Optimization of activated charcoal detoxification and concentration of chestnut shell hydrolysate for xylitol production.

OBJECTIVES: To increase xylose concentration of the chestnut shell hemicellulosic hydrolysate with an acceptable phenolic compound level in order to enhance xylitol production by Candida tropicalis M43. RESULTS: The xylose concentration and total phenolic compound concentration of the hydrolysate were obtained as 33.68 g/L and 77.38 mg gallic acid equivalent/L, respectively by optimization of detoxification parameters and concentration level (60 °C, 115 min contact time, 5.942% (w/v) dosage of activated charcoal, 120 strokes/min shaking rate and 0.2 volume ratio). Xylitol production was achieved in the hydrolysate by using Candida tropicalis M43. The maximum xylitol concentration was 6.30 g/L and productivity, yield and percentage of substrate conversion were calculated as 0.11 g/L h, 19.13% and 97.79%, respectively. In addition, the chestnut shell hydrolysate fortified with xylose and the maximum xylitol concentration increased to 18.08 g/L in the hydrolysate-based medium containing 80 g/L xylose. CONCLUSIONS: Optimizing detoxification conditions with concentration level was found to be useful for enhancing xylitol production. In addition, fortification of the hydrolysate caused a three fold increase in maximum xylitol concentration.

Evaluation of xylitol production using corncob hemicellulosic hydrolysate by combining tetrabutylammonium hydroxide extraction with dilute acid hydrolysis.

In this paper, we produced hemicellulosic hydrolysate from corncob by tetrabutylammonium hydroxide (TBAH) extraction and dilute acid hydrolysis combined, further evaluating the feasibility of the resultant corncob hemicellulosic hydrolysate used in xylitol production by Candida tropicalis. Optimized conditions for corncob hemicellulose extraction by TBAH was obtained via response surface methodology: time of 90min, temperature of 60°C, liquid/solid ratio of 12 (v/w), and TBAH concentration of 55%, resulting in a hemicellulose extraction of 80.07% under these conditions. The FT-IR spectrum of the extracted corncob hemicellulose is consistent with that of birchwood hemicellulose and exhibits specific absorbance of hemicelluloses at 1380, 1168, 1050, and 900cm(-1). In addition, we found that C. tropicalis can ferment the resulting corncob hemicellulosic hydrolysate with pH adjustment and activated charcoal treatment leading to a high xylitol yield and productivity of 0.77g/g and 2.45g/(Lh), respectively.

Ethanol and xylitol production by fermentation of acid hydrolysate from olive pruning with Candida tropicalis NBRC 0618.

Olive tree pruning biomass has been pretreated with pressurized steam, hydrolysed with hydrochloric acid, conditioned and afterwards fermented using the non-traditional yeast Candida tropicalis NBRC 0618. The main aim of this study was to analyse the influence of acid concentration on the hydrolysis process and its effect on the subsequent fermentation to produce ethanol and xylitol. From the results, it could be deduced that both total sugars and d-glucose recovery were enhanced by increasing the acid concentration tested; almost the whole hemicellulose fraction was hydrolysed when 3.77% was used. It has been observed a sequential production first of ethanol, from d-glucose, and then xylitol from d-xylose. The overall ethanol and xylitol yields ranged from 0.27 to 0.38kgkg(-1), and 0.12 to 0.23kgkg(-1) respectively, reaching the highest values in the fermentation of the hydrolysates obtained with hydrochloric acid 2.61% and 1.11%, respectively.

Two new compounds from the dry leaves of Pleioblastus amarus (Keng) keng f.

Two new compounds, xylitol 1-O-(6'-O-p-hydroxylbenzoyl)-glucopyranoside (1) and bambulignan B (2), together with three known ones gastrodin (3), glucovanillin (4), and rel-(7S,7'R,8R,8'S)-4,4'-dihydroxy-3,3',5,5'-tetramethoxy-7,7'-epoxyligna-9,9'-diol-9(or)9'-O-ß-glucopyranoside (5), were isolated from the 95% EtOH extract of the dry leaves of Pleioblastus amarus (Keng) keng f. Their structures were determined by UV, IR, HR-ESI-MS, CD, and 1D and 2D NMR data analyses as well as GC experiments.

Short synthesis of 3-(hydroxymethyl)xylitol and structure revision of the anti-diabetic natural product from Casearia esculenta.

