Impact of ball milling on maize (Zea mays L.) stem structural components and on enzymatic hydrolysis of carbohydrates

The impact of ball milling on structural components of maize (Zea mays L.) stem was investigated in relation to enzymatic hydrolysis of carbohydrates. Ball milling of extractive-free maize stem material was carried out with different milling times up to 12 h. Carbohydrate conversion from ball-milled maize stem material with cellulolytic preparation Onozuka R-10 increased to 79% with increasing ball milling time up to 4 h, but did not thereafter increase further. Ball milling caused drastic depolymerization of hemicelluloses as revealed by increasing amounts of monosaccharides released in absence of enzymes. Infrared spectroscopy showed that cellulose crystallinity decreased within the first 6 h milling thereafter reaching a plateau. Thioacidolysis of solid residue fractions obtained after treatment of ball-milled samples with Onozuka R-10 suggested that no extensive degradation of lignin occurred during the milling. The effect of lignin structure on enzymatic hydrolysis of associated carbohydrates was further studied independently of cellulose crystallinity. Two lignin-carbohydrate fractions comprising hemicellulose and lignin with either high or low amount of aryl ether linkages were used as model materials. Lignins abundant in aryl ether linkages appeared more detrimental than condensed lignins to enzymatic hydrolysis of associated carbohydrates

Isolation of structurally distinct lignin–carbohydrate fractions from maize stem by sequential alkaline extractions and endoglucanase treatment

Sequential fractionation of extractive-free maize stems was carried out using two mild alkaline extractions (0.5 and 2 M NaOH, 20 'C, 24 h) before and after endoglucanase treatment. This procedure provided two lignin–carbohydrate fractions (LC1 and LC2) recovered after each alkali treatment. LC1 and LC2 contained 39% and 8% of the total lignin amount, respectively. These two fractions contained structurally distinct lignin molecules. While the content of resistant interunit bonds in lignin was 77% in LC1, it was increased up to 98% in LC2. Not unexpectedly, both alkali-soluble fractions contained substantial amount of p-coumaric and ferulic acids ether-linked to lignins. These results outline heterogeneity of maize stem lignins related to fractionation of grass materials

Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption

A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m2/g) than SGB or oat husk materials. Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available

Aqueous Ammonia Pre-treatment of Wheat Straw

Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to determine the effects of ammonia concentration, treatment time and temperature on compositional and physicochemical changes [utilizing elemental analysis, cationic dye adsorption, FTIR spectroscopy, size-exclusion chromatography (SEC), and P-31 nuclear magnetic resonance (NMR) spectroscopy] as well as enzymatic hydrolysability of straw. Pretreatment at the highest severity (20% NH3, 160 degrees C) led to the maximum hydrolysability of 71% in a 24 h reaction time at an enzyme dosage of 15 FPU/g of pretreated straw. In contrast, hydrolysabilitiac remained low regardless of the severity when a low cellulase dosage was used, indicating competitive adsorption of cellulaseson nitrogen-containing lignin. In turn, our results showed efficient adsorption of cationic, anionic and uncharged organic dyes on nitrogen-containing lignin, which opens new opportunities in practical water remediation applications.Peer reviewe

Aqueous Ammonia Pre-treatment of Wheat Straw

Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to determine the effects of ammonia concentration, treatment time and temperature on compositional and physicochemical changes [utilizing elemental analysis, cationic dye adsorption, FTIR spectroscopy, size-exclusion chromatography (SEC), and P-31 nuclear magnetic resonance (NMR) spectroscopy] as well as enzymatic hydrolysability of straw. Pretreatment at the highest severity (20% NH3, 160 degrees C) led to the maximum hydrolysability of 71% in a 24 h reaction time at an enzyme dosage of 15 FPU/g of pretreated straw. In contrast, hydrolysabilitiac remained low regardless of the severity when a low cellulase dosage was used, indicating competitive adsorption of cellulaseson nitrogen-containing lignin. In turn, our results showed efficient adsorption of cationic, anionic and uncharged organic dyes on nitrogen-containing lignin, which opens new opportunities in practical water remediation applications.Peer reviewe

Editorial

There is a paradigm shift going on in lignin utilization. High-volume materials and chemicals, as well as more engineered materials, like carbon fibers or active carriers, are currently being developed. However, in order to enhance lignin utilization in these and other value-added products, there is a need for better understanding of lignin function in woody tissues plus control over isolation, fractionation and other processing technology. Therefore, part of this issue is dedicated to articles about lignin. These range from lignin extraction to scale-up of the colloidal lignin particle production process. Focus is on fundamental understanding of interactions, a necessity for successful applications of this complex biopolymer.Non peer reviewe

Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives

Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content ≤20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally cross-linked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content ≥30% allowed both inter- and intraparticle cross-linking at >150 °C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).Peer reviewe

Fractionation process for the protective isolation of ergosterol and trehalose from microbial biomass

A new process is described for the two phase extraction of ergosterol and trehalose from microbial biomass. Baker's yeast was used as a model organism to develop the method, which was then applied for extracting 13 oleaginous microbes. Major findings of the study were that the ergosterol content was not dependent on intracellular oil content and that 1-butanol and alkaline pH were needed to protect ergosterol. Saponification for 3-4. h at 85-100. °C followed by extraction of the reaction mixture with toluene gave the maximal ergosterol yield. Trehalose was stable at this temperature and remained in water solution, but the maximal yield was obtained after a shorter reaction time at lower alkalinity. Although trehalose alone is stable at alkaline pH, extraction yields of trehalose from yeast decreased with increasing alkalinity. This finding led us to propose a two-step process in which trehalose is separated in the first step and ergosterol in the second. The possibility to apply this method to fractionate oleaginous microbes in process scale is discussed from technical viewpoints.Peer reviewe

Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption

Abstract A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m 2 /g) than SGB or oat husk materials. Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available.

Primary interactions of biomass components during fast pyrolysis

Fast pyrolysis is an industrially attractive method to produce fuels and chemicals from biomass; however, to gain better control over the process, the reactions and interactions between the components and decomposition products need elucidation. This study investigated primary reactions during fast pyrolysis of biomass. Pyrolysis of the three main biomass components (cellulose, hemicellulose and lignin) and their blends was carried out with a micro-pyrolyser connected to a Gas Chromatograph-Mass Spectrometer/Flame Ionisation Detector (GC–MS/FID). The blends of the individual components were prepared in similar proportions to that of native biomass (birchwood) and were pyrolysed at 600 °C for 2 s. The results showed that the two-component blends decrease the production of saccharides to a large extent. This was especially noticeable for levoglucosan when cellulose was mixed with either hemicellulose or lignin. Similarly, in the presence of cellulose, the formation of phenolic compounds from lignin was inhibited by 62 %. However, no differences were found in yields of the main products for the xylan-lignin blend compared to those from the individual components. The yields of volatile products from the cellulose-xylan blend were promoted for a majority of the product categories and were most pronounced for the aldehydes. Furthermore, while the formation of the phenols and saccharides was slightly inhibited for the three-component blend, the aldehydes, ketones and furans showed an increased production compared to the weighed sum of products expected, based on the pyrolysis of the individual components. The native biomass showed a similar trend as the three-component blend in all product categories except for the saccharides, which were inhibited to a large extent. This study provides a better understanding of the interactions occurring between different components during fast pyrolysis of biomass