Research Report
Nutritional, Microbial and Sensory Quality of Solar Tent Dried (Samva Nyengo) and Open Sun Dried Copadichromis virginalis-Utaka (Pisces; Cichlidae) 
,
Mangani Katundu2 
,
Levison Chiwaula2 ,
Geoffrey Kanyerere1 ,
Maxon Ngochera1 ,
Kings Kamtambe1 2 Chancellor College, P.O Box 280 Zomba, University of Malawi, Malawi
Author Correspondence author
International Journal of Marine Science, 2017, Vol. 7, No. 11 doi: 10.5376/ijms.2017.07.0011
Received: 24 Mar., 2017 Accepted: 19 Apr., 2017 Published: 01 May, 2017
Banda J., Katundu M., Chiwaula L., Kanyerere G., Ngochera M., and Kamtambe K., 2017, Nutritional, microbial and sensory quality of solar tent dried (Samva Nyengo) and open sun dried Copadichromis virginalis-Utaka (Pisces; Cichlidae), International Journal of Marine Science, 7(11): 96-101 (doi: 10.5376/ijms.2017.07.0011)
A comparative analysis of solar tent drying (Samva Nyengo) and open sun drying were evaluated for their effectiveness on quality of Copadichromis virginalis on nutritional content, microbial load and sensory quality. Solar tent dried and open sun dried Copadichromis virginalis contained 62.89±0.05% and 62.73±0.096% of crude protein, 23.24±0.66% and 23.41±0.59% of fat, 7.22±0.021% and 16.31±0.36% of moisture 14.48±1.08% and 21.97±0.36% of ash respectively. Moisture and ash were significant difference (p = 0.001), crude protein and crude fat showed a non-significant difference (p = 0.05). Open sun dried had significantly higher bacteria load (4.1×105 CFU/g) (0.001) than solar tent dried fish (2.2×102 CFU/g). Isolated bacteria from solar tent dried and open sun dried fish were 1.2×101 and 5.0 ×103 for Total coliform, 0 and 1.0 × 104 for Escherishia coli, 0 and 6.1 × 103 for Salmonella, 0 and 3.8 ×103 for Shigella, 5.9×102 and 5.1×104 for Psuedomonas. Panellist had high preference for solar tent dried than open sun dried fish confirmed by scores for overall acceptability which were high at 3.8 and 2.2 respectively. The results reveal a possible application of solar tent drying as a SMART proven and emerging technology for fish processing in Malawi. It has proved that use of solar tent drying would support fish processors to produce quality dried fish with good nutritive value, reduced microbial contamination, and consumer acceptability that will be central to food security of the country.
Introduction
Fish contribute substantially in human diets as good sources of animal protein that also provide other important elements necessary for maintenance of healthy bodies (Ravichandran et al., 2012). However, it is an extremely perishable commodity due to high water activity, neutral pH and autolytic enzymes and quality losses occur very rapidly after catch (Musa et al., 2010; Dewi et al., 2011). This results to high post harvest losses estimated at 40% (FAO, 2010). These losses are manifested in physical damage, quality deterioration and finally market value. This results in fishermen losing considerable portion of their profit, as well as, the general public losing considerable nutritious food where fish provides 70% of animal protein, hence the need for proper processing techniques to avoid spoilage and quality losses.
In Malawi fish processing is achieved through para boiling, deep frying, smoking and open sun drying which is one of the vital approaches that enhances fish preservation of small fish species such as Copadichromis virginalis (Utaka) endemic to Lake Malawi. However, current processing methods have a lot of limitations. Open sun drying is very challenging during the rainy season due to high relative humidity and cloud cover as well as contamination by dust and insect infestation that carry faecal material and result to poor quality of the processed fish due to high microbial load (Hansen, 2008; Akinola et al., 2016) On the other hand, smoking is dominated by use of traditional open fire using firewood that renders the product with high levels of polycyclic aromatic hydrocarbons which are smoke deposits and unhygienic handling by the processors. Parboiled fish products are easily re-contaminated with bacteria and gets quickly spoiled. Deep frying degrades nutrients with high temperature through hydrolysis and oxidation of fatty acids (Rossel, 2011).
