Extraction of Anthocyanins from Black Bean Peel Based on Deep Eutectic Solvents and the Determination of Their Antioxidant Properties and Stability

To explore anthocyanins in black bean peel, the conditions of ultrasound-assisted deep eutectic solvents (DESs) were screened and optimized using the method of response surface optimization. After that, the purification of the anthocyanins was performed before investigating their antioxidant activity and stability. The results showed that the choline chloride–citric acid system was more suitable for the extraction of anthocyanins from black bean peel, and the maximum amount of 61.00 ± 2.73 mg C3GE/100 g DW anthocyanins was obtained with the following optimized conditions: extraction time, 40 min; ultrasonic power, 60 KHz; material–liquid ratio, 1:20 g/mL; and ultrasonic temperature, 50 °C. The purity of the anthocyanins increased to 193.62 mg C3GE/100 g after purification with AB-8 resin, which also significantly improved the ability to screen DPPH and ABTS radicals. The anthocyanins from black bean peel were sensitive to light, temperature, pH, and additives.