The principles of ‘green chemistry’ are gaining importance in agri-food sector due to the need to reduce pollution from toxic chemicals, make industrial processes safer and more sustainable, and to offer ‘clean-labeled products’ required by the consumers. The application of natural deep eutectic solvents (NADES) – natural product-based green liquids is considered the promising alternative to conventional organic solvents. This review is intended to summarize and discuss recent advances related to physicochemical properties of NADES, their applications, compatibility with analytic techniques and toxicological profile, pointing out the challenges and necessary improvements for their wider utilization in agri-food sector. NADES allow extraction of wide range of food compounds and they are proven to be convenient for food-related applications. However, their potential for industrial scale-up utilization is not completely investigated. Examined NADES are readily biodegradable, but only preliminary studies on NADES toxicity which include limited number of NADES molecules are available. Apart from fundamental research dealing with NADES formation and the nature of the interactions and structure underpinning the liquid phase formation, the question of purity of NADES obtained by different synthetic methodologies need to be addressed in the future. Data on physicochemical properties of synthetized NADES are still needed as they are relevant for industrial applications.

The aim of the present research was to develop green and sustainable extraction procedure for β-carotene recovery from pumpkin. A series of hydrophobic natural deep eutectic solvents (NADESs) based onfatty acids were prepared to establish high extraction efficiency of β-carotene and to increase stability of extracted carotenoids from the pumpkin. To intensify extraction process, NADES composed of C8 and C10 fatty acids (3:1) was selected and coupled with ultrasound assisted extraction. Response surface methodology and artificial neural network model (ANN) model was adopted to analyze significance of extraction parameters demonstrating high prediction levels of the β-carotene yield, experimentally confirming the maximum β-carotene content of 151.41 µg/mL at the optimal process condition. Extracted carotenoids in the optimal NADES extract have shown high stability during the storing period of 180 days. A switchable-hydrophilicity eutectic solvent system has been introduced as a successful way to recover extracted carotenoids from the NADES solvent. It was capable of precipitating 90% of carotenoids present in the extract. The proposed procedure is simple, easily scalable and has minimal impact on operators and the environment.

Ultrasound-assisted extraction was used for extraction of bioactive compounds and for production of Allium ursinum liquid extract. The experiments were carried out according to tree level, four variables, face-centered cubic experimental design (FDC) combined with response surface methodology (RSM). Temperature (from 40 to 80 °C), ethanol concentration (from 30% to 70%), extraction time (from 40 to 80 min) and ultrasonic power (from 19.2 to 38.4 W/L) were investigated as independent variables in order to obtain the optimal conditions for extraction and to maximize the yield of total phenols (TP), flavonoids (TF) and antioxidant activity of obtained extracts. Experimental results were fitted to the second order polynomial model where multiple regression and analysis of variance were used to determine the fitness of the model and optimal condition for investigated responses. The predicted values of the TP (1.60 g GAE/100 g DW), TF (0.35 g CE/100 g DW), antioxidant activity, IC50 (0.71 mg/ml) and EY (38.1%) were determined at the optimal conditions for ultrasound assisted extraction: 80 °C temperature, 70% ethanol, 79.8 min and 20.06 W/L ultrasonic power. The predicted results matched well with the experimental results obtained using optimal extraction conditions which validated the RSM model with a good correlation.

Wild thyme (Thymus serpyllum L.) herbal dust has been recognized as a potential underutilized resource for the recovery of antioxidants. The aim of this paper was to optimize natural deep eutectic solvent (NADES) extraction of polyphenols to obtain improved antioxidant activity of extracts determined by selected in vitro assays (DPPH, FRAP, and ABTS). Twenty different NADES systems were investigated in the first step of the screening of the extraction solvent and l-proline (Pro)–glycerine (Gly) based solvents provided the best results. Preliminary experiments organized by 2⁵⁻¹ fractional factorial design narrowed down the number of extraction factors from five (temperature, extraction time, NADES type, water content and L/S ratio) to three and determined their experimental domain for the final step. A face-centered central composite design with temperature (40–55–70 °C), extraction time (60–120–180 min) and L/S ratio (10–20–30 g NADES/g sample) was applied for influence analysis and process optimization. Multi-response optimization suggested a temperature of 65 °C, time of extraction of 180 min and L/S ratio of 28 g NADES/g DW as optimal extraction parameters. Experimental validation confirmed good agreement between experimental and predicted results in the extract obtained at optimal conditions and the interactions in the most suitable NADES (N16; Pro–Gly–H₂O; 1:2:1) were confirmed by the ¹H-NMR.