NUTRITIONAL POTENTIAL OF SYNSEPALUM DULCIFICUM PULP AND THE EFFECT OF THE METHANOLIC EXTRACT ON SOME BIOCHEMICAL PARAMETERS IN ALBINO RATS
The nutritive and antinutritive compositions of S. dulcificum pulp were analysed to augment the available information on the anti-diabetic effect of the plant. Biochemical parameters like liver function enzymes (ALT, AST, ALP) and bilirubin concentrations,serum total protein, serum albumin and globulin, kidney function parameters (creatinine and urea concentrations), blood glucose, serum lipid profile and lipid peroxidation were determined in rats that were administered different concentrations of the methanolic extract to ascertain their effects. The internal organs (liver and kidney) were also removed and used for histopathological studies. From the result of the study, the proximate composition shows that S. dulcificum contains 7.75% protein, 59.55% moisture content, 4.36% ash, 6.24% crude fibre, 3.26% fat and 18.84% carbohydrate.The result of the mineral analysis shows that S.dulcificum pulp contains 100 mg/g calcium, 24.20 mg/g iron, 9.49 mg/g zinc, 6.22 mg/g copper, 0.01 mg/g chromium and 0.01 mg/g cobalt. Vitamin analyses shows that the S. dulcificum pulp contains 0.04% vitamin A, 22.69% vitamin C, 0.01% vitamin D and 0.02% vitamin K. Antinutrient analyses of the pulp show 5.67% oxalate, 0.03% phytates and 0.02% hemagglutinin. Amino acid profile shows that S.dulcificum pulp contains 8.055% tryptophan, 1.35% phenylalanine, 0.7% isoleucine, 0.5% tyrosine, 1.05% methionine, 0.4% proline, 0.69% valine, 1.1% threonine, 0.4% histidine, 0.5% alanine, 1.02% glutamine, 1.6% glutamic acid, 0.7% glycine, 0.3% serine, 1% arginine, 0.1% aspartic acid, 1.23% asparagine, 0.6% lysine and 0.6% leucine. Quantitative phytochemical analysis shows that the pulp contains 3.45% saponins, 57.01%`flavonoids, 7.12% tannins, 0.0001% alkaloids, 0.0001% glycosides, 0.0003% resins, 0.0002% terpenoids, 0.0001% steroids and 0.0003% cyanogenic glycosides.The results of the acute toxicity show that the methanol extract is not toxic to the mice at concentrations up to 5000mg/kg body weight. From the results obtained, the animals receiving 100mg/kg b.w of the methanolic extract showed significantly reduced (p<0.05) serum levels of glucose, bilirubin, low density lipoprotein cholesterol and ALT after the 14 day study compared to the 28 day study. However, no significant difference (p>0.05) was also observed across the groups in their serum ALP, AST, creatinine, urea, cholesterol, TAG, albumin and globulin levels on the 14th day compared with the 28th day. A significant difference (p<0.05) was observed in the malondialdehyde and serum protein concentrations in the 500mg/kg b.w test group while glucose concentration decreased significantly (p<0.05) in the 100mg/kg b.w and 500mg/kg b.w test group after the 14 day study compared with the 28 day study. High density lipoprotein cholesterol level significantly increased (p<0.05) in the 200mg/kg b.w test group. Histopathological examination shows normal liver architecture across the groups at 100mg/kg b.w, 200mg/kg b.w and 500mg/kg b.w. Kidney sections of rats showing normal glomerulus (G) and renal tubules (arrow) at same concentrations.
TABLE OF CONTENTS
Table of Contents
List of Figures
List of Tables
List of Abbreviations
CHAPTER ONE: INTRODUCTION
1.1.1 Common Sweeteners and Their Production
126.96.36.199 Natural Sweeteners
188.8.131.52.2 Maple Syrup
184.108.40.206 Artificial Sweeteners
1.2 Synsepalum dulcificum
1.6.2 Vitamin C
1.6.3 Vitamin D
1.6.4 Vitamin E
1.6.5 Vitamin K
1.8 Some Minerals and Their Biological Functions
1.8.1 Calcium (Ca)
220.127.116.11 Metabolic Functions and Deficiency Symptoms of Calcium
1.8.2 Magnesium (Mg)
18.104.22.168 Metabolic Functions and Deficiency Symptoms of Magnesium
1.8.3 Zinc (Zn)
22.214.171.124 Metabolic Functions and Deficiency Symptoms of Zinc
1.8.4 Iron (Fe)
126.96.36.199 Metabolic Functions and Deficiency Symptoms of Iron
1.8.5 Copper (Cu)
188.8.131.52 Metabolic Functions and Deficiency Symptoms of Copper
1.9 Blood Glucose
1.9.1 Blood Glucose Regulation
1.10.1 Lipoproteins: Types and Functions
184.108.40.206 Very Low Density Lipoprotein (VLDL)
220.127.116.11 Low Density Lipoprotein (LDL)
18.104.22.168.1 Metabolism of Low Density Lipoprotein via LDL Receptor
22.214.171.124.2 Regulation of LDL Receptor
126.96.36.199 High Density Lipoprotein (HDL)
1.11 Total Cholesterol andCholesterol Balance in Tissues
1.11.1 Diet and Cholesterol Regulation
1.12 Liver Function Biomarkers
1.12.1 Alanine Aminotransferase
1.12.2 Aspartate Aminotransferase
1.12.3 Alkaline Phosphatase
1.12.4 Clinical and Diagnostic Significance of Liver Function Enzymes
1.12.6 Serum Protein
1.12.7 Serum Albumin
1.13 Renal Function Biomarkers
1.13.1 Blood Urea Nitrogen (BUN)
1.14 Lipid Peroxidation
1.14.4 Types of Lipid Peroxidation
188.8.131.52 Non- Enzymatic Lipid Peroxidation
184.108.40.206 Enzymatic Lipid Peroxidation
1.15 Research Objectives
1.15.1 General Objectives
1.15.2 Specific Objectives
CHAPTER TWO : MATERIALS AND METHODS
2.1.1 Plant materials
2.1.3 Chemicals and Reagents
2.1.4 Equipment /Instruments
2.2.1 Experimental Design
2.2.2 Extraction of Plant Material
2.2.3 Determination of the Extract Yield
2.2.4 Toxicological studies
220.127.116.11 Acute Toxicity Studies and Lethal Dose (LD50) Test
2.2.5 Proximate Analysis
18.104.22.168 Crude Protein
22.214.171.124 Crude Fat
126.96.36.199 Crude Fibre
188.8.131.52 Ash/Mineral Matter
184.108.40.206 Carbohydrate or Nitrogen Free Extract (NFE)
2.2.6 Estimation of Vitamins
220.127.116.11 Determination of Vitamin A
18.104.22.168 Determination of Vitamin C
22.214.171.124 Determination of Vitamin D
126.96.36.199 Determination of Vitamin E
188.8.131.52 Determination of Vitamin K
2.2.7 Determination of Mineral Content of S. dulcificum Pulp
184.108.40.206 Determination of Phosphorus
2.2.8 Determination of Amino Acid Profile
220.127.116.11 Defatting of the Pulp
18.104.22.168 Hydrolysis of the Pulp
22.214.171.124 Nitrogen Determination
126.96.36.199 Loading of the Hydrolysate into TSM Analyzer
188.8.131.52 Method of Calculating Amino Acid values using Chromatogram Peaks
2.2.9 Qualitative Phytochemical Studies on Synsepalum dulcificum Pulp
184.108.40.206 Test for Alkaloids
220.127.116.11 Test for Glycosides
18.104.22.168 Test for Cyanogenic Glycosides
22.214.171.124 Test for Tannins
126.96.36.199 Test for Saponins
188.8.131.52 Test for Flavonoids
184.108.40.206 Test for Resins
220.127.116.11 Test for Terpenoids and Steroids
2.2.10 Quantitative Phytochemical Analysis of S.dulcificum Pulp
18.104.22.168 Determination of Alkaloids
22.214.171.124 Determination of Cyanogenic Glycosides
126.96.36.199 Determination of Saponins
188.8.131.52 Determination of Flavonoids
184.108.40.206 Determination of Tannins
220.127.116.11 Determination of Steroids
18.104.22.168 Determination of Terpenoids
2.2.11 Antinutrient Analysis of S. dulcificum Pulp
22.214.171.124 Determination of Oxalates
126.96.36.199 Determination of Phytates
188.8.131.52 Determination of Haemagglutanins
2.2.12 Blood Sample Collection for Biochemical Analysis
2.2.13 Biochemical Assays
184.108.40.206 Assay of Alanine Aminotransferase (ALT) Activity
220.127.116.11 Assay of Aspartate Aminotransferase Activity
18.104.22.168 Assay of Alkaline Phosphatase (ALP) Activity
22.214.171.124 Determination of Bilirubin Concentration Using Colorimetric Method
126.96.36.199.1 Determination of Total Bilirubin (TB) Concentration
188.8.131.52 Total Serum Protein Assay
