ABSTRACT
This study assessed the effect of drying on smoked
horse mackerel fillets during storage at room temperature. Smoked horse
mackerel (Trachurus trachurus) fillets were prepared by smoking brined horse
mackerel fillets in a traditional improved kiln for 4 hours at 60 – 70oC.
The fillets were later oven-dried at 65-70oC for 0, 2, 4, 6, and 8
hours, spread on perforated trays and stored at room temperature of 24.5 – 34oC
and relative humidity range of 59 – 87% for a period of 30 days. The samples
were tested after every 10 days for physico-chemical, microbial and sensory
qualities as well as for amino acid composition. The results obtained showed
that smoking reduced the moisture content from 73.61 to 20.93% which led to
concentration of other proximate components. There was a significant difference
(p<0.05) in the proximate composition of the dried samples with drying
treatment and on storage. Drying treatment decreased the moisture content of the
smoked fillets from 20.93 to 14.57% on the 0 day while the other components
increased significantly presumably due to increase in dry matter with protein
forming the largest in quantity (65.30 – 70.93% on 0 day). With the exception
of control, caloric values for all the samples were within the range of United
States Recommended Dietary Allowance (US/RDA) of 450 – 600 kcal/100g.
Thiobarbituric acid value (TBA), peroxide value (PV), and free fatty acid (FFA)
increased with drying treatment while pH, soluble protein and in-vitro protein
digestibility (IVPD) decreased. Sample dried for 8hrs recorded the highest
range of values in TBA (0.574 to 1.040), PV (5.40 to 16. 88 M.eq/Kg), and FFA
(0.671 to 1.109% oleic acid). Control sample had the highest range of values in
pH (6.49 to 6.22), soluble protein (54.78 to 48.29%), IVPD (99.44 to 94.07%).
There was a general decline in all the analyzed parameters at the end of the
storage period. Drying treatment and storage severely affected the amino acid
composition with control sample showing highest concentration of 47.10 to 27.42
g/100g protein. Microbial growth was not detected in freshly smoked and dried
samples; however storage significantly increased the total viable and mould
growth to a range of 2.98x103 – 5.00x105 cfu/g and
2.76x103 – 4.73x103 cfu/g respectively for all the
treated samples on the 30th day with 8hrs dried sample recording the
least growth. Sensory results revealed decline in sensory qualities but was
still acceptable after 30 days of storage. The study showed that drying
treatment enhanced the shelf stability of the smoked horse mackerel fillets.
However, it also indicated that long time drying treatment and storage time
could negatively influence the protein quality of horse mackerel fillets stored
at room temperature.
TABLE OF CONTENTS
Title page
Table of contents
List of figures
List of tables
Abstract
CHAPTER ONE
1.0 Introduction
1.1 Fish production in Nigeria
1.2 Fish preservation and processing method in Nigeria
1.2.1 Freezing
1.2.2 Salting
1.2.3 Drying
1.2.4 Smoking
1.3 Quality, safety and nutritive value of smoke dried fish
1.4 Significance of study
1.5 Research objectives
1.5.1 Specific objectives
CHAPTER TWO
2.0 Literature Review
2.1 Introduction
2.2 World Fish Production
2.3 The Biology of Horse Mackerel
2.3.1 Appearance
2.3.2 Nutritional value
2.3.3 Annual fat cycle
2.4 Post mortem changes in fish
2.5 Post harvest losses and related food problems
2.6 Fish processing and preservation
2.6.1 Fish drying
2.6.2 Fish salting
2.6.3 Fish canning and bottling
2.6.4 Fish fermentation
2.6.5 Fish freezing
2.6.6 Fish smoking
2.7 Spoilage and microbial analysis of fish and fish products
2.8 Effects of smoking and drying on the physicochemical and consumer acceptability of fish
CHAPTER THREE
3.0 Materials and Methods
3.1 Procurement of raw-materials
3.2 Sample preparation/Fish processing
3.2.1 Smoking process
3.2.2 Drying of smoked fish fillets
3.3 Proximate analysis
3.3.1 Determination of moisture content
3.3.2 Determination of dry matter content
3.3.3 Determination of crude protein content
3.3.4 Determination of ash content
3.3.5 Determination of fat content
3.3.6 Determination of caloric value
3.4 Physicochemical analysis
3.4.1 Determination of pH
3.4.2 Determination of peroxide value
3.4.3 Determination of thiobarbituric acid (TBA) number
3.4.4 Determination of free fatty acid (FFA)
3.5 Protein quality analysis
3.5.1 Determination of soluble protein
3.5.2 Determination of in vitro protein digestibility
3.5.3 Determination of amino acid content
3.6 Microbiological analysis
3.6.1 Total viable count
3.6.2 Mould count
3.7 Sensory evaluation
3.8 Statistical analysis
CHAPTER FOUR
4.0 Results and Discussion
4.1 Weight loss during sample preparation (Filleting and Smoking)
4.2 Weigh loss during drying operation
4.3 Temperature and relative humidity of the storage room
4.4 Chemical composition of fresh and freshly smoked horse mackerel fillets
4.5 Changes in physicochemical quality of smoked and dried horse mackerel fillets during storage
4.5.1 Moisture content
4.5.2 Dry matter
4.5.3 Protein content
4.5.4 Fat content
4.5.5 Ash content
4.5.6 Caloric value
4.5.7 Peroxide value (PV)
4.5.8 Thiobarbituric acid (TBA) number
4.5.9 pH
4.5.10 Free fatty acid (FFA) content
4.6 Microbiological quality of smoked and dried horse mackerel fillets during storage
4.6.1 Total viable count (TVC)
4.6.2 Mould count
4.7 Changes in protein quality of smoked and dried horse mackerel fillets during storage
4.7.1 Protein solubility
4.7.2 In vitro protein digestibility
4.7.3 Amino acid composition
4.8 Changes in sensory qualities of smoked and dried horse mackerel fillets during storage
CHAPTER FIVE
5.0 Conclusion and Recommendation
References
Appendices
CHAPTER ONE
1.0 INTRODUCTION
Fish has been one of the main foods for humans for many centuries and constitutes an important part of the diet in many countries. Fish are nutritious foods that constitute desirable components of a healthy diet (Erkan et al., 2010). The advantages of fish as food are its easy digestibility and high nutritional value. It is much sought after by a broad cross section of the world’s population, particularly in developing countries. It is estimated that 60 percent of people in developing countries depend on fish for over 30 percent of their animal protein supplies, while almost 80 percent of most developed countries obtain not less than 20 percent of their animal protein from fish (FAO, 2005). However, with the increased awareness of the health benefits of eating fish and ensuring rise in fish prices, these figures are rapidly changing. Despite the ensuing prices, fish still represent a cheap source of animal protein.
