Table 1 Independent variables and their levels for central composite design. La Lactobacillus acidophilus, Lp Lactobacillus plantarum, St Streptococcus thermophilus
Independent variable | Code | Variable level (La–St) | Variable level (La–Lp) | ||||
|---|---|---|---|---|---|---|---|
−1 | 0 | +1 | −1 | 0 | +1 | ||
Incubation temperature (°C) | A | 37 | 40 | 43 | 34 | 37 | 40 |
Substrate concentration (%) | B | 4 | 5 | 6 | 4 | 5 | 6 |
Inoculum size (%) | C | 2 | 3 | 4 | 4 | 5 | 6 |
The initial medium pH | D | 4.5 | 5.5 | 6.5 | 5.5 | 6.5 | 7.5 |