ANTIOXIDANT ACTIVITY AND PHYTOCHEMICAL PROPERTIES OF METHANOL, ETHANOL, AND HEXANE SOME EXTRACTS OF ALSTONIABOONEI LEAVES
In traditional setting, Alstoniaboonei is used for the treatment of different ailments, this has been attributed to its rich phytochemical and antioxidant properties.The objective of the study was to evaluate the phytochemical properties and antioxidant activity of the methanol, ethanol and hexane extracts of Alstoniaboonei leaves. Qualitative analysis of phytochemical constituents such as tannins, saponins, cardiac glycosides flavonoids and phenols were carried out. Quantitative analysis of total phenolics, saponins and flavonoids was performed by well-known test protocol. Antioxidant activity reveals the presence of reactive oxygen species which helps to scavenge free radicals that are present in the body. The in vitro antioxidant activity was studied by diphenyl-2-picryl-hydrazyl (DPPH), ferric reducing antioxidant power (FRAP), reducing power (RP) and ferrous ion metal chelating. Results obtained for phytochemical studies revealed that flavonoids were highest in ethanol extract(101.6±1.35) while hexane extract (56.6±1.510) had the lowest content. Also phenol was highest in methanol extract (262±4.93) and lowest in ethanol extract (172.7±1.66). Result for total tannins (271±6) and proanthocyanidin (200.7±2.19) indicates that methanol and ethanol extract had the highest amount while hexane extract had and the lowest amount. IC5o values obtained by DPPH for ethanol extracts of Alstoniaboonei (2.362µg/ml), when compared with other extracts, and was significantly (P>0.05) lower than that of the standard vitamin C (12.81µg/ml). Also, the ethanol extract(0.026µg/ml) showed low IC50 value for ferrous ion metal chelating ability when compared with other extract, but this value was non significantly(P>0.05) lower than the standard(4.11µg/ml). Therefore, Alstoniaboonei has a great potential for use as a natural source of antioxidant and also help in the treatment of various ailments, or against free radical damage.
TABLE OF CONTENTS
Title page - - - - - - - - - - i
Certification - - - - - - - - - ii
Dedication - - - - - - - - - - iii
Acknowledgement - - - - - - - - iv
Table of content - - - - - - - - - v
Abstract - - - - - - - - - - vii
1.0. Introduction - - - - - - - - - 1
1.1. Literature review - - - - - - - - 3
1.2. Geographical distribution - - - - - - - 4
1.3. Ecology - - - - - - - - - 4
1.4. Medicinal and non medicinal uses - - - - - 4
1.5.Common names/local names------6
1.6. Phenolics - - - - - - - - - 9
1.7. Flavonoids - - - - - - - - - 11
1.8. Antioxidants - - - - - - - - 18
1.10. Specific objectives - - - - - - - - 22
2.0. Materials and methods - - - - - - - 23
2.1. Reagents - - - - - - - - 23
2.2. Sample collection - - - - - - - - 25
Preparation of plant extract - - - - - - - 25
2.5 Extraction of the leaves using different solvents. - - - 26
2.6 Antioxidants assays - - - - - -- - 26
2.6.2 Reducing power assay - - - - - - - 28
2.6.3 Ferric reducing antioxidant power (frap assay) - - - 28
2.6.4 Ferrous ion chelating ability - - - - - 29
2.7 Quantitative determination of phytochemicals - - - 29
2.7.1 Total phenolic content - - - - - - - 30
2.7.2 Total flavonoids - - - - - - - - 30
2.7.3 Total proanthocyanidin - - - - - - - 30
2.7.4 Total tannins - - - - - - - - - 30
2.8 Qualitative determination of pytochemicals - - - - 31
3.1 Percentage yield - - - - - - - - 32
3.2 Qualitative phytochemicals - - - - - - 33
3.3 Quatitative phytochemicals------33
3.4 Reducing power - - - - - - - - 34
3.5 ferrous ion metal chelating - - - - - - - 35
3.6 diphenyl ̵ 2 ̵ picrylhydrazyl (DPPH) - - - - - 36
3.7 ferric reducing antioxidant power ( FRAP) assay - - - 37
4.2. Discussion - - - - - - - - - 38
4.2. Conclusion - - - - - - - - - 41
References - - - - - - - - - - 42
A medicinal plant is any plant used for the extraction of pure substances either for direct medicinal use or for hemi-synthesis of medicinal compounds which can be used for therapeutic purpose or as a precursor for the synthesis of useful drugs (Sofwora, 1982). Approximately 10% of these plants are used either as food or for medical purposes (Borris, 1996)
Medicinal plants have been the mainstay of traditional herbal medicine amongst rural dwellers worldwide since antiquity to date. The therapeutic use of plants certainly goes back to the Sumerian and the Akkadian Civilizations in about the third millennium BC. Hippocrates (ca.460-377BC) one of the ancient authors who described medicinal natural products of plant and animal origins listed approximately 400 different plant species for medicinal purposes. Natural products have been an integral part of the ancient traditional medicine systems e.g Chinese, Ayurvedic and Egyptian (Sarker and Nahar 2007). Over the years they have assumed a very central stage in modern civilization as natural source of chemotherapy as well as amongst scientist in search of alternative sources of drugs.
