Optimization of Syringa oblata Lindl. Flower for Extraction of Polyphenols by Ultrasound-Assisted Deep Eutectic Solvents and Analysis of Antioxidant Activity

To establish an environmentally friendly and efficient method for extracting polyphenols from Syringa oblata Lindl. flowers and study the antioxidant activity of its polyphenols, this study used ultrasound-assisted deep eutectic solvents (UADESs) to extract polyphenols from Syringa oblata Lindl. flowers. Firstly, the choline chloride-malice acid, at a molar ratio of 1:1.5, and on the basis of the results of single-factor experiments, the extraction temperature, ultrasonic time, solid-liquid ratio and ultrasonic power, were selected as the key factors for optimization, and the extraction amount of polyphenols was used as the response value, and the Box-Behnken response surface method was used to optimize, and the scavenging ability of Syringa oblata Lindl. polyphenols on DPPH radicals and hydroxyl radicals was studied. The results showed that the optimized extraction parameters were extraction temperature of 60 ℃, ultrasonic time of 60 min, solid-liquid ratio 1:30 g/mL and ultrasonic power of 300 W, the polyphenol content could reach 52.19±0.13 mg/g, significantly higher than that of traditional extraction (60% ethanol, methanol) (P<0.05). Then in vitro antioxidant experiments showed that when the concentration of Syringa oblata Lindl. polyphenols was 2.0 mg/mL, the scavenging rates of DPPH and hydroxyl radicals were 93.28% and 52.57% respectively. This study would provide a green and efficient way for extracting polyphenols from Syringa oblata Lindl. using ultrasonic-assisted deep eutectic solvents and provide a theoretical foundation for the efficient extraction and practical utilization of Syringa oblata Lindl. polyphenols.