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Pakistan Journal of Nutrition 9 (7): 709-715, 2010
ISSN 1680-5194
© Asian Network for Scientific Information, 2010
Corresponding Author: Ekeanyanwu Raphael Chukwuma, Department of Chemical Sciences, Novena University, Ogume, Delta State,
Nigeria
709
The Phytochemical Composition and Some Biochemical Effects of
Nigerian Tigernut (Cyperus esculentus L.) Tuber
Ekeanyanwu Raphael Chukwuma , Njoku Obioma and Ononogbu Ikpendu Christopher
1 2 2
Department of Chemical Sciences, Novena University, Ogume, Delta State, Nigeria
1
Department of Biochemistry, University of Nigeria, Nsukka, Enugu State, Nigeria
2
Abstract: The phytochemical composition of the tigernut tuber and the effect of the aqueous extract on some
biochemical parameters such as blood glucose, serum protein, albumin and cholesterol, white blood cells,
red blood cells, haemoglobin, erythrocyte sedimentation rate and packed cell volume were determined in
rats administered different concentrations of the extract. From the result of the phytochemical analysis, the
presence of alkaloids, cyanogenic glycosides, resins, tannins, sterols and saponins were observed in the
raw tuber, however only alkaloids, sterols and resins were observed in the roasted tuber. Analysis of the
antinutrient composition yielded oxalates (0.25±0.65 g/100 g), phytate (1.97±0.81 mg/100 g), saponins
(0.88±0.02/100 g), tannins (9.50±0.46 mg/100 g) and cyanogenic glycosides (1.80±0.69 mg/100 g). Roasting
numerically decreased the levels of the anti-nutritive factors analyzed. At the end of the treatment period, the
mean weights of the animals increased. The blood glucose level decreased significantly in concentration
dependent manner (p<0.05) and serum albumin level increased significantly in a concentration dependent
manner (p<0.05) in the groups administered the different concentrations of the extract. There was no
significant effect (p>0.05) on serum cholesterol and protein and on total and differential white blood cell, red
blood cell, haemoglobin, packed cell volume and erythrocyte sedimentation rate. The results therefore
indicate the absence of undesirable effect in the use of the tigernut tuber even in the raw form at least at the
administered concentration and for the duration of feeding. The findings are of nutritional, health and
industrial relevance since the tuber is currently being used as food in many homes in Nigeria.
Key words: Cyperus esculentus, tigernut, phytochemicals, biochemical effects
INTRODUCTION
The worsening food crisis and the consequent wide
spread prevalence of malnutrition in developing and
underdeveloped countries have resulted in high mortality
and morbidity rates, especially among infants and
children in low income groups (Enujuigba and Akanbi,
2005). The reliance on starchy roots and tubers and
protein deficient cereals as main staples results in
consumption of non-nutritious foods. The insufficient
availability of nutrient rich diets and high cost of available
ones have prompted an intense research into
harnessing the potentials of the lesser known and
underutilized crops, which are potentially valuable for
human and animal foods to maintain a balance between
population and agricultural productivity, particularly the
tropical and subtropical areas of the world.
Cyperus esculentus (Tigernut) is an underutilized plant
of the family Cyperaceae, which produces rhizomes
from the base and tubers that are some what spherical
(Cortes et al., 2005). The plant is not really a nut but a
tuber first discovered some 4000 years ago (Lowe and
Whitewell, 2000). It has other names like yellow
nutsedge, chufa, flatsedge, rush nut, water grass, earth
almond, northern nut grass and nut grass (Shilenko et
al., 1979). Cyperus esculentus is known in Nigeria as
aya in Hausa, ofio in Yoruba and akihausa in Ibo.
Cyperus esculentus grows mainly in the middle belt and
northern regions of Nigeria (Okafor et al., 2003), where
three varieties (black, brown and yellow) are cultivated
(Umerie et al., 1997). Among these, only two varieties,
yellow and brown are readily available in the market. The
yellow variety is preferred to all other varieties because
of its inherent properties like its bigger size, attractive
colour and fleshier body (Belewu and Abodurin, 2006).