To deal with these problems, the Department of Fisheries is promoting use of solar tent dryers in collaboration with Chancelor College and World Fish Centre as a scientific and technological interventions to reduce fish spoilage, increase quality of processed fish and above all an environmental friendly (SMART) technology that reduces adverse pressure on natural resources such as removal of forests for fuel wood which is contributing to global climate change in the fisheries sector (Figure 1). Solar tent dryers assists in reducing postharvest losses, improving organoleptic properties, and decreasing microbial contamination which are the common limitations of open sun drying (Sablani et al., 2003; Basunia et al., 2011).
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Figure 1 Fire wood (L) smoking (c) and deep frying |
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Several studies regarding quality of processed fish from Lake Malawi are available (Banda et al., 2016). However, no work has been reported for Copadichromis virginalis (Utaka) an endemic species to Lake Malawi. The fact that the solar tent drying studies has never been done on Copadichromis virginalis (Utaka) underscores the need for such study to determine quality of the processed fish for its nutrient content, level of microbes and sensory scores. This paper endeavors to fill this knowledge gap for use by fish processors, consumers and regulators.
1 Materials and Methods
1.1 Solar tent dryer construction
The Solar tent dryer was made up of a UV treated polythene 200 µm sheet worn over a wooden frame (Figure 2). The dimensions of the solar tent dryer were 12 m × 5 m × 5.5 m (length × width × height at the center). The height at the side was 2.5 m. The solar tent dryer consisted of inlet air vent on the bottom with a dimension of 30 cm × 30 cm and outlet vents up on both sides of the vertex with a dimension of 40 cm × 40 cm. This provided for natural circulation of air to speed up 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 11 m × 1 m (length × width). In order to provide air circulation, the gap between drying racks was 90 cm. Air conditions (temperature and relative humidity) inside solar tent dryer and outside were monitored using Davis Vantage VUE data logger at 2 hr intervals.
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Figure 2 Solar tent dryer |
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1.1.1 The solar tent dryer theory
The Solar tent dryer works through evaporative drying using the greenhouse principle (Doe, 2002). When set up in the sun, solar energy passes through the transparent polythene but gets trapped within it thereby raising the internal temperature (Logesh et al., 2012). Cool air flowing in through inlet vents gets heated up and moves out moisture from fish laid on racks in the dryer through the outlet vents on the vertex.
1.2 Sample preparation
Fresh Copadichromis virginalis fish species were collected from cape maclear landing sites in the southern part 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 400 g (Figure 3).
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Figure 3 Solar tent drying (a) and Open Sun drying (b) |
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1.2.1 Analytical procedures
After drying, samples were packed and randomly selected for proximate, microbial analyses and sensory analyses.
1.2.2 Proximate analysis
Proximate analysis of the fish samples was done at Department of Aquaculture and Fisheries Science Laboratory Lilongwe University of Agriculture and Natural Resources (LUANAR), Bunda Campus. The milled fish samples were analyzed for crude protein, crude fat, ash, moisture content, following the procedure outlined by the Association of Official Analytical Chemists (AOAC, 2003).
1.3 Microbial analyses
A procedure earlier used by (Olokor et al., 2009) was followed for microbiological analysis of the fish samples. Fish sample (1 g) were randomly selected from the two processing methods were blended and mixed properly in a sterile mortar then ascetically transferred to a sample vial containing 9 mls of 0.1% sterile peptone water. The vial was closed and shaken thoroughly for 10 minutes then allowed to stand for 20 minutes, after which a 4 fold serial dilution was carried out in triplicates. Viable bacterial counts were enumerated in standard plate count agar after incubation at 37°C for 48 hours. Results were reported in CFU/g.
1.3.1 Identification and enumeration of bacteria
Morphological characteristics of the various bacterial isolates in vitro were noted in the agar plates, and 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.
1.4 Sensory evaluation
Sensory properties such as appearance, odor, and general acceptability of the dried samples were evaluated by 10 randomly chosen adults volunteers (age>20) using hedonic scale modified from Eyo (2001). Qualitative descriptive analysis (QDA) of the sensory properties of the dried fish samples was done after processing. The volunteers were asked to judge the sensory properties of the dried samples using a 5-point hedonic scale of liking.
1.5 Data analysis
Data on proximate contents, microbial analysis and sensory evaluation was recorded in excel. One way analysis of variance (ANOVA) was used to analyze data in SPSS for windows version 16.0 at P<0.05.
2 Results
Proximate composition for solar tent dried and open sun dried fish were 62.89% and 62.73% for protein, 23.24% and 23.41% for fats, 7.22% and 16.31% for moisture, and 14.48% and 21.97% for ash respectively (Table 1). Crude protein and crude fat showed non-significant differences (p=0.05), however, moisture and ash content were significantly different (p=0.050).
