Antioxidant properties of some leafy and non leafy vegetables in west africa

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This is a seminar report on the Antioxidant properties of some leafy and non leafy vegetables in west africa. Get my contact on to get a copy of this.

This is a seminar report on the Antioxidant properties of some leafy and non leafy vegetables in west africa. Get my contact on to get a copy of this.

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  • 1. 1 CHAPTER ONE 1.0 Introduction Oxidation, which is essential for the production of energy to fuel biological process usually produces free radicals and other reactive oxygen species that can damage tissues and causes cell death. Although almost all organisms possess antioxidant defence and repair systems that have evolved to protect them against oxidative damage, these systems are insufficient to prevent the damage activity entirely (Simic et al., 1992). However, antioxidant supplements or foods containing antioxidants may be used to help human body reduce oxidative damage. In recent years, there has been particular interest in the antioxidant and health benefits of phytochemicals in vegetables. Vegetables and herbs were the basis of nearly all medicinal therapy until synthetic drugs were developed in the nineteenth century but the use of these vegetables along with fruits and other herbs is still on the increase because of the numerous phytochemicals in addition to antioxidants present in them (Wei and Shiow, 2001). The presence of phytochemicals, in addition to vitamins and pro-vitamins, in fruits and vegetables has been considered of crucial nutritional importance in the prevention of chronic diseases, such as cancer, cardiovascular disease and diabetes (Doll and Petro, 1981). Organisms are endowed with endogenous (catalase, superoxide dismutase, glutathione peroxidase/reductase) and exogenous (vitamin C, E, ß-Carotene) antioxidant defence system against reactions of free radicals. However, the generation of free radicals in the body beyond its antioxidant capacity leads to oxidative stress which has been implicated in the aetiology of several pathological conditions such as lipid peroxidation, protein oxidation, DNA damage and cellular degeneration related to cardiovascular disease, diabetes, inflammatory disease, cancer and Parkinson disease. When left unpaired, it can cause base
  • 2. 2 mutation, single and double-strand breaks, DNA cross-linking, and chromosomal breakage and rearrangement (Ames et al., 1993). As a result of this, much attention is been focused on the use of antioxidants especially natural antioxidant to inhibit and protect damage due to free radicals and reactive oxygen species. Synthetic antioxidant such as butylated hydroxyanisole (BHA), tert-butylated hydroxyquinone and butylated hydroxytoluene have been of utmost concern to many researchers because of their possible activity as promoters of carcinogenesis (Atiqur et al., 2008). Plant based antioxidant are now preferred to the synthetic ones because of their safety. Epidemiological studies have shown that the consumption of vegetables and fruits can protect humans against oxidative damage by inhibiting or quenching free radicals and reactive oxygen species (Ames et al., 1993). Many plants including fruits and vegetables are recognized as sources of natural antioxidants that can protect against oxidative stress and thus play an important role in the chemoprevention of diseases that have their aetiology and pathophysiology in reactive oxygen species (Odukoya et al., 2001). These positive effects are believed to be attributable to the antioxidants; particularly the carotenoids, flavonoids, lycopene, phenolics and β-carotene (Amin et al., 2004). Thus, the objective of this paper is to discuss the antioxidant properties of some leafy and non-leafy vegetables.
  • 3. 3 CHAPTER TWO 2.0 Vegetables Vegetables are a large class of plants. They give variety of flavours and colour to feed and food and they include leaves, stems, seeds and flowers (Tindall, 1983). There has been a particular interest in the antioxidants and health benefits of phytochemicals in vegetables. This was as a result of their potential effect on human health (Wei and Shiow, 2001). Vegetables have been used for a large range of purpose including nutrition, medicine, flavourings, beverages and industries. Since pre-historic times, vegetables and herbs were the basis of nearly all therapies until synthetic drugs were developed in the nineteenth century (Wei and Shiow, 2001). However, vegetables along with fruits and other herbs are increasingly gaining popularity again over synthetic drugs because of the dreaded side effects of chemical accumulation in the body as a result of taking too much of synthetic drugs. On the other hand, vegetables and fruits contain phytochemicals that acts as antioxidants in the body. They also help to retain stronger bones. It has been shown to decrease the amount of calcium excreted in the urine (Wei and Shiow, 2001). Vegetables acts as an „alkaline buffer‟ neutralizing acid produced when fish and meat are digested. These acids would otherwise tend to increase the amount of calcium host in the urine but, sufficient vegetable consumption neutralizes this effect (Appel et al., 1997). 2.1 Classification of Vegetables Vegetables are classified based on morphological features. They are: i. Non-leafy vegetable types  Earthy vegetable roots e.g. sweet potatoes (Ipeoma batata), Carrots (Daucus carota), etc.  Buds bulbs e.g. Onions (Allium pa), Garlic (Allium salvum), etc.  Vine fruits e.g. Cucumber (Cucumis sativus), pumpkin (Cucurbita maxima), etc.