3-(Hydroxymethyl)xylitol, a compound reportedly isolated from the root of Casearia esculenta (Roxb.), along with its three possible stereoisomers, has been synthesized for the first time by way of a triple dihydroxylation reaction performed upon the simplest cross-conjugated hydrocarbon, [3]dendralene. The data for the natural product do not match any of the isomeric 3-(hydroxymethyl)pentitols. The structure of the natural product from the root of Casearia esculenta (Roxb.) has been corrected by reanalysis of the published data.

A novel pathway construction in Candida tropicalis for direct xylitol conversion from corncob xylan.

In this study, an integrated xylitol production pathway, directly using xylan as the substrate, was constructed in Candida tropicalis BIT-Xol-1 which could efficiently convert xylose into xylitol. In order to consolidate this bioprocessing, a ß-1,4-xylanase gene (atn) and a ß-xylosidase gene (atl) were cloned from Aspergillus terreus, and were constructed onto episomal plasmid pAUR123. Additionally, combination of the individual atn and atl expression cassette was also cloned onto pAUR123. After transforming, the positive C. tropicalis transformants co-expressing xylanase and xylosidase produced larger hydrolysis zones than those expressing xylanase alone, when incubated on xylan-congo red plates. The engineered C. tropicalis/pAUR-atn-atl-3 (C. tropicalis PNL3) secrete heterologous xylanase and xylosidase simultaneously, with the activities of 48.17 and 11.56 U/mL, respectively. The xylitol yields by C. tropicalis PNL3 utilizing xylan and corncob were 77.1% and 66.9%, respectively. The integrated pathway of xylitol production was feasible and efficient in utilization of xylan-rich renewable biomass via combining saccharification and transformation of xylan in engineered C. tropicalis.

Enhanced xylitol production through simultaneous co-utilization of cellobiose and xylose by engineered Saccharomyces cerevisiae.

As Saccharomyces cerevisiae cannot utilize xylose as a carbon source, expression of XYL1 coding for xylose reductase (XR) from Scheffersomyces (Pichia) stipitis enabled production of xylitol from xylose with a high yield. However, insufficient supply of NAD(P)H for XR and inhibition of xylose uptake by glucose are identified as major constraints for achieving high xylitol productivity. To overcome these problems, we engineered S. cerevisiae capable of converting xylose into xylitol through simultaneous utilization of xylose and cellobiose. An engineered S. cerevisiae (D-10-BT) expressing XR, cellodextrin transporter (cdt-1) and intracellular ß-glucosidase (gh1-1) produced xylitol via simultaneous utilization of cellobiose and xylose. The D-10-BT strain exhibited 40% higher volumetric xylitol productivity with co-consumption of cellobiose and xylose compared to sequential utilization of glucose and xylose. Furthermore, the overexpression of S. cerevisiae ALD6, IDP2, or S. stipitis ZWF1 coding for cytosolic NADP(+)-dependent dehydrogenases increased the intracellular NADPH availability of the D-10-BT strain, which resulted in a 37-63% improvement in xylitol productivity when cellobiose and xylose were co-consumed. These results suggest that co-utilization of cellobiose and xylose can lead to improved xylitol production through enhanced xylose uptake and efficient cofactor regeneration.

Xylitol production by genetically engineered Trichoderma reesei strains using barley straw as feedstock.

Xylitol, a naturally occurring five-carbon sugar alcohol derived from D-xylose, is currently in high demand by industries. Trichoderma reesei, a prolific industrial cellulase and hemicellulase producing fungus, is able to selectively use D-xylose from hemicelluloses for xylitol production. The xylitol production by T. reesei can be enhanced by genetic engineering of blocking further xylitol metabolism in the D-xylose pathway. We have used two different T. reesei strains which are impaired in the further metabolism of xylitol including a single mutant in which the xylitol dehydrogenase gene was deleted (∆xdh1) and a double mutant where additionally L-arabinitol-4-dehydrogenase, an enzyme which can partially compensate for xylitol dehydrogenase function, was deleted (∆lad1∆xdh1). Barely straw was first pretreated using NaOH and Organosolv pretreatment methods. The highest xylitol production of 6.1 and 13.22 g/L was obtained using medium supplemented with 2 % Organosolv-pretreated barley straw and 2 % D-xylose by the ∆xdh1 and ∆lad1∆xdh1 strains, respectively.

