Int. J. Chem. Sci. Vol. 7 No. 1, ISSN 2006-3550
PROXIMATE, MINERALS AND ANTI-NUTRITIONAL
ASSESSMENT OF CASSAVA (Manihot esculentus)
LEAVES
ijcs
Etong, D.I1; Mustapha, A.O1; Lawrence I.G2
1. Chemistry/Biochemistry Unit, Science Laboratory Technology Department, Federal
Polytechnic, P.M.B 420 Offa Kwara State. Nigeria.
2. Department of Food Technology, Federal Polytechnic P.M.B 420 Offa, Kwara State,
Nigeira.
(Date Received: 09/10/14; Date Accepted: 20/10/14)
Abstract
Three samples of cassava leaves (tender, matured and wilted) of the same variety were analyzed
for proximate and mineral contents and anti-nutritional factors. The leaves contained mean
values for crude protein as 14.41+ 2.46%, crude fibre 7.87 + 2.42%, Ash 6.22 + 2.89%, fat 1.53
+ 0.57, Total carbohydrate 26.25 + 13.20% and moisture 43.72 + 15.86%. K, Na, Fe, Zn, and Mg
were the most abundant minerals with mean values as follows 1906.84 + 31.35, 777.76 + 46.66,
241.27 + 4.31, 99.75 + 1.65 and 66.24 + 2.04 ppm respectively, while the least was Mn with
mean thus 0.52 + 04 ppm. Anti-nutritional factors varied in the order of tannin> oxalic acid >
saponin > phytic acid > cyanide. Mineral composition, crude fibre, ash content, and total
carbohydrate increased with maturity. Crude protein and the anti-nutritional factors decreased
with wilting.
Keywords: Minerals, proximate composition, maturity, anti-nutrients.
Correspondence author: E-mail: danetong2006@yahoo.com Tel: 08151072981
annually, representing about 25% of subsaharan Africa’s output. Although it is the
third most important food source in the
tropical world after rice and maize, and
provides calories for over 160m people in
Africa (Polsen and Spencer, 1991), its food
value is greatly compounded by the presence
of cyanogenic glucosides. Beside the root,
each hectare of cassava produces a large
amount of leaf.
The potential yield of cassava leaves varies
considerably, depending on cultivar, age of
plant, plant density, soil fertility, harvesting
frequency and climate (Gomez and
Valdivieso, 1984; Wanapat et al., 1997).
INTRODUCTION
Cassava or tapioca (Manihot esculenta
crantz) is an annual tuber and an all season
crop grown in several parts of the world,
including Africa and Nigeria specifically.
Asia and Latin America is well documented
(Longe, 1980; Rosling, 1987; Bradbury et al
, 1991). Cassava thrives in sandy-loamy
soils with low organic matter in areas
receiving low rainfall and at high
temperatures. It is a cash crop, second in
rank after rice, cultivated by small holder
farmers within the existing farming systems
in Vietnam (Duong et al., 2000). Nigeria
alone, currently produces over 14m tones
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Int. J. Chem. Sci. Vol. 7 No. 1, pp 26-36, 2015
Cassava leaves, a byproduct of cassava root
harvest is (depending on the varieties) rich
in protein (14-40% dry matter), mineral,
vitamin B1, B2, C and carotenes (Eggum,
1970; Adewusi and Bradbury, 1993).
According to some available literatures,
apart from lower lysine, methionine and
perhaps isoleuine content, the amino acid
profile of cassava leaf protein compares
favourably with those of milk, cheese,
soyabean, fish and egg (Ayodeji, 2005).
Cassava leaves, therefore are potential
protein supplement for ruminants, even man
in the tropics. Surprisingly, despite its
availability and high protein content, there
was little interest, until recently, to utilize
fresh cassava forage in ruminant feeding.
This reluctance is probably related to
possibilities of cyanide toxicity, as it content
of cyanogenic glucosides could, depending
on the variety, be 6 times higher than in the
roots. Apart from cyanide, tannin and
possibly phytin, may limit the nutritional
value of cassava leaves (Reeds et al., 1982).
Various cassava processing techniques lead
to substantial cassava detoxification, for
example wilting reduces cyanide toxicity in
fresh cassava foliage, it also reduces free
tannin levels and improves its acceptability
to ruminants (Doung et al, 2000). Apart
from the risk of acute cyanide intoxification
and death, chronic exposure to sub-lethal
levels increase the incidence of goiter
tropical neuropathy, glucose intolerance
(Oshuntokun , 1972; Akanji and Famuyiwa ,
1993) and konzo (spastic paraparesis)
(Howelett et al., 1990). Cassava foliage has
been fed to ruminants with good results
(Devendra, 1977; Wanapat et al, 1997;
Wanapant et al.,1998; Fernandez et al.,
1977; Teeluck et al., 1981; Ffoulkes and
Preston, 1978).
