by placing the dried
fish in a plastic bag or sleeve, which is flushed with the gas mixture immediately prior to sealing.
The plastic bag or sleeve must have a low permeability to the gases used. Usual MAP or CAP
process lines have the system to produce thermo-formed base trays from a continuous roll of the
plastic film into which the product is placed. After the dried fish is placed in the tray, it moves along
a conveyer belt to a section where a vacuum is drawn in the tray and the void is filled with the
appropriate mixture of gases. A film lid is then heat-sealed to the top edge of the tray, completing the
process.
Improved Traditional Drying Methods in Small-scale Operation
A. Drying rack covered by net
It is a modified traditional elevated drying rack, an iron, bamboo or wooden rack (6 m length × 1.2
Fig. 5. Drying rack covered by net (FAO, 2021)

11
m width × 0.9 m height), where four rear pillars (two pillars from each end) are further elevated to 2
feet and a triangular roof is made on it with three pieces of 20 feet long iron/wooden bars (FAO,
2021) (Fig. 5). The deck is covered by black polythene sheet to absorb heat from sunlight to expedite
drying process. The two rear mouths of the elevated triangles are fixed with mosquito net to prevent
flies and insects, but allow air flow. The entire structure is covered by thin, fine-meshed mosquito
net, which allows sunlight and wind but protect insects and flies. The device is oriented to wind
direction to easy natural air flow. A stand fan can be used to expedite expelling hot air, if electricity
is available.
B. Chorkor type tray oven dryer
A Chorkor type tray oven is in operation in small-scale fish drying during cloudy/rainy climate in
Cox’s Bazar (Toshihara, 2021). A series of trays taking fish are placed one top another (Fig. 6) and
fish are dried with the heat generated by an oven kept inside the chorkor device. Instead of wood,
methene gas or diesel serves as fuel of the oven.
Fig. 6. Chorkor type tray oven dryer (Toshihara, 2021)
C. Solar dryer for fish
Solar dryer is an environment friendly technology operated by renewable energy where sufficient
heat is generated from the sunlight by solar collectors to dry fish and products. In principle, solar
collector absorbs heat from the solar and the photovoltaic functions as an energy source. Solar
radiation passes through the clear glass or polythene sheet on the surface of solar collector and the
heat is trapped into the drying chamber. The absorber plate inside the solar collector in the chamber
heat the fish and create a convection current of cool air that enters an inlet vent at one side, heats up
and circulates through the fish in dryer and finally exits through a fan vent on other sides of drying

12
chamber. As the fish dries, moisture is carried away with the hot air. In terms of operation, solar
dyers are of 3 types: i) integral (direct) type; ii. distributed (indirect) type; and iii). mixed mode
(hybrid) solar dryer and these are reviewed for integration by Chavan et al. (2020).
In a simple direct solar fish dryer, a tunnel kept on elevated rack is covered by polythene. A 25% of
the tunnel inside is covered with a black painted steel or polythene sheet to generate heat. Rest of the
space is used for spreading fish. To expel out hot and moistured air from dryer one or more fans are
operated by photovoltaic cells. High heat and air flow help fish to dry quickly.
There are several designs of solar fish dryers tested in many parts of the globe like simple solar tent
dryer (Doe et al. 1977), shelf-type dryer (Selcuk et al. 1974, Hohenheim type tent dryer with
photovoltaic cells (Bala & Hossain, 1998; Bala & Mondol, 2001), box tunnel dryer without soler cell
(Nowsad, 2007), solar dome dryer (Sachithananthan et al.1985), cabinet dryer (Gustafsson, 1999),
UC Davis chimney dryer (Feed the Future Innovation Lab, 2023), etc. Potential advantages of
solar-drying techniques, compared with sun-drying, are: (i) drying rate is higher with reduced drying
time due to the higher temperatures attainable; (ii) higher temperature retards the activities of insects
and microorganism; (iii) no access to birds, rodents and cats; (iv) protected from wind-borne dust;
(v) lower moisture content increases the product shelf life (Sachithananthan et al. 1985). On the other
hand, major problems associated with solar fish drying are: small scale-production, case-hardening
and brittle products. In many solar drying devices, as with Hohenheim type tunnel dryer, the outer
surface of the fish is heavily dried and, sometimes burned, but the inside tissue remains soft, un-dried
and cooked, leading to brittle final product. This mainly happens due to excessive heat generated
inside the tunnel for slow passing out of highly moisturized air, may be due to long tunnel and
inadequate function of extract fans (Nowsad, 2007).
