Xylitol production and furfural consumption by a wild type Geotrichum sp

Background: Xylitol is a five carbons polyol with promising medical applications. It can be obtained from chemical D-xylose reduction or by microbial fermentation of Sugarcane Bagasse Hemicellulosic Hydrolysate. For this last process, some microbial inhibitors, as furfural, constitute severe bottleneck. In this case, the use of strains able to produce xylitol simultaneously to furfural neutralization is an interesting alternative. A wild-type strain of Geotrichum sp. was detected with this ability, and its performance in xylitol production and furfural consumption was evaluated. Furthermore, were analyzed its degradation products. Results: Geotrichum sp. produced xylitol from D-xylose fermentation with a yield of 0.44 g-g-1. Furfural was fully consumed in fermentation assay and when provided in the medium until concentration of 6 g-L-1. The furfural degradation product is not an identified molecule, presenting a molecular weight of 161 g-mol-1, an uncommon feature for the microbial metabolism of this product. Conclusion: This strain presents most remarkable potential in performing furfural consumption simultaneous to xylitol production. Subsequent efforts must be employed to establish bioprocess to simultaneous detoxification and xylitol production by Geotrichum sp.

New cultive medium for bioconversion of C5 fraction from sugarcane bagasse using rice bran extract

The use of hemicellulosic hydrolysates in bioprocesses requires supplementation as to ensure the best fermentative performance of microorganisms. However, in light of conflicting data in the literature, it is necessary to establish an inexpensive and applicable medium for the development of bioprocesses. This paper evaluates the fermentative performance of Scheffersomyces (Pichia) stipitis and Candida guilliermondii growth in sugarcane bagasse hemicellulosic hydrolysate supplemented with different nitrogen sources including rice bran extract, an important by-product of agroindustry and source of vitamins and amino acids. Experiments were carried out with hydrolysate supplemented with rice bran extract and (NH4)2SO4; peptone and yeast extract; (NH4)2SO4, peptone and yeast extract and non-supplemented hydrolysate as a control. S. stipitis produced only ethanol, while C. guilliermondii produced xylitol as the main product and ethanol as by-product. Maximum ethanol production by S. stipitis was observed when sugarcane bagasse hemicellulosic hydrolysate was supplemented with (NH4)2SO4, peptone and yeast extract. Differently, the maximum xylitol formation by C. guilliermondii was obtained by employing hydrolysate supplemented with (NH4)2SO4 and rice bran extract. Together, these findings indicate that: a) for both yeasts (NH4)2SO4 was required as an inorganic nitrogen source to supplement sugarcane bagasse hydrolysate; b) for S. stipitis, sugarcane hemicellulosic hydrolysate must be supplemented with peptone and yeast extract as organic nitrogen source; and: c) for C. guilliermondii, it must be supplemented with rice bran extract. The present study designed a fermentation medium employing hemicellulosic hydrolysate and provides a basis for studies about value-added products as ethanol and xylitol from lignocellulosic materials.

Evaluation of oat hull hemicellulosic hydrolysate fermentability employing Pichia stipitis

Oat hull hemicellulosic hydrolysate obtained by diluted acid hydrolysis was employed as fermentation medium for Pichia stipitis cultivation. A comparison between the use of treated hydrolysate with 1% activated charcoal to reduce the toxic compounds generated during the hydrolysis process and untreated hydrolysate as a control was conducted. In the cultures using treated hydrolysate the total consumption of glucose, low xylose consumption and ethanol and glycerol formation were observed. The medium formulated with untreated hydrolysate showed morphological cell modifications with consequently cell death, no ethanol formation and formation of glycerol as byproduct of fermentative process, probably as a response to stressful conditions to yeast due to presence of high concentration of toxic compounds. Thus, further studies are suggested in order to determine the best conditions for hydrolysis and detoxification of the hydrolysate to improve the fermentative performance of P. stipitis.

Evaluation of sorghum straw hemicellulosic hydrolysate for biotechnological production of xylitol by Candida guilliermondii

A preliminary study on xylitol production by Candida guilliermondii in sorghum straw hemicellulosic hydrolysate was performed. Hydrolysate had high xylose content and inhibitors concentrations did not exceed the commonly found values in other hemicellulosic hydrolysates. The highest xylitol yield (0.44 g/g) and productivity (0.19 g/Lh) were verified after 72 hours.

Xylitol production from wheat straw hemicellulosic hydrolysate: hydrolysate detoxification and carbon source used for inoculum preparation / Produção de xilitol em hidrolisado hemicelulósico de palha de trigo: destoxificação do hidrolisado e fonte de carbono utilizada para o preparo do inóculo

Wheat straw hemicellulosic hydrolysate was used for xylitol bioproduction. The use of a xylose-containing medium to grow the inoculum did not favor the production of xylitol in the hydrolysate, which was submitted to a previous detoxification treatment with 2.5 percent activated charcoal for optimized removal of inhibitory compounds.

Hidrolisado hemicelulósico de palha de trigo foi utilizado para a bioprodução de xilitol. O uso de meio contendo xilose para crescer o inóculo não favoreceu a produção de xilitol no hidrolisado, que foi submetido a um tratamento prévio de destoxificação com 2.5 por cento de carvão ativo para remoção otimizada de compostos inibitórios.

Polyurethane Foam Immobilization of Candida tropicalis for Xylitol Production / 微生物学通报

Immobilization conditions of Candida tropicalis to be absorbed in polyurethane foam carrier materials were studied on the xylitol production from corn hemicellulosic hydrolysate. Optimum batch-fermentation conditions were as follows: inoculum amount, 7% (volume ratio); polyurethane foam quantity, 1.0 g/100 mL; 30?C; initial pH, 6.0. Shaking speed was divided into two-phase to accommodate the dissolved oxygen, with 200 r/min at 0~24 h and 150 r/min at 24 h~46 h. The immobilized cells on polyurethane foam carrier have high density and good resistance to inhibitors in the hydrolysates. Average xylitol yield and volumetric productivity of polyurethane foam immobilized fermentation were much higher than the fermentation without immobilization. Corn cob hydrolysates can be directly biotransformed to xylitol without decoloration or ion-exchange treatment. This process can effectively reduce production costs, and it shows broad prospects of applications. Average xylitol yield was 67.6% and xylitol volumetric productivity was 1.92 g/(L?h).