Organosolv processing of vine shoots: Fractionation and conversion of hemicellulosic sugars into platform chemicals by microwave irradiation.

Vine shoots were subjected to a mild aqueous extraction (to remove water-soluble extractives), and the extracted solids were reacted in catalyzed media (containing water and 1-butanol) to achieve the one-stage solubilization of lignin and hemicelluloses, yielding a cellulose-rich solid. Operating in a microwave-heated reactor under optimized conditions (190 °C in media containing 2% of catalyst and 52% 1-butanol), 67.8% lignin was dissolved, and solids containing 75% cellulose were obtained. Lignin was recovered from the reaction medium and characterized, whereas the hemicellulose-derived products present in the aqueous phase (obtained under conditions leading to maximum concentrations of 17.7 g pentoses/L) were converted into furfural at 64.6% molar yield by acidic processing in the presence of recycled 1-butanol.

Extracting value from Eucalyptus wood before kraft pulping: effects of hemicelluloses solubilization on pulp properties.

Eucalyptus globulus wood samples were subjected to autohydrolysis for extracting hemicelluloses, and the resulting solids were assayed as substrates for kraft pulping and further Totally Chlorine Free (TCF) bleaching. The susceptibility of treated solids to kraft processing was assessed under selected experiments covering the optimum experimental range. In order to establish a basis for comparison, samples of untreated wood were also subjected to kraft delignification. The best kraft pulps obtained from autohydrolyzed solids were subjected to an optimized TCF bleaching sequence involving double alkaline oxygen and pressurized H(2)O(2) processing, and characterized using standard methods. The suitability of the final product obtained by autohydrolysis-kraft delignification-TCF bleaching for specific purposes is discussed on the basis of the experimental results.

Production of oligosaccharides and sugars from rye straw: a kinetic approach.

Following the biorefinery philosophy, the non-isothermal autohydrolysis of rye straw (an agroindustrial byproduct) was carried out to obtain liquors containing substituted xylooligosaccharides and solids enriched in cellulose (suitable as substrates for further enzymatic hydrolysis). The effects of temperature (in the range 185-220 degrees C) on the composition of solids and liquid phases were evaluated, and kinetic models were developed. When operation was carried out at 208 degrees C, 69.2% of the initial xylan was converted into xylooligosaccharides, leading to reaction liquors containing up to 22.4 g oligosaccharides/L. The effects of treatments on the DP of the target products and on their substituents were also measured. At 208 degrees C, the percentages of XOS having DP2-4, DP5-6 and DP>6 were 24.8%, 22.4% and 54.8%, respectively. Under selected conditions, the molar ratio Xyl:Ac:UA of the oligomers was 10:1.54:0.50. Finally, when the solid was subjected to enzymatic hydrolysis, 70.6% of cellulose and 63.8% of xylan were saccharified after 48 h.

L-lactic acid production from apple pomace by sequential hydrolysis and fermentation.

The potential of apple pomace (a solid waste from cider and apple juice making factories) as a source of sugars and other compounds for fermentation was evaluated. The effect of the cellulase-to-solid ratio (CSR) and the liquor-to-solid ratio (LSR) on the kinetics of glucose and total monosaccharide generation was studied. Mathematical models suitable for reproducing and predicting the hydrolyzate composition were developed. When samples of apple pomace were subjected to enzymatic hydrolysis, the glucose and fructose present in the raw material as free monosaccharides were extracted at the beginning of the process. Using low cellulase and cellobiase charges (8.5 FPU/g-solid and 8.5 IU/g-solid, respectively), 79% of total glucan was saccharified after 12 h, leading to solutions containing up to 43.8 g monosaccharides/L (glucose, 22.8 g/L; fructose, 14.8 g/L; xylose+mannose+galactose, 2.5 g/L; arabinose+rhamnose, 2.8g/L). These results correspond to a monosaccharide/cellulase ratio of 0.06 g/FPU and to a volumetric productivity of 3.65 g of monosaccharides/L h. Liquors obtained under these conditions were used for fermentative lactic acid production with Lactobacillus rhamnosus CECT-288, leading to media containing up to 32.5 g/L of L-lactic acid after 6 h (volumetric productivity=5.41 g/L h, product yield=0.88 g/g).

Production of L-lactic acid and oligomeric compounds from apple pomace by simultaneous saccharification and fermentation: a response surface methodology assessment.

