Xylitol production by Candida tropicalis from corn cob hemicellulose hydrolysate in a two‐stage fed‐batch fermentation process

BACKGROUND: Xylitol, a sugar alcohol widely used in food and pharmaceutical industries, can be produced through biological reduction of xylose present in hemicellulose hydrolysates by Candida tropicalis. However, the aeration rate and by‐products originating from hemicellulose hydrolysis strongly inhibit the production of xylitol in a fermentation process. A two‐stage fed‐batch fermentation system was developed to reduce these inhibitory effects and to improve xylitol production from corn cob hemicellulose hydrolysates by C. tropicalis. RESULTS: Results of batch fermentations indicated that high xylitol production could be obtained from C. tropicalis at an initial xylose concentration of 80 g L^?1 in corn cob hydrolysate medium at an aeration rate of 0.4 vvm at the micro‐aeration stage. In the two‐stage fed‐batch fermentation process, 96.5 g L^?1 xylitol was obtained after 120 h, giving a yield of 0.83 g g^?1 and a productivity of 1.01 g L^?1 h^?1, which were 12.16% and 65.57% higher than those in a batch fermentation. CONCLUSION: High xylitol production can be achieved in a two‐stage fed‐batch fermentation process, in which the negative effects of aeration rate and inhibitory compounds on xylitol formation can be considerably reduced. Copyright © 2011 Society of Chemical Industry     

Xylitol production by liquid emulsion membrane encapsulated yeast cells

BACKGROUND: Liquid emulsion membrane (LEM)‐encapsulated live cells can be used to produce various products. This work reports on LEM‐encapsulated cells for producing xylitol and models the production process. RESULTS: Encapsulated cells of Candida mogii ATCC 18364 were used to produce xylitol from xylose. Soybean oil LEM consisting of 5% (w/v) lanolin and microwaxes was found most suitable for this process. The LEM‐encapsulated cells were immobilized in a tubular biocatalytic loop. Xylitol was produced under oxygen‐limited and aerobic conditions. Xylitol productivity and yield were 0.005 g L^?1 h^?1 and 0.52 g g^?1, respectively, for oxygen‐limited operation. Under aerobic conditions, xylitol productivity increased greatly to 0.022 g L^?1 h^?1, but yield on xylose declined to 0.49 g g^?1. A mathematical model successfully described substrate consumption and product formation in the LEM‐immobilized cell system. CONCLUSION: Potentially, immobilized cell LEM systems are useful for certain fermentations and they can be successfully modeled, as shown by the example of xylitol from xylose process. Copyright © 2009 Society of Chemical Industry     

Improved xylitol production in media containing phenolic aldehydes: application of response surface methodology for optimization and modeling of bioprocess

BACKGROUND: The combined effects of vanillin and syringaldehyde on xylitol production by Candida guilliermondii using response surface methodology (RSM) have been studied. A 2² full‐factorial central composite design was employed for experimental design and analysis of the results. RESULTS: Maximum xylitol productivities (Q_P = 0.74 g L^?1h^?1) and yields (Y_P/S = 0.81 g g^?1) can be attained by adding only vanillin at 2.0 g L^?1 to the fermentation medium. These data were closely correlated with the experimental results obtained (0.69 ± 0.04 g L^?1 h^?1 and 0.77 ± 0.01 g g^?1) indicating a good agreement with the predicted value. C. guilliermondii was able to convert vanillin completely after 24 h of fermentation with 94% yield of vanillyl alcohol. CONCLUSIONS: The bioconversion of xylose into xylitol by C. guilliermondii is strongly dependent on the combination of aldehydes and phenolics in the fermentation medium. Vanillin is a source of phenolic compound able to improve xylitol production by yeast. The conversion of vanillin to alcohol vanilyl reveals the potential of this yeast for medium detoxification. Copyright © 2009 Society of Chemical Industry     

Use of response surface methodology to evaluate the optimum environmental conditions for the bioconversion of xylose into xylitol in eucalyptus hemicellulosic hydrolysate

Candida guilliermondii fermented a eucalyptus hemicellulosic hydrolysate that had been treated with calcium oxide, phosphoric acid and activated charcoal. The influences of different xylose and ammonium sulfate concentrations on the production of xylitol were studied. A response surface was obtained with value R² > 0.97 and p < 0.01. The model estimated a maximum xylitol production of 20.82 g dm^?3 in the culture medium supplemented with ammonium sulfate (1.8 g dm^?3) and xylose (45.5 g dm^?3). Copyright © 2003 Society of Chemical Industry     