Recent Advances in High Performance Smart Fish Drying
Recently, many advancements have been made in high performance mechanical and instrumental
drying. Commonly, the quality of such dried and dehydrated products are determined based on some
attributes (Table 1), as reviewed by Zhang et al. (2017).
Table 1. Quality attributes of dried products determined by advanced drying technologies
No.
Quality attributes of dried products
Author
1
Retention of flavor components which greatly influence organoleptic quality
of dried products
Chin et al. 2008
2
Retention of nutrients, especially heat-sensitive amino acids and oxygen-
sensitive unsaturated fatty acids, along with vitamins A, C, and thiamine
Sagar & Suresh,
2010
3
Inhibition of browning reaction to keep desirable color as it is closely
Arabhosseini et al.

13
associated with freshness, desirability and food safety
2009
4
Rehydration ability that represents the ability of restoring fresh product
properties when dried material is rehydrated in water
Contreras et al.
2012.
5
Uniform quality of products which is measured on the basis of temperature,
moisture content, color difference, shrinkage, etc.
Wang et al.2012
6
Appearance and texture as the results of complex interactions among food
components at macro- and micro- structural levels
Zhang et al. 2017
It is obvious that the advanced smart fish drying technologies have been evolved considering the heat-
sensitivity and easy degradation characteristics of protein and lipid of fish food. Some of the high
performance fish drying technologies of particular importance are discussed in brief.
1. Hot Air Drying
Owning to weather dependency of natural sun drying, hot air circulation by machine has been
introduced extensively now-a-days in fish drying industry because of its large volume of production
and well-designed sealed-hot air circulation system. It is now the single largest commercial fish
drying process after natural sun drying. This has two distinct advantages: i. hot air drying is very fast
and efficient drying due to hot air circulation, the anterior core muscles of fish of any thickness can
be dried with rapid raising of controlled temperature, so that high quality can be achieved; ii. drying
speed is regulated to keep different types of fishes in a suitable drying situation (Zhang et al. 2017).
This machine operated techniques are designed for any small, medium and large scale of operation
for various types of fish. The air drying electrical oven is equipped with a smart heat source, high
capacity blowing fans, drying chambers and trays. During drying, the fan blows the air to heat
sources, which is generated by the electricity. With an automatic temperature control system, both
over-heating and under-heating are avoided. The fish are evenly dried in hot air since the trays
provide dispersed space. Thus uniform color, texture and flavour are developed in the final product.
Final produce is vacuum-packed.
Problem associated with hot air drying is excessively high temperature sometimes reduce the quality
of dried products, because of lipid oxidation and Maillard browning reaction by exposure to the
air for long term. This may damage food structure and flavour development. Treatments with citric
acid (Marquez et al. 2009), glutathione (Wu & Wand, 2016) and high pressure (Mario et al. 2016)
have been suggested to improve the quality of hot air oven dried products.
2. Heat Pump Drying
Heat pump drying is a very effective new generation fish drying technology with high efficiency.
It uses the principle of reverse Carnot cycle to absorb heat from the air and transfer it to the

14
chamber, while increasing the temperature in the drying chamber. The heat is circulated through fans
and other equipment to achieve desired level of drying (Neslihan & Arif, 2009). In fact, it is the
combination of a heat pump system and traditional convection chamber, where the heat pump
absorbs heat from a low temperature heat source of 18-35°C and releases it to the drying
product. Therefore, it is especially suitable for aquatic products containing characteristic protein
and unsaturated fatty acids which are prone to heat denaturation and oxidative rancidity (Kang et al.
2022). The heat pump is generally composed of condenser-compressor and other devices to form a
circulating system. The refrigerant is circulated in the system through the compressor. Both drying
temperature, air velocity and air humidity are strictly controlled and it is more energy-efficient
under adjustable drying conditions, as observed in horse mackerel (Neslihan & Arif, 2009, Shi et
al. 2007).
