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International Journal of Biological Sciences and Applications
2017; 4(2): 19-24
http://www.aascit.org/journal/ijbsa
ISSN: 2375-3811
Keywords
Amino Acids,
Leafy Vegetables,
Amaranthus hybridus,
Protein,
Talinum triangulare,
Telfairia occidentalis,
Vernonia amygdalina,
Wukari
Received: March 13, 2017
Accepted: March 27, 2017
Published: June 13, 2017
Protein Levels and Amino Acids
Composition in Some Leaf
Vegetables Sold at Wukari in
Taraba State, Nigeria
Arowora K. A., Ezeonu C. S.*, Imo C., Nkaa C. G.
Department of Biochemistry, Federal University, Wukari, Nigeria
Email address
chuksmaristos@yahoo.com (Ezeonu C. S.)
*Corresponding author
Citation
Arowora K. A., Ezeonu C. S., Imo C., Nkaa C. G. Protein Levels and Amino Acids Composition
in Some Leaf Vegetables Sold at Wukari in Taraba State, Nigeria. International Journal of
Biological Sciences and Applications. Vol. 4, No. 2, 2017, pp. 19-24.
Abstract
This study was conducted to determine the protein and energy levels, and also amino
acids content in some leafy vegetables. Amino acids composition was determined using
High Performance Liquid Chromatography (HPLC) method, energy determination was
by the bomb calorimetric method while other analyses carried out on the vegetables were
adapted from well-known standardized methodologies by Association of Official
Analytical Chemists (AOAC). The result obtained shows that moisture content in the
leafy vegetables ranged between 10.20±0.00 and 10.875 ± 0.0071% with water leaf
(Talinum triangulare) having the highest mean percentage water content of
10.875±0.0071%. Also, protein values in the leafy vegetables gave a range of
11.1726±0.0232 to 25.036±0.0078% with the highest mean protein content of
25.036±0.0078% obtained in pumpkin leaf (Telfairia occidentalis). The amino acid
composition showed the following range in individual leaf vegetables: 1.035 ±0.0071 -
5.415±0.0071 g/100 g in spinach Leaf (Amaranthus hybridus), 1.14±0.0071 -
7.83±0.0141 g/100 g in bitter leaf (Vernonia amygdalina), 1.26±0.0141 - 8.745±0.0071
g/100 g in pumpkin leaf (T. occidentalis) and 0.985±0.0071-4.96±0.014 g/100 g in water
leaf (T. triangulare). It was discovered that the energy content was highest in T.
occidentalis (216.365±0.0212 Kcal/100g while the least was recorded for water leaf
(153.745±0.0071 Kcal/100g). Based on the findings in the analysis carried out in this
study, it can be concluded that T. occidentalis appeared to have superior nutritional
values than other leaf vegetables analyzed.
1. Introduction
Green foliage vegetables, especially the known leafy ones consumed in Nigerian
household are indispensable part of many culinary preparations in various household.
Many of these leaf vegetables are found all over the country, however, there are
particular types easily associated by some regions due to the importance attached to them
and rate of consumption in such regions in Nigeria. It is well known that vegetables
abound in nutrients especially minerals and vitamins which serve as sources of
replenishment of these nutrients in humans who need them on daily basis for proper
metabolic and biochemical functions. According to Omoyeni et al. [1] studies have
repeatedly shown that increasing colon and stomach cancer correlate with low vegetable
meals and it has been suggested that vegetables may help resist them.
International Journal of Biological Sciences and Applications 2017; 4(2): 19-24 20
There is also increasing epidemiological evidence in
favour of an association between nutrition and susceptibility
to infection. Health disorders such as appendicitis,
hemorrhoids, gall stones, heart diseases, obesity and
constipation can be either corrected, or treated by copious
consumption of vegetables [2]. According to Aregheore, [3]
green leafy vegetables provide cheap and abundant sources
of proteins. Vegetables can also synthesize amino acids from
a wide range of available primary materials such as carbon
dioxide, water and atmospheric nitrogen as in legumes [4-
11]. Vernonia amygdalina used as a fence post and pot-herb
in the home and villages is one of the most widely consumed
leaf vegetables in most countries in West and Central Africa
[12]. V. amygdalina plant commonly found around homes in
Southern Nigeria as a green vegetable or spice especially in
the popular “bitter-leaf soup” [13]. Amaranthus hybridus is
known to people from South Eastern Nigeria as ‘inene’ and it
belongs to the family Amaranthacae [14]. Spinach (A.
hybridus) tolerates varying soil and climatic conditions but
altitudes of over 1500 ft are unsuitable [15]. Fluted pumpkin
(Talfairia occidentalis Hoof) is a tropical vine grown
primarily for the leaves and edible seed as an important
component of food of many people in West Africa [16].
