Showing papers in "Applied Biochemistry and Biotechnology in 2006"

Macroscopic mass and energy balance of a pilot plant anaerobic bioreactor operated under thermophilic conditions.

Abstract: Intensive poultry production generates over 100,000 t of litter annually in West Virginia and 9×106 t nationwide. Current available technological alternatives based on thermophilic anaerobic digestion for residuals treatment are diverse. A modification of the typical continuous stirred tank reactor is a promising process being relatively stable and owing to its capability to manage considerable amounts of residuals at low operational cost. A 40-m3 pilot plant digester was used for performance evaluation considering energy input and methane production. Results suggest some changes to the pilot plant configuration are necessary to reduce power consumption although maximizing biodigester performance.

Ethanol Production From Steam-Explosion Pretreated Wheat Straw

Abstract: Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H2SO4 0.9% (w/w)] and water as preimpregnation agents. Acid- or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) or cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).

The Future of Coproducts From Corn Processing

Abstract: Increased demand for ethanol as a fuel additive has resulted in dramatic growth in ethanol production. Ethanol is produced from corn by either wet milling or dry-grind processing. In wet milling, the corn kernel is fractionated into different components, resulting in several coproducts. Wet-milling plants are capital intensive because of equipment requirements; they produce large volumes of ethanol and are corporate owned. In dry-grind processing, the corn kernel is not fractionated and only one coproduct, distillers’ dried grains with solubles (DDGS), is generated. Dry-grind plants require less equipment and capital than wet mills. They generate smaller volumes of ethanol, are producer owned, and add direct benefits to rural economies. Most of the increase in ethanol production during the past decade is attributed to growth in the dry-grind industry. The marketing of coproducts provides income to offset processing costs. For dry-grind plants, this is especially important, because only one coproduct is available. Several issues could affect DDGS marketing. The increasing volume of DDGS accompanying ethanol production could reduce market value; high phosphorous content could limit the use of DDGS, because of animal waste disposal issues. Water removal is a costly processing step and affects the economics of ethanol processing. Technologies to remove germ and fiber from DDGS could produce a new coproduct suitable for feeding to nonruminants; this would expand the markets for DDGS. Reducing phosphorus in DDGS would sustain markets for conventional DDGS. The development of more efficient methods of water removal would increase the efficiency of ethanol processing and reduce the costs of processing. New technologies could contribute to greater stability of dry-grind plants.

Feruloyl esterase: a key enzyme in biomass degradation.

Abstract: Feruloyl esterase forms a part of the enzyme complex that acts collectively and synergistically to completely hydrolyze xylan to its monomers. The enzyme has found potential uses in a wide variety of applications of interest to the agrifood and pharmaceutical industries. This review describes the enzymology of feruloyl esterases involved in xylan degradation. The occurrence of feruloyl esterases in various microorganisms and their physiochemical properties are presented. The nature of the enzyme substrates and products, the role of synergistic interactions with xylanases and other accessory enzymes, as well as the sequence-structure relating to the reaction mechanism are emphasized.

Effect of inhibitors released during steam-explosion pretreatment of barley straw on enzymatic hydrolysis.

Abstract: The influence of the liquid fraction (prehydrolysate) generated during steam-explosion pretreatment (210°C, 15 min) of barley straw on the enzymatic hydrolysis was determined. Prehydrolysate was analyzed for degradation compounds and sugars’ content and used as a medium for enzymatic hydrolysis tests after pH adjusting to 4.8. Our results show that the presence of the compounds contained in the prehydrolysate strongly affects the hydrolysis step (a 25% decrease in cellulose conversion compared with control). Sugars are shown to be more potent inhibitors of enzymatic hydrolysis than degradation products.

Variation of S/G Ratio and Lignin Content in a Populus Family Influences the Release of Xylose by Dilute Acid Hydrolysis

Abstract: Wood samples from a second generation Populus cross were shown to have different lignin contents and S/G ratios (S: syringyl-like lignin structures; G: guaiacyl-like lignin structures). The lignin contents varied from 22.7% to 25.8% and the S/G ratio from 1.8 to 2.3. Selected samples spanning these ranges were hydrolyzed with dilute (1%) sulfuric acid to release fermentable sugars. The conditions were chosen for partial hydrolysis of the hemicellulosic fraction to maximize the expression of variation among samples. The results indicated that both lignin contents and S/G ratio significantly affected the yield of xylose. For example, the xylose yield of the 25.8% lignin and 2.3 S/G (high lignin, high S/G) sample produced 30% of the theoretical yield, whereas the xylose yield of the 22.7% lignin and 1.8 S/G (low lignin, low S/G) was 55% of the theoretical value. These results indicate that lignin content and composition among genetic variants within a single species can influence the hydrolyzability of the biomass.