According to the World Health Organization, a medicinal plant is any which, in one or more of its organs, contain substances that can be used for therapeutic purpose, or which are precursors for chemo-pharmaceutical semi synthesis. Such a plant will have its parts including leaves, roots, rhizomes, stems, barks, flowers, fruits, grains or seeds employed in the control or treatment of a disease condition and therefore contain chemical components that are medically active.
Medicinal plants have been found to contain bioactive compounds called phytochemicals (phyto from Greek-phyto meaning plant) or phytoconstituents and are responsible for protecting the plant against microbial infections or infestations by pest (Abo et al., 1991;Lui, 2004;Nwezeet al.,2004; Doughariet al., 2009). They also contain secondary metabolite that can protect humans against diseases (Kumar et al., 2009). The study of natural products on the otherhand is called phytochemistry. Phytochemical have been isolated and characterized from fruits such as grapes and apples, vegetables such as broccoli and onion, spices such as turmeric, beverages such as green tea and red wine as well as many other sources (Doughari and Obidah, 2008; Doughariet al.,2009). Some important groups of thesePhytochemical (secondary metabolites) are involved in many in-vitro studies and assessment of haematological parameters, antioxidant, antimicrobial and analgesic effect (Finar, 1986).
This indigenous knowledge, passed down from generation to generation in various parts of the world, was significantly contributed to the development of different traditional systems of medicine. This exploration of biologically active products have played an important role in finding New Chemical Entities (NCEs) for example approximately 28% of NCEs n=between 1981 and 2002 were natural products or natural product derived (Newman et al., 2003).
Alstoniaboonei, a member of Apocynaceae family, is a deciduous plant found abundantly around Africa, from the rain forest of Senegal to Western Cameroon extending to Egypt in North and Uganda and Zaire in the East it is known by several common names in different localities (Amole and llori, 2010). Alstoniabooneiis reported to have adverse uses, it is given to ameliorate toothache and after child delivery, to aid in expelling the placenta. It is applied topically to reduce Oedema and to clear suppurant sores and exposed fractures. It is also used for ulcers and as a remedy for snake bite and arrow poison (Akinmoladunet al.,2007).
Traditional African medicine has also reported the use of Alstoniaboonei for treatment of chronic diarrhoea, dysentery, fever, pain and intestinal disorders (Amole and llori, 2010).
Numerous therapeutic properties have been attributed to Alstoniaboonei like antifugal, antibacterial, antiviral antithrombosis, anti-tumor. Anti-inflammatory, analgesic, antioxidant and antipyretic activities (Olayideet al., 2000; Akinloyeet al., 2013).