  • 4. 4  Berry fruits e.g. African eggplant (Solanum macrocarpon), Tomato (Lycopersium macrocarpon), etc.  Legumes e.g. Garden pea (Psium sativum), green beans (Vigna unguiculata), etc.  Sprout e.g. Asparagus (Brassica oleraceae), etc. ii. Leafy vegetable type  Leafy vegetables e.g. Jute Mallow (Corchorus olitorius), bitterleaf (Vernonia amygdalina), etc. (Tindall, 1983). 2.2 Antioxidants Antioxidants are substances that are capable of counteracting the damaging, but normal effects of the physiological process of oxidation in animal tissues (Gey, 1998). Oxidative stress occurs when the production of harmful free radicals is beyond the protective capability of the antioxidant defences. Antioxidant works to protect lipids from peroxidation by radicals. Antioxidants are effective because they are willing to give up their own electrons to free radicals. When a free radical gains the electron from an antioxidant; it is no longer capable of attacking the cell and the chain reaction of oxidation is broken (Dekkers et al., 1996). Antioxidants are nutrients (vitamins and minerals) as well as enzymes (proteins), they are manufactured within the body and can also be obtained from the food humans eat such as fruits, vegetables, seeds, nuts, meat and oil (Dekkers et al., 1996). Antioxidants acts as radical scavenger, hydrogen donors, electron donors and peroxide. A characteristic feature of antioxidants is their effectiveness at very low concentrations (0.001-0.1%). Some of them e.g. tocopherols, have definite concentrations, which if exceeded can cause a decrease in its antioxidant activity and higher concentrations can cause a pro-oxidant effect. Antioxidants can be divided into two groups: natural and synthetic. In recent years, many investigations suggest limitation of synthetic antioxidant use, with regard to their toxicity. Also, the consumer show larger interest in food products with natural sources of antioxidative compounds (Pszola, 2001).
  • 5. 5 Dietary antioxidants are considered beneficial because of their potential protective role against oxidative stress, which is involved in the pathogenesis of multiple diseases such as cancer and coronary heart disease. Antioxidants in vegetables appear to be of great importance in controlling damage by free radicals. Each antioxidant is unique in terms of its structure and functions. These antioxidants are: a) Vitamin E Vitamin E is a fat-soluble vitamin present in nuts, seeds, vegetables, fish oils, whole grains and cereals. Alpha-tocopherol is the most widely available isomer, which has the highest biopotency or strongest effect in the body. It safeguards cell membrane from damage by free radicals. Alpha-tocopherol also protects low-density lipoproteins (LDLs) from oxidation (Morrisey, 1999). Vitamin E is the major hydrophobic chain-breaking antioxidant that prevents the propagation of free radical reactions in the lipid components of membranes, vacuoles and plasma lipoproteins (Ricciarelli et al., 2001). b) Vitamin C Vitamin C also known as ascorbic acid, is a water-soluble vitamin present in citrus fruits and juices, green peppers, cabbage and strawberries (Kendall, 2000). It scavenges free radicals that are in the aqueous phase of cell. Vitamin C works synergistically with vitamin E to quench free radicals of the smokers. Vitamin C protects the body against cancer of the oesophagus, oral cavity and stomach. It also regenerates the reduced form of vitamin E (Mimica-Dukie, 2000). c) β-Carotene It is a precursor to Vitamin A (retinol) and is present in dark vegetables. In theory, β- carotene has remarkable antioxidant chemistry. β-carotene can interact with a free radical in the presence of oxygen to form peroxyl radicals. It is very effective in the protection against oxidative changes. β-carotene is a quencher of singlet oxygen and is also especially excellent at scavenging free radicals in low oxygen concentration (Bray, 1999).
  • 6. 6 d) Selenium It is a trace element. It is a mineral that humans need to consume only in small quantities. It forms the active site of several antioxidant enzymes including glutathione peroxidase. Similar to selenium, the minerals manganese and zinc are trace elements that form an essential part of various antioxidant enzymes (Kendall, 2000). e) Other antioxidants In addition to vitamins and minerals, there appear to be many other compounds that have antioxidant properties. Among them is co-enzyme Q10 (or ubiquinone) which is essential for energy production and can also protect the body from destructive radicals. Also, uric acid, a metabolic product of purine nucleotides, has become increasingly recognized as important antioxidant (Robin, 2004). 2.3 Mode of Action of Antioxidants Antioxidant defense system against oxidative stress is composed of several lines and the antioxidants are classified into four categories based on function: i. Preventive antioxidants, which suppress formation of free radicals (enzymes such as glutathione peroxidase, catalase, selenoprotein, carotenoids etc.). ii. Radical scavenging antioxidants suppressing chain initiation and/or breaking chain propagation reactions. iii. Repair and de novo antioxidants (some proteolytic enzymes, repair enzyme of DNA etc.) and iv. Adaptation where the signal for the production and reactions of free radicals induces formation and transport of the appropriate antioxidant to the right side (Bray, 1999). 2.4 Antioxidant Properties of Leafy Vegetables 2.4.1 Antioxidant Properties of Vernonia amygdalina (Bitter leaf) Vernonia amygdalina (plate 1) is a perennial shrub that belongs to the Asteraceae family and is popularly called bitter leaf in English. It is known as Ewuro in yoruba, Etidot in Ibibio, Onugbu in Igbo, Ityuna in Tiv, Ilo in Igala, Oriwo in Edo and Chusar-doki in Hausa. It
  • 7. 7 has petiolate leaves of about 6mm diameter and ellicptic in shape. The leaves are green with a characteristic odour and bitter taste (Akpaso et al., 2011). They are well distributed in tropical African and Asia and are commonly found along drainage lines and in natural forest or commercial plantation. In most part of Africa, the leaves of V. amygdalina are used as soup condiments after washing or boiled to get rid of the bitter taste. Specifically, it is used to prepare the popular Nigerian bitter leaf soup, Onugbo and as spice in the Cameroon dish called Ndole (Yeap et al., 2010). Huffman and Seifu (1989) reported the use of V. amygdalina in the treatment of parasite related disease in wild chimpanzee in Tanzania. This necessitated quite a great number of researches to test the efficacy of different part of the plant in managing a wide array of ailments. Many traditional medicine practitioners use different parts of the plants in treating various ailments for instance the whole plant is being used as antihelminth, antimalaria and as a laxative. Their traditional use is not limited to human alone, in northern Nigeria it has been added to horse feed to provide a strengthening or fattening tonic Chusan- Dokin in Hausa (Igile et al., 1994). Different extracts of V. amygdalina has been shown to possess antioxidant properties both in vitro and in vivo. Ayoola et al., (2008) showed the in vitro antioxidant properties of the ethanolic extract of leaves of V. amygdalina using the 2,2-diphenyl-1-picrylhydrazyl radical (DPHH) scavenging test. V. amygdalina was shown to have moderate inhibition of 77.7% thus indicating the scavenging ability of the vegetable. Also, the aqueous and ethanolic extract of V. amygdalina has further been shown to have potent antioxidant properties as they were able to inhibit bleaching of β-carotene, oxidation of linoleic acid and lipid peroxidation induced by Fe2+ /ascorbate in a rat liver microsomal preparation. This study showed that the antioxidant activity of the ethanolic extracts was higher than that of the aqueous extracts, and compared favourably with synthetic antioxidant BHT and BHA (Owolabi et al., 2008). However, another study reported that methanol extract displayed highest antioxidant activity followed by acetone and water extract (Erasto et al., 2007).
