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Copyright © 2017 by Modern Scientific Press Company, Florida, USA
International Journal of Food Nutrition and Safety, 2017, 8(1): 45-72
International Journal of Food Nutrition and Safety
Journal homepage: www.ModernScientificPress.com/Journals/IJFNS.aspx
ISSN: 2165-896X
Florida, USA
Review
Drying and the Different Techniques
Uwem Inyang 1,*, Innoccent Oboh 1, Benjamin Etuk 1
1Department of Chemical and Petroleum Engineering, University of Uyo, Uyo, Akwa Ibom State,
Nigeria
* Author to whom correspondence should be addressed; E-Mail:uweninyang7@yahoo.com
Article history: Received 30 May 2017, Revised 12 July 2017, Accepted 20 November 2017,
Published 20 December 2017.
Abstract: Drying is removing a large portion of the water contained in a product in order to
considerably reduce the reactions which leads to deterioration of the products. In less
developed countries where industry is not very important there is a general feeling that drying
is an easy operation and not too much input is needed and anybody can do it. Drying of foods
is a complex business and a mere translation from other fields is not often advisable. Drying
plays an important role in food and agricultural industries and is the oldest method of
preservation. The main feature of this process consists on lowering the water content in order
to avoid or slow down food spoilage by microorganism. This review focuses upon
conventional and new drying techniques and their advantages, limitations and applications.
Keywords: drying; moisture; preservation; food spoilage; deterioration of products
1. Introduction
Drying is probably the oldest and the most important method of food and vegetables preservation
practiced by humans (Doymaz, 2005a). It removes moisture and preserve products. Drying process
involves heat and mass transfer (Adeboye and Oputa, 1996; Bamire and Oke, 2003). Drying which is
the removal of moisture prevents the growth and production of microorganisms that causes decay; it
minimizes the moisture-mediated deteriorative reactions. It also can cause substantial reduction in
weight and volume, minimizing packaging, storage and transportation costs and enables storability of
the product under ambient temperature (Owolarefe et al., 2007). During drying a lot of changes occur
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46
which can be structural and physico-chemical modifications that can affect the final product quality
(Doymaz, 2005; Okos et. al, 1992).
Thermal damage incurred by a product during drying is directly proportional to the temperature
and time involved (Lin et al.1998), which means that decreasing drying time can improve the quality of
products.
However, drying has always been of great importance for the preservation of food, thus, the
major reason of drying food products is for the reduction of moisture content. Improvement of product
quality and reduction of post-harvest losses can only be achieved by the introduction of suitable drying
technologies (Bala and Janjai, 2009).
Drying processes can be classified into four categories namely solar drying, atmospheric drying,
sub atmospheric drying and novel drying technologies (Jayaraman and Gupta, 1995). Solar drying
includes sun or natural dryers, solar dryers-direct, solar dryers indirect and hybrid or mixed systems.
Atmospheric drying is either continuous or batch. Continuous drying utilizes dryers such as spray dryer,
fluidized bed dryer, belt dryer, rotary dryer, tunnel dryer and drum dryer whereas batch drying requires
dryers such as kiln dryer, cabinet or compartmental dryer and tower dryer. Sub-atmospheric drying
includes vacuum shelf dryer, continuous vacuum dryer and freeze dryer. Novel drying technologies are
microwave drying, infra-red radiation drying, electric or magnetic field drying, superheated steam
drying, explosion puffing, foam mat drying, acoustic drying and osmotic dehydration (Jayaraman and
Gupta, 1995).
In this paper, drying methods will be studies and their principles of operation, uses and the
advantages and disadvantages of these methods in terms of their drying effectiveness and efficiency will
be addressed, with the future prospects of drying and dryers discussed.
2. Methods of Drying
The essence of drying in the industries, especially processing and food industry cannot be
overestimated. To achieve the expected drying of materials, several methods of drying have been
developed and further researches are still been carried out. Some of these include but not restricted to
the following listed.
2.1. Air Drying
Air-drying is considered to be one of the simplest and most economical ways of commercially
processing fruit and vegetables (Brennan et al, 1990). This process takes place when materials are dried
with unheated forced air, taking advantage of its natural drying potential. The process is slow and
weather dependent (Roy, 2015).
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Air-drying could be considered as appropriate to developing countries as the product, suitably
packaged, can be stored for several months without the risk of spoilage (Marriott and Lancester, 1983).
2.2. Hot- air Drying
In hot-air drying, enough water must be removed to lower the water activity to a level which
inhibits the growth of microorganisms and reduces the rate at which enzymatic and non-enzymatic
reactions occur. Thus, one of the primary requirements in using hot-air drying is to understand the drying
process, to be able to predict drying times, establish the distribution of moisture throughout the solid
pieces during drying and the influence of the processing variables such as air temperature and velocity,
pretreatment and the size of the pieces on drying behaviour (Johnson, et al, 1998). Hot-air drying is an
alternative drying method. Using hot air dryers leads to a more uniform, hygienic and attractive products
that can be produced rapidly (Karathanos and Belessiotis, 1999).
2.3. Sun Drying
Sun drying is one of the oldest and accessible processes used by farmers to preserve different
foodstuffs. It is an efficient way to reduce wastes (Touré, 2012). Sun drying is the traditional method of
drying in developing countries and it denotes the spreading of foodstuff in the sun (direct sunlight) on a
suitable surface such as mat, roof, or drying floors (Bindu et al, 2016).
Sun-drying method is cheaply executed, takes a longer time and may be prone to contaminations
from microorganisms due to unhygienic exposures (Yarkwa and Uvir, 2015). Moreover, the direct
exposure to sunlight, or more precisely ultra-violet radiation, can greatly reduce the level of nutrients
such as vitamins in the dried product (Tunde and Akitunde, 2011).
Folaranmi (2008) asserted that sun drying is plagued with in – built problems, since the product
during drying is unprotected from theft, rain, storm, windborne dirt, dust and infestation by insects,
rodents, and other animals, encourages mould growth and may result in relatively high final moisture
content. Consequently, the quality of dried products may be adversely affected, falling to meet the
required local and international standards (Ivanova and Andonov, 2001; Abdelhaq and Labuza, 1987).
Moreover, since sun drying depends on uncontrolled factors, production of uniform and standard
products is not expected. The quality of sun dried foods can be improved by reducing the size of pieces
to achieve faster drying and by drying on raised platforms, covered with cloth or netting to protect against
insects and animals (Bolea et al, 2012; Papu et al, 2014).
2.4. Solar Drying
Solar drying technology seems to be one of the most promising alternatives to reduce the post-
harvest losses (Wiriya et al, 2009). Solar drying technology is one of the renewable energy resources
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48
particularly for low temperature heating and is a very attractive option for the small scale and resource
poor enterprise (Chavda and Kumar, 2009). The solar dried products have much better colour and texture
as compared to open sun dried products (Mulokozi and Svanberg, 2003). The attractiveness of solar
dryers is further enhanced by its ability to dry the product rapidly, uniformly and hygienically to meet
national and international standards with zero energy costs (Condori et al, 2001). The food is dried using
solar thermal energy in a cleaner and healthier way (TaTEDO, 2007). However, it has been noted that,
drying at higher temperatures may cause damage to the flavour, colour and nutrients of the dehydrated
products (Praveenkumar et al, 2006). Due to the current trends towards higher cost of fossil fuels and
uncertainty regarding future cost and availability, use of solar energy in food processing will probably
increase and become more economically feasible in the near future.
They can be constructed from locally available materials at a relatively low capital cost and there
are no fuel costs. Thus, they can be useful in areas where fuel or electricity are expensive, land for sun
drying is in short supply or expensive, sunshine is plentiful but the air humidity is high
(Velayudham et al, 2015; Bindu et al, 2016). They give faster drying rates by heating the air to
10 - 300C above ambient, which causes the air to move faster through the dryer, reduces its humidity
and deters insects. The faster drying reduces the risk of spoilage, improves quality of the product and
gives a higher throughput, so reducing the drying area that is needed. However, care is needed when
drying fruits to prevent too rapid drying, which will prevent complete drying and would result in case
hardening and subsequent mould growth (Papu et al, 2014; Gavhale et al, 2015). Solar dryers also
protect foods from dust, insects, birds and animals (Sacilik, et al, 2006). They allow for less spoilage
and less microbiological infestation, thus leads to improved and more consistent product quality (Tunde
and Akitunde, 2011).
Solar drying technology produces better quality products and is considered to be an alternative
for drying agricultural products in developing countries (Gürlek, et al, 2009). However, dependency on
weather for drying operation is one of the setbacks in solar drying technology. (Prakash and Kumar,
2013; Sontakke and Salve, 2016).