Updates on softwood-to-ethanol process development.

Abstract: Softwoods are generally considered to be one of the most difficult lignocellulosic feedstocks to hydrolyze to sugars for fermentation, primarily owing to the nature and amount of lignin. If the inhibitory effect of lignin can be significantly reduced, softwoods may become a more useful feedstock for the bioconversion processes. Moreover, strategies developed to reduce problems with softwood lignin may also provide a means to enhance the processing of other lignocellulosic substrates. The Forest Products Biotechnology Group at the University of British Columbia has been developing softwood-to-ethanol processes with SO2-catalyzed steam explosion and ethanol organosolv pretreatments. Lignin from the steam explosion process has relatively low reactivity and, consequently, low product value, compared with the high-value coproduct that can be obtained through organosolv. The technical and economic challenges of both processes are presented, together with suggestions for future process development.

Rail vs truck transport of biomass

Abstract: This study analyzes the economics of transshipping biomass from truck to train in a North American setting. Transshipment will only be economic when the cost per unit distance of a second transportation mode is less than the original mode. There is an optimum number of transshipment terminals which is related to biomass yield. Transshipment incurs incremental fixed costs, and hence there is a minimum shipping distance for rail transport above which lower costs/km offset the incremental fixed costs. For transport by dedicated unit train with an optimum number of terminals, the minimum economic rail shipping distance for straw is 170 km, and for boreal forest harvest residue wood chips is 145 km. The minimum economic shipping distance for straw exceeds the biomass draw distance for economically sized centrally located power plants, and hence the prospects for rail transport are limited to cases in which traffic congestion from truck transport would otherwise preclude project development. Ideally, wood chip transport costs would be lowered by rail transshipment for an economically sized centrally located power plant, but in a specific case in Alberta, Canada, the layout of existing rail lines precludes a centrally located plant supplied by rail, whereas a more versatile road system enables it by truck. Hence for wood chips as well as straw the economic incentive for rail transport to centrally located processing plants is limited. Rail transshipment may still be preferred in cases in which road congestion precludes truck delivery, for example as result of community objections.

Pretreatment of corn stover by low-liquid ammonia recycle percolation process

Abstract: A pretreatment method using aqueous ammonia was investigated with the intent of minimizing the liquid throughput. This process uses a flowthrough packed column reactor (or percolation reactor). In comparison to the ammonia recycle percolation (ARP) process developed previously in our laboratory, this process significantly reduces the liquid throughput to one reactor void volume in packed bed (2.0-4.7 mL of liquid/g of corn stover) and, thus, is termed low-liquid ARP (LLARP). In addition to attaining short residence time and reduced energy input, this process achieves 59-70% of lignin removal and 48-57% of xylan retention. With optimum operation of the LLARP to corn stover, enzymatic digestibilities of 95, 90, and 86% were achieved with 60, 15, and 7.5 filter paper units/g of glucan, respectively. In the simultaneous saccharification and fermentation test of the LLARP samples using Saccharomyces cerevisiae (NREL-D5A), an ethanol yield of 84% of the theoretical maximum was achieved with 6% (w/v) glucan loading. In the simultaneous saccharification and cofermentation (SSCF) test using recombinant Escherichia coli (KO11), both the glucan and xylan in the solid were effectively utilized, giving an overall ethanol yield of 109% of the theoretical maximum based on glucan, a clear indication that the xylan content was converted into ethanol. The xylooligomers existing in the LLARP effluent were not effectively hydrolyzed by cellulase enzyme, achieving only 60% of digestibility. SSCF of the treated corn stover was severely hampered when the substrate was supplemented with the LLARP effluent, giving only 56% the overall yield of ethanol. The effluent appears to significantly inhibit cellulase and microbial activities.