184.108.40.206 Serum Albumin Concentration
220.127.116.11 Blood glucose Assay
18.104.22.168 Estimation of Serum Lipid Concentrations
22.214.171.124.1 Estimation of Total Cholesterol Concentration
126.96.36.199.2 Estimation of Low Density Lipoprotein-Cholesterol Concentration
188.8.131.52.3 Estimation of High Density Lipoproteins (HDL)–Cholesterol Concentration
184.108.40.206.4 Estimation of Triacylglycerol
220.127.116.11 Estimation of Lipid Peroxidation
2.2.14 Histopathological Examination
2.2.15 Statistical Analysis
CHAPTER THREE: RESULTS
3.1 Proximate Composition of S. dulcificum Pulp
3.2 Mineral Composition of S. dulcificum Pulp
3.3 Vitamin Content of S.dulcificum Pulp
3.4 Amino Acid Profile of S. dulcificum Pulp
3.5 Phytochemical Composition of S. dulcificum Pulp
3.6 Antinutritional Composition of S.dulcificum Pulp
3.7 Acute toxicity (LD50) Studies
3.8 Mean Body Weights of Animals
3.9 Effect of S. dulcificumMethanolic Extract Administration on Alkaline Phosphatase (ALP) Activity in Rats
3.10 Effect of S. dulcificumMethanolic Extract Administration on Alanine Aminotransferase (ALT) Activity in Rats
3.11 Effect of S. dulcificumMethanolic Extract Administration on Aspartate Aminotransferase (AST) Activity in Rats
3.12 Effect of S. dulcificumMethanolic Extract Administration on Bilirubin levels in Rats
3.13 Effect of S. dulcificumMethanolic Extract Administration on Total Serum Protein concentration in rats
3.14 Effect of S. dulcificumMethanolic Extract Administration on Serum Albumin Concentration in Rats
3.15 Effect of S. dulcificumMethanolic Extract Administration on Serum Globulinin Rats
3.16 Effect of S. dulcificumMethanolic Extract Administration on Creatinine Level in Rats
3.17 Effect of S. dulcificumMethanolic Extract Administration on Urea Level in Rats
3.18 Effect of S. dulcificumMethanolic Extract Administration on Blood Glucose Concentration in Rats
3.19 Effect of S. dulcificumMethanolic Extract Administration on Cholesterol Concentration in Rats
3.20 Effect of S. dulcificumMethanolic Extract Administration on High Density Lipoprotein Cholesterol Concentration in Rats
3.21 Effect of S. dulcificumMethanolic Extract Administration on Low Density Lipoprotein Cholesterol Concentration in Rats
3.22 Effect of S. dulcificumMethanolic Extract Administration on Triacylglycerol Concentration in Rats
3.23 Effect of S. dulcificumMethanolic Extract Administration on Malondialdehyde Concentration in Rats
3.24 Effect of S. dulcificumMethanol Extract Administration on the Histopathology of Rat Liver [14 days duration]
3.25 Effect of S. dulcificumMethanol Extract Administration on the Histopathology of Rat Liver [28 days duration]
3.26 Effect of S. dulcificumMethanol Extract Administration on the Histopathology of Rat Kidney [14 days duration]
3.27 Effect of S. dulcificumMethanol Extract Administration on the Histopathology of Rat Kidney [28 days duration]
CHAPTER FOUR: DISCUSSION
4.3 Suggestions For Further Studies
LIST OF FIGURES
Figure 1 Structure of Sucrose
Figure 2 Syvsepalum dulcificum Fruit
Figure 3 Synsepalum dulcificum Tree
Figure 4 Structure of Cholesterol
Figure 5 Mechanism of Non-Enzymatic Lipid Peroxidation
Figure 6 Proximate Composition of S. dulcificum Pulp
Figure 7 Amino Acid Analyses of S. dulcificum Pulp
Figure 8: Effect of S.dulcificum Methanolic Extract Administration on Alkaline phosphatase Activity in Rat
Figure 9 Effect of S.dulcificum Methanolic Extract Administration on Alanine Aminotransferase Activity in Rat
Figure 10 Effect of S.dulcificum Methanolic Extract Administration on Aspartate Aminotransferase Activity in Rat
Figure 11 Effect of S.dulcificum Methanolic Extract Administration on Bilirubin Concentration in Rat
Figure 12 Effect of S.dulcificum Methanolic Extract Administration on Total Serum Protein in Rat
Figure 13 Effect of S.dulcificum Methanolic Extract Administration on Serum Albumin in Rat
Figure 14 Effect of S.dulcificum Methanolic Extract Administration on Serum Globulin in Rat
Figure 15 Effect of S.dulcificum Methanolic Extract Administration on Creatinine Level in rat
Figure 16 Effect of S.dulcificum Methanolic Extract Administration on Urea Level in Rat
Figure 17 Effect of S.dulcificum Methanolic Extract Administration on Blood Glucose Concentration in Rat
Figure 18 Effect of S.dulcificum Methanolic Extract Administration on Total Cholesterol in Rat
Figure 19 Effect of S.dulcificum Methanolic Extract Administration on High-Density Lipoprotein Cholesterol Concentration in Rat
Figure 20 Effect of S.dulcificum Methanolic Extract Administration on Low-Density Lipoprotein Cholesterol Concentration in Rat
Figure 21 Effect of S.dulcificum Methanolic Extract Administration on Triacylglycerol Concentration in Rat
Figure 22 Effect of S.dulcificum Methanolic Extract Administration on Malondialdehyde Concentration in Rat
Figure 23 Photomicrograph of Liver Sections of Rats 14 days Post Administration With S.dulcificum Methanolic Extract
Figure 24 Photomicrograph of Liver Sections of Rats 28 days Post Administration With S.dulcificum Methanolic Extract
Figure 25 Photomicrograph of Kidney Sections of Rats 14 days Post Administration With S.dulcificum Methanolic Extract
Figure 26 Photomicrograph of Kidney Sections of Rats 28 days Post Administration With S.dulcificum Methanolic Extract
LIST OF TABLES
Table 1: Uses for Common Artificial Sweeteners
Table 2: The Levels of Some Minerals in S. dulcificum Pulp
Table 3: Vitamin Content of S.dulcificum Pulp
Table 4: Phytochemical Composition of S.dulcificum Pulp
Table 5: Antinutrient Composition of S. dulcificum Pulp
Table 6: Result of the Acute Toxicity (LD50) Test of the Methanolic Pulp Extract of S. dulcificum
Table 7: The Mean Body Weight of Rats Administered Doses of S. dulcificum Methanolic Pulp Extract
The worsening food crisis and the consequent widespread prevalence of malnutrition in developing and under-developed countries have resulted in high mortality and morbidity rates, especially among infants and children in low-income groups (Enujiugba and Akanbi, 2005). Food has been defined as any substance containing primarily carbohydrates, fats, water, protein, vitamins and minerals that can be taken by an animal or human to meet its nutritional needs and sometimes for pleasure. Items considered as food may be sourced from plants, animals or fungus as well as fermented products like alcohol. Food is also anything solid or liquid that has a chemical composition which enables it provide the body with the material from which it can produce heat or any form of energy, provide material to allow for growth, maintenance, repair or reproduction to proceed and supply substances, which normally regulate the production of energy or the process of growth, repair or reproduction. Food is therefore, the most basic necessity of life (Turner, 2006).
Nutrition is the science that deals with all the various factors of which food is composed and the way in which proper nourishment is brought about. The average nutritional requirements of groups of people are fixed and depend on such measurable characteristics as age, sex, height, weight, degree of activity and rate of growth. Good nutrition requires a satisfactory diet which is capable of supporting the individual consuming it, in a state of good health by providing the desired nutrients in required amounts. It must provide the right amount of nutrients and fuel to execute normal physical activity. If the total amount of nutrients provided in the diet is insufficient, a state of under- nutrition develops.