2.4.1. Mechanism of solar dryer
A solar dryer has three main components and these are drying chamber, solar collector and some
type of airflow system. A drying chamber is an enclosed, insulated structure inside which both solar
collection and drying takes place. It is often insulated to increase efficiency (Chavda and Kumar, 2009).
The solar collector (or absorber) is often a dark coloured box with a transparent cover and Glass is
recommended for the absorber cover. The solar collector can be of any size and should be tilted toward
the sun to optimize collection. The size of solar collector required for a certain size of dryer depends on
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49
the ambient temperature, amount of sun, and humidity (Green and Shwartz, 2001; Chavda and kumar,
2009)
Tilting the collectors is more effective than placing them horizontally, for two reasons. First,
more solar energy can be collected when the collector surface is more nearly perpendicular to the sun's
rays. Second, by tilting the collectors, the warmer, less dense air rises naturally into the drying chamber
(Chua and Chou, 2003; Prakash and Kumar, 2013).
Solar dryers use one of two types of airflow systems which are natural (passive) and forced
(active) convection. The natural convection utilizes the principle that hot air rises, and forced convection
dryers force air through the drying chamber with fans. The effects of natural convection may be enhanced
by the addition of a chimney in which exiting air is heated even more (Eltawil et al, 2012). Additionally,
prevailing winds may be taken advantage of (Green and Shwartz, 2001; Zomorodian, et al, 2007).
The Solar Dryers may be classified into several categories, depending upon the mode of heating
or the mode of their operations and airflow systems. Depending on how heat is provided for drying, solar
dryers can be broadly divided into four categories namely; direct, indirect, mixed and hybrid types
(Fudholi et al., 2010; El-Sebaii and Shalaby, 2012).
2.5. Infra-red Drying
Infra-red is usually the best choice where a process requires high temperature and a lower capital
expense. It is used for heat setting as well as drying and curing thinner coatings, such as paints, ink paper,
textiles, adhesives in making films for appliances and electronics (Pawar and Pratape, 2017).
Infra-red drying involves heat transfer by radiation between a hot element and a material at lower
temperature. The peak wavelength of the radiation is dependent on the temperature of the heated element.
Thermal radiation is considered to be infrared in the electromagnetic spectrum between the end of the
visible 0.78µm and 1000 µm (Sulistiyanti et al, 2009).
In this method heating the product is performed without undesirable changes in structure, so the
structural quality of the product is improved, its biological yield is increased and costs of operation are
decreased (Strumillo and Kudra, 1987). Another advantage of drying using infrared radiation is the
minimization of product losses such as color change and shrinkage. Also IR radiation causes rapid and
direct heat concentration on the material compared to the convective dryers in which part of the heat is
absorbed by the inlet air and wasted. IR drying method in fact developed for high drying rate without
the risk of burning the material (Nonhebel, 1973).
In infrared method of drying, effective diffusion coefficient of moisture showed an increasing
trend with increasing radiation intensity and decreasing airflow rate. Increasing the intensity of radiation,
elevated the temperature gradient of the surface and underlying layers of the product. Also, decreasing
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50
the air velocity by reducing the cooling effect of air flow in this method increased the diffusion
coefficient inside the product (Saeid et al, 2011).
2.6. Microwave Drying
Microwave drying is an alternative method that has been used in the food industry. Microwaves
are electromagnetic waves which range between 0.3 GHz and 300 GHz. The most commonly used
frequencies are 915 MHz and 2450 MHz. The microwave heating method dehydrates food by
interactions between the electromagnetic energy and polar molecules within the material. Polar
molecules rotate in response to the applied oscillating electromagnetic waves. The reorientation of these
molecules in a high frequency electric field occurs frequently and rapidly, resulting in molecular friction
that generates heat (McGurk et al, 2017). Microwave heating is a desirable alternative drying method
since it enhances the energy efficiency and has less negative impact on the quality of the dehydrated
products (Huang, 2013).
Microwave drying of products has become common because microwave drying prevents a
decline in the quality of the product and; ensures the rapid and efficient distribution of heat within the
material (Li et al., 2009; Dong et al 2011; Silva et al., 2007). Moreover, microwave drying reduces
drying time and saves energy and also producing high quality dry products (Balbay et al., 2011; Li et al.,
2010).
Applying microwave energy under vacuum combines advantages of both vacuum drying and
microwave drying as far as improved energy efficiency and product quality are concerned. Vacuum dried
materials are characterized by higher porosity, depending on level of vacuum and less deterioration of
colour and volatile aroma ( Larrosa et al, 2017; shiby et al, 2015).
2.7. Drum Drying
In a drying operation, liquid, slurry, or puree material is applied as a thin layer onto the outer
surface of revolving drums that are internally heated by steam (Kasiri et al, 2004; Tang et al, 2010).
In drum drying, a large amount of thermal energy is released by the condensing steam in the
drum and conducted through drum wall to the product. During drying, a product may go through three
general periods. The first is the initial heating period where wet materials are applied onto the drum
surface in a thin layer. Intensive heat transfer occurs due to a great temperature difference between the
drum surface and the wet product and product temperature increases rapidly to reach the boiling point
of free water. The second period is the constant product temperature period where after reaching the
boiling temperature, a large amount of free water evaporates and product temperature remains constant.
The drum surface temperature, however, decreases due to an intense evaporative cooling. The third is
the rising product temperature period, where after removing most of the free water, the amount of
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51
moisture for evaporation is dramatically reduced. The heat transferred from the steam gradually exceeds
the energy used for evaporation. As a result, drum surface temperature increases. The bound water starts
to play a major role in controlling the rate of evaporation. As bound water has a higher boiling
temperature, product temperature gradually increases as drying proceeds (Rodriguez, et al, 1996).
In the operation of a drum dryer, a delicate balance needs to be established among feed rate,
steam pressure, roll speed, and thickness of the product film. It is desirable to maintain a uniform film
on the drum surface to ensure maximized throughput and consistent final moisture content. Problems,
however, are often encountered due to fluctuations in the moisture content and thickness of the feed.
Means have been developed to automatically detect the moisture content and temperature, integrated
with automated feedback control to minimize the fluctuations. (Rodriguez, et al, 1996)
Products containing high sugar contents, such as tomato puree, may be difficult to remove from
the drums at high temperatures due to the thermo plasticity of those materials. A cooling mechanism
(e.g., a jet of cold air) may be used at the location just before the product reaches the scraper. The purpose
of the cooling is to bring the product from a rubbery state into a glassy state to facilitate separation of
the product from the drum surface (Tang et al, 2010).
Drum dryers are used in the food industry for drying a variety of products, such as, milk products,
baby foods, breakfast cereals, fruit and vegetable pulp, mashed potatoes, cooked starch, and spent yeast
(Rodriguez et al, 1996).
2.8. Spray Drying
This technique enables the transformation of feed from a fluid state into dried particulate form
by spraying the feed into a hot drying medium. It is a continuous particle processing drying operation.
The feed can be a solution, suspension, dispersion or emulsion. The dried product can be in the form of
powders, granules or agglomerates depending upon the physical and chemical properties of the feed, the
dryer design and final powder properties desired (Michael, 1993).
Spray drying is presently one of the most exciting technologies for the pharmaceutical industry,
being an ideal process where the end-product must comply with precise quality standards regarding
particle size distribution, residual moisture content, bulk density and morphology. The production of
particles from the process of spraying has gained much attention in recent years (Suthur et al, 2009).
2.9. Oven Drying
In conventional oven heating, the heat is transferred from the surface to the interior of the
material. Thus a pressure is generated between the surface and interior due to evaporation, such that the
interior moisture is driven out and evaporation continues at the surface. However, conventional oven
heating has low energy efficiency with negative quality effects (Huang, 2013).
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The oven takes two or three times longer to dry food when compared with other dryers. Thus,
the oven is not as efficient and uses more energy. There are two types of ovens namely batch and
conveyor ovens. The oven uses convective process (force air convective and gravity convective). It is
used in various industrial applications for drying, curing (rubber), baking, etc. Lapses in oven drying are
due to induced evaporation. Explosion can occur since the product when dried reaches its combustion
level. It is difficult to get humidity of the oven due to lack of flow velocity for easy circulation (Brennand,
1994).
2.10. Vacuum Drying
Vacuum drying is a process that allows for materials to be dried in a reduced pressure
environment, which lowers the heat needed for rapid drying. This drying method is recommended to
counter the undesirable effects of Infrared drying method and to improve the product quality, as well as
nutritional value. The method allows effective moisture elimination under low pressure (Jaya and Das,
2003). Vacuum drying enhances the mass transfer because of an increased vapour pressure gradient
between the inside and outside of the product (Pere and Rodier, 2002).