High-Performance Production of Biosurfactant Rhamnolipid with Nitrogen Feeding

Nitrate is one of the most important factors for fermentative production of rhamnolipid, while it has not yet been conclusively demonstrated that nitrogen limitation or abundance is beneficial for improvement of rhamnolipid production. This study clarified that high concentration of NaNO₃ is conducive for high-performance production of rhamnolipid. An optimum rhamnolipid yield was achieved by 43.3 g L⁻¹ with an initial concentration of NaNO₃ equal to 10 g L⁻¹ during the regular fed-batch fermentation process by Pseudomonas aeruginosa ATCC 9027. Additionally, this rhamnolipid production was further improved to 61.2 g L⁻¹, which was two folds higher than that value obtained during batch fermentation, when the NaNO₃ concentration was maintained about 5 g L⁻¹. Furthermore, specific volume productivity of rhamnolipid was improved by over 30% in the presence of NaNO₃ at concentration ranging from 5 to 6 g L⁻¹ during sequential fed-batch fermentation, resulting a high value of 0.4 and 0.59 g L⁻¹ h⁻¹ within one batch of sequential fed-batch fermentation for a period of 17 days by P. aeruginosa ATCC 9027 and PAO1, respectively. It seems that sustaining high-concentration NaNO₃ during fed-batch fermentation is advantageous for high-performance production of rhamnolipid.     

Profiles of xylose reductase,xylitol dehydrogenase and xylitol production under different oxygen transfer volumetric coefficient values

BACKGROUND: Xylitol is a sugar alcohol (polyalcohol) with many interesting properties for pharmaceutical and food products. It is currently produced by a chemical process, which has some disadvantages such as high energy requirement. Therefore microbiological production of xylitol has been studied as an alternative, but its viability is dependent on optimisation of the fermentation variables. Among these, aeration is fundamental, because xylitol is produced only under adequate oxygen availability. In most experiments with xylitol‐producing yeasts, low oxygen transfer volumetric coefficient (K_La) values are used to maintain microaerobic conditions. However, in the present study the use of relatively high K_La values resulted in high xylitol production. The effect of aeration was also evaluated via the profiles of xylose reductase (XR) and xylitol dehydrogenase (XD) activities during the experiments. RESULTS: The highest XR specific activity (1.45 ± 0.21 U mg_protein^?1) was achieved during the experiment with the lowest K_La value (12 h^?1), while the highest XD specific activity (0.19 ± 0.03 U mg_protein^?1) was observed with a K_La value of 25 h^?1. Xylitol production was enhanced when K_La was increased from 12 to 50 h^?1, which resulted in the best condition observed, corresponding to a xylitol volumetric productivity of 1.50 ± 0.08 g_xylitol L^?1 h^?1 and an efficiency of 71 ± 6.0%. CONCLUSION: The results showed that the enzyme activities during xylitol bioproduction depend greatly on the initial K_La value (oxygen availability). This finding supplies important information for further studies in molecular biology and genetic engineering aimed at improving xylitol bioproduction. Copyright © 2008 Society of Chemical Industry     

Effect of glucose:xylose ratio on xylose reductase and xylitol dehydrogenase activities from Candida guilliermondii in sugarcane bagasse hydrolysate

The influence of glucose on xylose reductase (XR) and xylitol dehydrogenase (XDH) enzyme activity was evaluated from sugarcane bagasse hydrolysate fermentations with different glucose:xylose ratios (1:25, 1:12, 1:5 and 1:2.5) by employing an inoculum of Candida guilliermondii grown in media containing glucose, a mixture of glucose and xylose, or only xylose as carbon sources. According to the results, the glucose:xylose ratio affected positively this bioconversion and a correlation was not observed between the favourable conditions for xylitol production and the XR and XDH activities. Also, the results were influenced not only by the glucose:xylose ratio in the fermentation medium, but also by the carbon source employed in the growth medium of the inoculum. The optimum condition for xylitol production by C. guilliermondii in sugarcane bagasse hemicellulosic hydrolysate should use hydrolysate with a 1:5 glucose:xylose ratio and inoculum grown in medium containing xylose as the only carbon source. Copyright © 2006 Society of Chemical Industry     

Kinetic and technical studies on large-scale culture of Rhodiola sachalinensis compact callus aggregates with air-lift reactors

