ABSTRACT
Species of snails Archachatina marginata,Archatinafulica and Limicolaria flammea, and Archachatina marginata were assessed for proximate analysis aimed at establishing their nutritive values. The heavy metals levels of the flesh was also investigated. Analysis of the flesh revealed that the composition of crude protein varied from 34.90+ 0.23 to 36. 75 + 0.22% in all species, Ash content, moisture content, crude lipid, and carbohydrateranged from 6.15+ 0.99 to 16.06 + 0.75%, 9.41+ 0.33 to 27. 89+ 0.52%, 7.29+ 0.63 to 9.99+ 0.15%, 14.71+ 0.17 to 38.18+ 0.66% respectively. Crude fibre was not detected in any of the species.The concentration of zinc, copper, cadmium and lead in the flesh of the snails were in the range of 7.58+ 0.03 to 13.10+ 0.03 mg/kg, 0.99+ 0.01 mg/kg to 3.32+0.01 mg/kg, 0.09+ 0.00 to 0.50+ 0.00 mg/kg, and 0.90+ 0.00 to 2.90+0.00 mg/kg respectively.These values were low and within the WHO permissible limit. Amino acid profile indicates the presence of lysine, Alanine, Histidine, valine, leucine and Phenylalanine Arginine, Aspartic acid, threonine serine, Glutamic acid, proline, Glycine, Cystine, Isoleucine, Leucine and Tyrosine in the snail species. Lysine concentration varied from 15.67-16.00mg/g in all species. Histidine was 2.50.73mg/g, Arginine ranged from 16.11-16.85. Aspartic acid ranged from 9.66 – 10.54mg/g, Threonine concentration ranged from 8.34-9.01mg/g, serine (4.55 – 4.99 mg/g), Glutamic acid (11.64 – 11.94mg/g), proline (5.80–6.26mg/g), Glycine (4.01-4.86 mg/g), Alanine (2.98 – 3.31 mg/g), cystine (0.55-0.69mg/g), valine (7.9 – 8.21mg/g), methionine (1.93 -1.98mg/g), Isoeucine (8.91 – 9.00mg/g), leucine (9.51 – 9.98mg/g), Tyrosine (4.63 – 4.80 mg/g), phenylalanine (6.66 – 7.13 mg/g). Ammonia and Norleucine were not detected in all the snail samples. The result shows that snailcould complement the required trace minor elements needed for proper growth and development in human and hence recommended for regular consumption.
TABLE OF CONTENTS
Cover Page – – – – – – – – – i
Title Page – – – – – – – – – ii
Declaration – – – – – – – – – iii
Certification – – – – – – – – – iv
Dedication – – – – – – – – – v
Acknowledgement – – – – – – – – vi
Abstract – – – – – – – – – vii
List of Figures – – – – – – – – xi
List of Tables – – – – – – – – – xii
Abbreviations – – – – – – – – – xiii
CHAPTER ONE
1.0 INTRODUCTION – – – – – – – 1
1.1 Scientific Classification – – – – – – 2
1.2 Common Names of Snails – – – – – – 3
1.3 Economic Importance of Snail – – – – – 3
1.4 Heavy Metals – – – – – – – 6
1.5 Justification of the Study – – – – – – 8
1.6 Aim of the Study – – – – – – – 9
1.7 Objective of the Study – – – – – – 9
CHAPTER TWO
2.0 LITERATURE REVIEW – – – – – – 10
2.1 Studies on Bioaccumulation of Heavy Metals in Snails – – 10
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2.2 Nutritional Compositions of Snails – – – – 15
CHAPTER THREE
3.0 MATERIALS AND METHODS – – – – – 21
3.1 Collection of Samples – – – – – – 21
3.2 Preparation of Samples – – – – – – 21
3.3 Digestion of Snail Sample – – – – – – 21
3.4 Proximate Analysis Procedure – – – – – 22
3.4.1 Moisture Determination Using Oven method Procedure – – 22
3.4.2 Ash content determination – – – – – – 22
3.4.3 Crude Fibre – – – – – – – – 23
3.4.4 Determination of Fat – – – – – – – 24
3.4.5 Determination of Protein – – – – – – 25
3.4.6 Determination of Carbohydrates – – – – – 27
3.4.7 Determination of Oil – – – – – – – 28
3.4.8 Amino Acid profile – – – – – – – 28
CHAPTER FOUR
4.0 RESULTS – – – – – – – – 30
CHAPTER FIVE
5.0 DISCUSSION – – – – – – – 35
5.1 Physicochemical Properties of the Snail – – – – 35
5.2 Heavy Metals Level of Sampled Snail – – – – 35
5.2.1 Zinc – – – – – – – – – 35
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5.2.2 Copper – – – – – – – – 36
5.2.3 Cadmium – – – – – – – – 36
5.2.4 Lead – – – – – – – – – 37
5.3 Determination of Proximate Composition of the Snail Species – 37
5.3.1 The Moisture Content Samples – – – – – 37
5.3.2 The Crude Lipid Content – – – – – – 38
5.3.3 The Ash Content of the Snails Species – – – – 39
5.3.4 The Crude Protein of Snails Species – – – – – 40
5.3.5 The Crude Fibre of the Snails Sample – – – – 40
5.3.6 The Carbohydrate Content of the Snail Samples – – – 41
5.4 The Amino Acid Profile of the Snail Samples – – – 41
CHAPTER SIX
6.0 SUMMARY, CONCLUSION AND RECOMMENDATION – 43