  • 8. 8 Further confirmation of the antioxidant activities of V. amygdalina was reported by Oloyede and Ayila (2012). They investigated the antioxidant activity of different extracts, aqueous, methanol, hexane, ethylacetate and butanol extracts of Vernonia amygdalina using three methods: scavenging effect on 2,2-diphenyl-1-picryhydrazyl radical (DPPH), hydroxyl radical and peroxide oxidation by ferric thiocynate method. All fractions showed significant antioxidant activity (p<0.05) when compared with antioxidant standards like butylated hydroxyl anisole (BHA), ascorbic acid and α-tocopherol used in the assay. This plant contains natural antioxidants against aqueous radicals and reactive species ions (Erasto et al., 2007). Nwanjo (2005) reported the antidiabetic effect of the aqueous extract V. amygdalina in streptozotocin induced diabetic rats. He showed in his finding that V. amygdalina was capable of reducing plasma glucose, triglycerides, and LDL-cholesterol and the marker of oxidative stress malondialdehyde. These may be due to decreased oxidative stress which may be via direct scavenging of the reactive oxygen species or by increasing the synthesis of antioxidant molecule (Gutpa et al., 2002). Cold water, hot water and ethanol extract of V. amygdalina were found to induce apoptosis against acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) from the patients with IC50 ranging between 5 to 10 μg/ml. Ethanol extract was found to be most effective against both ALL and AML when compared to cold and hot water extract (Khalafalla et al., 2009). Petroleum ether/ethyl acetate leaf extract also possessed cytotoxic effect towards human hepatoblastoma (HepG2) and urinary bladder carcinoma (ECV-304) cell lines (Froelich et al., 2006). These findings establish the usefulness of V. amygdalina Del. in managing breast cancer. Thus, Vernonia amygdalina leaf is a vegetable with several potentials in the prevention and treatment of various ailments associated with oxidative stress.
  • 9. 9 Plate 1: Vernonia amygdalina (Bitter leaf)
  • 10. 10 2.4.2 Antioxidant Properties of Telfairia occidentalis (Fluted pumpkin) Telfairia occidentalis commonly called fluted pumpkin occurs in the forest zone of West and Central Africa, most frequently in Benin, Nigeria and Cameroon. It is a popular vegetable all over Nigeria. It has been suggested that it originated in south-east Nigeria and was distributed by the Igbos, who have cultivated this crop since time immemorial (Kayode and Kayode; 2011). It is a vigorous perennial vine, growing to 10m or more in length. The stems have branching tendrils and the leaves are divided into 3-5 leaflets. The fruits are pale green, 3-10 kg in weight, strongly ribbed at maturity and up to 25cm in diameter. The seeds are 3-5cm in diameter (FAO, 1985). The leaf is consumed in different parts of the country because of the numerous nutritional and medicinal attributes ascribed to it. It has different traditional names; among Igbos, it is known as Ugu, Iroko or Aporoko in Yoruba, Ubong in Efik, Umee in Urhobo and Umeke in Edo. Young succulent shoots and leaves are used as vegetables in the eastern part of Nigeria. The herbal preparation of the plant has been employed in the treatment of sudden attack of convulsion, gastrointestinal disorders, malaria and anaemia. Also the plant has agricultural and industrial importance in addition to its nutritional value (Oboh, 2005). Quite a number of researchers in the field of medical sciences have observed free radical scavenging ability and antioxidant property in Telfairia occidentalis. The darkish green leafy vegetable of Telfairia occidentalis and extracts (such as aqueous and ethanol extracts) from the leaves have been found to suppress or prevent the production of free radical and scavenge already produced free radical, lower lipid peroxidation status and elevates antioxidant enzymes (such as superoxide dismutase and Catalase) both in vitro and in vivo (Oboh and Akindahunsi, 2004). The latter reported that extracts of this vegetable using various solvents were able to offer a chemopreventive and protective effects on oxidative stress induced serum and organs like kidney, liver and brain. Studies have shown
  • 11. 11 that Telfairia occidentalis leaves are rich in antioxidants such as ascorbic acid and phenols (Oboh et al., 2006). Specifically, Oboh et al., (2006) in their study showed the antioxidant properties of Telfairia occidentalis by assessing their total phenolic content, reducing property and free radical scavenging properties against DPHH radical. From that study the aqueous extracts had a significantly higher total phenol content than the ethanolic extracts which clearly indicates that the phenols present in Telfairia occidentalis leaves are more water soluble than ethanol, consequently, the aqueous extracts could be a more potent antioxidant than the ethanolic extracts. This gives credit to the fact that aqueous extracts of the leaf is presently used in the management and prevention of anaemia and diabetes. This high phenol content in the aqueous extracts could have contributed to the prevention or management of haemolytic anaemia, diabetes which is associated with free radical damage (Oboh, 2004). Also in the same study it was observed that the aqueous extract had a significantly higher reducing power and higher free radical scavenging ability than the ethanolic extracts. The higher phenolic content in the aqueous extract would have accounted for the higher ability of the aqueous extract to reduce Fe (III) to Fe (II) in the FRAP test for reducing ability. Also, the chelating properties of phenols have been reported to have high reducing power which clearly indicate that Telfairia occidentalis leaf antioxidant potentials will be more harness in its aqueous extraction than the ethanolic extraction and this is in accord with the form in which the plant is presently been used. They also revealed in their study the high flavonoid content, total antioxidant content, lipid peroxidation inhibition, free scavenging activity towards hydroxyl radical and superoxide scavenging abilities of Telfairia occidentalis amongst other vegetables. Therefore the consumption of leaves of Telfairia occidentalis (plate 2) will provide adequate antioxidants capable of preventing diseases arising from oxidative stress thus promoting the general wellbeing of an individual.