Compact callus aggregates (CCA) of Rhodiola sachalinensis, spherical, smooth-surfaced clumps of 2–8 mm in diameter displaying some level of tissue differentiation, were successfully cultured in 10 dm³ and 100 dm³ air-lift reactors. High salidroside yields of 60·0 mg dm⁻³ were obtained, which were 10-fold the dispersed cell cultures. The salidroside accumulation was found to be growth-associated due to the differentiated structure of CCA. No ‘foaming’ was observed since the broth remained almost clear throughout the culture cycle. The size of CCA conformed to normal distribution with average diameters varying from 3·1 mm to 3·6 mm during the culture. The depositing velocity of CCA in culture broth was small enough to be readily retained in suspension, therefore avoiding the clogging of the reactors. The significant increase in solid hold-up of the culture system was suggested to contribute to the variation of k_La during the culture. © 1998 SCI     

The fermentation of mixtures of D‐glucose and D‐xylose by Candida shehatae,Pichia stipitis or Pachysolen tannophilus to produce ethanol

The fermentation of mixtures of D ‐glucose and D ‐xylose by three non‐traditional yeasts: Candida shehatae (ATCC 34887), Pachysolen tannophilus (ATCC 32691) and Pichia stipitis (ATCC 58376) have been studied to determine the optimal strain and initial culture conditions for the efficient production of ethanol. The comparison was made on the basis of maximum specific growth rate (µ_m), biomass productivity, the specific rates of total substrate consumption (q_s) and ethanol production (q_E) and the overall yields of ethanol and xylitol. All the experiments were performed in stirred‐tank batch reactors at a temperature of 30 °C. The initial pH of the culture medium was 4.5. The highest values of µ_m (above 0.5 h^?1) were obtained with P stipitis in cultures containing high concentrations of D ‐xylose. All three yeasts consumed the two monosaccharides in sequence, beginning with D ‐glucose. The values of q_s diminished during the course of each experiment with all of the yeasts. The highest values of the specific rates of total substrate consumption and ethanol production were obtained with C shehatae (for t = 10 h, q_s and q_E were above 5 g g^?1 h^?1 and 2 g g^?1 h^?1, respectively), although the highest overall ethanol yields were fairly similar with all three yeasts, at around 0.4 g g^?1. © 2002 Society of Chemical Industry     

Effect of oxygen transfer rates on alcohols production by Candida guilliermondii cultivated on soybean hull hydrolysate

BACKGROUND: In this research the use of soybean hull hydrolysate (SHH) as substrate for xylitol and ethanol production using an osmotolerant strain of Candida guilliermondii was studied. The production of alcohols was investigated in batch cultivations in which the variable parameter was the volumetric oxygen mass transfer coefficient (k_La) obtained from three different conditions of air supply: anaerobic (150 rpm, no aeration); microaerobic (300 rpm, 1 vvm), and aerobic (600 rpm, 2 vvm), corresponding to k_La values of 0; 8; and 46 h^?1, respectively. RESULTS: SHH, although presenting a very high osmotic pressure (1413 mOsm kg^?1), was completely metabolized under aerobic conditions with high biomass productivities of 0.49 g cells (L h)^?1, with little formation of ethanol. Xylitol was produced under microaeration, with product yield of 0.22 g g^?1 xylose, with the formation of glycerol as a by‐product. No xylose was metabolized under anaerobic conditions, but ethanol was produced from hexoses with high product yields of 0.5 g g^?1. CONCLUSION: These results suggest that the hydrolysis of soybean hull and its conversion to ethanol and other alcohols could be an important use of this agro‐industrial waste, which could be used for biofuel, xylitol or biomass production, depending on the aeration conditions of the cultures. Copyright © 2008 Society of Chemical Industry     

Effect of Media Components and Growth Conditions for Improved Linoleic Acid Production by Beauveria Species

Beauveria species are well-known insect pathogenic fungi, and Beauveria bassiana is used as a biopesticide against various pests in agriculture. However, the Beauveria species has not been reported as producers of microbial oils. In this study, Beauveria spp. MTCC 5184 was used to produce microbial oil with high linoleic acid (LA) content. Ten experiments were performed to evaluate the effects of several media parameters, such as carbon and nitrogen sources, pH, various concentrations of carbon and nitrogen, growth duration, and oleic acid (OLA) supplementation for maximum LA and dry biomass production by the fungus. Several of these parameters had a significant impact on the production of LA, as well as dry biomass. The glucose yeast extract (GYE) medium supplemented with 1.5% (w/v) peptone yielded maximum LA (0.32 ± 0.01 g L⁻¹) and biomass (5.51 ± 0.26 g L⁻¹). However, through the addition of 1.0% (w/v) OLA, the precursor of LA, LA production was enhanced 12-fold (1.24 ± 0.03 g L⁻¹), and the biomass production increased by 5-fold (11.05 ± 0.46 g L⁻¹) in comparison to those in the basal (GYE) medium. Using lactose as the sole carbon source produced the lowest LA (0.05 ± 0.00 g L⁻¹) and biomass (1.04 ± 0.10 g L⁻¹). The results of this study will be useful for the commercial exploitation of this fungus for the production of LA-rich microbial oil for use in the production of lubricants, greases, paints, cosmetics, etc.     

