Effect of starting xylose concentration on the microaerobic metabolism of Debaryomyces hansenii: the use of carbon material balances.

Xylitol production by Debaryomyces hansenii NRRL Y-7426 was performed on synthetic medium varying the initial xylose concentration between 50 and 300 g/L. The experimental results of these tests were used to investigate the effect of substrate level on xylose consumption by this yeast. Satisfactory values of product yield on substrate (0.74-0.83 g/g) as well as volumetric productivity (0.481-0.694 g/L x h) were obtained over a wide range of xylose levels (90-200 g/L), while a worsening of kinetic parameters took place at higher concentration, likely due to a substrate inhibition phenomenon. The metabolic behavior of D. hansenii was studied, under these conditions, through a carbon material balance to estimate the fractions of xylose consumed by the cell for different activities (xylitol production, biomass growth, and respiration) during the lag, exponential, and stationary phases.