Some of the advantages of heat pump drying system over the other advanced drying methods, as
observed by Kang et al. (2022) are: i. heat pump drying fully meets the food safety requirements; ii.
it maintains clean and safe conditions; ii. it produces good colored and luster finished products; iv. it
is almost fully auto-controlled with lesser manual operation; v. no waste water, exhaust, or waste
residue in the process line; vi. it has long service life, low running cost and good economy; vii.
automatic control of temperature and humidity- thus produces stable and reliable products. Solar-
assisted heat pump dryer, as a modified heat pump system, has been found highly effective in
macroalgae drying with original color and flavor are maintained as intact (Kang et al. 2022).
Moreover, coating with hydrocolloid and treating ultrasound are found to be effective innovation
in improving the drying efficiency and quality attributes of dried products produced by heat pump
drying (Shi et al. 2019, Zhu et al. 2021).
3. Freeze Drying
Freeze drying, often known as lyophilization, is a method of dehydration in super cold vacuum
condition where water is removed from the drying material by sublimation (Zhang et al. 2017). By
freezing the product and lowering the pressure, the moisture content of the product is removed
(Lewicki, 2006). Super cold temperature and pressure below the triple point of water provide
excellent quality to freeze-dried products (Zhang et al. 2017). The freeze drying process facilitates
preservation of the original shape, colour and properties of the heat-sensitive products like fish and
generates insignificant changes in color, flavor, chemical composition and texture, while long term
preservation of an aquatic product without affecting its integrity is achieved (Zhang et al. 2019).
The product quality obtained from freeze drying is considered to be the highest of any dehydration

15
techniques (Nawirska et al. 2009). However, freeze drying is a very lengthy, time-consuming and
expensive process.
Freeze dryers are used to preserve a wide variety of products, like pharmaceutical preparations,
different foods and beverages including seafood, soil samples, flowers and archaeological artefacts
(Zhang et al. 2017).
A drying chamber, a vacuum pump and a refrigeration system are the major equipment for freeze
drying. In its function, the moisture in fish is transformed into minute ice crystals under vacuum,
which are directly sublimated from solid ice to gaseous water vapor. Thus, the product is dehydrated.
Now-a-days, freeze drying technology is applied to dry very high-grade aquatic products, viz.,
shark fin, abalone, sea cucumber, etc. Very high operational cost of freeze drying technique, however, limits
its wide applications in aquatic products.
4. Microwave Drying
Microwave drying is a very widely used drying method in food industry, as it covers a wide variety
of aquatic products (Azmi & Osman, 2021). Microwave drying has become increasingly popular due
to its comparative advantages, like significantly reduced drying time, substantial energy savings,
uniform temperature distribution and improved quality products maintaining intact nutrition and
flavour (Alibas, 2007). In a general principle, microwaves penetrate materials, heat the products
without supplemental thermal gradients and contributes to heat transfer during dehydration (Jiang et
al. 2010). In fact, a high-frequency electromagnetic wave is radiated into the product that causes
friction in the internal molecules to generate heat. Most important advantage of microwave method
is the formation of heat directly inside the food products. Therefore, the water molecules in the food
are heated up and removed away, quickly enough than other fish drying methods (Sokhansanj &
Jayas, 2014).
Microwave drying has several drawbacks too, like limited penetration depth, inherent
nonuniformity and the “puffing” phenomenon (Zhang et al., 2006). High frequency microwave
often damages the quality of fishery products and causes huge energy consumption. However,
present day combination of microwave application under vacuum has helped lowering drying
temperature and increasing drying efficiency, whereby improving the retention of nutrients and
color and rehydration rate of aquatic products. In addition, the oxidation of lipid compounds has
been reduced due to the vacuum environment in drying chamber, as applied in sea cucumbers (He
at al. 2021), squids (Pankyamma et al. 2019), mackerel (Viji et al. 2019) and scallops (Yin et al.
2022).

16
5. Hybrid or Combination Drying
To improve the efficiency of drying in terms of reducing drying time and maintaining quality of
products like texture, colour and flavour, different drying technologies are combined (Huang et al.