1.1. LITERATURE REVIEW
Bionomialname:Alstoniaboonei De wild. Burkhill H.M1985
1.2. GEOGRAPHICAL DISRIBUTION
Alstoniaboonei De Wild (Devil tree) of the family Apocynaceae, is an African evergreen deciduous crude medicinal tree up to 45m tall with bole branchless, fluted at the base with steep buttresses. They are mostly in forest up to 1200m altitude at places like Uganda, Gambia, Western Ethiopia and Senegal (Afolabiet al., 2007). It is found in dry peripheral Semi-evergreen Guineo-Congolian forest and transitional rainforest. It occurs in similar habitats and in swamp and riverine forest. Alstoniaboonei requires large amounts of light and colonizes gaps in the forest. It has plenty of natural regeneration in young secondary forest.
In Nigeria Alstoniaboonei occurs in moist low land and forest but may extend into drier types including gentle to steep, rocky hillsites in Liberia, but most commonly found scattered or in small groups in wet or marshy places that are occasionallyinundated it’s the tree of the swampy high forest in west Africa, it can tolerate a wide range of sites, from rocky hillslides to seasonal swamps in general it prefers damp situations but it grows satisfactorily on well drained slopes.
1.4. MEDICINAL AND NON MEDICINAL USES
Alstonia a genus of the family Apocynaceae to which many other medicinally important plants belong like Rauwolfia Serpentine and Vincarosea which have been producing well known remedy for various disorders like Schizophrenia and Cancer (Das et al., 2014). The traditional method of medications has long been known in the developing countries like India and China.
Previous study detected the presence of secondary metabolites such as alkaloids, tannins, Saponnins, resins, flavonoids, steroids, glycosides and terpenoids in the pulverized dried leaves (Kuceroet al.,1972;Fashola and Egunyemi., 2005; Afolabiet al., 2007). However the various species of Alstonia are highly rich in alkaloids, steroids and triterpenoids and phenolic compounds which contributes to the toxicity of Alstoniaboonei. Moreover the plant was found to contain poisonous alkaloid comprising ditamine, echitamine and echitamidine (Adoteyet al, 2012).
It’screamy white wood is utilized for light constructions in interior Joineries, Furniture, household equipments, sculptures, boats, boxes, matches, pencils, moldings and plywood. It serve as shade tree for people who want to relax under a shade and take their drinks, as well as in the cultivation of banana plantains. Famous Asante stools in Ghana and sound boxes of musical instruments of Nigerian Yorubasare made from Alstoniaboonei (Olajideet al.,2000). It is not edible as food, it possess roots, stems, banks, leaves, fruits, seeds, flowers and latex which are claimed to have medicinal properties in some cultures and climes. The plants and its latex are applied in traditional medicine for treating many diseases. There are records on the use of alcoholic or aqueous extracts of most parts of Alstoniaboonei. The stem bark is utilized for treating febrile illness, painful urination, rheumatic conditions and Jaundice (Ojewole, 1984; Asuzu andAnago 1991), malaria fever (Phillipsonet al., 1987; Majekodunniet al., 2008; Bello et al., 2009; Mazekodunmi and Odeku, 2009).Intestinal helminthes (Wescheet al., 1990). Rheumatism, reversible anti-fertility (Rajiet al., 2005), and hypertension (Olajideet al., 2000; Terashima, 2003; Abel and Busia, 2005; Belti, 2007).As an anti-venon against snake bite and antidote against arrowpoisoning.Other pharmacological uses are anti-inflammatory, antipyretic and as an analgesic (Olajide., 2000).
1.5. COMMON NAMES/LOCAL NAMES
English (stool wood, cheese wood, pattern wood, alstonia, luganda (mujua, mubaJandalabi, mukoge, musoga), Ghana (sinupo), Cameroon (botuk), Ivory Coast (emien). (Amole and llori, 2010), Yoruba (Ahun), Igbo (Egbu-ora), Edo (Ukhu) and Urhobo (Ukpukunu), (Dalziel., 1997; Bever, 1986).
Alstoniaboonei is a large deciduous tree, up to 45 m tall and 1.2 m in diameter; bole often deeply fluted to 7 m, small buttresses present; bark greyish-green or grey, rough; slash rough-granular, ochre-yellow, exuding a copious milky latex; branches in whorls.
