International Journal of Advancements in Research & Technology, Volume 2, Issue 9, September-2013
ISSN 2278-7763
8
Determination of Essential Elemental Concentration Profile in
Ghanaian Shea (Vitellaria Paradoxa L) Fruit Pulp using
Instrumental Neutron Activation Analysis
Aaron N. Adazabra, Samuel-Quarcoo Dotse, E. Alhassan
1
Department of Applied Physics, Faculty of Applied Sciences, University for Development Studies, P. O. Box 24, Navrongo, Upper East Region,
Ghana;
2
National Nuclear Research Institute, Ghana Atomic Energy Commission, P.O. Box LG 80, Legon – Accra, Ghana.
Email: adazabraaron@yahoo.com
ABSTRACT
Studies have shown that the Shea (Vitellaria paradoxa L) tree is an important ecological, nutritional and socio-economic resource
for upgrading the standard of living of the indigenous population in the Sub - Sahelian region of Ghana. However, little is
known about the essential elements concentration profile of the widely- consumed fruit pulp of this tree. The aim of this study
therefore was to ascertain the essential elements present in the Shea fruit pulps as well as other contaminants using the well –
established Instrumental Neutron Activation Analytical Technique. All fresh Shea fruit pulps samples contain high concentrations of K, Ca and Mg with the rest being Cl Na, Zn, Cr, Co, Cu and Fe which were also found in significant amounts. Sb and As
were found in traces in some of the samples. This data is paramount in the estimation of essential minerals dietary intake for
humans as well as the evaluation of their exposure to toxic elements.
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Keywords : Shea fruits; activation analysis; relative method; Elemental analysis; Ghana.
1 INTRODUCTION
F
RUITS form an integral part of food needed to meet the
mineral requirements of the human body. They are noted
to contain a wide variety of complex phytochemicals and
secondary metabolites that protect the human body from various biotic and abiotic stresses, diseases and help develop defense mechanisms for fighting various ailments by boosting
the immune system [1]. The consumption of fruits which are
abound with minerals, vitamins, enzymes and are easily digestible, have a tradition of being a natural staple of human
diets since ancient times [2]. Hence, aside been used as a dietary supplement, fruits have a central role in health care by
increasing lifespan and improving general well-being of humans.
One of such fruits is the Shea (Vitellaria paradoxa L) fruit.
The Shea tree is one of the most predominant trees in northern
Ghana. It is an important multipurpose tree, which plays important ecological and socio-economic role, and is the principal source of income for the indigenous population in the Sahel region [3]. The Shea tree, locally termly “the African wonder”, is synonymous to crude oil in the oil industry because
every part of this plant has a useful purpose.
For instance, the pulp which could be removed by fermentation can be processed into juice [4]. The wood, which is termite-resistant, is used as building poles. The kernels in the
nuts are processed into butter or oil. This butter/oil aside been
widely used for cooking African foods and traditional medicines, is used in factories to produce baking fat, margarine,
chocolate, cocoa butter substitutes, various moistening beauty
and pharmaceutical products. Also, the unsaponifiable components are used to cure third degree burned victims [5]. The
Copyright © 2013 SciResPub.
hard shells of the nuts are used as native mosquito repellent
materials for combating malaria. An edible caterpillar [4]
which feeds only Vitellaria paradoxa leaves is dried and sold in
the markets of some countries. The flowers are prepared into
edible fritters. The roots are used as chewing sticks. Infusion
of the bark is used to neutralize the venom of splitting cobra.
Sap from the barks is an invaluable raw material in the gum
and rubber industry [6].
However, most research work related to this plant targets
only the economic important nuts and its products [7], [8], [9],
[10]. Even though, the nutritional importance of many trace
elements is well established [11] and their concentrations in
fruits widely studied in developing countries [12], not much
however, is known about these essential elements present in
the Ghanaian Shea fruit. These elements are extensively studied because; first, at optimal levels they play important roles in
biochemical, metabolic, catabolic and enzymatic reactions in
the living cells of human beings; secondly, deficiency causes
diseases; whereas thirdly, excessive intake of some of these
elements may adversely affect the human biomedical function
[9], [13], [14]. Moreover, due to the general lack of an ingenious way of packaging and handling of Shea fruit, it is necessary to check the elemental content for toxic elemental (As, Sb)
contaminants levels in an ever – increasing industrialized and
ecological polluted environment.
Since the essential elements, which constitute a minute
fraction, are being considered “inorganic switches” in an ever
evolving complex biological systems coupled with the possible masking of major elemental constituents, a highly sensitive, selective and reliable instrumental method is necessary to
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International Journal of Advancements
Kwabeng in Research & Technology, Volume 2, Issue 9, September-2013
ISSN 2278-7763
9
u
us
bud
R. A
collect precise and accurate data [15], [16], [17]. Aside the re- Atomic Energy Commission.