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Table 1 Proximate composition Note: Data presented as Mean ±SD. Means with the same superscript along a column are not significantly different (p>0.05) |
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Table 2 Bacteria isolates |
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Table 3 Sensory evaluation Note: On the scale used in this assessment, the higher the value, the higher the quality |
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3 Discussion
Proximate composition is a reliable objective indicator for determining nutritional value and quality of fish (Olvera et al., 1994; Hernandez et al., 2001; Sutharshiny et al., 2011). Results shows an increase in the crude protein in solar tent dried and open sun dried Copadichromis virginalis, this indicates that fish protein nitrogen in drying period is not going to be lost. The study echoed results by Gokoglu et al. (2004) who reported that increase in crude protein content after drying is due to dehydration which increases the nutritional value of fish. Solar tent dried Copadichromis virginalis had low moisture content than open sun dried. Fish spoilage has shown to be a function of moisture content. The total amount of body water of fish species, depend on morphological and chemical differences, physical properties and the fish storing. Dried fish with moisture level of 6 to 8% retards the rate of microbial spoilage as the water activity is reduced during storage hence increasing the shelf life. Oparaku et al. (2010) indicated that products with high moisture content above 35% are susceptible to attack by flies that result to development of maggots during storage. Low levels of moisture was achieved for products from solar tent dryer than in the open sun dried fish products. This was due to high temperatures and low humidity associated with solar tent drying that created an ideal condition in drying of fish than open sun drying which had low temperature and high relative humidity (Table 4). This suggests that high relative humidity had minimal influence in drying of fish on the racks as it limits the amount of water the air can absorb. In their study (Sablani, 2003) reported that dryers that give low moisture content have lower humidity and higher temperatures inside the drying units.
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Table 4 Meteorological data |
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Results of microbial analysis are shown in Table 3. Total Viable Counts for solar tent dried and open sun dried Copadichromis virginalis were 2.5×102 and 4.1×105 respectively. In all fresh samples, the microbial population was 3.0×102. The results is an indicative of possible contamination. This observation was validated by analyses and isolation of pathogens and spoilage flora in open sun dried fish. Escherichia coli, Psuedomonas, Salmonela, Shigella and Vibrio were detected in worrying concentrations in open sun dried Copadichromis virginalis. However they were totally absent in solar tent dried Copadichromis virginalis dried samples. These pathogens are associated with food toxiinfections and are indicators of very poor hygienic quality of the processing method (Huany et al., 2010). These bacteria are probably from soil, human and animal origin and have contaminated Lake water (Oramadike, 2009). This clearly shows microbial contamination by pathogens for open sun dried fish may be considered as an important warning signal for human consumption. Consequently, it is imperative that measures are taken to promote use of solar tent dryers as a hygienic processing technology to dry small fish.
Appearance and colour in this study appeared to be the two most important parameters which influenced panel’s preference for dried fish products. The preference was confirmed to a greater extent by scores for overall acceptability which were also high than open sun dried. In their study, Reza et al. (2009) reported that solar tent dried fish gave superior quality. In this regards, if a value added fish product can have high scores during organoleptic assessment then the possibility of acceptance for the products at the market is there. The significant difference in the overall acceptability score apparently indicated that solar tent drying produced the desirable effect. This observation agrees with the sensory evaluation done on fish dried by open-sun drying and low cost solar driers by Sengar et al. (2009). Hence, use of solar tent drying is more effective and has more acceptability in terms of organoleptic properties than open-sun drying.
4 Conclusion
The study findings have shown that solar tent dryer have a potential in maintaining quality of processed fish. As such, the use of solar tent dryers can help in strengthening of the fisheries value chain by not compromising product quality during processing as well as building capacity among fisherfolks to adapt to climate change by reducing adverse pressure on natural resources such as removal of forests for fuel wood so that the potential role of fish in improving nutrition security in Malawi is enhanced.
Acknolwedgments
We thank the Australian International Food Security Centre, ACIAR, and the International Development Research Centre, Ottawa, Canada financial support. 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. Special thanks are expressed to Dr. Joseph Nagoli, Dr. Lucy Binauli, Professor Magalasi, Dr. Jupiter Simbeye, and Mr. Essau Chisale for the conceptualization of the whole project idea.
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