ABSTRACT
Glutathione Peroxidase (GPx) family of enzymes plays important roles in
the protection of organisms from oxidative damage. GPx converts reduced
glutathione (GSH) to oxidized glutathione (GSSG) while reducing lipid
hydroperoxides to their corresponding alcohols or free hydrogen peroxide to
water. This study was conducted to investigate the possible effects of temperature
in vivo on Glutathione peroxidase (GPX) oxidative activity in fish tissues.An
adult fully grown cat fish, (the African flathead catfish, Clariasgariepinus) about 0.7m
in length and 0.15 in width, weighing 15Kg was obtained from the school pond.
The fish was humanely killed and its liver was cut off from the rest of the
body. Glutathione peroxidase was extracted and purified from the liver of the
fish using the purification method of Ezeet
al(2010).The extracted and purified GPX was then divided into 23 test tubes and
labeled. Each test tube was heated at different temperatures ranging from -30°C
to 50°C, after which Glutathione and Hydrogen Peroxide substrates were
introduced to each test tube.Results showed that measurements were higher in
test tubes were heating temperature were either exactly at or close to the
acclimation temperature of the African Flathead Catfish.
CHAPTER ONE
INTRODUCTION
1.1.
INTRODUCTION
1.1.1 FISH: SOURCE OF FOOD FOR MAN.
Food is one
of the basic needs of man (Morey, 1940; Pierce, 2010). Since agriculture
produces the food that provides the calories and micronutrients essential for a
healthy and productive life, it is interlinked in many important ways to human
nutrition and health (Michael, 2011). These nutrients include carbohydrates,
proteins, fats and oil, minerals, vitamins and water. Of these nutrients, it is
the proteins that supply the body with amino acids necessary for growth and
repair of damaged tissues. The sources of protein include plants and animals.
Animal sources are preferred because of the presence of essential amino acids
and higher digestibility. However, the major disadvantage is higher cost. The
animal sources include fish, poultry, dairy, pork, snail, and rabbit.
Fish
accounts for one fifth of world total supply of animal protein (FAO, 1991;
Olagunjuet al., 2007). It is an important source of protein to a
large number of Nigerians. It provides 40% of the dietary intake of animal
protein of the average Nigerian (FDF, 1997; Sogbesanet al., 2006). According to Adekoya and Miller (2004), fish and
fish products constitute more than 60% of the total protein intake in adults
especially in rural areas.
Amiengheme
(2005) enumerated the importance of fish in Human Nutrition as follows:
·
Fish food has a nutrient profile superior to
all terrestrial meats (beef, pork and chicken) being an excellent source of
high quality animal protein and highly digestible energy;
·
Fish is a good source of sulphur and
essential amino acids such as lysine, leucine, valine and arginine. It is
therefore suitable for supplementing diets of high carbohydrate contents;
·
It is an extremely rich source of
polysaturated (Omega III) fatty acids, which are important in lowering blood
cholesterol level and high blood pressure, reducing the risk of sudden death
from heart attacks and reduces rheumatoid arthritis, lowering the risk of age-
related muscular degeneration and vision impairment; decreasing the risk of
bowel cancer and reducing insulin resistance in skeletal muscles.
·
Fish is also a good source of thiamine fat
soluble vitamins (A, D and E), water soluble vitamins (B complex) and minerals
(calcium, phosphorus, iron, iodine and selenium);
In Nigeria,
fisheries occupy a unique position in the agricultural sector of the economy
(Kudi et al., 2008). Its contribution
to Gross Domestic Product (GDP) rose from 76.76 billion in 2001 to N162.61
billion in 2005 (CBN Report, 2005). Nigerians are large consumers of fish, with
an annual average demand estimate at 1.4 million metric tonnes, (Kudiet al., 2008). Domestic fish production
of about 0.5 million metric tonnes is supplied by artisan fishermen (85%), and
fish farmers (15%) (Adekoya and Miller, 2004; Emokaro, 2010; BusinessDay,
2011). However a demand and supply gap of at least 0.7 million metric tonnes
exists nationally with import making up the short fall at a cost of 400 billion
United States dollars per year. According to FAO (2007), this figure (0.7
million metric tonnes) makes Nigeria the largest importer of fish in the
developing world.
To take
advantage of the large market created by this deficit, the immediate past and
current Governments has promoted a backward integration plan for increased fish
farming and production in Nigeria,
Nigerians are also complementing Government efforts by increasing their
participation in aquaculture, with many fish farmers focusing on African
flathead catfish, Clariasgariepinus
as they have been shown to have a potential market value of two to three times
that of other cultivable species like Tilapia and Heterobranchus (FAO, 2000;
Fafioye and Oluajo, 2005; Emokaroet al.,
2010; Businessday, 2011).
