Fig. 5

Three-dimensional (3D) response surface plots: effects of extraction time (X1) and extraction power (X2) (a), extraction time (X1) and ethanol concentration (X3) (b), extraction time (X1) and solid–liquid ratio (X4) (c), extraction power (X2) and ethanol concentration (X3) (d), extraction power (X2) and solid–liquid ratio (X4) (e), and ethanol concentration (X3) and solid–liquid ratio (X4) (f).