Ultrasound-Assisted Extraction of Anthocyanins from Aronia melanocarpa with Acidic Natural Deep Eutectic Solvents and Its Stability and Antioxidant Activity

A green and efficient ultrasonic-assisted acidic natural deep eutectic solvents for the extraction of anthocyanins from Aronia Melanocarpa was developed. The extraction conditions were optimized by the artificial neural networks and genetic algorithms, and the stability and antioxidant activity of anthocyanins extracts were investigated. A series of acidic natural deep eutectic solvents were prepared using betaine and organic acids as hydrogen bond acceptor and hydrogen bond donor respectively. Their physical and chemical properties such as density, viscosity, pH value were measured. The structure and formation mechanism of natural deep eutectic solvents were studied by infrared spectroscopy. The optimal extraction conditions were optimized by artificial neural network combined with genetic algorithm. The photostability, thermal stability and antioxidant activity of anthocyanins extract were evaluated. The experimental results showed that the natural deep eutectic solvents formed by the hydrogen bond interaction between betaine and lactic acid had the characteristics of density as low as 1.19, viscosity as low as 24.75 mPa·s and pH as 2.89. The optimal extraction conditions were as follows: betaine and lactic acid were used to prepare natural deep eutectic solvents, molar ratio was 1:3, water content was 32%, ultrasonic power was 124 W, ultrasonic time was 24 min and initial ultrasonic temperature was 32 ℃. Under this condition, the anthocyanins extraction yield reached 23.62 mg/g. Compared with traditional solvents and other methods, the method is green, efficient and simple to operate. The results of stability and antioxidant experiments showed that light can accelerate the degradation of anthocyanins in the extract. When the temperature was higher than 50 ℃, the thermal degradation of anthocyanins accelerated with the first-order kinetic degradation constant k>0.0234. When the mass concentration was 200 μg/mL, the DPPH free radical scavenging rate and total antioxidant capacity of anthocyanins extracts were 62.30% and 6.39 mmol/L FeSO₄·7H₂O equivalent, and at a mass concentration of 30 μg/mL, the ABTS⁺ free radical scavenging rate of anthocyanins extracts was 85.14%. The antioxidant activity of anthocyanins extracts was significantly (P<0.05) higher than that of V_C, and was proportional to the concentration. Therefore, the ultrasonic-assisted acidic natural deep eutectic solvents method can effectively improve the extraction yield of anthocyanins from Aronia Melanocarpa, and provide a scientific basis for the development and utilization of Aronia Melanocarpa resources.