Maintenance and growth requirements in the metabolism of Debaryomyces hansenii performing xylose-to-xylitol bioconversion in corncob hemicellulose hydrolyzate.

In order to improve the biotechnological production of xylitol, the metabolism of Debaryomyces hansenii NRRL Y-7426 in corncob hemicellulose hydrolyzate has been investigated under different conditions, where either maintenance or growth requirements predominated. For this purpose, the experimental results of two sets of batch bioconversions carried out alternatively varying the starting xylose concentration in the hydrolyzate (65.6 < or = S(0) < or = 154.

Submerged citric acid fermentation on orange peel autohydrolysate.

The citrus-processing industry generates in the Mediterranean area huge amounts of orange peel as a byproduct from the industrial extraction of citrus juices. To reduce its environmental impact as well as to provide an extra profit, this residue was investigated in this study as an alternative substrate for the fermentative production of citric acid. Orange peel contained 16.

Influence of inhibitory compounds and minor sugars on xylitol production by Debaryomyces hansenii.

To obtain in-depth information on the overall metabolic behavior of the new good xylitol producer Debaryomyces hansenii UFV-170, batch bioconversions were carried out using semisynthetic media with compositions simulating those of typical acidic hemicellulose hydrolysates of sugarcane bagasse. For this purpose, we used media containing glucose (4.3-6.

Purification of xylitol obtained by fermentation of corncob hydrolysates.

Hydrolysates obtained by autohydrolysis-posthydrolysis of corncobs were detoxified with charcoal, concentrated, supplemented with nutrients, and fermented with Debaryomyces hansenii. After biomass removal, the fermented media contained 0.1137 kg of nonvolatile components (NVC)/kg of liquor, which corresponded mainly to xylitol (0.

Xylose metabolism in Debaryomyces hansenii UFV-170. Effect of the specific oxygen uptake rate.

The new yeast Debaryomyces hansenii UFV-170 was tested in this work in batch experiments under variable oxygenation conditions. To get additional information on its fermentative metabolism, a stoichiometric network was proposed and checked through a bioenergetic study performed using the experimental data of product and substrate concentrations. The yeast metabolism resulted to be practically inactive under strict oxygen-limited conditions (qO2 = 12.

Kinetics and bioenergetics of Spirulina platensis cultivation by fed-batch addition of urea as nitrogen source.

The cyanobacterium Spirulina platensis was cultivated in bench-scale miniponds on bicarbonate/carbonate solutions using urea as nitrogen source. To minimize limitation and inhibition phenomena, urea was supplied semicontinuously using exponentially increasing feeding rates. The average growth rates obtained alternately varying the total mass of urea added per unit reactor volume (275 < mT < 725 mg/L) and the total feeding time (9 < tT < 15 d) clearly evidenced nitrogen limitation for mT< 500 mg/L and excess nitrogen inhibition above this threshold.

Carbon material and bioenergetic balances of xylitol production from corncobs by Debaryomyces hansenii.

The effect of oxygenation on xylitol production by the yeast Debaryomyces hansenii has been investigated in this work using the liquors from corncob hydrolysis as the fermentation medium. The concentrations of consumed substrates (glucose, xylose, arabinose, acetate and oxygen) and formed products (xylitol, arabitol, ethanol, biomass and carbon dioxide) have been used, together with those previously obtained varying the hydrolysis technique, the level of adaptation of the microorganism, the sterilization procedure and the initial substrate and biomass concentrations, in carbon material balances to evaluate the percentages of xylose consumed by the yeast for the reduction to xylitol, alcohol fermentation, respiration and cell growth. The highest xylitol concentration (71 g/L) and volumetric productivity (1.

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.