Leaves in whorls of 5-8, simple, subsessile to petiolate, stipules absent; petiole 2-10 (max. 15) mm long, stout; blade oblanceolate to obovate, rarely elliptic, 7-26 x 3-9.3 cm; apex acute to rounded or sometimes emarginate; base narrowly cuneate; margins entire, sub-coriaceous to coriaceous, dark shiny green top surface, light green on under surface; midrib more prominent below.
Inflorescence terminal, compound with 2-3 tiers of pseudo-umbels;
primary peduncles 0.5-7 cm long, greyish pubescent; bracts ovatetriangular, 1-1.5 mm long, pubescent; pedicels about 5 mm long. Flowers regular, hermaphrodite, pentamerous; calyx cupular tube about 1 mm long; lobes ovate, about 1.5 mm long, spreading; corolla pale green tube up to 14 mm long; lobes slightly obliquely ovate, up to 6 mm long and wide, pubescent outside.
Fruit formed by 2 pendent green follicles up to 60 cm long, longitudinally striate, dehiscing lengthways while on the tree; seeds numerous, flat, about 4 x 2 mm, with tufts of hair at each end 10 mm long. ‘Alstonia’ is named after Dr C. Alston (1685-1760), a professor of botany at Edinburgh University.
Phytochemicals (from the Greek word phyto, meaning plant) are biologically active, naturally occurring chemical compounds found in plants, which provide health benefits for humans further than those attributed to macronutrients and Micronutrients (Harvey,2004). Theyprotect plants from disease and damage and contribute to the plant’s colour, aroma and flavour. In general, the plant chemicals that protect plant cells from environmental hazards such as pollution, stress, drought, UV exposure and pathogenic attack are called as phytochemicals (Mathai, 2000). Recently, it is clearly known that they have roles in the protection of human health, when their dietary intake is significant. More than 4,000 phytochemicals have been catalogued and are classified by protective function, physical characteristics and chemical characteristics (Mueller,1999) and About 150 phytochemicals have been studied in detail. In wide-ranging dietary phytochemicals are found in fruits, vegetables, legumes, whole grains, nuts, seeds, fungi, herbs and spices (Mathai, 2000). Broccoli, cabbage, carrots, onions, garlic, whole wheat bread, tomatoes, grapes, cherries, strawberries, raspberries, beans, legumes, and soy foods are common sources. Phytochemicals accumulate in different parts of the plants, such as in the roots, stems, leaves, flowers, fruits or seeds. Many phytochemicals particularly the pigment molecules, are often concentrated in the outer layers of the various plant tissues. Levels vary from plant to plant depending upon the variety, processing, cooking and growing conditions(Moorachian,2000). Phytochemicals are also available in supplementary forms, but evidence is lacking that they provide the same health benefits as dietary phytochemicals .These compounds are known as secondary plant metabolites and have biological properties such as antioxidant activity, antimicrobial effect, modulation of detoxification enzymes, stimulation of the immune system, decrease of platelet aggregation and modulation of hormone metabolism and anticancer property. There are more than thousand known and many unknown phytochemicals. It is well-known that plants produce these chemicals to protect themselves, but recent researches demonstrate that many phytochemicals can also protect human against diseases (Narasinga,2003).
The exact classification of phytochemicals could have not been performed so far, because of the wide variety of them. In recent years Phytochemicals are classified as primary or secondary constituents, depending on their role in plant metabolism. Primary constituents include the common sugars, amino acids, proteins, purines and pyrimidines of nucleic acids, chlorophyll’s etc. Secondary constituents are the remaining plant chemicals such as alkaloids, terpenes, flavonoids, lignans, plant steroids, curcumines, saponins, phenolics,
flavonoids and glucosides. Literature survey indicate that phenolics are the most numerous and structurally diverse plant phytoconstituents.
Phenolic phytochemicals are the largest category of phytochemicals and the most widely distributed in the plant kingdom. The three most important groups of dietary phenolics are flavonoids, phenolic acids, and polyphenols.
