Microelement Contents of Locally Produced and Imported Wheat Grains in Yemen

In the last few decades, wheat-based products have received considerable attention in view of their potential role in transporting of microelements into the human diet. In Yemen, bread is the staple food, produced in different kinds from local and imported wheat. Most of it is not subjected to microelemental analysis. The objective of this study is to determine quantitatively the microelement such as Fe, Cu, Mn, Zn, Co, Cd and Pb in samples of wheat grains produced locally from different cultivated regions in Yemen as well as those imported from USA and Austria. Flame atomic absorption spectrophotometry was used for analysis. The results show that the contents of the microelements in the studied samples are generally within the permissible levels except cadmium. The samples collected from middle altitude and eastern plateau the cadmium is above the permissible level. Keyword: Microelement, Wheat, Yemen, Spectrophotometeric analysis


Introduction
Metals have an impact on human health in many ways.Some elements such as Cu, Mn and Zn are essential micronutrients with a human requirement of not more than a few milligrams per day.However, micronutrients may become harmful when their ingestion rates are too high.In contrast, trace elements such as Cd and Pb are well known as toxic if their intake through ingestion or inhalation is excessive.The deficiencies, excesses or imbalances in the supply of inorganic elements from dietary sources can have an important deleterious influence on human health [1][2] .The amount of element ingested by human is directly related to alimentary habits and their content in foodstuffs.
In the last few decades, cereal products including wheat-based products have received considerable attention in view of their potential role in transporting of toxic microelements into the human diet.Since 1973, As, Cu, Cd, Fe, Hg, Pb, and Zn have been considered by the joint FAO/WHO Codex Alimentarius Commission to be potentially toxic for human diet with As (as arsenite) being carcinogenic 3 .
Bread is the staple food in Yemen that is produced in different kinds from wheat.In Yemen, the total cultivated area ranges from 1.1-1.8 million hectare depends upon sufficient rain fall.In the year 2004, the total cultivated area reached to 1.1 million hectare, cereals crops occupy 57.6% of it, from which 12.2% is occupied by wheat crop.The total cultivated area of wheat crop in the year 2004 is 83801 hectare, with a total production of 103265 tons of wheat grain.The quantities of wheat grain imported in 2004 is 1.806.332ton.This indicates that the self -sufficiency of wheat grains in Yemen ranges 4 from 5.5 to 13.4% A survey 5-9 of toxic elements in wheat grain has been carried out in a number of countries.The objective of this study is to determine quantitatively seven microelements such as Cu, Fe, Pb, Co, Cd, Mn, and Zn in wheat grain samples representing some different growing regions in Yemen, harvested in 2004 and two samples of imported wheat grains usually imported from USA and from Austria.

Sampling
Wheat crop is mainly cultivated in the northern altitude constituting the governorates of Sana'a and Amran.The altitude of these areas is more than 2000 m above sea level.It is also grown in the middle altitudes that include the governorates of Dhmar and Albidah.The crop is irrigated in these areas by rain fall during summer season.Another wheat cultivated area in Yemen is the eastern plateau that represents governorates of Hadramout, Mareb and Aljouf.The crop is irrigated by tube wells.Samples of wheat grains were collected from different fields during the harvest period as mentioned by Bruggemann, Kumpulainen, and GEMS / Food-EURO [10][11][12] .Samples of the imported wheat grains were collected from Aden seaport using the quartering method.

Microelements analysis
Aliquots of the composite wheat grain samples were manually cleaned and milled in a hammer mill, having sieve of 0.5 mm to obtain fine whole meal flour.Flour was stored in clean polyethylene flasks at 5 ‫ﮦ‬ C. Sub-sample of fresh whole meal flour about 5 g on dry matter basis was dissolved in 10 mL of concentrated nitric acid and heated under reflux.Then, 10 mL of concentrated perchloric acid was added and heated until formation of nitrous fumes stopped.The digestion temperature did not exceed 85 ‫ﮦ‬ C. The solution was placed in a 50 mL volumetric flask and made up to the volume with deionised water.Samples were analyzed 13 by flame atomic absorption spectrometer (FAAS) model VARIO -6.
All metal concentrations were determined by direct aspiration of the aqueous solution into air-acetylene flame AAS.All chemicals used in the sample treatments were of ultra pure grade purchased from MRCK.

