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212
E-ISSN: 2347-5129
P-ISSN: 2394-0506
(ICV-Poland) Impact Value: 5.62
(GIF) Impact Factor: 0.549
IJFAS 2017; 5(5): 212-218 ©
2017 IJFAS
www.fisheriesjournal.com
Received: 27-07-2017
Accepted: 28-08-2017
James Banda
Fisheries Science Department,
Mzuzu University, Private Bag
201, Mzuzu 2. Malawi, East
Africa
Petros Chigwechokha
Fisheries Science Department,
Mzuzu University, Private Bag
201, Mzuzu 2. Malawi, East
Africa
Wales Singini
Fisheries Science Department,
Mzuzu University, Private Bag
201, Mzuzu 2. Malawi, East
Africa
John Kamanula
Chemistry Department, Mzuzu
University, Private Bay 201,
Luwinga, Mzuzu 2. Malawi, East
Africa
Orton Msiska Fisheries
Consultant, P.O. Box 833.
Mzuzu, Malawi, East Africa.
Jupiter Simbeye
Mathematics Department,
Chancellor College, P.O Box 280,
Zomba, Malawi, East Africa.
Correspondence
James Banda
Fisheries Science Department,
Mzuzu University, Private Bag
201, Mzuzu 2. Malawi, East Africa
International Journal of Fisheries and Aquatic Studies 2017; 5(5): 212-218
The Shelf life of Solar Tent Dried and Open Sun Dried
Diplotaxodon limnothrissa (Ndunduma)-Pisces;
Cichlidae
James Banda, Petros Chigwechokha, Wales Singini, John Kamanula,
Orton Msiska and Jupiter Simbeye
Abstract
The study evaluated changes in chemical, physical, microbial quality of solar tent dried and open sun
dried Diplotaxodon limnothrissa fish species from Malembo landing site after 9 weeks of storage at
ambient temperature. The shelf life of solar tent dried and open sun dried Diplotaxodon limnothrissa fish
species was estimated at 7 and 3 weeks respectively. Spoilage indicators Total Volatile Basic Nitrogen
(g/100mg) and pH range were 15.45-17.31, 6.26-6.6.35 for solar tent dried fish and 15.74-20.56,
6.326.41 for open sun dried fish. At the period of sensory rejection, total bacteria viable counts, Total
Volatile Basic Nitrogen and pH were 5.7×106 cfu/g, 18.98 and 6.38, respectively, for open sun dried. On
the other hand, solar tent dried fish registered 4.1×102 cfu/g total bacteria viable counts, 17.28 Total
Volatile Basic Nitrogen and pH 6.33. Relatively higher levels of Esherichian coli, Salmonella, Vibrio and
Micrococcus bacteria were detected in open sun dried compared to the solar tent dried fish. Protein range
for solar tent dried and open sun dried samples were 63.3±0.15-61.09±0.07% and 63.3±0.34-
58.19±0.21% respectively. Moisture content remained constant and significant (p= 0.001) at 8.3±0.12
and 17.0±0.01% for solar tent dried and open sun dried Diplotaxodon limnothrissa respectively. Visible
fungal growth was observed from week 2 of storage in open sun dried fish and the isolates of Aspergillus
3.3×101 and Penicilium 3.3×101 were identified. The results confirmed the application of solar tent
drying as an efficient technology for fish processing in Malawi. The study recommend use of solar tent
drying to increase shelf life and safeguarding markets for value addition of small fish products in
Malawi.
Keywords: Diplotaxodon limnothrissa, sensory, microbiological analysis, chemical analysis, Lake
Malawi
1. Introduction
The global consumption of fish and fish products has greatly increased in recent decades, due
to a number of factors [1]. Foremost among these factors is the growing knowledge that fish
constitute an important and healthy part of the human diet, mainly owing to the presence of
ω3 polyunsaturated fatty acids, which play an essential role in human health, presence of
micronutrients (vitamins, minerals) and proteins with a high biological value [2]. Fish
constitute a significant proportion of diets in Malawi, contributing over 50% total animal
International Journal of Fisheries and Aquatic Studies
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protein consumption
by the population [3].
