Microwave-Ultrasonic Extraction of Proanthocyanidins from Nitraria and Its Antioxidant Analysis

The single-factor combined response surface method was used to optimize the microwave-ultrasonic extraction of Nitraria tangutorum proanthocyanidins, and their antioxidant activity was evaluated by assessing ABTS and DPPH free radical scavenging capacity and total reduction ability. The results showed that the liquid–material ratio, ethanol concentration, microwave time and ultrasonic temperature had significant effects on the extraction rate of proanthocyanidins. The optimal extraction conditions were as follows: ethanol concentration of 65%, liquid-material ratio of 14.5 mL/g, microwave time of 2 min, and ultrasonic temperature of 50 ℃. The average extraction rate of proanthocyanidins from Nitraria tangutorum was (17.289±0.402) mg/g, with only a 2.4% difference from the theoretical prediction, indicating that the optimal extraction conditions optimized by the model were stable and reliable and had practical application value. The purity of the extract after purification with macroporous resin reached 81.4%. The results of in vitro antioxidant experiments showed that the proanthocyanidins of Nitraria tangutorum had suitable ABTS (IC₅₀=0.261 mg/mL) and DPPH (IC₅₀=0.159 mg/mL) free radical strong scavenging capacity, it also had a certain ability to scavenging hydroxyl radicals (IC₅₀=0.712 mg/mL), with good reduction ability. Therefore, microwave-ultrasonic combine can improve the extraction efficiency significantly, and Nitraria tangutorum proanthocyanidins has strong anti-oxidative activity in vitro. It provides a scientific reference for the comprehensive utilization of Nitraria.