The Effect of Sun Drying on the Nutritive Value of Bagrus bayad

Introduction

Fish plays a very important role in nutrition supply for people. Scientists believe that better health of the people can be ensured quickly and economically through greater production of fish (Bargstram, 1961). Nutritional studies have proved that fish protein rank in the same class as chicken protein and are superior to beef protein, milk and egg albumin

(Srivastava, 1959)

Fish and fishery products are highly nutritious, in addition to the high percentages of animal protein, they provide several other nutrients such as vitamins A and B especially in the liver, and E and K vitamins, and they are good sources of some minerals like calcium, phosphorus and iron (Lunven, 1982).

Fish is a perishable food commodity; it requires preservation for future uses. Several preservation methods are followed over the world for preserving fish. Aims of all these methods are same to extend the shelf-life of fish so that the fish can be used in future properly (Adesiyun, 1993).

It is well known and documented that a large percentage of the fish caught in the developing countries are lost through poor handling. Therefore, there is need for improved processing and preservation techniques (Oladele and Odedeji, 2008). The quality of preserved fish can be assessed using a range of physical, chemical and organoleptic methods. Modern quality control procedures such as HACCP (Hazard Analysis Critical Control Point) programs are increasingly used in fish industries (Doe, 2003).

In Sudan the importance of fish in the diet, seems to follow a markedly regional pattern. Handling and post harvest treatment of fish in Sudan shows a wide spectrum as regards the choice, consumption and ways of utilization. People consume fish as fresh or preserved in one way or another (salted, dried or smoked) (Abu Gideiri, 1973).

The preservation methods according to (Peter and Ann, 1992) include cooking (boiling and frying), salting, smoking and drying collectively known as curing (lowering the moisture content) and fermentation (lowering the pH).

Drying is the oldest known method of preserving perishable food items including fish. Drying is used to describe any process involving the removal of water from fish or fish product by evaporation (Eyo, 2001).

Dry fish is also an important source of high-quality and highly digestible protein and a respectable source of essential minerals (Nettleton, 1992).

Bagrus bayad which is selected for this study is the most important dietary fish in Sudan; it is amongst the top twenty species of the inland water resources of the Sudan, they are found in abundance all the year round. They are consumed as fresh or treated products (Karrar, 1997).

The main objective of this study is to determine the effect of salting and drying on the nutritive value of dried Bagrus bayad product and to contribute in the development of post harvest treatments of fish to reduce losses.

Literature Review:

Nutritive value of fish:

Fish provides a good source of protein and essential micronutrients. Studies on the nutritive value of fish have great importance as they have a direct impact on human health, In addition to its vital roles in solving the problems of protein deficiency malnutrition and to overcome increasing demand for animal protein source (Munro, 1975).

Protein content of fish flesh does not show any regular cycle throughout the year (Love, 1960). (Geiger and Borgstrom, 1962) noticed an inverse relationship between protein and fat contents, and recorded that moisture content and the relative size of the fish are factors affecting the protein content. They also determined the range of protein in fish flesh between 30 – 90 % of the dry weight.

Moisture content of fish body does not seem to be constant in view of the inter–relationship with many biological and physiological factors. Variations coincide with the spawning season were mentioned by Love (1960).

Fat content shows a wide range of variations exemplified by decreases in times of food scarcity indicated by (Love, 1960).

Post harvest fish losses:

Mayboom (2010) reported that 15% of the total fish catch is lost because of spoilage and breakage between the sources of supply and the consumer. Also (Ogbonnaya, 2009) stated that the gap between the demand and supply of fish is widening due to increase in population, poor post harvest handling, lack of processing and storage facilities and utilization of unconventional fish species.

The use of appropriate methods of preservation creates the possibility of having greater increase in the amount of fish available for human consumption. The purpose of preservation is to reduce the moisture content of the fish because micro-organism that is responsible for spoilage and wastage cannot survive without moisture (Ogunleye, 2006).

