PROXIMATE ANALYSIS OF FISH DRIED WITH SOLAR DRIERS

Abstract

Nutritional composition of two fish species dried with solar driers were compared with other common methods of drying. For fish dried with solar driers, moisture content was 10.77-11.20 for C. gariepinus and 3.60-3.99 for O. niloticus; protein was 64.88-66.48 for C. gariepinus and 58.75-63.28 for O. niloticus; crude fibre was low in the two species <1.00%; fat was 8.19-8.96 for C. gariepinus and 6.80-7.82 for O. niloticus; carbohydrate was 4.68-5.68 for C. gariepinus and 11.03-17.00 for O. niloticus. The nutrient compositions of the species dried with the solar driers were high and compared well with other methods of open drying.

Headnote

ABSTRACT

Nutritional composition of two fish species dried with solar driers were compared with other common methods of drying. For fish dried with solar driers, moisture content was 10.77-11.20 for C. gariepinus and 3.60-3.99 for O. niloticus; protein was 64.88-66.48 for C. gariepinus and 58.75-63.28 for O. niloticus; crude fibre was low in the two species <1.00%; fat was 8.19-8.96 for C. gariepinus and 6.80-7.82 for O. niloticus; carbohydrate was 4.68-5.68 for C. gariepinus and 11.03-17.00 for O. niloticus. The nutrient compositions of the species dried with the solar driers were high and compared well with other methods of open drying.

Keywords: moisture, oven, protein, proximate analysis, solar driers, smoking kiln

INTRODUCTION

Drying of fish is an age long practice for preserving fish for a fairly long time to prevent deterioration and spoilage in the quality of the product. It is also to reduce post harvest losses and make available the product in times of shortage, thereby ensuring cheap protein availability to people. Drying increases the shelf life, enhance the quality, provide ease of handling, further processing and sanitation (MUJUMDAR, 2007). Drying involves the application of heat to vaporize moisture or remove water vapour from a product (VISAVALE, 2012). The removal of water will stop or slow down the growth of microbes, oxidation of fat and autolytic activities in the fish with resultant reduction in weight and volume.

Various drying methods have evolved and in use over the years in sub-Saharan Africa. These include direct open sun drying, solar drying, smoking and smoke drying with the use of ovens. The use of one particular method depends on the product, availability of energy sources, cost, skill, and storage facilities. The advantages and disadvantages of each method have been summarized by BERKEL et cd. (2004). However, a good drying method must be the one in which the nutritional quality of the fish is enhanced or minimally affected. OPARAKU and MGBENKA (2012) and HUDA et cd. (2010) observed that different drying methods have different effects on the nutritional compositions of fish. TURRAN (2008) and WHITTLE (1997) also linked the availability of vital nutrients in fish to the methods of preservation and shelf life of the fish.

The use of solar driers most especially lowcost ones against the traditional open drying, smoking kiln and ovens is on the rise and becoming widely accepted in sub-Saharan Africa. It is therefore necessary to test for the nutritional qualities of the final dry products produced by these low cost solar driers. Proximate composition is an indicator of the nutritional value of food material and in fish species could vary depending on environment, age, sex, food and feeding habits, migration, methods of preservation, morphology, structure of the species, seasonality in abundance and catch. According to RODINGO (1998), the principal nutritional components of fish include water, protein, ash, lipids, fats and fibre. SESUGH et cd. (2012) OGBONAYA (2009), OJIKUTU et cd. (2009), EFFIONG and FAKUNLE (2012), OPARAKWU and MGBENKA (2012), RAHMAN et od. (2012), AKINWUMI et cd. (2011) AHMED et cd. (2011) TAO and LINCHUN (2008), OGBONAYA and IBRAHIM (2009), ADEBOWALE et cd. (2008) have all analysed the nutritional and proximate compositions of various species of fish dried under different methods.

This study was carried out to evaluate the nutritional composition of two highly important commercial tropical African fish species Ciarías gariepinus (African sharp tooth catfish) and Oreochromis niloticus (Nile tilapia) dried using low cost solar drier and comparing it with the common methods of open sun drying, smoking kiln and electric oven.

