AMERICAN JOURNAL OF FOOD AND NUTRITION Print: ISSN 2157-0167, Online: ISSN 2157-1317, doi:10.5251/ajfn.2013.3.2.73.82

2013, ScienceHu, http://www.scihub.org/AJFN

Effect of traditional fish processing methods on the proximate composition of red fish stored under ambient room conditions

1Holma, K. Ayinsa, and 1B.K. Maalekuu*

Department of Horticulture Faculty of Agriculture Kwame Nkrumah University of Science and Technology Kumasi.* Corresponding author: kbmaalekuu.agric@knust.edu.gh

ABSTRACT

The effects of three different traditional processing methods (smoking, frying and salting) on proximate composition of red fish stored under ambient room conditions were determined. Fresh red fish were obtained from Elmina fish market. These were used for the study to determine the proximate properties of the raw fish, smoked fish, fried fish and salted fish before and after storage. The parameters studied were moisture, crude protein, crude fat, ash, crude fibre, and nitrogen-free extract contents. The results indicated that traditional processing methods have significant effects on the proximate composition of red fish. Mean moisture, crude protein, crude fat, ash, crude fibre, and nitrogen-free extract contents of the raw fish were 80.0, 72.49, 9.99, 6.00, 1.01, and 0.51 respectively. The changes in all the parameters after processing but before storage were found to be significant at (P < 0.05) for the three traditional processing methods studied. After storage under ambient room conditions for 14 days, changes in ash, crude fibre, nitrogen-free extract, moisture, and crude fat content of the processed fish were found to be significant (P < 0.05) for the three traditional processing methods studied. Changes in the protein content were not significant at (P < 0.05) between salted and dried pre-stored and post- stored red fish. .

Keywords: Traditional fish processing, smoking, frying, salting

INTRODUCTION

In 2002, world total fishery production (excluding aquatic plants) was reported to be 133.0 million tonnes, of which 41.9 million tonnes from aquaculture practices. World capture fisheries production amounted to 93.2 million tonnes, representing a slight increase of 0.4% compared to that of 2001 (Vannuccini, 2004).

In Africa, some 5 percent of the population, about 35 million people, depend wholly or partly on the fisheries sector, mostly artisanal fisheries, for their livelihood (FAO, 2001). In Ghana, the fisheries sector contributes 3% of the national GDP. It is estimated that about 2 million Ghanaians comprising 860,000 females and 1,140,000 males are employed or dependent on activities in the sector (extrapolation from GSS, 2002). Fish is one of Ghanas most important non-traditional export commodities. Nevertheless, Ghana is a net importer of fish since domestic fish supplies; continue to fall short of meeting total domestic demand. About 75% of the total domestic production of fish is consumed locally with marine fish accounting for nearly 80% of the fish production. Most of the artisanal landings are consumed within the country but they do not meet the demand for fish.

Fish is an important component in the diets of many Ghanaians. It is a good source of protein; fish constitute the major source of animal protein intake in Ghana. It is estimated that 60% of the total animal protein requirement in the Ghanaian diet comes from fish. Fish is also an important source iron, calcium, iodine, potassium, vitamin A, vitamin B2, vitamin B6, poly-unsaturated fatty acids, other minerals, vitamins, micronutrients (USDA, 2002). Fish is consumed by the majority of people in Ghana from the rural poor to the urban rich. With a population of about 20 million people, the average per capita fish consumption is 27 kg per annum, which is higher than the worlds average of 13 kg (Nti et al., 2002, Antwi, 2006).Though fishing is done on a continuous basis in Ghana, a noticeable and significant bumper harvest occurs around the seasonal herring catch from July to September each year. Hence to ensure the availability of fish throughout the year, especially during the lean season, it is essential to process the fish to preserve it in appreciable quantities in good condition until its use is required (FAO, 2001).

One of the constraints to such an attainment aside seasonality of fish food, is the fact that, in general, fish is made up of 70-84 percent water, 15-24 percent protein, 0.1-22 percent fat and 1-2 percent minerals.

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Taking note of the moisture content, fish is extremely perishable. Fish is highly susceptible to deterioration without any preservative or processing measures and immediately a fish dies, a number of physiological and microbial deterioration set in and thereby degrade the fish (Davies and Davies, 2009). It has been estimated that in the high ambient temperatures of the tropics, for which Ghana is a part, fish spoils within 12-20 hours of being caught, depending on species and size hence a considerable proportion of the landed catch is processed to preserve most of their catch by artisanal methods (FAO, 2001).