The potential of apple pomace for lactic acid production by simultaneous saccharification and fermentation (SSF) was evaluated. The effects of the cellulase to solid ratio (CSR), the liquor to solid ratio (LSR), and the beta-glucosidase to cellulase ratio (BCR) on the kinetics of lactic acid generation were assessed, and a set of mathematical models was developed to reproduce and predict the lactic acid concentration of fermentation broths. Operating at low cellulase and cellobiase charges (1 FPU/g and 0.25 IU/FPU, respectively) and short reaction times (10 h), SSF media containing 27.8 g of lactic acid/L were obtained with a volumetric productivity of 2.78 g/Lh. Material balances showed that the SSF processing of 100 kg of dry apple pomace results in the production of 36.6 kg of lactic acid, 18.3 kg of oligomeric carbohydrates (which can be used as ingredients for functional foods), 8.4 kg of microbial biomass, and 8 kg uronic acids.

Supplementation requirements of brewery's spent grain hydrolysate for biomass and xylitol production by Debaryomyces hansenii CCMI 941.

The effect of nutrient supplementation of brewery's spent grain (BSG) hydrolysates was evaluated with respect to biomass and xylitol production by Debaryomyces hansenii. For optimal biomass production, supplementation of full-strength BSG hydrolysates required only phosphate (0.5 g l(-1) KH(2)PO(4)), leading to a biomass yield and productivity of 0.60 g g(-1) monosaccharides and 0.55 g l(-1 )h(-1), respectively. Under the conditions studied, no metabolic products other than CO(2) and biomass were identified. For xylitol production, fourfold and sixfold concentrated hydrolysate-based media were used to assess the supplementation effects. The type of nutrient supplementation modulated the ratio of total polyols/total extracellular metabolites as well as the xylitol/arabitol ratio. While the former varied from 0.8 to 1, the xylitol/arabitol ratio reached a maximum value of 2.6 for yeast extract (YE)-supplemented hydrolysates. The increase in xylitol productivity and yield was related to the increase of the percentage of consumed xylose induced by supplementation. The best xylitol yield and productivity were found for YE supplementation corresponding to 0.55 g g(-1) and 0.36 g l(-1 )h(-1), respectively. In sixfold concentrated hydrolysates, providing that the hydrolysate was supplemented, the levels of xylitol produced were similar or higher than those for arabitol. Xylitol yield exhibited a further increase in the sixfold hydrolysate supplemented with trace elements, vitamins and minerals to 0.65 g g(-1), albeit the xylitol productivity was somewhat lower. The effect of using activated charcoal detoxification in non-supplemented versus supplemented sixfold hydrolysates was also studied. Detoxification did not improve polyols formation, suggesting that the hemicellulose-derived inhibitor levels present in concentrated BSG hydrolysates are well tolerated by D. hansenii.

Refining of autohydrolysis liquors for manufacturing xylooligosaccharides: evaluation of operational strategies.

When xylan-containing lignocellulosic materials are subjected to the action of heat in an aqueous medium (autohydrolysis reaction) under suitable operational conditions, the heterocyclic ether bonds of the polymeric chain are split to give xylooligosaccharides (XO) and a variety of other products derived from hemicelluloses, lignin and extractives. For product applications requiring high-purity XO, subsequent purification stages have to be implemented. Various strategies have been evaluated for refining Eucalyptus wood autohydrolysis liquors, including the two-stage reaction, precipitation and solvent extraction of freeze-dried, dewaxed liquors. Data on the degree of xylooligosaccharide recovery as well as on the composition of the isolates (measured in terms of hemicellulose-derived products and non-saccharide products) are provided for the various operational procedures assayed.

Production of oligosaccharides by autohydrolysis of brewery's spent grain.

Brewery's spent grain was treated with water in a process oriented towards the production of xylo-oligosaccharides (XOS). A wide range of temperatures and reaction times were tested and the effects of these operational variables on hemicellulose solubilization and reaction products were investigated. The maximal XOS yield (61% of the feedstock xylan) was obtained at 190 degrees C after 5 min of reaction. Several oligosaccharide mixtures with different molecular weight distributions were obtained depending on temperature and reaction time. Longer reaction times led to decreased oligosaccharide production and enhanced concentrations of monosaccharides, sugar decomposition products and acetic acid. With reaction times leading to the maximal yields of XOS, little decomposition into organic acids and aldehydes was found at all the temperatures assayed. From the composition of processed solids, it was calculated that 63-77% of the initial xylan was selectively solubilized in autohydrolysis treatments.

Recovery of lignin and furfural from acetic acid-water-HCl pulping liquors.

The feasibility of the HCl-water-acetic acid pulping technology (Acetosolv process) depends on the efficiency of solvent and byproduct recovery. Experimental data and computer simulation calculations are presented to assess these points. The recovery of precipitable, dissolved solids derived from lignin by mixing pulping liquors and water in various proportions was studied. Computer simulation of selected operational strategies enabling the recovery of furfural from the liquors obtained in the lignin-precipitation stage are also presented.

