Optimization Technology of Ultrasonic Degradation of Polymeric Prodelphinidin by Response Surface Methodology and Its Antioxidant Activity

In this research, polymeric prodelphinidins (PPs) were extracted and prepared from bayberry leaves and characterized using HPLC-DAD-ESIMS. Then effects of ultrasonic time, temperature, power and duty cycle on PPs were analyzed using one single factor test. On the above bases, the response surface methodology with Box-Behnken design was employed to study the ultrasonic conditions. Furthermore, the antioxidant capacity of PPs were determined before and after ultrasonic treatment by DPPH· and ABTS·⁺ methods. The results showed that yield of PPs from bayberry leaves was 5.96% (dry weight) with an average degree of polymerization of 27.8 and with a main structural component of EGCG. Ultrasonic treatments with different conditions had different influence on PPs degradation. Factors of ultrasonic time, temperature, power and duty cycle had significant effects (P<0.05). The optimized ultrasonic conditions were as follows: Ultrasonic time 74 min, temperature 44 ℃, ultrasonic power 361 W, and duty cycle 67%. Under these conditions, the yield of oligomeric prodelphinidins was 17.31%. After sonication, PPs possessed more significant antioxidant capacity than before (P<0.01).