Xylitol production is increased by expression of codon-optimized Neurospora crassa xylose reductase gene in Candida tropicalis.

Xylose reductase (XR) is the first enzyme in D: -xylose metabolism, catalyzing the reduction of D: -xylose to xylitol. Formation of XR in the yeast Candida tropicalis is significantly repressed in cells grown on medium that contains glucose as carbon and energy source, because of the repressive effect of glucose. This is one reason why glucose is not a suitable co-substrate for cell growth in industrial xylitol production. XR from the ascomycete Neurospora crassa (NcXR) has high catalytic efficiency; however, NcXR is not expressed in C. tropicalis because of difference in codon usage between the two species. In this study, NcXR codons were changed to those preferred in C. tropicalis. This codon-optimized NcXR gene (termed NXRG) was placed under control of a constitutive glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter derived from C. tropicalis, and integrated into the genome of xylitol dehydrogenase gene (XYL2)-disrupted C. tropicalis. High expression level of NXRG was confirmed by determining XR activity in cells grown on glucose medium. The resulting recombinant strain, LNG2, showed high XR activity (2.86 U (mg of protein)(-1)), whereas parent strain BSXDH-3 showed no activity. In xylitol fermentation using glucose as a co-substrate with xylose, LNG2 showed xylitol production rate 1.44 g L(-1) h(-1) and xylitol yield of 96% at 44 h, which were 73 and 62%, respectively, higher than corresponding values for BSXDH-3 (rate 0.83 g L(-1) h(-1); yield 59%).

Enhancement of xylitol production in Candida tropicalis by co-expression of two genes involved in pentose phosphate pathway.

The yeast Candida tropicalis produces xylitol, a natural, low-calorie sweetener whose metabolism does not require insulin, by catalytic activity of NADPH-dependent xylose reductase. The oxidative pentose phosphate pathway (PPP) is a major basis for NADPH biosynthesis in C. tropicalis. In order to increase xylitol production rate, xylitol dehydrogenase gene (XYL2)disrupted C. tropicalis strain BSXDH-3 was engineered to co-express zwf and gnd genes which, respectively encodes glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6-PGDH), under the control of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter. NADPH-dependent xylitol production was higher in the engineered strain, termed "PP", than in BSXDH-3. In fermentation experiments using glycerol as a co-substrate with xylose, strain PP showed volumetric xylitol productivity of 1.25 g l(-1) h(-1), 21% higher than the rate (1.04 g l(-1) h(-1)) in BSXDH-3. This is the first report of increased metabolic flux toward PPP in C. tropicalis for NADPH regeneration and enhanced xylitol production.

Influence of 3-hydroxymethyl xylitol, a novel antidiabetic compound isolated from Casearia esculenta (Roxb.) root, on glycoprotein components in streptozotocin-diabetic rats.

Casearia esculenta root (Roxb.) is widely used in traditional system of medicine to treat diabetes in India. An active compound, 3-hydroxymethyl xylitol (3-HMX), has been isolated, and its optimum dose has been determined in a short duration study and patented. In addition, the long-term effect of 3-HMX in type 2 diabetic rats on antihyperglycemic, antioxidants, antihyperlipidemic, and protein metabolism and kidney marker enzymes was investigated, and its effect was shown previously. In this study, we investigated the effect of 3-HMX on plasma and tissue glycoproteins in streptozotocin-diabetic rats. Animals were divided into five groups viz., control group, 3-HMX (40 mg/kg of body weight) treated group, diabetic group, diabetic+3-HMX (40 mg/kg of body weight), and diabetic+glibenclamide (600 µg/kg of body weight). 3-HMX was administered orally at a dose of 40 mg/kg of body weight for 45 days. The study shows significant increases in the level of sialic acid except kidney and elevated levels of hexose, hexosamine, and fucose in the liver and kidney of diabetic rats, and the treatment with 3-HMX and glibenclamide showed reversal of these parameters toward normalcy. Thus, the study indicates that 3-HMX possesses a significant beneficial effect on glycoprotein components.

Utilisation of corn (Zea mays) bran and corn fiber in the production of food components.

