World Journal of Agricultural Sciences 5 (2): 256-258, 2009
© IDOSI Publications, 2009
Influences of Drying Methods on Nutritional Properties of
Tilapia Fish (Oreochromis nilotieus)
Department of Agricultural Engineering, Sultan Qaboos University,
P.O. Box 34, Postal Code 123, Al-Khod, Muscat, Oman
Abstract: The effects of two different drying methods (smoking kiln and electric oven) on nutritional properties
of tilapia fish (Oreochromis nilotieus) were determined. Purchased quantities of tilapia fish were shared into
two parts: one part was used to determine the nutritional properties of the raw fish and the other part was sub-
divided into two; a part was dried using smoking kiln at a temperature range of 70-85°C for 20 hours and the
remaining one was dried using electric oven at a temperature range of 110°C for 45 minutes. The nutritional
properties of the dried samples were determined. Mean moisture, protein, lipids, ash, fibre, carbohydrate,
vitamin A, potassium and phosphorus contents of raw fish were 70.15±0.04, 23.06±0.04, 12.85±0.05, 28.16±0.02,
1.91±0.01, 3.67±0.04, 2.5 x 10G ±4 x10
G , 1.2 x 10
and 1.2 x
G %, respectively while the energy valu
was 5.94±0.03 J/100g and vitamin C content was 2.3 x 10G3±4 x 10
G4 mg/ml. The changes in moisture, lipids,
energy value and vitamin A contents were found to be significant (P < 0.05) for the two drying methods.
Protein, ash, fibre, carbohydrate, vitamin C, potassium and phosphorus contents showed no significant
differences (P < 0.05) for the two drying methods studied. The results indicate that drying methods have effects
on the nutritional properties of tilapia fish. Electric oven drying is recommended for healthy eating if reduced
lipids content and increased vitamin A content are desired and also for longer shelf-life of dried fish.
Key words: Drying methods % Electric oven % Nutritional properties % Smoking kiln % Tilapia fish
degrees with moisture levels in the final product ranging
from about 10% to 60%. Processing temperatures may
Fish is a very important source of animal protein
range from less than 5°C to up to 120°C and processing
in the diets of man. Smoked or dried fish is a traditional
times from half an hour to several months. The fish may
part of the diet of a large section of the world’s
be dried only or smoked only or there may be a
population. However, the gap between the demand and
combination of smoking and drying. In some countries the
supply of fish is widening due to increase in population,
fish is boiled before being smoked and/or dried. Adding
poor postharvest handling, lack of processing and
to this complexity, the fish species used as raw
storage facilities and utilization of unconventional fish
material may be freshwater or marine species and may
species. For instance, the estimated fish demand in
range from very lean to fatty fishes and its condition from
Nigeria in 1994 was put at 1,139,833 tonnes based on the
fresh to stale. This variation makes it difficult to arrive at
population figure of 94,986,044 and per capita
general conclusions regarding processing effects of
consumption of 12.0kg which was considered globally
smoking and drying on nutritional compositions of the
adequate for normal and healthy growth. However, only
280,307 tonnes were produced, indicating a deficit of
The effects of different processing and cooking
methods on nutritional compositions of different species
Methods of drying and smoking fish vary between
of fish have been studied. Nutritive and organoleptic
different countries and within the same country
changes of Nigerian traditionally-processed freshwater
depending on the species of fish used and the type of
fish species were studied by Afolabi et al.
. The effect
product desired. The fish may be dehydrated to various
of traditional drying processes on the nutritional values
Corresponding Author: Ogbonnaya Chukwu, Department of Agricultural Engineering,
Sultan Qaboos University, P.O. Box 34, Postal Code 123, Al-Khod, Muscat, Oman
World J. Agric. Sci., 5 (2): 256-258, 2009
of fish was studied by Eves and Brown . Changes in
MATERIALS AND METHODS
chemical composition and nutritional quality of fried
sardine (Clupea pilchardus) produced by frozen storage
freshly harvested tilapia fish
and microwave reheating were reported by Castrillon et al.