Phenolic are hydroxyl group (-OH) containing class of chemical compounds where the (-OH) bonded directly to an aromatic hydrocarbon group. Phenol (C6H5OH) is considered the simplest class of this group of natural compounds. Phenolic compounds are a large and complex group of chemical constituents found in plants (Walton et al.,2003). They are plant secondary metabolites, and they have an important role as defence compounds. phenolics exhibit several properties beneficial to humans and its antioxidant properties are important in determining their role as protecting agents against free radical-mediated disease processes. Flavonoids are the largest group of plant phenols and the most studied (Dia and Mumper.,2010). Phenolic acids form a diverse group that includes the widely distributed hydroxybenzoic and hydroxycinnamic acids. Phenolic polymers, commonly known as tannins, are compounds of high molecular weight that are divided into two classes: hydrolysable and condensed tannins.
Fig 2. Phenol/chemical compound/Britannica.com
Flavonoids are polyphenolic compounds that are ubiquitous in nature. More than 4,000 flavonoids have been recognized, many of which occur in vegetables, fruits and beverages like tea, coffee and fruit drinks. The flavonoids appear to have played a major role in successful medical treatments of ancient times, and their use has persisted up to now. Flavonoids are ubiquitous vascular plants and occur as aglycones, glucosides and methylated derivatives. More than 4000 flavonoids have been described so far. within the parts of plants normally consumed by humans and approximately 650 flavones and 1030 flavanols are known(Harborne and Baxter, 1999). Small amount of aglycones (i.e., flavonoids without attached sugar) are frequently present and occasionally represent a considerably important proportion of the total flavonoid compounds in the plant . The six-membered ring condensed with thebenzene ring is either -pyrone (flavones and flavonols ) or its dihydroderivative (flavanone and flavan-3-ols ). The position of the benzenoid substituent divides the flavonoids into two classes: flavone (2-position) and isoflavone (3-position). Most flavoniods occur naturally associated with sugar in conjugated form and, within any one class, may be characterized asmonoglycosidic, diglycosidic, etc. The glycosidic linkage is normally located at position 3 or 7 and the carbohydrate unit can be L-rhamnose, Dglucose, glucorhamnose, galactose or arabinose (Pretorius et al.,2003)
Fig 3 Quercetin: A versatile flavanoid
From a chemical point of view it is difficult to define tannins since the term encompasses some very diverse oligomers and polymers. It might be said that the tannins are a heterogeneous group of high molecular weight polyphenolic compounds with the capacity to form reversible and irreversible complexes with proteins (mainly), polysaccharides (cellulose, hemicellulose, pectin, etc.), alkaloids, nucleic acids and minerals, etc(Schofield et al.,2001) . On the basis of their structural characteristics it is therefore possible to divide the tannins into four major groups: Gallotannins, ellagitannins, comtannins, and condensed tannins(Manga,1988).
Gallotannins are all those tannins in which galloyl units or their meta-depsidic derivatives are bound to diverse polyol-, catechin-, or triterpenoid units.
Ellagitannins are those tannins in which at least two galloyl units are C–C coupled to each other, and do not contain a glycosidically linked catechin unit. Complex tannins are tannins in which a catechin unit is bound glycosidically to a gallotannin or an ellagitannin unit. Condensed tannins are all oligomeric and polymeric proanthocyanidins formed by linkage of C-4 of one catechin with C-8 or C-6 of the next monomeric catechin. Tannins are found commonly in fruits such as grapes, persimmon, blueberry, tea, hocolate, legume forages, legume trees like Acacia spp., Sesbania spp., in grasses i.e; sorghum, corn, etc. Several health benefits have been recognized for the intake of tannins and some epidemiological associations with the decreased frequency of chronic diseases have been established (Serranoet al.,2009).In medicine, especially in Asian (Japanese and Chinese) natural healing, the tannin-containing plant extracts are used as astringents, against diarrhoea, as diuretics, against stomach and duodenal tumors, and as anti-inflammatory, antiseptic, antioxidant and haemostatic pharmaceuticals (Dolaraet al.,2005). Tannins are used in the dyestuff industry as caustics for cationic dyes (tannin dyes), and also in the production of inks (iron gallate ink). In the food industry tannins are used to clarify wine, beer, and fruit juices. Other industrial uses of tannins include textile dyes, as antioxidants in the fruit juice, beer, and wine industries, and as coagulants in rubber Production (Gyamfi and Aniya., 2002). Recently the tannins have attracted scientific interest, especially due to the increased incidence of deadly illnesses such as AIDS and various cancers. The search for new lead compounds for the development of novel pharmaceuticals has become increasingly important, especially as the biological action of tannin-containing plant extracts has been well documented(Muller-Harvey,1999).