Cyperus esculentus can be eaten raw, roasted, dried,
baked or be made into a refreshing beverage called
kuunu (Oladele and Aina, 2007).
Cyperus esculentus was reported as healthy and helps
in preventing heart, thrombosis and activates blood
circulation. It helps in preventing cancer, due to high
content of soluble glucose. It was also found to assist in
reducing the risk of colon cancer (Adejuyitan et al.,
2009). The nut is rich in energy content (starch, fat,
sugars and protein), mineral (phosphorus, potassium)
Pak. J. Nutr., 9 (7): 709-715, 2010
710
and vitamins E and C (Belewu and Belewu, 2007).
Cyperus esculentus is suitable for diabetic persons and
also helps in loosing weight (Borges et al., 2008).
Food contains various compositions of nutrients and
antinutrients and could have important or deleterious
effects in the body when consumed. The composition of
the nutrients and antinutrients, usually leads to side
effects found in most plants which may lead to toxicity,
hyperlipidaemia, excessive weight gain, hyperglycaemia,
carotenemia, constipation, kidney stones, body odour,
bad breath, allergies, diarrhoea, frequent urination and
acne (Anonymous, 2009). In most of these side effects,
the biochemical and haematological parameters are
usually altered. For a food to be considered safe for
human and animal health, its effect on these
parameters need to be investigated to understand the
nutritional potentials and safety of such foods with a view
to determining their acceptability.
The aim of the present study is to determine the
phytochemical composition of the tuber and to ascertain
if the tuber could have beneficial effect on biochemical
parameters such as blood glucose, serum albumin,
protein, cholesterol, red blood cell, haemoglobin,
erythrocyte sedimentation rate, packed cell volume, and
total and differential white blood cell of the rats as our
model for the research.
MATERIALS AND METHODS
Collection and preparation of tigernut tuber flour and
the aqueous extract: Fresh tigernut tuber was
purchased from a local market in Katsina, Katsina state,
Nigeria. The tuber was identified and authenticated by Mr
A. Ozougwu of Botany department, university of Nigeria,
Nsukka, Enugu state. The tigernut tubers were cleaned,
sorted and washed. The fresh tubers were dried in an
oven (GallenKamp, England) at 37 C for one hour,
o
milled separately using a laboratory electric mill (Retsch,
5657, GmbH, Germany) to pass through a 40-mesh
sieve, packaged in glass jars and stored at 4C in a
o
refrigerator until analysis. A Quantity, 400 g of the fresh
milled tubers was extracted by shaking it with 3 litres of
n-hexane for one hour, three times to remove the oil. The
defatted milled tubers were dried in a desiccator under
vacuum. The water extract was obtained by stirring the
dry defatted milled tubers with seven (7) litres of distilled
water at room temperature (27±1 C) for twelve hours.
o
The suspension was centrifuged at 3000 rpm for 10 min
and the supernatant was filtered through white muslin
cloth and then whatman filter paper No.1 under vacuum.
The extract was concentrated using water bath at an
optimum temperature of 65 C to avoid the denaturation
o
of the bioactive compounds. The weight of the dry extract
was determined. The different concentrations (500,
1000, 1500 and 2000 mg/kg) of the extract were
prepared.
Table 1: The phytochemical composition of the tigernut tuber
Phytochemical Raw Roasted
Alkaloids +++ +
Glycosides - -
Cyanogenic glycosides + -
Resins +++ +++
Flavonoids - -
Cardiac glycosides - -
Tannins + -
Sterols +++ +++
Saponins + -
+++ = Present in very high concentration, ++ = Present in
moderately high concentration, + = Present in trace
concentration, - = Not detected
Experimental animals: Adult male Wistar albino rats
were purchased from the faculty of biological sciences
animal house, University of Nigeria, Nsukka, Enugu
state, Nigeria. The animals were about 12 weeks with
average weight of 112.37±11.7 g. The animals were kept
under standard conditions for 7 days with free access to
water and food before starting the experiment. Albino
mice, 20.50±4.27 g weights were used for the acute
toxicity tests. The animals were housed in standard
cages with food and water ad libitum at room
temperature and provided with pelletized feed.