  • 12. 12 Plate 2: Telfairia occidentalis (Fluted pumpkin)
  • 13. 13 2.4.3 Antioxidant Properties of Ocimum (Basil) The genus ocimum (plate 3) is represented by over 50 species of herbs and shrubs in Africa. Ocimum basilicum and Ocimum gratissimum are known in Africa for the management of different diseases. They belong to the family of plant known as Lamiaceae. Local names of different species of ocimum in various ethnic groups include Efirin (Yoruba), Neh-anwu (Ibo), Ntion (Efik) and Dai-doya ta gida (Hausa). The leaves can be petiolate or sessile, often toothed at the margin. They are erected and have characteristic pleasant aroma due to their volatile oil. Ocimum gratissimum leaf or the whole plant is known to be popular treatment remedy for diarrhoea (Dalziel, 1959). The plant is rich in volatile oils, which contain up to 75 percent of thymol, the antimicrobial activity of which is well known. Ocimum gratissimum (OG) is effective in the management of upper respiratory tract infection, diarrhoea, headache, skin disease, pneumonia, fever, and conjuctivitis (Onajobi, 1986). Traditionally, Ocimum basilicum (basil) has been used as a medicinal plant for various ailments, such as headaches, coughs, diarrhoea, constipation, warts, worms and kidney malfunction. It is also thought to be an antispasmodic, stomachicum, carminative, antimalarial, febrifuge and stimulant (Wome, 1982). A comparative study on the antioxidant properties of two Nigerian species of Ocimum showed that the methanolic extract of Ocimum gratissimum possess a higher polyphenolic, flavonoid component and free radical scavenging activities when compared to the methanolic extract of O. basillicum (Omale et al., 2008). Thus, this may be reason behind wider utilization of O. gratissimum in Nigerian folk medicine than O. basillicum. Further studies of the phytochemical and antioxidant activity of methanolic and aqueous extract of Ocimum gratissimum revealed the presence of flavonoids, steroids, cardiac glycosides, tannins, phlobatannins in both extract (Akinmoladun, 2007). The methanolic extract of OG was shown to exhibit a higher DPHH scavenging activity (84.6%) at 250 μg/ml and a reductive
  • 14. 14 potential of 0.77 at 100 μg/ml comparable with those of gallic acid, 91.4% at 250 μg/ml and ascorbic acid, 0.79 at 60 μg/ml as standards for DPPH scavenging activity and reductive potential, respectively (Omale et al., 2008). Thus, O. gratissimum leaf extracts possess antioxidant potential probably because of its phytochemical constituents which has also been reported in other studies (Dubey et al., 2000). The methanolic extract of leaf of Ocimum gratissimum was also shown to be capable of scavenging the free radicals 2,2-diphenylpicryl-1-hydrazyl (DPPH) radical, superoxide anion radical, hydroxyl radical, nitric oxide radicals, as well as inhibiting lipid peroxidation, using appropriate assay systems compared to natural and synthetic antioxidants. The analgesic and hepatoprotective activity of the methanolic extract of O. gratissimum leaves in carbon tetrachloride hepatoxic-albino rats was reported. A significant decrease in the liver enzymes were observed in the hepatoxic albino rats after treatment with the methanolic extract of O. gratissimum thus showing its protective effect on the damaged liver (Uhegbu, 2012).