MATERIALS AND METHODS

Five different solar driers constructed from inexpensive and readily available materials were used for drying of the two fish species. The driers used were:

1. Plastic drier: This was constructed using a thermopile plastic material. It has a square size of 0.61 x 0.61 m. Inside the drier was placed a wooden stand having a dimension of 0.46 x 0.46 x 0.15 m (length, width and height). A 0.52 x 0.52 m wire mesh in which the fish species were placed was put on top of the stand (Fig. 1).

2. Aluminum drier: This was constructed from aluminum sheet. It has the same size, shape and dimensions with the plastic drier. Inside it was also placed a wooden stand and wire mesh of the same dimensions with that of the plastic. The drier was however coated both inside and outside with black paint (Fig. 2).

3. Glass drier: This was made of transparent glass. It has the same size, shape and dimensions with aluminum dryer. The drier also had a wooden stand wire mesh of the same dimensions with aluminum drier to hold the fish species during dying (Fig. 2).

4. Glass drier containing black stones: This is similar to the glass drier in evey respect but with a black (igneous rock) stone placed in it (Fig. 2).

5. Mosquito net dyer: This was constructed by using plywood for the frame (edges). The drier was subsequently covered with mosquito net all around the wooden frame. The size, shape and dimensions of the drier were the same with the others. Inside it was also placed a wooden stand having a wire mesh on top. The dimensions of the wooden stand and the wire mesh were the same with the other driers (Fig. 3).

An unenclosed 0.61 x 0.61 m steel plate was used for open dying by exposure directly to the sun (Fig. 4). A smoking kiln constructed from steel drum with firewood as the source of energy and an electric oven were used in dying the fish samples (Fig. 5). Temperature of the electric oven was set at 120°C, dried for 30 min (OGBONAYA and IBRAHIM, 2009) in order to completely remove the water content from the fish species in no time. All the solar driers and the unenclosed drier were placed on top of a story building at the Physics laboratory of the University of llorín, llorín, Nigeria with no obstruction to sun rays and facing the direction of the prevailing mind.

Fresh samples Ciarías gariepinus and Oreochromis niloticus used for this work were obtained from Kwara State Ministry of Agriculture, llorín, Nigeria. The fish samples were weighed and the total length measured. They were descaled (O. niloticus only) gutted and mob dried. The fish samples were then reweighed and measured before placing them in each drier and the control. Dlying in the smoking kiln was done outdoor, while drying in the oven was done indoor in the laboratory.

Proximate analysis

Proximate analysis to determine the nutrient composition of the two fish species after drying in the different driers and the open sun drying was done according to AOAC (2005) and PEARSON (1981). The moisture, ash, crude fibre, crude protein, fat and carbohydrate contents of the dried fish samples were determined.

Measurement of temperature in the driers

Temperature measurement in all the driers was measured by using a laser sensor thermometer, while that of the electric oven was set at a value of 120°C in the oven.

Statistical analysis

SPSS (15) was used for the statistical analysis. The data were subjected to Analysis of Variance (ANOVA) with the Duncan New Multiple Range Test (DNMRT) used to examine the differences in the mean values and the significance put at P<0.05.

RESULTS

The results of the proximate analysis of the dried fish samples from the five different solar driers, open sun drying, smoking kiln and electric oven are presented in Table 1. Significant differences (P<0.05) were observed in the proximate composition between the two species and among the nutrients composition in the two species. The percentage moisture content in the solar driers and open sun-drying ranged from 10.26 to 11.42% for C. gariepinus and 3.68 to 4.00% in O. niloticus. The highest percentage protein was 66.48% in C. gariepinus and 63.28% in O. niloticus. Crude fibre content in the two species was low ranging from 0.50 to 0.81% in C. gariepinus and 0.89 to 1.00% in O. niloticus. Fat content of the two species was highest in black stone inserted glass drier with a percentage of 8.96% for C. gariepinus and 7.82% for O. niloticus. The percentage of carbohydrate was highest in O. niloticus than in C. gariepinus with the highest of 17.00% recorded from the glass drier, while the lowest of 4.68% was observed for C. gariepinus also from the glass drier. The highest percentage of ash was found in C. gariepinus recorded from the smoking kiln, while electric oven recorded the highest percentage in O. niloticus.

