Optimization of Ultrasound-Assisted Extraction of Total Flavonoids from Dendranthema indicum var. aromaticum by Response Surface Methodology

Table 1

Independent variables and their levels in central composite circumscribed (CCC) design.

Symbol	Independent variable	Factor level
		−1.68	−1	0	1	1.68
X1	Extraction time (min)	13	20	30	40	47
X2	Solid/liquid ratio (g/mL)	1 : 03	1 : 10	1 : 20	1 : 30	1 : 37
X3	Extraction temperature (°C)	33	40	50	60	67