  • 15. 15 Plate 3: Ocimum (Basil)
  • 16. 16 2.4.4 Antioxidant Properties of Adansonia digitata (Baobab) Baobab (Adansonia digitata) (plate 4) is a tree found widely throughout Africa and known locally in African countries as the “tree of life” due to its ability to sustain life owing to its water holding capacity, as well as its many traditional medicinal and nutritional uses (Wickens, 2008). The baobab tree is an important food, water and shelter source in many African countries. Adansonia digitata is commonly called Kukah by the Hausa of Northern Nigeria, Niger Konian, Kenyans Mwambom, Mali Sira, Senegal, Goui. Adansonia digitata is one of eight species of the Adansonia genus, and its name originates from the fact that the oblong leaves of the tree, often formed in groups of five, look like the fingers or digits of the human hand. It is a deciduous tree which has four growth phases and produces a fruit consisting of a yellowish-white pulp which has a floury texture and numerous hard, round seeds, enclosed in a tough shell (Wickens, 2008). The leaves are typically sun-dried and either stored as whole leaves or pounded and sieved into a fine powder (Sidibe et al., 1996). The Powdered leaves are used as a tonic and an antiasthmatic and known to have antihistamine and anti-tension properties. The leaves are also used to treat insect bites, guinea worm and internal pains, dysentery, diseases of the urinary tract, opthalmia and otitis (Sidibe et al., 2002). In Indian medicine, powdered leaves are similarly used to check excessive perspiration (Sidibe et al., 2002). Baobab leaves are used medicinally as a diaphoretic, an astringent, an expectorant and as a prophylactic against fever (Wickens, 1979). Baobab leaves have been investigated in an attempt to identify the potential bioactives associated with this part of the plant. Certain bioactive compounds may be responsible for the treatment of certain ailments, as well as containing properties that can be beneficial to overall health. Examples of such bioactive compounds include tannins, phlorotannins, terpenoids, glycosides, saponins and terpenoids as well as antioxidants including flavonoids and
  • 17. 17 polyphenols (Vertuani et al., 2002). The chemical profile of the methanolic and aqueous extracts of the leaves of the plant was also investigated (Shri et al., 2004). They reported the presence of glycosides, phytosterols, saponins, protein and amino acid, phenolic compounds and tannins, gums, mucilage and flavanoids. A. digitata leaves, fruit-pulp and seeds have earlier been reported to show antiviral activity against influenza virus, herpes simplex virus and respiratory syncytial virus and polio. Chemical analyses have reported the presence of various potentially bioactive ingredients including triterpenoids, flavonoids and phenolic compounds (Chadare et al., 2009). These bioactive compounds especially flavonoids and phenolic may be responsible for the nutritive and medicinal properties of this vegetable. Karumi et al., (2008) also reported the gastro protective effect of Adansonia digitata leaf on ethanol induced ulceration. This study elucidated a significant dose-dependent increase both in preventive ratio and percentage ulcer reduction after pre-treatment with Adansonia digitata leaves. Ethanol is an established ulcerogen especially in empty stomach. The ulcerogenicity of ethanol is due to intracellular oxidative stress producing mitochondrial permeability, transition and mitochondrial depolarization which results to the death of cells in gastric mucosa (Hernandez et al., 2000). This is because of its congestive inflammation and tissue injury. It is a known fact that flavonoids and anti-oxidant (Vitamin A, E and C) present in this plant has protective role. This view is supported by the fact that gastric mucosa is known to have certain antioxidant activity thereby reducing mucosal damage mediated by free radicals (Penisi and Piezzi, 2009) which in turn attack cell membrane causing a lipid derived free radicals such as conjugated diene and lipid hydroperoxides which are extremely reactive and unstable. This study corroborate with previous report on the anti-ulcerative properties of the aqueous extract of Adansonia digitata leaves against ethanol induced ulceration in rats (Bagchi et al., 1998). Although, the precise mechanism of action of A.
  • 18. 18 digitata is not clear, it was proposed that the gastroprotective role of this vegetable extract may be partly due to its high content of flavonoids and antioxidants (Arrigori, and De Tullio, 2002) which are well known compounds that prevent and combat the formation of reactive oxygen species. Another possible mechanism is the fact that the leaves being an astringent may have precipitated microproteins on the site of ulcer thereby forming an impervious protective pellicle over the lining to prevent absorption of toxic substance and resist the attack of proteolytic enzymes (Nwafor et al., 1996).
  • 19. 19 Plate 4: Adansonia digitata (Baobab) Source:
  • 20. 20 2.4.5 Antioxidant Properties of Corchorus olitorius (Jute Mallow) Corchorus olitorius is a leafy vegetable that belongs to the family Tiliaceae and commonly called Jute mallow in English and Ewedu in the south western Nigeria (plate 5). It is an animal herb with a slender stem and an important green leafy vegetable in many tropical area including Egypt, Sudan, India, Bangladesh, in tropical Asia such as Philippine and Malaysia, as well as in tropical Africa, Japan, the Caribbean and Cyprus (Samra et al., 2007). The plant is widely grown in the tropics for the viscosity of its leaves. The leaves (either fresh or dried) are cooked into a thick viscous soup or added to stew or soup and are rich sources of vitamins and minerals (Tindall, 1983). In West African countries including Ghana, Nigeria and Sierra Leone, the vegetable is cultivated for the stem bark which is used in the production of fibre (Jute) and for its mucilaginous leaves which are also used as food vegetable (Zakaria et al., 2006). The leaf extract of the plant is also employed in folklore medicine in the treatment of gonorrhoea, pain, fever and tumour (Ndlovu and Afolayan, 2008). It is reportedly consumed as healthy, vegetable in Japan because of its rich contents of carotenoids, vitamin B1, B2, C and E, and minerals. Its leaves and roots are eaten as herbal medicine in South-East Asia (Ndlovu and Afolayan, 2008). In some part of Nigeria, its leaves decoctions are used for treating iron deficiency, folic acid deficiency, as well as treatment of anaemia. Its leaves also act as blood purifier and the leaf twigs is used against heart troubles while cold leaf infusion is taken to restore appetite and strength, leaves used for ascites, pains, piles, tumours, gonorrhoea and fever (Fasinmirin and Olufayo, 2009). The phenolic antioxidants in the leaves of Corchorus olitorious was identified to include phenolic [5-caffeoylquinic acid (chlorogenic acid), 3, 5-dicaffeoylquinic acid, quercetin 3-galactoside, quercetin 3-glucoside, quercetin 3-(6-malonylglucoside), and quercetin 3-(6-malonylgalactoside) (tentative)] were identified from the leaves of Corchorus olitorious by NMR and FAB-MS. The contents of these phenolic compounds, ascorbic acid,