The mean maximum and minimum temperatures in the low cost solar driers, open sundying, smoking kiln and electric oven showed that electric oven had the mean maximum and minimum temperatures at 120 °C, followed by smoking kiln with rage of 70° to 90°C. The temperatures in the black stone inserted glass drier ranged between 24.50° to 60.50°C while open sun dying had the least temperature range of 20.00° to 38.00°C among all the driers (Table 2). Significant differences (P<0.05) in the maximum and minimum temperatures was observed in all the solar driers and in the open sun dying, smoking kiln and the electric oven.

DISCUSSION

The ranges of the nutrient composition of the two species dried under the five low cost solar driers were in agreement with other workers such as ADAM-SULIEMAN and SIDAHMED (2012). The nutrient composition of the two fish samples, C. gariepinus and O. niloticus dried under the different low-cost solar driers were high and compared favourably well with traditional open sun dying, smoking kiln and electric oven. The low moisture contents recorded in the two species showed the effectiveness of the driers in evaporating water from the fish samples. Although electric oven evaporated more water from the fish in less time than the other driers but the cost of the oven and electricity used for operation beyond the reach of most people in subSaharan Africa. AKINWUMI et al. (2011) has also reported that electric oven produced the lowest moisture content in dried fish samples.

Consequently, the low moisture content increased the protein content in the fish species by coagulating the crude protein. According to STEFFENS (2006), protein forms the largest quantity of dy matter in fish. CLUCAS (1982) reported that a fish with moisture content reduced to 25% is well dried and if further reduced to 15% growth of mould will cease and shelf life increased. The higher moisture content in the C. gariepinus was as a result of the fish having higher water content that O. niloticus. This observation has also been reported by GALLAGHER et al (1991). The same scenario was also found in the fat contents of the fish species. SESUGH et al. (2012) recorded a higher fat content in smoked C. gariepinus than in smoked O. niloticus. Higher ash content, crude fibre and carbohydrates were however recorded in O. niloticus. Substantial loss of moisture was responsible for the higher ash content in the fish species, most especially from smoking kiln and electric oven which produced the highest ash contents on the account of a higher heat source used in the two dying methods. The ash content in O. niloticus was similar to the values recorded by IPINMOROTI (2012) on Tilapia zilli.

A low fibre contents was recorded in all the solar driers which was not significantly different from what was obtain in the smoking kiln and electric oven. AKINNEYE et al. (2007), AKINWUMI et al. (2011) and OGBONNAYA (2009) have all recorded low fibre content in Ciarías gariepinus and O. niloticus dried with electric oven, open sun dying and smoking kiln.

Ciarías gariepinus could be described as a fatty fish even after dying because of its higher fat contents which was higher than that of O. niloticus. Low fat content in O. niloticus has been reported by OMOTOSHO and OLU (1995). Lower fat content which was observed in smoking kiln and electric oven was due to the high heat treatment of the two driers which tend to exude the fats from the species. OGBONNAYA (2009) had noticed low fat contents in fish dried with smoking kiln. The higher percentage of carbohydrates, low fat and low protein in O. niloticus than C. gariepinus could be explained in terms of the feeding habits of the species being a herbivorous one which forages on phytoplankton, while C. gariepinus is mainly a carnivorous species feeding on proteineous prey. The high fibre content in O. niloticus could also be related to the high carbohydrates in fish. O. niloticus is a lean fish with low fat content as compared to C. gariepinus even after dying.

Dying in these solar driers have shown to significantly reduce the moisture content, improve protein quality and increasing the shelve life of the two species. Glass drier with black stone was the most efficient of the solar driers due to its ability to evaporate large amount of water and high protein content. The drier was able to achieve this feat because of the black stone in it which absorb, retain and radiate heat to the fish samples. Although complete dying in these solar driers takes on the average a total of 10 days with relative effect of rainfall. BERKEL (2004) had reported that naturally fish needs about 3-10 days to dy. These solar driers were found to be faster and efficient and effective in drying the two species than the open sun drying. This is in agreement with CHAVAN et cd. (2011) observation that solar drier are faster in drying than open sun-drying, while BERKEL (2004) showed that the quality of products dried with solar driers are higher than smoking.

CONCLUSION

The proximate analysis of the solar dried fish species showed that the nutrient composition especially the moisture contents of the species which was reduced significantly and the protein contents which was significantly higher to be good enough for consumption after dlying. The nutritional qualities of the fish samples dried by these solar driers were high, hygienic, better, more preserved and acceptable.

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Paper received November 5,2013 Accepted January 9,2014