Table 3.

Variables studied (encoded values) and respective response in terms of Y_P/S in the 2^8-4 Statistical Fractional Factorial Design

Run	Glycerol	NaNO3	NaCl	MgSO4	FeCl3	CaCl2	Yeast Extract	Trace Elements	YP/S mg/g
1	-	-	-	-	-	-	-	-	9,7
2	+	-	-	-	-	+	+	+	11,5
3	-	+	-	-	+	-	+	+	11,1
4	+	+	-	-	+	+	-	-	5,1
5	-	-	+	-	+	+	+	-	19,0
6	+	-	+	-	+	-	-	+	9,0
7	-	+	+	-	-	+	-	+	8,5
8	+	+	+	-	-	-	+	-	4,3
9	-	-	-	+	+	+	-	+	5,3
10	+	-	-	+	+	-	+	-	3,9
11	-	+	-	+	-	+	+	-	5,1
12	+	+	-	+	-	-	-	+	4,3
13	-	-	+	+	-	-	+	+	14,5
14	+	-	+	+	-	+	-	-	0,8
15	-	+	+	+	+	-	-	-	5,3
16	+	+	+	+	+	+	+	+	2,1
Center point	0	0	0	0	0	0	0	0	4,6 ±1,3

Encoded values (-), (0) and (+) represents respectively, low level, center point (intermediate level) and high level for each variable studied. For glycerol, (-), (0) and (+) correspond to 10.0 , 20.0 and 30.0 g/L; for NaNO₃ correspond to 1.0, 3.4 and 5.8 g/L; for NaCl correspond to 0.0, 1.0 and 2.0 g/L; for MgSO₄ correspond to 0.0, 0.1 and 0.2 g/L; for FeCl₃ correspond to 0.00, 0.01 and 0.02 g/L; for CaCl₂ correspond to 0.00, 0.02 and 0.04 g/L; for yeast extract correspond to 0.0, 0.1 and 0.2 g/L; and for trace elements (aqueous solution) correspond to 0.0, 0.5 and 1.0 mL/L, respectively.