Table 1. Codes and Actual Levels of the Independent Variables for the Design of the Experiment.

		code levels
independent variables	symbols	–2	–1	0	1	2
extraction temperature (°C)	T	40	45	50	55	60
extraction time (min)	t	30	60	90	120	150
solvent composition (%)	C	20	40	60	80	100
liquid–solid ratio	V	10	15	20	25	30