This study investigated the effect of enclosed solar drying on the nutritive quality of unsalted and salted Oreochromis niloticus. Sensory and proximate evaluations were carried out on the salted and unsalted fish after drying. Acceptability, appearance, colour, odour, taste and texture of salted and unsalted fish differed significantly (P< O.05). The moisture, protein lipid and ash contents differed significantly (P< O.05. All dried fish samples from the enclosed dryers showed high levels of acceptability and protein content. However, fish samples brined at 25% and dried using Solar Tent Dryer had the highest acceptability and protein content

Oyero, J.O.

Aquatic Commons

MATEIUALS A"II) METHODS
Ihree Enclosed Solar Drying Systems enDS) wen: used. These were: Solar rent Dryer, Natural
Airflow Solar Cabinet Dryer and Forced Airflow Solar Cabinet Dryer. I'he Solar Tent Dryer (S'l 0)
was made up of polythcnc sheet stretched over a wooden framework (Lim wide x 1.1m lung x 1.5111
high) with side <Inti top vent of (0.25m x 0.25m), A. framed wire gauzcd rack (1m x 0.54m) With a
drying area of 0.54m2 was suspended at about 60cm off the ground. Underneath the rack was the heat
collector made up of' a spread of irregularly shaped granite stones painted black. The Natural Airflow
Solar Cabinet Dryer (NACD) has a drying chamber that was painted black both inside and outside.
Inside the drying chamber was a framed wire gauzed drying rack (1m x 0.54m) with a drying area of
0.54m' (2).A solar collector mac..le of glass was connected to the drying chamber to produce the
drying energy required. Airtlow was generated by natural convection through the collector through
the drying chamber and moist air leaves the dryer through the upper chimney-like opening. The
Forced Airflow Solar Cabinet Dryer (FACD) has drying chamber that was painted black both inside
and outside. Inside the drying chamber were a framed wire gauzed drying rack (1m x 0.54111) with a
drying area of 0.541111 and an electric powered two blade fan fixed to the ceiling of the drying
chamber to force out the moist air. A solar collector made of glass was connected to the drying
chamber to produce the drying energy required. Airflow was generated by natural convection through
the collector through the drying chamber and moist air leaves the dryer through the upper chimney-
like opening. The solar drying was camed out in each EDS simultaneously. Sixty (()O) fresh 0.
niloticus were dried in each EDS used for the experiment. In each EI)S the fish were divided into five
groups and were salted using Nael at different levels as described by Oyero, (2006). First Level -
INTRODUCTION
Open air sun-drying of fish has many limitations. These include the fact that long periods of sunshine
without rain an: required. drying rates are low and in areas of high humidity. and it is often difficult to
dry the fish sufficiently. The quality of open-air dried fish is likely to be low due to slow drying,
insect damage and contamination from air-borne dust, and it is difficult to obtarn n uniform product
(1.:.)'0. 2001). Thus. 111 the search for Improved drying techniques IIsing naturally abundant solar
energy, the use of enclosed solar drying systems have recently been mvestigated as an alternative to
traditional open-air sun drying. These enclosed systems are called solar dryers. Solar dryers employ
some means olcollccting 01' concentrating solar radiation with the result that elevated temperatures
and, in turn, lower relative humidities are achieved for drying. When using solar dryers, the.drymg
rate can be increased, lower moisture contents can be attained and product quality IS higher, The
dryers are less susceptible to variations in weather, although drying is obviously slower during
Inclement weather. and they do provide shelter from the ram. The high internal temperatures
discourage the entry of' pests into the dryer and can be lethal to those that enter (Trim and Curran,
19H3).Many forms of solar dryer for use with agricultural and fisheries products have been developed
In Nigeria. IIowever, only a few of these have been developed spccrfically for fish. Pew workers
(Olokor (1/ al., 1997 and Ogali ; Eyo, 1998) have reported respectively on some aspects of
biochemical changes in fish dried US111gtent and box types of solar dryers, In order 10 Improve the
quality of open-air tined fish and to provide mforrtation on the nutritive and keeping qualities of solar
dried fish. this experiment was conducted to assess the d·li.'<.:ls or enclosed solar drying 111 the quality
of fresh and differently salted Outiloticus,
ABSTRA cr ./
This study investigated the effect of enclosed solar drying on the nutritive quality of unsalted and
salted Oreochromis niloticus. Sensory and proximate evaluations were carried out on the salted and
unsalted fish after drying. Acceptability, appearance, colour, odour, taste and texture of salted and
unsalted fish differed significantly (P<0.05). The moisture, protein lipid and ash contents differed