A survey by
Addo (2005) revealed that Nigerian children below the age of 18 years, who make
up about 47% of our total population are still victims of stunting, wasting and
under-weight, so with the increased establishment of more aquaculture in
Nigeria, it is possible to reverse this trend of malnourishment among Nigerians
in this age bracket.
1.2.
THE AFRICAN CATFISH
The African
catfish – Clariasgariepinus, an
omnivorous freshwater fish, is a popular delicacy in Nigeria. It is a prominent
culture species because of its fast growth rate and resistance to diseases and
stress factors like over-stocking and poor water quality (Olojoet al., 2005). It is distributed mainly
in fresh waters of Africa hence the name African catfish, although it is also
seen in Asia. It is named ‘catfish’ because they possess prominent barbels
which resemble cat’s whiskers. It has a slender body, flat bony head and broad
terminal mouth with four barbels. The pectoral fins have spines. Its dendritic
organ is an accessory breathing organ and it is a modification of the gill
arches (Ahmed et al., 2008). The
adult of about 1.5m weighs up to 29kg (Teugel, 1986).
Habits:
They are nocturnal omnivorous animals feeding on living as well as dead organic
matter. They are capable of swallowing large prey because of large mouth
(Teugel, 1986).They can crawl on the ground to escape drying pools but can also
survive in shallow mud for long periods of time between rainy and dry seasons.
They can produce croaking sound. They spawn mostly at night in the shallow
areas of rivers, lakes and streams. Development of the larva is rapid as they
are able to hatch 24 hours and swim within 48 – 72 hours after fertilization.
1.3 ENZYMES AND THE GENERAL EFFECTS OF
TEMPERATURE
The living
cell is the site of tremendous biochemical activity. Catalysis, through
enzymes, makes possible biochemical reactions, which are necessary for all life
processes. Enzymes are responsible for
bringing about almost all of the chemical reactions in living organisms.
Without enzymes, these reactions take place at a rate far too slow for the pace
of metabolism.
Like most
chemical reactions, the rate of an enzyme-catalyzed reaction is affected by
temperature. Variations in reaction temperature as small as 1 or 2 degrees may
introduce changes of 10 to 20% in the results. In the case of enzymatic
reactions, this is complicated by the fact that many enzymes are adversely
affected by high temperatures.
The enzyme Glutathione
Peroxidase which catalyses the reduction of hydrogen peroxides is the main
focus of this study. Understanding the effects of temperature on the activity
of this enzyme in the catfish, could help in determining the best storage
temperature for this fish such that harvested catfish can be kept fresh for a
longwhile for consumption after
1.4. STATEMENT OF PROBLEM
Despite the
clear increase in interest for aquaculture and fish consumption in Nigeria, a
major problem of storage exists. This is clearly observed in the lack of fresh
iced or well dried catfish options in the market. It is also manifest in the
‘point and kill’ marketing phenomenon, which has invariably restricted catfish
farming to retail/subsistence levels intended for consumption by members of the
immediate locale were the farm is sited, and discourages large scale catfish
farming intended for consumers across state and even national borders.
1.5. RESEARCH OBJECTIVES
The aim of
this study is to isolate the enzyme Glutathione Peroxidase (GPx) from the liver
of the African catfish (Clariasgariepinus)
and carryout investigations in vitro to determine
I.
The optimum temperature range wherein the
enzyme Glutathione peroxidase best catalyses the reduction of hydroperoxides
and other free radicals, thereby protecting the tissues of the Flat Head
Catfish from oxidative stress and damage.
II.
The temperature range wherein rate of the
catalytic reduction activity of the enzyme Glutathione peroxidase is lowest.
1.6. SCOPE OF
STUDY
This study
will be carried on only the African Catfish (Clariasgariepinus), as survey has shown that it is the by far the
catfish variety most consumed by inahbitants of Eastern Nigeria.
1.7. SIGNIFICANCE OF THE STUDY
The importance of this study are
as follows:
I.
Results obtained at the end will accurately
advise the best storage temperature for the Flat Head Catfish that will ensure
optimum protection of its muscles and other edible tissues from oxidative
stress and damage,
II.
Thereby increasing its shelf life,
III.
Encourage farmers to engage in larger
cultivation of this popular species of fish for wider consumption,
IV.
This in turn reduces production and
processing costs; and wastage and loss due to deterioration and decay,
V.
Ensure that fish which is an important but
currently expensive source of protein is made cheaper and consumed more
frequently by citizens of all income and age brackets;
VI.
And finally help reduce the malnutrition
problem earlier mentioned in the last.
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