Vacuum dryers offer low-temperature drying of thermolabile materials and are suitable for
solvent recovery from solid products containing solvents (Parikh, 2015) and also less energy usage
and hence greater energy efficiency, improved drying rates, and in some cases, less shrinkage of the
product (Alibas, 2007; Alibas, 2009).
2.11. Freeze Drying
Lyophilization or freeze drying is a process in which water is frozen, followed by its removal
from the sample, initially by sublimation (primary drying) and then by desorption (secondary drying).
Freeze drying is a process of drying in which water is sublimed from the product after it is
frozen.(Akers et al,1987; Chien and Yiew, 1981). The term “lyophilization” describes a process that
produce a product that “loves the dry state” (Remington, 2000a).
Intact cake, sufficient strength, uniform color, sufficiently dry, sufficiently porous, sterile, free
of pyrogens, free of particulates, chemically stable are the desired characteristics freeze dried products
(Khairnar et al, 2013; Pandhare et al, 2015; Rajeevini et al, 2015).
Three methods of freeze drying are commonly used namely; manifold drying, batch drying, and
bulk drying. Each method has a specific purpose, and the method used depends on the product
and the final configuration desired. Since freeze drying is a change in state from the solid phase to the
gaseous phase, material to be freeze dried must first be adequately prefrozen (Khairnar et al,2013;
Gaidhani et al, 2015; Rajeevani et al, 2015).
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It is a drying process applicable to manufacture of certain pharmaceuticals and biologicals that
are thermo labile or otherwise unstable in aqueous solutions for prolonged storage periods, but that are
stable in the dry state. The knowledge of how to control, or at least manipulate, the freezing step will
help to develop more efficient lyophilization cycles and biopharmaceutical products with an improved
stability (Kasper and Friess, 2011; Esfandiary et al, 2016).
2.12. Osmotic Drying
Osmotic dehydration is the phenomenon of removal of water from lower concentration of solute
to higher concentration through semi permeable membrane results in the equilibrium condition in both
sides of membrane (Tiwari 2005). Osmotic dehydration found wide application in the preservation of
food-materials since it lowers the water activity of fruits and vegetables. Osmotic dehydration is
preferred over other methods due to their color, aroma, nutritional constituents and flavor compound
retention value (Yadav and Singh, 2014; Alakali et al., 2006; Torres et al., 2006; Pokharkar and Prasad,
1998). Osmotic dehydration results in increased shelf-life, little bit loss of aroma in dried and semidried
food stuffs, lessening the load of freezing and to freeze the food without causing unnecessary changes
in texture (Petrotos and Lazarides, 2001).
Osmotic dehydration involves the immersion of foods (fish, vegetables, fruits and meat) in
osmotic solution such as salts, alcohols, starch solutions and concentrated sugars, which some extent to
dehydrates the food (Erle and Schubert, 2001). Different types of solutes such as fructose, corn syrup,
glucose, sodium chloride and sucrose are used as osmotic agent for OD (Azuara and Beristain, 2002).
It involves dehydration of fruit slices in two stages, removal of water using as an osmotic agent
(osmotic concentration) and subsequent dehydration in a dryer where moisture content is further reduced
to make the product shelf stable (Ponting, 1973).
Therefore, the characteristics of the product can be varied by controlling temperature, sugar syrup
concentration, concentration of osmosis solution, time of osmosis etc., to make osmotic concentration
process faster (Chavan and Amarowicz, 2012).
2.13. Foam Mat Drying
The foam mat drying is a process in which the trans-formation of products from liquid to stable
foam is followed by air drying (Franco et al, 2015; Sangamithra et al, 2015; Affandi et al, 2017).
Stable gas-liquid foam is the primary condition for successful foam drying. Proteins, gums and
various emulsifiers such as glycerol monostearate, propyleneglycerol monostearate, carboxymethyl
cellulose [CMC], trichlorophosphate are used as foaming agents. Mixtures are whipped to form stable
foams using blender or specially designed device. The foam is then spread as a thin sheet or mat and
exposed to a stream of hot air until it is dried to desired moisture content (Rajkumar et al, 2007). Drying
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54
is carried out at relatively low temperatures to form a thin porous honeycomb sheet or mat, which is
disintegrated to yield a free-flowing powder. The larger surface area exposed to the drying air is the main
cause of moisture removal acceleration (Brygidyr et al. 1977). However, capillary diffusion is also the
main reason for the moisture movement within the product during foam mat drying (Sankat and
Castaigne 2004).The dried product obtained from foam mat drying is of better quality, porous and can
be easily reconstituted.
This process can be used for large-scale production of fruit powders because of its suitability for
all types of juices, rapid drying at lower temperature, retention of nutritional quality, easy reconstitution
and is cost-effective for producing easily re-constitutable juice powders. Fruit juice powders obtained
through this process have high economic potentials over their liquid counterparts such as reduced volume
or weight, reduced storage space, simpler handling and transportation, and much longer shelf life
(Sangamithra et al, 2015; Sharifi et al, 2015; Chandrasekar et al, 2015; Singh and Dixit, 2014;). The
fruit powders obtained through this method can find applications in snacks, beverages, ice creams,
bakery products, as a starter for the preparation of instant foods, pastes, etc. (Sangamithra et al, 2015)
A proper understanding of selection of suitable foaming agents, foaming properties such as foam
density, foam expansion, foam stability, method of drying, drying temperature, are required for the
process optimization, in order to obtain products with better nutritional characteristics and process yield
(Kandasamy et al, 2014; Kumar et al, 2015; Ismaila et al, 2016).
2.14. Impingement Drying
Air impingement drying is not a new technology but it is a complicated process and it is used for
food and agricultural product processing. Impingement drying can be affected by many factors such as
drying temperature, air velocity and relative humidity which can influence its drying characteristics and
quality (Xiao et al, 2010).It is an efficient drying process and has been used successfully in paper and
textile industries and also with the purpose of drying, cooling, or heating different artefacts and metals.
It has only recently been applied to food products (Moreira 2001). One of the obvious advantages of
impingement drying techniques is rapid drying. In air impingement processing, the air impinges on
the product surface at high velocity, removes thermal boundary layers of moisture and cold air
and increases the rate of heat transfer (Anderson and Singh 2006). The high-velocity air from the nozzles
creates a bed of hot air that suspends the products; thus, temperature at the center of the product rises
rapidly to the drying air temperature. So, air impingement drying can greatly accelerate heat transfer and
reduce process time (Mujumdar 1986). Uniform, hygienic and attractively colored product can be
produced rapidly using air impingement drying (Xiao et al, 2010).
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Energy consumption and environmental issues are naturally important factors in drying processes
and impingement jet drying are no exception (Ljung et al, 2017).
2.15. Acoustic Drying
This process can cause the removal of moisture from a material under high intensity sound field
(audible and ultrasound frequency range). There are two phenomenas involve in acoustic drying. In
primary phenomena, the factors involve in acoustic drying are sound frequency, intensity, sound pressure
and particle velocity while the change of hydrodynamic condition, barometric pressure and turbulent
agitation of air at the boundary layer close to the material is the secondary phenomena(Seya and Otsuka,
1980; Kouchakzadeh, 2013).
2.16. Explosion Puffing Drying
This is a new drying technology that uses high temperature and pressure to dry products. It has
the combine advantages of a convective hot air and a vacuum freeze drying. The puffed fruits and
vegetables are natural, healthy foods and contain plentiful nutrition, also it has excellent qualities and
wide application prospects (Sullivan and Craig Jr, 1994; Kozempel et al, 2008).
2.17. Hybrid Dryers
There are different types of hybrid dryers available with different operational techniques and
designs. Their major advantages are increased drying rates, better, safer, efficient and effective and good
quality of products. Solar dryers may be useful as hybrid dryer when added as a means of heating air for
artificial dryers to reduce fuel costs (Fellows, 1997). The combined process of osmotic dehydration (OD)
and freezing is called osmodehydrofreezing which is used to get better texture properties of fruits and
vegetables as well as lessen the structural collapse and drip loss. Giannakourou and Taoukis (2003)
studied that change in quality of osmodehydrofrozen of green peas treated with maltitol and trehalose
combined with CaCl2 and NaCl and they observed that osmotic treatment lowered the quality changes
in term of texture, color and retention of ascorbic acid for frozen samples. The dehydrofreezing process
also concerned with improving of quality (Khan, 2012).