2012). Hybrid drying applications have shorten drying time, reduced power consumption and
improved the quality of dried aquatic products (Bircan & Saliha, 2010, Duan et al. 2010,
K
€
ose
&
Erent
u
€
rk,
2010
). Some of the popular combined drying technologies are microwave and freeze
drying (sea cucumber), microwave and hot air drying (tilapia, grass carp and Atlantic krill), heat
pump and hot air drying (tilapia), heat pump and freeze drying (Atlantic krill, sea cucumber), etc.
Very high efficiency electro-magnetic drying, radio frequency drying and infrared drying
technologies are also combined with microwave drying or freeze drying for shrimp, fish or
echinoderms (Deng et al. 2011, Moon et al. 2014). Combined technologies have shown distinct
advantages over any individual high performance drying methods discussed above and improved
the drying efficiency and quality of dried products (Huang et al. 2012). Combined drying techniques
include both parallel and tandem drying (Zhang et al. 2017). In parallel drying, two or more drying
methods are implemented simultaneously, while tandem drying involves the use of one drying
method first, followed by one or more other drying methods combined (Huang & Zhang, 2012).
As the combination drying method requires several drying equipment in a single process line, the
conversion point of drying is difficult to determine for different aquatic products. This has been
seen to be a serious setback of combined technologies for steady-state non-stop large-scale
production. In order to satisfy the demand of high efficiency drying of different fishery products,
more advanced combined technologies need to be developed.
6. Further Trends of Smart Fish Drying Technologies
To increase drying efficiency and obtain high-quality dried fish, some other smart drying methods
are tested, like electrohydrodynamic drying (Bai & Sun, 2011), radio frequency drying (Uemura et
al. 2017) and infrared drying (Deng et al. 2011). The efficiency of these methods was compared
with traditional sun-drying and hot air drying in seafood (Bai et al. 2013, Li et al. 2023, Moon et al.
2014). Although better texture and sensory characteristics are obtained in sea cucumber with lesser
energy consumption, the drying rate is much lower in the former two methods, while infrared drying
showed little positive impacts. Overall, these emerging methods are found not very suitable for
present-day industrial application, and much research is required to draw out any conclusion on these
smart technologies.

17
Quality Control of Sun-dried Product
Main challenges of traditional sun drying are slow process, environmental dependency, insect
infestation, inadequate packaging and unhealthy storage, those affect on the quality, colour and
flavour of the consumer products. Due to inadequate process, packaging, storage and marketing,
post-harvest loss in dried fish is about 30-45% in different countries (FAO, 2020; 2021). To mitigate
these problems and improve quality, traditional practices have been improved with good protocols
and use of net-covered drying room, installed with extract fans and use of vacuum packaging. But
the success rate of adoption of such improved practices is still very negligible in South Asian and
African countries (FAO, 2020).
On the other hand, in case of high performance new generation drying, like hot air oven drying,
freeze drying, hot pump drying or microwave drying, in addition to improved drying rate and energy
utilization, the products are in good quality in terms of both texture and colour. However, since the
quality of dried fish and drying efficiency are always the key elements to consider, these can be further
improved by - i). pretreating the raw-material appropriately (application of salt, blanching,
ultrasound, high pressure, edible coating, etc.; and ii). optimizing the structure of drying equipment
to minimize energy utilization.
In spite of tremendous development in new generation drying technologies, traditional sun-drying
still occupies the toped position globally by both volume and value. The characteristic elastic texture
and soft-fermented flavour developed in traditional sun drying are relished by huge ethnic people and
oriental/African consumers (FAO, 2021). In addition, high price of new generation product
manufactured by smart technologies has still been a prime constraint that has made these products
un-affordable to the common public. On the other hand, the comparatively harder texture and
associated taste of the mechanically developed products are not often liked by mainstream
consumers. To protect the nutritional requirement of traditionally made dried fish and to reduce
huge post-harvest loss, traditional process line must need to be improved. Although traditional
drying seems to be very simple, technical knowledge on careful selection of raw material quality and
maintenance of hygiene and sanitation in drying area are necessary. Improved quality dried fish can
be produced by using good quality fish and improved drying rack, maintaining good sanitation and
hygiene, and employing adequate packaging and storage of the products.
