Using response-surface methodology to evaluate xylitol production by Candida guilliermondii by fed-batch process with exponential feeding rate

Effect of an exponential feeding regime on the production of Rhodotorula araucariae epoxide hydrolase in Yarrowia lipolytica

AIMS

To evaluate the effect of and exponential feeding regime on the production of epoxide hydrolase (EH) enzyme in recombinant Yarrowia lipolytica in comparison to a constant feed strategy.

METHODS AND RESULTS

An exponential feed model was developed and fermentations were fed at six different exponential rates. A twofold increase in EH productivity and a 15% increase in volumetric EH activity was obtained by applying exponential glucose feed rates in fed-batch cultivation. These responses were modelled to obtain a theoretical optimum feed rate that was validated in duplicate fermentations. The model optimum of 0.06 h(-1) resulted in a volumetric EH activity of c. 5500 U l(-1) h(-1) and a maximum activity of 206,000 U l(-1). This correlated well with model predictions, with a variance of <10%.

CONCLUSIONS

The use of an exponential feed strategy at a rate of 0.06 h(-1) yielded best results for all key responses which show a clear improvement over a constant feed strategy.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study was the first evaluation of an exponential feed strategy on recombinant Y. lipolytica for the production of EH enzyme. The results suggest a strategy for the commercial production of a valuable pharmaceutical enzyme.

Metabolic behavior of immobilized Candida guilliermondii cells during batch xylitol production from sugarcane bagasse acid hydrolyzate

Candida guilliermondii cells, immobilized in Ca-alginate beads, were used for batch xylitol production from concentrated sugarcane bagasse hydrolyzate. Maximum xylitol concentration (20.6 g/L), volumetric productivity (0.43 g/L. h), and yield (0.47 g/g) obtained after 48 h of fermentation were higher than similar immobilized-cell systems but lower than free-cell cultivation systems. Substrates, products, and biomass concentrations were used in material balances to study the ways in which the different carbon sources were utilized by the yeast cells under microaerobic conditions. The fraction of xylose consumed to produce xylitol reached a maximum value (0.70) after glucose and oxygen depletion while alternative metabolic routes were favored by sub-optimal conditions.