Several fish species,
including
Diplotaxodon
limnothrissa probably
the most abundant
cichlid with high
biomass estimates in
the pelagic zone alone
are popular diet
constituents in
Malawi. The species is
exploited
commercially in the
South Eastern and
Western Arm of the
lake [4].
Fish is recognised as
being highly
perishable, having a
relatively short shelf
life. Fish’s shelf life is
influenced by a
number of factors. The
peculiarity chemical
composition of fish is
a major factor
responsible for their
high perishability [5].
The high content of
water, non-protein
nitrogenous
compounds,
unsaturated fatty acids,
presence of bacterial
flora on the skin
surface and in gastro-
intestinal tract and the
activity of endogenous
enzymes contribute to
the high perishability
of fish. Furthermore,
the high ambient
temperature hastens
fish spoilage by
accelerating the
activities of bacteria,
enzymes and chemical
oxidation of fat in
fresh fish [6]. This call
for proper processing
technologies to
minimize rate of
spoilage and increase
shelf life of processed
fish. It is reported that
fish processing
reduces spoilage and
microbial
contamination that would pose a threat to the health and safety of the consumer [7]. A number
of studies have indicated that quality is still the key buying cue for fish purchasers [8].
~ ~
Besides, in order to secure food safety, it is important to keep the quality of processed fish products
acceptable to consumers over a range period of time [9].
In Malawi, common fish processing methods include para boiling, smoking and sun drying [10]. The
characteristic of dried fish that renders them long shelf life is the low water activity that prevents
growth of spoilage microorganisms [11, 12]. Although sun drying is used most frequently, it is very
imperfect during the rainy season due to excessive rainfall, high relative humidity and cloud cover.
Sun drying is also fraught with other problems such as contamination by dust and insect infestation
that carry faecal material and result in poor quality of the processed fish due to high microbial load
[13]. A number of studies have indicated that contamination of food with mycotoxin is unavoidable
and unpredictable hence posing a unique challenge to food safety [14]. Furthermore, food safety
issues are a concern worldwide due to increased risks related to food borne illnesses such as
melamine, salmonella, and cholera [15]. To get better quality-dried fish with longer shelf life, it is
very essential to use improved methods of fish drying. In additional, it is also important to
maintain required hygiene during the different phases of fish drying. Shelf life studies provide
important information to both researchers and consumers ensuring that consumers appreciate a
high quality product for a significant period of time after production. Thus, in the search for
improved drying techniques using naturally abundant solar energy, solar tent drying systems have
been investigated and tested on Lake Malawi by the Fisheries Research Unit of the Department of
Fisheries as an alternative to open sun drying.
The fact that the solar tent drying is a new processing technology for processing small fish species
like Diplotaxodon limnothrissa in Lake Malawi underscores the need for estimating the duration of
safety for processed fish. The information is greatly required by consumers, processors and for
adequate post-harvest management and processing. It is against this background that shelf life of
solar tent dried and open sun dried Diplotaxodon limnothrissa were assessed for the chemical,
physical and microbiological changes after storage at room temperature for nine weeks.
2. Materials and methods
2.1 Study area
The study was conducted at Malembo landing site in South West Arm (SWA) of Lake Malawi at
Monkey bay in Mangochi district. Mangochi is in the Southern region of Malawi covering an area
of 6, 273 km2 with a population of
610, 239 [16].
2.2 Solar tent dryer
The Solar tent dryer was made up of a UV treated polythene 200 µm sheet worn over a wooden
frame (Fig 1.0). The dimensions of the solar tent dryer were 12m x 5m x 5.5m (length x width x
height at the center). The height at the side was 2.5m. The solar tent dryer consisted of inlet air
vents on the bottom with a dimension of 30cm × 30cm and outlet vents up on both sides of the
vertex with a dimension of 40cm x 40cm. This enhanced natural circulation of air through the
convection current process. Both vents well sealed with galvanized fine meshed gauze wire to
prevent entry of flies. The dimensions of the drying racks were 11m x 1 m (length x width). In
order to provide air circulation, the gap between drying racks was 90cm.