Experimental design: An acute toxicity study of the
aqueous extract of tigernut was done by the method of
Lorke (1983). Twenty five (25) male Wistar albino rats of
12 weeks were divided into five groups of five rats each
of average weight were randomly assigned to five (5)
cages labelled I, II, III, IV and V respectively and kept at
room temperature (25 C). All the rats were allowed free
o
access to water and feed ad libitum for a week to
acclimatize them to laboratory conditions. After this
period, the control animals (group I) were administered
0.2 ml of normal saline (0.9% NaCl) while groups II, III,
IV and V were administered different concentrations of
the extract. The extracts were administered for 30 days
to the animals using the oral route by means of
polythene cannula. The weights of the animals were
taken before commencement of the feeding experiment
and then later every six days interval. At the end of the 30
days, blood samples from each rat were collected
through the orbital technique for analysis of
haematological parameters like total and differential
white blood cells, red blood cell, haemoglobin, packed
cell volume, erythrocyte sedimentation rate and
biochemical parameters like blood glucose, serum
protein, albumin and cholesterol.
Phytochemical analysis: The phytochemical test for the
presence and absence of saponins, alkaloids,
flavonoids, cyanogenic glycosides, tannins, glycosides,
and sterols were carried out according to the method
described by Harbone (1984).
Pak. J. Nutr., 9 (7): 709-715, 2010
711
Antinutrient analysis: Percentage compositions of 1984) as most of these phytochemicals are thermally
some antinutrients like oxalates, phytates, cyanogenic unstable.
glycosides, saponins and tannins were determined by Analysis of the antinutrients composition of the raw
the method described by AOAC (1990). All tubers of C. esculentus showed that it contained
determinations were done in triplicate determination. 0.60±0.32 g/100 g oxalates, 2.40±0.40 mg/100 g
Biochemical studies: Serum cholesterol was g/100 g tannins and 1.08±0.69 mg/100 g cyanogenic
determined by the method of Meiatini et al. (1978), glycosides. The roasted C. esculentus tuber contained
serum total protein by the method of Wooten (1964), 0.55±0.36 g/100 g oxalates, 1.06±0.24 mg/100 g phytate,
blood glucose by the glucose oxidase method of Marks 0.67±0.40 mg/100 g saponins, 7.10±0.35 g/100 g
and Dawson (1965), serum albumin by the method of tannins and 0.86±0.44 mg/100 g cyanogenic glycosides.
Doumas et al. (1971). The levels of antinutrients analyzed were very low
Haematological studies: The haemoglobin (Ejigui et al., 2005). The presence of phytates in
concentration was estimated using the cyanome- biological systems may chelate divalent metals like
thaemoglobin photometric method. The packed cell calcium, magnesium, or block the absorption of
volume was estimated using the micro-haematocrit essential minerals in the intestinal tract (Dan, 2005)
centrifuge. The red blood cell and differential white blood thus decreasing their bioavailability (Oberleas, 1973).
cell was estimated using the improved Neubauer Phytates chelate with mineral elements thereby having
haemocytometer. Erythrocyte sedimentation rate was significant effects on the utilization of the minerals. They
determined using the Westergren method (1957). also react with basic residues of protein. Tannins and to
RESULTS AND DISCUSSION
The result of phytochemical screening shows that a
higher content of alkaloids, sterols and resins than
cyanogenic glycosides, saponins and tannins were
detected in the raw Tigernut tuber. However, in the
roasted Tigernut tuber, only alkaloids sterols and resins
were detected and no other phytochemical assayed was
detected. Alkaloids, saponins and tannins are known to
have antimicrobial activity, as well as other physiological
activities (Sofowora, 1993; Evans, 2005). Alkaloids are
known for their toxicity, but not all alkaloids are toxic.
They inhibit certain mammalian enzymic activities such
as those of phophodiesterase, prolonging the action of
cAMP. They also affect glucagons and thyroid stimulating
hormones, while some forms have been reported to be
carcinogenic (Okaka et al., 1992). Some have been used
either as an analgesic, antispasmodic, bactericidal
agents (Frantisek, 1991). Saponins have been reported
to be useful in reducing inflammation of upper
respiratory passage and also chiefly as foaming and
emulsifying agents and detergents (Frantisek, 1991).