Results and Discussion
Generally, microelement concentrations in foodstuffs depend on soil characteristics, such as content of organic matter, pH, and clay mineralogy, which can affect the bioavailability of elements.Besides environmental pollution, a matter of concern is the addition of chemical products such as fertilizers, fungicides, insecticides and herbicides to crops.On the other hand, wheat grains was mainly milled in the national millers with an extraction rate of about 76% .The majority of minerals left in bran was lost during the milling.Table 1 shows the content of microelements in the studied representing wheat samples.From the results shown in Table 1, the content of iron in the local wheat samples ranges from 51 to 53 µg/g.This content is near to the normal iron content in wheat 46 µg/g as stated by Kent 14 , but the content in the imported samples ranges from 57.60 to 60.0 µg/g.These contents were to some extent, higher than the normal content if compared to the local samples.Still both of those contents are considered low if compared with the study of Biljana and Antonija, different representative samples of wheat grown in different growing areas in Serbia into which the content of iron ranged from 51.7 to165 µg/g, with a mean content 15 of 807 µg/g.On the other hand , the imported grains of wheat was mainly milled in the national millers, with an extraction rate of 76% .The majority of minerals left in bran was lost during the milling .Such situation forces the local authorities to issue a rule to fortify the white wheat flour with iron.According to a technical report from a local research work executed by Almussali et.al 16 , the iron content in the white wheat flour milled locally from imported wheat has 50 µg/g.This level of iron content in flour may be due to fortification.Mohammed and Taha collected samples of wheat from different markets in Yemen and other Arab countries (Saudi Arabia, Egypt ,Oman, Dubai, and Australia) and found that the concentration of iron ranged from 1.5 µg/g in Egypt to 3.13 µg/g in Yemen 9 .Those researchers did not define the markets in Yemen and also they didn't know whether the samples were collected form the locally produced wheat or from the imported ones our results, as well as other different local studies are totally different from the results of Mohammed and Taha.

Zinc (Zn)
The normal content of zinc in wheat, according to Kent 14 is 33 µg/g.Table 1 indicates that the content of zinc in the local samples as well as imported one were 10.05 and 17.13 µg/g, which was some what low.Based on the results of the study conducted by Claudia 17 , the determined microelements in wheat grown in different areas in Argentine, the content of zinc was 36.87 µg/g.Another study by Lavado 18 in the same country, but in plateau away from the cities, concluded that the content of this element in wheat reached to 44.37 µg/g.Another study by Nagel 19 in Germany, found that wheat grains contain 35.50 µg/g of Zinc.The researcher Mingchu 20 found that wheat crop supplied with organic fertilizer has zinc content in its grains ranging from 23.89 to 30.62 µg/g.
It is clear, from the above foreign studies results that the content of zinc in wheat grains were higher, compared to its contents found in our study either for local or imported samples.Salama and Radwan from Egypt, collected wheat grains among some foodstuffs from the local market and determined the content of some heavy metals in them.They found that zinc content 8 was about 12.02 µg/g, which is around the content of zinc found in our study.This is an important indication concerning the level of this microelement especially in the imported wheat grains; make us report to the local authorities of this deficiency.We think that more studies are needed, mainly in the imported wheat grains from other countries, so that one can give a final recommendation for the fortification of these microelements in the white wheat flour.Zinc values are ordered as U.S.A > Eastern Plateau > Middle Altitude >Austria > Northern .Altitude.

Manganese (Mn)
The normal value of manganese in wheat as stated by Kent 14 is 40 µg/g.The tabulated results stated in Table 1 show that the content of manganese in wheat samples from the northern altitude and eastern plateau were the same about 35 µg/g.The manganese content in the imported samples were 41.33 and 44.10 µg/g respectively, which is nearly the same and also similar to the normal value.The samples collected from the middle altitude (2000 m above sea level) had 49.82 µg/g, which is some what higher in content compared to other samples.After all the content of this element either in the local or imported samples are considered of normal value.Keeping in mind that milling will reduce such contents to about more than 50%.The results indicate that manganese concentration is in the order Middle Altitude > Austria > U.S.A > Northern Altitude >Eastern plateau.