Infrared radiation has been used in conjunction with several drying methods because it has
advantages of increasing the drying efficiency (Ratti and Mujumdar, 1995). Examples are the Infrared –
vacuum drying (Swasdiasevi et al, 2009; Saetan et al, 2013; Yunhong et al, 2015; Alaei and Chayjan,
2015), Foam mat – cabinet dryer (Thirupathi et al, 2008; Rajkumar et al, 2007), microwave – vacuum
dryer (Berteli et al, 2009); Yongsawatdigul and Gunasekaran,1996); Clary et al, 2007), vacuum – spray
dryer (Wisniewski, 2015), oven vacuum dryer (Amellai and Benamara ,2008); Kumaravel et al, 2012),
low – pressure superheated steam drying and far infrared radiation (LPSSD – FIR),Nimmol et al, 2007;
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56
Pawar and Pratape (2017), impingement and superheated steam drying (Moreira, 2001), impingement
and hot air drying (Xiao et al, 2012; Jambunathan et al, 1992; Xiao et al, 2014), etc. Efforts are been
made to design more of these hybrid dryers which can perform better under adverse weather conditions.
3. Advantages, Limitations and Applications of Drying Methods
Table 1 gives a summary of all the drying techniques discussed with their advantages,
limitation(s) and application(s).
Table 1: Advantages, limitations and applications of drying methods
S/N
METHOD
ADVANTAGE(S)
LIMITATION(S)
APPLICATION
REFERENCES
1.
Natural(Open)
air Drying
Simplest and
most economical
way of drying.
Use unheated
heat(free air)
Natural drying
potential
Can be stored for
some months
without spoilage
No equipment
Kept in open
space
Has problem of
contamination,
infestation, microbial
attack and the drying
time is long.
Cannot handle large
quantities and to
achieve consistent
quality standards.
Problem of predators
Process is slow and
weather dependent.
Fruits and
Agricultural
products e.g
corn, rice, millet,
bean, pepper,
okro, groundnut,
yam, sorghum,
plantain chips,
etc Practiced in
tropical
countries.
Itodo et al, 2002
Togrul and
Pehlivan, 2004
Bolaji, 2005
2.
Hot air Drying
Rate of drying is
fast
Low capital and
maintenance
cost
Flexible in
operation
Water activity
will be reduced
to a level that
inhibits growth
of
microorganism
Influence the
processing
variables e.g
temperature, air
velocity,
humidity
Low energy
efficiency
Quality loss and long
drying time during
falling rate period
Relatively poor
quality/control as
food dries rapidly if
close to heat source.
Food and
agricultural
products
Boudrioua et al,
2003
Johnson et al , 1998
3.
Fluidized Bed
drying
Thorough
mixing of solids
which results in
efficient mass
and heat
transfer.
Rapid and
economic drying
Ease of control
Loss of product
qualities such as
color, texture,flavour
and nutrients
Food and
Agricultural
products
Sagar and Kumar,
2010
Elkhodiry et al,
2015
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
57
Temperature
uniformity
Easy handling
and transport of
material
4.
Sun Drying
Natural heat
from sun
Cheap to use
and economical
Spreading of
foodstuff under
direct sunlight
on a suitable
surface
Require little
expertise
Efficient(drying)
way to reduce
waste
Reducing the
thickness of the
product for
faster drying.
Poor quality due to
vulnerability to
contamination by
insects, birds and dust
Direct exposure to
sunlight (or ultra –
violet radiation) can
reduce the level of
nutrients.
Unprotected from
theft, rain and
infestation
May result in
relatively high final
moisture content
which encourages
mould growth
Takes longer time to
dry
Due to uncontrollable
factors, production of
uniform and standard
products is not
expected.
Food and
agricultural
products
Ivanova and
Andonov, 2001
Yarkwa and Uvir,
2015
Abdelhaq and
Labuza, 1987
Karathanos and
Belessiotis, 1997
Bolea et al, 2012
Papu et al, 2014
5.
Solar Drying
Require little
maintenance
Low
temperature
heating
Most cost
effective: uses
energy from
the sun to heat
a stream of air
to provide air.
Uses natural or
forced
convective air
Less
contamination
because it is in
a closet
Less
susceptible to
adverse
weather
conditions
Depending on
the size and
sophistication
of the dryer.
Reduces land
required when
compare to air
drying.
Requires adequate
solar radiation
UV radiation can
damage food
nutrients
Expensive than direct
sun drying
Need skilful fellow to
construct.
Each location have
different
configuration/type
Food and
agricultural
products
Akbulut and
Durmus, 2010
Bolaji and olalusi,
2008
Chavda and Kumar,
2009
Wiriyi et al, 2009
Mulokozi and
Svanberg, 2003
Praveenkumar et al,
2006
Fellows, 1997
Gurlek et al, 2009
Sontakkre and
Salve, 2016
Condori et al, 2001
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
58
Attractive to
small scale
entrepreneur
It is hygiene,
prevent
contamination
and infestation
6.
Infra-red
Drying
Requires
heating at high
temperature
Cost of
operation is
reduced
minimization of
product losses
Rapid and
direct heat
concentration
on the material.
Gives high
drying rate
without
burning the
material.
Has an increasing
radiation intensity
Decreases airflow
rate
Diffusion coefficient
inside the product is
increased.
Requires electricity
Dryer is a
sophisticated one and
maybe difficult to
repair.
It is used for heat
setting as well as
drying and
curing thinner
coatings such as
paints, ink paper,
textiles,
adhesives in
making films for
appliances and
electronics.
Sulistiyanti et al,
2009
Pawar and Pratape,
2017
Ratti and Mujumdar,
1995
Nonhebel, 1973
Saeid et al, 2011
7.
Microwave
Drying
Short or
reduces drying
time
Temperature
and moisture
gradients are in
the same
direction
Enhances
energy
efficiency and
has distribute
more thermal
efficiency
Improve
quality and
flavour of the
product.
Non uniform heating
(uneven distribution
of microwave field
can occur)
Overheating may
take place
Quality deterioration
can take place.
Food,
agricultural and
dairy products
Huang, 2013
Balbay et al, 2011
Li et al, 2010
Larrosa et al, 2017
Shiby et al, 2015
Silva et al, 2007
Dong et al, 2011
8.
Drum Drying
Have high
drying rate
High energy
efficiencies
Suitable for
slurries drying
High capital cost of
machined drum
High damage to
sensitive foods
Electricity failure
could affect the
operation
Fluctuations in the
moisture content and
thickness of the feed
Product like puree
may be difficult to
remove at high
temperature due to
the thermal
plasticity.
Food industry
e.g Potato flakes,
cereals, fruits
purees, baby
foods, etc
Rodriguez et al,
1996
Kasiri et al, 2004
Tang et al, 2010
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
59
9.
Spray Drying
Rapid drying
Low labour
cost
Relatively
simple
operation and
maintenance
Reduces the
transport
weight of foods
Compliance
with the
product
standards.
High capital cost
High feed moisture
content to ensure that
it is pump to the
atomiser
Food processing
and
Pharmaceutical
industries.
Products like
milk, ice cream ,
egg yoghurt,
juice, etc
Michal, 1993
Surthur et al, 2009
10.
Oven Drying
Removes
moisture content
Low labour cost
Flexibility in
operation
Less
contamination
from infestation
Cost efficient
Longer drying time
Harder to control
than drying with
dehydrator
Not efficient and uses
more energy
Explosion might
occur due to induced
evaporation
Case Harding of
product may take
place because of
much heat
Food and
agricultural
products
Bennand, 1994
Huang, 2013
11.
Vacuum Drying
It allows effective
moisture
elimination under
low pressure
Enhances the
mass transfer
because of an
increased vapour
pressure gradient
between the
inside and outside
of the product
Improved drying
rates
Offer low-
temperature
drying for
thermolabile
materials
Suitable for
solvent recovery
from solid
products
containing
solvents
Operating under low
pressure only
Uses to counter infra
red effect
Uses much energy
Less shrinkage of the
product
Food and
agricultural
products
Parikh, 2015
Alibas,2007,2009
Alaei and Chayjan,
2015
Jaya and Das, 2003
Pere and Rodier,
2002
12.