Fig 1: Solar Tent Dryer
International Journal of Fisheries and Aquatic Studies
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2.3 Sample collection,
preparation and
processing Fresh
Diplotaxodon limnothrissa
fish species were collected
from pair fish trawlers at
Malembo landing sites in the South West Arm of Lake Malawi. The fish were thoroughly washed
and arranged on the racks within the solar tent dryer and open sun drying racks in sub samples of
4000g.
2.4 Analytical procedures
Dried samples of Diplotaxodon limnothrissa were used for
the analytical procedures. Fresh dried samples from the solar
tent dryer and open sun drying were packed in sealed plastic
packet in 60 μm polythene papers. Samples for each
processing technique were kept in separate shelves at ambient
atmospheric temperature for 9 weeks. Shelf life determination
of the products was carried out by using turn-over time, end
point study and accelerated testing.
In all these methods, quantity of samples were subjected to
laboratory tests for microbiological organisms, chemical
factors, physical and sensory evaluation which were carried
out at weekly intervals. For the preparation of samples, whole
dried fish samples were homogenised before analysis.
2.5 Chemical analysis
2.5.1 Total Volatile Basic Nitrogen (TVB-N)
Total Volatile Bases (TVB-N) were determined by a slight
modification of Conway Microdiffusion Method [17]. About
25g of the fish samples muscle tissues were removed,
chopped and thoroughly mixed with 75 ml distilled water in a
250 ml beaker. The pH was adjusted to 5.2 by addition of few
drops of 2N HCl, followed by heating at 70 °C and cooling to
room temperature. After cooling, the sample was filtered into
a conical flask with the aid of a Whatman No. 1 filter paper.
After that, 2ml of 0.025N HCl was transferred to the central
compartment of the microdiffusion dish by pipetting,
followed by the addition of 2ml of the extract and 1ml of
saturated K2CO3 solution into the outer ring. The dish was
covered immediately with a glass plate and the set-up was left
at room temperature for 24hours. Thereafter, the HCl in the
inner compartment was titrated with 0.025N NaOH using 2-3
drops of methyl red indicator. Results were reported as
TVBN in mg/100 of fish flesh using the formula shown
below.
Where
V= Volume of hydrochloric acid added for titration and C=
Concentration of acid added for titration
2.5.2 pH analysis
About 10 g of the fish muscle was removed, weighed and
homogenized in 50 ml of distilled water. The sample was then
centrifuged in 10000 rpm using a Yamato Mag-Mixer Model
MH 800 (Yamato Scientific Company Limited, Japan) and
the mixture was filtered using Whatman filter paper No.1. A
calibrated pH meter (Model No. WTW-8120, West Germany)
electrode was then inserted into the homogenate to measure
the pH at ambient temperature after calibration using standard
buffers of pH 7 and 4 at 25 oC.
2.5.3 Protein content
Crude protein content in dried fish samples was determined
following the Kjeldahl method 1g fish sample selected from
the two processing methods were separately digested in a
kjeldahl flask using sulphuric acid (98%) and catalyst made
from Cupric Sulphate and Potassium Sulphate. The two
samples were distilled and the distillate titrated against
standard 0.05N sodium hydroxide (NaOH) solution. To
quantify the crude protein%, the nitrogen was converted to
protein by multiplying with a conversion factor of 6.25.
(Protein contains 16% nitrogen hence 6.25 is 100/16).
2.5.4 Moisture content
One gram sample of ground fish was placed in a crucible and
dried at 105 degrees Celsius to a constant weight after the
initial weighing. Moisture content of the fish was calculated
by subtracting the initial from the final weight of the fish
sample.