significantly (P<0.05). All dried fish samples from the enclosed dryers showed high levels of
acceptability and protein content. However, fish samples brined at 25% and dried using Solar Tent
Dryer had the highest acceptability and protem content.
J.O.OYERO
Department of Water Resources, Aquaculture and Fisheries Technology,
Federal Unlversity of Technology, Minna, Nlgeria.
Nl'TRITlv"R F.VALl JATION OF ENCLOSED SALTED-SOLAR nnren Oreochromis uiloticus
ENCLOSED DRYING SYSTEMS (EDS) AND SALT LEVEI_<;
FIgure 1 Mean values of acceptability of 0. niloticus differently salted and dried using enclosed
drying systems (EDS)
_rorced Air-flov. CabI
w::JI\JluralAir-no" Cal>
mel Oryer
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4 'i
4O
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2.5
2.0
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UF.S1JLTS A.~J) DISCUSSIOK
Figure 1 shows the acccptabiliry of the sensory evaluation of di fferently salted 0. niloticus dried lIsing
Enclosed Sular Drying Systems (I:DS). Acceptability, appearance, colour, odour, taste and texture
diffc red significantly (P<O.05), There was a direct relationship between the various parameters
(appearance, colour, odour, taste texture and acceptability) of the dried 0. uiloticus products from the
three solar dryers (STD, "IA(,O and FACO). Dried samples from STD and ]\i\CO showed high levels
of acceptability especially S'lD 25 NACO 25 treatments. None of the dned products in these two
enclosed drying systems had a value less than 2 5 un till' ) point hedonic scale of measurement ThiS
indicated that all the dried products from the t\HJ systems were widely accepted. However, despite
this acceptabihty the unsalted treatment dned products III the STO and NACO showed the least
values. lhe reverse was the case in the FACD. Only the unsalted treatment dried product in foACD
showed a high value of 3.80 on 5 point hedonic scale of measurement. 11115 could be attributed to the
fact that the initial rate of drying 1S governed by heal and mass transfer processes external to the fish
relative to the air speed all have direct effect on the drymg rate. Thus in the early stages of drying the
rate can be increased by increasing the air speed and temperature and reducing the air relative
humidity. However, according to Doe and Olley (1990), there is a limit: if dried 100 fast a relatively
imA)ermeable layer can develop un the surface of the fish (case hardening) and at temperatures above
40 C (depending on the fish species) This could be the situation here as it could be deduced that the
forced airflow and the salting levels contributed tu fast drying of the products.
,
I
Unsalted treatment (US) - The fish were not salted. Second Level - 25% brined treatment (25B) - the
fish were immersed in 25% brine for one hour. The b-ine was prepared by dissolving 250g ofNaClm
1 litre of water. Third Level - 50% brincd treatment (50% B) - the fish were immersed 111 50 per cent
brine for one hour. The brine was prepared by dissolving 500g of Na(,1 in 1 litre of water. Fourth
Level 75% brined treatment (75B) - the fish were immersed in 75 per cent brine for one hour TIll:
brine was prepared by dissolvmg 750g of NaCl .n I litre of water. Fifth Level 100% Or), Salted
treatment (DS) the fish were rubbed on the surface and mside of the fish. Each level of salung
represented a treatment. The drying took place at the Federal University of Technology, Minna. The
fish were solar dried for one week. The sensory evaluation of the dried fish samples were evaluated
weekly for four weeks by a trained panel of five evaluators. The evaluation was done on Iledomc
scale of 5 based on the method of Doe and Olley, (1990). The parameters evaluated were taste, colour.
odour/smell, texture, appearance and acceptability. The chemical analyses of proximate cornposiuon
of the dried samples of 0. nilottcus were carried out using the methods of Association of Analytical
Chemists (l\OJ\l. 1990). The parameter <; analvzed include moisture, crude protem, hpid and ash.
There was a strong inverse relationship between the moisture and crude protein contents. The
three unsalted dned products had the highest moisture contents, This same trend was observed for all
other products. After four weeks of storage, all the dned products showed crude protem contents well
above 50% with the highest being that ufFACD which "vas 6S,Y9% and was not srgmficant at.P'~O.05
from NArD 25 treatment which was 65.95%, All the dried products had 10"' levels of crude lipid
content apart from r'ACD unsalted treatment wluch was 2087% and could be ant ibutcd to the nature
of 0. niloticus, wluch is classified as a lean fish (ll.O-WEP, 1982). The reason for the exceptionally
high crude protem content in the FACD unsalted treatment could not be adduced.
There was no consistency in the ash contents of the dl ied products and could be due to the