6.1 Summary – – – – – – – – 43
6.2 Conclusions – – – – – – – – 45
6.3 Recommendation – – – – – – – 46
REFERENCES – – – – – – – 47
APPENDICES – – – – – – – 52
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CHAPTER ONE
1.0 INTRODUCTION
Snail is a common name that is applied most often to land snails, terrestrial pulmonate, gastropod mollusce. Snail is also applied to most of the members of the molluscan class gastropoda that have a coiled shell large enough for theanimal to retract completely into. “Snail” is used in this most general sense; it includes not just land snails but also thousands of species of sea snails and fresh water snails. Snail-like animals that naturally lacka shell, or have only an internal shell, are usually called slugs, and land snails that have only a very small shell that they cannot retract into are often called semislugs.
Snails are one of the earliest known types of animals in the world. They are able to adapt to a variety of living condition and they do not require large amounts of food. They have been able to continually evolve to survive the condition around them which many researchers find to be very fascinating. All snails are classified as mollusks because of the hard shell that protects their bodies; snails are found in many locations and have a very diverse type of habitat where they can be found. As a snail moves it leaves behind a trail of slims, this allows it to easily move across any type of terrain without injuring itsbody. They are not able to hear at all. So they rely on their sense of touch to interact with each other. They use their sense of smell to help them find food. You will find that snails are the most active at night and may come out during the early morning hours as well(Frederick, 2010).
Snails have prominent tentacles on which, in many species, the eyes are often located, many snails are as small as 0.1cm (0.04inch) long; others, such as conches and
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the African land snail, are as long as 20cm (8inch). The spiral shell into which the snail withdraws serves mainly as protection against predators and desiccation. Land snails are particularly well adapted to changes in moisture and some desert species are able to remain sealed within their thick shells for two or more years. Land snail species of more moist habitats usually have thinner shells. Slugs, which live in very moist places and are often considered snails, have only vestigial shells.
Snails can be found in a very wide range of environments, including ditches, deserts, and the abyssal depths of the sea. Although land snails may be more familiar to people, marine snails constitute the majority of snails’ species and have much diversity. Numerous kinds of snail can also be found in fresh water.
Most snails have thousands of microscopic tooth-like structures located on a ribbon-like tongue called a radula used to cut food into small pieces. Many snails are Herbivorous, eating plants or rasping algae from surfaces with their radula. However, a few land species and many marine species are omnivores, predatory or carnivores. The life span for snails depends on their habitat and the species. Some of them only live for about 5 years however; others in the wild are believed to live at least 25 years old. The life span of snails is decreasing due to humans destroying their habitat and due to pollution.
1.1 Scientific Classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
(Fredericks, 2010)
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1.2 Common Names Of Snails
English – Snail Hausa – Dodon kodi Igbo – Ejule Yoruba – Igbin
Figure 1: A typical land snail
1.3 Economic Importance Of Snail
The economic and medicinal benefits from snails are immense. These run from their foot tissue to shells (Wosu, 2003). They serve as valuable sources of nutrition to human and animals with high levels of protein, iron, lysine, leucine, arginine, calcium and phosphorus, relatively low amount of sodium, fat and cholesterol compared to poultry and other livestock[Thompson, (1996); Wosu. (2003)].Many common health problems can be prevented or alleviated with a healthy diet (Clinical Nutrition Board, 2011). Our bodies need the correct balance of nutrients in food we take to function optimally.Snails are cheap to rear at subsistent and commercial levels with high returns on low input.