2.6 Microbial analyses
The microbiological analysis of fish samples in this study
followed a previously used procedure [18]. Fish sample (1 g)
Fig 2: Fish processing methods employed. Solar tent drying (a) and open sun dying (b)
International Journal of Fisheries and Aquatic Studies
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selected from the two processing methods were blended and
mixed properly in a sterile mortar then ascetically transferred
to a sample viral containing 9 ml of 0.1% sterile peptone
water. The viral was closed and shaken thoroughly for 10
minutes then was allowed to stand for 20 minutes, after which
the top part was used to carry out a 6 fold serial dilution in
duplicates. Viable bacterial counts were enumerated in
standard plate count agar after incubation at 37 °C for 48
hours. Results were reported in CFU/g.
2.6.1 Identification and enumeration of bacteria
Morphological characteristics of the various bacterial isolates
in vitro were observed in the agar plates, and under
microscopy. After staining reactions and several biochemical
tests, individual microbial species were identified.
Representative isolates were re-plated on various selective
media to observe their habits and specific colony attributes.
2.7 Sensory evaluation
Organoleptic properties such as appearance, colour, odor and
general acceptability of the dried samples of D. limnothrissa
from the two processing techniques were evaluated by 10
randomly chosen adult volunteers (age >25). The volunteers
were asked to judge the organoleptic properties of the dried
samples using a 5-point hedonic scale which were as follows:
very good (5), good (4), fair (3), poor (2), and bad (1).
2.8 Data analysis
Data on chemical, microbial analyses and sensory evaluation
was entered into Microsoft Excel and analysed using SPSS
for Windows version 16.0 software at P<0.05. Treatment
means were compared using one way Analysis of Variance
(ANOVA) at 5% level of significance.
3. Results
The shelf life of solar tent dried and open sun dried
Diplotaxodon limnothrissa stored at ambient temperature was
carried out using total volatile basic nitrogen (TVB-N), pH,
protein, moisture content, total viable counts and sensory
evaluation.
Fig 3: Total Volatile Basic Nitrogen (TVB-N) g N/100mg of stored
D. limnothrissa
Level of TVB-N g/100mg for solar tent dried and open sun
dried fish range were 15.45-17.31 and 15.70-20.56
respectively. At the period of sensory rejection, the level of
TVB-N were 17.20 g/100 and 17.14 for open sun dried and
solar tent dried fish respectively. It was observed that TVB-N
levels increased with storage time but the increase was very
pronounced in open sun dried D. limnothrissa indicating a
shorter storage life.
Fig 4: Changes in pH values of dried D. limnothrissa as time of
storage progressed
The level of pH significantly increased throughout the storage
period up to week four from initial pH of 6.32 to 6.40 in open
sun dried D.limnothrissa than 6.26 to 6.34 for solar tent dried
D. limnothrissa. It then fluctuated between week 5 and week
9 from 6.36 to 6.41 and 6.32 to 6.35 for open sun dried and
solar tent dried D.
limnothrissa respectively.
Table 1: Protein and Moisture content of dried D. limnothrissa
under storage
Solar tent dried
Open sun dried
Period
(weeks)
Protein
(%)
Moisture
(%)
Protein
(%)
Moisture
(%)
0
63.3±0.15
8.3 ±0.12
63.3±0.34
17.0±0.01
1
63.16±0.13
8.3±0.12
62.02±0.12
17.0±0.01
2
63.04±0.11
8.3±0.12
61.2±0.10
17.0±0.01
3
62.55±0.13
8.3±0.12
60.32±0.14
17.0±0.01
4
62.31±0.12
8.3±0.12
60.28±0.15
17.0±0.01
5
62.20±0.13
8.3±0.12
60.21±0.14
17.0±0.01
6
61.34±0.10
8.3±0.12
59.13±0.07
17.0±0.01
7
61.22±0.11
8.3±0.12
59.04±0.16
17.0±0.01
8
61.17±0.09
8.3±0.12
58.44±0.11
17.0±0.01
9
61.07±0.07
8.3±0.12
58.19±0.21
17.0±0.01
Protein ranged from 63.3±0.15% - 61.07±0.07% and
63.3±0.34% -58.19±0.21% for solar tent dried and open
sun dried D. limnothrissa respectively. Moisture content
remained constant at 8.3% and 17.0% for solar tent dried
and open sun dried D. limnothrissa. At rejection by
sensory panels 61.22±0.11% and 60.32±0.14% protein for
solar tent dried and open sun dried D. limnothrissa were
obtained. There were greater reductions in protein content
of open sun dried than solar tent dried D. limnothrissa.
