Microwave-assisted extraction of valuable phenolics from sunflower pomace with natural deep eutectic solvents and food applications of the extracts

A green process, both in terms of solvent (natural deep eutectic solvents, NADES) and extraction method (microwave-assisted extraction, MAE) for the recovery of bioactive components from sunflower pomace (SFP, a by-product of oil extraction process), was designed to contribute to their sustainable valorization. For the extraction of valuable phenolics from sunflower pomace, nine potential NADES were prepared. Among them, choline chloride-urea-water (CC-U-W) at a molar ratio of 1:2:4 was selected for extraction, showing better yield and physicochemical properties. Operational parameters (extraction temperature, time, water ratio, and solvent-to-solid ratio) for MAE were optimized and modeled utilizing response surface methodology. Under optimal conditions, the antioxidant properties of SFP extract were evaluated by CUPRAC, ABTS, and DPPH methods. The total phenolic contents of extracts were evaluated by the Folin–Ciocalteu method. Phenolics were characterized by using the HPLC–PDA system. The results showed that SFP NADES extract had potential antioxidant activity which was higher than that of traditional solvents. In order to better evaluate SFP extract as a valuable food ingredient, SFP extracts at a ratio of 5, 10, and 20% added smoothie-like beverages with strawberries and yogurt were prepared. Fortification of beverages with NADES extract enhanced antioxidant efficiency, increasing total antioxidant capacity in a range of 12.4 to 68.6% and free radical scavenging capacity between 0.4 to 67.9% during both the initial and the in vitro gastrointestinal digestion stages. The addition of SFP NADES extract to food samples made a positive contribution in terms of the antioxidant activity of the final product. The results of this study revealed that sunflower by-products can be evaluated as a potential antioxidant source which is easily accessible, and the proposed extraction process has an important potential to recover bioactive compounds with high efficiency.