Ghanaian artisans employ various traditional methods to preserve and process fish for consumption and storage. These methods include smoking, drying, salting, frying and fermenting sun-drying, grilling and frying, and various combinations of these. The predominant type of fishery product in any particular country is, however, closely related to the food habits and purchasing power of the population. Specific types of fishery products are best suited as the local staple food. Furthermore, due to the lack of a good transport infrastructure for the transportation of fresh fish to remote towns and villages, cured fish is the most convenient form in which fish can be sent to such areas. Smoking is the most widely practiced method. Practically all species of fish available in the country can be smoked and it has been estimated that 70-80 percent of the domestic marine and freshwater catch is consumed in smoked form (FAO, 1992, 2001).

On the other hand, some traditional processes in food preservation may also destroy or remove some essential nutrients or decrease their digestibility. Ghanaian traditional food preservation techniques may exhibit these effects in the quality of the preserved products (Antwi, 2006).

It has been observed that different processing methods have different effects on the nutritional compositions of fish. This is because heating, freezing and exposure to high concentration of salt lead to chemical and physical changes and therefore digestibility is increased, due to protein denaturation protein, but the content of thermolabile compounds and polyunsaturated fatty acids is often reduced (Chukwu and Shaba, 2009).

Therefore the quality of fish processed by the various methods cannot be the same and hence its subsequent effect on the fishs shelf life also varies.

The objective of this study is to investigate the proximate quality changes of a traditionally smoked, fried and salted red fish at ambient conditions.

Specific Objectives include: To determine the proximate composition of raw unprocessed fresh red fish, smoked, fried and salted red fish and to determine the effect of processing and storing red fish under ambient conditions for 14 days on the proximate composition.

MATERIALS AND METHODS

Location and Duration: The experiment was conducted in a laboratory at the department of Horticulture and at the fisheries laboratory at the Faculty of Renewable Natural Resources at KNUST in Kumasi. The experiment lasted for a month and a half.

Experimental material and source of material

The experimental material used for the experiment was red fish and this was obtained from the Elmina fish market. Twenty-four (24) pieces of the fish were obtained.

Experimental Layout

PHASE 1- PROCESSING AND PRE STORAGE

The experiment focused on the effect that traditionally frying, smoking and salting of red fish had on the proximate composition of the fish.

Experimental material Fresh red fish

Treatments: Traditional fish processing methods;

Unprocessed Fresh Red Fish

Red fish processed by smoking

Red fish processed by salting

Red fish processed by frying

Red fish were purchased at the Elmina beach fish market. Twenty-four (24) samples of fish were purchased. These were washed, scales removed and internal contents removed as well. Of these, six (6) fish were brought to the Fisheries laboratory of Faculty of Renewable Natural Resources at KNUST in Kumasi to be analyzed fresh.

On arrival at the laboratory, the fish was allowed to thaw at room temperature. The fishs bone and flesh was separated. The fish was then washed until it was free from blood. Three (3) fish samples were selected from the six (6) and this was homogenized by grinding in a porcelain can. 2g of the selected and homogenized sample was selected to determine

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moisture, crude fat, crude fibre and 0.5g to determine crude protein content. After the various analyses, a sum of the results obtained was subtracted from 100% to obtain the nitrogen free extract (carbohydrate). This was replicated three (3) times. This would serve as the control for the experiment.

The remaining 18 fish, which were not brought to the laboratory, were given to selected fish processors to process. The fish were divided into three (3) groups (6samples each). The first group were smoked, the second, were salted and dried and the third group were fried. After thorough processing they were transported to the laboratory. At the laboratory they were grounded using a porcelain mortar and pistil. They were then subjected to the same proximate analysis as stated above.

Phase 2- Storage and Post-Storage

Experimental material- traditional processed red fish. The remaining processed red fish were stored under ambient conditions in the horticulture science laboratory. That is, they were put in an uncovered container and left in the laboratory for 14 days. After the 14

th day they were taken to the laboratory and

prepared for analysis.

Processing Procedures

Smoking Process: The fish were placed on a metal net in the cylindrical mud oven. Firewood from varied trees was used to generate the smoke used to smoke and cook the fish. The fish were turned at intervals to ensure uniform smoking and cooking of the fish. The process took 2 days.

Frying Process: Frying pan was placed on fire and oil poured into it. The oil was allowed to heat up and after that, the fish were put into the fire. After some time, the fish were turned to fry the other side of the fish.

