Value-added foods provide health benefits above normal nutrition. Dietary fibre, vitamins, minerals and antioxidants enhance health in general. Nowadays, interest in the utilization of alternative grains in food production has been growing [1
] due to consumers’ demand for food promoting health and well-being. The awareness of toxic and potentially harmful substances has been rising as well.
Teff (Eragrostis tef
L.), originating from Ethiopia, is commonly used in flat bread production [2
]. Unfortunately, only scarce research has been conducted to examine teff’s potential and its rich nutritional benefits. Two types of teff are distinguished according to seed colour—white or brown—both belonging to the millet group [3
]. Currently, Dutch markets have a focus on growing teff [5
]. However, as only a small quantity of teff grown in Europe actually appears in local markets, most teff is still imported from Bolivia.
Trace and toxic elements have attracted public attention regarding their possible impact on health. However, their dietary intakes still need to be monitored to establish their safety in foods. Inorganic contaminants, such as As, Cd, Pb, Sn, Al and Hg, are the most studied toxic elements. The Joint Food and Agriculture Organization/World Health Organization (FAO/WHO) Committee on Food Additives (JECFA) has set the values of provisional tolerable weekly (PTWI) and monthly intakes (PTMI), as well as establishing further contaminants in food [6
]. Teff is a valuable source of minerals; in particular, Ca, Fe, Mn and Zn are present in larger amounts. Since teff is consumed as a whole grain, it may provide desirable nutrients and bioactive compounds. Unfortunately, literature data focusing on particular trace and toxic elements in teff and data evaluating the contribution of teff grains to the RDA (Recommended Dietary Allowance), AI (Adequate intake), PTWI and PTMI values has been scarce.
Consequently, this study was conducted to determine the content of minerals (Na, P, K, Mg and Ca) and trace elements (Mn, Zn, Fe, Cu, Be, Ni, Al, Ga, Co., Li, Sc, Ag, Sr, Ba, Tl, Bi, Ce, Cs, Ho, Ta, Tb, U, Y, Cr, Se, Sn, As, Pb, Hg, Cd and Ti) in brown and white teff grains by Inductively coupled plasma mass spectrometry(ICP-MS) and to establish their contributions to RDA, AI, PTWI and PTMI values.
2. Materials and Methods
2.1. Grain Sample Preparation and Reagents
Samples of Eragrostis tef L. were prepared from white and brown grains from Bolivia, harvested in 2016 and 2017, and from brown grains produced in the EU in 2017. European and Bolivian grains were bought at local markets in the Czech Republic, each as five packages of 250 g. Teff samples originating in the USA were bought at local markets in Idaho—five packages of 450 g. The samples were stored in dark air-lid plastic boxes. Each sample was analysed five times.
ICP-MS STANDARD 13 standard series (As, Ca, Cd, Cr, Fe, Hg, K, P, Na, Pb, Se, Sn and Ti), ICP-MS STANDARD 23 standard series (Be, Zn, Cu, Ni, Al, Ga, Mg, Co., Li, Sc, Ag, Mn, Sr, Ba, TI, Bi, Ce, Cs, Ho, Ta, Tb, U, Y), ICP-MS INT Rh (Analytika Ltd., Czech Republic), Analpure ultra H2O2 and 67% Analpure ultra HNO3 were purchased from Analytika (Prague, Czech Republic). Helium and argon were obtained from Linde Gas (Zlín, Czech Republic), and ultrapure water was supplied by Purelab Classic Elga water system (Labwater/VWS Ltd., London, UK).