KW7mentioned above, Instrumental Neutron Activaquirements
tion Analysis (INAA), has add advantages of been freedom 2.2 Spample and Standards Preparation
GR.9
The samples were further washed with de – ionized water
from reagent
blanks corrections, good detection limit (ppm to
DRYbefore
DUMP
peeling the pulps using a stainless steel knife at the
ppb), rare interferences, seldom matrix and
offers
easy
sample
GR.6
AREA
GR.2 of samples was freeze - dried for 48–72
GR.5
Centre.
Each category
preparation [18]. Hence, it was the methodKW6of choice
for
this
M
hours
using
a
Christ
LMC-1 freeze dryer, milled into fine
I
analysis. The determination
of essential elemental concentraGR.3
N
GR.8
E
powder
and
then
homogenized
for analysis. Aliquots (betion profile in Ghanaian Shea (Vitellaria
GR.7paradoxa L) fruit pulp
GR.1
KW3
S
tween
200mg
and
250
mg)
of
the
homogenized
samples were
KW1
using instrumental neutron activation analysis is therefore,I
T weighed onto clean polyethylene films wrapped and heat
KW5
justified.
E
SLIME RETENTION
sealed. Ten replicates of these samples from each district were
AREA
prepared. Also, 3 replicates each of two biological Standard
2 MATERIALS AND METHODS
Reference Materials (SRMs) obtained from the U.S. National
LEGEND
KW2
Institute of Standard and Technology (NIST), namely Oyster
2.1 Sampling
Individual fresh Shea fruits pulps (Vitellaria paradoxa L) variety Tissue (SRM 1566b) and Apple leaves (SRM 1515), were also
Road
comparator
standards in the relative
were randomly obtained, from local farmers, from most dis- prepared for analysis as
ATEWA
RANGE
River
method.
All
standards
and
samples
were
located in polyethtricts in the Upper East Region of Ghana where the Shea tree is
cotton in other
to maintain reproducible
RESERVE
wildly distributed asDiverted
shownWatercourse
by the sampling points in Fig., 1. ylene vials, stack withFOREST
The region is located
the North-East corner of Ghana be- geometry and heat sealed for irradiation.
GR
OldonSampling
Point
GR.4
tween latitudesKW
10º 30´ to 11º North and longitudes 0º to 1º 30´
KW4 and Counting
2.3 Irradiation
New
Sampling
Point
West
within
the
White
Volta
River
Basin
Samples
and
standards were transferred into the inner (No. 2)
(www.ghanahealthservice.org).
3 kg of fresh edible
Contours (50ftAbout
intervals)
irradiation
sites
of Ghana’s Miniature Neutron Source Reactor
fruits were sampled from each administrative district. The
(MNSR)
via
pneumatic
transfer system at a pressure of 0.6
samples were thoroughly hand – rinsed with distilled water,
Mpa.
The
stability,
homogeneity,
and reproducibility of the
shaken to remove any excess water and then gently blotted
0 towel.
100 The
200 samples
600 800
m.
with a paper
were1000
wrapped
with clean Ghana’s MNSR neutron flux for neutron activation analysis
polyethylene, frozen and then placed into clean polyethylene have previously been reported [19]. Counting of all the samcontainers for transportation to the Ghana Research Reactor – ples was done a distance of 7.2 cm on top of the gamma-ray
1 Centre at the National Nuclear Research Institute of Ghana spectroscopic detector.
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Fig. 1. Location of study areas and administrative districts in Upper East Region, Ghana
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International Journal of Advancements in Research & Technology, Volume 2, Issue 9, September-2013
ISSN 2278-7763
3 RESULTS AND DISCUSSION
It is an irrefutable fact that though the single (k 0 – INAA)
comparator method is considered to be the most highly optimized and economic version of the INAA, it is very complex
in its formulation and implementation [20], [21]. Paradoxically, the k 0 – INAA community are still suspicious about the
reliability of k 0 – values of some isotopes [22], [23]. Thus to
completely avoid the complexities posed by the use of nuclear
constants, irradiation site parameters and several correction
factors, the relative comparator method of INAA was used in
our work for the determination of essential elements as well as
toxic elements in all the samples. A detail study about the applicability of this method in our laboratory has previously
been presented [24]. Also, validation of the relative comparator method at Ghana’s MNSR has been described, discussed
and compared with various different matrix reference materials by various authors over the years in published literature
[25], [26], [27], [28].
The distinct energy signatures from the neutron – capture
reaction of the various radioisotopes of interest as well as their
half-lives [20], [29] are presented in Table 1. A careful assessment of Table 1 shows that the characteristic half – lives of all
the elements studied varied by a wide spectrum. Therefore, in
other to reduce high background activities posed by some elements resulting in masking of other elements of interest and
for obtaining; better counting statistics, improved signal – to –
noise ratio of the gamma – ray spectrum and, higher precision
and specificity at much lower detection limits of the gamma –
ray spectroscopic system, all the elements were critically categorized into three main optimized irradiations schemes.
Table 1. Nuclear data of nuclides determined in this work.
