Optimization of Extraction Process of Anthocyanins from Purple-fleshed Potatoes and Its Stability and Antioxidant Activity

The natural deep eutectic solvent (DES) was prepared by using betaine as hydrogen bond acceptor and organic acid, sugar group and alcohol group as hydrogen bond donor. Based on microwave-assisted extraction method, the extraction process of purple-fleshed potatoes anthocyanins (PPA) was optimized by single factor experiment combined with response surface analysis. The effects of microwave time, microwave power, solvent water content and solvent molar ratio on the extraction content of PPA were investigated. Moreover, the stability of PPA under different temperature and light conditions, and the free radical scavenging rates of DPPH, ABTS⁺ and OH were compared with conventional solvents to determine the antioxidant capacity in vitro. The results showed that the acidic deep eutectic solvent with betaine and citric acid (molar ratio of 1:2.1) and a water content of 28.6%, under the conditions of microwave power of 800 W and microwave time of 28 s, the extraction content of PPA could reach 228.658±1.241 mg/100 g, which was 56.92% higher than that of the conventional extraction process. In addition, the stability of PPA obtained by DES was significantly improved under different light and temperature conditions. The sunlight had the biggest effect on the PPA. The results showed that the preservation rate of PPA could reach more than 90% in the case of light avoidance, while the preservation rate of conventional solvent extraction was only 82.78%. Moreover, the content of anthocyanins would decrease continuously with the increase of temperature, and the preservation rate of both decreased significantly. Antioxidant capacity results demonstrated that the antioxidant capacity of PPA obtained from DES was stronger, and the values of IC₅₀ for different radical scavenging capacity were less than the conventional solvent extraction. The IC₅₀ values of DPPH radical scavenging capacity ranged from 45.95 μg/mL to 41.54 μg/mL, ABTS⁺ radical scavenging capacity IC₅₀ values from 17.81 μg/mL to 11.30 μg/mL, OH radical scavenging capacity IC₅₀ values from 162.00 μg/mL to 22.44 μg/mL. Therefore, the content, stability and antioxidant activity of PPA are closely related to the extraction solvent, and our extraction process provides a new idea for the utilization and development of purple-fleshed potatoes anthocyanins.