Literatures have revealed that substantial
work have been done on the nutritional
value and the effect of processing on the
nutritional value of cassava root and leaves,
but little have been reported on the effect of
maturity on the nutritional value. The
present study therefore looks at this
forgotten area to ascertain the stage at which
the maximum nutritional value of cassava
can be harness by looking at the effect of
maturity on the nutritional value of cassava
leaf.
MATERIALS AND METHODS
The leaves analyzed were harvested from a
local variety (same species) which was
obtained from Alaya area of Offa in Kwara
State, Nigeria. All samples were cultivated
in the humid tropical rain forest zone, where
the rains which fall between March and
September/October, average between 11502000 mm annually. Three samples each of
the tender, matured and wilted leaves were
processed and analyzed for proximate
composition, minerals and anti-nutritional
values.
Sample preparations
Chemicals evaluations were determined in
triplicates.
Analyses
for
proximate
constituents were carried out according to
AOAC, (1990) methods. The sodium and
potassium contents were determined by
flame photometry, and phosphorus was
determined by the vanodo-molybdate
method (AOAC, 1980). The other mineral
elements (Ca, Mg, Fe, Zn, Co, Cu, and Mn)
were determined after wet digestion with a
27
Proximate, Minerals and Anti-Nutritional Assessment of Cassava (Manihot esculentus) Leaves
mixture of nitric acid, sulphuric and
hydrochloric acid using atomic absorption
spectrophotometer (AAS Model sp9).
Tannin was analyzed using Markkar and
Goodchild, (1996) method. Phytic acid was
assessed using Wheele and Ferrel, (1971)
method. Hydrocynanic acid was determined
by Bradbury et al, (1991). Oxalate was
analyzed using Day and Underwood (1986)
method, and saponins by Brunner (1984)
method.
The carbohydrate content was determined
by simple differences, and energy value
estimated using Atwater factors by
multiplying the proportion of protein, fat
and carbohydrate by their respective
physiological fuel values of 4, 9, and 4
kcal/g respectively and taking the sum of the
products (Eneche, 1999).
RESULTS AND DISCUSSION
Table 1: Proximate composition of tender, matured and wilted cassava leaves (%)
Constituents
Moisture
Crude Fat
Ash
Crude Fibre
Crude Protein
Total
carbohydrate
Dry matter
Energy Value
kCal/g
A+SD
56.67+0.1
1.70+0.1
3.90+0.01
6.00+0.02
15.02+0.1
16.71+0.01
B+SD
48.47+0.01
2.00+0.01
5.30+0.02
7.00+0.03
16.50+0.01
20.73+0.01
C+SD
26.03+0.1
0.90+0.01
9.46+0.03
10.60+0.01
11.70+0.03
41.31+0.01
a
Mean
43.72
1.53
6.22
7.87
14.41
26.25
%CV
36.28
37.25
46.46
30.75
17.07
50.29
+SD
15.86
0.57
2.89
2.42
2.46
13.20
SK
-0.90
-0.89
-096
-1.08
-0.74
1.25
Range
26.03-56.67
0.90-2.00
3.90-9.46
6.0-10.60
11.70-16.50
16.71-41.31
43.33+0.02
142.22
51.53+0.03
166.92
73.97+0.02
220.14
56.28
176.43
28.18
22.57
15.86
39.82
0.90
0.72
43.33-73.97
142.22-220.14
+SD = Standard Deviation, A = Tender cassava leave, B = Matured, C = Wilted
a
CV = Coefficient of Variation:
Mean= Mean of triplicate determination, SK = Skewness.
Table 2: Mineral constituents (ppm) of tender, matured and wilted cassava leaves
Element
Na
K
Ca
Mg
Fe
Zn
Cu
Co
Mn
P
Ca/P
Na/K
a
Tender
737.50
1873.12
12.40
64.61
236.59
98.22
1.96
4.24
0.26
0.33
37.58
0.39
Matured
766.87
1912.30
15.59
65.59
242.14
101.49
2.61
5.55
0.33
0.65
23.98
0.40
Wilted
828.90
1935.10
17.95
68.53
245.07
99.53
3.26
6.53
0.98
1.31
13.70
0.43
a
Mean
777.76
1906.84
15.31
66.24
241.27
99.75
2.61
5.44
0.52
0.76
+SD
46.66
31.35
2.79
2.04
4.31
1.65
0.65
1.15
0.40
0.50
%CV
6.00
1.64
18.22
3.08
1.79
1.65
24.90
21.14
76.92
65.79
SK
0.70
-0.52
-0.30
0.96
-0.61
0.40
0.00
-0.29
1.43
0.66
Range
737.50-828.90
1873.12-1935.10
12.40-17.95
64.61-68.53
236.59-245.07
98.22-101.49
1.96-3.26
4.24-6.53
0.26-0.98
0.33-1.31
Means for triplicate determination, +SD = Standard deviation, SK = Skewness; CV = Co-efficiency of variation.