Optimization of Biodiesel Production From Castor Oil

Abstract: The transesterification of castor oil with ethanol in the presence of sodium ethoxide as catalyst is an exceptional option for the Brazilian biodiesel production, because the castor nut is quite available in the country. Chemically, its oil contains about 90% of ricinoleic acid that gives to the oil some beneficial characteristics such as its alcohol solubility at 30°C. The transesterification variables studied in this work were reaction temperature, catalyst concentration and alcohol oil molar ratio. Through a star configuration experimental design with central points, this study shows that it is possible to achieve the same conversion of esters carrying out the transesterification reaction with a smaller alcohol quantity, and a new methodology was developed to obtain high purity biodiesel.

Adenoviral vectors: a promising tool for gene therapy.

Abstract: Gene therapy is a promising tool for treatment of the human diseases that cannot be cured by rational therapies, and its primary success depends on suitable vectors to deliver therapeutic genes. Adenoviruses (Ads) are among the most commonly used vectors for gene therapy, second only to retroviruses. During the last decade, remarkable progress has been made in the development of Ad vectors and in the understanding of the toxicity related to the Ad vector system. Ad vector has certain advantages such as high transduction efficiency for different quiescent and dividing cell types and high levels of short-term expression to provide therapeutic benefits. However, researchers are facing the challenges associated with tissue-specific targeting of vectors and the vector-mediated immunogenicity. This review mainly focuses on the studies that have employed methods to improve Ad vectors and reduce viral toxicity for different applications. These methods include minimization or elimination of viral genes, retargeting of vector to the tissue of interest, and generation of immunocompromised recombinant vectors that lead to safer use of Ad vector systems that improve persistence of transgene expression. Moreover, the therapeutic applications of Ad vectors for liver-targeted gene therapy, suicide gene therapy, delivery of small interfering RNA, and production of recombinant vaccine under regulated conditions used in clinical trials are discussed.

Production of L-asparaginase, an anticancer agent, from Aspergillus niger using agricultural waste in solid state fermentation.

Abstract: This article reports the production of high levels of L-asparaginase from a new isolate of Aspergillus niger in solid state fermentation (SSF) using agro-wastes from three leguminous crops (bran of Cajanus cajan, Phaseolus mungo, and Glycine max). When used as the sole source for growth in SSF, bran of G. max showed maximum enzyme production followed by that of P. mungo and C. cajan. A 96-h fermentation time under aerobic condition with moisture content of 70%, 30 min of cooking time and 1205-1405 micro range of particle size in SSF appeared optimal for enzyme production. Enzyme yield was maximum (40.9 +/- 3.35 U/g of dry substrate) at pH 6.5 and temperature 30 +/- 2 degrees C. The optimum temperature and pH for enzyme activity were 40 degrees C and 6.5, respectively. The study suggests that choosing an appropriate substrate when coupled with process level optimization improves enzyme production markedly. Developing an asparaginase production process based on bran of G. max as a substrate in SSF is economically attractive as it is a cheap and readily available raw material in agriculture-based countries.

Optimization and modeling of laccase production by Trametes versicolor in a bioreactor using statistical experimental design.

Abstract: Experimental design and response surface methodologies were applied to optimize laccase production by Trametes versicolor in a bioreactor. The effects of three factors, initial glucose concentration (0 and 9 g/L), agitation (100 and 180 rpm), and pH (3.0 and 5.0), were evaluated to identify the significant effects and its interactions in the laccase production. The pH of the medium was found to be the most important factor, followed by initial glucose concentration and the interaction of both factors. Agitation did not seem to play an important role in laccase production, nor did the interaction agitation x medium pH and agitation x initial glucose concentration. Response surface analysis showed that an initial glucose concentration of 11 g/L and pH controlled at 5.2 were the optimal conditions for laccase production by T. versicolor. Under these conditions, the predicted value for laccase activity was >10,000 U/L, which is in good agreement with the laccase activity obtained experimentally (11,403 U/L). In addition, a mathematical model for the bioprocess was developed. It is shown that it provides a good description of the experimental profile observed, and that it is capable of predicting biomass growth based on secondary process variables.

Preliminary results on optimization of pilot scale pretreatment of wheat straw used in coproduction of bioethanol and electricity.

