Antioxidant properties of some leafy and non leafy vegetables in west africa
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
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
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.
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),
Buds bulbs e.g. Onions (Allium pa), Garlic (Allium salvum), etc.
Vine fruits e.g. Cucumber (Cucumis sativus), pumpkin (Cucurbita maxima), etc.
Berry fruits e.g. African eggplant (Solanum macrocarpon), Tomato (Lycopersium
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).
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.,
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).
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
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).
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
iii. Repair and de novo antioxidants (some proteolytic enzymes, repair enzyme of DNA
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
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).
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.,
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
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
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.
Plate 2: Telfairia occidentalis (Fluted pumpkin)
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
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).
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
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.
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).
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,
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
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.
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
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
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.
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
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
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).
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).
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
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).
3.0 Conclusion and Recommendations
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.
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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