Fish preservation:

Preservation is the processing of food so that, they can be stored longer. Man is dependent on products of plant and animal origin for food. Most of these products are available only during certain seasons of the year, and because fresh food spoils very quickly, methods have been developed to preserve foods. Preservation must be seen as a way of storing excess foods that are abundantly available at certain times of the year, so that they can be consumed in times when food is scarce and decreases the nutritional value (Van Berkel,; Boogaard, and Heijnen, 2004).

Fish drying:

Sudan as one of the developing tropical countries is no exception in practicing the traditionally sun drying of fish all over the country. Sudanese people practice a simple fish drying process to produce a dried fish product locally known as Kejeik (Dirar, 1993).

Drying is regarded as a traditional and primitive method of preservation of fish. It is of a vital importance in the developing countries of the world. About eight million tons of fish (25 -30 %) of the present world catch for human consumption are dried, salted, smoked, or treated by some combination of these processes each year (Azam, Basher, Ali, et al., 2003).

Drying process can simply be achieved by exposure to direct sun, or natural air current (Jason, 1965).

Traditionally fish is dried without control of heat, the result of which usually is unsatisfactory end products. However if acceptable and suitable drying temperature(s) are used, post harvest losses as a result of under-drying and over-drying would be greatly reduced. (Rahman< 2006) reported 90⁰C and 60⁰C as maximum and minimum drying temperatures for fish.

Fish salting:

Salting is one of the earliest techniques for preserving fish. Salting preserves by lowering the moisture content of the fish to the point where bacterial and enzymatic activities are retarded (Wheaton and Lawson, 1985).

Brining is a type of salting in which the fish is soaked in a solution of water and salt. Brining is not used as such as preservation method but as preparation for smoking or drying, the use of a light salt solution ensures a decrease in bacterial growth on the surface of the fish during the smoking or drying process. It also protects the fish against insects and other vermin and the protection provided is not complete.

(FAO, 1981) mentioned three types of fish salting methods, dry salting (characterized by the fish being salted with dry crystalline salt), wet or salt brine type (a process by which the fish is salted in a previously prepared solution of salt) and mixed salting (a method by which the fish is salted simultaneously with salt and with brine).

Materials and Methods

Sample preparation:

Fresh fish specimens of Bagrus bayad were obtained for this study from Omdurman fish market (Al Mowrada). Fish specimens were washed with tap water, gutted, eviscerated and washed again. A representative sample was taken randomly to be analyzed as control fresh sample. Then the remaining fish sample was divided into two sub samples. The first one was subjected to direct sun drying without any predrying treatment. The second was brined in (20%) sodium chloride solution.

Fish drying:

Samples were then dried under direct sun with daily weight recording to constant weight that indicates the completion of the drying process. Dried samples were transformed into powder for lab analysis.

Proximate analysis:

Moisture content:

The moisture content was calculated by determining the difference in weight before and after drying, one gram of the sample in a drying oven adjusted at 100 – 105 Cº, as described by (AOAC, 1990). Then the moisture content was calculated using the following formula:

Protein content:

Protein content was determined by the Micro – Kjeldahl method, and applying the factor 6.25 to the nitrogen content of the sample, as described by (AOAC,1990). The protein percentage was given by the following formula:

The Effect of Sun Drying on the Nutritive Value of Bagrus bayad - Image 2

Where:

V₁ = Volume of HCl used in titration.

V₂ = Volume of HCl used in blank titration.

N = Normality of HCL used in titration.

14/1000 = Conversion ratio from ammonium sulphate to nitrogen.

Wt. = Weight of sample.

6.25 = Conversion factor from nitrogen to protein.

