Fermentation behavior of an osmotolerant yeast D. hansenii for Xylitol production

Abstract

Realizing the importance of xylitol as a high-valued compound that serves as a sugar substitute, a new, one step thin layer chromatographic procedure for quick, reliable, and efficient determination of xylose and xylitol from their mixture was developed. Two hundred and twenty microorganisms from the laboratory stock cultures were screened for their ability to produce xylitol from D-xylose. Amongst these, an indigenous yeast isolate no.139 (SM-139) was selected and identified as Debaryomyces hansenii on the basis of morphological and biochemical characteristics and (26S) D1/D2 r DNA region sequencing. Debaryomyces hansenii produced 9.33 gL(-1) of xylitol in presence of 50.0 gL(-1) of xylose in 84 h at pH 5.5, 30°C, 200 rpm. In order to utilize even higher concentrations of xylose for maximum xylitol production, a xylose enrichment technique was developed. The strain of Debaryomyces hansenii was obtained through xylose enrichment technique in a statistically optimized medium containing 0.3% yeast extract, 0.2% peptone, 0.03% MgSO(4) .7H(2) O along with 1% methanol. The culture was inoculated with 6% inoculum and incubated at 30°C and 250 rpm. A yield of 0.6 gg(-1) was obtained with a xylitol volumetric productivity of 0.65 g/L h(-1) in the presence of 200 gL(-1) of xylose although up to 300 gL(-1) of xylose could be tolerated through batch fermentation. Through this technique, even higher concentrations of xylose as substrate could be potentially utilized for maximum xylitol production.

Rhodosporidium toruloides cultivated in NaCl‐enriched glucose‐based media: Adaptation dynamics and lipid production

“…200 g/L) has been reported when glycerol has been employed as fermentation substrate by wild or mutant Y. lipolytica strains . Likewise, besides mannitol and erythritol, due to their high osmotic tolerance, halotolerant yeasts have been proposed as candidates for bioethanol production , enzyme production as well as xylitol biosynthesis . However, none of these microorganisms has ever been reported as oleaginous.…”

Production of valuable compounds by molds and yeasts

“…Bioconversion of 300 g l − 1 xylose to xylitol by Debaryomyces hansenii amounted to 110 g l − 1 . 147 The yield was 0.48 g g − 1 . Repeated fed-batch fermentation (lasting 750 h) with high-cell density cultures of Candida magnolia TISTR 5663 in a 2-l stirred tank fermenter under oxygen limitation with feeding of xylose and nitrogen and a starting xylose concentration of 60 g l − 1 led to production of 284 g l − 1 of xylitol, 148 the highest titer ever achieved.…”