  • 21. 21 and alphatocopherol in C. olitorius leaves were determined, and their antioxidative activities were measured using the radical generator-initiated peroxidation of linoleic acid. The results obtained showed that 5-caffeoylquinic acid was a predominant phenolic antioxidant in C. olitorius leaves (phenolic antioxidants from the leaves of Corchorus olitorius). None of these phenolic compounds was detected in recent study on the chemical composition and in vitro antioxidant properties of some selected vegetables (Salawu et al., 2006). Oboh et al., (2009) carried out a comparative study of the antioxidant properties of hydrophilic extract (HE) and lipophilic extract (LE) constituents of the Corchorus olitorius. HE and LE of the leaf were prepared using water and hexane, respectively and their antioxidant properties were determined. HE showed a significantly higher 1, 1-diphenyl-2- picrylhydrazyl radical-scavenging ability, reducing power, trolox equivalent antioxidant capacity than LE. Conversely, LE showed a significantly higher hydroxyl scavenging activity than HE while there was no significant difference in their Fe (II) chelating ability. The higher 1,1-diphenyl-2-picrylhydrazyl radical-scavenging ability, reducing power and trolox equivalent antioxidant capacity of the hydrophilic extract may be due to its significantly higher total phenol (630.8 mg/100 g), total flavonoid (227.8 mg/100 g) and non-flavonoid polyphenols (403.0 mg/100 g), and its high ascorbic acid content (32.6 mg/100 g). The higher OH Scavenging ability of LE may be due to its high total carotenoid content (42.5 mg/100 g). Therefore, the synergistic antioxidant activities of the hydrophilic and lipophilic constituents may contribute to the medicinal properties of C. olitorius leaf (Oboh et al., 2009). Further study illustrated the protective effect of aqueous extract of Corchorus olitorius leaves (AECO) against sodium arsenite-induced toxicity in experimental rats (Das et al., 2010). A significant inhibition of hepatic and renal antioxidant enzymes such as superoxide dismutase, catalase, glutathione-S-transferase, and glutathione peroxidase and glutathione reductase were observed. The level of reduced glutathione decreased while the levels of oxidized
  • 22. 22 glutathione and thiobarbituric acid reactive substances in the selected tissues were increased following arsenic intoxication. Treatment with AECO at doses of 50 and 100mg/kg body weight for 15days after arsenic intoxication significantly improved hepatic and renal antioxidant markers in a dose dependant manner. AECO treatment also significantly reduced the arsenic-induced DNA fragmentation of hepatic and renal tissues.
  • 23. 23 Plate 5: Corchorus olitorius (Jute Mallow)
  • 24. 24 2.5 Antioxidant Properties of some non-leafy vegetables 2.5.1 Antioxidant Properties of Mushrooms Mushrooms (plate 6) have been used for many years as nutritional food and food flavouring materials as well as medicines (Tel et al., 2012). Because of their flavour and aroma, mushrooms are greatly appreciated in many countries. According to the definition of Chang and Miles (1992), a mushroom is a macrofungus with a distinctive fruiting body, which can be hypogeous or epigeous, large enough to be seen with the naked eye and to be picked by hand. They constitute at least 14000 and perhaps as many as 22000 known species. The number of mushroom species on the earth is estimated to be 140000, suggesting that only 10% are known. Research indicates mushrooms have potential antiviral, antimicrobial, anticancer, antihyperglycemic, cardioprotective, and anti-inflammatory activities (Lindequist et al., 2005). Mushrooms such as Ganoderma lucidum (Reishi), Lentinus edodes (Shiitake), Inonotus obliquus (Chaga) and many others have been collected and used for hundreds of years in Korea, China, Japan, and Eastern Russia. They are reputed to possess anti-allergic and anticholesterol activities. Aqueous extracts from Pleurotus sajor-caju have been proven good in renal failure (Bahl, 1983). Bahl (1983) showed mushrooms cure epilepsy, wounds, skin diseases, heart ailments, rheumatoid arthritis, cholera besides intermittent fevers, diaphoretic, diarrhoea, dysentery, cold, anaesthesia, liver disease, gall bladder diseases and used as vermicides. Three species of Pleurotus florida, P. pulmonarius and P. citrinopileatus were examined for their antioxidant potentialities with a view to popularizing medicinal mushrooms among common middle-class people at low-cost instead of administering costly medicines. Reducing power, chelating activity of Fe2+ and total phenol were observed to be higher in P. florida than in P. pulmonarius and P. citrinopileatus respectively. Among
  • 25. 25 antioxidative enzymes, P. florida exhibited highest peroxidase and superoxide dismutase (SOD) whereas catalase activity was found to be highest in P. pulmonarius (Khatun et al., 2009). Previous workers obtained 6.001±0.04 μmg-1 , 7.501±0.10 μmg-1 and 6.72±0.05 μmg-1 of phenol components in ethanol extract of P. sajor-caju, P. florida and P. aureovillosus respectively (Laganathan et al., 2010). It is showed that antioxidant activity of Phellinus rimosus seems to be more effective than the Pleurotus florida, P. sajour-caju and G. lucidum (Ajith and Janardhanan, 2003). Fruiting bodies of medicinal mushroom (G. lucidum) contain polysaccharides, triterpenoids, adenosine, germanium, protein (L2-8), amino acids which have been found to have antitumor and immuno-modulating effect (Sing et al., 2008). Methanol extract of P. rimosus have been shown to effectively reduce ferric ion in FRAP assay and scavenged DPPH radicals (Ajith and Janardhanan, 2007). Extracts from fruiting bodies and mycelia of G. lucidum occurring in South India were found to possess in vitro antioxidant activity and antimutagenic activities (Jones and Janardhanan, 2000). Antioxidant assays of the ethyl acetate, methanol and aqueous extract of G. lucidum effectively scavenged the O2 and OH radicals (Ajith and Janardhanan, 2007). However, the aqueous extract was not effective to inhibit the ferrous ion induced lipid peroxidation (Jones and Janardhanan, 2000). The extract showed significant reducing power and radical scavenging property as evident from FRAP assay and DPPH radical scavenging assay. The antioxidant potential of L. edodes methanol extract was investigated in the search for new bioactive compounds from natural resources. The measured DPPH radical scavenging activity was depicted by Sasidharan et al., (2010). The free radical scavenging activities were 39.0%, 41.0% and 66.00% for the L. edodes extract, vitamin E and BHT, respectively. The EC50 value is 4.4 mg/mL (y = 11.7x - 1.693, R2 = 0.988) which is the concentration of the crude extract that decreases the initial DPPH radical concentration by 50%. Effectiveness of antioxidant properties was found to be inversely correlated to EC50
  • 26. 26 values. Cheung and Cheung (2005) also reported the antioxidant activity of L. edodes against lipid peroxidation. They found that the low molecular weight sub-fraction of the water extract of L. edodes had the highest antioxidant activity against lipid peroxidation of rat brain homogenate, with IC50 values of 1.05 mg/mL. In addition, other mushrooms have also been reported to possess antioxidant activity. Wong and Chye (2009) reported the antioxidant activity of Pleurotus porrigens, Hygrocybe conica, Xerula furfuracea (Rooted oude), Schizophyllum commune, Polyporus tenuiculus (Pore fungus) and Pleurotus florida. Petroleum ether (PE) and methanolic extracts from these edible wild mushrooms were effective in DPPH radical scavenging and metal chelating ability. PE extracts were more effective than methanolic extracts in antioxidant activity using the DPPH, whereas methanolic extracts were more effective in reducing power and metal chelating ability.
