Table 1 Independent variables with their respective coded values and levels used in the Box–Behnken design
Coded value | Independent variable | Level | ||
|---|---|---|---|---|
Low | Middle | Upper | ||
− 1 | 0 | + 1 | ||
X1 | Yeast extract (g L−1) | 6 | 8 | 10 |
X2 | Hydrolyzate (% v/v) | 50 | 75 | 100 |
X3 | Time (h) | 18 | 24 | 30 |
X4 | pH | 7.0 | 7.2 | 7.4 |