Tittle page
Table of contents

1.         Background of the study
1.2.      Statement of problem
1.3.      Justification
1.4.      Objective of the study
1.5.      Significance of the study

2.1.      Fish
2.2. World fish production Statistics
2.3.      Fish production statistics in Nigeria
2.4.      Chemical composition of fish
2.5.      Catfish
2.6.      Mackerel
2.7.1.   Fish processing methods
2.7.2.   Smoking
2.7.3.   The chemistry of wood smoke
2.7.4.   Bactericidal property of smoke
2.7.5.   Fish smoking process
2.7.6.   Smoking kiln
2.8.1.   Moisture content of foods
2.8.2. Water activity
2.8.3.   Controled water activity environment
2.8.4.   Moisture sorption isotherms
2.8.5.   Determination of moisture sorption isotherm
2.8.6.   Moisture sorption isotherm models
2.8.7.   Sorption isotherms of foods
2.8.8.   Isosteric heat of sorption

3.1.      Materials
3.2.      Smoking kiln description and operation
3.3.1.   Evaluation of the empty smoking kiln
3.3.2.   Fish smoking and drying performance evaluation Sample preparation Smoking operation
3.4. Determination of phenolic content of the smoked fish
3.5. Sensory evaluation
3.6.Proximate analysis of smoke dried catfish and mackerel
3.6.1.   Determination of moisture content
3.6.2.   Determination of crude protein
3.6.3.   Determination of ash content
3.6.3.   Determination of fat content
3.6.4.   Determination of carbohydrate content
3.7. Sorption experiment
3.7.1.   Materials
3.7.2.   Experimental procedure
3.7.3.   Fitting of EMC data to various isotherm models
3.7.4.   Net isosteric heat of sorption
3.7.5.   Apparent sorbate surface areas for sorption
3.8.      Statistical analysis

4.1. Performance evaluation of the smoking kiln
4.1.1.   Temperature distribution during heating of the empty kiln
4.1.2.   Air flow rate
4.1.3.   Moisture content of fish during smoking
4.1.4.   Temperature distribution during fish smoking
4.1.5.   Phenolic content of smoked fish
4.2.      Sensory characteristics of smoke dried catfish and mackerel
4.3. Proximate composition of smoke dried catfish and mackerel
4.4. Moisture sorption characteristics
4.5. Application of Henderson model to sorption data
4.6.      Application of BET model to sorption data
4.7.      Application of Oswin model to sorption data
4.8.      Application of GAB model to sorption data
4.9.      Net isosteric heat of sorption
4.10. Apparent sorbate surface areas for sorption

5.1.      Conclusion
5.2.      Recommendations

This study evaluated the performance of a modified smoking kiln, smoking quality and moisture

sorption properties of smoked dried catfish and mackerel. A modified smoking kiln with the three chambers made of double jackets of aluminum and properly lagged with fibre glass was evaluated by firstly arranging and igniting the saw dust and fire wood in the fire place of the kiln and heating up the empty kiln for five hours during which the temperature and air flow rate through the empty kiln was measured and recorded. The raw fishes (catfish and mackerel) were cleaned, eviscerated cut into smaller sizes, weighed, then placed in the smoking kiln for smoking and packaged in polyethylene bags. During smoking, rate of moisture loss from the fishes, air flow rate through the kiln and smoking temperature were also recorded. The proximate and phenolic content of the smoke dried fish samples were analyzed. Integral gravimetric method was used to determine the equilibrium moisture content (EMC) within water activity range of 0.147 and 0.982 at the 20, 30 and 40 oC. The EMC’S were fitted to Henderson, BET, GAB and Oswin models, while the net isosteric heat of sorption and apparent sorbate surface areas (so) were determined using standard methods. The air flow rate in the empty kiln was between 2.16 and 3.33 m/s while the temperature profile of the empty kiln within the first one hour of heating averaged 95 oC and increased to 250 oC within five hours due to lagging of the chambsers. The smoke dried catfish and mackerel were accepted (p < 0.05) by sensory panelist. Smoked dried catfish protein, ash, fat and moisture ranged between 73.37 and 73.80%, 5.00 and 5.40 % 10.30 and 11.05 % and 8.05 and 8.12 % respectively and for smoked dried mackerel 70.58 and 70.67 %, 5.00 and 5.94 %, 12.99 and13.15 %, and 6.14 and 6.37 % respectively. The phenolic content ranged from 34.72 to 36.94 mg/ml for catfish, 33.24 to 34.88 mg/ml for mackerel while the moisture sorption isotherm showed typed III BET isotherm with marked hysteresis at all temperatures. The type III isotherm exhibited by smoke dried catfish and mackerel is as would be expected since food materials rich in protein have been found to show the type III shapes. The values of the root means square ranged from 3.4 to 6.8, 4.8 to 9.1, 5.9 to 13.9 and 4.1 to 13.2 for Henderson, BET, GAB and Oswin model respectively while coefficient of determination ranged from 0.95 to 0.99 %, 0.93 to 0.96 %, 0.83 to 0.94 and 0.91 to 0.94 for Henderson, BET, GAB and Oswin model respectively. The % RMS and coefficient of determination showed that Henderson model gave the best fit to the moisture sorption data. The isosteric heat of sorption for adsorption pathways were 4.55 and 1.22 kj/mol for catfish and mackerel respectively while the isosteric heat of sorption for desorption pathways were 4.07 and 1.10 kj/mol respectively. The apparent sorbate surface area decreased from 99.38 to 85.02m2/ g solid for catfish and 76.01 to 66.25 m2/g solid for mackerel with increased temperature from 20 to 40 oC.

1. 1. Background
Fish are vertebrates living in fresh or salt water bodies. A fish is any member of paraphyletic group of organisms that consist of all gill bearing aquatic animals that lacks limbs. More than 25,000 fish species have been identified and 15,000 more species are yet to be identified (Nelson, 1994). Common edible species are catfish, croaker, mackerel, salmon, redfish, sardines, dogfish, tilapia among others. Fish is an important source of food for humans, containing high amount of protein. It is cheap and highly acceptable with little or no religious biases which gives it an advantage over pork or beef (Eyo, 2001). Fish has high biological value and contain all the essential amino acids (Strilakshmi, 2003). The fats of fish are readily digestible and are valuable sources of energy, rich in polyunsaturated fatty acids (PUFA) and Omega 3 fatty acids (Osibona et al., 2009).

Catfishes (Clarias gariepinus) are named due to their prominent barbels which resemble cat's whiskers. Catfish range in size from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wells catfish of Eurasia, to detrivores and even to a tiny parasitic species commonly called the candiru (Vandellia cirrhosa). There are armour-plated types and also naked types, neither having scales. Despite their name, not all catfishes have prominent barbels. Catfish are of considerable commercial importance. Many of the larger species are farmed or fished for food, while other smaller ones are important in the aquarium hobby. The African catfish is a dominant freshwater fish which can grow from 1.4 and 2 m long and can weigh anything from 8 kg to 59 kg (Bruton, 1996).....

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