Housewives in Nigeria prefer the female leaves of T.
occidentalis leading to higher demand [17]. The young
shoots and leaves of the female plant form main ingredients
in edikangikong, a soup favoured by people in Cross River
and Akwa Ibom state, Nigeria [17]. Fluted pumpkin
commonly known as ‘ugu’ is the most sought after vegetable
used in all culinary activity in Eastern Nigeria. Water leaf
(Talinum triangulare) is a common vegetable cultivated and
consumed in all parts of Nigeria in combination with other
vegetables such as bitter leaf and fluted pumpkin in vegetable
soup where it is believed to provide much needed softness in
texture of such soups considering that other vegetables are
relatively hard. It is also prepared with tomatoes when used
in stew preparation. This research is aimed at quantification
of the level of proteins and amino acid composition in some
selected leafy vegetables popularly sold in Wukari market,
Taraba State, Nigeria.
2. Materials and Method
2.1. Study Location
The study was conducted at Federal University Wukari in
Taraba State, which is located in north-eastern region of
Nigeria on Longitude 9.783°E and Latitude 7.850°N. The
physico-chemical analysis was carried out at the Department
of Animal Production Laboratory of Adamawa State
University, Mubi, Adamawa State.
2.2. Amino Acid Assay
Amino acid analysis was carried out with the aid of
High Performance Liquid Chromatography (HPLC)
equipped with UV 338 nm detector, column with C18, 2.5
x 200 mm, 5 µm column and a mobile phase of 1:2:2 (100
mM sodium sulphate, pH 7.2; acetonitrile; methanol
(v/v/v) at a flow rate of 0.45 ml/min and an operating
temperature of 40°C.
2.3. Sources of Leaf Vegetable Samples
The leafy vegetables used for this project were
purchased from new market at Wukari in Taraba State.
These leaf vegetables are; bitter leaf (Vernonia
amygdalina), spinach leaf (Amaranthus hybridus),
pumpkin leaf (Telfiaria occidentalis), and water leaf
(Talinum triangulare).
2.4. Treatment of Sample
The harvested individual leaf vegetable samples were
washed using clean distilled water, destalked, mixed together
and air-dried. The dried samples of each leaf vegetable were
mixed and kept in a polythene bag in a cool and dried place
pending analysis.
2.5. Physico-Chemical Analysis
Standard methodologies by Association of Official
Analytical Chemists [18] were used to determine:
2.6. Protein Analysis
Protein levels in samples were carried out using the
Kjeldahl nitrogen determination of protein with results
adjusted through calculation as:
2.7. Moisture Content Determination
Moisture contents of the various leaf vegetable were
determined by using oven (GenlabMiNO/30 UK).
Differences in weight are calculated as:
!" # $%&'()* &" # $&'()
$
2.8. Gross Energy Composition
Determination
The gross energy composition of the samples was
determined using Gallen Kamp oxygen ballistic bomb
calorimeter. Calculate the energy value of the sample in kcal
per gram of sample [18].
21 Arowora K. A. et al.: Protein Levels and Amino Acids Composition in Some Leaf Vegetables Sold at
Wukari in Taraba State, Nigeria
3. Result
All the leafy vegetables showed appreciable energy
content (Table 1) with highest mean energy
(216.37+,-() obtained in pumpkin leaves. The
mean water content per dry mass in all the leaves was below
11% in all samples (Table 2). The highest (25.04±0.01%) and
lowest (11.17±0.02% mean protein percentage were obtained
in pumpkin and water leaves respectively (Table 3). Amino
acid analysis (Table 4) shows mean amount of its contents.