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Int. J. Chem. Sci. Vol. 7 No. 1, pp 26-36, 2015
Table 3: Anti-nutritional constituents of tender, mature and wilted cassava leaves (mg/100g Dry
matter)
a
Anti-nutrient
Tender Matured Wilted
Mean
+SD
766
993
511
756.67
24. 11
Saponin
4322
4348
3656
4108.67
39.22
Tannin
783
989
453.0
741.67
27.04
Phytic Acid
1935
1890
1811
1878.67
62.77
Oxalic Acid
4.24
4.55
3.80
4.20
0.38
HCN
a
Means for triplicate determination, +SD = Standard deviation, SK = Skewness
The results of proximate analysis, mineral
and anti-nutritional constituents of tender,
matured and wilted cassava leaves of local
variety are recorded in Table 1, 2 and 3
respectively. Proximate composition (Table
1) indicated that the moisture content
decreased with maturity, where 56.67% was
recorded for the tender and 26.03% for
wilted leaf. This is as a result of loss of
water through transpiration due to maturity
since less cell activities is needed in that
stage. Fat content decreased with maturity.
The ash, crude fibre, total carbohydrate, and
dry matter increase with maturity. The crude
protein was high for the matured (16.50%)
and least for the wilted (11.70%), this may
be attributed to denaturalization of protein
molecules as the leave wilted. The protein
content was lower than that reported for
different varieties range 33.2-36.3%, the
crude fat, and fibre were lower, while the
ash content (9.46%) of the wilted sample
were higher than for all the varieties
reported by Ayodeji (2005). The co-efficient
of variation ranged from 17.07% (crude
protein) to 50.28% (total carbohydrate). The
crude protein which ranged from
11.70+0.3%
(wilted)
to
16.50+0.01
(matured) was higher than that reported for
whole cassava plant (9.0%), unpeeled
cassava tuber (4.72%) and cassava tender
SK
-0.12
-0.54
-0.46
-0.54
-0.02
Range
511-993
3656-4348
453-989
1811-1935
3.80-4.55
% CV
31.87
9.55
36.46
3.34
9.04
stem (10.70%) (Akinfala et al, 2002), the
crude fibre was also higher except for the
tender stem. The leaves were richer in crude
protein and fat than the seed of Carica
papaya but lower than the unripe seed of
Citrus sinensis (Abulude , 2000).
The variability of the proximate composition
was low as shown in the standard deviation
which was 15.86 and 13.20 for moisture and
total carbohydrate respectively but others
were less than 3 as depicted by the %
coefficient of variation. They were both
positively and negatively skewed. Thus any
stage of the leaves could be use effectively
for animal/poultry feed.
The mineral content (Table 2) ranged from
0.26 ppm for manganese to 1873.12 ppm for
potassium in the tender leaf, 0.33 ppm Mn to
1912.30ppm K in the matured and 0.98 ppm
(manganese) to 1935.10 ppm (potassium) in
the wilted leaf. Potassium, sodium, Iron,
zinc and magnesium were the most abundant
in the following range (1873.12 tender to
1935.10 ppm) wilted, (737.50 to 828.90
ppm), (236.59 to 245.07 ppm), (98.22 to
101.49 ppm), and (64.61 to 68.53 ppm)
respectively. Mn was the least abundant in
the range of (0.26 to 0.98 ppm). The
concentration of all the metals increases
with maturity i.e. there was a directly
relationship between maturity and the
29
Proximate, Minerals and Anti-Nutritional Assessment of Cassava (Manihot esculentus) Leaves
concentration of the metals except for zinc
in which the matured has the highest
concentration of 101.49 ppm. The leaves
were richer in K, Na, Mg, and less in Ca, P,
Mn, Cu, Zn and Co than the seed of Carica
papaya and Citrus sinensis (Abulude, 2000).