Plants are primary sources of medicines, food, shelters and other items used by humans everyday. Their roots, stems, leaves, flowers, fruits and seeds provide for humans (Amaechi, 2009; Hemingsway, 2004). Fruits are sources of minerals, fibre and vitamins which also provide essential nutrients for the human health (Anaka et al., 2009). Some fruits are also known to have antinutritional factors such as phytate and tannins,that can diminish the nutrient bioavailability if they are present at high concentrations (Baum, 2007). It has been reported that these anti-nutritional factors could also help in the treatment and prevention of certain important diseases like the anti-carcinogenic activities reported for phytic acid which has been demonstrated both invivo and invitro (Anaka et al., 2009).
The reliance on starchy roots and tubers and certain cereals as main staples result in consumption of non-nutritious foods. The insufficient availability of nutrient rich diets and the high cost of available ones have prompted an intense research into harnessing the potentials of the lesser known and underutilized crops, which are potentially valuable for human and animal foods to maintain a balance between population and agricultural productivity, particularly in the tropical and sub-tropical areas of the world. The challenge of improper nutrition especially in developing countries which include Nigeria, is indeed alarming. The World Health Organization (WHO, 2007) reported that poor nutrition contributes to one out of two deaths associated with infectious diseases among children within five yearsand the aged. Poor diet can have an injurious impact on health, causing deficiency diseases such as scurvy, beriberi and kwashiokor, health-threatening conditions such as obesity, metabolic syndrome, and such common other diseases as cardiovascular diseases, diabetes and osteoporosis. Under-nutrition among pregnant women in developing countries leads to one out of six infants being born with low birth weight, which is a risk factor for neonatal deaths, learning disabilities, mental retardation, poor health and premature death. One out of three people in developing countries is affected by vitamin and mineral deficiencies making them prone to infectious diseases and impaired psycho intellectual development. Under and chronic nutrition problems and diet related chronic diseases account for more than half of the world’s diseases (WHO, 2007). In most of these side effects or diseases, the biochemical and haematological parameters are usually altered. For a food to be considered safe for human and animal consumption, its effect on these parameters need to be investigated to understand the nutritional potentials and safety of such foods with a view to determining their acceptability.
Sweeteners are food additives that are used to improve the taste of everyday foods. Natural sweeteners are sweet-tasting compounds with some nutritional value; the major ingredient of natural sweeteners is either mono- or disaccharides. Artificial sweeteners, on the other hand, are compounds that have very little or no nutritional value. This is possible because artificial sweeteners are synthesized compounds that have high-intensities of sweetness, meaning less of the compound is necessary to achieve the same amount of sweetness. Artificial sweeteners are used in products intended to limit caloric intake or prevent dental cavities. Sugar alcohols are natural compounds with varying degrees of sweetness which are often added to boost or fine tune flavours of products while increasing their sweetness. They are often used in conjunction with natural or artificial sweeteners in order to achieve a desired degree of sweetness, taste or texture. Sugar alcohols typically provide some amount of nutrition but have other benefits such as not affecting insulin response or promoting tooth decay which makes them a popular sweetening choice.
Common Sweeteners and Their Production
A sugar substitute is a food additive that replicates the effect of sugar in taste, but usually has less food energy. Some sugar substitutes are natural while others are synthetic, those that are not natural are referred to as artificial sweeteners (Mattes and Popkin, 2009). An important class of sugar substitutes is known as high-intensity sweeteners. These are compounds with sweetness that is many times that of sucrose, a common table sugar. As a result, much less sweetener is required, and energy contribution often negligible. The sensation of sweetness caused by these compounds is sometimes notably different from sucrose, so they are often used in complex mixtures that achieve the most natural sweet sensation. This may be seen in soft drinks labelled as “diet” or “light”; they contain artificial sweeteners and often have notably different mouth feel. In the United States, six intensely-sweet sugar substitutes have been approved for use (Mattes and Popkin, 2009). They are saccharin, aspartame, sucralose, neotame, acesulfame potassium, and stevia. The US Food and Drug Administration regulates artificial sweeteners as food additives. The majority of sugar substitutes approved for food use are artificially-synthesized compounds. However, some bulk natural sugar substitutes are known, including sorbitol and xylitol, which are found in berries, fruit, vegetables and mushrooms (Mattes and Popkin, 2009). Some non-sugar sweeteners are polyols, also known as “sugar alcohols.” These are, in general, less sweet than sucrose, but have similar bulk properties and can be used in a wide range of food products. Sometimes the sweetness profile is ‘fine-tuned’ by mixing high-intensity sweeteners. As with all food products, the development of a formulation to replace sucrose is a complex proprietary process.
18.104.22.168 Natural Sweeteners
Natural sweeteners are extracted from natural products without any chemical modifications during the production or extraction process. Some of these sweeteners have been in use for decades while other for centuries. Natural sweeteners are well known and their production processes have been perfected over time making their cost low and leaving their demand high.
Honey is a sweet food made by certain insects using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans. Honey produced by other bees and insects has distinctly different properties. Honey bees transform nectar into honey by a process of regurgitation and evaporation. They store it as a food source in wax honeycombs inside the beehive (National Honey Board, 2012). Beekeeping practices encourage overproduction of honey so that the excess can be taken without endangering the bee colony. Honey gets its sweetness from the monosaccharides fructose and glucose and has approximately the same relative sweetness as that of granulated sugar (74% of the sweetness of sucrose, a disaccharide) (NHB, 2012). It has attractive chemical properties for baking, and a distinctive flavour which leads some people to prefer it over sugar and other sweeteners. Most micro-organisms do not grow in honey because of its low water activity (Arcot and Brand-Miller, 2005). The main uses of honey are in cooking, baking, as a spread on breads, and as an addition to various beverages such as tea and as a sweetener in some commercial beverages. Honey is also used as an adjunct in beer. Its glycaemic index ranges from 31 to 78, depending on the variety (Arcot and Brand-Miller, 2005).
Honey is a mixture of sugars and other compounds. With respect to carbohydrates, honey is mainly fructose (about 38.2%) and glucose (about 31.0%).The remaining carbohydrates in honey include maltose, sucrose, and other complex carbohydrates (Martos et al., 2000). Honey contains trace amounts of several vitamins and minerals (Gheldof et al., 2002). As with all nutritive sweeteners, honey is mostly sugars and is not a significant source of vitamins or minerals. Honey also contains tiny amounts of several compounds thought to function as antioxidants, including chrysin, pinobanksin, vitamin C, catalase, and pinocembrin (Gheldof et al., 2002). The specific composition of any batch of honey depends on the flowers available to the bees that produce the honey. A typical honey analysis shows the following: fructose: 38.2%, glucose: 31.0%, sucrose: 1.5%, maltose: 7.2%, water: 17.1%, higher sugars: 1.5%, ash: 0.2%. Honey has a density of about 1.36 kg/L (36% denser than water) (NHB, 2012). The pH of honey is between 3.2 and 4.5. This relatively acidic pH level prevents the growth of many bacteria (Arcot and Brand-Miller, 2005).
Maple syrup is a sweetener made from the sap of some maple trees. In cold climate areas, these trees store sugar in their roots before the winter and the sap which rises in the spring can be tapped and concentrated (Ball, 2007). The sap has only 3 to 5% total solids, consisting mainly of sucrose. Other components of the maple syrup include organic acids (primarily malic acid) and minerals (potassium and calcium), amino compounds (trace) and vitamins (trace). Maple Syrup has about the same 50 cal/tbsp as white cane sugar. However, it also contains significant amounts of potassium (35 mg/tbsp), calcium (21 mg/tbsp), small amounts of iron and phosphorus, and trace amounts of β- complex vitamins. Its sodium content is as low as 2 mg/tbsp. The sugar content of sap averages 2.5% and the sugar content of syrup averages 66.5% (Ball, 2007).
Molasses is a viscous byproduct of sugar cane or sugar beets processing into sugar. The quality of molasses depends on the maturity of the sugar cane or sugar beet, the amount of sugar extracted, and the method of extraction exployed (Taubes, 2011). Molasses has the molecular formula C6H12NNaO3S, molecular weight of 201.22 g/mol, and a density of 1.41 g/cm3 (Taubes, 2011). A typical composition of molasses shows the following substances: sucrose 35.9 %, fructose 5.6 %, nitrogen 1.01 %, reducing substances 11.5 %, glucose 2.6 %, and sulfur 0.78 % (Taubes, 2011).