Table 2: Total Viable Counts of Diplotaxodon limnothrissa stored
at room Temperature
Solar tent drying
Open sun drying
International Journal of Fisheries and Aquatic Studies
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Period (weeks)
TVC (cfu/g)
Fungi
(cfu/g)
TVC (cfu/g)
Fungi
(cfu/g)
0
3.9×102
0
5.2×106
0
1
3.9×102
0
5.2×106
0
2
4.1×102
0
5.5×106
2.0×101
3
4.3×102
0
5.7×106
3.1×101
4
4.3×102
0
5.9×106
3.3×101
5
4.5×102
0
6.1×106
3.5×101
6
4.5×102
0
6.3×106
3.7×102
7
4.5×102
0
6.5×106
4.0×102
8
4.7×102
0
7.1×106
4.1×102
9
4.7×102
0
7.1×106
4.1×102
Open sun dried had significant (p = 0.002) higher total
viable count ranged from 5.2 ×106 cfu/g to 7.1×106 cfu/g
than solar tent dried which had lower total viable counts
ranging from 3.9×102 to 4.7×102cfu/g. At the time of
sensory rejection which was weeks 3 for open sun dried
bacterial population were 5.7×106 cfu/g and 2.0 ×101cfu/g
for moulds. Week 7 was the rejection period for solar tent
dried with bacterial population being at 4.5×102 cfu/g
respectively (Table 2.0). The overall observation was that
total viable bacterial counts for open sun dried fish
increased constantly during the storage period. However,
populations were not above acceptable norms (108cfu/g2)
[19].
Sensory attribute scores namely appearance, colour, and
overall acceptability for open sun dried D. limnothrissa
decreased steadily throughout the storage period compared to
solar tent dried D. limnothrissa which remained in steady
acceptability by consumers (table 3.0).
4. Discussion
As expected, solar tent dried samples of Diplotaxodon
limnothrissa had higher shelf-life than sundried samples. This
was confirmed by Total Volatile Base Nitrogen (TVB-N)
which is an important compound providing a measure of the
progress of spoilage that is dependent on sensory assessment.
In the present study, the TVB-N content of solar tent dried
and open sun dried D. limnothrissa were found to vary from
15.45 (0 week) to 17.31 mg N/100g (9 weeks) and 15.74 (0
week) to 20.56 mg N/100g (9 weeks) respectively (figure
3.0). The trend was similar to dry, wet and mixed salting of
Sardinella eba and Clupea harrengus [19]. The level of TVB-N
in fish and fish products are mostly used as spoilage indicator
through bacterial activity [20]. In this study, the rate of TVB-N
formation was different, being highest for open sun dried than
solar tent dried D. limnothrissa. The values did not exceed
level for rejection of TVB-N which is 30-40mgN/100g for
dried fish stored at ambient temperature [21, 22]. The increase in
these volatile bases was pronounced in open sun dried fish
that led to deterioration of colour in dried fish. This is
evidenced with the dimeric scores of dried D. limnothrissa.
Furthermore, high TVB-N values are associated with
unpleasant smell in fish and meat [23]. This is due to the extent
of degradation of proteins and non-protein nitrogenous
compounds which can be explained by proteolysis, due to
enzymatic and microbial activities in the samples upon
storage [24].
