Vitamin C contents of tropical vegetables and foods determines by voltammetric and titrimetric methods and their relevance to the medicinal uses of the plants

Abstract

Vitamin C contents measured as ascorbic acid, in thirty-eight samples of tropical leafy vegetables and foods were determined by two methods. One was by cyclic voltammetry using glassy carbon, Ag/AgCl and platinum electrode system in 0.1M phosphate buffer, pH 2.0 containing 1mM Na 2 EDTA in a potential range of 200 mV – 1000 mV using a scan rate of 50 mV/S. The anodic peak current for the electrochemical oxidation of ascorbic acid to dehydroascorbic acid was recorded at 580 mV. The other method involved titration of aqueous mixtures of the samples using N-bromosuccinimide. Samples identified to be rich in vitamin C include red pepper (123.73 mg/100 g) and the leaves of white camwood (211.20 mg/100 g), climbing black pepper (181.19 mg/100 g), curry plant (140.50 mg/100 g), fluted pumpkin (129.39 mg/100 g), amaranth globe (97.49 mg/100 g) and jute mallow (serrated edge, 89.94 mg/100 g). Boiling of aqueous mixtures of some vegetables reduced the vitamin C content by 20-43%. The results obtained by both methods were comparable for several samples but were appreciably different for some green leafy vegetables. The data in this report further enlarge the database of vitamin C contents in tropical fruits and vegetables which are sparse in literature and will serve as a useful guide in the selection of plants which are rich in vitamin C. The relevance of the vitamin C contents with medicinal uses of some of the plants is discussed.

Full text

Int. J. Electrochem. Sci., 5 (2010) 105 - 115
International Journal of
ELECTROCHEMICAL
SCIENCE
www.electrochemsci.org
Vitamin C Contents of Tropical Vegetables and Foods
Determined by Voltammetric and Titrimetric Methods and
Their Relevance to the Medicinal Uses of the Plants
M. Ogunlesi
*
, W. Okiei, L. Azeez, V. Obakachi, M. Osunsanmi, G. Nkenchor
Chemistry Department, University of Lagos, Akoka, Lagos, Nigeria
*
E-mail: mayogunlesi@yahoo.com
Received: 29 August 2009 / Accepted: 11 January 2010 / Published: 31 January 2010
Vitamin C contents measured as ascorbic acid, in thirty-eight samples of tropical leafy vegetables and
foods were determined by two methods. One was by cyclic voltammetry using glassy carbon, Ag/AgCl
and platinum electrode system in 0.1M phosphate buffer, pH 2.0 containing 1mM Na
2
EDTA in a
potential range of 200 mV – 1000 mV using a scan rate of 50 mV/S. The anodic peak current for the
electrochemical oxidation of ascorbic acid to dehydroascorbic acid was recorded at 580 mV. The other
method involved titration of aqueous mixtures of the samples using N-bromosuccinimide. Samples
identified to be rich in vitamin C include red pepper (123.73 mg/100 g) and the leaves of white
camwood (211.20 mg/100 g), climbing black pepper (181.19 mg/100 g), curry plant (140.50 mg/100
g), fluted pumpkin (129.39 mg/100 g), amaranth globe (97.49 mg/100 g) and jute mallow (serrated
edge, 89.94 mg/100 g). Boiling of aqueous mixtures of some vegetables reduced the vitamin C content
by 20-43%. The results obtained by both methods were comparable for several samples but were
appreciably different for some green leafy vegetables. The data in this report further enlarge the
database of vitamin C contents in tropical fruits and vegetables which are sparse in literature and will
serve as a useful guide in the selection of plants which are rich in vitamin C. The relevance of the
vitamin C contents with medicinal uses of some of the plants is discussed.
Keywords: Vitamin C, Cyclic voltammetry, N-bromosuccinimide, Tropical leafy vegetables,
Medicinal uses
1. INTRODUCTION
Most tropical countries have vegetation containing a diversity of leafy vegetables such as
spinach, amaranth, lettuce that serve as indispensible constituents of the human diet. The use of green
leafy vegetables for the preparation of soups cuts across different cultures in Nigeria and other parts of
West Africa. Vegetables supply the body with minerals, vitamins, certain hormone precursors as well
as proteins and energy [1-4]. Consumption of fruits and vegetables in diet has been reported to protect