Abstract: The overall objective in this European Union-project is to develop cost and energy effective production systems for coproduction of bioethanol and electricity based on integrated biomass utilization. A pilot plan reactor for hydrothermal pretreatment (including weak acid hydrolysis, wet oxidation, and steam pretreatment) with a capacity of 100 kg/h was constructed and tested for pretreatment of wheat straw for ethanol production. Highest hemicellulose (C5 sugar) recovery and extraction of hemicellulose sugars was obtained at 190°C whereas highest C6 sugar yield was obtained at 200°C. Lowest toxicity of hydrolysates was observed at 190°C; however, addition of H2O2 improved the fermentability and sugar recoveries at the higher temperatures. The estimated total ethanol production was 223 kg/t straw assuming utilisation of both C6 and C5 during fermentation, and 0.5 g ethanol/g sugar.

Ethanol production from dilute-Acid softwood hydrolysate by co-culture.

Abstract: Dilute-acid softwood hydrolysate, with glucose and xylose as the dominant sugars was fermented to ethanol by co-cultures. The strains used include Saccharomyces cerevisiae 2.535 (1#), Pachysolen tannophilis ATCC 2.1662 (2#), and recombinant Escherichia coli (3#) constructed in our laboratory carrying both pdc and adhB genes derived from Zymomonas mobilis. Before fermentation, the co-cultures were adapted for five batches. Observation under light microscope showed aggregation of adapted strains, which could possibly improve their ability to degrade inhibitors. In addition, we tried to detoxify the dilute-acid softwood hydrolysate with a combined method before fermentation. Our study showed that fermentation of detoxified hydrolysate by adapted co-culture (1# + 2@) generated an exceptionally high ethanol yield on total sugar of 0.49 g/g, corresponding to 96.1% of the maximal theoretical value after 48h; fermentation of detoxified hydrolysate by adapted co-culture (1# + 3#) is faster (24h) and could reach a high ethanol yield (0.45 g/g total sugar). These experiments suggest that both adaptation and detoxification significantly improve hydrolysate fermentation and ethanol production.

Enzymatic conversion of waste cooking oils into alternative fuel--biodiesel.

Abstract: Production of biodiesel from pure oils through chemical conversion may not be applicable to waste oils/fats. Therefore, enzymatic conversion using immobilized lipase based on Rhizopus orzyae is considered in this article. This article studies this technological process, focusing on optimization of several process parameters, including the molar ratio of methanol to waste oils, biocatalyst load, and adding method, reaction temperature, and water content. The results indicate that methanol/oils ratio of 4, immobilized lipase/oils of 30 wt% and 40°C are suitable for waste oils under 1 atm. The irreversible inactivation of the lipase is presumed and a stepwise addition of methanol to reduce inactivation of immobilized lipases is proposed. Under the optimum conditions the yield of methyl esters is around 88–90%.

Development of a multicriteria assessment model for ranking biomass feedstock collection and transportation systems.

Abstract: This study details multicriteria assessment methodology that integrates economic, social, environmental, and technical factors in order to rank alternatives for biomass collection and transportation systems. Ranking of biomass collection systems is based on cost of delivered biomass, quality of biomass supplied, emissions during collection, energy input to the chain operations, and maturity of supply system technologies. The assessment methodology is used to evaluate alternatives for collecting 1.8 × 106 dry t/yr based on assumptions made on performance of various assemblies of biomass collection systems. A proposed collection option using loafer/stacker was shown to be the best option followed by ensiling and baling. Ranking of biomass transport systems is based on cost of biomass transport, emissions during transport, traffic congestion, and maturity of different technologies. At a capacity of 4 × 106 dry t/yr, rail transport was shown to be the best option, followed by truck transport and pipeline transport, respectively. These rankings depend highly on assumed maturity of technologies and scale of utilization. These may change if technologies such as loafing or ensiling (wet storage) methods are proved to be infeasible for large-scale collection systems.

Resveratrol-induced cell inhibition of growth and apoptosis in MCF7 human breast cancer cells are associated with modulation of phosphorylated Akt and caspase-9.

