VOLUME 71 : 2023

We have successfully applied in this work the response surface methodology (RSM) involving central composite planes (CCD) in order to study the effect of the temperature of incubation (x1 ), pH (x2 ) and Inoculum size (x3 ) on lactic acid production by the Lactococcus lactis DBH10 strain. After statistical analysis, the quadratic terms of the variable (x1 2 , x2 2 , x3 2 ) as well as those of the variables (x2 , x3 ) in linear terms and their interactions (x1 x2 ; x1 x3 ) were found to have significant effects on the response of interest. The analysis of the second order polynomial regression model obtained by multiple regression analysis, allowed us to reach a maximum lactic acid concentration of 486 ± 2.4 °D. The mathematical relationship of lactic acid production by Lactococcus lactis DBH10 strain related to the three significant independent variables was performed by a satisfactory fitting model. The predicted values were found to be in good agreement with the experimental values, displaying a coefficient of determination of R2 = 0.989, demonstrating good significance of the proposed model. The adjustment of the levels of the factors predicted by the model resulted in a maximum lactic acid concentration, when the optimal combination of inculum size, temperature, and pH, are respectively at 2.8% (v/v), 21.5 °C and 4.8. The Validation of the predicted model was carried out by performing three more experiments at the optimal levels of these variables, thus confirming its robustness.