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Independent variables and their levels used for Box-Behnken design (BBD).
| Independent Variables | Coded Levels of Variables | ||
|---|---|---|---|
| −1 | 0 | 1 | |
| Extraction time (X1) (min) | 30 | 40 | 50 |
| Ultrasonic temperature (X2) (°C) | 60 | 70 | 80 |
| Ultrasonic power (X3) (W) | 180 | 220 | 260 |
