## 4 Discussion
Moreover, differences in the distribution of mineral nutrients between the pericarp and the seeds may occur not only due to the mechanical strength of this structure but also to its ability to confer chemical resistance against predators [31]. In a recent study carried out with samples collected in the state of Sao Paulo, Brazil, and analyzed by ICP-MS [10], a comprehensive analysis was performed, and results for 16 macro and micronutrients as well as contaminants were reported for the seeds. The results for macronutrients, such as calcium, magnesium, and potassium, are on the same order of magnitude (percentage range) but slightly higher than those obtained here, while results for phosphorus were not reported. The results for micronutrients, such as copper, iron and zinc (in order of ppm), are also presented here, with iron showing the greatest variability in measured values, and zinc and copper exhibiting little variability. Finally, our results are in better agreement with those from samples collected in a nearby region in the state of Para, which were analyzed using atomic absorption spectrometry [11]. This suggests that the differences found in nutritional content are likely due to the climatic and cultivation conditions of the plant. In summary, the WD-XRF standardless application used in this study can provide reliable results for the inorganic composition of plant material. It is fast and requires minimal sample preparation, and it is adequate for the purpose of evaluating the content of macro and micronutrients. However, it has limitations regarding the determination of the presence of heavy metals, such as mercury or lead. The limits of detection (LOD) for these metals are reported to be in the order of 10 ug g\({}^{-1}\) using a WD-XRF standardless application in the organic matrix [20]; however, international standards regarding the presence of toxic heavy metals in food are around 0.1-0.2 ug g\({}^{-1}\)[33]. In the present study, we did not detect those heavy metals in our samples. Using WD-XRF, we observed that sulfur is slightly more concentrated in the pericarp than in the seeds. From XANES spectra, we gathered information regarding the distribution of oxidation states of sulfur atoms in different samples. XANES spectra are very sensitive to the chemical environment around the selected atom. This method is shown to be suitable for performing sulfur chemical speciation in several materials including the following: coal, petroleum, and asphaltenes [26; 34; 35; 36; 37; 38]; soils and related samples [28; 39; 40; 41; 42; 43; 44; 45]; biological systems [46; 47; 48; 49]; plants [15; 16; 50]; and other materials [14; 24; 27; 51; 52; 53; 54; 55; 56]. In XANES, the chemical environment of an atom is probed by tuning the excitation energy and scanning the selected core electron binding energy. This method probes the excitation of core electrons for empty or partially filled molecular orbitals, providing information about the chemical binding of the selected atom in the molecule. In complex samples such as plants, the spectrum is a superposition of all the different oxidation states of the selected atom in the molecules. By applying data processing tools (Principal Component Analysis and Target Transformation [16]) and Linear Combination Fitting, it is possible not only to identify the oxidation states of sulfur in those molecules but also to determine the fraction of each oxidation state that computes to the sample spectrum. To achieve this, the normalized sample spectrum is modeled as a linear combination of the normalized spectra of model compounds, and the coefficients of each model represent the fraction of sulfur atoms in the sample that belong to the same sulfur chemical groups [50]. Therefore, in the XANES approach, it is important to have some knowledge of the samples in order to select the model compounds that provide a chemical meaning to the fitting, avoiding the problems related to the fact that similar sulfur functional groups may show differences in XANES spectra [53].