The amino acid composition showed the following range in
individual leaf vegetables: 1.035 ±0.0071 - 5.415±0.0071
g/100 g in spinach leaf (A. hybridus), 1.14 ± 0.0071 - 7.83 ±
0.0141 g/100 g in bitter leaf (V. amygdalina), 1.26 ± 0.0141 -
8.745 ± 0.0071 g/100 g in pumpkin leaf (T. occidentalis) and
0.985 +. * / + g/100 g in water leaf (T.
triangulare).
Table 1. Energy composition of samples analyzed.
Samples Mean (kcal/100 g))
Pumpkin leaves 216.37
+
Spinach 187.55
+
Water leaves 153.75
+
Bitter leaf 197.87
+
Table 2. Moisture content of sample analyzed.
Sample Mean (%)
Pumpkin leaves 10.75
+
Spinach 10.53
+
Water leaf 10.88
+
Bitter leaf 10.20
+
Table 3. Protein composition of samples analyzed on dry matter basis.
Samples Mean (%)
Pumpkin leaves 25.04
+
Spinach 16.28
+
Water leaf 11.17
+
Bitter leaf 18.41
+
0.02
Table 4. Amino Acid Profile.
Amino acid Mean (g/100 g) Pumpkin
(T. occidentalis)
Mean (g/100 g) Spinach leaf
(A. hybridus)
Mean (g/100 g) Bitter leaf
(V. amygydalina)
Mean (g/100 g) Water leaf
(T. triangulare)
Lysine 3.71
+
2.12
+
3.42
+
2.84
+
Threonine 2.11
+
1.44
+
0
2.06
+
1.24
+
Cysteine 1.26
+
1.04
+
1.15
+
0.99
+
Valine 4.12
+
2.65
+
3.99
+
2.17
+
Tryptophan 5.35
+
3.88
+
4.67
+
3.13
+
Methionine 2.26
+
0.01 1.455
+
1.98
+
0.00 1.29
+
Isoleucine 2.53
+
1.77
+
2.15
+
0.01 1.86
+
Leucine 5.95
+
3.57
+
0.01 5.11
+
0.01 2.97
+
Tyrosine 2.87
+
1.56
+
0.01 2.58
+
2.21
+
Phenylalanine 3.52
+
2.96
+
0.01 3.65
+
0.01 3.42
+
Histidine 2.28
+
1.34
+
0.01 2.38
+
0.01 1.07
+
Arginine 3.97
+
3.01
+
3.84
+
2.88
+
Aspartic acid 6.83
+
0.01 5.42
+
6.55
+
4.96
+
Serine 4.32
+
2.77
+
4.55
+
1.87
+
Glutamic acid 8.75
+
5.05
+
7.83
+
4.75
+
0.00
Proline 2.13
+
1.27
+
0.00 3.63
+
1.26
+
0.01
Glycine 2.87
+
0.01 1.39
+
2.76
+
0.01 1.35
+
Alanine 2.76
+
0.01 1.09
+
2.52
+
2.27
+
0.01
4. Discussion
4.1. Moisture Content
Water is one of the major nutrients required by the body
for proper development. It aids in digestion and absorption of
food. Water constitutes by far bulk of each fresh vegetable or
leguminous substance for absorption by plants, as food is
dependent on the presence of water [19]. According to
Fontana, [20] the water activity (moisture content) of a food
describes the energy state of water in the food, and hence its
potential to act as a solvent and participate in
chemical/biochemical reactions and growth of
microorganisms. It is an important property that is used to
predict the stability and safety of food with respect to
microbial growth, rates of deteriorative reactions and
chemical/physical properties. The moisture content of food
item could be used as an index of stability and susceptibility
to fungal and bacterial infection [21]. Result obtained for
moisture determination of pumpkin, spinach, water, and
bitter leaves studied showed that the level of moisture
content in each of the leaves by dry mass estimation are
similar and moderately high showing values greater than
10% and below 11 (Table 2). In the analysis carried out, it
was discovered that water leaf has the highest water content
(10.88 + %) compared to other samples. The moisture
content values obtained in this work was lower than those of
Adegunwa et al. [22], whose analysis of bitter leaf (V.
amygdalina), fluted pumpkin (T. occidentalis), water leaf (T.
triangulare), and indian spinach (Basella alba) with dry
matter content ranged from 35.5% to 39.3%. The high-water
content of leafy vegetables may therefore be responsible for
their higher rate of perishability since favourable
International Journal of Biological Sciences and Applications 2017; 4(2): 19-24 22
environment is provided for fungi and bacteria deterioration.