Salting Process: Salting was done immediately after they were scaled, gutted and washed. The

salting

was done by placing crude solar salt in the gut cavity and outside

the fish. The fish were arranged in plastic

container, and more salt were sprinkled on the fish. The salted fish were covered and left for a day. After salting the fish were removed and spread out to dry in the sun. Drying lasted for 2 day.

Proximate Analysis:

Moisture Determination: The official method for moisture determination was used. This method is based on drying a sample in an oven and determining moisture content by the weight difference between

dry and wet material according to Olvera-Novoa et al., (1994). Apparatus used Oven, 100-200

0C,

Porcelain crucibles, 20-25ml, Dessicator.

Procedure: Crucibles which would contain the samples were weighed empty, using an electronic balance 20.5g of the fish were weighed and put into the crucibles. The crucibles were then again weighed to obtain the value of the crucible containing the sample. The samples in the crucible were then put into an air oven at 105

0C. The samples were then

allowed to dry overnight (i.e. more than 18hours). The crucibles plus samples were taken out after that and put in a desiccator to allow them to cool. They were re-weighed to obtain the value of the dry samples. The samples were put back into the oven and the weight checked again every 2hrs until constant weights of the dry samples were obtained.

Calculation

Where:

A = weight of clean, dry porcelain crucible (g) B = weight of porcelain crucible + wet sample (g) C = weight of porcelain crucible + dry sample (g)

Crude Protein Determination: Analysis was by Kjeldahl's method, which evaluates the total nitrogen content of the sample after it has been digested in sulphuric acid with a mercury or selenium catalyst (FAO, 1994).

It is usually considered to be the standard method of determining protein concentration. Because the Kjeldahls method does not measure the protein content directly a conversion factor (F) is needed to convert the measured nitrogen concentration to a protein concentration. A conversion factor of 6.25 (equivalent to 0.16 g nitrogen per gram of protein) is used for many applications; however, this is only an average value. The Kjeldahls method can conveniently be divided into three steps: digestion, neutralization and titration.

Apparatus used included: Kjeldahls flasks, Digestion unit, Distillation unit, 250 ml Erlenmeyer flasks, Glass beads (boiling chips)

Reagents used included: digestion tablet (K2SO4 and Se powder), NaOH-Na2SO4 reagent: dissolve 500g NaOH, and 25g Na2SO4.5H20 in water and dilute to 1litre, Conc. H2SO4, standard HCl or H2SO4, 0.02N,

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mercuric oxide, reagent grade, paraffin wax, boric acid (H3BO3) indicator solution, Glass beads

Procedure: 0.50g of the fresh fish sample was weighed and put into a digestion flask containing 50ml distilled water and 10ml of Conc. H2SO4. One digestion tablet and boiling chips were then added to the solution in the flask. The flask is placed tilted at an angle in the digester of the digestion unit, and this took it to its boiling point and retained it until the solution was clear. And then further heating continued for 30 minutes more. The digest was then left to cool. After cooling the content of the digestion flask was diluted with 300ml of distilled, de-ionized water and then its content transferred to the distillation apparatus.

When it was cool, 50ml of NaOH-Na2SO4 was added and then stirred. After this the solution was placed in the distillation unit immediately. Distillate was collected in 50ml boric acid in a 250 ml Erlenmeyer flask until the content of the flask was 200 ml.

This was then titrated with 0.02N HCl, until a violet colour appearance indicating an end-point was observed. Then after that a reagent blank was run with equal volume of distilled water and the titration volume subtracted from that of the sample titration volume.

Calculations

Crude protein (%) = nitrogen in sample 6.25 Where: A = Hydrochloric acid used in titration (ml) [ml HCl - ml blank], B = normality (N) of standard acid and C = weight of sample (g) Crude Fat Determination: Ether extract (Fat) determination method was used to determine the crude fat content of the red fish. This was done by extracting the dry sample with ether. The weight of the extract was determined after distilling the ether and weighing the residue. The ether extraction may be conducted with suitable apparatus such a Soxhlet or Goldfish extractor. Ether extraction however does not remove all the fat especially phospholipids or fats bound to protein

Apparatus used included Whatman No.2 filter paper, absorbent cotton wool, soxhlet apparatus.

Procedure: The sample was put into a filter paper which had been folded in a manner to hold the sample intact. A second filter paper was wrapped it. This was left open at the top like a thimble. A piece of

cotton wool was placed at the top to evenly distribute the solvent as it dropped on the sample during extraction. After this the sample was placed in the butt tubes of the Soxhlet extraction apparatus.