(Oreochromis nilotieus) were obtained from Fish
. Proximate and mineral compositions of dried salted
Market at Seeb in Muscat, Oman. The mean weight
roes of hake (Merluccius merluccius, L.) and ling (Molva
and length of the fish were respectively 320.12±1.65g
molva, L.) were reported by Rodrigo et al.
and 28. 45±1.22 cm. The thirty-two fish were shared into
two equal parts: sixteen were used to determine the
compositions of raw and cooked Thai freshwater and
nutritional properties of the raw fish and the other
marine fish were studied by Puwastien et al. .
sixteen were divided into two, each part being eight
Experimental investigation on solar drying of fish
fish. Eight fish were prepared (eviscerated, beheaded
using solar tunnel dryer was carried out by Bala and
and washed) and dried using smoking kiln at a
Mondol . Effects of cooking methods on the proximate
temperature range of 70°C-85°C for 20 hours and the
compositions and mineral contents of rainbow trout
remaining eight were prepared and dried using electric
(Oncorhynchus mykiss) were studied by Gokoglu et al.
oven at a temperature of 110°C for 45 minutes. After
. Tao and Linchun  reported influences of hot air
drying using the two methods, all fish for each drying
drying and microwave drying on nutritional and
method were homogenized using a kitchen blender.
odorous properties of grass carp (Ctenopharyngodon
idellus) while Turkkan et al.  studied effects
Nutritional Analysis: The nutritional compositions were
of cooking methods on the proximate and fatty
assayed as described by AOAC . All chemicals used
acid compositions of seabass (Dicentrarchus
were of analytical grade and supplied by Sigma Co. (St.
labrax, L. 1758).
Louis, USA). Each analysis was carried out in triplicates.
It has been observed that different processing and
drying methods have different effects on nutritional
Statistical Analysis: The design was completely
randomized. Nutritional composition analysis was
compositions of fish. This is because heating, freezing
replicated three times (n = 3). Results presented are mean
and exposure to high concentration of salt lead to
values of each determination±standard deviation (SD).
chemical and physical changes and therefore digestibility
Analysis of variance was performed by one-way ANOVA
is increased, due to protein denaturation, but the content
procedures (SPSS 12.0 for Windows). Differences
of thermolabile compounds and polyunsaturated fatty
between the mean values of the treatments were
acids is often reduced [3, 9, 11]. Therefore, the qualities of
determined by the least significant difference (LSD) test
fish dried using different methods cannot be the same.
and the significance was defined at P < 0.05.
Also the shelf life of fish dried in an electrically-operated
oven varies from that of fish dried using a smoking kiln.
RESULTS AND DISCUSSION
The objective of this study is to determine the nutritional
properties of raw tilapia fish and tilapia fish dried using
The nutritional properties of raw and dried tilapia fish
smoking kiln and electric oven so as to ascertain the
are presented in Table 1. Each value is the mean±standard
effects of drying methods on nutritional properties
deviation of triplicate determinations. Raw samples
of the fish.
presented low protein, lipids, vitamin A, potassium and
Table 1: Nutritional Properties of Raw and Dried Tilapia Fish (Oreochromis nilotieus)
Energy value (J/kg)
Vitamin A (%)
Vitamin C (mg/ml)
Values in the same row followed by different letters are significantly different (P < 0.05).
World J. Agric. Sci., 5 (2): 256-258, 2009
phosphorus; intermediate energy value; high moisture
Afolabi, O.A., O.A. Arawomo and O.L. Oke, 1984.
and ash contents, similar findings reported by Eyo [11,
Quantity Changes of Nigeria Traditional Processed
13]. Decrease of moisture and increase of protein, lipids,
Freshwater Species I: Nutritive and Organoleptic
vitamin A, potassium and phosphorus contents were the
Changes. J. Food Technol., 19: 333-340.
most prominent changes in tilapia fish after drying.
Eves, A. and R. Brown, 1993. The Effect of
Moisture, protein, lipids and vitamin A contents increased
Traditional Drying Processes on the Nutritional
significantly in processed samples (P<0.05). This trend is
Values of Fish. Tropic. Sci., 33:183-189.
in agreement with those obtained by Tao and Linchun .