Due to inadequate processing, packaging and storage, traditional dried fish may have some defects or
signs of spoilage, which are mentioned below, along with possible preventive measures.

18
a. Cage hardening
The product has a chalk-white appearance and is hard and brittle. This is caused by over-rapid
drying, which leads to drying out of the outer surface of fish, while the inside is still moist and/or
cooked. Shelf life of such product is very less. To avoid this problem, adequate sunlight and air
should be allowed to the drying rack and fish should be turned up several times for uniform drying.
b. Brittle product
Dried fish becomes brittle if the fish is cooked out during drying process, due to high temperature
generated (above 55-60 °C) inside of the rack or tunnel. This generally happens in solar tunnel dryer
when moisture released from the fish cannot be expelled outside rapidly. The brittle product loses
natural elasticity of dried fish and causes fragmentation. To avoid this problem, inside tunnel
temperature should be constantly monitored for not to raise > 50 °C. Temperature can be controlled
by adequate ventilation.
c. Mold growth
The growth of black, blue and green molds on dried fish is evident sometimes. This is due to high
moisture content of the final product, either because it is not dried properly, or it reabsorbs moisture
from the environment. To avoid mold growth, moisture content in the final product should be
maintained within 15-18% and adequate vacuum packaging should be done.
d. Reddening
Reddening sometimes occurs in stored dried fish. Reddening is caused by red halophiles (salt-loving
bacteria) which grow on the fish when contaminated salt is used during drying. To avoid this
problem, improved quality solar salt should be used.
Dried fish prepared from spoiled or adulterated fish can be differentiated from those prepared from
good quality fish by analyzing the final product as shown in Tables 2 and 3.
Table 2. Characteristics of dried fish prepared from fresh and rotten raw material
Sl.
Dried products from fresh fish
Dried products from rotten fish
1
Whitish in color.
Greyish in color.
2
Skin is shiny and glassy.
Original skin is lost or distorted; rough surface.
3
Elastic texture.
Non-elastic but hard and rigid texture, often brittle.
4
Fresh fishy and dried fish flavour.
Pungent-spoiled flavour.
5
Slightly salty-sweet in taste.
Bitter in taste.
6
Substantial shrinkage in the muscle occurs: dried
fish becomes shorter in size than that of original
fresh fish.
Fish becomes longer than the original one after drying.
This happens due to the enlargement of vertebral column
during spoilage.

19
Table 3. Characteristics of pesticide-treated and pesticide-free dried fish
Sl.
Dried fish treated with pesticide
Dried fish without pesticide
1
Skin is smooth and shiny.
Skin of fresh product is shiny and smooth but not as much
as those treated with pesticides; skin of old product is not
smooth as signs of insect infestation are frequently visible.
2
Devoid of characteristic dried fish flavour.
Characteristic dried fish flavour persists all along.
3
Bitter in taste when touched at the tip of the
tongue.
Mostly blunt or slight salty-sweet in taste.
4
No live flies or insects are found around; no adult
beetle, eggs, pupae or cast are visible inside the
basket or container.
Blow flies are found flying all around the products; adult
insects, pupae or casts of pupae are found at the bottom of
the container or basket.
References
Alibas, I. (2007). Energy consumption and colour characteristics of nettle leaves during microwave,
vacuum and convective drying. Biosyst Eng., 96:495–502.
Arabhosseini,
A.,
Padhye,
S.,
Huisman,
W.,
Boxtel,
A.
&
M
u
€
ller,
J.
(2009). Effect of drying on
the color of tarragon (Artemisia dracunculus L.) leaves. Food Bioprocess Tech., 4(7):1281–1287.