The extraction then was done with petroleum ether for about 6 hours without interruption by gently heating it. The apparatus was then allowed to cool and then the extraction flask was dismantled and the ether was evaporated on a steam bath until no odour of ether remained. After this process the setup was allowed to cool at room temperature.

The flask was then weighed on the scale. But before the weighing was done, all dirt and moisture on the flask were carefully removed so as to obtain a true value.

Calculation

(A+B) A=B

% ether extract = B/C 100

A= flask weight, B= ether extract weight, C= sample weight

Ash Content Determination: Ash is the inorganic residue remaining after the water and organic matter have been removed by heating in the presence of oxidizing agents, which provides a measure of the total amount of minerals within a food. Analytical techniques for providing information about the total mineral content are based on the fact that the minerals (the analyte) can be distinguished from all the other components (the matrix) within a food in some measurable way. The most widely used methods are based on the fact that minerals are not destroyed by heating, and that they have a low volatility compared to other food components, (FAO, 1994).

The dry ashing method was used in this experiment. Apparatus used included muffle furnace, porcelain crucible, desiccator with magnesium perchlorate desiccant

Procedure: The ash crucibles were removed from the oven and placed in the desiccators to cool it before weighing them. A sample weight of 2.0g was taken and put into the porcelain crucible. This was then put into the muffle furnace for 2 hours at 600

0C.

After the 2 hours, the crucibles were taken out from the furnace and put into the desiccator to allow them to cool. When they were cool enough the weight was taken to determine the ash content.

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Calculation (A+B) A = B (A+C) A = C %Ash = C/B 100

A= crucible weight B= sample weight C= ash weight.

Crude Fibre Content: Apparatus used included condenser, digestion flask- 700ml Erlenmeyer flask, linen cloth (or filtering cloth of such character that no appreciable solid matter passes through when filtration is rapid), air-tight sample containers, muffle furnace, Gooch crucible.

Reagents used included: sulphuric acid solution: 0.225 N: 1.25g H2SO4/100ml distilled water, sodium hydroxide solution: 0.312 N: 1.25g NaOH/100ml distilled water, antifoaming agent: N-tributyl citrate 95% ethanol.

Procedure: Transfer about 2g of residue from ether extract to a digestion flask. Add about 200ml of the boiling H2SO4 solution, add anti-foaming agent. Immediately connect digestion flask with condenser and heat. At the end of 30 minutes, remove flask, filter immediately through linen and wash with boiling water until washings are no longer acid.

Heat a quantity of NaOH solution to boiling point and keep at this temperature under reflux condenser until used. Wash residue back into flask with 200ml of the boiling NaOH solution. Connect flask with condenser and immediately filter through the Gooch crucible. After thorough washing with boiling H2O, wash with

about 15ml of 95% ethanol and then dry the crucible and its content at 110

0C to constant weight. Then

cool in a desiccator and weigh. Weight loss gives the crude fibre content.

Calculation

% Crude fibre= (A-B)/C 100

A= weight of dry crucible and sample, B= weight of incinerated crucible and ash, C= sample weight

Statistical Analysis

Phase 1- Experimental design - four (4) by one (1) completely randomized design.

Phase 2- Experimental design- Six (6) by two (2) factorial design.

All data were analyzed using Statistix 9 statistical tool. Differences among treatment means were resolved using pair-wise comparison at the least significant difference (LSD) >0.05.

RESULTS

Effect of Traditional Processing Methods on the Proximate Composition of Red Fish Before Storage: The proximate composition of raw and traditionally smoked, fried and salted red fish before storage are presented in Table 1. Table 1, fundamentally gives the effect that traditional processing methods have on the proximate composition of raw fresh red fish. Each value is the mean standard deviation of triplicate determinations.

Table 1: Proximate composition of fresh fish and traditionally smoked, fried and salted red fish.