  • 27. 27 Plate 6: Mushrooms Source:
  • 28. 28 2.5.2 Antioxidant Properties of Peppers (Capsicum species) Genus Capsicum is a member of family Solanaceae and has five species that are commonly recognized as domesticated: Capsicum annuum, Capsicum baccatum, Capsicum chinense, Capsicum frutescens, and Capsicum pubescens. The word „Chile‟ is the common name for any Capsicum species in Mexico, Central America and the South-Western USA. In Asia, the spelling „chilli‟ is more common and is always associated with highly pungent varieties of Capsicum annuum and Capsicum frutescens, while the non-pungent sweet bell peppers are referred to as „Capsicums‟ and it is native to Mexico. In American English, it is commonly known as the Chilli Pepper or Bell Pepper. In British English, they are all called Peppers, whereas in Australian and Indian English, there is no commonly used name encompassing all its forms, the name Capsicum being commonly used for bell peppers exclusively. Pungent fruits of all cultivated Capsicum species as a collective class are called „chillies‟ in the Food and Agriculture Organization (FAO) Yearbook (Anon., 1997). Different varieties of the genus Capsicum are widely grown for their fruits, which may be eaten fresh, cooked, as a dried powder, in a sauce, or processed into oleoresin (Poulos, 1993). Peppers (figure 2.7) are well-known for their health benefits. Herbalists have long promoted peppers for their health-enhancing effects. These include clearing the lungs and sinuses, protecting the stomach by increasing the flow of digestive juices, triggering the brain to release endorphins (natural painkillers), making your mouth water, which helps to neutralize cavity-causing acids, and helping protect the body against cancer through antioxidant activity. Peppers have been reported to contain an anticoagulant that helps prevent the blood clots that can cause heart attacks (Andrews, 1995). Peppers offer a number of nutritional values. They are excellent sources of vitamin C and vitamin A. They also are a source of vitamin B6, folic acid, beta-carotene, and fiber. Red peppers also contain lycopene, believed important for reducing risk of certain cancers (GMF, 2008). Pepper have many health benefits like the protection against free radicals, reduce risk
  • 29. 29 of cardiovascular disease, promote optimal health, promote lung health, protect us against rheumatoid arthritis and seeing red may mean better eyesight (Ensminger and Esminger, 1986). Peppers, among vegetables, have become extremely popular for the abundance and the kind of antioxidants they contain. Among the antioxidant phytochemicals, polyphenols deserve a special mention due to their free radical scavenging properties. These compounds whose levels vary strongly during growth and maturation are also important because of their contribution to pungency, bitterness, colour and flavour of fruits (Estrada et al., 2000). The attractive red colour is due to the various carotenoid pigments, which include β- carotene with pro-vitamin A activity and oxygenated carotenoids such as capsanthin, capsorubin and cryptocapsin, which are exclusive to this genus and are shown to be effective free radical scavengers (Matsufuji et al., 1998). Red peppers also contain moderate to high levels of neutral phenolics or flavonoids, namely quercetin, luteolin and capsaicinoids (Hasler, 1998). Antioxidant compounds and their antioxidant activity in 4 different coloured (green, yellow, orange, and red) sweet peppers (Capsicum annuum) were investigated. The total phenolics content of green, yellow, orange, and red peppers determined by the Folin- Ciocalteau method were 2.4, 3.3,3.4, and 4.2 μmol catechin equivalent/g fresh weight, respectively. The red pepper had significantly higher total phenolics content than the green pepper. Among the 4 different coloured peppers, red pepper contained a higher level of β- carotene (5.4 μg/g), capsanthin (8.0 μg/g), quercetin (34.0 μg/g), and luteolin (11.0 μg/g). The yellow pepper had the lowest β-carotene content (0.2 μg/g), while the green one had undetectable capsanthin and the lowest content of luteolin (2.0 μg/g). The free radical scavenging abilities of peppers determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method were lowest for the green pepper (2.1 μmol Trolox equivalent/g) but not significantly different from the other 3 peppers (Sun et al., 2007).