Stevia is one of the newest sweeteners available in the market. It has been known since 1899 for its sweet taste and has been cultivated in Japan since 1970. It was not until recently that a safe and successful extraction of glycosides (the chemical in the Stevia plant which gives it a sweet taste) allowed for the Food and Drug Administration (FDA) to approve Stevia as a general sweetener (Raji and Mohamed, 2012). Stevia is also known under different trade names as TruVia and PureVia patents by Coca Cola and Pepsi(Raji and Mohamed, 2012). Many different forms of Stevia as sweeteners exist such as: Reb A, B, C, D, Rebiana, Stevioside, Sun Crystals and Enliten. Each has a small variation in the manufacturing process or how it is used.
Stevia is an all natural sweetener because it is extracted from the Stevia plant and undergoes no chemical changes in the manufacturing process. This makes it very desirable to many consumers looking for healthy alternatives to sucrose sugar. Stevia is a general term referring to a plant, Stevia Rebaudiana (Bertoni), native to Paraguay. The plant contains a number of diterpene glycosides that taste sweet; the main ones are stevioside and rebaudioside A. These glycosides are 200 and 300 times sweeter than sucrose respectively (Mattes and Popkin, 2009).
Sucrose is a disaccharide, formed from the monosaccharides glucose and fructose. It is the organic compound commonly known as table sugar and sometimes called saccharose.It has the molecular formula C12H22O11 and a molecular weight of 342.30 g/mol. In sucrose, the component sugars glucose and fructose are linked via an α (alpha) 1 on the glucose, to a β (beta) 2 on the fructose glycosidic linkage.
Sucrose forms a major element in confectionery and desserts. Cooks use it for sweetening, its fructose component which has almost double the sweetness of glucose makes sucrose distinctively sweet in comparison to other carbohydrate foods (Taubes, 2011). It can also act as a food preservative when used in sufficient concentrations. It is a common ingredient in many processed and junk foods.
Artificial sweeteners are derived from chemical synthesis of organic compounds which may or may not be found in nature. They are relatively new and their uses are being researched and extended every day. Much controversy surrounds artificial sweeteners and their health effects as they may break down into harmful chemical sub-compounds. New artificial sweeteners are always being researched and due to their low cost and ease of production, they will likely become the primary sweetening compounds in the future (Mattes and Popkin, 2009).
Synsepalum dulcificumis a shrub that grows up to 6.1m high in its native habitat but does not usually grow higher than 10ft (3.048m) in cultivation (Wiersema and Leon, 1999).Its leaves are 5-10cm long, 2-3.7cm wide and glabrous below. They are clustered at the end of the branchlets. It is an evergreen plant that produces small orange fruits (Duke and Ducellier, 1993). The seeds are about the same size as coffee beans (fig. 2). The plant is also known as Richardelladulcificum (old name), miracle fruit, magic fruit, miraculous or flavor fruit (Duke and Ducellier,1993). The miracle fruit plant (Synsepalum dulcificum) produces fruits or berries that, when eaten, causes sour foods (including lime and lemon) consumed later to taste sweet (fig. 3) (Joseph et al., 2009). The fruit was first documented by explorer Chevalier des Marchais who searched for many different foods during a 1725 excursion to its native West Africa (Rocklin and Leung, 1987). Marchais noticed that local tribes picked the fruit from shrubs and chewed it before meals.
The berry contains an active glycoprotein molecule, with some trailing carbohydrate chain called miraculin (Forester and Waterhouse, 2009). When the fleshy part of the fruit is eaten, the molecule binds to the tongue’s taste buds, causing sour foods to taste sweet. While the exact cause of this change is unknown, one theory is that the glycoprotein, miraculin works by distorting the shape of sweetness receptors so that they become responsive to acids, instead of sugar and other sweet things (Duke and Ducellier,1993).This effect can last for 10min-2hr (Joseph et al.,2009).
In Africa, S. dulcificum leaves are attacked by lepidopterous larvae and fruits are infested with larvae of fruit flies. A fungus which has been found on this plant is microporous (Duke and Ducellier, 1993). In tropical West Africa where this specie originates, the fruit pulp is used to sweeten palmwine (Joseph et al., 2009). Attempts have been made to make a commercial sweetener from this fruit with an idea of developing this for patients with diabetes (Joseph et al., 2009). Fruit cultivators also report a small demand from cancer patients, because the fruit allegedly counteracts a metallic taste in the mouth that may be one of the many side effects of chemotherapy. This claim has not been researched scientifically. In Japan, miracle fruit is popular among patients with diabetes and dieters (Duke and Ducellier, 1993).
The detailed scientific classification of the plant is as follows:
Binomial name: Synsepalumdulcificum
(Source: Wiersema and Leon, 1999)
A nutrient is any substance that is assimilated by an organism to promote growth (Harper, 1999). Nutrients consist of various chemical substances in the foods that make up each diet. Many nutrients are essential for life and an adequate amount of the nutrients in the diet is necessary for providing energy, building and maintaining of the body organs and for various metabolic processes (Morrison and Mark, 1999). There are six major classes of nutrients found in the food: carbohydrate, protein, fats, vitamins (both fat soluble and water soluble), mineral and water.
Carbohydrates are one of the main dietary components of food. This category of foods includes sugars, starches and fibres. Carbohydrates are important in the body as sources of energy. They can be found in a wide range of plant and animal food sources. In plants, they are generally end products of photosynthesis- the process in which plants convert carbon dioxide and water into simple sugars such as glucose. In foods, carbohydrates are important for adding flavour, texture and colour (Harper, 1999).
Dietary proteins are powerful compounds that build and repair body tissues from hair and fingernails to muscles. In addition to maintaining the body’s structure, proteins as enzymes speed up chemical reactions in the body, as well as serve as chemical messengers in the body, fight infection and transport oxygen from the lungs to the body’s tissues. Proteins play an important role in biochemical, biophysical and physiological processes. The deficiency of proteins lead to weakness, anaemia, protein-energy malnutrition (kwashiorkor and marasmus), delayed wound and fracture healing, decreased resistance to infection because antibody formation is decreased and sprue syndrome (Wardlaw,1999).
Fats in the body serve as energy sources and as protective cushion around organs.
Saturated fats are usually solid at room temperature while unsaturated fats remain liquid at room temperature. They provide insulation for the body, protect vital organs, and aid in the absorption and transportation of the fat soluble vitamins A, D, E and K. A lot of health disorders arise when proper amount of essential fats are not absorbed. This leads to autoimmune, inflammatory and cardiovascular diseases (Wardlaw, 1999). Those suffering from degenerative diseases such as obesity, cancer, cardiovascular disease, diabetes and liver disorders usually have low levels of essential fatty acids in their tissues. A deficiency of some essential fats will retard growth and produce eczema, acne, dry skin and dandruff, dull, brittle and sparse hair, soft brittle and flaking nails, dry eyes and mouth, diarrhoea, allergies, varicose vein, decreased or increased weight,gallstone, decreased radiation resistance, heart disease ,cancers, deterioration of skin, sterility, swollen joints, liver deterioration, fatigue, emotional agitation, decreased immunity, e.t.c. Excess fat has been shown to produce an abnormal weight gain and diminishing metabolism (Wardlaw, 1999).
Phytochemicals are naturally occurring, biologically active chemical compounds in plants. They act as a natural defence system for host plants and provide colour, aroma and flavor. Phytochemicals are protective and disease-preventing particularly for some form of cancer and heart disease. The most important action of these chemicals with respect to human beings is somewhat similar in that they function as antioxidants that react with the free oxygen molecules or free radicals in our bodies (Sofowora, 1993). Phytochemicals that have been discovered are grouped based on function and sometimes sources. These groupings include the flavonoids, phyto-estrogens, phytosterols and carotenoids. These classes and others can be further divided into subclasses (Frantisek, 1991). The flavonoids include more than 1500 separate compounds with varied functions. Flavonoids enhance the effect of vitamin C and function as antioxidants. They are also known to be biologically active against liver toxins, tumours, viruses and other microbes, allergies and inflammation (Sofowora, 1993). Some of the important flavonoids include hesperidin, quercitin, tangeretin, resveratrol and anthocyanins. Phyto-oestrogens are naturally occurring plant compounds that structurally resemble mammalian oestrogen. They copy or counteract the effect of oestrogen in the body. Consumption of isoflavone, a phytoestrogen, is associated with cancer prevention, improved cardiovascular health and bone health (Evans, 2005). Phytosterols are plant sterols that occur in many plant species but appear to be more abundant in the seed of green and yellow vegetables. They are important in the human diet because they help to reduce the amount of dietary cholesterol absorbed by the body by blocking uptake in the intestine. They also facilitate cholesterol excretion from the body. Carotenoids are plant pigments found in bright yellow, orange and red fruits and vegetables. Carotenoids are generally well known as vitamin A precursors (Frantisek, 1991). Phytochemicals are found in all plant products. Some good sources include vegetables, spinach, tomatoes, peppers, carrots, watermelon, citrus fruits, mangoes, papaya, grapes, apples, red grape, pears, oats, barley, sweet potatoes, corn, ginger, thyme, onions, green tea (Okaka et al., 1992).