Fish Sample % Moisture % Ash %Fat %Protein % Fibre % NFE

Fresh 10.0 (80.0)a 6.00 a 9.99 a 72.49 a 1.01 a 0.51 a

Smoked 4.00 (50.0) b 6.07 a 10.00 a 73.94 b 1.52 b 4.47 b

Salted 5.90 (48.0) c 30.00 b 9.67 b 52.77 c 1.32 b 0.34 c

Fried 3.99 (31.0) b 6.00 a 20.02 c 66.52d 1.34 b 2.11 d

Lsd 5% 0.0965 0.1041 0.2722 0.1239 0.2354 0.1148

CV% 0.86 0.46 1.16 0.10 9.64 3.28

*Values in bracket are the moisture content of fresh (unprepared) sample

On the whole, traditional processing of red fish by smoking, frying and salting had a significant effect on the proximate composition of the fish. Fresh red fish recorded the highest moisture content and lowest ash. It also recorded low values for the other parameters too. This was in agreement with the work

by DSouza and Musaiger, (2008) and Kumolu-Johnson, (2010).

Crude protein contents were generally high in the red fish, which was an expected outcome since fish weree a good source of protein, (Tidwell, 2001). Smoked fish, recorded the highest crude protein content, crude fibre and nitrogen free extract.

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However, the difference between it crude fibre content and that of fresh and salted red fish was not significantly different from each other.

Fried fish recoded the lowest moisture content similar to the work by DSouza and Musaiger, (2008). Fried fish notwithstanding also recorded the highest crude fat content and this was very significant form the other treatments. There were no significant differences between the crude fat content of fresh, smoked and fresh.

Salted fish recorded the lowest crude protein and crude fat content. However, it recorded the highest ash content which usually is used an index of mineral content.

Table 2 present a result of the effect that traditional smoking, salting and frying had on the proximate composition of red fish stored under ambient room conditions for 14 days. From the table, it could be seen that, after storage the smoked fish had the highest moisture, crude protein and nitrogen free extract. Fried fish had the lowest moisture and crude fibre content. But it also recorded the highest crude

fat and nitrogen-free extract content. Salted fish recorded the highest ash and crude fibre content among the processed fish and also recorded the lowest crude protein, nitrogen-free extract and together with the smoked fish they recorded the lowest crude fat content. But the given the area of interest in assessing the effect that both processing and storage has on red fish an interactive analysis involving comparison of both pre-storage and post-storage proximate value of red fish has to be used. Hence it was observed, by comparison of these values with the pre-storage values that there was an increase in the moisture, ash, and fibre (excluding fried fish) content of red fish stored under ambient condition for 14 days. And there was a reduction in the crude protein content (with the exception of smoked fish), crude fat content (with the exception of fried fish) and also there was reduction in nitrogen-free extract composition (with the exception of salted fish).

Tables 3 to 8 present the interactions of processing with storage and their resultant effect on the proximate composition of red fish.

Table 2 Proximate composition of traditionally processed red fish after 14 days storage under ambient room conditions.

Processing Method % Moisture % Ash %Crude Fat %Crude Protein %Crude Fibre %NFE

Frying 32.0 8 21.07 63.35 0.63 0.95

Smoking 54.0 6.67 5 77.28 2.03 0.96

Salting 50.0 32 5 53.47 2.05 0.48

Table 3 Effect of traditional processing methods on the ash content of red fish stored for 14 days under ambient room temperature.

Processing Methods (P)

Storage (S) (Ambient room temperature) Means Pre-Storage Post-Storage

Frying 6.003e 8.000c 7.002a

Smoking 6.073e 6.673d 6.373b

Salting and drying 30.003d 32.000a 31.002c

Means 14.027b 15.558a

Lsd. (5%) S=0.2500 P=0.3062 S*P=0.4331

CV%= 1.61

Table 3 indicates that there were significant differences among all the various traditional processing methods after storage though before storage there was no significant difference between frying and smoking and these differences were

significant when their pre-storage and post-storage content were compared. Salting which recorded the highest ash content pre-storage increased significantly in its ash content after storage under ambient condition for 14days.

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Table 4 Effect of traditional processing methods on the crude fat content of red fish stored for 14 days under ambient temperature.

Processing Methods (P)

Storage (S) (Ambient temperature) Means Pre-Storage Post-Storage

Frying 20.023 b 21.073 a 20.548 a

Smoking 10.000 c 5.000 e 7.500 b

Salting and drying 9.667 d 5.000 e 7.333 c

Means 13.230 a 10.358 b

Lsd. (5%) S=0.1260 P=0.1543 S*P=5.000

CV%= 1.02

Table 4 indicates that there were significant differences among the various traditional processing methods pre- storage but post- storage values of the crude fat content of smoked and salted fish were not significantly different. There were also significant

differences when their pre-storage and post-storage crude fat content were compared. Salted and Smoked red fish observed a reduction in crude fat levels whiles frying observed an increase.