Tannins have astringent properties that hasten the
healing of wounds and prevention of decay. Tannin
compounds have antimicrobial activities and are
responsible for preventing and treating urinary tract
infections and other bacterial infections. The result of the
determination of phytochemical test indicated that the
tuber possess some biologically active compounds
which could serve as potential source of vegetable
drugs in herbal medicine. These phytochemicals exhibit
diverse pharmacological and biochemical actions when
ingested by animals (Amadi et al., 2006). They are
usually present at low concentration in edible fruits, nuts,
tubers and vegetables. Roasting reduced the amount of
these phytochemicals in plant products (Piorrock et al.,
phytates, 0.88±0.02 mg/100 g saponins, 9.62±0.29
compared to those reported for nuts like the peanuts
some extent oxalates, binds to proteins thereby making
them difficult to digest in the body. Oxalates can remove
calcium in the form of calcium oxalate (Savage, 1993) in
the blood and thus may result to kidney damage.
Saponin reduces the uptake of certain nutrients
including glucose and cholesterol at the gut through
intra-lumenal physicochemical interaction (Price et al.,
1987). They also exhibit structure dependent biological
activity (Savage, 1993). The potential toxicity of a food
produced from a cyanogenic plant depends on the
likelihood that its consumption will produce a
concentration of Hydrogen Cyanide (HCN) that is toxic to
exposed humans. Cyanide causes an increase in blood
glucose and lactic acid levels and a decrease in the
ATP/ADP ratio indicating a shift from aerobic to
anaerobic metabolism. Cyanide also activates
glycogenolysis and shunts glucose to the pentose
phosphate pathway decreasing the rate of glycolysis and
inhibiting tricarboxylic acid cycle (Akintonwa and
Tunwashe, 1992). Odumodu (1992) and Okafor et al.
(2003) had earlier reported low contents of these
antinutrients in tigernut tuber flour compared with other
local fruits, nuts, tubers and vegetables. Roasting
numerically reduced the antinutrient composition of
tigernut tuber flour.
Acute toxicity test are generally the first test conducted in
any toxicity study. They provide data on the relative toxicity
likely to arise from a single or brief exposure to any
substance. Different plant extracts have been known to
possess different levels of toxicity which majorly
depends on the levels of antinutrients inherent in the
plants (Sofowora, 1993). Preliminary investigations on
the acute toxicity of the tuber extract of C. esculentus in
mice showed that the aqueous extract of C. esculentus
(tigernut) tuber was not toxic to mice at the administered
concentrations.
Pak. J. Nutr., 9 (7): 709-715, 2010
712
Table 2: The antinutrient composition of the tigernut tuber
Components
------------------------------------------------------------------------------------------------------------------------------------------------------------
Oxalates Phytate Saponin Tannins Cyanogenic glycosides
Sample (g/100 g) (mg/100 g) (g/100 g) (mg/100 g) (mg/100 g)
Raw 0.60±0.32 2.40±0.40 0.88±0.02 9.62±0.29 1.08±0.69
Roasted 0.55±0.36 1.06±0.24 0.67±0.40 7.10±0.35 0.86±0.44
Values are mean±standard deviation of triplicate determination
Table 3: The biochemical parameters of the animals at the end of experimental period
Groups
------------------------------------------------------------------------------------------------------------------------------------------
Group II Group III Group IV Group V
Parameters Group I NS 500 mg/kg 1000 mg/kg 1500 mg/kg 2000 mg/kg
Blood glucose (g/dl) 71.5±4.04 60.25±3.40* 56.75±2.50* 54.00±3.46* 48.50±4.66*
Serum protein (g/dl) 6.92±0.27 7.43±0.63 7.39±0.45 7.16±0.61 7.19±0.35
Serum albumin (g/dl) 3.35±0.48 3.14±0.72 4.08±0.29* 4.18±0.31* 3.93±0.30*
Serum cholesterol (mg/dl) 88.10±15.12 86.49±17.65 91.35±3.24 75.94±18.89 79.91±8.79
Values are mean±standard deviation of quintuplicate determination, *Means significant different (p<0.05) compared to the control.