Compared to similar analysis elsewhere as explained above,
water content from the leafy vegetable in this study showed
that it may have better shelf life. Diet wise, good quantity of
water is provided by the leafy vegetables which is sufficient
in biochemical reactions during human metabolism.
4.2. Crude Protein
The protein content obtained is known as “crude protein”
because most other forms of nitrogen may be digested as
protein such as nucleic acids and nitrogen [23]. About 80%
of protein from vegetables sources is absorbed by the body.
Crude protein levels obtained in this research were higher in
pumpkin leaves (T. occidentalis) (25.036+.1) than in
other samples: spinach (A. hybridus) (16.28±0.02%), water
leaf (T. triangulare) (11.17±0.02%) and bitter leaf (V.
amygdalina) (18.41±0.02%). This value is corroborated by
the findings of Mohammed and Mann, [24] whose crude
protein value obtained from T. occidentalis (21.95%) was
slightly lower than the value obtained in this work. Also, the
level of crude protein is much higher in the analyzed
pumpkin leaves in this research than in the level (3.15g/100
g) obtained for nutritive value of pumpkin leaves elsewhere
[25]. However, the values obtained by Adegunwa et al. [22],
showed that the protein content obtained in sun-dried
vegetables samples ranged from 23.4% in V. amygdalina to
31.1% in T. accidentalis. In their blanched and sun-dried
samples, the protein content ranged from 19.5% in T.
triangulare to 23.4% in T. occidentalis. Other values of crude
protein in leafy vegetables analyzed obtained elsewhere [23]
were higher than those of this research with the exception of
pumpkin leaves (T. occidentalis). Variation in soil nutrient,
environmental influence, and period of cultivation could be
the reason for the differences observed. Generally, the
activities of enzymes involved in metabolic pathways like the
nitrate reductase enzyme, carboxypeptidases, amino
peptidases and endopeptidases are higher in the pumpkin
leave [26]. In adults, more than 250 g of protein are
synthesized and degraded per day, compared to an average
daily intake of approximately 55 - 100 g per day [27]. This
therefore means that there is need for steady replacement of
protein and leaf vegetables could be ideal source of
replenishment of extra protein thus needed. According to the
Food and Nutrition Board (FNB) at the Institute of Medicine,
the recommended dietary allowance of protein for both adult
men and women is 800 mg of good quality protein per kg of
body weight per day [28]. Implication of the finding is that
all the vegetables examined have moderate contents of
protein while the pumpkin leaves indisputably source of
choice for protein content in vegetables
4.3. Calories
In the analysis carried out, it was observed that fluted
pumpkin has the highest level of calories compared to other
samples (Spinach (187.55±0.01 kcal/100 g), Water leaf
(153.75±0.01 kcal/100 g) and bitter leaves (197.87±0.01
kcal/100 g). The fluted pumpkin has about 216.37 +
kcal/100 g in terms of energy composition. It is quite
possible because the leaves are photosynthetically more
active (due to higher chlorophyll content and exposure to
sunlight). The energy values of the vegetables obtained by
Mohammed and Mann, [24] showed that it was highest in the
stem of African spinach (183.93 kcal/100 g) which is
comparable but lower than the value obtained in this
research. Their lowest gross energy was in the root of water
leaf plant (37.73 kcal/100 g) which is lower than the least
value of 153.75±0.01 kcal/100 g obtained in the water leaves
analyzed in this work. Thus, the energy value agrees with the
general observation that vegetables have low energy values
[29].
4.4. Amino Acid
Amino acid analysis (Tables 4) show mean amount range
of sample contents: pumpkin leaves between 2.11±0.01 to
5.95±0.01% for the essential amino acids and 1.26 ± 0.01 to
8.75 ± 0.01% for the non-essential amino acids (Table 4),
spinach leaves between 1.34±0.01 to 3.88±0.01% for
essential amino acids and 1.04±0.01 to 5.42±0.01% for non-
essential amino acids (Table 4), bitter leaves has range of
1.98±0.00 to 5.11±0.01% for essential amino acids and
1.15±0.01 to 7.83±0.01% for non-essential amino acids,
while water leaves has range of 1.07±0.01 to 3.42±0.01% for
the essential amino acids and mean range of 0.99±0.01 to
4.96±0.01% for non-essential amino acids (Table 4),
respectively.
