Determination of Proximate Composition, Ascorbic Acid and Heavy Metal Content of African Walnut (Tetracarpidium conophorum)
Christopher A. Dosunmu,
Bassey Francesca I.
The proximate composition, ascorbic acid and heavy metal
content of (African walnut) Tetracarpidium conophorum were evaluated
using chemical analysis. The result of the proximate composition showed
the following; moisture (48.70%), carbohydrate (53.20%), crude protein
(35.22%), crude fat (6.21%), crude fiber (3.34%) and ash (2.03%).It also
contained 53.50mg/100ml of ascorbic acid. The heavy metal concentrations
in the fruit is Fe (0.064ppm), Mn (0.012ppm), Cr (0.001ppm), Ni (0.005ppm)
while the concentrations of Hg, Pb and Cd were not detected. The results
revealed that the T. conophorum is rich in ascorbic acid and carbohydrate
with moderate valves of crude protein while the ash content was shown
to be very low. This result shows that T. conophorum nut is not
polluted with heavy metals since the concentrations of the heavy metals
were all below WHO permissible limits. This nut is therefore shown to
be safe for public consumption.
Tetracarpidium conophorum, known as Ekporo by the
Efiks and Ibibios of Cross River and Akwa Ibom states in Nigeria is a
woody perennial climber that belongs to the family Euphorbiacea. Its common
name is African walnut. It is found in the forest regions of Africa and
India (Oke, 1995; Petrova, 1980). In Nigeria it is found in Abak, Uyo,
Etinan, Akamkpa Akpabuyo, Lagos and Ibadan. T. conophorum plant
is cultivated principally for the nuts which are cooked and consumed as
snacks (Oke, 1995). A bitter taste is usually observed upon drinking water
immediately after eating the nuts. This could be attributed to the presence
of chemical substances such as alkaloids. Ayodele (2003) reported the
presence of oxalates, phylates and tannin in the raw T. conophorum
nuts. Though T. conophorum nuts are generally eaten in Nigeria,
very little work has been done on the proximate composition and heavy
metal content of this nut. Oyenuga (1997) reported on the amino acid and
fatty acid components of the nut and on the use of its leaf juice for
the treatment of prolonged and constant hiccups. Nwokolo (1987) also reported
on the impact of traditional processing on the nutrient and sensory qualities
of the nut. Okpero (2001) reported on the methods of processing the T.
conophorum nuts while Okafor (1988) reported on the use of T. conophorum
seeds and processing waste in livestock feed formulation. This work is
aimed at assessing the proximate composition and ascorbic acid content
of African walnut with the view of knowing its chemical composition. The
heavy metal content of the nut will also be determined in order to ascertain
the effect of its consumption on health.
Materials and Methods
Sample collection: The T. conophorum nut used in this study
were obtained from a private plantation in Ikot Ekong, Akpabuyo L.G.A.
South East of the University of Calabar, Calabar in Cross River State.
Thirty (30) nuts of T. conophorum (African walnut) were obtained
from the plantation in six polythene bags and transported to the laboratory
within few hours of harvesting. The samples were analyzed in composite.
Sample preparation: The nuts were washed with deionized distilled
water and wiped with kitchen tissue. The nuts were then chopped into pieces
using a knife with steel blade. Portions were taken for moisture and ascorbic
acid content determination.
The rest of the nuts were dried in a hot air circulating oven (Gallenkamp
DV 330) at 65oC to a constant weight for 18-24h. The dried
samples were ground using an electric blender with steel blades and stored
in screw-capped bottles at 4-6oC.
Analysis: Moisture content was determined by drying about 3g of
the fresh sample to constant weight in a hot air circulating oven at 100oC.
Proximate composition which included percentage moisture, fat, crude protein,
fibre and ash were determined according to the standard method of the
AOAC (1984). Total carbohydrate was calculated by difference obtained
after subtracting the protein, ash, fat and fibre contents from the total
dry mass. Ascorbic acid was determined by titrating ascorbic acid extract
prepared from 30g of the fresh sample against N-bromosuccunmide by the
method of Haddad (1977). The determination of Ni, Fe, Cr, Mn, Hg,Cd and
Pb was done using an atomic absorption spectrophotometer (AAS) (Pye Unicam
2900), according to the procedure of the AOAC (1984).
||Proximate composition (g/100g, dry sample) and ascorbic acid content
of African walnut (tetracarpidium conophorum)
||Heavy metal concentration of Tetracarpidium conophorum nut (ppm)
Results and Discussion
Table 1 shows the proximate composition and ascorbic
acid content of T.conophorum. The moisture content was shown
to be 48.7%, carbohydrate 53.20%, crude protein 35.22%, crude fat 6.21%,
crude fiber 3.34% and ash 2.03% while Ascorbic acid content was 53.50mg/100ml.
The result reveals that the nut of T. conophorum is very
rich in ascorbic acid and carbohydrate while it has a moderate amount
of protein with a very low ash content. The study revealed that T.
conophorum nuts could be used to boost the ascorbic acid, carbohydrate
and protein content of most food products sold in our markets. The low
moisture content of the fruit shows that it could be stored for sometime
without going bad.
Table 2 shows the heavy metal concentrations in
T. conophorum nut. From the result (Table 2),
the concentrations of the heavy metals is Fe (0.064ppm), Mn (0.012ppm)
Cr (0.001ppm), Ni (0.005ppm). The concentration of Hg, Pb and Cd were
not detected. The study revealed that Fe has the highest concentration
of (0.064) followed by Mn (0.012) and Ni (0.005). Cr has the lowest
concentration of 0.001 in the nut. This result shows that T. conophorum
nut is not polluted with heavy metals as all the concentrations of
the metals determined are below WHO (1991) permissible limits. It has
been revealed by this study that the metals investigated do not pose health
hazard to consumers as they are below the WHO permissible limits.
Conclusion: This study has shown that nuts of T. conophorum
are good sources of ascorbic acid and carbohydrate and moderate sources
of protein. The heavy metal content of the nut is also shown to be below
WHO permissible limit which makes the nut safe for public consumption
without any fear of heavy metal pollution.
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2: Ayodele, O.B., 2003. Nutrition in Nigeria Ibadan. Catoon Publishers, USA
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