Application of emerging technologies for extraction of pigments using green solvents: case of deep eutectic solvents combined with ultrasound-assisted extraction technique

Pigments/colorants including betalains, anthocyanins, carotenoids, and curcuminoids are widely used in food, pharmaceutical, and cosmetic sectors. The increasing interest in natural pigments is related to their biological properties and safety. Deep eutectic solvents (DES) emerged as sustainable and promising solvents for the extraction of bioactive compounds. The application of ultrasound-assisted extraction (UAE) presents many advantages for the recovery of pigments compared to conventional extraction techniques. This review examines the emerged combination of DES and UAE (DES-UAE) as performant recovery systems of pigments. The factors affecting the DES-UAE system, efficiency of DES-UAE for the recovery pigments such as anthocyanins, betalains, carotenoids, and curcuminoids, as well as their stability and bioavailability were discussed. It resulted that the DESs, combined with ultrasound-assisted extraction (DES-UAE) as an extraction system of pigments, showed higher performance compared to the conventional methods such as maceration, percolation, stirring-assisted extraction, and soxhlet extraction. Factors such as DES composition, solvent-to-sample ratio, extraction duration, temperature, pH, ultrasound frequency, and power greatly influence the performance of DES-UAE. The optimum temperature, time, pH, ultrasound frequency, and power for the maximum recovery of the pigments are 20–90 °C, 5–70 min, pH 1–3, 18–80 kHz, and 60–750 W, respectively. Moreover, the pigment-rich extracts obtained with DES-UAE showed strong thermal stability and high bioavailability of pigments.