Abstract: Resveratrol (trans-3,4N,-5-trihydroxystilbene), a phytoalexin present in grapes and red wine, is emerging as a natural compound with potential anticancer properties. Here we show that resveratrol affects the growth of human breast cancer cell lines MCF7, MDA-MB-231, SK-BR-3, and Bcap-37 in a dose-dependent manner and that MCF7 is the most sensitive among the four cell lines. MCF7 cells treated with resveratrol showed typical characteristics of apoptosis including the poly (ADP-ribose) polymerase cleavage, TdT-mediated dUTP nick end labeling-positive staining, and morphologic changes. Phosphorylation of the oncogene product Akt was significantly reduced followed by decreased phosphorylation and increased processing of pro-caspase-9 on resveratrol treatment. These results indicate that resveratrol seems to exert its growth-inhibitory/apoptotic effect on the breast cancer cell line MCF7 via the Akt-caspase-9 pathway.

The BTL2 process of biomass utilization entrained-flow gasification of pyrolyzed biomass slurries.

Abstract: Forschungszentrum Karlsruhe has developed a concept for the utilization of cereal straw and other thin-walled biomass with high ash content. The concept consists of a regional step (drying, chopping, flash-pyrolysis, and mixing) and a central one (pressurized entrained-flow gasification, gas cleaning, synthesis of fuel, and production of byproducts). The purpose of the regional plant is to prepare the biomass by minimizing its volume and producing a stable and safe storage and transport form. In the central gasifier, the pyrolysis products are converted into syngas. The syngas is tar-free and can be used for Fischer-Tropsch synthesis after gas cleaning.

Simultaneous saccharification and fermentation of cassava bagasse for L-(+)-lactic Acid production using Lactobacilli.

Abstract: Saccharification and fermentation of cassava (Manihot esculenta) bagasse was carried out in a single step for the production of L-(+)-lactic acid by Lactobacillus casei and Lactobacillus delbrueckii. Using 15.5% w/v of cassava bagasse as the raw material, a maximum starch to lactic acid conversion of 96% was obtained with L. casei with a productivity rate of 1.40mg/mL·h and maximum yield of 83.8 mg/mL. It was 94% with L. delbrueckii with a productivity rate of 1.36 mg/mL·h. and maximum yeild of 81.9 mg/mL. Supplementation of bagasse with 0.01% w/v MnCl2 showed positive influence on the lactic acid production by L. casei.

Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates.

Abstract: Alkaline detoxification strongly improves the fermentability of diluteacid hydrolysates in the production of bioethanol from lignocellulose with Saccharomyces cerevisiae. New experiments were performed with NH4OH and NaOH to define optimal conditions for detoxification and make a comparison with Ca(OH)2 treatment feasible. As too harsh conditions lead to sugar degradation, the detoxification treatments were evaluated through the balanced ethanol yield, which takes both the ethanol production and the loss of fermentable sugars into account. The optimization treatments were performed as factorial experiments with 3-h duration and varying pH and temperature. Optimal conditions were found roughly in an area around pH 9.0/60°C for NH4OH treatment and in a narrow area stretching from pH 9.0/80°C to pH 12.0/30°C for NaOH treatment. By optimizing treatment with NH4OH, NaOH, and Ca(OH)2, it was possible to find conditions that resulted in a fermentability that was equal or better than that of a reference fermentation of a synthetic sugar solution without inhibitors, regardless of the type of alkali used. The considerable difference in the amount of precipitate generated after treatment with different types of alkali appears critical for industrial implementation.

Surface modification of neural probes with conducting polymer poly(hydroxymethylated-3,4- ethylenedioxythiophene) and its biocompatibility.

Abstract: A novel conducting polymer, poly(hydroxymethylated-3,4-ethylenedioxy-thiophene) (PEDOT-MeOH), was electrochemically deposited onto the electrodes of micromachined neural probes. Uniformly distributed film was obtained from aqueous solution when doped with polystyrenesulfonate. The surface morphology was rough and had good cellular adhesion. Impedance spectroscopy showed that the magnitude of coated electrode was lower than that of the bare gold over a range of frequencies from 100 to 105 Hz. Since the biocompatibility of the interface between the neural probes and brain tissue plays an important role when the probes are implanted in the central nervous system for long-term application, biomolecules were incorporated into the coating. Nonapeptide CDPGYIGSR was codeposited as the counterion in the conducting films. The surface morphology of the coating was fuzzy, providing many bioactive sites for interaction with neural cells. The magnitude of impedance was as low as 53 kω at the biologically relevant frequency of 1 kHz. An in vitro experiment demonstrated that the neuroblastoma cells grew preferentially on the PEDOT-MeOH/CDPGYIGSR-coated electrode sites and spread beyond the electrode area.

