Statistical optimization of lactic acid production by Lactococcus lactis strain, using the central composite experimental design

The individual and interactive effects of a total inoculums size (% v/v), fermentation temperature and skim milk dry matter added (% w/v) on the lactic acid production by Lactococcus lactis LCL strain were studied by quadratic response surface methodology. The central composite design (CCD) was employed to determine maximum lactic acid production at optimum values for process variables and a satisfactory fit model was realized. The mathematical relationship of the lactic acid production on the three significant independent variables can be approximated by a nonlinear polynomial model. Predicted values were found to be in a good agreement with experimental values (R2 of 96.7% and R2(adj) of 92.1% for response Y). The result of optimization predicted by the model has shown that the maximal result for lactic acid production revolved around 92°D at the optimal condition with 2% of inoculums size, temperature at 30°C and skim milk dry matter added at a central point of 2% (w/v). Key words: Central composite design, Lactococcus lactis, lactic acid production, inoculum size, temperature, skim milk dry matter.