Table 2. Box-Behnken design and response values observed.

Run	Extraction variable				Response value (Extraction yield, %)
	X1	X2	X3	X4
1	−1 (20)	0 (60)	0 (60)	1 (40)	9.296
2	0 (30)	0 (60)	−1 (40)	1 (40)	8.199
3	0 (30)	0 (60)	0 (60)	0 (30)	8.921
4	−1 (20)	1 (70)	0 (60)	0 (30)	8.966
5	−1 (20)	0 (60)	1 (80)	0 (30)	8.268
6	0 (30)	0 (60)	1 (80)	−1 (20)	7.657
7	1 (40)	1 (70)	0 (60)	0 (30)	9.257
8	0 (30)	0 (60)	0 (60)	0 (30)	8.685
9	0 (30)	1 (70)	1 (80)	0 (30)	8.641
10	1 (40)	0 (60)	1 (80)	0 (30)	8.546
11	0 (30)	0 (60)	1 (80)	1 (40)	8.699
12	0 (30)	−1 (50)	0 (60)	1 (40)	8.962
13	0 (30)	0 (60)	0 (60)	0 (30)	8.990
14	−1 (20)	0 (60)	0 (60)	−1 (20)	8.615
15	−1 (20)	0 (60)	−1 (40)	0 (30)	7.963
16	0 (30)	1 (70)	0 (60)	1 (40)	9.095
17	1 (40)	0 (60)	0 (60)	1 (40)	9.074
18	1 (40)	0 (60)	0 (60)	−1 (20)	8.699
19	1 (40)	0 (60)	−1 (40)	0 (30)	7.824
20	0 (30)	−1 (50)	1 (80)	0 (30)	8.267
21	1 (40)	−1 (50)	0 (60)	0 (30)	8.661
22	0 (30)	1 (70)	−1 (40)	0 (30)	7.831
23	−1 (20)	−1 (50)	0 (60)	0 (30)	8.846
24	0 (30)	0 (60)	0 (60)	0 (30)	8.782
25	0 (30)	0 (60)	0 (60)	0 (30)	8.532
26	0 (30)	−1 (50)	0 (60)	−1 (20)	8.395
27	0 (30)	0 (60)	−1 (40)	−1 (20)	7.629
28	0 (30)	1 (70)	0 (60)	−1 (20)	8.463
29	0 (30)	−1 (50)	−1 (40)	0 (30)	7.781