Valorization of sesame (Sesamum indicum L.) seed coats: Optimization of polyphenols’ extraction using Ired-Irrad® and assessment of their biological activities

Sesame (Sesamum indicum L.) seed coat (SSC) is a by-product generated during the production of sesame paste, known as tahini. Research has demonstrated that this by-product is abundant in valuable nutritional compounds. Various extraction methods are employed to enhance the value of industrial waste by recovering its bioactive compounds. The study aims to optimize the extraction of polyphenols utilizing an infrared technique Ired-Irrad® (IR), in comparison to the water bath (WB) extraction. To optimize the extraction of polyphenols from SSC using both the IR and WB extraction methods, the study utilized Response Surface Methodology (RSM). Under optimal conditions, IR extraction resulted in an improved polyphenol yield, which was 20% higher than that obtained using WB extraction. Similarly, the antiradical activity, quantified as mg of Trolox equivalent per milliliter, increased from 0.58 mg TE/mL in the WB extract to 0.68 mg TE/mL in the IR extract. The phytochemical profile of the IR and WB extracts was examined through High-Performance Liquid Chromatography (HPLC). The major polyphenols identified in both extracts were the flavonoids rutin (3.87 mg/L in IR, 1.72 mg/L in WB) and catechin (3.05 mg/L in IR, 1.32 mg/L in WB). The IR extract revealed the highest yield of polyphenols among the majority of compounds, compared to WB. The lyophilized SSC extracts obtained through both the IR and WB methods demonstrated the most effective antibacterial activity against Listeria monocytogenes, with a minimal bactericidal concentration (MBC) value exceeding 100 mg/mL. However, minor antibacterial effects were detected against the Gram-negative strains, Salmonella Typhimurium, and Escherichia coli O157:H7, for extracts obtained with both the IR and WB methods.