The level of pH is an indicator of the extent of microbial
spoilage in fish and some proteolytic microbes producing acid
after decomposition of carbohydrate, which increases the acid
level of the medium. The normal pH in fresh fish is almost
neutral [25]. In this study, pH values were found to vary from
6.26 in week (0) to 6.35 in week (9) for solar tent dried and
6.32 in week 0 to 6.41 in week (9) for open sun dried D.
limnothrissa (figure 4.0). The pH values of dried D.
limnothrissa from both processing methods showed a gradual
increase with storage period up to week 5. However, the
increase was more pronounced in open sun dried D.
limnothrissa. This was due to decomposition of nitrogenous
compounds leading to an increase in pH in the stored fish [26].
The increase in pH indicates the loss of fish quality with
storage time. Dried fish products are acceptable up to a pH of
6.8 but are considered to be spoiled above pH of 7.0 [27]. The
pH values later on dropped and fluctuated between week 5
and 8. The drop might have been caused by accumulation of
end products of spoilage of both alkaline and acidic nature
which tend to neutralize each other. The increase in pH
coincided with increase in Total Viable Counts toward
sensory rejection for open sun dried fish in this study. This
indicates accumulation of alkaline compounds as well as
Table 3: Sensory evaluation of D. limnothrissa stored at room Temperature
Solar tent drying
Open sun drying
Storage
(weeks)
Appearance
Colour
Acceptability
Appearance
Colour
Acceptability
0
4.8±0.43
4.6±0.52
4.9±0.32
4.1±0.57
4.0±0.67
3.9±0.32
1
4.6±0.52
4.4±0.52
4.7±0.48
3.7±0.6
3.8±0.63
3.6±0.52
2
4.4±0.67
4.2±0.79
4.5±0.53
3.3±0.52
3.4±0.52
3.2±0.63
3
4.2±0.42
3.9±0.39
4.1±0.32
2.6±0.62
2.5±0.56
2.4±0.57
4
3.9±0.74
3.7±0.67
3.6±0.52
2.5±0.53
2.4±0.52
2.4±0.57
5
3.6±0.52
3.4±0.52
3.3±0.48
2.1±0.73
1.8±0.42
2.1±0.70
6
3.3±0.67
2.8±0.42
2.9±0.57
1.8±0.42
1.5±0.53
1.9±1.3
7
3.1±0.62
2.5±0.53
2.6± 0.70
1.5±0.53
1.3±0.52
1.5±0.52
8
2.7 ± 0.70
2.2±0.57
2.3 ± 0.52
1.3 ±0.52
1.1±0.51
1.2±0.52
9
2.4 ± 0.74
2.0±0.59
2.1 ± 0.53
1.0 ±0.55
1.0±0.52
1.0±0.51
International Journal of Fisheries and Aquatic Studies
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volatile bases produced by autolytic activities and metabolism
of spoilage bacteria [28]. This explains the rapid spoilage and
reduced shelf life for open sun dried D. limnothrissa as
demonstrated by sensory demerit scores. The important link
between increased pH and spoilage of dried fish is that it
favours more microbial activity [29], hence high total viable
counts for open sun dried than solar tent dried D.
limnothrissa.
Protein forms the largest component of dry matter in fish and
its amount in fish muscle is usually between 15% and 20%
[30]. Changes in crude protein of dried fish samples during
storage was more pronounced in open sun dried than in solar
tent dried D. limnothrissa denoting loss in nutrient content
(table 1.0). The gradual degradation of the initial crude
protein to more volatile products such as total volatile bases
which was also higher in open sun dried D. limnothrissa in
turn affected the colour and consumer acceptability of the
dried fish products [6]. Consequently, it is apparent that the
pronounced reduction of crude protein for open sun dried D.