  • 30. 30 Plate 7: Peppers Source:
  • 31. 31 2.5.3 Antioxidant Properties of Eggplants (Solanum melongena) Eggplant or Solanum melongena (figure 2.8) is a common and popular vegetable crop grown in the subtropics and tropics. Eggplant is a perennial but grown commercially as an annual crop. The ripe fruit of eggplant is primarily used as a cooking vegetable for the various dishes all over the world. Eggplants are coming from various kinds of varieties, which are highly variable for fruit colour, as well as fruit shape and size. Therefore different varieties of eggplant consist of different phenolic compound and antioxidant properties. Furthermore, eggplant is a local vegetable, easy to find and it is commonly being a side dishes of Malaysian and yet it have many nutritional benefits, not only provided antioxidant properties but also help in development of blood vessels, required to prevent tumor growth and metastasis, and also inhibit inflammation that can lead to atherosclerosis (Matsubara et al., 2005). The antioxidant activities of five varieties of eggplant were correlated with the total amount of phenolic and flavonoid. There was significant correlation between the hepatoprotective activities and total phenolic/flavonoid content and antioxidant activities, indicating the contribution of the phenolic antioxidants present in eggplant to its hepatoprotective effect on t-BuOOH-induced toxicity (Akanitapichat et al., 2010). Different genotypes of eggplant had nutraceutical and antioxidant properties (Mennella et al., 2010). Thermal treatment commonly used before consumption was found to increase the content and biological activity of antioxidant compounds of eggplants. Extracts from purple-coloured, small size eggplant fruit demonstrated better antioxidant activities than the other samples (long green, purple-coloured moderate size) and this was attributed to the higher phenolic and anthocyanin content since a linear relation was observed between the Total Phenolic Content (TPC) and the antioxidant parameters (Nisha et al., 2009). Anthocyanins from the peels of different accessions of eggplant showed significant antioxidant activities (Matsubara et al., 2005). Eggplant and pea sprout extracts contained high phenolic compounds, anthocyanins, and ascorbic acids which appeared to be responsible for their antioxidant activities and scavenging effects (Bor et al., 2006).
  • 32. 32 Plate 8: Eggplants (Solanum melongena) Source:
  • 33. 33 2.3.4 Antioxidant Properties of Carrots (Daucus carota) Carrot is one of the major vegetable crops cultivated worldwide (figure 2.9). The domesticated types are divided into two groups: the Eastern or Asian carrots (var. atrorubens), with mainly purple and yellow roots; and the Western carrots (var. sativus) with mainly orange roots. Carrots were thought to be domesticated in Afghanistan as the primary centre of diversity and they were spread over Europe, Asia and the Mediterranean area, and the origin of western cultivated carrots were thought to be in the Asia Minor Centre, primarily Turkey (Simon 1996). Carrot was found to exert antioxidant activity though it is not very strong compared to other vegetables. Reactive oxygen species was shown to play a key role as a signalling molecule for the stress-induced accumulation of polyphenol content in carrots (Cao et al., 1996). Carrots dehydrated by ultrasound were found to retain more vitamin C and β-carotene compared to convective air drying (Frias et al., 2010). Carrot ingestion was found to decrease lipemia and improve the antioxidant status in mice (Nicolle et al., 2004). Purple carrot juice was shown to attenuate or reverse all changes in high-carhohydrate, high-fat diet-fed rats, while β-carotene did not reduce oxidative stress, cardiac stiffness, or hepatic fat deposition. As the juice itself did not contain high concentrations of carotenoids, it is more likely that the anthocyanins were responsible for the antioxidant and anti-inflammatory properties of purple carrot juice to improve glucose tolerance as well as cardiovascular and hepatic structure and function (Poudyal et al., 2010). Chlorogenic acid was a major antioxidant in all seven coloured carrots, but anthocyanins were the major antioxidant in purple-yellow and purple- orange carrots. Carotenoids were not found to contribute to the total antioxidant capacity, but correlated well with antioxidant capacity of hydrophobic extracts. Both the DPPH and ABTS assays showed that the hydrophilic extract had higher antioxidant capacity than the hydrophobic extract. Purple-yellow carrots had the highest antioxidants capacity, followed by
  • 34. 34 purple-orange carrots, and the other carrots did not significantly differ (Sun et al., 2009). The white, yellow, and solid-coloured purple carrot cultivars showed quite low contents of carotenoids, but the solid-coloured purple contained most phenolic compounds. The red cultivar was the only one to contain lycopene. The α-carotene showed noteworthy differences in the orange cultivar and the purple cultivar with an orange core, with higher α-carotene content resulting in a higher antioxidative capacity. Also, the lycopene content in red cultivar was higher in 2004 than in 2003, which again lead to an increased antioxidative capacity. Higher phenolics values were found for the purple-coloured cultivars in 2004, which only in the case of the purple cultivar with an orange core, however, led to a higher antioxidative capacity (Grassmann et al., 2007).
  • 35. 35 Plate 9: Carrots Source:
  • 36. 36 CHAPTER THREE 3.0 Conclusion and Recommendations 3.1 Conclusion This paper has reviewed some vegetables (both leafy and non-leafy) and their antioxidant properties. There is still a great deal of vegetables whose antioxidant studies have been carried out both at the preliminary and advanced stage. The consumption of these vegetables, fruits and mushrooms is capable of preventing and protecting against some of the diseases arising from the ingestion of mycotoxin contaminated foods in both humans and livestock. These vegetables are useful for the general wellbeing of man and livestock. They help in improving the body functions and preventing of diseases associated with oxidative stress in the body cells. Since vegetables are cheap to obtain and they are sufficiently available, their consumption will reduce dependency on the use of synthetic antioxidants by human and livestock. 3.2 Recommendations A substantial quantity of vegetables should be consumed because of their importance to the body. Those required to be processed before consumption should not be over-processed so as not to destroy the nutrients in them particularly their antioxidant properties. Fruits, vegetables and berries are to be planted in gardens at home backyards. This will increase their readily availability in time of their need. Animals should be fed greens so that they will have access to ready vitamins and other nutritionally needed nutrients.
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