Although the free amino acids dissolved in plasma and
tissue (some gotten from leaf vegetables) represents only a
very small proportion of the body’s total mass of amino
acids, they are critical for the nutritional and metabolic
control of the body’s proteins. Unlike total body protein, the
concentrations of individual free amino acids in body fluids
can change substantially in response to dietary variations or
pathological conditions [30] thus the leafy vegetables
examined in this research could provide specific amino acids
needed by the body. The body’s capacity to conserve
individual amino acids at low intakes varies widely, so the
pattern of amino acids needed in the diet to match their
individual catabolic rates does not correspond precisely with
the composition of body protein [31]. The outstanding
essential amino acid in this research was leucine which
content is dominant in all the leafy vegetables investigated
viz: pumpkin leaf (5.95±0.01%), spinach (3.57±0.01%),
bitter leaf (5.11±0.01%), and water leaf (2.97±0.01%). The
values derived from consumption of these vegetable is
attributable to the leucine content and their importance as
explained by Gold, [32] some of which are: healing and
repair of muscle tissues, clotting at site of injuries,
production of growth hormones, regulation of blood sugar,
increasing endurance and provision of energy in the body.
Other essential amino acids with appreciable contents
obtained in the analyzed vegetables include: tryptophan in
pumpkin leaf (5.35±0.01%), spinach (3.88±0.01%), bitter
leaf (4.67±0.01%) and water leaf (3.13±0.02%) and
23 Arowora K. A. et al.: Protein Levels and Amino Acids Composition in Some Leaf Vegetables Sold at
Wukari in Taraba State, Nigeria
phenylalanine in pumpkin leaf (3.51±0.01%), spinach
(2.96±0.01%), bitter leaf (3.65±0.01%) and water leaf
(3.42±0.01%). Gold, [32] explained that phenylalanine is
needed in treating brain disorder, normal functioning of the
central nervous system, control of symptoms of depression
and chronic pain, while tryptophan is important in the
manufacture of neurotransmitter serotonin, which regulates
mood and sleep pattern, treatment of jet lag, depression and
binge eating. It is also required for treating vascular
migraines, panic attacks, rheumatoid arthritis, and normal
functioning of the central nervous system. The most notable
non-essential amino acids in this research were: aspartic acid
in pumpkin leaf (6.83±0.01%), spinach (5.42±0.01%), bitter
leaf (6.55±0.01%), and water leaf (4.96±0.01%) and glutamic
acid in pumpkin leaf (8.75±0.01%), spinach (5.05±0.01%),
bitter leaf (7.83±0.01%) and waterleaf (4.75 +0.00%).
Cysteine is observed to be the limiting amino acid in this
research showing the lowest content of 0.99+% in water
leaf. In some circumstances such as illness or non-
availability of enzymes, some non-essential amino acids,
such as glutamine, tyrosine, and arginine, may not be
synthesized by the body. When this occurs, such non-
essential amino acids are said to be conditional essential
amino acids and thus must be provided through food intake.
This is why even the non-essential amino acids from leaf
vegetables as understudied are important should such
situation arise.
5. Conclusion
This research shows that the leafy vegetables studied
contain appreciable levels of calories, protein, and amino
acids. They are also good sources of quality protein and
amino acids. Considering the levels of protein and amino
acids composition in these leaf vegetables, they may be
useful as sources of cheap and quick amino acid and protein
replenishment for malnourished children especially pumpkin
leaves with high protein levels and good quality amino acids,
coupled with high energy composition. However, in as much
as some leaf vegetables show exceptionally good qualities of
amino acid, it is advisable to consume different varieties so
as to provide the body with the assorted amino acids required
for proper functioning.
Acknowledgement
Authors acknowledge the assistance of Mr & Mrs Nkaa,
Louis who funded this research and Mr. Yahaya Baba Kiri
(AISLT) of the Department of Animal Production Laboratory
of Adamawa State University, Mubi, Adamawa State for his
technical assistance.
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