The minerals were higher than that reported
by Eugene and Gloria (2002) for selected oil
seeds used in the preparation of Nigerian
diets. Except for calcium, the values were
also higher than that reported by Fadavi et al
(2005) for ten pomegranate cultivars
(Punica granutum L) grown in Iran. The
values for Ca, Mg, P, and K, except Na were
lower than that reported for nine accessions
of Canavalia ensiformis (jack beans) by
Vadivel and Janardhanan, (2001), the
mineral values were also lower than that
reported for mushroom (Ola and Oboh,
2000), water melon, pumpkin and parika
seed flours (Tarek and Kaled, 2001). Apart
from Mn and phosphorus with % CV 79.92
and 65.79, respectively others were less than
25% showing low level of variability. K, Ca,
Fe, and Co was negatively skewed while
others were positively skewed. Considering
the most important major mineral element
(calcium and phosphorus), high calcium
with corresponding low phosphorus in the
leaves with Ca/P ratios 37.58 tender,
matured 23.98 wilted 13.70 accessions
reflect the disproportionate distribution of
calcium and phosphorus. This may affect
their utilization for ideal growth and bone
formation (Balogun and Fatuga, 1986). In
mineral profile, a very strong positive
correlation occurs between sodium and
magnesium (r = 0.997) and between
magnesium and phosphorus contents (r =
0.997).
Comparing the proximate and mineral
contents in this study with approximate
indices of nutritional potential or quality, it
would appear that cassava leaves protein fall
between those of most legumes and animal
protein. However, the high crude fibre
content of the wilted (10.60%) are of
nutritional concern (especially in nonruminants) since high dietary fibre can cause
intestinal irritation, lower digestibility and
over all decreased nutrient utilization
(Johnson, 1987).
The anti-nutritional potential in Table 3,
showed that saponnin varied from a range of
511 mg/100g in wilted to 993 mg/100 g in
the matured sample, with a CV of 31.87%.
The total polyphenols (as tannic acid
equivalent) ranged from 3656 mg/100 g in
the wilted to 4348 in the matured with a CV
of 9.55%, phytic acid content ranged from
453 mg/100g in wilted to 989 mg/100g in
the matured with a CV of 36.46%, oxalic
acid content ranged from 1811 mg/100g in
the wilted to 1935 in the tender sample with
a CV of 3.34%. The cyanogenic potential
was the least, with values of 3.80 mg/100g
in the wilted to 4.55 mg/100g in the
matured, with a CV of 9.04%. They were all
negatively skewed with tannin and oxalic
acid been moderate. The results generally
show an increase in anti-nutritional factors
with maturity to a peak and falls with
wilting, except oxalic acid that decreased
with maturity, and also confirms the
suggestion by Duong et al. (2000) that
wilting reduces cyanide in fresh cassava
foliage. Wilting not only lowers potential
cyanide toxicity, but also reduces the free
tannin levels and improves its acceptability
to ruminants. The values of HCN and tannin
30
Int. J. Chem. Sci. Vol. 7 No. 1, pp 26-36, 2015
were lower and phytin higher than that
reported for four other varieties of cassava
leaves (Ayodeji, 2005), tannin values were
higher and phytic acid lower than that
reported for water melon, pumpkin and
parika seed kernel and seed flours (Tarek
and Khaled, 2001), the values were also
higher than that reported for sweet and bitter
lupin seed protein isolate (El-Adawy, et al.,
2001), ripe and unripe Carica papaya and
Citrus sinensis seeds (Abulude , 2000). For
oxalates the value was higher but
hydrocyanic acid was lower than that
reported for two snail species (Archachatina
marginata and Achatina achatina) by
Ebenso et al. (2006).
The values for oxalate and tannin were
higher compared with values reported by
Udo et al. (1995) for L. aurora (381.00
mg/100 g) and (592 mg/100g) respectively,
but the cyanide values for L. aurora (112
mg/100 g) was higher. In the present study,
oxalate and hydrogen cyanide were below
the lethal dose of (2 – 5 g/100 g) (Oke,
1969) and (50-60 mg/100 g) respectively
(Chakraborty and Eka, 1978), making it safe
for human. Because of the risk of acute
intoxification
associated
with
the
consumption of high cyanide-containing
cassava products, most studies on the toxic
or potentially toxic constituents of cassava
leaves have been skewed rather heavily in
favour of the cyanogenic constituents.