Fig 4: Phytojournal.com
Alkaloids are natural product that contains heterocyclic nitrogen atoms, are basic in character. The name of alkaloids derives from the “alkaline” and it was used to describe any nitrogen-containing base. Alkaloids are naturally synthesis by a large numbers of organisms, including animals, plants, bacteria and fungi. Some of the fires natural products to be isolated from medicinal plants were alkaloids when they first obtained from the plants materials in the early years of 19th century, it was found that they were nitrogen containing bases which formed salts with acid. Hence they were known as the vegetable alkalis or alkaloids and these alkaloids are used as the local anaesthetic and stimulant as cocaine. Almost all the alkaloids have a bitter taste. The alkaloid quinine for example is one of the bitterest tasting substances known and is significantly bitter (1x10-5) at a molar concentration(Georgeet al.,2002). Alkaloids are so numerous and involve such a variety of molecular structure that their rational classification is difficult. However, the best approach to the problem is to group them into families, depending on the type of heterocyclic ring system present in the molecule. For historical reasons as also because of their structural complexities, the nomenclature of alkaloids has not been systematized. The names of individual members are therefore generally derived from the name of the plant in which they occur, or from their characteristic physiological activity. The various classes of alkaloids according to the heterocyclic ring system they contain are listed below.
Pyrrolidine alkaloids: they contain pyrrolidine(tetrahydropyrrole) ring system. E.ghygrine found in erythroxylum coca leaves. Pyridine alkaloids: they have piperidine (hexahydropyridine) ring system. E.g coniine, piperine and isopelletierinepyrrolidine-pyridine alkaloids: The heterocyclic ring system present in their alkaloids is pyrrolidinepyridine.E.gmyosmine, nicotine alkaloid found in pyridine-piperidinealkaloids:This family of alkaloids contains a pyridine ring system join to a piperidine ring system the simplest member is anabasine alkaloid isolated from poisonous Asiatic plant anabasis aphyllan.
Quinoline Alkaloids: These have the basic heterocyclic ring system quinoline .E.g quinine occurs in the bark of cinchona tree.It has been used for centuries for treatment of malaria.Synthetic drugs such as primaquinine have largely replace quinine as an anti-malarial.
Isoquinoline alkaloids: They contain heterocyclic ring system isoquinoline. E.g opium alkaloids like narcotine, papaverine, morphine, codeine, and heroine
Fig 5 LON-CAPA. Botany online: the secondary metabolism of plants-Alkaloids
Saponins are a group of secondary metabolites found widely distributed in the plant kingdom They form a stable foam in aqueous solutions such as soap, hence the name “saponin”. Chemically, saponinsasa group include compounds that are glycosylated steroids, triterpenoids, and steroid alkaloids. Two main types of steroid aglycones are known, spirostan and furostan derivatives. The maintriterpeneaglycone is a derivative of oleanane (Traoreet al.,2000). The carbohydrate part consists of oneor more sugar moieties containing glucose, galactose, xylose, arabinose, rhamnose, or glucuronic acid glycosidically linked to a sapogenin (aglycone). Saponins that have one sugar molecule attached at the C-3 position are called monodesmosidesaponins, and those that have a minimum of two sugars, one attached to the C-3 and one at C-22, are called bidesmosidesaponins(Lacailleet al.,2000)
Saponin: Wikipedia,the free encyclopedia
An antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates and Inhibit other oxidation reactions by being oxidize themselves. As a result, antioxidants are often reducing agents such as ascorbic acid or polyphenols.Although oxidation reactions are crucial for life, theycan also be damaging; hence, plants and animals maintain complex systems of multiple types of antioxidants, such as glutathione, vitamin C and vitamin E, aswell as enzymes such as catalase, superoxide dismutase and various peroxidases. Low levels of antioxidants, orinhibition of the antioxidant enzymes, causes oxidativestress and may damage or kill cells. As oxidative stressmight be