Castrillon, A.M., P. Navarro and E. Alvárez-Pontes,
The significant increase in protein levels (P<0.05) in dried
1997. Changes in Chemical Composition and
tilapia fish, when compared with the raw fish, suggests
Nutritional Quality of Fried Sardine (Clupea
that protein nitrogen was not lost during drying. This is
pilchardus) Produced by Frozen Storage and
in accordance with the findings of Puwastien et al. ,
Microwave Reheating. J. Sci. Food and Agric.,
Gokoglu et al.  and Tao and Linchun . However,
there was no significant difference between smoking kiln
Rodrigo, J., G. Ros, J. Priago, C. Lopez and J. Ortuno,
drying and electric oven drying for protein, ash, fibre,
1998. Proximate and Mineral Compositions of Dried
carbohydrate, potassium and phosphorus contents.
Salted Roes of Hake (Merluccius merluccius, L.) and
After drying, there was a significant increase in lipids
Ling (Molva molva, L.). Food Chemistry, 63 (2): 221-
content. Smoking kiln-dried samples retained higher lipids
content than electric oven-dried samples (P<0.05). This
Puwastien, P., K. Judprasong, E. Kettwan, K.
result indicates that the fat loss phenomenon was more
Vasanachitt, Y. Nakngamanong and L. Bhattacharjee,
intensive in the electric oven-dried fish than in smoking
1999. Proximate Composition of Raw and Cooked
kiln-dried samples. Fat may exude with the moisture
Thai Freshwater and Marine Fish. J. Food
evaporation during electric oven drying and that seems to
Composition and Analysis, 12: 9-16.
enhance the phenomenon of lipids loss.
Bala, B.K. and M.R.A. Mondol, 2001. Experimental
Investigation on Solar Drying of Fish Using Solar
Tunnel Dryer. Drying Technol., 19: 427-436.
Gokoglu, N., P. Yerlikaya and E. Cengiz, 2004. Effects
In general, there were significant influences of drying
of Cooking Methods on the Proximate Composition
on nutritional properties of tilapia fish. Lack of negative
Mineral Contents of Rainbow Trout
influence of the drying processes on the protein, lipids,
(Oncorhynchus mykiss). Food Chemistry, 84:19-22.
vitamin A and mineral contents of tilapia fish is of great
Tao, W. and M. Linchun, 2008. Influences of Hot Air
practical importance, although drying resulted in a
Drying and Microwave Drying on Nutritional and
significant loss of ash, fibre, carbohydrate and energy
Properties of Grass Carp
value. These results show that different nutritional
idellus) Fillets. Food
components of fish undergo different changes at elevated
Chemistry, 110 (3): 647-653.
temperatures. However, electric oven drying could
10. Turkkan, A.U., S. Cakli and B. Kilinc, 2008. Effects of
improve the protein quality in tilapia fish, as compared
Cooking Methods on the Proximate Composition and
with the conventional smoking kiln drying. The electric
Fatty Acid Composition of Seabass (Dicentrarchus
oven-dried samples showed higher lipids loss and slightly
labrax, L. 1758). Food and Bioproducts Processing,
higher protein content than smoking kiln-dried samples.
This research provides basic nutritional information on
11. Eyo, A.A., 2001. Fish Processing Technology in the
freshwater tilapia fish, both raw and dried. The present
Tropics. National Institute for Freshwater Fisheries
study also provides a possible application of electric oven
Research (NIFFR), New Bussa, Nigeria, pp: 10-170.
drying as an efficient drying process for fish in Oman and
12. AOAC., 2005. Official Methods of Analysis (18th
ed.). Association of Official Analytical Chemists
International, Maryland, USA.
13. Eyo, A.A., 1998. Shelf-life of Moonfish (Citharinus
citharus) and Tumk Fish (Mormyrus rume) During
Food and Agriculture Organization, FAO., 1999.
Storage at Ambient Temperature and on Ice. FAO
World Production of Fish, Crustaceans and
Fisheries Report No.574, pp: 35-37.
Molluscs by Major Fishing Areas. Fisheries
Information and Statistics Unit (FIDI), Fisheries
Department, FAO, Rome.