Table 1 Response surface methodology experimental design showing the code and levels of the two tested variables
|  | Levels | α = 0.5 | ||||
|---|---|---|---|---|---|---|
Factors | Code | − 1 | 0 | 1 | − α | +α |
Concentration/percentage of added extract %(vol/vol) | A | 0.0375 | 0.075 | 0.1125 | 0 | 0.15 |
Time of addition | B | 1.5 | 3 | 4.5 | 0 | 6 |