In Vitro Bioaccessibility and Speciation of Toxic and Nutritional Trace Elements in Brazil Nuts

Brazil nuts (<i>Bertholletia excelsa</i>), mainly from the Amazon, are notable for their exceptionally high selenium (Se) content and are widely consumed as a natural dietary supplement. They also contain potentially harmful elements, including barium (Ba), and exhibit an unusual capacity to accumulate radioactive radium (Ra). In this study, we quantified the concentrations of Se, Ba, strontium (Sr), lanthanum (La), europium (Eu), and the radionuclides ²²⁶Ra and ²²⁸Ra, and assessed their in vitro bioaccessibility-data largely unavailable for these elements to date. Se was highly bioaccessible (≈85%), whereas Ba and Ra, both chemo- and/or radiotoxic, exhibited low bioaccessibility (≈2% each). Nuclear magnetic resonance (NMR) spectroscopy revealed Se to occur predominantly as selenomethionine (SeMet), alongside phytate, amino acids, peptides, and other polar low-molecular-weight compounds. The influence of Brazil nut flour (BNF) on Eu(III) speciation in simulated gastrointestinal fluids, and the effect of chelating agents such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and the hydroxypyridinone 3,4,3-LI(1,2-HOPO) were investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Results indicate that the food matrix has only a minor impact on the decorporation efficacy of these chelators. These findings provide novel insights into the bioaccessibility and chemical speciation of nutritionally and toxicologically relevant elements in Brazil nuts.