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Experimental values and coded levels of the independent variables used for the 30-full factorial design
| xi | X 1 (%) | X 2 (min) | X 3 (°C) | X 4 |
| −1 | 40 | 30 | 40 | 1 |
| 0 | 60 | 40 | 50 | 2 |
| 1 | 80 | 50 | 60 | 3 |
xi: coded variable level; X 1: ethanol concentration; X 2: extraction time; X 3: extraction temperature; X 4: number of extraction cycles