Comparative study of methods for extraction and purification of environmental DNA from soil and sludge samples.

Abstract: An important prerequisite for successful construction of a metagenome library is an efficient procedure for extracting DNA from environmental samples. We compared three indirect and four direct extraction methods, including a commercial kit, in terms of DNA yield, purity, and time requirement. A special focus was on methods that are appropriate for the extraction of environmental DNA (eDNA) from very limited sample sizes (0.1 g) to enable a highly parallel approach. Direct extraction procedures yielded on average 100-fold higher DNA amounts than indirect ones. A drawback of direct extraction was the small fragment sizeof approx 12 kb. The quality of the extracted DNA was evaluated by the ability of different restriction enzymes to digest the eDNA. Only the commercial kit and a direct extraction method using freeze-thaw cell lysis in combination with an in-gel patch electrophoresis with hydroxyapatite to remove humic acid substances yielded DNA, which was completely digested by all restriction enzymes. Moreover, only DNA extracted by these two procedures could be used as template for the amplification of fragments of several 16S rDNA, 18SrDNA groups under standard polymerase chain reaction conditions.

Enzyme catalyzed production of biodiesel from olive oil.

Abstract: Biodiesel (fatty acid methyl esters) was produced by transesterification of triglycerides (triolein) present in olive oil with methanol and Novozym435. The effect of the molar ratio of methanol to triolein, semibatch (stepwise addition of methanol) vs batch operation, enzyme activity, and reaction temperature on overall conversion was determined. Stepwise methanolysis with a 3:1 methanol to triolein molar ratio and an overall ratio of 8:1 gave the best results. The final conversion and yield of biodiesel were unaffected by initial enzyme concentrations greater than 500 U/mL olive oil. The optimum reaction temperature was 60 degrees C. Comparison of conversion data between a test-tube scale reactor and a 2-L batch reactor revealed that the difference in conversion was within 10%. Experiments were also carried out with used cooking oil; the conversion with used cooking oil was slightly lower but no major differences were observed. The efficacy of Novozym435 was determined by reusing the enzyme; although the enzyme's relative activity decreased with reuse, it still retained 95% of its activity after five batches and more than 70% after as many as eight batches.

Complete bioconversion of hemicellulosic sugars from agricultural residues into lactic acid by Lactobacillus pentosus.

Abstract: On the basis of previous knowledge, different agroindustrial wastes were submitted to dilute-acid hydrolysis with H2SO4 to obtain hemicellulosic sugars and then employed for lactic acid production by Lactobacillus pentosus. Toxic compounds released from lignin did not affect lactic acid fermentation when hydrolysates from trimming vine shoots, barley bran husks, or comcobs were employed as carbon source, and complete bioconversion of hemicellulosic sugars was achieved. Nevertheless, Eucalyptus globulus hydrolysates had to be submitted to a detoxification process with activated charcoal. Maximum lactic acid concentration (33 g/L) was reached employing barley bran hydrolysates, whereas corncobs, trimming vine shoots, and detoxified E. globulus hydrolysates yielded 26, 24, and 14.5 g/L of lactic acid, respectively. The maximum product yield from pentoses (0.76 g/g) was achieved using hydrolysates from trimming vine shoots, followed by hydrolysates from detoxified E. globulus (0.70 g/g), barley bran (0.57 g/g), and corncob (0.53 g/g). These results confirm that L. pentosus can be employed to ferment hemicellulosic sugars (mainly xylose, glucose, and arabinose) from acid hydrolysates of most agricultural residues without appreciable substrate inhibition.

Enzymatic production of xylooligosaccharides from corn stover and corn cobs treated with aqueous ammonia.