The milling of corn for the production of food constituents results in a number of low-value co-products. Two of the major co-products produced by this operation are corn bran and corn fiber, which currently have low commercial value. This review focuses on current and prospective research surrounding the utilization of corn fiber and corn bran in the production of potentially higher-value food components. Corn bran and corn fiber contain potentially useful components that may be harvested through physical, chemical or enzymatic means for the production of food ingredients or additives, including corn fiber oil, corn fiber gum, cellulosic fiber gels, xylo-oligosaccharides and ferulic acid. Components of corn bran and corn fiber may also be converted to food chemicals such as vanillin and xylitol. Commercialization of processes for the isolation or production of food products from corn bran or corn fiber has been met with numerous technical challenges, therefore further research that improves the production of these components from corn bran or corn fiber is needed.

Release of D-xylose from wheat straw by acid and xylanase hydrolysis and purification of xylitol.

Xylitol is a valuable sweetener produced from xylose-rich biomass. Our objective was to optimize conditions for maximum release of D-xylose from wheat straw by acid or enzyme hydrolysis with minimal release of other monosaccharides, and to purify xylitol from three other alditols. Ground straw was treated with 10 parts of 0.2-0.4 M sulfuric acid at 110-130 degrees C for 15-45 min or at reflux with 0.75-1.25 M sulfuric acid for 1.5-3 h. Under optimum conditions of either 0.3 M acid at 123 degrees C for 28 min or 1.0 M acid at 100 degrees C for 3 h, 18 or 19% of D-xylose plus approximately 6% other sugars were produced from straw (dry basis). A 16% yield of D-xylose plus 6% other sugars was obtained when hydrothermally (10% straw, 160 degrees C, 1 h) treated straw was incubated with a commercial xylanase. The lack of enzyme specificity for D-xylose release was attributed to the autohydrolysis of polysaccharides during the pretreatment plus slow hydrolysis of cellulose during enzyme digestion. Xylitol with a purity of 95% was obtained in 10% yield from straw after the reduction of an acid-hydrolyzate followed by fractional crystallization. Purification of the mixture of four alditols by open-column chromatography on a strongly basic anion-exchange resin in hydroxide form gave 7% xylitol crystals with a purity of 99%.

Occurrence of the alpha-glucosidase inhibitor 1,4-Dideoxy-1,4-imino-D-arabinitol and related iminopentitols in marine sponges.

The alpha-glucosidase inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (1) was isolated from two marine sponges collected in Western Australia and shown by LC-MS to be responsible for the alpha-glycosidase inhibitory activity in different sponge extracts collected over a wide geographic area. The configuration of 1 was determined by application of Marfey's method. The two most inhibitory extracts contained only 1, while the less inhibitory extracts contained 1,4-dideoxy-1,4-imino-D-xylitol (2) or the putative diastereomeric imino pentitols 3 and 4. The least active or inactive extracts showed no detectable imino pentitols. While both 1 and 2 are known from plants, this is the first report on the isolation and detection of 1 and 2 in marine invertebrates.

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 (0.6249 kg/kg of NVC) but also to minor amounts of inorganic components (measured as ashes), proteins, nonfermented sugars (xylose and arabinose), uronic acids, arabitol, and other nonvolatile components (ONVC). The media were subjected to further processing (sequential stages of adsorption, concentration, ethanol precipitation, concentration, and crystallization) to obtain food-grade xylitol. Adsorption experiments were carried out at various solid-to-liquor ratios. Under selected conditions (1 kg of charcoal/15 kg of liquors), the xylitol content increased to 0.6873 kg/kg of NVC, and almost total decoloration was achieved. The resulting liquor was concentrated by evaporation to increase its NVC content to 0.4032 kg/kg of liquor (corresponding to a xylitol concentration of 0.280 kg/kg of liquor), and ethanol was added to precipitate a part of the NVC (mainly proteins, but also uronic acids, ashes, and other nonvolatile compounds). Refined liquors (containing 0.7303 kg of xylitol/kg of NVC) were concentrated again, and ethanol was added (to reach 40-60% volume of the stream) to allow crystallization at -10 or -5 degrees C. Under selected conditions, 43.7% of xylitol contained in the initial fermentation broth was recovered in well-formed, homogeneous crystals, in which xylitol accounted for 98.9% of the total oven-dry weight. Material balances are presented for the whole processing scheme considered in this work.

Purification of xylitol from fermented hemicellulosic hydrolyzate using liquid-liquid extraction and precipitation techniques.