Antinutrients are chemical substances found in food that usually interfere with digestion, absorption or utilization of proteins (Price et al., 1987). The three broad classes of antinutrients are anti-proteins, anti-vitamins and anti-minerals.
Anti-proteins are substances that interfere with the digestion, absorption or utilization of proteins. They occur in many plants and some animals (Ayyagari et al., 1989). Various protease inhibitors affect proteolytic enzymes of the gut usually by binding to the enzyme’s active site. Lectins are anti-proteins that have binding site for cell receptors similar to what antibodies have. Hemagglutinins cause red blood cell to agglutinate. Trypsin and chymotrypsin inhibitors can be found in legumes, vegetables, milk, wheat and potatoes (Ayyagari et al., 1989).
Antivitamins are substances that inactivate or destroy vitamins or inhibit the activity of a vitamin in a metabolic reaction and increase an individual’s need for the vitamins. They destroy or inhibit the metabolic effect of vitamins. Examples of antivitamins in foods include thiaminase (an antivitamin B present in raw fish and other animal foods), caramel colourants (antivitamin B6) and dicoumarol (antivitamin K). Antinutrients are sometimes consumed as natural component of food or medication (Liener, 1980). These vitamins can cause deficiency symptoms similar to those observed when the corresponding vitamins are not present. The administration of the specific vitamins reverses the deficiency symptoms. Isotonic acid hydrazide, also called isoniazid used to treat tuberculosis, can cause deficiency of niacin and vitamin B6. The deficiency symptoms are reversed after giving supplement of these two vitamins.
Anti-minerals are substances that interfere with absorption and metabolic utilization of minerals. Some examples are phytates, oxalates, glucosinolates, dietary fibre and gossypol. Phytic acid is found in bran and germ of many seeds and grains, legumes and nuts. In addition, phytic acid can compromise the absorption of magnesium, zinc, copper and manganese, usually forming precipitates. Formation of soybean-phytate complexes during processing has been associated with a reduction in bioavailability of minerals such as Ca, Zn, Fe and Mg. On the other hand, fermentation and other processing techniques are useful in reducing phytate levels (Liener, 1980). Oxalic acid, like phytic acid reduces the availability of bivalent cations. Sources of oxalic acid include rhubarb, spinach, beets, potatoes, teas, coffee and cocoa. Glucosinolates reduce an enlargement of the thyroid gland and inhibit iodine uptake into the thyroid. Rutabaga, turnips, cabbage, peaches and strawberries are good sources of glucosinolates (Liener, 1980).
Vitamins are essential organic substances needed in small amounts in the diet for the normal function, growth and maintenance of body tissues. Although vitamins themselves provide no energy to the body, some can facilitate energy–yielding chemical reactions. Vitamins A, D, E and K dissolve in organic solvents such as ether and benzene and are referred to as fats – soluble vitamins. The B-vitamins and vitamins C, in contrast, dissolve in water and are the water soluble vitamins.
Vitamins are generally indispensable in human diets because they can’t be synthesized in sufficient quantities to meet individual needs. Again synthesis is curtailed by environmental factors or they also can’t be synthesized at all (Hampl and Gordon, 2007).
To be classified as a vitamin, the compound must be organic and must meet the criteria to be an essential nutrient – the body is unable to sy nthesize enough of the compound to maintain health and the absence of the compound from the diet for a defined period of time produces deficiency symptoms that, if caught in time, are quickly cured when the substance is resupplied. A substance does not qualify as a vitamin merely because the body can’t make it. Evidence must suggest that health declines when the substance is not consumed (Hampl and Gordon, 2007).
Vitamin A (Beta-carotene)
Beta-carotene is an unstable fat-soluble primary alcohol. It is necessary for the production and resynthesis of rhodopsin (visual purple) and may protect against (or reverse) radiation damage (Watty, 2000). Beta-carotene acts as an antioxidant to scavenge radiation induced oxygen radicals and reduce lipofuscin (a component of drusen).
Consuming foods rich in beta-carotene appears to protect the body from damaging molecules called free radicals (Gaziano et al., 2007). The antioxidant action of beta-carotene makes it valuable in protecting against and in some cases even reversing precancerous conditions affecting the breast, mucous membranes, throat, mouth, stomach, prostate, colon, cervix and bladder (Gaziano et al., 2007). Individuals with high levels of β-carotene intake have lower risks of lung cancer, coronary artery heart disease, stroke and age-related eye diseases than individuals with low levels of β-carotene intake. Too much intake of β-carotene may cause or and may be mistaken for jaundice (Gaziano et al., 2007). Beta-carotene is richly found in yellow, orange and green leafy fruits and vegetables such as carrots, spinach, lettuce, tomatoes, sweet potatoes, broccoli, cantaloupe and winter squash (Bjelakovic, 2007). Deficiency of vitamin A causes night blindness, xerophthalmia (an extreme dryness of the conjunctiva), keratosis (an epidermal lesion of tissue overgrowths) and infections (Watty, 2000).
Vitamin C (Ascorbic acid)
Ascorbic acid is a sugar acid with antioxidant properties. Its appearance is white to light-yellow crystals or powder, and it is water-soluble. One form of ascorbic acid is commonly known as vitamin C (Shigeoka et al., 2002). Most animals are able to produce this compound in their bodies and do not require it in their diet. In cells, it is maintained in its reduced form by reaction with glutathione, which can be catalysed by protein disulfide isomerase and glutaredoxins (Jacob, 1996). Ascorbic acid is a reducing agent and can reduce and neutralize reactive oxygen species generated by molecules such as H2O2 (Shigeoka et al., 2002). Vitamin C neutralizes potentially harmful reactions in the aqueous parts of the body, such as the blood and the fluid inside and surrounding cells (Khaw and Woodhouse, 1995). Vitamin C may help decrease total LDL cholesterol and triacylglycerol, as well as increase HDL levels. Vitamin C antioxidant activity may be helpful in the prevention of some cancers and cardiovascular diseases (Padayatty, 2003). It is found in high concentrations in ocular tissue. It is a potent antioxidant and prevents scurvy, a condition that causes ulceration of the gums, skin and mucous membranes. The antioxidants properties of vitamin C are thought to protect smokers, as well as people exposed to secondary smoking (passive smokers), from the harmful effects of free radicals (i.e. prevents the conversion of nitrates from tobacco smoke). As a powerful antioxidant, vitamin C may help to fight against cancer by protecting healthy cells from free-radical damage and inhibiting the proliferation of cancerous cells (Bjelakovic, 2007). In addition to its direct antioxidant effects, ascorbic acid is also a substrate for the antioxidant enzyme ascorbate peroxidase, a function that is particularly important in stress resistance in plant (Shigeokaet al., 2002). Foods containing the highest sources of vitamin C include green peppers, citrus fruit and juices, strawberries, tomatoes, pineapple, pawpaw, sweet and white potatoes, and cantaloupe (Jacob, 1996).
Vitamin D is a fat soluble vitamin that is used by the body in the absorption of calcium which is essential for normal development and maintenance of healthy teeth and bones. It helps in maintaining adequate blood levels of calcium and phosphorus. It is also called the ‘sunshine vitamin’ because the body manufactures the vitamin after being exposed to sunshine. Vitamin D is found in the following foods: dairy products like cheese, butter, margarine, cream, fortified milk, fish, oysters and fortified cereals. Deficiency of vitamin D leads to osteoporosis in adults or rickets in children. Excessive doses of vitamin D can result in increased calcium absorption from the intestinal tract. This may cause increased calcium resorption from the bones, leading to elevated levels of calcium in the blood. Kidney stones, vomiting and muscle weakness may also occur due to the ingestion of too much vitamin D.
1.6.4 Vitamin E
Vitamin E is a fat-soluble antioxidant vitamin known to occur in the human body and it prevents free radical damage of biological membranes (Traber and Atkinson, 2007). Vitamin E is actually a generic term that refers to all entities that exhibit biological activity of the isomer α – tocopherol. The alpha-tocopherols are the most widely available isomer that have the highest bio-potency effect in the body (Schneider, 2005).
