Use of deep eutectic solvents to increase yield and diversity of antioxidant capacity/activity determination methods

Deep eutectic solvents (DES) are gaining attention as a sustainable and efficient option for the solubilization and extraction of bioactive compounds with antioxidant properties found in foods. Furthermore, DES are considered excellent alternatives to organic solvents due to their low cost, potential biodegradability, negligible toxicity, and simpler manufacturing procedures. In the first part of the thesis, the total antioxidant capacity of cereal products consisting of buckwheat, wheat germ, barley, rye, oats and wheat was determined using the QUENCHER- CUPRAC and QUENCHER-ABTS methods in a ChCl-EG deep eutectic solvent. Using wheat germ from the cereal samples, parameters such as water content (%), stirring rate (rpm), and stirring time (min), which play an important role in increasing antioxidant capacity yield, were determined using response surface methodology. Optimal experimental conditions were determined using the Box-Behnken experimental design matrix. The results were determined based on the response variable TAC (mmol TE kg⁻¹) and compared with the original QUENCHER-CUPRAC and QUENCHER-ABTS methods used as reference methods. In the xxii second part of the thesis, microwave-assisted extraction (MDE) of various tomato products and dried carrot food samples was performed in the AcOH-TBP deep eutectic solvent and total antioxidant capacity was determined using the CUPRAC method. Using response surface methodology for the MDE procedure, parameters such as extraction temperature (°C), solvent volume (mL), and extraction time (min), which play a significant role in increasing extraction efficiency, were optimized using the Box-Behnken experimental design matrix. The CUPRAC method was used to measure the total antioxidant capacity of carotenoid-rich extracts prepared under optimal conditions. Furthermore, the results were compared with those obtained from the hexane-ethanol-acetone (2:1:1, v/v/v) mixture extraction process. The proposed DES method demonstrated that some lipophilic antioxidants, as well as hydrophilic antioxidants, could be partially extracted. The amounts of carotenoids and polyphenolic compounds in the extracts were measured using the HPLC-DAD system.