Table 5 Effect of traditional fish processing methods on the crude fibre content of red fish after 14 days storage under ambient room conditions

. Processing Methods

(P) Storage(S) (Ambient temperature)

Means Pre-Storage Post-Storage

Frying 1.3367 b 0.6267 c 0.9817 b

Smoking 1.3467 b 2.0267 a 1.6867 a

Salting and drying 1.3167 b 2.0533 a 1.6850 a

Means 1.3333 b 1.5689 a

Lsd. (5%) S=0.1740 P=0.2131 S*P=0.3013

CV%= 11.41

Table 5 shows that after traditionally smoking, frying and salting red fish for 14 days under ambient conditions, the above processing methods which were not significantly different were frying; which recorded the lowest value, now becoming significantly

different from salting and smoking. It also shows that there was significant increase in the pre-storage and post-storage crude fibre content of the smoked and salted red fish but a reduction in that of fried fish.

Table 6: Effect of traditional fish processing methods on moisture content (%) of red fish after 14 days storage under ambient room conditions.

Processing Methods (P)

Storage (S) (Ambient temperature) Means Pre-Storage Post-Storage

Frying 4.0033 b 6.0033 ab 5.0017 b

Smoking 6.0033 ab 8.0000 a 7.0017 a

Salting and drying 5.9033 ab 8.0000 a 6.9517 a

Means 5.3033 b 7.3333 a

Lsd. (5%) S=1.4927 P=1.8282 S*P=2.5854

CV%= 22.49

There was significant interaction between the processing methods and storage condition as shown

in Table 6 above. A significant increase in moisture content of all post-storage fish products, was

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observed compared with the pre-storage products, however no significant difference was observed

between the smoked and salted fish.

Table 7 Effect of traditional fish processing methods on nitrogen-free extract content (%) of red fish after 14 days storage under ambient room conditions

Processing Methods (P)

Storage(S) (Ambient temperature) Means Pre-Storage Post-Storage

Frying 2.11 ab 0.95 bc 1.53ab

Smoking 3.13 a 1.02bc 2.08a

Salting and drying 0.34c 0.48bc 0.41b

Means 1.86a 0.82b

Lsd. (5%) S=0.9671 P=1.1844 S*P=1.6850

CV%= 68.77

A significant interaction was observed between Processing methods and storage conditions as shown in Table 7 above. There was a significant reduction in the nitrogen-free extract content of the stored red fish and this was consistent with the

nitrogen-free extract content of the fried and smoked fish. But the salted red fish deviated by recording an increase in nitrogen-free extract and this was significantly different with the nitrogen-free extract of smoked fish.

Table 8 Effect of traditional fish processing methods on crude protein (%) of red fish after 14 days storage under ambient room conditions.

Processing Methods (P)

Storage(S) (Ambient temperature) Means Pre-Storage Post-Storage

Frying 66.520 c 63.350 d 64.935 a

Smoking 73.450 b 77.277 a 75.363 b

Salting and drying 52.770 e 52.467 e 52.618 c

Means 64.247 a 64.364 a

Lsd. (5%) S=0.4127 P=0.5054 S*P=0.7147

CV%= 0.61

A significant interaction was recorded between the processing methods and storage conditions as indicated in table 8 above. There were significant differences in protein content between the processing methods. Smoked fish recorded the highest protein content pre-storage (73%) and post-storage (77.3) respectively among the processing methods. However there were also significant decreases in the protein contents of fried fish but not that of the salted fish.

DISCUSSION

The effect of traditional fish processing methods on proximate composition of red fish before storage: Moisture content: Fresh red fish recorded the highest moisture content of 80% this was in the range given by Davies and Davies (2009) who peg fish to be made up of 70-84 percent water. Fresh fish also recorded the lowest ash and crude fibre content. This is in agreement with DSouza and Musaiger, (2008) and Kumolu-Johnson, (2010).

Protein contents were generally high in the processed red fish studied, which is an expected outcome since fish is a good source of protein, (Tidwell, 2001). The higher crude protein content in fish is important from a dietary point of view since; the quality of fish protein is very high because of its essential amino acid composition. Further, reports also indicate that fish muscle is more digestible than other animal protein due to lower level of connective tissue. (DSouza and Musaiger, 2008)

Smoked fish in this experiment, recorded the highest crude protein content and this was in accordance with the findings of Chukwu, (2009) and Kumolu-Johnson, (2010). The significant increase in protein levels (P

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fish as opined by Koral et al., (2009) that, the percentage of total protein, lipid and ash contents of smoked garfish increased due to water loss during smoking.

