Table 2.

Design matrix for the optimization of gelatin extraction procedure

Design points	Independent variable levels
	X1	X2	X3	X4
1	−2	0	0	0
2	+2	0	0	0
3	0	+2	0	0
4	0	−2	0	0
5	0	0	+2	0
6	0	0	+2	0
7	0	0	0	+2
8	0	0	0	+2
9	−1	−1	−1	0
10	+1	−1	−1	0
11	−1	+1	−1	0
12	+1	+1	−1	0
13	−1	−1	+1	0
14	+1	−1	+1	0
15	−1	+1	+1	0
16	+1	+1	+1	0
17	−1	−1	−1	+1
18	+1	−1	−1	+1
19	−1	+1	−1	+1
20	+2	+1	−1	+1
21	−1	−1	+1	+1
22	+1	−1	+1	+1
23	−1	+1	+1	+1
24	+1	+1	+1	+1
25	0	0	0	0
26	0	0	0	0
27	0	0	0	0

X₁ = Concentration of NaOH, X₂ = Soaking time (min.), X₃ = Extraction temp., X₄ = Extraction time (h).