Apart from being a good source of animal protein, fish also provide other nutrients such as fat soluble vitamins, and they are good sources of some minerals like calcium, phosphorous and iron (Belitz et al., 2009). They also contain significant amounts of all essential amino acids, particularly lysine in which cereals are relatively poor. Fish protein can be used therefore to complement the amino acid pattern and improve the overall protein quality of a mixed diet (Osibona et al., 2009). The flesh is consumed when prepared as a form of delicacy or the other; various brands of oil are extracted from the flesh and the fluids of the fish (Ayolabi and Fagade, 2010). Fish farming, its harvesting, handling, processing and distribution provide livelihood for millions of people as well as providing foreign exchange earning to many countries (Davies and Davies, 2009), especially those situated along the riverrine and coastal areas. Industries process many inferior fish and fish waste products into glue, livestock feed and fertilizers. Fish products are also employed in pharmaceutical industries. Therefore, the importance of the fisheries product in satisfying the nutritional and health needs of the people as well as providing foreign exchange and employment cannot be overstated.
1.1 FISH PRODUCTION IN NIGERIA
Nigeria with a population of about 150 million people (2006 census), is the largest single consumer of fish and fish products in the African Region. The country which has an area of 913, 072.64 square kilometers is well watered by the rivers of Niger and Benue and its tributaries, hence abundance of potentials for aquaculture.
Aquaculture, the farming of aquatic organisms including fish, molluscs, crustaceans and aquatic plant is often cited as one of the means of efficiently increasing food production in food deficit countries. In Nigeria, total domestic fish production fluctuated between 562,972 to 524,700 metric tonnes in 1993 to year 2003; while the output of fish farming during this period was 20,476 to 52,000 metric tonnes (Inoni, 2007). Although the outlook of aquaculture production is worrisome given the growing demand for fish and the declining yield of natural fish stocks due to over-exploitation, fish farming still holds the greatest potentials to rapidly boost domestic animal protein supply in Nigeria. According to Tobor (1990), there are about 1.75 million hectares of suitable land for aquaculture in Nigeria and 25% of this will yield 656,820 tonnes of fish per year when placed under cultivation. Fish in Nigeria is caught from the sea, inland, and more recently from ponds and from other artificial culture systems. Most of the coastal fishing is carried out by local fisher folks from canoes operating from surf-beaten beaches and riverrine areas. In spite of the great potentials of fish farming in Nigeria, factors such as low technical knowledge on the part of fish farmers, high cost of production inputs and mad rush for white-collar jobs have constrained its contribution to increased food supply and poverty reduction. However, with harnessing and development of the fishing sector in the Niger Delta as one of the amnesty deal, there could be renewed interest in fish farming in Nigeria.
With increased awareness on the health benefits of fish consumption, fish consumption in Nigeria is on the high side. They are consumed as smoked, dried, fried, boiled or canned fish. Traditionally smoke-dried fish represents a low cost source of high quality protein (Sourness, 1988). Smoke-dried fish products are consumed more than fish prepared through any other means. They are favoured because the smoke-drying process imparts characteristic aroma, taste, colour and texture (crispiness) on processed fish (Kumolu-Johnson et al., 2010). Smoke-dried fish are less expensive than canned fish and can store better than fried and boiled fish. The product is consumed all over the country as there is no religious or cultural objection to its consumption.
1.2 FISH PRESERVATION AND PROCESSING METHODS IN NIGERIA
Nigeria as one of the developing tropical countries is no exception in practicing the traditional system of smoking and drying (curing) all over the country. Fish mongers practice a simple and inexpensive fish smoke-drying process to produce a dried fish that is commercially accepted all over the country. Sun drying of fish is practiced in the Northern part of the country. In the process, the fish is eviscerated, gutted and split and in some cases.....
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