Optimization of ultrasonic-assisted extraction of flavonoids from Lactuca indica L. cv. Mengzao and their antioxidant properties oleh Junfeng Hao, Zhijun Wang, Yushan Jia, Lin Sun, Zhihui Fu, Muqier Zhao, Yuyu Li, Ning Yuan, Baiming Cong, Lixing Zhao, Gentu Ge