2.2. ICP-MS Analysis
2.2.1. Sample Preparation
High purity 18.2 MΩcm water was obtained from Purelab Classic Elga system. Five millilitres of 67% HNO3 and 1 mL of H2O2 were added to each sample, resulting in sample weights of 1.0 ± 0.0001 g. Then they were decomposed by a microwave system, Milestone Ethos One (Sorisole, Italy), set to the following parameters: 500 W for 10 min, 1500 W for 15 min and finally, 500 W for 15 min. Two sets of calibration standard series were prepared to be matched with the expected concentration ranges in the samples: a high standard series (23 elements) (9Be, 66Zn, 63Cu, 60Ni, 27Al, 71Ga, 24Mg, 59Co, 7Li, 45Sc, 107Ag, 55Mn, 88Sr, 137Ba, 205Tl, 209Bi, 140Ce, 133Cs, 165Ho, 181Ta, 159Tb, 238U and 89Y) at concentrations of 3–35 µg/l and a low standard series (13 elements) (75As, 44Ca, 111Cd, 52Cr, 57Fe, 202Hg, 39K, 31P, 23Na, 208Pb, 77Se, 118Sn and 48Ti) with concentrations between 0.5 and 1.0 µg/L. Rhodium 103Rh, at a concentration of 100 µg/L, was used as an internal standard. Statistical evaluation was performed by certified reference material analysis (CRM) of green algae Metranal®8 (Analytica Ltd., Jílové, Czech Republic) producing values in mg/kg for As (41 ± 3), Ca (1380 ± 80), Cd (0.023 ± 0.004), Co. (18.0 ± 1.6), Cu (34,0 ± 1.6), Fe (290 ± 20), Hg (0.017 ± 0.010), Mg (1580 ± 120), Mn (43.0 ± 3.4), Ni (0.8 ± 0,1), Pb (0.21 ± 0.01) and Zn (38 ± 3).
2.2.2. ICP-MS Instrumentation
Analyses were performed by a quadrupole-based Thermo Scientific iCAP Qc inductively coupled plasma-mass spectrometer (ICP-MS) (Thermo Scientific, MA, USA). Furthermore, a collision cell (QCell) containing helium was applied to remove undesirable molecule ions by distinguishing their kinetic energy (CCT, collision cell technology; KED, kinetic energy discrimination mode). Specific working parameters were set as follows: 1550 W power, sampling depth of 5-mm, cool gas flow rate of 14.0 L/min, auxiliary gas flow rate of 0.8 L/min, nebulizer gas flow rate of 1.015 L/min, He flow rate of 4.1 mL/min, nebulizer pump speed of 40.00 rpm and chamber temperature of 2.7 °C. Samples were analysed five times.
2.3. Evaluation of Minerals Contribution to the RDA, AI, PTWI and PTMI Values
Dietary intake levels for nutrients from teff were established and compared with the RDA or AI (if the RDA had not been set) as recommended by the IOM (Institute of Medicine) [7
]. Intake levels of toxic elements were also estimated and compared with the PTWI or PTMI (if the PTWI had not been established) recommendations [11
]. Since there is no recommendation for the daily intake of teff grains, a portion size of teff was set to 100 g. Intake levels were determined for both females and males aged between 31 and 50, for males weighing 80 kg and females weighing 65 kg.
2.4. Statistical Analysis
All analyses were repeated 5 times (n = 5). The results are reported as the mean ± standard deviation (SD) in fresh weight and were statistically evaluated by one-way analysis of variance (ANOVA). Subsequently, the Scheffe test was applied to identify differences between all possible pairs of samples (multiple comparisons). The level of significance was set to 0.05.
This study provided data on the minerals in white and brown teff grains that may be suitable as markers of essential, trace and risk elements. It also discussed nutritional dietary intakes and compared the amount of trace elements in teff with other cereal species.
Teff grains are rich in manganese, copper, phosphorus, iron, manganese, calcium and zinc. Their daily intakes have been calculated by applying the RDAs or AIs. It should be highlighted that teff originating in the USA contained substantial amounts of zinc. An arsenic concentration higher than the average arsenic content in cereals consumed in the EU was recorded in brown teff from Bolivia harvested in 2017. The contribution of teff to the PTWIs or PTMIs for metals was within the limits set by the FAO/WHO. Therefore, average teff consumption does not pose a health risk.
The interest in producing teff outside Ethiopia and providing it to food markets will continue to grow. As this study has shown, nutrient-dense teff grains may be considered to be a valuable source of minerals and other substances with desirable health benefits. Teff should be included into a common diet as it can improve the health of the general population.