limnothrissa during storage is a nutritional concern. Moisture
content of dried D. limnothrissa remained constant in both
processing methods, however, it was noted that moisture
content of the dried fish product seems to be an exact
indicator of the liability of a product to undergo microbial
spoilage and eventually reduced storage life. In this study,
solar tent dried D. limnothrissa had lowest moisture content
that prevented multiplication of bacteria as well as growth of
moulds that led to increase storage life than open sun dried D.
limnothrissa (table 2.0). It has been reported that fish well
dried or moisture content reduced to 25% will not be affected
by microbes and if further dried to 15%, the growth of mould
will cease and thus increasing the shelf life [31]. Total Viable
Counts of stored dried packed fish indicated high level of
bacteria for open sun dried than solar tent dried fish.
Although dried fish from both processing methods had
microbial load below the permissible limit, it was high in
open sun dried fish due to unhygienic condition of the drying
process and higher moisture content of the dried D.
limnothrissa. The least bacterial load for solar tent dried fish
was due to hygienic condition of the processing method and
low moisture content of the dried D.limnothrissa which
retarded the bacterial growth. Furthermore, open sun drying
created a conducive environment and was in favour of spore-
former fungi as a result there was spreading of spores by air
since the fish were exposed to ambient atmosphere during
open sun drying. This probably explains the occurrence of
fungi colonies in open sun-dried D. limnothrissa from week 2
of storage. Fungi are commonly related to food contamination
[32]. This emphasizes the economic losses caused by these
contaminants and human health problems from mycotoxins
which are secondary metabolites. Enumeration of pathogenic
microbes in open sun dried fish during storage proved the loss
of shelf life for the dried fish. Apparently, this possess highest
food safety risk because the products are most susceptible to
microbiological deterioration and possible for growth of
pathogenic organisms.
Sensory attribute values namely appearance, colour, and
overall acceptability for open sun dried D. limnothrissa
decreased steadily throughout the storage period compared to
solar tent dried D. limnothrissa (table 3.0). Decrease in the
sensory attribute values during storage might be due to
excessive microbial and enzymatic proteolysis of the tissue
causing tissue disintegration [33]. Consumers showed high
level of preference for solar tent dried fish than open sun
dried as confirmed further by scores for appearance, colour
and general acceptability which were 4.8, 4.6, 4.9 and 4.1,
4.0, 3.9 respectively. [34, 35, 36] indicated that enclosed solar
dried fish gave superior quality during storage. Consumers
started disliking open sun dried D. limnothrissa after 2 weeks
of storage and eventually rejected the samples after 3 weeks
of storage. Week 7 was the rejection point of solar tent dried
fish and the scores for appearance, colour, and general
acceptability were 3.3, 2.8 and 2.9. The high scores during
sensory evaluation indicates the possibility of general
acceptance of solar tent dried D. limnothrissa products in the
market.
5. Conclusion
The chemical, physical and microbiological changes during
storage were much less in the solar tent dried fish as
compared to the open sun dried fish. The solar tent dried have
shown to be superior over open sun dried D. limnothrissa
throughout the storage period. Thus solar tent drying can be
regarded as suitable improved methods of drying D.
limnothrissa in Lake Malawi. This would help fish processors
to supply safe and high-quality fish-products that have a
longer shelf life hence giving a unique value for the processed
fish. However, in order to further improve on quality, it might
be necessary to treat samples with brine.
6. Acknowledgments
This work was carried out with the aid of a grant from
Canada’s International Development Research Centre
(IDRC), www.idrc.ca, and the Australian Centre for
International Agricultural Research (ACIAR),
www.aciar.gov.au. We also thank members of staff in the
Department of Biology at Chancellor College and
Aquaculture and Fisheries Science at Bunda College of
Agriculture, Malawi for accommodating this study at their
laboratories. Many thanks are expressed to Levision
Chiwaula, Joseph Nagoli, Geoffrey Zentute Kanyerere and
Essau Thunga Gandifolo Chisale for the conceptualization of
the whole project idea.
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