Oil content:

Fat content was determined by extracting one gm of sample with petroleum ether (boiling point 60 – 80 Cº) for six hours in Soxhelt apparatus. The extract was then dried in an oven at 100 – 105 Cº for removal of extra ether traces, following the method described by (AOA, 1990). The fat content was given by the following formula:

The Effect of Sun Drying on the Nutritive Value of Bagrus bayad - Image 3

Oil content:

The Effect of Sun Drying on the Nutritive Value of Bagrus bayad - Image 4

Minerals content:

Minerals were determined by further analysis of ash following the method described by (Koddebuch, 1988).

Statistical analysis:

One way analysis of variance (ANOVA) and Duncan multiple range tests with significant level (0.05) were carried out for the data obtained throughout the course of this study.

Results

The results obtained from this study focus mainly on the effect of sun drying in combination with salting on the nutritive value of Bagrus bayad. The parameters used for the comparison of the nutritive value of fish products include: protein, oil, moisture and ash. And some minerals namely: sodium, potassium, iron and calcium. The results obtained are illustrated in tables (1 and 2).

From the statistical analysis of the results it was observed that, the moisture content was 75.467 %, 6.248 and 5.204 %, for the control sample, the fresh sun dried and the 20% salted sun dried respectively (figure 1). Moisture among the different treatments was significantly different (P<0.05).

Ash content was 14.59 %, 16.69 % and 27.39 %, for the control sample, the fresh sun dried and the 20% salted sun dried respectively (figure 1). Ash content shows clear significance among the different treatments (P<0.05).

Protein content was found to be 73.667 %, 53.552 % and 57.926 % for the control sample, the fresh sun dried and the 20% salted sun dried respectively (figure 1). Protein content among the different treatments was highly significantly different (P<0.05).

Oil content was found to be 10.467 %, 8.186 % and 6.954 % for the control sample, the fresh sun dried and the 20% salted sun dried respectively (figure 1). Oil content among the different treatments was not significantly different (P>0.05).

Sodium, calcium and iron contents showed no significant differences, whereas potassium was significantly different among the three treatments (figures 2).

Table (1): Effect of sun drying on the proximate composition of Bagrus bayad.

Table (2): Effect of sun drying on minerals content of Bagrus bayad.

Figure (1): Effect of sun drying on the proximate composition of Bagrus bayad.

Figure (2): Effect of sun drying on minerals content of Bagrus bayad

Discussion

(Ogunleye, 2006) observed that the use of appropriate methods of preservation creates the possibility of having greater increase in the amount of fish available for human consumption. The purpose of preservation is to reduce the moisture content of the fish because micro-organism that are responsible for spoilage and wastage cannot survive without moisture.Some of the preservation methods/ techniques according to (Peter and Ann, 1992) include cooking(boiling and frying), salting, smoking and drying collectively known as curing (lowering the moisture content) and fermentation (lowering the pH).

(Ojutiku, Kolo and Mohammed 2009) working on Hyperopisus bebe occidentalis showed that the proximate analysis of the fresh Hyperopisus bebe were 74% moisture, 29.96% crude protein, 1.57% ashand 0.2% crude fibre .

(Mohamed, Eman, Hegazyet al (2011) worked on Oreochromis niloticus anddetermine thephysicochemical properties and mycotoxins contents of Tilapia fish fillets after solar drying and storage, their Results showed that the values reported for moisture, crude protein, fat and ash were 74.99, 18.69, 3.86 and 1.19% for fresh sample, while these values were 18.51-13.42, 57.47- 62.04, 14.73-15.62 and 6.75-7.85% for dried tilapia fillets, respectively. Total volatile basic nitrogen (TVBN) values were significantly (P<0.05) higher in all dried samples as compared to the fresh one.

Conclusion

The moisture content decreased from the control sample to fresh sun dried and 20% salted sun dried.Ash content increased for control sample to fresh sun dried and 20% salted sun dried.Protein content decreased then increased for the three treatments.Oil content decreased for the three treatments.Sodium,calcium and iron showed no differences, while potassium was different among the three treatments.

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