Table 4.

Identification of significant variables for proteolytic enzymes production by A. niger I1 using Plackett-Burman design.

Variables	t-ratio	P value
Intercept	17.16	<0.0001
Temperature	−3.67	0.0032*
HGW	−1.88	0.0847
SP	0.75	0.4704
KH2PO4	3.84	0.0024*
MgSO4	−1.16	0.2698
NaCl	−1.18	0.2601
Initial pH	2.20	0.0478*
ZnCl2	−1.92	0.0787
Na2HPO4	0.44	0.6682
CaCl2	−1.36	0.2000
Inoculum's size	−0.03	0.9760

*Statistically significant at 95% of confidence level.