Table 1.
Experimental design of response surface methodology with factors and their levels.
| Independent factors | Units | Levels |
||
|---|---|---|---|---|
| Low (−1) | Medium (0) | High (1) | ||
| X1: Ethanol concentration | % | 70 | 80 | 90 |
| X2: Extraction time | h | 2 | 4 | 6 |
| X3: Solid-to-liquid ratio | g/v | 1:15 | 1:18 | 1:21 |