Table 6.

Statistical analysis of Plackett–Burman design showing coefficient values, t and p values for each variable on rhamnolipid production (g/l)

Variables	Coefficient	t statistics	p value	Confidence level (%)
Intercept	2.682	–	–	(1−p value) × 100
Culture volume (ml)	0.102	0.640	0.567	43.3
Culture pH	−0.458	−2.875	0.064	93.6
Aeration (rpm)	0.428	2.687	0.075	92.5
Carbon source (%)	0.848	5.324	0.013	98.7
Urea (%)	0.998	6.266	0.008	99.2
(NH4)2SO4	0.458	2.875	0.064	93.6
KH2PO4	0.622	3.905	0.030	97
Na2HPO4	−0.192	−1.205	0.314	68.6
MgSO4·7 H2O	0.072	0.452	0.682	31.8
CaCl2·2H2O	0.418	2.624	0.079	92.1
FeSO4·7H2O	−0.638	−4.005	0.028	97.2
CuSO4·7H2O	−0.138	−0.866	0.450	55
MnSO4·.5H2O	0.402	2.524	0.086	91.4
H3BO3 (M)	0.182	1.143	0.336	66.4
ZnSO4·7H2O (M)	−0.122	−0.766	0.499	50.1
MnO3 (M)	−0.492	−3.089	0.054	94.6