N = 5, NS = Normal Saline
The result of the effect of administration of the various haematological parameters such as red blood cells,
concentrations (500, 1000, 1500 and 2000 mg/kg) of C. total and differential white blood cells, haemoglobin,
esculentus tuber extract on biochemical parameters packed cell volume and erythrocyte sedimentation rate
such as blood glucose, serum protein, albumin and is presented in Table 4. The result show that there was
cholesterol are presented in Table 3. The result showed no significant effect (p>0.05) on these haematological
that there was significant increase (p<0.05) in serum parameters. The results obtained for all treatment
albumin and a significant decrease (p<0.05) in blood groups indicate nutritional adequacy of the tuber extract
glucose, but there was no significant effect (p>0.05) on and the rat diet since they did not indicate malabsorption
serum protein and cholesterol. Since total serum or under nutrition (Church et al., 1984). These
proteins and albumin are generally influenced by total observations were related to the composition of the
protein intake (Onifade and Tewe, 1993), the results tuber extract and health status of the animals since none
obtained indicate nutritional adequacy of the dietary and of the animals died as a result of any diseases.
the extract proteins. Abnormal serum albumin usually Hackbath et al. (1983) had earlier recorded a strong
indicates an alteration of normal systemic protein influence of food components on haematological traits,
utilization (Apata, 1990). Awosanya et al. (1999) have packed cell volume and haemoglobin concentration
demonstrated the dependence of blood protein on the being very strong indicators of nutritional status of
quality and quantity of protein source. The reported low animals. It is well known that various antinutritional
level of phytate in the tuber could also have led to the substances and xenobiotics can cause haemolysis,
increased absorption of protein from the rat diet. Phytate nutrients malabsorption and abnormal haemopoesis
acts as a chelator, forming proteins and mineral which could arise from liver damage (Chubb, 1982),
bioavailability (Davies and Gathlin, 1991). Since glucose antinutrient analysis of the tigernut tuber shows that it
level was significantly (p<0.05) lowered and cholesterol has low concentration of these antinutrients. The result
levels were not affected abnormally, possibilities of of the total and differential white blood cell count indicate
anorexia, diabetes, liver dysfunction and mal-absorption that the animals were healthy because decrease in
of fat, which are the symptoms of abnormal glucose and number of white blood cells is an indication of allergic
cholesterol levels in blood (Bush, 1991) are ruled out. conditions, anaphylactic shock and certain parasitism
The glucose lowering potentials of the extract may be while elevated value indicate to the existence of a recent
ascribed to modifications in glucose uptake in the infection, usually with bacteria (Ahamefule et al., 2008).
intestine. It is well known that soluble fibres generally The mean body weight change in rats after every six
increase transit time through the gut, slow emptying of days following administration of 500, 1000, 1500 and
the stomach and slow glucose absorption 2000 mg/kg body weight extract of C. esculentus tuber
(Swaminathan, 2002). Cyperus esculentus tubers have extract are presented in Table 5. A general increase in
high dietary fibre content (Umerie and Enebeli, 1997), so physical activities, food and water intake were observed
they may play a major role in lowering blood glucose for all the animals during the feeding experiment. There
level. This observation supports an earlier hypothesis was initial increase in weight which was sustained. The
that the tuber may be important for diabetics and those increased weight could be due to increased feed and
seeking to reduce weight (Kordyias, 1990). water intake observed all through the experimental
The result of the effect of administration of the various period. The increase in weight of the animals suggests
concentrations (500, 1000, 1500 and 2000 mg/kg) of C. that they increasingly accumulated calories from the
esculentus (tigernut) aqueous tuber extract on normal rat diet and from the nutrient rich extracts.