Int. J. Electrochem. Sci., Vol. 5, 2010
106
the human body from degenerative diseases [5, 6]. In addition vegetables are important in the diets of
postpartum women as they aid the contraction of the uterus. The main protective action of vegetables
has been attributed to the antioxidants present in them. The oxidative stress experienced by a tissue,
organelle or organ results from the balance between the production and removal of potentially
damaging reactive oxygen species. Antioxidants can prevent the chemical damage caused by reactive
oxygen species such as free radicals that are generated by a variety of sources including pesticides,
tobacco smoke, exhaust fumes, certain pollutants and organic solvents [7-9]. The potential cancer-
inducing oxidative damage might be prevented or limited by dietary antioxidants found in fruits and
vegetables.
Vitamin C also known as ascorbic acid is a water soluble antioxidant which is found in variable
quantities in fruits and vegetables [10, 11] and has been found to prevent tissue damage [12-14]. It has
been identified to prevent sperm agglutination thus making them more motile with resultant
improvement in male fertility. It also enhances sperm quality [15, 16]. Several doctors in Nigeria
routinely prescribe vitamin C to aid recovery in several ailments and diseases including cold, cough,
influenza, sores, wounds, gingivitis, skin diseases, diarrhoea, malaria and bacterial infections.
The increased knowledge of the role of vitamin C has necessitated the development of accurate
and specific methods for its determination. Numerous methods based on instruments, titrations or
colour-formation reactions are available in literature for the determination of vitamin C. Instrument-
based methods which involve the use of specialized and expensive equipment have been reported [17-
20].
Several workers who reported the contents of vitamin C in leafy vegetables grown in Nigeria
and other tropical countries used titrimetric [21-25] and spectrophotometric methods [26, 27]. Direct
spectrophotometric determination of vitamin C in the ultraviolet region is prone to matrix effect since
many organic compounds in complex samples may also exhibit ultraviolet absorbance. Thus there is a
need to adopt a procedure that will determine the contents of vitamin C in tropical leafy vegetables
accurately. Electrochemical methods such as cyclic voltammetry can be used because ascorbic acid is
readily oxidized to dehydroascorbic acid, thus the reaction is electroactive [28-31]. In the cyclic
voltammetric method there is no need to determine end point, thus no error arises from this and there is
little interference by colour. The method is sensitive, fast and peak currents are recorded by the
instrument hence no reading error. In a previous report, we presented values of vitamin C contents in
fifty tropical fruits and seeds determined by cyclic voltammetry and compared to the values obtained
by titrimetric method using N-bromosuccinimide (NBS) [32]. In order to enlarge the database, the
values of vitamin C contents in several tropical leafy vegetables and foods are hereby presented. The
medicinal uses of the plants in diseases where vitamin C can promote healing are discussed.
2. EXPERIMENTAL PART
2.1. Materials and Methods
N-Bromosuccinimide, L-ascorbic acid, sodium dihydrogen phosphate and oxalic acid were
purchased from Sigma-Aldrich Chemie (Steinheim, Germany). The reagents and reference solutions