an important part of many human diseases, the use of antioxidants in pharmacology is intensivelystudied, particularly as treatments for stroke and neurodegenerative diseases. However, it is unknownwhetheroxidative stress is the cause or the consequence ofdisease. Antioxidants are also widely used as ingredientsin dietary supplements in the hope of maintaining healthand preventing diseases such as cancer and coronary heart disease. Although initial studies suggested thatantioxidant supplements might promote health, later largeclinical trials did not detect any benefit and suggested instead that excess supplementation may be harmful. In addition to these uses of natural antioxidants in medicine, these compounds have many industrial uses, such as preservatives in food and cosmetics and preventing thedegradation of rubber and gasoline. For many yearschemists have known that free radicals cause oxidationwhich can be controlled or prevented by a range of antioxidants substances (Bjelakovicet al., 2007). It is vital that lubrication oils should remain stable and liquid should not dry up like paints. For this reason, such usually has small quantities of antioxidants such asphenol or amine derivatives, added to them. Although plastics are often formed by free radical action, they can also be broken down by the same process, so they too, require protection by antioxidants like phenols or naphthol. Low density polythene is also of protected by carbon black which absorbs the ultraviolet light which causes radical production (Sies, 1997).
Sources and origin of antioxidants
Antioxidants are abundant in fruits and vegetables, as well as in other foods including nuts, grains and some meats, poultry and fish. The list below describes food sources of common antioxidants. Beta-carotene is found in many foods that are orange in color, including sweet potatoes, carrots, cantaloupe, squash, apricots, pumpkin and mangoes. Some green, leafy vegetables, including collard greens, spinach and kale, are also rich in beta-carotene (Borek, 1991). Lutein, best known for itsassociation with healthy eyes, is abundant in green, leafy vegetables such as collard greens, spinach, and kale.
Lycopene is a potent antioxidant found in tomatoes,watermelon, guava, papaya, apricots, pink grapefruit,blood oranges and other foods. Estimates suggest 85% of American dietary intake of lycopene comes from tomatoes and tomato products (Rodriguez-Amaya, 2003; Xianquanet al., 2005).
Vitamin A is found in three main forms: retinol (Vitamin A1), 3,4-didehydroretinol (Vitamin A2), and 3-hydroxyretinol (Vitamin A3). Foods rich in vitamin A include liver,sweet potatoes, carrots, milk, egg yolks and mozzarella cheese (Baubliset al., 2000). Vitamin C is also called ascorbic acid and can be found in high abundance in many fruits and vegetables and is also found in cereals,beef, poultry, and fish (Antioxidants and Cancer Prevention, 2007).
Vitamin E, also known as alpha-tocopherol, is found inalmonds, in many oils including wheat germ, safflower, corn and soybean oils, and is also found in mangoes, nuts,broccoli, and other foods (Herrera and Barbas, 2001).
Classification of antioxidants
Antioxidants are grouped into two namely;
(1) Primary or natural antioxidants.
(2) Secondary or synthetic antioxidants.
Primary or natural antioxidants
They are the chain breaking antioxidants which react with lipid radicals and convert them into more stable products. Antioxidants of this group are mainly phenolic in structures and include the following (Hurrell, 2003):
(1) Antioxidants minerals. These are co-factor of antioxidants enzymes. Their absence will definitely affect metabolism of many macromolecules such as carbohydrates. Examples include selenium, copper, iron, zinc and manganese.
(2) Anti oxidants vitamins – It is needed for most body metabolic functions. They include-vitamin C vitamin E.
1.13. AIMAND OBJECTIVES
To evaluate the in vitro phytochemical and antioxidant properties of methanol,ethanol and hexane extracts of Alstoniaboonei leaves with view to determine the appropriate solvent that would provide the best yield of the bioactive compounds.
1.14. SPECIFIC OBJECTIVES
To determine the antioxidant properties ofAlstoniaboonei leaves.
To determine the phytochemical constituentsof Alstoniaboonei leaves..