The smoked fish also accounted for the high nitrogen-free extract (energy) content. This is because according to Aberoumad and Pourshafi (2010), the lower the percentage of water, the greater the lipids and protein content and the higher the energy density of the fish. Thus given that the smoked fish had the highest protein content, it nitrogen free extract content was high; it is bound to have a high energy level.

But then, the fried fish which had the lowest moisture content was not having the highest level. DSouza and Musaiger, (2008) reported a study on the effects of heating on the digestibility of the protein in hake, a type of fish and found that, fish meat heated for 10 minutes at 130C (266F), showed a 1.5% decrease in protein digestibility. Similarly, heating of hake meat in the presence of potato starch, soy oil, and salt caused a 6% decrease in amino acid content. Thus given that frying was done in cooking oil and under an uncontrolled high and intense heat, could have caused the reduction in the crude protein level.

Salted fish recorded the lowest crude protein level. This may be due appreciably to the level of loss in protein which occurs as a result of salting as it was reported by Pace et al., (1989) in a study on processed tilapia and trigger fish. He said that salting or procedures which involved salting were usually accompanied by protein losses.

Salting again, saw a decrease in the fat content (lowest crude fat content) of the red fish. This may be due to physical losses facilitated by the breakdown of tissue cells during salting, followed by the heating effect of sun-drying (Pace, 1989)

However, salting recorded the highest ash content. The significant increases in ash content per unit of dry matter after salting and drying were due to the crude solar salt, which added more ash components to the product (Beauchamp, 1991) Fried red fish observed the highest crude fat content and the lowest moisture content level. This is consistent with the study by Echarte et al., (2001) and DSouza and Musaiger (2008). The high crude fat content of fried fish was as a result of uptake of oil by the fish muscles (Echarte et al., 2001) and the low moisture level of red fish is consistent with the study by DSouza and Musaiger (2008).

The effect on the proximate composition of the red fish is generally as a result of moisture loss which concentrates the nutrient. But however, it must be said that, the concentration of these nutrient may not necessarily mean an increased availability of the

concentrated nutrient since this could be affected by other factors not covered in this study.

Effect of traditional fish processing methods on the proximate composition of red fish after 14 days in storage: The high ash content recorded by salting pre-storage, increased after storage under ambient condition for 14 days this may be due principally to the fish muscle absorbing more of the salt which were sprinkled and put into their gut during processing.

Reduction in crude fat content could have been due to oxidation and crude fat break down into other components. That is, oxidation of poly-unsaturated fatty acids (PUFA) contained in the fish tissue to products such as peroxides, aldehydes, ketones and the free fatty acids (Daramola et al., 2007). Fish oil has been found to be more liable to spoilage than other oils due to their greater number of unsaturated fatty acids as shown by the lower specification number and higher iodine value. The greater the degree of instauration, the greater would be the tendency for fat oxidation (rancidity). There might be high risks of rancidity during prolonged storage conditions due to the fatty nature of fish (Daramola et al., 2007).

Crude protein is inversely proportional to fat content in fish (Daramola et al., 2007). Taking note of the protein value, it is observed that, only the fried red fish observed a reduction in protein level hence the corresponding increase in crude fat content of the red fish.

The increase in the crude fibre content of salted and smoked red fish could be accounted for by the fact that in these samples, there had been an oxidation of their poly-unsaturated fatty acids (PUFA) components, contained in their tissues to products such as peroxides, aldehydes, ketones and free fatty acids, (Daramola et al., 2007). Also increase in their protein component could also have increased the crude fibre content of the fish.

Increase in moisture content could be attributed to the difference in the moisture of the processed fish relative to the surroundings, (Daramola et al., 2007).

Reduction in the percentage crude protein of the species during the period of storage could be due to gradual degradation of the initial crude protein to more volatile products such as Total Volatile Bases (TVB), Hydrogen sulphide and Ammonia. Changes observed in protein content during storage may also have been due to leaching out of some extractable soluble protein fraction (Daramola et al., 2007).

CONCLUSION

Proximate quality changes of raw and traditionally smoked, fried and salted red fish were studied right after

Am. J. Food. Nutr, 2013, 3(3): 73-82

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processing and after storage under ambient conditions for 14 days.

It was observed that processing and storage significantly affected the proximate composition of red fish. The most important is their general reduction effect on the moisture content which is an index of perishability. But however during storage with the exception of salted fish, moisture content of fried and smoked fish increased after storage.

