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International Journal of Advancements in Research & Technology, Volume 2, Issue 9, September-2013 8 ISSN 2278-7763

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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 1Department of Applied Physics, Faculty of Applied Sciences, University for Development Studies, P. O. Box 24, Navrongo, Upper East Region, Ghana; 2National Nuclear Research Institute, Ghana Atomic Energy Commission, P.O. Box LG 80, Legon – Accra, Ghana. Email: [email protected]

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 concentra-tions 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. Keywords : Shea fruits; activation analysis; relative method; Elemental analysis; Ghana.

1 INTRODUCTION 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 vari-ous biotic and abiotic stresses, diseases and help develop de-fense 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 di-gestible, have a tradition of being a natural staple of human diets since ancient times [2]. Hence, aside been used as a die-tary supplement, fruits have a central role in health care by increasing lifespan and improving general well-being of hu-mans.

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 im-portant ecological and socio-economic role, and is the princi-pal source of income for the indigenous population in the Sa-hel region [3]. The Shea tree, locally termly “the African won-der”, 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 fermenta-tion can be processed into juice [4]. The wood, which is ter-mite-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 medi-cines, is used in factories to produce baking fat, margarine, chocolate, cocoa butter substitutes, various moistening beauty and pharmaceutical products. Also, the unsaponifiable com-ponents are used to cure third degree burned victims [5]. The

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 stud-ied 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 ingen-ious way of packaging and handling of Shea fruit, it is neces-sary 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 possi-ble masking of major elemental constituents, a highly sensi-tive, selective and reliable instrumental method is necessary to

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collect precise and accurate data [15], [16], [17]. Aside the re-quirements mentioned above, Instrumental Neutron Activa-tion Analysis (INAA), has add advantages of been freedom from reagent blanks corrections, good detection limit (ppm to ppb), rare interferences, seldom matrix and offers easy sample preparation [18]. Hence, it was the method of choice for this analysis. The determination of essential elemental concentra-tion profile in Ghanaian Shea (Vitellaria paradoxa L) fruit pulp using instrumental neutron activation analysis is therefore, justified.

2 MATERIALS AND METHODS 2.1 Sampling Individual fresh Shea fruits pulps (Vitellaria paradoxa L) variety were randomly obtained, from local farmers, from most dis-tricts in the Upper East Region of Ghana where the Shea tree is wildly distributed as shown by the sampling points in Fig., 1. The region is located on the North-East corner of Ghana be-tween latitudes 10º 30´ to 11º North and longitudes 0º to 1º 30´ West within the White Volta River Basin (www.ghanahealthservice.org). About 3 kg of fresh edible fruits were sampled from each administrative district. The samples were thoroughly hand – rinsed with distilled water, shaken to remove any excess water and then gently blotted with a paper towel. The samples were wrapped with clean polyethylene, frozen and then placed into clean polyethylene containers for transportation to the Ghana Research Reactor – 1 Centre at the National Nuclear Research Institute of Ghana

Atomic Energy Commission.

2.2 Spample and Standards Preparation The samples were further washed with de – ionized water

before peeling the pulps using a stainless steel knife at the Centre. Each category of samples was freeze - dried for 48–72 hours using a Christ LMC-1 freeze dryer, milled into fine powder and then homogenized for analysis. Aliquots (be-tween 200mg and 250 mg) of the homogenized samples were weighed onto clean polyethylene films wrapped and heat sealed. Ten replicates of these samples from each district were prepared. Also, 3 replicates each of two biological Standard Reference Materials (SRMs) obtained from the U.S. National Institute of Standard and Technology (NIST), namely Oyster Tissue (SRM 1566b) and Apple leaves (SRM 1515), were also prepared for analysis as comparator standards in the relative method. All standards and samples were located in polyeth-ylene vials, stack with cotton in other to maintain reproducible geometry and heat sealed for irradiation.

2.3 Irradiation and Counting Samples and standards were transferred into the inner (No. 2) irradiation sites of Ghana’s Miniature Neutron Source Reactor (MNSR) via pneumatic transfer system at a pressure of 0.6 Mpa. The stability, homogeneity, and reproducibility of the Ghana’s MNSR neutron flux for neutron activation analysis have previously been reported [19]. Counting of all the sam-ples was done a distance of 7.2 cm on top of the gamma-ray spectroscopic detector.

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M I N E S I T ESLIME RETENTIONAREA

DRY DUMPAREA

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budusu

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RoadRiverDiverted WatercourseOld Sampling PointNew Sampling Point

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Contours (50ft intervals)

Fig. 1. Location of study areas and administrative districts in Upper East Region, Ghana

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3 RESULTS AND DISCUSSION It is an irrefutable fact that though the single (k0 – INAA) comparator method is considered to be the most highly opti-mized and economic version of the INAA, it is very complex in its formulation and implementation [20], [21]. Paradoxical-ly, the k0 – INAA community are still suspicious about the reliability of k0 – 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 ap-plicability of this method in our laboratory has previously been presented [24]. Also, validation of the relative compara-tor method at Ghana’s MNSR has been described, discussed and compared with various different matrix reference materi-als 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 assess-ment 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 el-ements 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 cate-gorized into three main optimized irradiations schemes. Table 1. Nuclear data of nuclides determined in this work.

Element Target Isotope

Product Isotope

Half – live

γ- Ray, keV

As 75As 76As 26.4 h 559 Ca 46Ca 47Ca 4.536 d 1292 Cl 37Cl 38Cl 37.24 m 1642.7 Co 59Co 60Co 5.271 y 1173

1332.5 Cr 50Cr 51Cr 27.7 d 320 Cu 65Cu 66Cu 5.088 m 1039.2 Fe 58Fe 59Fe 44.50 d 1099.3

1291.6 K 41K 42K 12.36 h 1524.6 Mg 26Mg 27Mg 9.46 m 843.8 Na 23Na 24Na 15.03 h 1368 Sb 121Sb 122Sb 2.70 d 564.2

692.7 Zn 64Zn 65Zn 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 irra-diation scheme and the rest (Ca, Co, Cr, Fe, Sb, Zn) using the long irradiation scheme.

All the samples taken from Bulisa, Kassena/Nankana, Bol-gatanga Municipal, Bongo Talensi – Nabdam, Bawku West, Bawku Municipal and Garu – Tempane as shown in Fig. 1

were codified as BUL, KAN, BOM, BON, TAN BAW, BAM and GAT respectively for easy reference. The results of 12 dif-ferent 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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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 con-centrations 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 en-dowed 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 rel-atively 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 sam-pling 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 rec-orded 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 toxicolog-ical effects, hence they are classified among the most danger-ous 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 particu-lar 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 differ-ences 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.

4 CONCLUSION A very simple but highly sensitive, selective and specific nu-clear analytical method was used in the determination of es-sential 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 “Af-rican wonder” fruit pulps are a rich source of various essential elements that could help upgrade the health status of the pop-ulace. The fruit pulps were found to particularly contain high concentrations of Ca, K, Mg and Na. Toxic elements (As, Sb) were generally found in traces suggesting the safe consump-tion of this natural food product. We therefore recommend that, further research works should be conducted on other toxic elements before the commercialization of this food prod-uct.

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, Nav-rongo Campus, for this support and mentorship.

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