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Traditionally, snail is used in the preparation of concoctions for various cases such as reduction of labour pains, blood loss during delivery and in the cure of small pox (Akinnusi, 1997). It is also implicated in the treatment of anaemia, hyperension, high blood pressure and other fat related ailments (Wosu,2003).
Umoh and Bassir (1977) and Mba (1980) highlighted a good number of lesser known animals foods such as clam, periwinkle and land snails.The consumption of these food were limited to a small population owing to lack of adequate information about their nutritional potential.
It has been revealed by Imevbore and Ademosun (1988) that land snails meat contains as high as 88.3 of protein. Adeyeye (1996) reported 20.6%, 14.52% and 17.51% of protein in Archachatina marginata, Archatina species and limicolaria spp respectively. Lymnaen stangials (Pond snail) popularly called “Igbin Oluweri” by Yoruba tribe of western Nigeria, is a species of snails and belongs to the class gastropoda.It is used as food by the “Oluweri”, (Pond or river worshippers) and is available all year round in ponds(Yusuf,2004). The economy importance of snail can be classified as follows:
i. Agriculture:The practice ofrearing snails for food is known as heliciculture. The snails are kept in a dark place in a wired cage with dry straw or dry wood-coppiced wine-grape vines. During the rainy period the snails come out of hibernation and release most of their mucus onto the dry wood/straw. The species use for these purpose are known as agricultural and garden pest. They are edible delicacy, and occasionally a household pet.
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ii. Cosmetic: recently, Halix aspersa has gained some popularity as the chief ingredient in skin creams and gels (cream/gel de carecol) sold within the Latino community in the USA. These creams are promoted as being suitable for use on wrinkles, scars, dry skin and acne(Andes, 2006).A screen of the secretions that Halix aspersasnail produces under stresspossesses pharmacological properties(skin-regenerative properties). The secretions contain antioxidant, superoxide, dismutase and glutathione S-transferase (GSTS). The secretions stimulate fibroblast proliferation, stimulation of extracellular matrix assembly and the regulation of metalloproteinaseactivities.
iii. Cultural Depiction: Due to its slowness, the snail has traditionally been seen as a symbol of laziness. In Christian culture, it has been used as a symbol of the deadly sin of sloth. Psalm 58:8 uses snail slime as a metaphorical punishment. The Greekpoet Hesiod wrote that snails signified the time of harvest by climbing the stalks, while the Aztec moon god tecciztecatl bore a snail shell on his back. This symbolized rebirth; the snail penchant forappearing and disappearing was analogized with the moon (Andes, 2006).
iv. Snail as Food: several species of land snails provide and easily harvested source of protein to many people in poor communities around the world. Many land snails are valuable because they can feed on a wide range of agricultural wastes, such as shed leaves in banana plantations. In some countries, giant African land snails are produced commercially for food. Land snails, freshwater snails, and sea snails are all eaten in a number of countries. (principally spam, Philippines, morocco, Nigeria, Algeria, Cameroon, France, sicily, Portugal, Greece, Belgium, Vietnam, Laos,
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Cambodia, Cyprus, Ghana, malta, teraiofnepal, southwestern China, northeast India states such as Manipur, Tripura and parts of the USA).
1.4 Heavy Metals
Heavy metals are elements with atomic weight between 63 and 201 and specific gravity above 5.0. They are metals with high density and toxic or poisonous at low concentration (Lenntech, 1998).
Heavymetals occur naturally in the eco-system with large variation in concentrations. They cannot be degraded or destroyed to a small extent, and hence enter our bodies via food chain, drinking water and air. High concentrations of heavymetal can lead to poisoning. Heavy metal toxicity can result in damaged or reduced mental and central nervous function, lower energy levels and damages to blood composition, lungs, kidney sliver and other vital organs. Long – term exposure may result in slowly progressing muscular and neurological degeneration process that mimic AlZheimer’s diseases, parkion’s disease, muscular dystrophy and uncommon and repeated long – term contact with some metals or their compound may a case cancer (John,2002).