Freeze Drying
Uses sublimation
technique
Oxidizable
substances are
well protected
under vacuum
conditions
Volatile compounds
may be removed by
high vacuum
Single most
expensive unit
operation
Pharmaceutical
s and
biologicals that
are
thermolabile
Pharmaceutical
and
Long et al, 2013
Rajeevini et al, 2015
Harish et al, 2017)
Gatin et al, 2008
Khairnar et al, 2013
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
60
Long
preservation
period owing
water removal
Loading quantity
accurate and
content uniform
Little
contamination
owing to aseptic
process
Minimal loss in
volatile
chemicals and
heat-sensitive
nutrient and
fragrant
components
Minimal changes
in the properties
because microbe
growth and
enzyme effect
can not be
exerted under low
temperature
Transportation
and storage under
normal
temperature
Rapid
reconstitution
time
Constituents of
the dried material
remain
homogenously
dispersed
Product is
process in the
liquid form
Sterility of
product can be
achieved and
maintained
Stability problems
associated with
individual drugs
Some issues
associated with
sterilization and
sterility assurance of
the dryer chamber
and aseptic loading
of vials into the
chamber.
biotechnology
industry
In Food
Industry
In
Technological
Industry for
chemical
synthesis and
bioseparations
Pandhare et al,
2015
Akers et al,1987
Chien and Yiew,
1981
Sunderland, 1980
Shuka, 2011;
Ciurzynska and
Lenart,2011
Gaidhani et al, 2015
Sanjith and Gatin,
1993
13.
Osmotic Drying
Removal of water
from lower
concentration of
solute to higher
concentration
through semi
permeable
membrane results
in the equilibrium
It lowers the
water activity
Retention value
of color, aroma,
nutritional
constituents and
flavor compound
Some of the
osmotic agent may
be costly and not
readily available.
The high viscosity
of the osmotic
solution
low density
difference between
the solid and the
solution
It is a time taking
process
The reduction in
acidity level
reduces the
Preservation of
food-materials
Fruits and
vegetables such
as banana,
sapota,
pineapple,
mango, and leafy
vegetables, etc
Tiwari, 2005
Yadav and Singh,
2014
Alakali et al., 2006;
Torres et al., 2006
Petrotos and
Lazarides, 2001
Azuara and
Beristain, 2002
Giannakourou and
Taoukis, 2003
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
61
Decrease the
energy costs
Lessening the
load of freezing
Inhibiting the
browning of
enzymes
Conducted at low
or ambient
temperature.
characteristic taste
of some products
Khan, 2012
Pokharkar and
Prasad, 1998
Ponting, 1973
Chavan and
Amarowicz, 2012
14.
Foam mat
Drying
Used for large-
scale production
of fruit powders
because of its
suitability for all
types of juices
Rapid drying at
lower
temperature
Retention of
nutritional
quality
Easy
reconstitution of
the product
powders
cost-effective
for producing
easily re-
constitutable
juice
have high
economic
potentials over
their liquid
counterparts
much longer
shelf life
Low bulk density
High cost of water
removal
Energy demand
Reduces drying time
Necessity to addition
of forming agent for
stability of the liquid
or semi – solid food
material which make
such products
unavailable in their
pure form.
In food
processing
industry:
Applications in
snacks,
beverages, ice
creams, bakery
products, as a
starter for the
preparation of
instant foods,
pastes, etc
Sangamithra et al,
2015
Chandrasekar et al,
2015
Franco et al, 2015
Affandi et al, 2017
Rajkumar et al,
2007
Brygidyr et al. 1977
Sankat and
Castaigne 2004
Kudra and Ratti
2006
Kandasamy et al,
2014
Kumar et al, 2015
Ismaila et al, 2016
Kadam et al. 2010a
15.
Impingement
Drying
Most suitable
for products that
have a high
surface area
Used to increase
the convection(
i.e convective
heat transfer)
Rapid drying
increases the
rate of heat
transfer
Thermal damage
incurred by a
product during
drying is directly
proportional to the
temperature and
time involved
Heat transfer at the
surface of the
product
High capital cost
Web tension issues
Energy
consumption and
environmental
issues
Paper, textile and
metal industry.
Food and
agricultural
product
processing.
Ljung et al, 2017
Xiao et al, 2010
Mujumdar 1986
Anderson and Singh
2006
Moreira, 2001
Lin et al.1998
16.
Acoustic
Drying
Effective at
lower
temperatures
Uses high
intensity
It is expensive
Usefulness is
limited because of
sophistication
Needs to be used in
combination with
Pharmaceuticals,
food and
chemical
industry
Seya and Otsuka,
1980
Kouchakzadeh,
2013
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
62
It improve
elasticity
The rate of
water removal
increased when
acoustical
energy is
applied
Enhancing
drying
other process(e.g
heating)
Posible damage by
free radical
Complex mode of
action
17.
Explosion Puff
Drying
Faster
rehydration of
product
Rapid drying
Gives low
moisture content
Retention of
texture and
flavour of
product
Lower nit
processing cost
Processing of
large pieces of
product feasible
Labour intensive
Loss of product
intergrity
High level of heat
Food and
agricultural
products like
apple,
blueberries,
carrots, potatoes,
etc
Sullivan and Craig
Jr, 1984
Kozempel et al,
2008
4. Future Prospects
Drying researches and developments have seen exponential growth over the past three decades.
Initially driven by the need to conserve energy in this highly energy-intensive operations found in almost
all industrial sectors, and focuses on product quality, environmental impact, safety issues, new products,
and processes. Drying provides challenging areas for multi- and cross-disciplinary research of
fundamental as well as applied nature coupling transport phenomena with material science. New areas
of development in drying technologies are Hybrid drying, Superheated Steam drying, Pulse Combustion
drying, Intermittent drying, Spray drying, Impingement drying, etc. Further development in design of
dryers like the continuous foam dryer for example will help to achieve stable foam, which in turn results
in dried powder of high quality and also studies on the microstructure characterization of foams and
foam-dried powders, computer simulation techniques for the prediction of moisture and temperature
distribution in the product requires the attention of researchers for further up gradation of the process. It
is highly expected that the further improvement in foam mat drying process, as well as the use of other
drying method combined with foam mat drying, will intensify the adoption of this renewed method in
the food industry (Sangamithra et al, 2015).The need for industry-academia interaction and for a stake
of industry in academic research is noted as a key step towards successful transfer of innovative drying
technologies to industry (Mujumdar, 2004).
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
63
5. Conclusion
Drying is an important process to preserve raw food materials and the drying process occurs
when water vapor is removed from its surface into the surrounding space, resulting in a dried material
with an extended shelf life and reduced water activity of food products. During drying, the moisture
content can be reduced to a level ranging 1 – 5%, which avoids microbial and undesirable enzymatic
reactions.
There is lots of drying methods and each of these has its own advantages and disadvantages and
could be applied effectively. We also have a combination of two or three methods as in the cases of
hybrid which can give better drying.
Traditional drying methods (sun, oven and solar) are simple to use, however they are not
economical. They have low energy efficiency and require longer drying time. As a result, it negatively
affects the flavour, nutrient content, and may lead to undesirable colours in the dried end product. In
addition, case-hardening is another problem in drying products with these traditional methods. Since the
evaporation of surface water is faster than the movement of water inside the food, case hardening occurs
which prevents the proper drying of the food to its optimal moisture level for storage. The formation of
the outer hard case not only affects the appearance but also the taste of the dried products. Compared to
conventional drying methods, microwave drying has more thermal efficiency and provides an end
product with improved quality and flavour (Huang, 2013).
Acknowledgments
The authors gratefully acknowledge the University of Uyo for superseding.
References
Abdelhaq, E H. and Labuza, T. P. (1987). Air drying characteristics of apricots. Journal of Food
Science, 52(2): 342-345.
Adeboye, O.C., and Oputa, C.O., (1996). Effect of galex on growth and fruit nutrient composition of
okra. Journal of Agriculture, 18 (1/2): 1-9
Affandi, N., Zzaman, W., Yang, T. A. and Easa, A. M. (2017) Production of Nigella sativa beverage
powder under foam – mat drying using egg albumen as a foaming agent, Beverages, 3(9):1 - 15
Alaei, B. and Chayjan, R. A. (2015). Modelling of Nectarine Drying under near Infrared- Vacuum
conditions, Acta Sci. Pol. Technol. Aliment, 14(1): 15- 27
Alakali, J.S., Ariahu, C.C. and Nkpa, N.N. (2006). Kinetics of osmotic dehydration of mango. Journal
of Food Processing and Preservation. 30: 597-607
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
64
Akers, M. J., Fites, A.L.and Robinson, R. L.(1987). Types of parenteral administration, Journal of
parenteral science and Technology, 41: 88 - 95.
Amellai, H. and Benamara, S. (2008) Vacuum drying of common date pulp cubes. Dry technology, 26:
378 - 382
Anderson B.A. and Singh, R.P. (2006). Modeling the thawing of frozen foods using air impingement
technology. Int. J. Refrig. 29: 294-304.
