Table 5.

Experimental design and results of the central composite design (CCD) for the recovery of elastase (Y)

No.	Coded level		Real values		Y (%)
	x1	x2	X1	X2
16	−1	−1	21.2	9.8	71.2
17	1	−1	25.2	9.8	76.8
18	−1	1	21.2	13.8	72.9
19	1	1	25.2	13.8	69.8
20	−1.41421	0	20.4	11.8	76.5
21	1.41421	0	26.0	11.8	68.8
22	0	−1.41421	23.2	9.0	67.4
23	0	1.41421	23.2	14.6	60.0
24	0	0	23.2	11.8	89.8
25	0	0	23.2	11.8	87.6
26	0	0	23.2	11.8	90.6
27	0	0	23.2	11.8	88.9
28	0	0	23.2	11.8	90.0

X ₁: Concentration % (w/w) of PEG 2 000; X ₂: Concentration % (w/w) of KH₂PO₄-K₂HPO₄; Y: Recovery of elastase (%); x ₁=(X ₁−23.2)/2.0; x ₂=(X ₂−11.8)/2.0. The experiments were conducted in triplicate, with Y being the average value