Azmi, S.K. & Osman, I. (2021). Microwave drying of fish, chicken and beef samples. Food Sci
Technol., 58(1):281–291. https://doi.org/10.1007/s13197-020-04540-0
Bai, Y. & Sun, B. (2011). Study of electrohydrodynamic (EHD) drying technique for shrimps. J
Food Process Preserv., 35(6):891-897. https://doi:10.1111/j.1745-4549.2011.00542
Bai, Y., Qu, M., Luan, Z., Li, X. & Yang, Y. (2013). Electrohydrodynamic drying of sea cucumber
(Stichopus japonicus). LWT - Food Science and Technology, 54(2):570-576.
https://doi:10.1016/j.lwt. 2013.06.026
Bala, B.K. & Hossain, M.D. (1998). Experimental investigation of solar drying of fish using tunnel
dryer. WREC, Elsevier Science Ltd: 2049-2052.
Bala, B.K. & Mondol, M.R.A. (2001). Experimental investigation of solar drying of fish using tunnel
dryer. Drying Technology, 19(2):1-10.
Bircan, K. & Saliha E. 2010. Drying characteristics of mistletoe (Viscum album L.) in convective and
UV combined convective type dryers. Industrial Crops & Products, 32(3):394-399.
https://doi:10.1016/ j.indcrop. 2010.06.008
Chavan, A., Vitankar, V., Mujumdar A. & Thorat, B. (2020). Natural convection and direct type
(NCDT) solar dryers: a review. Drying Technology,
https://doi.org/10.1080/07373937.2020.1753065
Chin, S. T., Nazimah, S. A. H., Quek, S. Y., Che Man, Y. B., Abdul Rahman, R. & Hashim, D. (2008).
Changes of volatiles’ attribute in durian pulp during freeze- and spray-drying process. LWT-
Food Science and Technology, 41(10):1899–1905.
Clucas, I.J. (2003). Mission report - Technical backstopping on low cost fish processing, quality
control and food safety aspects. GoB/UNDP/FAO Project: BGD/97/017. Food and Agriculture
Organization, Dhaka.
Clucas, I. J. & Ward, A. R. (1996). Post-harvest Fisheries Development: A Guide to Handling,
Preservation, Processing and Quality. Chatham Maritime. Kent ME4 4TB, United Kingdom.
Contreras, C., Mart´ın-Esparza, M. E. & Mart´ınez-Navarrete, N. (2012). Influence of drying method
on the rehydration properties of apricot and apple. J. Food Process. Eng., 35(2):178–190.
Deng, Y., Liu, Y. & Qian, B. (2011). Impact of far-infrared radiation-assisted heat pump drying on
chemical compositions and physical properties of squid (Illex illecebrosus) fillets. Eur Food Res
Technol., 232(5):761-768. https://doi:10.1007/s00217-011-1441-9
Doe, P.E. (2002). Fundamentals of fish drying. In: Textbook of Fish Processing Technology, Indian
Council of Agricultural Research.

20
Doe, P. E., Ahmed, M., Muslemuddin, M. & Sachithananthan, K. A. (1977). Polythene Tent Dryer
for Improved Sun Drying of Fish. Food Technol. Aust., 29: 437–441.
Duan, Z., Jiang, L., Wang, J., Yu, X. & Wang, T. (2010). Drying and quality characteristics of tilapia
fish fillets dried with hot air-microwave heating. Food Bioprod Process, 89(4):472-
476. https://doi:10. 1016/j.fbp.2010.11.005
Feed the Future Innovation Lab For Horticulture (2023). Chimney Solar Dryer Manual. Reid, M.
&Thomson, J. (authors). Retrieved March 27, 2023.
https://horticulture.ucdavis.edu/information/ chimney-solar-dryer-
manual?utm_source=homepage-mh-block&utm_medium=homepage
Food and Agriculture Organization (1981). The Prevention of Losses in Cured Fish. FAO Fisheries
Technical Paper No. 219. FAO, Rome.
Food and Agriculture Organization (2020). The State of World Fisheries and Aquaculture-
Sustainability in Action. FAO, Rome.
Food and Agriculture Organization (2021). Demonstration training manual on fish drying using
improved drying rack. Nowsad, AKM.A. (author). FAO, Dhaka.
Gustafsson, G. (1999). Solar Assisted Grain Drying in Hot and Humid Areas; Rapport, Sveriges
Lantbruksuniversitet: Lund.