Azura, E and Beristai, C.I.(2002). Osmotic dehydration of apples by immersion in concentrated
sucrose / matlodextrin solution. Journal of Food Processing hesewation. 26: 295 - 306
Bala, B. K. and Janjai, S. (2009). solar drying of fruits, vegetables, spices, medicinal plants and fish:
Developments and potentials. International solar food processing conference
Balbay, A., Sahin, O. and Karabatak, M.(2011) An investigation of drying process of shelled pistachio
in a newly designed fixed bed dryer system by artificial neural network, Drying technology, 28:
1685 - 1696
Bamire, A.S., and Oke, J.T., (2003). Profitability of vegetable farming under rainy and dry season
production in South-Western Nigeria. Journal of Vegetable Crop Production 9: 11-18.
Berteli, M. N., Rodier, E. and Marsaioli Jr, A. (2009). Study of the microwave vacuum drying
process for a granulated product, Brazilian journal of chemical engineering, 26(2): 317 - 329
Bindu, S. J., Rekha, T. and Chandran, V. (2016) Smart solar tunnel dryer, IOSR Journal of electrical
and electronics engineering, 11(5):43 - 51
Bolaji, B. O. (2005) Development and performance evaluation of box type absorber solar air collector
for crop drying, Journal of food technology, 3(4): 515 - 600
Bolaji, B. O. and olalusi, A. P. (2008) Performance evaluation of a mixed – mode solar dryer, AU Journal
of technology, 11(4): 2225 - 231
Bolea, Y., Grau, A. and Miranda, A. (2012) SDSim: A novel simulator for solar drying processes,
Mathematical problems in engineering, volume 2012, 25 pages
Boudrioua, N., Giampaoli, P. and Bonazzi, C. (2003) Changes in aromatic components of banana
during ripening and air drying, LWT – Food science and technology, 33:633 - 642
Brennan, J. G., Butters, J. R., Cowell, N. D. and Lilly, A. E. V.(1990). Food engineering operations,
applied science, London, pp33 - 70
Brennand, C. P. (1994). Home drying of food, Utah State University extension, All Archive Publications,
Merrill – crazier Library, paper 606
Brygidyr, A, M., Rzepecka, M.A. and McCornell, M.B. (1977). Characterization and drying of tomato
paste foam by hot- air and microwave energy. Canadian institute of food science and technology
Journal, 9: 313 - 319
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
65
Chandrasekar, V., Gabriela, J. S., Kannan, K. and Sangamithra, A. (2015) Effect of foaming agent
concentration and drying temperature on physicochemical and antimicrobial properties of foam
mat dried powder, Asian Journal dairy and food research, 34(1): 39 - 43
Chavan, U. D. and Amarowicz, R. (2012) Osmotic dehydration process for preservation of fruits and
vegetables, Journal of food research, 1(2): 202 - 209
Chavda, T. V. and Kumar, N.(2009). Solar Dryers for High Value Agro Products at Sprier, Solar food
processing and back-up systems, International Solar Food Processing Conference, 14-16,
January 2009. India.
Chien and Yiew W.(1981). Pharmaceutical Dosage forms: Parenteral Medications. Indian Journal of
pharmaceutical science and technology, 35:106 -118
Chua, K. J. and Chou, S. K. (2003) Low cost drying methods for developing countries- review, Trend in
food science and technology, 14:519 - 528
Ciurzynska, A. and Lenart, A. (2011). Freeze drying- application in food processing and
biotechnology: A review, Polish Journal of food and nutrition sciences, 61(3): 165 - 171
Clary, C. D. M., Mejia-meza, E., Wang, S. and Petrucci, V. E. (2007) Improving grape quality using
microwave - vacuum drying associated with temperature control, Journal of food science, E:
food Engineering and Physical properties, 72(1): E23 - E28
Condori, M., Echazu, R. and Saravia, L. (2001). Solar drying of sweet pepper and garlic using the tunnel
greenhouse drier. Journal of Renewable Energy, 22: 447 - 460.
Dong, J. Ma, X., Fu, Z. and Guo, Y. (2011)Effects of microwave drying on the contents of functional
constituents of Eucommia ulmoides flower tea, Industrial crops and products, 34: 1102 - 1110
Doymaz, L., (2005a). Drying behavior of green beans, Journal of Food Engineering, 69:161-165
El-Sebaii A. A. and Shalaby, S. M. (2012). Solar drying of agricultural products: A review. Renewable
and Sustainable Energy Reviews 16: 37 - 43
Eltawil, W. A., Abouzaher, S. E. and El –Hadad, W. Z. (2012) Solar – wind ventilation to enhance the
cabinet dryer performance for medicinal herbs and horticurtural products, Agric. Eng. Int: CIGR
Journal 14(4):56 - 74
Esfandiary, R., Gattu, S. K., Stewart, J. M. and Patel, S. M. (2016) Effect of freezing on lyophilization
process performance and drug product cake appearance, Journal of pharmaceutical sciences,
105(4): 1427 - 1433
Fellows, P.S. (1997). Food processing technology: Principles and practice. Wood Head Rebleing ltd,
New York, pp 65 - 310
Folaranmi, J. (2008). Design, construction and testing of simple solar maize dryer. Electronic
Journal of Practices and Technologies 13:122 - 130
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
66
Franco, T. S., Perussello, C. A. Ellendersen, L. S. and Masson, M. L. (2015) Foam mat drying of yacon
juice: Experimental analysis and computer simulation, Journal of food engineering, 158:48 - 57
Fudholi A., Sopian K., Ruslan M. H., Alghoul M. A. and Sulaiman, M. Y. (2010). Review of solar dryers
for agricultural and marine products. Renewable and Sustainable Energy Review, (1): 1 - 30.
Gaidhani, K.A., Harwalkar, M, Bhambere, D.and Nirgude (2015).lyophilization / freeze drying – a
review, World Journal of Pharmaceutical research, 4(8): 516 - 543
Gatin, L.A., Auffret, T., Shalaev, E.Y., Speaker, S. M. and Teagarden, D. L.(2008) Freeze Drying
Concepts: The Basics in Formulation and delivery, InformaHealthcare, New York, 15:177-195.
Gavhale, M., Kawale, S., Nagpure, R., Mujbaile, V. N. and Sawarkar, N. S. (2015) Design and
development of solar seed dryer, International Journal of innovative science, engineering and
technology, 2(4):1005 - 1010
Giannakourou, M. C and Taoukis, P. S. (2003). Stability of dehydrofrozen green peas pretreated with
non conventional osmotic agents. Journal of Food Science. 68: 2002-2014
Green, M. G. and Schwartz, D. (2001) Solar drying equipment: Notes on three dryers. GATE
Technical information, E015e, 1 - 5
Gurlek, G, Ozbalta, N. and Gungor, A. (2009). Solar tunnel drying characteristics and mathematical
modeling of tomato. Journal of Thermal science Technology, 29(1):15 - 23
Harish, G. G. S., Naveen, K. V. and Gangadharappa, H. V. (2017) Lyophilization – The process and
industrial use, International Journal of universal pharmacy and biosciences, 6(2):198 - 205
Huang,Y. (2013): Impact of Banana (Musa acuminata) ripening on resistant and non-resistant starch
using hot-air and microwave drying, A thesis at Department of Bioresource Engineering, McGill
University, Montreal, Canada
Ismaila, A. R., Sogunle, K. A. and Adebayo, Q. (2016) Foam density characteristics of sweet potato
paste using glyceryl monostearate and egg albumin as foaming agents, European Journal of food
science and technology, 4(1):1 - 9
Itodo, I. N., Obetta, S. E. and Satihemin, A. A. (2002) Evaluation of a solar crop dryr for rural
application in Nigeria, Botswana Journal of technology, 11:58 - 62
Ivanova, D. and Andonov, K. (2001). Analytical and experimental study of combined fruit and
vegetable dryer. Journal of Energy Conversion Management 42: 975 - 983
Jambunathan, K., Lai, E., Moss, M. A. and Button, B.C. (1992) A review of heated transfer data for
single circular jet impingement, International journal of heat and fluid flow, 13(2):106 - 115
Jaya, S., and Das, H. (2003). A vacuum drying model for mango pulp. Drying Technol., 21(7):1215-
1234
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
67
Jayaraman K S, and Gupta D. K. (1995). Drying of fruits and vegetables. In: Handbook of industrial
drying. Mujumdar AS (Ed.). Marcel Dekker Inc., New York, USA. pp. 643-690.