Vitamin E appears to be the first line of defence against peroxidation of polyunsaturated fatty acids contained in cellular and subcellular membrane phospholipids (Murray et al., 2003). The phospholipids of the mitochondria, endoplasmic reticulum and plasma membranes possess affinities for α–tocopherol, and the vitamin appears to concentrate at these sites. The tocopherol acts as antioxidants, breaking free-radical chain reactions as a result of their ability to transfer phenolic hydrogen to a peroxyl free radical of a peroxidized polyunsaturated fatty acid. The phenoxyl free radical formed may react with vitamin C to regenerate tocopherol or it reacts with a further peroxyl free radical so that the chromane ring and the side chain are oxidized to the non-free radical product (Murray et al., 2003).
Vitamin E is an antioxidant that helps to stabilize cell membranes and protect the tissues of the skin, eyes, liver, breast and testis, which are more sensitive to oxidation (Watty, 2000). It retards cellular aging of the eyes due to oxidation, it strengthens the capillary walls and supplies oxygen to the blood, which is then carried to the eyes (Watty, 2000). Vitamin E is a blood thinner, which should be used with caution in cases of exudative (wet) muscular degradation. Vitamin E is found in many common foods, including vegetable oils (such as soybean, corn, cotton seed and safflower) and products made from these oils (margarine),avocado, milk, egg, wheat germ, nuts and green leafy vegetable (Schneider, 2005).
Vitamin K is a fat soluble vitamin that helps blood to clot and stop bleeding. Food sources of vitamin K include cabbage, cauliflower, spinach and other green leafy vegetables as well as cereals. Vitamin K is also made in the body by normal beneficial gastrointestinal bacteria. Deficiency problems of vitamin K are thin blood that does not adequately coagulate.
Antioxidants are radical scavengers which protect the human body against free radicals (Poteract, 1997). A free radical is an atom or molecule that has one or more unpaired electron(s) and is capable of independent existence (Halliwell et al., 1995). The most biologically significant free radicals are the reactive oxygen species (ROS) (Murray et al., 2000), which include hydroxyl radical (OH˚) and superoxide radical (O 2˚). ROS are formed due to various exogenous and endogenous factors such as exposure to radiation from the environment and the utilization of oxygen during aerobic respiration (Krishnaiah et al., 2007).
Imbalance in favour of the generation of reactive oxygen species against the activity of the antioxidant defences leads to a pathophysiological condition known as oxidative stress. Oxidative stress is defined, in general, as excess formation and/or insufficient removal of highly reactive molecules such as ROS (Johansen et al., 2005). Oxidative stress is associated with a lot of diseases such as cancer, atherosclerosis, diabetes, rheumatoid arthritis, Parkinson’s disease, malaria and HIV/AIDS (Aruoma, 1993).
MINERALS AND THEIR BIOLOGICAL FUNCTIONS
Minerals of biological importance are classified into macro and micro (trace) elements.
Macro minerals are those that are required by the system in large amounts while micro (trace) minerals are required in minute quantities. Macro minerals include calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), potassium (K) while micro minerals include iron (Fe), copper (Cu), zinc (Zn), iodine (I), chromium (Cr), selenium (Se) and manganese (Mn) (Chaney, 2002).
These minerals play very important roles in physiological activities.
1.8.1 Calcium (Ca)
Calcium is essential for living organisms in particular in cell physiology. A 70kg normal adult human body has about 1200g of calcium which amounts to about 1–2% of body weight. About 99% of it is found in mineralized tissues such as bones and teeth. The remaining 1% is found in the blood extracellular fluid, muscles and other tissues. In food, calcium occurs as salt or it gets associated with other dietary constituents in the form of complexes of calcium ions. Calcium must be released in a soluble and ionized form before it can be absorbed. Absorption occurs basically in the intestine (Girventet al., 2005).
Metabolic functions and deficiency symptoms of calcium
Calcium is required for normal growth and development of the skeleton. Adequate calcium intake is critical to achieving optimal peak bone mass (PBM) and modifies the rate of bone loss associated with aging (Girventet al., 2005). Calcium mediates some hormonal responses and is required by many enzymes as co-factor. Muscle contractility and normal neuromuscular activity and irritability require the presence of calcium (Chaney, 2002).
Calcium deficiency results in muscle cramp and osteoporosis. Chronic inadequate intake or poor intestinal absorption of calcium is suspected to play some role in the aetiologies of hypertension and colon cancer (Girventet al., 2005).
1.8.2 Magnesium (Mg)
Magnesium, another abundant mineral in the body is essential for healthy functions of the system. Total magnesium (50-60%) is found in bone while the other half, is found within body tissues and organs. About 1% is found in the blood (Rude, 1998; Girventet al., 2005).
Metabolic functions and deficiency symptoms of magnesium
Magnesium is required for several enzyme activities particularly those involving ATP synthesizing as ATP–Mg 2+ complex; and for neuromuscular transmission (Chaney, 2002). It also enhances the condensation of chromatin.
Magnesium deficiency does not appear to be a problem in healthy individuals since its homeostasis can be maintained by a wide range of intakes. Its deficiency is only seen as a secondary complication of a primary disease state as in cardiovascular and neuromuscular mal-functions, endocrine disorders and muscle wasting (Girventet al., 2005).
1.8.3 Zinc (Zn)
Zinc is a ubiquitous mineral in the body. It is the most abundant intracellular trace element. About 2g of zinc is found in adults with 60% and 30% are present in muscles and bones respectively. It is absorbed from the small intestine and transported in the plasma by albumin and a 2–macroglobulin (Girvent et al., 2005).
Metabolic functions and deficiency symptoms of zinc
Zinc functions as a cofactor. Over 300 zinc metalloenzymes that have been described to date include a number of regulatory proteins and both RNA and DNA polymerases (Chaney, 2002). The structural functions are found in the zinc finger motif in proteins. Zinc is required by protein kinases that participate in signal transduction processes (Girventet al., 2005).
Zinc deficiency in children is usually marked by poor growth and impairment of sexual development (Chaney, 2002). Poor wound healing results from zinc deficiency in both adults and children. Other malfunctions resulting from zinc deficiency include decreased taste sense and impaired immune function (Girvent et al., 2005).
The iron content of a typical 70kg adult man is approximately 4–5g. About two–thirds of this is utilized as functional iron such as haemoglobin, myoglobin and other haem (cytochromes and catalase) and non-haem (NADH dehydrogenase) enzymes. Others are stored as ferritin and hemosiderin (Girvent et al., 2005).
Iron from food is absorbed mainly in the duodenum by an active process that transports iron from the gut lumen into the mucosal cell. When required by the body for metabolic processes, iron passes directly through the mucosal cell into the blood stream where it is transported by transferrin, together with the iron released from old blood cells to the bone marrow and other tissues. Iron absorbed in excess is stored in the liver, spleen or bone marrow. It is usually released from these stores for utilization in times of high need, such as during pregnancy (Girventet al., 2005).
Metabolic functions and deficiency symptoms of iron
Iron present in haemoglobin and myoglobin is required for transport of oxygen during cellular respiration and storage in muscles. Being part of the tissue enzymes makes it critical for energy production. It also plays a role in the functioning of the immune system (Girvent et al., 2005).
A major deficiency symptom of iron is anaemia. This results from insufficient haemoglobin for the production of new erythrocytes. This is most common in infants, preschool children, adolescents and women of child–bearing ag e particularly in developing countries (Chaney, 2002).
1.8.5 Copper (Cu)
Copper is a micronutrient present in a number of important metallo enzymes including cytochrome C oxidase, dopamine-β-hydroxylase and superoxide dismutase (Chaney, 2002).
About 50–75% dietary copper is absorbed mostly thr ough the intestinal mucosa from a typical diet. The absorption of copper is primarily influenced by the amount ingested; increased ingestion leads to decreased absorption (Chaney, 2002). Other factors that influence the absorption of copper or that affect its bioavailability include the antagonistic effects of zinc, iron, ascorbic acid, sucrose and fructose (Girvent et al., 2005).
Metabolic functions and deficiency symptoms of copper
As a component of several enzymes, cofactors and proteins, it is essential for important bioactivities. It is required for proper functioning of the immune, nervous and cardiovascular systems. It plays a role in iron metabolism and formation of erythrocytes. It also functions as an electron transfer intermediate in redox reactions (Girventet al., 2005).