Int. J. Electrochem. Sci., Vol. 5, 2010
107
were prepared daily and stored in amber bottles to avoid oxidation. 0.1 M phosphate buffer solution
was made up from 0.1M NaH
2
PO
4
and adjusted to pH 2.0 with phosphoric acid. pH measurements
were made with a Metrohm pH meter model 780. De-ionized water was used for the preparation of all
solutions.
2.2. Samples Selected For Analysis
38 samples of tropical leafy vegetables and foods commonly consumed in Nigeria were
obtained from Nigerian Institute of Horticulture (NIHORT), Ibadan, Nigeria and Mushin and Oyingbo
markets in Lagos and environs. The samples obtained from the open markets were identified in
NIHORT. The vegetable and food samples analyzed include, African bush mango leaves (Oro,
Yoruba) (Irvingia gabonesis), amaranth globe leaves (Utazi, Igbo), (Gongronema latifolium), bitter
leaf (Vernonia amygdalina), cabbage leaves (Brassica oleracea), carrot (Daucus carota), climbing
black pepper (leaves and seeds) (Uziza, Igbo) (Piper guinenses), cucumber unpeeled (Cucumis
sativus), curry leaf (Murraya koenigii), fluted pumpkin leaves (Ugu, Igbo) (Telferia occidentalis),
ginger (unpeeled) (Zingiber officinale), green (Amunututu, Yoruba) (Basella alba), green amaranth
(tete, Yoruba) (Amaranthus hybridus), groundnut seeds (Arachis hypogaea), jute mallow leaves
(serrated edge) (Ewedu awoyaya, Yoruba) (Corchorus spp), jute mallow leaves (smooth edge) (Ewedu
angbadu, Yoruba) (Corchorus olitorius), koko vine leaves (Okazi, Igbo) (Gnetum africanum), lemon
grass leaves (Cymbopogon citratus), lettuce (Lactuca sativa), locust bean (Igba, Yoruba) (Parkia
biglobosa), mint leaf (Efinrin, Yoruba) (Ocimum gratissimum), miracle berry leaves (Ewe moinmoin,
Yoruba) (Thaumatococcus danielii), myriantus leaves (Ujuju, Igbo) (Myrianthus arboreus), nut grass
(Ofio, Yoruba) (Cyperus escillentus), Potato (Irish) (Solanum tuberossum L), potato (sweet) (Ipomoea
batatas), raddish (red) (Raphanus sativus), raddish (white), (Raphanus sativus acanthiformis), roselle
calyx [(Isapa,Yoruba) Hibiscus sabdariffa, green variety)], roselle calyx [(Zobo, Hausa) (Hibiscus
sabdariffa, red variety)], sour sop (Annona muricata), spinach (Spinacia oleracea), water hyacinth
(Eichhornia crassipes) which is used as animal feed, water leaf (Gbure, Yoruba) (Talinum
triangulare), water lettuce (Oju-oro, Yoruba) (Pistia stratioles), white camwood leaves (Oha, Igbo)
(Pterocarpus mildbraedii) and yam (Dioscorea spp). Honey though not a vegetable was included in
the samples because it is added to some plant materials and juices in several dietary menu and herbal
preparations. (Yoruba and Igbo are some Nigerian Languages).
2.3. Determination of ascorbic acid by titration with N-bromosuccinimide
The determination was essentially as described in a previous report [32]. A weighed amount of
the sample (5 g) was washed, minced and blended with 0.5% oxalic acid solution for approximately
one minute and filtered through glass wool. The filtrate was transferred to a 100 cm
3
volumetric flask
and the volume made up to the mark with 0.5% oxalic acid solution. A mixture of 10 cm
3
of the
sample solution, 2 cm
3
of 3 % ethanoic acid, 5 cm
3
of 4 % KI and 10 drops of starch indicator was
titrated using 0.01% N-bromosuccinimide as titrant. The mean of three titre values was recorded. All

Int. J. Electrochem. Sci., Vol. 5, 2010
108
analyses were done in triplicate. The ascorbic acid contents in the samples were obtained from the
calibration curves and were used to obtain the values in mg/100 g of sample.
2.4. Determination of ascorbic acid using cyclic voltammetry [32]
A BASI-Epsilon potentiostat/galvanostat was used in the study. A weighed amount (5-6 g) of
the sample was minced and blended with 30 cm
3
of the phosphate buffer for approximately one
minute. The homogenized sample was filtered through glass wool. 15 cm
3
of the filtrate was
transferred to the electrochemical cell, purged with nitrogen for 10 min before scanning the potential
between 200 mV and 1000 mV using a three electrode system consisting of glassy carbon (3 mm) as
working electrode, Ag/AgCl as reference and platinum (1.6 mm) as the auxiliary electrode. The values
of the anodic peak current obtained at 580 mV were used to calculate the concentration of the ascorbic
acid in the vegetable samples using the calibration curve.
2.5. Effect of Heat on Vitamin C Contents of Some Vegetables
The vitamin C contents of jute mallow leaves (C. olitorius), bitter leaf (V. amygdalina) and
fluted pumpkin leaves (T. occidentalis) were also determined by cyclic voltammetry after boiling them
in water for 20 min to ascertain the effect of heat on the vitamin C contents of these leafy vegetables.
3. RESULTS AND DISCUSSION
The voltammograms of the calibration and the generated calibration curve were as reported
previously [32]. The voltammograms for the determination of ascorbic acid content of jute mallow
(Corchorus olitorius) before and after boiling are shown in Figures 1a and 1b.
Figure 1. Voltammograms of Corchorus olitorius extract in 0.1M phosphate buffer, pH 2.0. a=before
boiling; b=after boiling in water for 20 min.
Table 1 shows the ascorbic acid contents of the different vegetables and foods determined by
the two methods. Vegetables found to have high concentrations of ascorbic acid (as measured by
a
b
[
Type a quote