possible inconsistency in the bone removal of the dried products before milhng for analysis. However,
the ash contents of all the dried product" showed '''ppreciable levels to mdicate the tined fish products
as good sources of mineral contents. All the salted-dried products from the three enclosed solar dryers
showed higher levels of acceptability and nutritive quality in terms of protein content when compared
to the outcome of Oyero et al. (2006). It is thus recommended that any of the EDS should be used as
an alternative to open-air solar drying,
SALT LEVELS MOISTURE % PROTEIN % LIPID % ASH %
UNSALTED 10.01 k 58.86a 13.40k 18.0(i'
srn 25%BRINEV R.9Jc 65.4i 13.49" 13.06'
50%BRNED R.81d 64.711' 14.2i 12.S2c
75% RRJ)IED 8.65' 6~.20· 14.03h 13 101'
DRY SAl TED 9.62:-: 63A5d 12.351- 13 63'
UNSALlED 10,03k 59.03" IS.S5m 15.44J
25% BRINEl) 9.04f 65.9Sk 12,QOf 12.04c
NACO 50% BRINED ~U3b 65.03~ 14.42k 12.03"
75% BRIl\'ED ~.52b 64.98" 14.35j 12.23J
DRY SALTED 9.73i 63,SOd 14.35j 12.63'
UNSAl.TED s.so' 60.25c 20.87" 9.03a
25% BRTNED 8.81d 65.991; 13.53d 11.65°
FACD 50% BRINED 8.45a 65.5Sj 13.95l! 12.06c
75%BRINED 8.443 65.2610 12.87c 13.431
DRY SALTED 9.6811 64.15e 14.491 11.65"
Data in the same column carrying the same superscript do 110tdiffer Significantly from each other
(P>O.05)
Table 1 Mean values of moisture, protem, lipid and ash contents of 0. uiloticus differently sailed and
dried using enclosed drying ystcms (EDS)
Table 1 shows the moisture, crude protein, crude lipid and ash contents of differently salted O.
niloticus dried using Enclosed Solar Drying Systems. Moisture, crude protein, crude lipid and ash
contents differed significantly (p<O.05). All the treatments had moisture content values below 10%.
The moisture contents obtained were lower than those obtained by Trim and Curran (19R3). Moisture
content was 25% was in the brined products and 25-40% moisture content in dry salted products. This
low moisture content indicated that the dried fish products have the tendency to be very stable. From
Tnm and Curran (1983) results, the bnncd and dry salted products had a ...hel r life of approximately
100 days. In all the three drying methods, FACO showed the least of the muixtur,: content when
compared at different levels of salting. The moisture content decreased rcspccuvcly ill thl' brincd
dned products, of 25% bnned, 50%, brined and 75% bnned treatments, according to the level or
salung, It was observed that the higher the level of salting of the fish. the lower the moisture content.
As expected, the unsalted dried products had the highest moisture contents In all the three drying
methods. This was In lmc with IIomer (J 994) that the objective of dehydration is to remove water
from the deepest part of the flesh quickly enough to reduce water activity below the minimum for
microbial growth before SIgnificant spoilage takes place, the objective of salting IS to ensure that sail
penetration is rapid enough to SImilarly lower the water activity 111 the deepest parts of the flesh,
REFERENL~S
A.O.A.C. (1990). Official Methods of Analysis (1Sth edn.) - Heidrich. Association of Official
Analytical Chemists, Virginia, U.S.A. 1298pp.
Doe. P. and Olley, J. (1990). Drying and dried fish products. In Seafood: Resources, Nutritional
Cornposinon and Preservation. CRe Pn.'SSBoca Ranton, Florida. Chapter 8 p 125-46.
Eyo, A.A. (2001). Fish Processing Technology In the Tropics. A publication of National Institute tor
Freshwater Fishenes Research (NTFFR). New Bussa, Nigeria 403pp.
Homer, W.F.A. (1994). Preservation of fish by curing (drying, salting and smoking). In Fish
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VCH Publishers, Inc., New York pp 31-71
ILO - WEP, (1982). Small-scale processing of fish. TECHNOLOGY SERIES. Technical
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Ogali, E.L. and Eyo A.A. (1998). Evaluation of the effectiveness of a box type solar dryer in drying
fish in Kainji Lake Area, Nigeria. FAO FIsheries Report. No. 574. Pp 100-102
Olokor, J.O .. A.A. Eyo, M. Mdarhili, J.K. Okornoda and Ayanda J.O. (1997). Promotion of fish
drying using solar energy in VIllages around Lake Kainji. In: Proceedings of the io" Annual
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Oycro, .I. O. (2006) Effects of different processing techniques on the nutritional quality of salted Nile
Tilapia Oreochromis niloticus. Ph.D Thesis, Federal University of Technology, Minna, Nigeria.
Oyero, J. 0., Sadiku, S. O. E., Ajiscgin, c. S. A. and Eyo, A. A. (2006). Effect of open air drying on
the quality of unsalted and salted Oreochromis niloticus. Journal oj Sustainable Tropical
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Report of the tropical Products Institute, London, L60 pp38


Nutritive evaluation of enclosed salted-solar dried Oreochromis niloticus

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Nutritive evaluation of enclosed salted-solar dried Oreochromis niloticus

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