This is relatively rare in humans and animals on typical, varied diets. Most features of severe copper deficiency can be explained by a failure of one or more of the copper-dependent enzymes like superoxide dismutase, lysyl oxidase, tyrosinase, e.t.c. For instance, lysyl oxidase plays one of the most important and best understood roles of copper in the body (Girvent et al., 2005). This is the main enzyme involved in cross- linking of connective tissues. Optimal functioning of lysyl oxidase ensures the proper cross-linking of collagen and elastin, vital for the strength and flexibility of our connective tissue. A reduction in lysyl oxidase activity affects the integrity of numerous tissue including the skin, bones and blood vessels. Not surprising, some of the hallmarks of copper deficiency are connective tissue disorders, osteoporosis and blood vessel damage (Chaney, 2002).
Glucose transported through the blood stream from the intestines to other tissues and organs is the primary source of energy for the body’s cells (Spiller, 1992). Blood sugar concentration or glucose level is tightly regulated in the human body. Normal blood glucose level is maintained between 4 and 6mM. Normal blood glucose concentration (homeostasis) is about 90mg/100ml; which works out to 5mM/L as the molecular weight of glucose. The normal total amount of glucose in circulating blood is therefore about 3.3 to 7.0g (Henry, 2001). Glucose concentration rises after meal for an hour or two and is usually lowest in the morning, before the first meal of the day. Failure to maintain blood glucose in the normal range leads to conditions of persistently high (hyperglycaemia) or low (hypoglycaemia) blood sugar. Although it is called ‘blood sugar’, other simple sugars such as fructose and galactose aside from glucose are found in the blood. Only glucose concentrations are used as metabolic regulation signals (Sacher and Mcpherson, 2001). Despite the long intervals between meals and the occasional consumption of meals with a substantial carbohydrate load, human blood glucose concentrations normally remain within a remarkable narrow range. In most humans, this varies from about 80mg/dl to perhaps 120mg/dl (3.9 to 6.0mml/litre) except shortly after eating when the blood glucose concentration rises temporarily. In a healthy adult male of 75kg body weight with a blood volume of 5litres, a blood glucose level of 100mg/dl or 5.5mmol/litre corresponds to about 5g in the total body water (Henry, 2001).
1.9.1 Blood glucose regulation
The homeostatic mechanism which keeps the blood value of glucose in a remarkably narrow range is composed of several interacting systems, of which hormone regulations is the most important. There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels: catabolic hormones such as glucagon, growth hormone (e.g. pituitary hormone), glucocorticoids(e.g. cortisol) and catecholamines (e.g. norepinephrine, epinephrine,dopamine) which increase blood glucose; anabolic hormone (insulin), which decreases blood glucose.
The human body maintains blood glucose in a very narrow range. Insulin and glucagon are the hormones which make this possible(John and Harry, 2001). Both insulin and glucagon are secreted from the pancreas, and thus are referred to as pancreatic endocrine hormones. It is the production of insulin and glucagon by the pancreas which ultimately determines if a patient has diabetes, hypoglycemia, or some other forms of sugar problems (John and Harry, 2001).
Insulin is normally secreted by the beta cells (a type of islet cells) of the pancreas. The stimulus for insulin secretion is high blood glucose. Although there is always a low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Similarly, as blood glucose falls, the amount of insulin secreted by the pancreatic islets goes down. Insulin has an effect on a number of cells, including muscle, red blood cells, and fat cells. In response to insulin, these cells absorb glucose out of the blood, having the net effect of lowering the high blood glucose levels the normal range (John and Harry, 2001).
Glucagon is secreted by the alpha cells of the pancreatic islets in much the same manner as insulin except in the opposite fashion. If blood glucose is high, then no glucagon is secreted. When blood glucose goes low, however, (such as between meals and during exercise), more and more glucagon is secreted. The effect of glucagon is to make the liver release the glucose it has stored in its cells into the blood stream, with the net effect of increasing blood glucose.
Lipids constitute a group of naturally occurring molecules that include fats, waxes, sterols, fat soluble vitamins (such as vitamins A, D, E and K), monoacylglycerol, diacylglycerol, triacylglycerol, phospholipids and others (Fahy et al., 2009). The main biological function of lipids includes energy storage, signaling and acting as structural components of cell membranes (Fahy et al., 2009). Lipids have found application in cosmetic and food industries as well as in nanotechnology (Mashaghi et al., 2013).
Lipids may be broadly defined as hydrophobic or amphiphilic small molecules, the amphiphilic nature of some lipids allow them to form structures such as vesicles, liposomes or membranes in an aqueous environment. Biological lipids originate entirely or in part from two distinct types of biochemical subunits or “building blocks”: ketoacyl and isoprene groups (Fahy et al., 2009). Although the term lipids is sometimes used as alternative for fats, fats are a group of lipids called triacylglycerol. Lipids also encompass molecules such as fatty acids and their derivatives as well as other sterol containing metabolites such as cholesterol. Although humans and other mammals use various biosynthetic pathways to breakdown and synthesize lipids, some essential lipids cannot be made this way and must be obtained from the diet (Fahy et al., 2009).
1.10.1 Lipoproteins: Types and Functions
Lipoproteins consist of a non polar core and a single surface layer of amphipathic lipids. The non polar core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules. These are oriented so that their polar groups face outwards to the aqueous medium, as in the cell membrane. The protein moiety of a lipoprotein is known as apolipoprotein or apoprotein, constituting nearly 70% of some HDL as little as 1% of chylomicrons (Murray etal., 2008).
Because fat is less dense than water, the density of a lipoprotein decreases as the proportion of lipid to protein increases. In addition to FFA, four major groups of lipoproteins have been identified that are important physiologically and in clinical diagnosis. These include:
Chylomicrons, derived from intestinal absorption of triacylglycerol and other lipids; Very low density lipoproteins (VLDL, or pre- β – lipoproteins), derived from the liver for the export of triacylglycerol; Low-density lipoproteins (LDL, or β -lipoproteins), representing a final stage in the catabolism of VLDL; and High- density lipoproteins (HDL, or α- lipoprotein), involved in VLDL and chylomicron metabolism and also in cholesterol transport.
Triacylglycerol is the predominant lipid in chylomicrons and VLDL, whereas cholesterol and phospholipids are the predominant lipids in LDL and HDL, respectively. Lipoproteins may be separated according to their electrophoretic properties into α-,β-, and pre- β- lipoproteins.
Chylomicrons in connection with the movement of dietary triacylglycerols from the intestine to other tissues are the largest of the lipoproteins and the least dense, containing a high proportion of triacylglycerol. Chylomicrons are synthesized in the endoplasmic recticulum of epithelial cells that line the small intestine, then move through the lymphatic system and enter the bloodstream via the left subclavian vein (Nelson and Cox, 2005).
Larger particles are catabolized more quickly than smaller ones. Fatty acids originating from chylomicron triacylglycerol are delivered mainly to the adipose tissue, heart and muscle (80%), while about 20% goes to the liver (Murray etal., 2008). However, the liver does not metabolize native chylomicrons or VLDL significantly; thus, the fatty acid in the liver must be secondary to their metabolism in extrahepatic tissues (Murray etal., 2008).
The apoproteins of chylomicrons include apo B-48(unique to this class of lipoproteins), apoE, and apoC-II. ApoC-II activates lipoprotein lipase in the capillaries of adipose, heart, skeletal muscle, and lactating mammary tissues, allowing the release of free fatty acids to these tissues. Chylomicrons thus carry dietary fatty acids to tissues where they will be consumed or stored as fuel. The remnant of chylomicrons (depleted of most of their triacylglycerols but still containing cholesterol, apoE, and apoB-48) move through the bloodstream to the liver. Receptors in the liver bind to the apoE in the chylomicron remnants and mediate their uptake by endocytosis. In the liver, the remnants release their cholesterol and are degraded in lysosomes (Murray etal., 2008).
Very Low Density Lipoprotein (VLDL)
When diets contain more fatty acids than are needed immediately as fuel, they are converted to triacylglycerol in the liver and packaged with specific apolipoproteins into very-low-density-lipoprotein (VLDL). Excess carbohydrates in the diet can also be converted to triacylglycerols in the liver and exported as VLDLs (Nelson and Cox, 2005).