Int. J. Electrochem. Sci., Vol. 5, 2010
109
cyclic voltammetry) in the range of 90-211 mg/100 g of sample include the leaves of amaranth globe,
climbing black pepper, curry leaves, fluted pumpkin, jute mallow (serrated edge) red pepper and white
camwood. Lower but significant levels of ascorbic acid determined by cyclic voltammetry in the range
of 10-75 mg/100 g of sample were found in African bush mango leaves, bitter leaf, cabbage, climbing
black pepper seeds, ginger (unpeeled), green leaves, green amaranth, groundnuts, jute mallow (smooth
edge), koko vine leaves, lettuce, locust bean, mint leaves, miracle berry leaves, myrianthus leaves, nut
grass, potato (Irish), raddish (red and white), roselle calyx (green and red), sour sop, spinach, water
hyacinth, water leaf, water lettuce and honey. Thus when honey is added to menu or herbal
preparations, there is enhancement of vitamin C content.
Low levels of ascorbic acid in the range of 6-10 mg/100 g (cyclic voltammetric determination)
were found in carrot, cucumber, lemon grass, potato (sweet) and yam.
Comparing the values obtained by the two methods, it is observed that the values differ by not
more than 10 mg/100 g that is, 0.1 mg/g in 28 samples, thus are comparable. In 6 samples, the values
differ by 10-20 mg/100 g of sample. In three of these, the differences are 12.58, 10.62, 11.97 mg/100 g
in carrot, green amaranth leaves and jute mallow leaves (serrated edge) respectively. These values are
just above the 10 mg/100 g and can be considered reasonable. The remaining three samples are locust
bean, water leaf and roselle calyx (red variety) where the differences are 19.47, 14.90 and 13.86
mg/100 g respectively. It is also observed that in all the six samples, except green amaranth, the values
obtained by titrimetric are consistently higher. Thus the differences may be due to inaccurate detection
of the end point especially in the coloured materials. However, in five samples, namely bitter leaf,
climbing black pepper leaves, curry leaves, fluted pumpkin leaves and white camwood leaves, the
differences are 93.32, 122.1, 39.66, 41.90 and 82.23 respectively. The values obtained by cyclic
voltammetry are higher in climbing black pepper leaves, curry leaves and white camwood leaves.
Interferences with the reagent or the working electrode by enzymes in the samples may account for the
differences observed.
The effect of heat on the ascorbic acid content of vegetable samples is shown in Figures 1a and
1b for jute mallow leaves (C. olitorius). The vitamin C content of 40.21 mg/100 g for the fresh sample
was found to decrease to 30.65 mg/100 g after boiling the vegetable in water for 20 min. The
reductions of 21% and 47% in the vitamin C contents of bitter leaf (V. amygdalina) and fluted
pumpkin leaves (T. occidentalis) were similarly obtained when these samples were boiled in water for
20 min.
Ejoh et al., 2005 reported ascorbic acid content of 166.5 mg/100 g for bitter leaf (V.
amygdalina) by titrimetric method using the N-bromosuccinimide [22]. Chinma and Igyor, 2007 [25]
reported 14.61 mg/100 g, 21.03 mg/100 g and 12.50 mg/100 g for climbing black pepper leaves,
amaranth globe leaves and white camwood leaves respectively by titrimetric method using 2,6-
dichloroindophenol reagent after the samples had been washed in water and dried in the oven at 60
o
C
for 24 h. The 2,6 dichloroindophenol reagent and the excessive exposure of the samples to heat make it
difficult to draw any comparison between the values of Chinma and Igor [25] and those contained in
this report.