He, X., Lin, R., Cheng, S. et al. (2021). Effects of microwave vacuum drying on the moisture
migration, microstructure, and rehydration of sea cucumber. J Food Sci., 86(6):2499.
https://doi:10.1111/1750-3841.15716
Huang, L. & Zhang, M. (2012). Trends in development of dried vegetable products as snacks. Dry
Technol., 30(5):448–461.
Huang, L., Zhang, M., Wang, L., Mujumdar, A.S. & Sun, D. (2012). Influence of combination
drying methods on composition, texture, aroma and microstructure of apple slices. LWT -
Food Science and Technology, 47(1):183-188. https://doi:10.1016/j.lwt.2011.12.009
Jiang, H., Zhang, M. & Mujumdar, A. S. (2010). Physico-chemical changes during different stages of
MFD/FD banana chips. J. Food Eng., 101(2):140–145.
Kang, H., Zhang, G., Mu, G. et al. (2022). Design of a greenhouse solar-assisted heat pump
dryer for kelp (Laminaria japonica): System performance and drying kinetics. Foods,
11(21):3509. https:// doi:10.3390/foods11213509
K
€
ose,
B.
& Erent
u
€
rk,
S.
(
2010).
Drying
characteristics
of
mistletoe
(
Vis-
cum album L.) in convective
and UV combined convective type dryers. Ind. Crop. Prod., 32(3):394–399.
Lewicki, P. P. (2006). Design of hot air drying for better foods. Trends Food Sci. Tech., 17(4):153–
163.
Li, Y., Jiang, S., Zhu, Y., et al. (2023). Effect of different drying methods on the taste and volatile
compounds, sensory characteristics of Takifugu obscurus. Food Sci Human Wellness,
12(1):223-232. https://doi:10.1016/j.fshw. 2022.07.012
Mario, P., Roberto, L. & Gipsy, T. (2016). Modelling of red abalone (Haliotis rufescens) slices
drying process: Effect of osmotic dehydration under high pressure as a pretreatment. Innov Food
Sci Emerg Technol., 34:127-134. https://doi:10.1016/j.ifset.2016.01.014
Marquez, E., Ocaño, V.M. & Maeda, A.N. (2009). Citric acid as pretreatment in drying of Pacific
Lion's paw scallop (Nodipecten subnodosus) meats. Food Chem., 112(3):599-603. https://doi:
10.1016/j. foodchem. 2008.06.015
Moon, J.H., Kim, M.J., Chung, D.H., Pan. C. & Yoon, W.B. (2014). Drying characteristics of sea
cucumber (Stichopus japonicas selenka) using far infrared radiation drying and hot air drying. J
Food Process Preserv., 38(4): 1534-1546. https://doi:10.1111/jfpp.12113
Nawirska,
A.,
Figiel,
A.,
Kucharska,
A.Z.,
Sok
´
o
»
-
º
e
˛towska,
A.
&
Bie
siada, A. (2009). Drying
kinetics and quality parameters of pumpkin slices dehydrated using different methods. J. Food
Eng., 94(1):14–20.

21
Neslihan, C. & Arif, H. (2009). A review of heat pump drying: Part 1-Systems, models and
studies. Energy Convers Manag., 50(9):2180-2186. https://doi:10.1016/j.enconman.2009.04.031
Nowsad, AKM. A. (2007). Participatory Training of Trainers: A New Approach Applied in Fish
Processing. Bangladesh Fisheries Research Forum, Dhaka.
Nowsad, AKM.A. (2014). Post-harvest Fishery Losses and Mitigation Measures. Department
Fisheries Technology, BAU, Mymensingh.
Pankyamma, V., Mokam, S.Y., Debbarma, J. & Rao, B.M. (2019). Effects of microwave vacuum
drying and conventional drying methods on the physicochemical and microstructural properties
of squid shreds. J Sci Food Agric., 99(13):5778-5783. https://doi.10.1002/jsfa.9846
Pereira, R. N. & Vicente, A. A. (2010). Environmental impact of novel thermal and non-thermal
technologies in food processing. Food Res. Int. 43(7):1936–1943.
Sachithananthan, K., Trim, D. S. & Speirs, C. I. (1985). A solar-dome dryer for drying fish.
Proceedings of the FAO Expert Consultants of Fish Technology In Africa, Lusaka Zambia. Part
329: 161-172.
