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Levels of independent variables used in the center composite design (CCD)
| Independent variables | Levels | ||
|---|---|---|---|
| Low (−1) |
Centre (0) |
High (+1) |
|
| SPI (% w/v) | 3 | 4 | 5 |
| HPMC (% w/v) | 0.2 | 0.3 | 0.4 |
| Olive oil (% v/v) | 0.8 | 0.9 | 1.0 |
| Potassium sorbate (% w/v) | 0.1 | 0.2 | 0.3 |
