Optimization of a synthetic medium for Candida bombicola growth using factorial design of experiments

Abstract

The yeast Candida bombicola produces a mixture of sophorolipids when it grows on glucose and/or oil substrates. Sophorolipids show surfactant properties that can be used in several industries such as pharmaceutical, cosmetic, etc. Maximum sophorolipid production has been achieved using a resting cells process. A good knowledge of growth conditions and medium formulation are necessary to obtain enough biomass in the sophorolipid production process. Two facts permit the study of yeast growth and sophorolipid production separately. These compounds are nongrowth-associated products. Two carbon sources for the sophorolipid synthesis are necessary. In this work, an optimization of a synthetic medium for C. bombicola growth has been achieved by factorial design and analysis of experiments. First, a design using four factors (glucose, nitrogen, phosphorus, and magnesium) at two levels was studied. Glucose showed different behaviors at these two levels, making it difficult to determine the influence of other nutrients. It was necessary to separately study the influence of glucose concentration using limiting nutrient experiments. Once the optimum level of glucose was determined, the quantitative composition of the synthetic medium was fixed according to the literature. A new design was made using three factors (N, P, Mg) and three levels which made it possible to observe curvature effects in the results of the analysis. It was found that magnesium had no significant influence on growth while nitrogen and phosphorus gave optimum values. Finally, the medium proposed in the literature and the optimal medium found in this work have been compared for C. bombicola growth on both orbital shakers and stirrer and sparged tank bioreactors.