Copper and Zinc have essential physiological and biochemical functions in plants and animals (Schlosseret al., 2007). However, excessive levels can be damaging to environmental health (Murariuet al.,2010). Cd and Pb have no known vital or beneficial effect on organisms (Nordbery et al., 2002), except for diatoms, where a Cd – based enzyme play an essential role in role in regulating atmospheric carbon Lane et al., (2005).
Laskowski and Hopkin (1996) showed that land snails can concentrate high levels of Cu, Zn Cd and Pb in their soft tissue without revealing any major metabolic disorder. These heavy metals were found to accumulate into the snail shell, often resulting in
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alterations of shell geometry or size. In polluted soils Cu, Zn, Cd, and Pb are taken by vegetation, and subsequently they can be transferred along food chain to herbivorous organism. Cu, Zn, Cd, and Pb accumulate in dead plant and animal materials, and thereafter, they are ingested by organisms that feed on decaying organic matter (detritivore organism). Because snails act on tropic level, both as herbivorous and deritivore organism, they can be involved in heavy metals biomagnifications along the food chain Notten et al., (2005).
Cadmium derives its toxicological properties from its chemical similarity to zinc an essential micronutrient for plants, animals and humans. Cadmium is bio-persistent and once absorbed by an organism, remains resident for many yearsin humans. Long-term exposure is associated with renal dysfunction, high exposure can lead to obstructive lung disease and has been linked to lung cancer.Cadmium may also produce bone defects (osteomalacia, osteoporosis) in humans and animals. The metal can be linked to increased blood pressure and effects on the myocardium in animals(Lenntech, 1998).
Copper is an essential substance in human life, but in high doses, it can cause anemia, liver and kidney damage. People with Wilson’s disease areat greater risk for health from over exposure to copper. Copper normally occurs indrinking water from copper pipes, as well as from additive, designed to control algal growth (Lenntech, 1998).
Human’sexposure to lead can result in a wide range ofbiological effect depending on level and duration ofexposure. High levels ofexposure may result to toxic biochemical effects in humans whichinturn cause problems in the syndissertation of hemoglobin, effects on kidneys, gastrointestinal tract, joints, reproductive system and acute or aleuronic damage to the nervous system (Afal and Wiener, 2014). Lead poisoning, which
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is so severe as to cause evident illness, is now very rare indeed. At intermediate concentrations, there is persuasive evidence that lead can have small, subtle sub-clinical effects, particularly on neuropsychological developments in children. Some studies suggest that there may be a loss of up to 21Q points for a dry in blood lead levels from10to 20mg/dl in young children (Afal and Wiener, 2014).Average daily lead intake for adults intheUK is estimated at 1.6 mg from air, 20mg from drinking water and 28mg from food (WHO, 1993).In adult population the major exposure pathway is from food and water. Food, air, water and dust/soil are the major potential exposure path ways for infants and young children (Afal and wiener, 2014).
Zinc is needed by human and other animals in small amounts, but in larger amount, it can cause damage to the nervous system, fatigue and irritability(Afal and Wiener, 2014). Zinc accumulates in living tissue, causing high zinc content in fish and other organisms and causing greater health problem in human over a lifetime of over exposure. These health problems include hair and finger nail loss, damage to kidney and liver tissue, damage to circulatory tissue and more severe damage to the nervous system(Lenntech, 1998).
1.5. Justification Of The Study
A major task facing the world today is that of providing sufficient food of adequate quality for the rapidly increasing human population. The food deficit situation is more intense with protein deficiency when compared to the availability of carbohydrate and the micro elements.Adesehinwa and Ogunmodede (1995) reported that humans have used snails for food for many generations.Despite this, most of the scientific work done; on snails have been from the point of view of animal’s parasitology where snails act as
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intermediate host of pathogenic nematodes(Wosu, 2003). Due to the increased in the demand and consumption of snails, it has become necessary to know the level of heavy metals concentrations present in snail in order to ascertain their safety for consumption.It is also imperative to investigate the amino acid profile to create awareness to the general public on their nutritional status.
1.7 Aim Of The Study
The aim of this research is to ascertain the concentration levels of some heavy metals in some species of snail and investigate their nutritional values.
1.8 Objective Of The Study
i. To determine the concentrations of copper, cadmium, zinc and lead in Archatina fulica, Limicolaria flammea and Archachatina marginata snails.
ii. To determine the nutritional values in the flesh of the snail species.
iii. To determine the amino acids present in the flesh of the snails species.
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