Johnson, P-N. T., Brennan G. and Addo-Yobo F. Y. (1998) Air-drying Characteristics of Plantain
(MussaAAB) Journal of Food Engineering 31:233-242
Kadam, D.M., Patil, R.T. and Kaushik, P. (2010). Foam mat drying of fruit and vegetable products. In
Drying of foods, vegetables and fruits – Volume 1(S.V. Jangam, C.L. Law and A.S. Mujumdar,
eds) pp. 113–124, ISBN: 978-981-08-6759-1, Published in Singapore.
Kadam, D M, Wilson, R A and Kaur, S. (2010).Determination of biochemical properties of foam mat
dried mango powder. International Journal of Food Science and Technolology, 45(8): 1626-
1632
Kandasamy, P., Varadharaju, N., Kalemullah, S. and Maladhi, D. (2014) Optimization of process
parameters for foam – mat drying of papaya pulp, Journal of food science and technology,
51(10):2526 - 2534
Karathanos, V.T., and Belessiotis, V.G. (1999). Application of a thin-layer equation to drying data of
fresh and semi-dried fruits. Journal of Agricultural Engineering Research, 74:355-361
Kasiri, N., Hasanzadeh, M. A. And Moghadam, M. (2004) Mathematical modelling and computer
simulation of a drum dryer, Iranian Journal of scinec and technology, 28(6):679 - 687
Kasper, J. C. and Friess, W. (2011) The freezing step in lyophilization: Physico-chemical
fundamentals, freezing methods and consequences on process performance and quality
attributes of biopharmaceuticals, European Journal of Pharmacy Bioparm, 78(2): 248 - 263
Khairnar, S., Kini, R., Harwalkar, M., Salunkhe, K. and Chaudhari, S. R. (2013) A review on freeze
drying process of pharmaceuticals, International Journal of research in pharmacy and science,
4(1):76 - 94
Khan, M. R. (2012) Osmotic dehydration technique for fruits preservation- A review
Pakistan Journal of Food Sciences, 22(2): 71‐85
Kozempel, M. F. , Sullivan, J. F. Craig Jr, J. C. and Konstance, R. P. (2008) Explosion puffing of `fruits
and vegetables, Journal of food science, 53(3):772 - 773
Kouchakzadeh, A. (2013). The effect of acoustic and solar energy on drying process of Pistachios,
Energy conversion and management, 67:351 - 356
Kumar, V., Singh, B. R., Samshar, S. C. and Singh, S. (2015) A review on tomato drying by different
methods with pretreatments, International Journal of food and fermentation technology, 5(1): 15
- 24
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
68
Kumaravel, S., Hema, R. and Kamaleshwari, A. (2012) Effect of oven drying on the nutritional
properties of whole egg and its components, International journal of food and nutrition
science, 1(1): 4- 12
Larrosa, A. P. Q., Comitre, A. A., Vaz, L. B. and Pinto, L. A. A. (2017) Influence of air temperature on
physical characteristics and bioactive compounds in vacuum drying of arthrospira spirulina,
Journal of food process engineering, 40(2): e12359
Li, Z., Raghavan, G.S., Wang, N. and Gariepy, Y. (2009) Real time, volatile – detection – assisted control
for microwave drying, Computers and Electronics in agriculture, 69:177 - 184
Li, Z., Raghavan, G.S.V. and Orsat, V. (2010) Optimal power control strategies in microwave
drying. Journal of food engineering, 99:263 - 268
Lin, T.M., Durance, T.D. and Scanman, C.H. (1998). Characterization of vacuum microwave, air and
freeze dried carrot slices. Food Res. Int. 31, 111-117.
Long, X., Jun, X. J. and Mei, Y.L.(2013) Study on the effect of picked cabbage using freeze –
drying protective agent, Advance Journal of food science and technology, 5(19):1404 - 1406
Ljung, A. L., Andersson, L. R., Andersson, A. G., Lundstrom, T.S. and Eriksson, M.(2017). Modelling
the Evaporation Rate in an Impingement Jet Dryer with Multiple Nozzles, International Journal
of Chemical Engineering, 2017: 1 - 9
Marriott, J. And Lancester, P. A. (1983) Banana and plantains, In: Chan, H. T. (ed) Handbook of
tropical foods, Marcel Dekker, New York, pp 85 - 143
McGurk, S. J., Martin, C. F. Brandani, S., Sweatman, M. B. and Fan, X. (2017) Microwave swing
regeneration of aqueous monoethanolamine for post – combustion CO2 capture, Applied energy,
195:126 - 133
Michael, J.K. (1993) Spray drying and spray congealing of pharmaceuticals. In: Encyclopedia of
pharmaceutical technology. Marcel Dekker INC, NY, 14, 207-221.
Moreira, R. G. (2001) Impingement drying of foods using hot air and superheated steam, Journal of food
engineering, 49(4):291 -295
Mujumdar, A.S. (1986). Impingement drying. In Handbook of Industrial Drying (A.S. Mujumdar, ed.)
pp. 498–502, Marcel Dekker, New York, NY.
Mujumdar, A.S.(2004), Research and Development in Drying: Recent Trends and Future Prospects,
Drying Technology: An international Journal, 22(1-2)
Mujumdar, A.S.,(2008), Guide to Industrial Drying: Principles, Equipments & New Developments, 3rd
Ed; Three S Colors Publications, India.
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
69
Mulokozi, G. and Svanberg, U. (2003). Effect of traditional open sundrying and solar cabinet drying on
carotene content and vitamin a activity of green leafy vegetables. Journal of Plant Foods for
Human Nutrition 58: 1 - 15.
Nimmol, C., Devahastin, S., Swasdisevi, T. and Soponronnarit, S. (2007). Drying of banana slices using
combined low pressure superheated steam and far–infrared radiation, Journal of food
engineering, 81(3): 624 - 633
Nonhebel, G. (1973). Drying of solids in the chemical industry. England: Butterworth
Owolarafe, O.K., Muritala, O.A., and Ogunsina, B.S., (2007). Development of an okra slicing
device, Journal of Food Science and Technology, 44 (4):426-429.
Okos, M.R., Narasimban, G., Singh, R.K., and Witnauer, A.C., (1992).Food dehydration Ln D.R
Heldman and D.B. Lund (Eds) Handbook of food engineering. New York: Marcel Dekker
Pandhare, S., Harwalkar, M., Mahale, N. B. and Chaudhari, S.R. (2015) Review on lyophilization
process of pharmaceuticals, world journal of pharmaceutical research, 4(6):1991 - 2002
Papu, S., Singh, A., Jaivir, S., Sweta, S., Arya, A. M. and Singh, B. R. (2014) Effect of drying
characteristics of garlic: A review, Journal of food processing and technology, 5(4): 1 - 6
Parikh, D. (2015) Vacuum drying: Basics and application, chemical engineering, 122(4):48 - 54
Pawar, S. B. and Pratape, V. M. (2017) Fundamentals of infrared heating and its application in
drying of food materials: A review, Journal of food process engineering, 40(1): 1-15,
e12308
Pere, C., and Rodier, E. (2002). Microwave vacuum drying of porous media: experimental study and
qualitative considerations of internal transfers. Chem. Eng. Process., 41(5): 427–436
Petrotos, K. B. and Lazarides, H.N. (2001). Osmotic concentration of liquid foods. Journal of Food
Engineering. 49:201-206
Pointing, J. D. (1973) Osmotic dehydration of fruits recent modifications and applications. Journal of
process biological technology, 12(8):8 -20
Pokharkar, S. M. and Prasad, S. (1998) Mass transfer during osmotic dehydration of banana slices,
Journal of food science technology, 35(4):336 - 338
Prakash, O. and Kumar, A. (2013) Historical review and recent trends in solar drying systems,
International Journal of green energy, 10:690 - 738
Praveenkumar, D. G., Umesh-Hebber, H. and Ramesh, M. N. (2006). Suitability of thin layer models for
infrared-hot air drying of onion slices. Lebensmittel-Wissenschaft and Technologie 39: 700 - 705
Rajeevini, K., Mahalakshmi, K. and Uma, M. R. V. (2015) Review on Lyophilization technique,
International Journal of trends in pharmacy and life sciences, 1(1):130 - 140
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
70
Rajkumar, P., Kailappan, R., Viswanathan, R. and Raghavan, G. S. V. (2007) Drying characteristics of
foamed alphonso mango pulp in a continuous type foam mat dryer, Journal of food engineering,
79:1452 - 1459
Rajkumar, P., Kailappan, R., Viswanathan, R., Raghavan, G. S. V. and Ratti, C. (2007) Foam mat
drying of alphonso mango pulp, Drying Technology, 25(2):357 - 365
Ratti, C. and Mujumdar, A. S. (1995). Infrared drying. In A. S. Mujumdar (Ed.), Handbook of
industrial drying, New York: Marcel Dekker, 1:567 - 588.