Int. J. Electrochem. Sci., Vol. 5, 2010
110
Table 1. Vitamin C contents of tropical vegetables and foods obtained by cyclic voltammetry (CV)
and titration with N-bromosuccinimide (NBS).
S/No
Sample Amount of ascorbic
acid
%
Diff
eren
ce
Absol
ute
Differ
ence
Relevant
medicinal
uses [33]
Common Name Botanical Name CV
mg/100g
NBS
mg/100g
1. African Bush
mango leaves
[Oro (Yor)]
Irvingia
gabonensis
23.30 27.51 18 4.21 Spleen
infections
2. Amaranth globe
leaves [Utazi
(
Igbo
)]
Gongronema
latifolium
97.49 100.00 3 2.51 Sore gums
3. Bitter leaf
[Ewuro (Yor)]
Vernonia
amygdalina
32.15 125.47 290 93.32 Gingivitis,
diabetes,
malaria, anti-
mi
crobial.
4. Cabbage leaves Brassica
oleracea
var capitata
23.05 13.59 41 9.46 Skin
diseases,
antimicrobial
5.
Carrot
Daucus carota
9.28
21.86
136
12.58
6. Climbing black
pepper leaves.
Uziza (Igbo)
Piper guinenses 181.19 59.01 67 122.18 Impotence,
hypertension,
antimicrobial
7. Climbing black
pepper seeds.
Uziza
(Igbo)
Piper guinenses 14.59 15.48 6 0.89 Impotence,
hypertension,
antimicrobial
8. Cucumber
(unpeeled)
Cucumis sativus 6.99 14.35 105 7.36 Diuretic
9. Curry leaves Murraya
koenigii
140.50 100.84 28 39.66 Herpes, fever
10. Fluted Pumpkin
leaves. Egusi
iroko (Yor), Ugu
(Igbo)
Telfaria
occidentalis
129.39 171.29 32 41.90 Anti-
inflamm-
atory,
arthritis,
cancer, blood
tonic
11. Ginger (unpeeled)
Zingiber
officinale
11.50 15.00 30 3.50 Cold, cough,
malaria,
fever.
12. Green leaves.
Amunututu,
(
Yor)
Basella alba 65.32 70.15 7 4.83 Laxative
13. Green amaranth
Tete abalaye,
(Yor)
Amaranthus
viridis.
60.12 49.50 18 10.62 Eye diseases,
gonorrhea,
diuretic, anti-
inflammatory
14. Groundnuts Arachis
hy
pogaea
43.74 42.95 2 0.79 Antimicrobia
l
15. Jute mallow
leaves
(serrated
Corchorus spp 89.94 101.91 13 11.97 Abscesses,
fever.

Int. J. Electrochem. Sci., Vol. 5, 2010
111
edge). Ewedu
awoyaya (Yor)
16. Jute mallow
leaves (smooth
edge) Ewedu
angbadu(Yor)
Corchorus
olitorius
40.21 44.74 11 4.26 Abscesses,
fever
17. Koko vine leaves
Okazi, (Igbo)
Gnetum
africanum
56.27 46.36 18 9.91 Wounds,
colds and
spleen
18. Lemon grass
leaves
Cymbopogon
citrates
9.37 10.00 7 0.63 Malaria,
coughs, cold,
diuretic
19. Lettuce leaves Lactuca sativa 22.27 13.00 42 9.27 Diuretic,
constipation
20. Locust bean.
[Igba (Yor)]
Parkia biglobosa 73.23 92.65 27 19.47 Wounds,
malaria, high
blood
pressure,
anti-tumour.
21. Mint leaf.
Efinrin-nla (Yor)
Ocimum
gratissimum
52.75 46.00 13 6.75 Wounds, anti
bacterial,
cold,
hypertension
22. Miracle berry
leaves. [Ewe
moimoin
(Yor)]
Thaumatococcus
danielii
28.67 26.40 8 2.27
23. Myriantus leaves
[Ujuju (Igbo)]
Myrianthus
arboreus
15.93 10.55 34 5.38 Dysentery,
cough,anti-
tumour
24. Nut grass
[
Ofio
, (Yor)]
Cyperus
esculen
tus
11.45 13.37 17 1.92
25. Potato (Irish) Solanum
tuberosum
L
11.45 8.00 30 3.45
26. Potato (sweet) Ipomoea batatas 6.15 4.28 30 1.87 Boils,
wounds,
antimicrobial
27. Raddish (red) Raphanus
sativus
36.20 36.45 1 0.25
28. Raddish (white) Raphanus
sativus
acanthiformis
39.19 40.82 4 1.63
29. Red pepper
[Bawa (Hau)]
Capsicum spp 123.73 126.05 2 2.32 Colds. Anti-
inflammatory
30. Roselle calyx
(green variety)
[Isapa (Yor)]
Hibiscus
sabdariffa
27.50 29. 20 6 1.70 Cough,
dressing of
wounds,
diuretic
31. Roselle calyx (red
variety).
Hibiscus
sabdariffa
32.14 46.00 43 13.86 Cough,
diuretic,

