Table 2 Plackett-Burman design factors and levels
From: Optimization of fermentation conditions for surfactin production by B. subtilis YPS-32
Factor | Variable | Level | |
|---|---|---|---|
Low level (-1) | High level (+ 1) | ||
X1 | Molasses (g·L− 1) | 20 | 30 |
X2 | Glutamic acid (g·L− 1) | 10 | 15 |
X3 | Soybean meal (g·L− 1) | 3 | 4.5 |
X4 | KCl (g·L− 1) | 0.25 | 0.375 |
X5 | K2HPO4 (g·L− 1) | 0.5 | 0.75 |
X6 | MgSO4 (g·L− 1) | 0.25 | 0.375 |
X7 | Fe2(SO4)3 (mg·L− 1) | 1.2 | 2.25 |
X8 | Time (h) | 30 | 45 |
X9 | pH | 5 | 7.5 |
X10 | Temperature (℃) | 28 | 35 |
X11 | Inoculation size (%) | 2 | 3 |