Remington, L. W. K. (2000). The Science and practice of pharmacy, Parenteral Preparation, 20th ed,
ISE publication, Phelabelphia. 2000, 1: 804-819.
Remington, L. W. K. (2000). The science and practice of pharmacy, 21st ed, Gennaro RA, Lippincott
Williams & wilkins publisher
Rodriguez, G.; Vasseur, J. and Courtois, F.(1996). Design and Control of Drum Dryers for the Food
Industry. Part 2. Automatic Control. J. Food Eng., 30:171-183.
Rodriguez, G.; Vasseur, J.; Courtois, F. (1996). Design and Control of Drum Dryers for the Food
Industry. Part 1. Set-Up of a Moisture Sensor and an Inductive Heater. J. Food Eng.,
28:271-282
Roy, S. (2015) Effect of different softeners on moisture absorption and transmission properties of knitted
cotton fabric, B.Sc Project, Daffodil International University, Dhaka (unpublished)
Sacilik, K., Keskin, R. and Elicin, A. K. (2006). Mathematical modeling of solar tunnel drying of thin
layer organic tomato. Journal of Food Engineering 73: 231 - 238.
Saeid Minaei, Ali Motevali, Gholamhassan Najafi, Seyed Reza and Mousavi Seyedi( 2011), Influence
Of drying methods on activation energy, effective moisture diffusion and drying rate of
pomegranate arils(Punica Granatum), Australian Journal of Crop Science, 6(4): 584 - 591
Saetan, P., Pratinthong, N. And Swasdisevi, T. (2013) Tumeric drying using a combined vacuum and
far – infrared dryer, The 14th TSAE national conference and the 6th TSAE international
conference, FE – 09, Pg 123 - 126
Sangamithra, A., Sivakumar, V., Swamy, G. J. and Kannan, K. (2015). Foam mat drying of food
materials: A review; Journal of food processing and preservation, 39(6): 3165 - 3174
Sanjith, N. L. and Gatin, L.A.(1993). Freeze drying: Annealing principles and practice. NP publication;
2:163 – 233
Seya, K. and Otsuka, T. (1980) Acoustic drying, Japanese journal of applied physics, 20(3):165 - 168
Sharifi, A., Niakousari, M., Maskooki, A. and Mortazavi, S. A. (2015) Effect of spray drying conditions
on the physicochemical properties of barberry (Berberis vulgaris) extract powder, International
food research journal, 22(6):2364 - 2370
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
71
Shiby, V. K., Tabassum, A., George, J., Pandey, M. C. and Radhakrishna, k. (2015)Effect of drying
methods on moisture sorption, microstructure and other quality characteristics of chicken cubes,
International Journal of advanced research, 3(12):1200 - 1213
Shuka, S. (2011) Freeze drying process: A review, International Journal of pharmaceutical sciences
and research, 3:3061 - 3068
Silva, F. A., Maxima, G. J., Marsaioli jr, A. and Silva, M. A. P. (2007)Impact of microwave drying on
the sensory profile of macadamia nuts, ciencia e tecnologia de alimentos, 27(3):553 - 561
Singh, S. and Dixit, D. (2014) A review on spray drying: Emerging technology in food industry,
International Journal of applied engineering and technology, 4(1):1 - 8
Sontakke, M. S. and Salve, S. P. (2016) Study and experimental investigation of solar dryer by using
concentric dish collector, International engineering research journal, special edition, pp 1072 -
1082
Strumillo, C. and Kudra, T. (1987). Drying: Principles, applications and design. USA: Gordon and
Breach Science. Publication
Sulistiyanti, S. R., Setyawan, F. X. A. and Susanto, A. (2009) Histogram characteristions of infrared
images captured by a modified digital camera, International Journal of electronic engineering
research, 1(4):329 - 336
Sullivan, J. F. and Craig Jr, J. C. (1984). The development of explosion puffing, Food and agriculture
organization (FAO) of the united nation
Sunderland, J. E. (1980) Microwave freeze drying, Journal of food process engineering, 4(4):195 - 212
Suthur, A. M., Patel, R.P., and Patel, M. P. (2009): Spray Drying Technology: An Overview,
Indian Journal off Science and Technology, 2(10).
Swasdisevi, T., Devahastin, S., Sa-Adchom, P and Soponronnarit, S. (2009) Mathematical modelling of
combined far – infrared and vacuum drying banana slice, Journal of food engineering, 92:100-
106.
Tang J., Feng, H. and Shen, G.,(2010), Drum Drying in Encyclopedia of Agricultural, Food, and
Biological Engineering by Marcel Dekker, Inc., New York
TaTEDO (2007). Solar Drying for Food Preservation. [www.gaiamovement.org/files/030_Solar
Drier.pdf] site visited on 14/08/2016.
Thirupathi, V., Sasikala, S. And Rajkumar, P. (2008) studies on foam mat drying of whole egg liquid in
cabinet dryer, Madras agricultural journal, 95(1- 6):141 - 150
Togrul, I. T. And Pehlivan, D. (2004) Modelling of thin layer drying kinetis of some fruits under open
air sun drying process, Journal of food engineering, 65:413 - 425
Int. J. Food Nutr. Saf. 2017, 8(1): 45-72
Copyright © 2017 by Modern Scientific Press Company, Florida, USA
72
Torres, M. A., Jones, J. D. And Dangl, J. L. (2006) Reactive oxygen species signalling in response to
pathogens. Plant physiology 141:373 - 378
Toure Siaka(2012): The Application Of a Mathematical Modelling of Drying kinetics in the Natural
Solar Drying of Banana, 6(10):1560 - 1569
Tunde and Akitunde, T. Y. (2011). Mathematical modelling of sun and solar drying of chili pepper.
Renewable Energy, 36: 2139 - 2145.
Tiwari R. B..(200) Application of osmo-air dehydration for processing of tropical fruits in rural areas.
Indian Food Ind.; 24(6):62-69
Velayudham, G., Brighton, J. M. and Dhineshkumar, V. (2015) Experimental investigation on
drying of vegetables in solar tunnel dryer, International Journal of food, agriculture and
veterinary sciences, 5(2):28 - 32
Wiriya, P., Paiboon, T. and Somchart, S. (2009). Effect of drying air temperature and chemical
pretreatments on quality of dried chilli. International Food Research Journal 16: 4 - 7
Wisniewski, R. (2015) Spray drying technology review, 45th international conference on
environmental systems, 12 – 16 July, 2015, Bellevue, Washington, Pg 1 - 46
Xiao, H., Gao, Z., Hai Lin, H. and Yang, W. (2010). Air impingement drying characteristics and
quality of carrot cubes, Journal of Food Process Engineering, 33(5):899 - 918
Xiao, H. W., Yao, X. D., Lin, H., Yang, W. X., Meng, J.S. and Gao, Z. J. (2012) Effect of superheated
steam blanching(SSB) time and drying temperature on hot air impingement drying kinetics and
quality attributes of yam slices, Journal of food process engineering, 35(3):370 -390
Xiao, H. W., Law, C. L., Sun, D. W. and Gao, Z. J. (2014) Colour change kinetics of American
ginseng(panax quinquefolium) slices during air impingement drying, Journal of drying
technology, 32(4): 418 - 427
Yadav, A. K. And Singh S. V. (2014), Osmotic dehydration of fruits and vegetables: A review,
Journal of food Science Technology, 51(9):1654 - 1673
Yarkwa, B. and Uvir, R. H. (2015) Effects of Drying Methods on the Nutritional Composition of Unripe
Plantain Flour, Food Science and Quality Management, 41: 1 - 7
Yongsawatdigui, J. and Gunasekaran, S. (1996) Pulsed microwave – vacuum of cranberries. Part 1,
Energy use and efficiency, Journal of food processing and preservation, 20(2):121 - 143
Yunghong, L., Shuai, M. Jianye, W., Jianxue, L, Huichun, Y and Duan X. (2015) Drying
characteristics and modelling of vacuum – far infrared radiation drying of flos lonicerae,
Journal of food processing and preservation, 39(4): 338 - 348
Zomorodian, A., Zare, D. and Ghasemkhani, H. (2007). Optimization and evaluation of a semi-
continuous solar dryer for cereals (Rice, etc). Desalination 209:129 - 135.