Background: Authentication of food and agricultural products is important to trace out the right product and ensure the customer’s preference and their health. Sesame (Sesamum indicum L.) is one of the most important crops used for food and medicine in Ethiopia and different varieties and cultivars are produced in different regions of the country. This study was undertaken to determine the total flavonoid content, total phenolic content, antioxidant activity, and fatty acids profile of black and white sesame seed varieties. Samples were obtained from three major sesame seed-producing districts of Ethiopia. Results: The total phenolic content (TPC), total flavonoid content (TFC), and the half-maximal inhibitory concentration (IC₅₀) were ranged from 2.95 to 6.95 mgGAE/g, 2.13–4.99 mgCE/g and 8.3–16.8 AAE/g of the sample, respectively. In general, white sesame seed samples showed the highest TPC, TFC, and antioxidant activity than the black variety. Location wise, samples collected from the Metema district were found to contain a relatively higher concentration of the phytochemicals. The white seed variety was characterized by significantly higher content of oil (53.2–58.2% by mass of the sample) than the back variety (47.6–51.4%).The oil content of the seeds was found to contain nine identifiable fatty acids (FAs). The total unsaturated fatty acids constituted more than 82% of the total FAs, while the saturated FAs were lower than 18% of the total FAs. Among the unsaturated FAs, linoleic acid (C18:2, omega-6 FAs) was the dominant FA (42.5–44.3%) followed by oleic acids (37.2–38.9%). On the other hand, palmitic acids (9.35–11.2%) and stearic acid (5.78–6.52%) were the dominant FAs among the saturated FAs. Conclusions: The studied samples had higher concentration of linoleic acid (omega-6 FA) than oleic acid, as opposed to other reported accessions of sesame seeds. Furthermore, white sesame seeds were richer in oil content than the black variety. The high concentration of unsaturated FAs, omega-6 FA, and phenolic compounds make sesame seeds nutritionally and medicinally important for the human diet. Unlike the fatty acids profiles, the level of phenolic compounds in sesame seeds was highly dependent on the geographical region and varietal type of the seeds.

Water contamination by organic dyes has become a reason for severe environmental pollution and has been threatening the aquatic ecosystem. In this study, kaolin-supported silver nanoparticle (Ag-NP) composites were synthesized by a facile two-step adsorption-reduction method through the reduction of silver ions adsorbed onto locally available, inexpensive, and easily pretreated kaolin surfaces by using sodium borohydride (NaBH₄) for the catalytic degradation of methylene blue (MB) dye in aqueous solution. The morphology, structure, surface area, and interaction of the synthesized materials were investigated by scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy, respectively. Characterization results showed the successful growth of Ag-NPs on the kaolin surface. To understand the catalytic degradation performance of the catalyst, batch experiments were carried out using MB dye as a model dye. The catalytic reduction tests confirmed the importance of Ag-NPs and the high catalytic activities of the synthesized Ag-NPs/kaolin composite toward MB dye reduction. The degradation results indicated that the increased Ag-NP content on the kaolin surface through repeating cycles could effectively enhance the removal of MB dye from an aqueous solution. The kinetic analysis of the MB dye degradation of the catalyst has fitted the pseudo-first-order kinetic model. More than 97% removal efficiency was still present after five reuse cycles, demonstrating exceptional stability and reusability of the composite. In conclusion, the Ag-NPs supported kaolin (Ag-NPs/kaolin) composite was found to be a promising catalyst for the excellent catalytic activity to reduce a model dye MB from the aqueous solution in the presence of NaBH₄ with catalytic efficiency higher than 97% and a reduction rate constant, k _red, higher than 0.86 min^-1.