Consequently, information on the content of
other potential toxicant or anti-nutrients has
remained scanty. The present study shows
that apart from cyanide (Table 3) which
averaged 4.20 mg/100 g DM; the leaves
contained
high
level
of
tannin
4108.67+39.22 mg/100 g DM, saponin
756.67+ 24.11 mg/100 g DM and oxalic
acid 1878.67+62.77 mg/100 g DM, while
the cyanide levels in these variety was lower
than those reported for other varieties
(Ayodeji, 2005; Lancaster and Brooks,
1983; Ravindran et al, 1987), tannin content
of the leaves was higher than that found in
most grain legumes and cereals. The
nutritional significance of dietary cyanide
derives from several observations (Tewe et
al., 1976; Frake and Sharma, 1986; Aletor
and Fetuga, 1988; Aletor, 1993) that cyanide
either in synthetic or organic forms can
cause marked changes in weight gain,
nutrient utilization, liver enzymes activities
and thiocyanate concentrations in serum and
urine of rats and hamsters. The cyanide
detoxification route in man and animals,
cyanide-thiocyanate sulphur transferase
(rhodanase) pathway generally requires
organic sulphur donors in the form of
methionine and cystine thereby precipitating
methionine deficiency in otherwise balance
diet. Tannin, on the other hand brings about
their nutritional influences (especially in
non-ruminants) largely, by binding dietary
proteins and digestive enzymes into
complexes that are not readily digestible and
reducing its nutritive value (Ford and
Hewitt, 1979). But the level at which tannin
would be noticeable harmful is unclear
(Makoto et al., 1987). The poor palatability
generally associated with high tannin diets
are ascribed to its astringent property which
is a consequence of its ability to bind with
proteins of saliva and mucosal membranes
(Menhansho et al., 1987). Paradoxically,
there is ample evidence that subject to
certain dietary levels, tannin may not always
be anti-nutritional in ruminants. For
31
Proximate, Minerals and Anti-Nutritional Assessment of Cassava (Manihot esculentus) Leaves
examples, condensed tannin in lotus
pedunculana
while
reducing
rumen
degration of carbohydrates may enhance
amino acids absorption in the small intestine
(Barry and Manley, 1986) via a “bypass”
process. The presence of phytin in cassava
leaves agree with earlier report (Aletor and
Adeogun, 1995) of their widespread
occurrence in plants. Phytic acid is not
usually available to man (Tewe et al., 1976),
except in circumstance where fermentation
favours the activity of phytase , an enzyme
which hydrolyzed phytic acid into
phosphoric acid and inositol. Humans do not
possess phytase for the liberation of
phosphorus (Cantarow and Schepartz ,
1968). Phytic acid intake of 4-9 mg/100 g
DM is said to decrease non-absorption in
humans (Wheele and Ferrel, 1971). The
anti-nutritional nature of phytin lies in its
ability to chelate certain mineral elements
e.g. Ca, Mg, Zn, and Fe (Forbes and Erdman
1983), and protein (Maga, 1983) reducing
their availability to consumers. Dietary
phytin is of particular importance in nonruminants (including man) who lack phytase
to break down phytin to release phosphorus
for metabolism. Phosphorus utilization has
become an important current issue on the
question of environmental pollution arising
from the poor digestibility of phosphorus
especially in foods/feed of vegetable origin
(Huisman, 1991), where a high proportion of
the phosphorus may be present as the poorly
digestible phytin-phosphorus in nonruminants.
In
such
circumstances,
considerable amounts of dietary phosphorus
may be voided in faces leading to the
pollution of the environment. High level of
oxalate has been known to inhibit the
absorption and utilization of mineral
elements by animals including man. Oxalic
acid is known to precipitation calcium salts
and some divalent mineral elements thus
rendering then unavailable to consumers
(Davidson et al., 1979). In the present study,
levels of oxalate are not considerable high
enough to pose any threat to the availability
of mineral elements because it is below the
lethal dose.
CONCLUSION
Cassava leaves, indicated high potential to
be used as an unconventional protein and
mineral resources for both humans and
animals. The matured stage was the most
resourceful because of its high protein,
moderate fibre and high mineral contents.
However, anti-nutritional values were high
which can easily be reduced by processing
techniques. For example shredding +
sundrying or sundrying alone are highly
efficient processing techniques for cyanide
removal from cassava leaves (i.e. from 56.5
mg HCN/100 g in the fresh sample to 1.6 or
1.8 mg HCN/100 g respectively). Maturity
affects both the proximate composition,
mineral and anti-nutritional values of
cassava leaf, positively and negatively, for
proximate composition, crude fibre, ash,
total carbohydrate and dry matters (DM)
increase positively but protein and fat rise
and fall. For minerals, the effect was
positive except for Zn that rise and fall. For
anti-nutritional factor oxalic acid was
negative but for other factors they rise
(positive) and fall (negative).
32
Int. J. Chem. Sci. Vol. 7 No. 1, pp 26-36, 2015
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