Xylitol was produced by Candida guilliermondii by fermentation of sugarcane bagasse hemicellulosic hydrolysate. Undesirable impurities were extracted from the broth using either ethyl acetate, chloroform or dichloromethane. The best results on clarification of the broth without xylitol loss were obtained with ethyl acetate. When ethanol, acetone or tetrahydrofuran were used for precipitation of impurities, only tetrahydrofuran clarified the fermented broth, but a high xylitol loss (approximately 30%) was observed.

1,5-Anhydroxylitol from leaves of Olea europaea.

1,5-Anhydroxylitol, a compound never found previously in the vegetal kingdom was obtained from Olea europaea leaves in approximately 0.5-1% yield.

Optimal experimental condition for hemicellulosic hydrolyzate treatment with activated charcoal for xylitol production.

Rice straw was hydrolyzed into a mixture of sugars using diluted H(2)SO(4). During hydrolysis, a variety of inhibitors was also produced, including acetic acid, furfural, hydroxymethylfurfural, and lignin degradation products (several aromatic and phenolic compounds). To reduce the toxic compounds concentration in the hydrolyzate and to improve the xylitol yield and volumetric productivity, rice straw hemicellulosic hydrolyzate was treated with activated charcoal under different pH values, stirring rates, contact times, and temperatures, employing a 2(4) full-factorial design. Fermentative assays were conducted with treated hydrolyzates containing 90 g/L xylose. The results indicated that temperature, pH, and stirring rate strongly influenced the hydrolyzate treatment, temperature and pH interfering with all of the responses analyzed (removal of color and lignin degradation products, xylitol yield factor, and volumetric productivity). The combination of pH 2.0, 150 rpm, 45 degrees C, and 60 min was considered an optimal condition, providing significant removal rates of color (48.9%) and lignin degradation products (25.8%), as well as a xylitol production of 66 g/L, a volumetric productivity of 0.57 g/L.h, and a yield factor of 0.72 g/g.

Batch xylitol production by Candida guilliermondii FTI 20037 from sugarcane bagasse hemicellulosic hydrolyzate at controlled pH values.

Batch fermentation of sugarcane bagasse hemicellulosic hydrolyzate by the yeast Candida guilliermondii FTI 20037 was performed using controlled pH values (3.5, 5.5, 7.5). The maximum values of xylitol volumetric productivity ( Q(p)=0.76 g/l h) and xylose volumetric consumption ( Q(s)=1.19 g/l h) were attained at pH 5.5. At pH 3.5 and 7.5 the Q(p) value decreased by 66 and 72%, respectively. Independently of the pH value, Y(x/s) decreased with the increase in Y(p/s) suggesting that the xylitol bioconversion improves when the cellular growth is limited. At the highest pH value (7.5), the maximum specific xylitol production value was the lowest ( q(pmax)=0.085 g/l h.), indicating that the xylose metabolism of the yeast was diverted from xylitol formation to cell growth.

[Separation of xylose and xylitol in fermentation liquid by capillary zone electrophoresis].

Xylitol may be produced with microbial fermentation technology when xylose is used as the raw material. It is important in scientific research and production fields concerned with xylose and xylitol to develop the method of separation and detection. The anionic complexes with strong UV absorption at 195 nm will form by dissolving xylose and xylitol in borax solution. They may be separated with borax buffer by use of capillary zone electrophoresis. It was shown that the resolution between xylose and xylitol gradually increased with the increase of borax concentration, but its maximum concentration was 130 mmol/L at room temperature. The resolution depended on the pH of running buffer with a maximum at pH 9.55. The resolution was independent of cetyltrimethylammonium bromide when its concentration was between 4 x 10(-6) mmol/L-8 x 10(-4) mmol/L. So the optimum conditions were as follows: borax concentration of 130 mmol/L, pH 9.55 and cetyltrimethylammonium bromide concentration of 5 x 10(-5) mmol/L in running buffer; separating voltage of -12 kV; column temperature of 25 degrees C. Xylose and xylitol could be separated on base line in 6 min under these conditions. Samples from fermentation process and the recoveries of spiked samples were determined. The relative standard deviations of the results were between 1.42%-3.11% for xylose, and 0.62%-1.32% for xylitol. The recoveries were between 96.0%-108.0% for xylose and 94.0%-109.0% for xylitol.