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Range of extraction condition variables at different levels for the central composite design.
| Independent Variables | Parameter | Coded Levels | ||||
|---|---|---|---|---|---|---|
| −1.68 | −1 | 0 | 1 | 1.68 | ||
| Extraction time (min) | X1 | 9.5 | 30 | 60 | 90 | 110.5 |
| Solvent to solid ratio (mL/g) | X2 | 13.2 | 20 | 30 | 40 | 46.8 |
| Temperature (°C) | X3 | 24.8 | 35 | 50 | 65 | 75.2 |