Sagar, V. R. & Suresh, K. P. (2010). Recent advances in drying and dehydration of fruits and
vegetables: a review. J. Food Sci. Tech., 47(1):15–26.
Selcuk, M. K., Ersay, O. & Akyurt, M. (1974). Development, Theoretical Analysis and Performance
Analysis of Shelf Type Solar Dryers. Solar Energy, 16:81–88. https://doi.10.1016/0038-
092X(74)90003-6
Shi, Q., Xue, C., Zhao, Y. et al. (2007). Optimization of processing parameters of horse mackerel
(Trachurus japonicus) dried in a heat pump dehumidifier using response surface methodology.
J Food Eng., 87(1):74-81. https://doi:10.1016/j.jfoodeng.2007.11.010
Shi, Q., Tian, Y., Zhu, L. & Zhao, Y. (2019). Effects of sodium alginate-based coating
pretreatment on drying characteristics and quality of heat pump dried scallop adductors. J Sci
Food Agric., 99(10):4781-4792. https://doi:10.1002/jsfa.9728
Sokhansanj, S. & Jayas, D.S. (2014). Drying of foodstuffs. In: Handbook of Industrial Drying,
Mujumdar, A.S. (ed), CRC Press, New York.
Toshihara, T. (2021). Chorkor type oven dryer for drying fish in cloudy weather. Fisheries
Engineering Co., Japan International Cooperation Agency.
Uemura, K., Kanafusa, S., Takahashi, C. & Kobayashi, I. (2017). Development of a radio frequency
heating system for sterilization of vacuum-packed fish in water. Bioscience,
Biotechnology, and Biochemistry, 81(4):762-767. https://doi:10.1080/09168451.2017.1280660
Viji, P., Shanmuka, S.K., Debbarma, J. et al. (2019). Evaluation of physicochemical
characteristics of microwave vacuum dried mackerel and inhibition of oxidation by essential
oils. Journal of Food Science and Technology, 56:1890
-
1898. https://doi:10.1007/s13197-019-
03651-7
Wang, Y., Zhang, M. & Mujumdar, A. S. (2011). Trends in processing technologies for dried aquatic
products. Dry Technol., 294):382–394.
Wang, Y., Zhang, M., Mujumdar, A. S., & Mothibe, K. J. (2012). Quality changes of dehydrated
restructured fish product from silver carp (Hypophthalmichthys molitrix) as affected by drying
methods. Food Bioprocess Technology, 6(7):1664–1680.
Wu, S., & Wang, L. (2016). Anti-browning of the adductor muscles of bay scallop by glutathione
during hot air drying. J Aquatic Food Product Technology, 25(8):1278-1283.
https://doi:10.1080/10498850. 2015.1056397
Yin, M., Matsuoka, R., Yanagisawa, T. et al. (2022). Effect of different drying methods on free
amino acid and flavor nucleotides of scallop (Patinopecten yessoensis) adductor muscle.
Food Chem., 613. doi:10.1016/j.foodchem.2022.133620
Zhang, J., Cao. J. & Pei, Z. (2019). Volatile flavour components and the mechanisms
underlying their production in golden pompano (Trachinotus blochii) fillets subjected to
different drying methods: A comparative study using an electronic nose, an electronic tongue

22
and SDE-GC-MS. Food Research International, 123: 217-225.
https://doi:10.1016/j.foodres.2019.04.069
Zhang, M., Chen, H., Mujumdar, A.H., Tang, J., Miao, S. & Wang, Y. (2017). Recent
developments in high-quality drying of vegetables, fruits, and aquatic products. Critical Reviews
in Food Science and Nutrition, 57 (6): 1239–1255.
Zhang, M., Tang, J., Mujumdar, A. S. & Wang, S. (2006). Trends in microwave-related drying of
fruits and vegetables. Trends Food Sci Tech., 17(10):524–534.
Zhu, Z., Zhao, Y., Zhang, Y. et al. (2021). Effects of ultrasound pretreatment on the drying kinetics,
water status and distribution in scallop adductors during heat pump drying. J Sci
Food Agric., 101(15): 6239-6247. https://doi:10.1002/jsfa.11290