Aside the effect of salting which facilitates protein loss upon processing, frying and smoking maintained and concentrated the crude protein content. And after storage there was a reduction in crude protein content of the fried fish rather. This was as a result of the inverse interaction between the crude protein and fat content. After processing, crude fat content continued to increase in fried fish but reduced in the salted and smoked fish. Crude fibre content was higher at processing and after storage but after storage crude fibre content of fried fish reduced drastically. Smoked fish which recorded the highest energy content (nitrogen-free content) upon processing reduced sharply after storage. This could be due to utilization of energy component by the spoilage organism.

REFERENCES

Abdulrahman, M. O. and Reshma DSouza, (2008). The effects of different methods of cooking on proximate,mineral and heavy metal composition of fish and shrimps consumed in the Arabian Gulf. Archivos Latinoamericanos De Nutricion Organo Oficial de la Sociedad Latinoamericana de Nutricin 58 (1), 103-109

Aberoumad, A. and Pourshafi K., (2010). Chemical and Proximate Composition of Different Fish Species Obtained from Iran. World Journal and Marine Sciences 2(3): 237-239.

Afolabi, O.A., O.A. Arawomo and O.L. Oke, (1984). Quantity Changes of Nigeria Traditional Processed Freshwater Species I: Nutritive and Organoleptic Changes. (Journal on Food Technology) 19: 333-340.

Antwi Victor, (2006). Sustainability impact assessment of proposed WTO Negotiations: the fisheries sector. Country case study: Ghana pp 9-10.

Beauchamp, G.K, Engelman K., (1991). High salt intake, Sensory and behavioral factors: (Hypertension); 17 (1S): I176-81.

Chukwu, O., (2009). Influences of Drying Methods on Nutritional Properties of Tilapia Fish (Oreochromis

nilotieus). World Journal of Agricultural Science 5 (2): 256-258

Chukwu O., and Shaba I. M., (2009). Effects of Drying Methods on Proximate Compositions of Catfish (Clarias gariepinus) World Journal of Agricultural Sciences 5 (1): 114-116

Davies, R.M and Davies. O.A, (2009). Traditional and Improved Fish Processing Technologies in Values of Fish. (Tropical Science) 33:183-189.

Daramola, J. A. ; Fasakin, E. A. and Adeparusi, E. O., (2007).Changes In Physicochemical And Sensory Characteristics Of Smoke-Dried Fish Species Stored At Ambient Temperature, (African Journal of Food Agriculture Nutrition and Development): 7 (6) . www.biolone.org.br/nd (Assessed on 30th April, 2011)

Echarte, M, Zulet MA, Astiasaran I., (2001) Oxidation process affecting fatty acids and cholesterol in fried and roasted salmon. Journal on Agric Food Chemistry 49 (11): 5662-7.

FAO, (1992). Fish Processing Characteristics. Fermented fish in Africa: A study on processing marketing and consumption. http://www.fao.org/docrep/t0685e/T0685E05.htm (Assessed on 12th February, 2011)

FAO, (2001). Example of successful in agriculture and rural development in the south. Sharing innovative experience 5: 240-254

Koral, S., Kse Sevim, Tufan Bekir, (2009). Investigating the Quality Changes of Raw and Hot Smoked Garfish (Belone belone euxini, Gnther, 1866) at Ambient and Refrigerated Temperatures, (Turkish Journal of Fisheries and Aquatic Sciences) 9:53-58

Kumolu-Johnson, C. A., Aladetohun N. F and Ndimele P. E., (2010). The effects of smoking on the nutritional qualities and shelf-life of Clarias gariepinus. African Journal of Biotechnology 9 (1): 073-076

Nti, C. A., Plahar W. A. and Patience Mateko Larweh, (2002). Impact of adoption in Ghana of an improved fish processing technology on household income, health and nutrition International Journal of Consumer Studies, 26:102108

Pace, R. D., Plahar, W.A, and Lu, J.Y., (1989). Status of Traditional Food Preservation Methods for Selected Ghanaian Foods Food Reviews International, 3(1): 1-12

Tidwell, J.H. and Allan, G.L, (2001). Fish as food: aquacultures contribution Ecological and economic impacts and contributions of fish farming and capture fisheries. Science and Society; 2 (11): 95863.

Vannuccini, S., (2004). Overview of Fish Production, Utilization, Consumption and Trade, FAO, Fishery Information, Data and Statistics Unit: p2.