Pak. J. Nutr., 9 (7): 709-715, 2010
713
Table 4: The red blood cell count, total and differential white blood cell count haemoglobin concentration, erythrocyte sedimentation
rate and packed cell volume of the animals at the end of experimental period
Group II Group III Group IV Group V
Haematological indices Group I NS 500 mg/kg 1000 mg/kg 1500 mg/kg 2000 mg/kg
RBC (x10 /µL) 8.50±0.19 8.74±0.58 8.63±0.67 8.54±1.55 8.67±0.15
6
Hb (g/dl) 17.25±1.28 16.94±1.29 16.99±0.95 17.71±1.00 17.91±0.63
PCV (%) 44.37±2.56 46.00±1.08 45.63±4.23 45.00±0.00 44.13±1.32
ESR (mmHr) 0.76±0.12 0.73±0.07 0.82±0.10 0.70±0.55 0.69±0.07
tWBC (x10 /µL) 13.96±2.64 13.51±1.82 13.57±2.72 16.61±2.72 14.53±1.33
3
Neutr (x10 /µL) 2.78±0.82 2.52±0.46 1.59±0.44 2.77±1.00 3.18±1.24
3
Lymph (x10 /µL) 10.69±1.88 10.73±1.50 11.62±2.61 13.38±2.62 11.03±1.42
3
Eosin (x10 /µL) 0.06±0.07 0.07±0.08 0.11±0.13 0.09±0.10 0.00±0.00
3
Mono (x10 /µL) 0.39±0.20 0.24±0.15 0.24±0.18 0.33±0.13 0.18±0.67
3
Baso (x10 /µL) 0.03±0.06 0.03±0.07 0.00±0.00 0.40±0.80 0.12±0.15
3
Values are mean±standard deviation of quintuplicate determination, *Means significant different (p<0.05) compared to the control.
N = 5, NS = Normal Saline. RBC = Red Blood Cell, Hb = Haemoglobin, PCV = Packed Cell Volume, ESR = Erythrocyte Sedimentation
Rate, tWBC = total White Blood Cell, Neutr = Neutrophil, Lymph = Lymphocyte, Eosin = Eosinophil, Mono = Monocytes, Baso = Basophils
Table 5: The mean body weight of rat administered aqueous tuber extract of tigernut
Group II Group III Group IV Group V
Periods Group I NS 500 mg/kg 1000 mg/kg 1500 mg/kg 2000 mg/kg
0 day 113.25±15.09 113.50±6.62 114.74±12.20 111.24±9.62 110.47±5.83
6 day 138.05±8.00 115.20±9.97 139.00±16.02 121.50±17.65 134.40±13.00
th
12 day 147.30±11.47 130.32±9.35 142.94±15.35 125.38±17.26 139.34±12.42
th
18 day 157.07±8.60 141.90±8.20 149.40±14.57 133.90±17.92 152.14±14.02
th
24 day 160.15±9.47 143.80±9.30 158.10±15.06 141.02±18.45 159.14±15.40
th
30 day 174.95±7.61 149.92±10.45 166.48±15.87 148.36±19.06 171.28±11.53
th
Values are mean±standard deviation of quintuplicate. N = 5, NS = Normal Saline
Although the animals used in this study were fed with Ahamefule, F.O., B.E. Obua, I.A. Ukweni, M.A. Oguike and
normal rat diet, the tigernut tuber extract might have
allowed proper absorption of the nutrients which have
allowed proper utilization of the nutrients. Low level of
active/toxic principles may have stimulated appetite and
increased feed utilization resulting in increased weight
gain. The tuber of C. esculentus is used in making a
refreshing beverage called kuunu in Nigeria which is
consumed mostly in the Northern region of Nigeria
(Belewa and Abodurin, 2008). There have not been any
reported cases of toxicity in humans.
The present study confirms the tigernut tuber contains
important nutrients and some essential macro and
micro nutrient necessary for good human and animal
health. Roasting the tuber as a processing step reduced
the antinutrients composition. But unlike several other
underutilized crops, it does not produce any undesirable
effects even when consumed raw. The findings indicate
that the tigernut tuber which is popularly eaten raw is rich
in important food properties when compared with other
crops has no negative effect, at least in rats and
considering the economic situation in Nigeria and the
near zero economic value of this tuber, its cultivation and
consumption should be encouraged.
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