**4. Conclusions**

Microbial fermentation is complex and it is quite difficult to understand its complete details process. The central composite design (CCD) proposed in this study seems pertinent to describe the optimum biomass production of *S. cerevisiae*. A second order polynomial model was developed to evaluate the quantitative effects of temperature, pH and reducing sugar concentration in order to discover the optimum conditions for the biomass production from date extract. According to the experimental results, a maximum biomass concentration of 40 g/L was obtained at the optimum condition of temperature (32.9 ◦C), pH (5.35) and total reducing sugars (70.93 g/L).

In addition, among three unstructured kinetic models, both Monod and Verhulst models represent the experimental data of biomass production kinetics; nevertheless, the Verhulst model was the most suitable model to signify the baker's yeast production on date extract medium.

**Acknowledgments:** This work was financially supported by University Frères Mentouri Constantine 1. The authors are very grateful to the students; MALKI R. and LEKIKOT Z. (UMC-1, Algeria) for the collaboration and assistance to carry out this study.

**Author Contributions:** M.K. performed the experiments, wrote the paper; N.O. and A.B. helped in the statistical analysis and modeling; A.A.K and S.B. helped in interpretation and analysis of data, C.R. revised English; N.K.C. supervised the activities, contributed laboratory, reagents and materials.

**Conflicts of Interest:** The authors declare no conflict of interest.