In addition to triacylglycerols, VLDLs contain some cholesterol and cholesteryl esters, as well as apoB-100, apoC-I, apoC-II, apoC-III and apo-E.These lipoproteins are transported in the blood from the liver to muscle and adipose tissue, where activation of lipoprotein lipase by apoC-II causes the release of free fatty acids from the VLDL triacylglycerols. Adipocytes take up these fatty acids, reconvert them to triacylglycerols and store the products in intracellular lipid droplets; mycocytes in contrast, primarily oxidize the fatty acids to supply energy. Most VLDL remnants are removed from the circulation by hepatocytes. The uptake, like that for chylomicrons, is receptor-mediated and depends on the presence of apoE in the VLDL remnants. The loss of triacylglycerol converts some VLDL to VLDL remnants (also called intermediate density lipoprotein, IDL) (Nelson and Cox, 2005).
Low Density Lipoprotein (LDL)
Metabolism of low density lipoprotein via LDL receptor
The liver and many extrahepatic tissues express the LDL (B-100, E) receptor. It is so designated because it is specific for apoB-100 but not B-48, which lacks the carboxyl terminal domain of B-100 containing the LDL receptor ligand, and it also takes up lipoproteins rich in apoE. This receptor is defective in familial hypocholesterolemia. Approximately 30% of LDL is degraded in extrahepatic tissues and 70% in the liver. A positive correlation exists between the incidence of coronary atherosclerosis and the plasma concentration of LDL cholesterol (Murray et al., 2008).
Regulation of LDL receptor
Low density lipoprotein (LDL) receptor is highly regulated. LDL (apo B-100,E) receptors occur on the cell surface in the pits that are coated on the cytosolic side of the cell membrane with a protein called clathrin. The glycoprotein receptor spans the membrane the B-100 binding region being at the exposed amino terminal end. After binding, LDL is taken up intact by endocytosis. The apoprotein and cholesteryl esters are then hydrolysed in the lysosome and cholesterol is translocated into the cell. The receptors are recycled to the cell surface. This influx of cholesterol inhibits in a co-ordinated manner HMG-CoA synthase, HMG CoA reductase and therefore cholesterol synthesis; stimulates ACAT activity and down-regulates synthesis of LDL receptor. Thus, the number of LDL receptors on the cell surface is regulated by the cholesterol requirement for membranes, steroid hormones, or bile acid synthesis. The apo B-100, E receptor is a ‘high affinity’ LDL receptor, which may be saturated under most circumstances. Other ‘low- affinity’ LDL receptors also appear to be present in addition to a scavenger pathway, which is not regulated (Murray etal., 2008).
In Western countries, the total plasma cholesterol in humans is about 5.2mmol/L, rising with age, though there are wide variations between individuals. The greater part is found in the esterified form. It is transported in lipoprotein of the plasma and the highest proportion of cholesterol is found in the LDL. Dietary cholesterol equilibrates with the plasma cholesterol in days and with tissue cholesterol in weeks. Cholesteryl esters in the diet are hydrolysed to cholesterol, which is then absorbed by the intestine together with dietary unesterified cholesterol and other lipids. With cholesterol synthesized in the intestines,it is then incorporated into chylomicrons. Of the cholesterol absorbed, 80-90% is esterified with long-chain fatty acids in the intestinal mucosa. Ninety-five percent of the chylomicron cholesterol is delivered to the liver in chylomicron remnants, and most of the cholesterol secreted by the liver in VLDL is retained during the formation of LDL and ultimately LDL, which is taken up by the LDL receptor in liver and extrahepatic tissues (Murray etal., 2008).
Further removal of triacylglycerol from VLDL produces low density lipoprotein (LDL). Very rich in cholesterol and cholesteryl esters and containing apoB-100 as their major apolipoprotein, LDLs carry cholesterol to extrahepatic tissues that have specific plasma membrane receptors that recognize apoB-100. These receptors mediate the uptake of cholesterol and cholesteryl esters (Nelson and Cox, 2005).
High Density Lipoprotein (HDL)
The fourth major lipoprotein type, high-density lipoprotein (HDL), originates in the liver and small intestine as small, protein-rich particles that contain relatively little cholesterol and no cholesteryl esters. HDLs contain apoA-I, apoC-I, apoC-II, and other apolipoproteins, as well as the enzyme lecithin-cholesterol acyltransferase (LCAT), which catalyses the formation of cholesteryl esters from lecithin (phosphatidylcholine) and cholesterol. LCAT on the surface of nascent (newly forming) HDL particles converts the cholesterol and phosphatidylcholine of chylomicron and VLDL remnants to cholesteryl esters, which begin to form a core, transforming the disk-shaped nascent HDL to a mature, spherical HDL particle. This cholesterol- rich lipoprotein then returns to the liver, where the cholesterol is unloaded, some of this cholesterol is converted to bile salts (Nelson and Cox, 2005).
HDL may be taken up in the liver by receptor mediated endocytosis, but at least some of the cholesterol in HDL is delivered to other tissues by a novel mechanism.HDL can bind to plasma membrane receptor proteins called SR-B1 in hepatic and steroidogenic tissues such as the adrenal gland. This receptor mediates not only endocytosis but also partial and selective transfer of cholesterol and other lipids in HDL into the cell (Nelson and Cox, 2005).
Depleted HDL then dissociates to recirculate in the bloodstream and extract more lipids from chylomicron and VLDL remnant. Depleted HDL can also pick up cholesterol stored in extrahepatic tissues and carry it to the liver, in reverse cholesterol transport pathways. In one reverse transport path, interaction of nascent HDL with SR-B1 receptors in cholesterol-rich cells triggers passive movement of cholesterol from the cell surface into HDL, which then carries it back to the liver. In a second pathway, apoA-I in depleted HDL interacts with an active transporter, the ABC1 protein, in a cholesterol- rich cell. The apoA-1(and presumably the HDL) is taken up by endocytosis, then resected with a load of cholesterol, which it transports to the liver (Nelson and Cox, 2005).
The ABC1 protein is a member of a large family of multidrug transporters, sometimes called ABC transporters, because they all have ATP- binding cassettes; they also have two transmembrane domains with six transmembrane helices. These proteins actively transport a variety of ions, amino acids, vitamins, steroid hormones and bile salt across plasma membranes. The CFTR protein that is defective in cystic fibrosis is another member of this ABC family of multidrug transporters (Nelson and Cox, 2005).
Total cholesterol and cholesterol balance in tissues
Cholesterol is a lipid that is made in the liver from fatty foods. It is found in cell membranes of all tissues and is transported in blood plasma of all animals. Cholesterol is also considered a sterol (Stryer, 1995). Most of the cholesterol in the body is synthesized by the body and some have dietary origin. Cholesterol is more abundant in tissues which either synthesize more or have more abundant densely packed membranes, for example, the liver, spinal cord and brain. It plays a central role in many biochemical processes such as the composition of cell membranes and the synthesis of steroid hormones (Smith, 1991). Since cholesterol is insoluble in blood, it is transported in the circulatory system within lipoproteins, complex spherical particles which have an exterior composed mainly of water, soluble proteins; fats and cholesterol are carried internally (Stryer, 1995). Cholesterol is required to build and maintain cell membranes; it regulates membrane fluidity over a wide range of temperature. Some research indicates that cholesterol also aid in the manufacture of bile and is also important for the metabolism of fat soluble vitamins and of the various steroid hormones (Haines, 2001). Conditions with elevated concentrations of oxidized LDL particles are associated with atheroma formation in the walls of arteries, a condition known as atherosclerosis, which is the principle cause of coronary heart disease and other forms of cardiovascular diseases. Abnormally low levels of cholesterol are termed hypocholesterolemia. Research into the cause of this state is relatively limited but some studies suggest a link with depression, cancer and cerebral haemorrhage. It is unclear whether the low cholesterol concentrations causes for these conditions or something which occurs along side them (Shepherd et al., 1995). Normal values for serum cholesterol are 3.6 or 5.0 – 6.5mmol/l or 120 or 140 – 200 or 250mg/dl (Deepak et al., 2007).
In tissues, cholesterol balance is regulated as follows: cell cholesterol increase is due to uptake cholesterol- containing lipoproteins by receptors e.g. the LDL receptor or the scavenger receptor; uptake of free cholesterol from cholesterol-rich lipoproteins to the cell membrane; cholesterol synthesis, and the hydrolysis of cholesteryl esters by the enzyme cholesteryl ester hydrolase. Decrease is due to the efflux of cholesterol from the membrane to HDL, promoted by LCAT (lecithin cholesterol acyltransferase); esterification of cholesterol by ACAT (acyl coA: cholesterol acyltransferase); and utilization of cholesterol for synthesis of other steroids, such as hormones or bile acids in the liver (Illingworth, 2000).