Oxygen transfer and uptake in Streptomyces coelicolor A3(2) culture in a batch bioreactor

This paper provides quantitative information on oxygen transfer as well as the kinetic and metabolic parameters related to oxygen uptake in Streptomyces coelicolor A3(2) cultured in a 20 dm³ computer controlled bioreactor using both defined and complex media. It is evident from the literature that production of antibiotics is strongly affected by the dissolved oxygen concentration. Many processes of antibiotic fermentations have been developed to the point at which the microbial oxygen demand exceeds the oxygen transfer capability of the existing fermentation facilities. As a consequence, the oxygen transfer rate has become the rate limiting factor in such processes. It is necessary to know the oxygen kinetic and metabolic parameters of an aerobic fermentation for a successful scale-up and operational control of the process. In the literature, information concerning the oxygen uptake kinetics of the Streptomyces cultures is scarce despite their industrial importance. This paper, therefore, provides useful quantitative information on oxygen transfer and uptake rates in S. coelicolor cultures. In the defined medium, the total oxygen uptake rates were in the range of 5–6 mmol O₂ dm⁻³ h⁻¹ throughout the active growth phase, the maximum specific oxygen uptake rate was 7·44 mmol O₂ g cell⁻¹ h⁻¹, the specific oxygen maintenance demand was 1·88 mmol O₂ g cell⁻¹ h⁻¹, and the k_La values were in the range of 40–100 h⁻¹. In the complex medium, however, the k_La values varied in the range of 18–70 h⁻¹. © 1998 Society of Chemical Industry     

Research note: Effect of dissolved oxygen level on lactase production by Kluyveromyces fragilis

The influence of dissolved oxygen (% DO) on lactase production by Kluyveromyces fragilis (NRRL-Y-1109) in chemostat culture using a defined medium was studied. The aim was to determine conditions for both high specific enzyme activity and high volumetric enzyme productivity. Significant differences in the specific enzyme activity and specific and volumetric enzyme productivity were found at the corresponding steady states when the DO was varied between 0 and 90%. Maximum lactase production was attained at 10% DO. Under this condition the best results were an enzyme activity of 5910 IU g⁻¹, specific production rate of 1810 IU g⁻¹ h⁻¹ and volumetric production rate of 1530 IU dm⁻³ h⁻¹. This seem to be due to the fact that at low aeration conditions the yeast metabolism is more reductive and as a consequence it verifies both higher specific lactose consumption rate and higher enzyme expression than in full aeration conditions. The results of this investigation are also compared with those of other studies of lactase production by Kluyveromyces sp. © 1998 Society of Chemical Industry     

Effect of cobalt oxide on characteristics of micro-arc oxidation coatings on TC11 alloy

In order to improve the comprehensive performance of TC11 titanium alloy and make it more widely used in the field of oil and gas wells, cobalt oxide micro-powder from 0 to 0.8 g·L⁻¹ was added in the electrolyte. The effects of cobalt oxide micro-powder concentration on properties of micro-arc oxidation (MAO) coatings were analyzed by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical workstation. With cobalt oxide micro-powder increased, the oxide voltage increased, and the discharge coating micropores became more uniform. The increase in thickness and hardness also improved corrosion resistance. The comprehensive performance after added 0.6 g·L⁻¹ of cobalt oxide was the best, with a doubling increase in thickness and hardness, reaching 32.1 µm and 721.2 HV, respectively. The corrosion rate reduced to 4.19 × 10⁻¹⁰ mm·a⁻¹, which reduced by three orders of magnitude. In addition, the substrates and samples prepared with 0.6 g·L⁻¹ cobalt oxidation were used for the erosion corrosion tests in different NaCl solutions, and it was found that the weight loss and rate of the MAO sample (slight corrosion) were lower than substrates, indicating that the cobalt oxide doped coatings had better corrosion resistance.     