Recovery of lactic acid from simultaneous saccharification and fermentation media using anion exchange resins.

The physicochemical properties (capacity, kinetics and selectivity) of the ion exchange resins Amberlite IRA900, IRA400, IRA96 and IRA67 were determined to evaluate their comparative suitability for lactic acid recovery. Both the kinetics of lactic acid sorption from aqueous solutions and the equilibrium were assessed using mathematical models, which provided a close interpretation of the experimental results. The best resins (Amberlite IRA96 and IRA67) were employed in further fixed-bed operation using aqueous lactic acid solutions as feed. In this set of experiments, parameters such as capacity, regenerant consumption, percentage of lactic acid recovery and product concentration were measured. Amberlite IRA67, a weak base resin, was selected for lactic acid recovery from SSF (simultaneous saccharification and fermentation) broths. Owing to the presence of nutrients and ions other than lactate, a slightly decreased capacity was determined when using SSF media instead aqueous lactic acid solutions, but quantitative lactic acid recoveries at constant capacities were obtained in four sequential load/regeneration cycles.

Carboxymethylcellulose from totally chlorine-free-bleached milox pulps.

High purity cellulose pulp was obtained from Eucalyptus globulus wood by using an environmentally friendly delignification technique (Milox pulping) and subsequent bleaching by totally chlorine free technology. The pulp obtained under optimised experimental conditions was used for the manufacture of carboxymethylcellulose in a heterogeneous medium. By means of an experimental design, the effects of selected operational variables on the composition and chemical properties of reaction products from the carboxymethylation reaction were assessed for optimisation purposes. The distribution of the different carboxymethylglucose mole fractions (un-, mono-, di- and tri-substituted) was determined and compared with theoretical predictions. The maximum average degree of substitution (1.26) was determined at a NaOH/cellulose mole ratio of 4.8 and at a MCA/cellulose mole ratio of 2.0.

Manufacture of xylose-based fermentation media from corncobs by posthydrolysis of autohydrolysis liquors.

Milled corncob samples were mixed with water and heated to obtain a liquid phase containing oligosaccharides, sugars, and acetic acid as main reaction products (autohydrolysis reaction). To hydrolyze the sugar oligomers to the correspondent monomers, sulfuric acid was added to the autohydrolysis liquors to reach 0.5-2 wt% of solution, and the reaction media were heated at 101.5-135 degrees C. With this operational procedure, sugar solutions suitable as fermentation media (containing xylose as the major component) were obtained. The kinetics of the posthydrolysis step was characterized on the basis of experimental data concerning the time courses of the concentrations of xylooligosaccharides, xylose, furfural, and acetic acid. The concentrations of other reaction byproducts (glucose or arabinose) were also measured.

Resin selection and single-step production and recovery of lactic acid from pretreated wood.

Four ion-exchange resins (Amberlite IRA 900, IRA 400, IRA 96, and IRA 67) were employed for lactic acid recovery from simultaneous saccharification and fermentation (SSF) media. The best resins (Amberlite IRA 900 and IRA 400) were assayed for capacity, regenerant consumption, percentage of lactic acid recovery, and product concentration. Almost quantitative lactic acid recoveries at constant capacities were achieved in four sequential loading/regeneration cycles. A strong-base resin (Amberlite IRA 400) was selected for intermittent lactic acid separation in a typical SSF process, in which pretreated wood was saccharified by cellulases in the presence of Lactobacillus delbrueckii. The dynamics of lactic acid generation and lactic acid recovery were established.

Generation of xylose solutions from Eucalyptus globulus wood by autohydrolysis-posthydrolysis processes: posthydrolysis kinetics.

Eucalyptus wood samples were treated with water under selected operational conditions (autohydrolysis reaction) to obtain a liquid phase containing hemicellulose-decomposition products (mainly acetylated xylooligosaccharides, xylose and acetic acid). In a further acid-catalysed step (posthydrolysis reaction), xylooligosaccharides were converted into xylose, a carbon source for further fermentation. The kinetic pattern governing the posthydrolysis step was established by reacting xylooligosaccharide-containing liquors at 100.5 degrees C, 115 degrees C, 125 degrees C or 135 degrees C in media containing 0.5, 1.0, 1.5 or 2 wt% of catalyst (sulphuric acid). The time course of the concentrations of xylooligosaccharides, xylose, furfural and acetic acid were determined, and the results were interpreted by means of a kinetic model which allowed a close reproduction of the experimental data. Almost quantitative conversion of xylooligosaccharides into xylose was achieved under a variety of experimental conditions. The first-order, kinetic coefficient for xylooligosaccharide hydrolysis (k1, h(-1)) varied with both temperature (T, K) and molar sulphuric acid concentration (C) according to the equation In k1 = 36.66 + 1.00lnC - 108.0/(8.314T). The hydrolysis of acetyl groups followed a first-order kinetics. The corresponding kinetic coefficient (ka, h(-1) was correlated with the operational conditions by the equation Inka = 26.80+ 1.18 InC - 73.37/(8.314T).