Int. J. Electrochem. Sci., Vol. 5, 2010
112
[Zobo (Hau)] dressing of
wounds
32. Sour sop Annona muricata
10.51 13.63 30 3.12 Fever
33. Spinach Spinacia
oleracea
35.67 38.75 9 3.08
34. Water hyacinth Eichhornia
crassipes
10.19 16.34 60 6.15 Skin care,
goiter
35. Water leaf [Gbure
(Yor)]
Talinum
triangulare
21.82 36.72 68 14.90 Shistosomias
is, scabies,
fresh cuts,
high blood
pressure,
anaemia.
36. Water lettuce
[Oju oro (Yor)]
Pistia stratiotes 21.02 19.00 10 2.02 Skin rashes,
boils, sores,
colds.
37. White camwood
leaves [ Oha
(Igbo)]
Pterocarus
mudbraedii
211.20 129 39 82.2
38. Yam tuber Dioscorea
rotundata
7.77 7.52 3 0.25
39. Honey 27.78* 33.47* 21 5.69 Cold, cough,
wound
healing
*Values as mg/ 100 cm
3
KEY: CV = cyclic voltammetric determination; NBS = N-Bromosuccinimide titrimetric
determination; Yor = Yoruba; Hau = Hausa.
It is pertinent to relate the vitamin C content of these vegetables and food samples to the
alleged curative uses in herbal medicine. Several of these samples are alleged to be useful in the
treatment of sores, cuts, wounds, abscesses, malaria, skin diseases and cold [33]. These medicinal uses
are stated in Table 1. Such samples include amaranth globe (97.49), bitter leaf (32.15), cabbage
(23.05), ginger (11.50), honey (27.78), jute mallow (serrated, 89.94; smooth, 40.21), koko vine
(56.27), lemon grass (9.37), locust bean (73.23), mint leaf (52.75), potato (sweet, 6.15), red pepper
(123.73), roselle calyx (green variety) (27.50), roselle calyx (red variety) (32.14), water leaf (21.82),
water lettuce (21.02). These plants, except ginger, lemon grass and potatoes (sweet) have medium-high
vitamin C content. Potatoes (sweet) are often consumed in larger quantities than vegetables and thus
significant quantities of vitamin C will be present in such menu.
Vitamin C has been reported to be protective and therapeutic in cardiovascular diseases [34-36]
and some of these plants are alleged to be useful as diuretic or antihypertensive [33]. These include
climbing black pepper [leaves (181.19), seeds (14.59)], cucumber (unpeeled, 6.99), lemon grass (9.37),
locust bean (73.23), mint leaf (52.75) and roselle calyx [(green variety) (27.50), (red variety) (32.14)].
Several of these plants have high vitamin C content. Raised blood pressure is a major cause of stroke
and studies have shown that high intake of fruits and vegetables is associated with reduced risk of

Int. J. Electrochem. Sci., Vol. 5, 2010
113
ischemic stroke [37, 38]. Thus, the plants listed have the potential to reduce high blood pressure and
hence would have preventive activity against stroke.
Vitamin C has also been reported to be protective and therapeutic in cancer [39]. Fluted
pumpkin (129.39) is alleged to be useful in the herbal treatment of cancer while myriantus (15.93) is
alleged to be helpful as an antitumour herbal medicine [33]. While fluted pumpkin leaves are rich in
vitamin C, myriantus leaves will not be considered rich. Thus myrianthus leaves probably contain
other anti-cancer constituents.
Vitamin C is also reported to be protective and therapeutic in eye diseases [40]. Green
amaranth is moderately rich in vitamin C (60.12). It is used as herbal treatment for eye diseases [33,
41].
Vitamin C, functioning as an antioxidant, has been reported to be relevant in the treatment of
male infertility factor [15, 16]. Climbing black pepper (leaves, 181.19, seeds, 14.59) are used in herbal
medicine to treat impotence which is synonymous with male infertility in local terminology.
Thus several plants which are rich in vitamin C appear to have therapeutic values although
there may be no clinical trials to support this observation.
4. CONCLUSIONS
This report further enlarges the database for the vitamin C content in several tropical fruits,
vegetables, seeds and foods. The results presented in this report will provide a suitable guide to the
population in their choice of vegetables with high content of vitamin C. Adequate consumption of the
vegetables with high vitamin C content will result in improved health thereby reducing cardiovascular
diseases, diabetes, eye diseases, infertility and cancers that are prevalent in Africa.
The cyclic voltammetric method can be used in Quality Control laboratories for rapid and
accurate determinations of quantitative values of vitamin C in agricultural samples and in
pharmaceutical preparations.
ACKNOWLEDGMENTS
We wish to express appreciation to Professor Omowunmi Sadik of State University of New York,
Binghamton, USA for her interest and helpful suggestions. We are also grateful to Dr. A. Akintoye of
the vegetable Department, Nigerian Institute of Horticulture Ibadan for identification of vegetable and
food samples.
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