Analysis of major and trace elements in teff (Eragrostis tef)

1 Introduction

Teff (Eragrostis tef) has been used for centuries as one of the main sources of nutrient in Ethiopia. It is grown majorly in the central and northern part of the country. Teff is reported to have higher nutrition and fiber content as compared to cereals such as wheat, rice, oats, and barley (Gebremariam et al., 2014). In addition, it is a gluten free grain that could be suitable for use in the diet of patients with celiac disease (CD), a disorder that leads to gluten intolerance (Hopman et al., 2008, Spaenij-Dekking et al., 2005).

Trace elements play a vital role in proper functioning of enzymes through modulating reactions, constitute their active sites, stabilize their structure, and mediate oxidation-reduction process (Fraga, 2005, Ingrao et al., 1995). They also play an important role in the proper functioning of the immune system (Rolla et al., 1983). While several metals like Cu, Zn, and Fe are essential micronutrients, metals such as Cd and Pb, constitute non-essential and toxic elements (Luis-Gonzalez et al., 2015). Contamination of food by these metals commonly occur from sources such as municipal and industrial discharges, irrigation water, geogenic, agricultural imputes, pharmaceutical, and atmospheric sources (Gimou et al., 2014; Hajeb et al., 2014; He et al., 2005). Despite the fact that various studies on teff grain have been published, only limited data are available regarding its major and trace element contents. Moreover, the data reported for elements such as Fe, Mg, and Ca are not consistent and show great variations in literature. Therefore, the present study aimed at detecting and quantifying trace elements in E. tef using ICP-MS.

2 Material and methods

3 Results and discussion

In the current study, a total of 44 elements were detected and quantified in teff grain samples (Table 1). The most abundant elements measured were K (1289 mg/kg), P (992 mg/kg), Ca (444 mg/kg), Mg (543 mg/kg), and Na (127 mg/kg) respectively (Fig. 1). The least abundant elements were Er, Eu, and Sb with a concentration of 0.001 mg/kg. While the number of major and trace elements detected and quantified using ICP-MS in this study represents the highest number of elements ever identified in E. tef, concentrations of few elements such as Fe and Mg have previously been reported in literature. Comparison of our result against the values reported in literature shows that the concentration of Fe in white (11 mg/kg) and red (14 mg/kg) teff varieties are comparable to concentrations reported for wheat (15 mg/kg) and corn (13 mg/kg) (Table 1). On the other hand, previous studies indicated that teff has the highest concentration (196 mg/kg) of Fe among cereals including wheat and corn (Mengesha, 1966). However, this conclusion was contradicted by a study done by Besrat et al. (1980), which suggested that soil contaminations contribute to the high Fe content observed in teff. Likewise, concentrations of Ba, Co, Ca, and Zn measured by ICP-MS in the current study were also lower than those previously reported in literature (Table 1).

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Fig. 1

Selected element content in white and red teff grain.

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According to Kibatu et al., concentration of iron is found to be 16.05 ± 1.63 (mg/100 g dry weight) in white teff (Kibatu et al., 2017) as measured by portable total X-ray fluorescence spectrometer (PTXRF). Similarly the previously reported concentrations of B in both white and red teff varieties and Al in white teff however, were less than the values we measured in this study. According to Abebe et al., Fe, Ca, and Zn contents of red teff were 37.7, 124, and 2.8 (mg/100 g) respectively, while their concentration in white teff were 150, 155, and 4.02 (mg/100 g) respectively (Abebe et al., 2007); these values are comparable with the concentrations we measured and lower than the values that were reported by Mengesha (Mengesha, 1966).

The elements concentration ranges observed among literature could be due to a number of factors, including the local environment (soil, pH, organic matter, water, and contaminants), and instrument differences both in sensitivity and accuracy. In addition, sample variations plays a role as the grain shows considerable diversity in terms of agronomic, genetic, and morphological characters (Assefa et al., 2015; Espelund et al., 2000). On the other hand, the values we obtained using ICP-MS agree reasonably well with the figures reported for wheat and corn standard samples (Table 1). Based on their overall abundance and their detection in other grains (corn and wheat), these trace elements appear to be normal constituents of teff but have not been previously reported. Since ICP-MS is a method of choice for the identification and quantification of trace metals in a biological sample, it is reasonable to accept the values derived via this instrument over those measured by other analytical tools (Benkhedda et al., 2000, Heitland and Koster, 2006).

4 Conclusions

In the current study we were able to identify and quantify a total of 44 major and trace elements in teff grain samples. This number represents the highest number of major and trace elements ever detected and quantified in teff grain. As this study, however, was conducted on a limited sample size, extensive study covering samples collected from the different teff growing areas in the country should be conducted in order to establish the level of major and trace elements in the grain.