Abstract: A novel method of producing food-grade xylooligosaccharides from corn stover and corn cobs was investigated. The process starts with pretreatment of feedstock in aqueous ammonia, which results delignified and xylan-rich substrate. The pretreated substrates are subjected to enzymatic hydrolysis of xylan using endoxylanase for production of xylooligosaccharides. The conventional enzyme-based method involves extraction of xylan with a strong alkaline solution to form a liquid intermediate containing soluble xylan. This intermediate is heavily contaminated with various extraneous components. A costly purification step is therefore required before enzymatic hydrolysis. In the present method, xylan is obtained in solid form after pretreatment. Water-washing is all that is required for enzymatic hydrolysis of this material. The complex step of purifying soluble xylan from contaminant is essentially eliminated. Refining of xylooligosaccharides to food-grade is accomplished by charcoal adsorption followed by ethanol elution. Xylanlytic hydrolysis of the pretreated corn stover yielded glucan-rich residue that is easily digestible by cellulase enzyme. The digestibility of the residue reached 86% with enzyme loading of 10 filter paper units/g-glucan. As a feedstock for xylooligosaccharides production, corn cobs are superior to corn stover because of high xylan content and high packing density. The high packing density of corn cobs reduces water input and eventually raises the product concentration.

Enhanced secondary metabolite biosynthesis by elicitation in transformed plant root system: effect of abiotic elicitors.

Abstract: Plants generally produce secondary metabolites in nature as a defense mechanism against pathogenic and insect attack. In this study, we applied several abiotic elicitors in order to enhance growth and ginseng saponin biosynthesis in the hairy roots of Panax ginseng. Generally, elicitor treatments were found to inhibit the growth of the hairy roots, although simultaneously enhancing ginseng saponin biosynthesis. Tannic acid profoundly inhibited the hairy root growth during growth period. Also, ginseng saponin content was not significantly different from that of the control. The addition of selenium at inoculum time did not significantly affect ginseng saponin biosynthesis. However, when 0.5 mM selenium was added as an elicitor after 21 d of culture, ginseng saponin content and productivity increased to about 1.31 and 1.33 times control levels, respectively. Also, the addition of 20 microM NiSO4 resulted in an increase in ginseng saponin content and productivity, to about 1.20 and 1.23 times control levels, respectively, and also did not inhibit the growth of the roots. Sodium chloride treatment inhibited hairy root growth, except at a concentration of 0.3% (w/v). Increases in the amounts of synthesized ginseng saponin were observed at all concentrations of added sodium chloride. At 0.1% (w/v) sodium chloride, ginseng saponin content and productivity were increased to approx 1.15 and 1.13 times control values, respectively. These results suggest that processing time for the generation of ginseng saponin in a hairy root culture can be reduced via the application of an elicitor.

Evaluation of Cellulase Preparations for Hydrolysis of Hardwood Substrates

Abstract: Seven cellulase preparations from Penicillium and Trichoderma spp. were evaluated for their ability to hydrolyze the cellulose fraction of hardwoods (yellow poplar and red maple) pretreated by organosolv extraction, as well as model cellulosic substrates such as filter paper. There was no significant correlation among hydrolytic performance on pretreated hardwood, based on glucose release, and filter paper activity. However, performance on pretreated hardwood showed significant correlations to the levels of endogenous β-glucosidase and xylanase activities in the cellulase preparation. Accordingly, differences in performance were reduced or eliminated following supplementation with a crude β-glucosidase preparation containing both activities. These results complement a previous investigation using softwoods pretreated by either organosolv extraction or steam explosion. Cellulase preparations that performed best on hardwood also showed superior performance on the softwood substrates.

Ethanol production from pretreated olive tree wood and sunflower stalks by an SSF process.

Abstract: Olive tree wood and sunflower stalks are agricultural residues largely available at low cost in Mediterranean countries. As renewable lignocellulosic materials, their bioconversion may allow both obtaining a value-added product, for fuel ethanol, and facilitating their elimination. In this work, the ethanol production from olive tree wood and sunflower stalks by a simultaneous saccharification and fermentation (SSF) process is studied. As a pretreatment, steam explosion at different temperatures was applied. The water insoluble fractions of steam-pretreated sunflower stalks and steamed, delignified olive tree wood were used as substrates at 10% w/v concentration for an SSF process by a cellulolytic commercial complex and Saccharomyces cerevisiae. After 72-h fermentation, ethanol concentrations up to 30 g/L were obtained in delignified steam-pretreated olive tree wood at 230°C and 5 min. Sunflower stalks pretretated at 220°C and 5 min gave maximum ethanol concentrations of 21 g/L in SSF experiments.

Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol.

Abstract: Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H2SO4, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H2SO4. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H2SO4 and 220 degrees C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2 wt% H2SO4 at 190 degrees C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.