Effect of zeolite addition on ethanol production from glucose by Saccharomyces bayanus

Zeolite NaY at 5 g dm⁻³ concentration, was selected to improve the production of ethanol fermentation by Saccharomyces bayanus from high glucose concentration media. The highest ethanol productivity (3·07 g dm⁻³ h⁻¹) was obtained from a 220 g dm⁻³ initial glucose concentration, while the highest ethanol concentration (130 g dm⁻³) was obtained from a 350 g dm⁻³ glucose medium. The zeolite is believed to have acted as a pH regulator, maintaining the pH value around 3·7–3·8. Under these conditions cellular viability was preserved and metabolic activity was maintained. Thus all the glucose was consumed, and high ethanol productivity and concentration were obtained. Therefore, the addition of zeolite improved ethanol production from high concentrations of glucose by Saccharomyces bayanus. © 1998 Society of Chemical Industry     

葡萄糖和木糖共发酵的产氢特性

引言化石能源面临枯竭,石油价格不断攀升,摆脱对化石能源的依赖是国内外亟待解决的重大问题。氢气因热值高、可再生且燃烧后无污染,成为21世纪最理想的能源。在众多制取氢气的方法中,厌氧发酵制氢反应条件温和,设备简单,而且可利用的原料来源广泛,从而引起了广泛的关注。     

Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry     

Sugarcane bagasse hydrolysis with phosphoric and sulfuric acids and hydrolysate detoxification for xylitol production

The effectiveness of phosphoric acid to release xylose from sugarcane bagasse hemicellulose was assessed through a 2³ full factorial design. The maximum xylose concentration in the hydrolysate (17.1 g dm^?3) was attained when the bagasse was treated at 160 °C for 60 min, using 70 mg of phosphoric acid per gram of dry‐bagasse. Hydrolysis carried out with sulfuric acid, under optimum conditions previously determined, provided a hydrolysate with a similar xylose concentration (17.2 g dm^?3). After vacuum concentration, these hydrolysates were detoxified and used for xylitol production with the yeast Candida guilliermondii. Two different detoxification strategies, which consisted of adjusting the pH of the hydrolysates to 5.5 with either calcium oxide or ammonium hydroxide, both followed by active charcoal adsorption, were tested. The best xylitol productions (18.1 and 19.2 g dm^?3) were observed when calcium oxide was used to adjust the pH of both the phosphoric and the sulfuric acid hydrolysates, respectively. Copyright © 2004 Society of Chemical Industry     

Performance of different immobilized‐cell systems to efficiently produce ethanol from whey: fluidized batch,packed‐bed and fluidized continuous bioreactors

BACKGROUND: The bioconversion of whey into ethanol by immobilized Kluyveromyces marxianus in packed‐bed and fluidized bioreactors is described. Both batch and continuous cultures were analyzed using three different strains of K. marxianus and the effect of the operating mode, temperature, and dilution rates (D) were investigated. RESULTS: All immobilized strains of K. marxianus (CBS 6556, CCT 4086, and CCT 2653) produced similar high yields of ethanol (0.44 ± 0.01 g EtOH g^?1 sugar). Significant variations of conversion efficiencies (66.1 to 83.3%) and ethanol productivities (0.78 to 0.96 g L^?1 h^?1) were observed in the experiments with strain K. marxianus CBS 6556 at different temperatures. High yields of ethanol were obtained in fluidized and packed‐bed bioreactors continuous cultures at different D (0.1 to 0.3 h^?1), with the highest productivity (3.5 g L^?1 h^?1) observed for D = 0.3 h^?1 in the fluidized bioreactor (87% of the maximal theoretical conversion), whereas the highest ethanol concentration in the streaming effluent (28 g L^?1) was obtained for D = 0.1 h^?1. Electronic micrographs of the gel beads showed efficient cell immobilization. CONCLUSION: Batch and continuous cultivations of immobilized K. marxianus in fluidized and packed‐bed bioreactors enable high yields and productivities of ethanol from whey. Copyright © 2012 Society of Chemical Industry     

Improved Ethanol Production by Saccharomyces cerevisiae with EDTA,Ferrocyanide and Zeolite X Addition to Sugar Beet Molasses

The influence of ethylenediaminetetra acetic acid (EDTA), potassium ferrocyanide and zeolite X on ethanol production from sugar beet molasses by Saccharomyces cerevisiae was studied. For all of the three substances used, the effect was more pronounced when added to the fermentation medium rather than to the growth medium; 1·9 mmol dm⁻³ potassium ferrocyanide caused an increase in the final ethanol concentration of about 16·4% and 47·5% with respect to control culture on addition to growth and fermentation media respectively. The greatest stimulation in product yield was obtained with zeolite X introduced during the fermentation stage; 8·0 g dm⁻³ zeolite X increased ethanol concentration by 53·3%. © 1997 SCI.