Table 1 Independent variables and their levels test in the Plackett–Burman experiment
Independent variable | Component code | Low level (− 1) | High level (+ 1) |
|---|---|---|---|
Oil concentration | X1 | 0.5% | 1.0% |
Glucose | X2 | 0.5% | 1.0% |
(NH4)2So4 | X3 | 0.5% | 1.0% |
NH4Cl | X4 | 0.5% | 1.0% |
(NH4)H2Po4 | X5 | 0.5% | 1.0% |
yeast extract | X6 | 0.1% | 0.5% |
KH2Po4 | X7 | 0.1% | 0.5% |
K2HPo4 | X8 | 0.1% | 0.5% |
Inoculum size | X9 | 1.0% | 3.0% |
pH | X10 | 5.0 | 7.0 |
Culture volume | X11 | 30Â ml | 50Â ml |