Element
Target
Product Half
– γ- Ray,
Isotope
Isotope
live
keV
75
76
As
As
As
26.4 h
559
46Ca
47Ca
Ca
4.536 d
1292
37Cl
38Cl
Cl
37.24 m
1642.7
59Co
60Co
Co
5.271 y
1173
1332.5
50Cr
51Cr
Cr
27.7 d
320
65Cu
66Cu
Cu
5.088 m
1039.2
58Fe
59Fe
Fe
44.50 d
1099.3
1291.6
41K
42K
K
12.36 h
1524.6
26Mg
27Mg
Mg
9.46 m
843.8
23Na
24Na
Na
15.03 h
1368
121Sb
122Sb
Sb
2.70 d
564.2
692.7
64Zn
65Zn
Zn
244.3 d
1115
Thus to enhance the sensitivities of each element determined
by INAA method; short irradiation schemes were employed
for Mg, Cu and Cl with Na, As and K using the medium irradiation scheme and the rest (Ca, Co, Cr, Fe, Sb, Zn) using the
long irradiation scheme.
All the samples taken from Bulisa, Kassena/Nankana, Bolgatanga Municipal, Bongo Talensi – Nabdam, Bawku West,
Bawku Municipal and Garu – Tempane as shown in Fig. 1
10
were codified as BUL, KAN, BOM, BON, TAN BAW, BAM
and GAT respectively for easy reference. The results of 12 different elemental concentrations were statistically evaluated
using SPSS version 16 and Microsoft excel statistical package
and expressed as mean ± absolute standard deviation (SD)
from triplicate measurements as shown in Table 2.
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International Journal of Advancements in Research & Technology, Volume 2, Issue 9, September-2013
ISSN 2278-7763
Significant differences between the means of the results
were determined by using the Tukey HSD test. A criterion of p
≤ 0.05 was considered to be significant. Even though the concentrations of essential elements were mostly varied amongst
the various samples as depicted in Table 2, nevertheless it is
evident that Vitellaria paradoxa L variety fruits pulps are endowed with a rich variety of various complex pharmacological
bioavailable phytochemicals that could protect against several
chronic diseases when consumed [30].
The concentration of major essential elements (Ca, K, Mg
and Na) is in the range of 9 – 37 mg/10g. These values are relatively high compared to similar fruits pulps analyzed in
Uganda by Okullo et al., [31]. However, similar results were
obtained in Nigeria by Adepoju [32]. Aside the major essential
elements, Cl recorded the highest concentration (106.0 – 334.5
µg/g) in the Shea fruit pulps from all sampling points. The
increasing order of this observed element in the various sampling points was TAN < KAN < BAW < BUL < BON < BOM <
BAM < GAT. Other observed essential elements of substantial
concentrations in all samples were Zn, Fe and Cu. A perusal of
Table 2 shows that, in all sampling areas; As, Sb and Co recorded the lowest concentration in the ranges of 0.106 – 0.312
µg/g, 0.656 – 1.090 µg/g and 1.08 – 3.02 µg/g respectively. Sb,
As and elements such as Pb, Hg, Cd are said to have toxicological effects, hence they are classified among the most dangerous groups of anthropogenic environmental pollutants [18].
Thus the low concentrations of As and Sb re-affirms the
popular belief that natural products are safe for consumption
[33]. A careful scrutiny of Table 2 again shows that no particular sampling point recorded highest values of all elements
studied. We have no explanation to this observation yet.
However, the variation in elemental concentration of the same
Shea fruit pulp species can mainly be attributed to the differences in the mineral composition of the soil and climatological
conditions in which the plants are grown [34].
Other factors could be due to contamination during the
harvesting and handling of the fruit pulps. The accountability
of the different elements present and their concentration levels
in terms of their physiological, pharmacological, nutritional
and biochemical roles may be a search light for physicians and
dieticians / nutritionist. Hence, it is not discussed in the study.
11
ACKNOWLEDGMENT
We wish to express our ultimate gratitude to Mrs Rose Mma
Atidoo, for her tremendous support of this work during the
collection of samples from the various district, to Madam
Gladys B. Tampoare we are very appreciative for her technical
and constructive critic of the manuscript and to Mr. Valentine
Anamloya Adazabra for proof reading this manuscript. Our
thanks also goes to Mr Apori Ntiforo, Head of Department of
Applied Physics, University for Development Studies, Navrongo Campus, for this support and mentorship.
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4 CONCLUSION
A very simple but highly sensitive, selective and specific nuclear analytical method was used in the determination of essential elements in the Shea (Vitellaria paradoxa L) fruit pulps in
the Upper East Region of Ghana. Aside the highly economic
beneficial nuts of the Shea (Vitellaria paradoxa L) tree, the “African wonder” fruit pulps are a rich source of various essential
elements that could help upgrade the health status of the populace. The fruit pulps were found to particularly contain high
concentrations of Ca, K, Mg and Na. Toxic elements (As, Sb)
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Copyright © 2013 SciResPub.
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