Once the significant factors were i

Once the significant factors were identified in the Plackett–Burman design,
a central composite design was used to optimize their levels. The design matrix
was a 24 full factor design combined with six central points, and eight axial
points where one variable was set at an extreme level while other variables were
set at their central point level (Table 3). The coded and real values of each
parameter are shown in Table 4. Based on experimental results obtained in
Table 3, the responses (cell dry weight and DHA yield) were correlated as