Copper (Cu)
Table 1 shows that the content of copper in the imported wheat grains as well as in the local samples, collected from the eastern plateau, are 4.70, 5.24 µg/g and 5.73 µg/g respectively , which is nearly the same.However the content of the same element in the northern and middle altitude samples were, 8.30 µg/g and 9.02µg/g, which is approximately double.A local study conducted by Kathem, found the content of 5 µg/g of copper in wheat samples collected from the eastern plateau which is agreement with our results 21 .Other studies reported that the content 15,18,19 of this element ranged from 5-11 µg/g.The normal value of this element is 6 µg/g as stated by Kent 14 .It is clear that the order of the content of copper in the samples is Middle Altitude >Northern Altitude >Eastern plateau > U.S.A >Austria.

Cobalt (Co)
The contents of cobalt in wheat grain samples collected from eastern plateau (1500 m above sea level) as well as that imported samples from Austria, was of 0.043 and 0.071 µg/g respectively.This content is near to the normal content of cobalt in wheat 0.05 µg/g, as stated by Kent 14 .While those wheat grain samples collected from the middle altitude and imported from the U.S.A were 0.154 and 0.177 µg/g respectively, which was approximately about three times higher when compared to the normal content.In the samples collected from the northern altitude, cobalt has not been detected.The researcher Lavado from Argentina conducted a study to determine the heavy metals in wheat grains cultivated in soil treated organically, did not detect this element in studied wheat grain samples 18 .

Cadmium (Cd)
Table 1 shows that the cadmium was not detected in the local wheat samples collected from the northern altitude as well as the imported sample from Austria.Its concentration in the samples collected from the middle altitude and eastern plateau were 0.246 and 0.294 µg/g respectively.These contents were more than twice of the content found in the imported samples from the U.S.A, which is 0.117 µg/g.
The content of cadmium in the wheat samples collected from the middle altitude and the eastern plateau were 0.246 µg/g.and 0.296 µg/g respectively.Cadmium content in wheat imported from the U.S.A. is similar to the study by Lavado 18 on Argentina wheat grains.
But the researcher Nagel 19 concluded in his study that the cadmium content was 0.08 µg/g, which is of low content compared to the content in the samples of our study.After Kent 14 stated that the normal content of cadmium in wheat grains is 0.1 µg/g, whereas Walker 22 stated that the permissible limits for cadmium in all foodstuffs is 0.05 µg/g.A local study 8 in Egypt conducted to determine the cadmium in some foodstuffs and found that the content of this element in wheat grains is 0.131 µg/g, which is nearly the same content in the sample imported from the U.S.A.

Lead (Pb)
The normal content 14 of lead in wheat is 0.80 µg/g.Also, Fergusion 23 stated that the permissible level of lead in food is 0.75 µg/g.From Table 1, it is clear that the content of lead in the northern altitude samples is 0.257 µg/g and in the middle altitude and those imported samples from the U.S.A. is 0.367 µg/g.Lead has not been detected in the wheat samples collected from the eastern plateau and those imported from Austria.In the earlier report 15,19 it is found that the content of this element in wheat is 0.0366 µg/g and 0.015 µg/g, respectively.The content of this element in the samples of our study especially collected from middle altitude and those from the U.S.A agreed mostly with the earlier results 15, 8 of lead content was 0.398 µg/g.After all, grains are subjected to milling to get white flour where the content of lead was reduced to about 50%.

Conclusions
The results of this study provide valuable information about the microelement contents in wheat, the main substance of bread, and the staple food of Yemeni citizens.The results show that the contents of the micro-elements in local and imported studied wheat are generally below the permissible levels, except cadmium, of which its content in the samples collected from the middle altitude and the eastern plateau was above the permissible level.More attention should be taken through deep studies towards cadmium content in wheat grain in such regions.However, these results can also be used to test the chemical quality of other foodstuffs in order to evaluate the possible risk associated with their consumption by humans.

Table 1 .
Microelements content of the studied samples of wheat grain.