Antioxidant and antimicrobial effects of extracts from hydrolysates of lignocellulosic materials.

The antioxidant and antimicrobial activities of ethyl acetate extracts obtained from acid hydrolysates of several lignocellulosic materials (Eucalyptus globulus wood, barley bran, corn cobs, and corn leaves) were evaluated. The minimum inhibitory and bactericide concentrations (MIC and MBC, respectively) were determined against a selection of bacteria and yeasts. Extracts from Eucalyptus wood hydrolysates were the most active for inhibiting bacteria and yeast growth, with MIC in the range of 10(2)--5 x 10(3) microg/mL and MBC in the range of 10(3)--0(5) microg/mL. Bacteriogenic and bacteriostatic activities of extracts from Eucalyptus wood and barley bran acid hydrolysates were slightly higher than those of corn cobs and leaves. Both the radical scavenging capacity and the inhibition of the beta-carotene bleaching caused by extracts were determined and compared with those of synthetic antioxidants. The antioxidant activity of extracts increased with their concentrations in the media, the stronger properties corresponding to those obtained from Eucalyptus wood hydrolysates.

Cogeneration of cellobiose and glucose from pretreated wood and bioconversion to lactic acid: a kinetic study.

Samples of Eucalyptus globulus wood were subjected to sequential treatments of delignification and swelling, and the solid residues were hydrolysed with a cellulase complex deficient in beta-glucosidase activity. In experiments carried out at 45 degrees C, the highest cellulose conversion (61.9%) was achieved in media containing 28 filter paper units/g using a liquor/solid ratio of 30 g/g. Models for the generation of cellobiose and glucose were developed assuming two sequential reactions (conversion of cellulose into cellobiose and hydrolysis of cellobiose to glucose) with end-product that results in competitive inhibition. Selected regression parameters were correlated with the operational conditions by means of empirical models (including linear and interaction terms) and a generalized calculation procedure that allows a close reproduction of data and shows a satisfactory ability for quantitative predictions was developed. Further experiments were carried out to study the bioconversion of hydrolysates by Lactobacillus delbrueckii into lactic acid. The kinetic modelling of the fermentation stage allowed a close interpretation of the experimental data.

Xylitol production from wood hydrolyzates by entrapped Debaryomyces hansenii and Candida guilliermondii cells.

Debaryomyces hansenii cells were entrapped in Ca-alginate beads and used for producing xylitol from wood hydrolyzates. Batch experiments showed that bioconversion was severely hindered when Ca-alginate beads were hardened with Al3+ solutions. As an alternative to Al3+ hardening, the improvements in both mechanical stability of bioparticles and fermenting ability of the immobilized system derived from using increased concentrations of sodium alginate were assessed. The best results were obtained using a 4% (w/v) Na-alginate solution in the gelification step. This concentration was selected to perform continuous fermentations in a packed-bed reactor using raw or charcoal-treated hydrolyzates (15.5 g of xylose/L) with two different yeasts: Candida guilliermondii and Debaryomyces hansenii. With a final cell concentration of about 50 g of cells/L (0.075 g of cells/g of beads), the volumetric productivities reached with these yeasts in media made from charcoal-treated hydrolyzates were 0.58 and 0.91 g/L.h, respectively.

Development of a generalized phenomenological model describing the kinetics of the enzymatic hydrolysis of NaOH-treated pine wood.

Pinus pinaster wood samples were treated during 3 h with alkaline solutions (containing 1, 5.5, or 10 weight percent NaOH) at 100, 115, or 130 degrees C using liquor/wood ratios of 6, 8, or 10 g/g. The solid residues obtained in treatments were used as substrates for enzymatic hydrolysis. In the hydrolysis assays, the reaction time (in the range 0-48 h) was considered as an operational variable. The cellulose conversion achieved at the end of assays were highest for samples pretreated at high temperature and high alkali concentration using low liquor/wood ratios. The experimental results obtained in each hydrolysis trial were fitted to an empirical model based on the assumption that the cellulose contained in substrates was composed by two fractions having different susceptibility to hydrolysis. The kinetic parameters obtained for the various experiments performed were correlated with the operational variables by means of empirical, statistically significant equations, which provided a generalized interpretation of the process.