From Oilseed Waste to High-Value Bioactives: Deep Eutectic Solvents as Sustainable Refining Media

The global oil-processing industry generates substantial quantities of by-products and secondary streams, including oilseed cakes, pomaces, hulls, and wastewaters, which remain largely underutilized despite being rich sources of high-value bioactive compounds. The development of sustainable strategies for the valorization of these residues is increasingly recognized as a key component of circular bioeconomy and biorefinery frameworks. In this context, deep eutectic solvents (DESs) have attracted considerable attention as a new generation of designer solvents owing to their tunable physicochemical properties, low vapor pressure, ease of synthesis, and potential environmental compatibility. This review critically discusses the current state of knowledge regarding the application of DESs in the processing and valorization of oil industry by-products. Particular emphasis is placed on the relationship between DES composition, physicochemical characteristics, and extraction performance. Recent advances in the recovery of phenolic compounds, proteins, saccharides, and tocopherols from oilseed-derived residues are comprehensively examined, including the integration of DESs with intensified extraction techniques such as microwave-, ultrasound-, and ohmic-assisted extraction. Furthermore, the role of DESs in oil purification processes and the treatment of technological waste stream is evaluated. Emerging evidence indicates that DES-based systems not only enhance extraction efficiency and selectivity but may also improve the stability, bioaccessibility, and purity of the recovered compounds. Finally, the opportunities and challenges associated with the implementation of DES-based technologies within integrated biorefinery schemes are discussed, including solvent recovery, product scalability, sensory acceptability, and regulatory considerations. The available literature demonstrates that DESs constitute a versatile platform for the sustainable valorization of oil-processing residues, supporting the transition from conventional waste management approaches toward resource-efficient and circular production systems.