Organosolv lignin aggregation behaviour of soluble lignin extract from Miscanthus x giganteus at different ethanol concentrations and its influence on the lignin esterification

Background Lignin is the second most abundant naturally occurring biopolymer from lignocellulosic biomass. While there are several lignin applications, attempts to add value to lignin are hampered by its inherent complex and heterogenous chemical structure. This work assesses the organosolv lignin aggregates behaviour of soluble lignin extract derived from Miscanthus × giganteus using different ethanol concentrations (50%, 40%, 30%, 20%, 10% and 1%). The effect of two different lignin concentrations using similar ethanol concentration on the efficacy of esterification was studied. Results Overall, particle size of lignin analysis showed that the particle size of lignin aggregates decreased with lower ethanol concentrations. 50% ethanol concentration of soluble lignin extract showed the highest particle size of lignin (3001.8 nm), while 331.7 nm of lignin particle size was recorded at 1% ethanol concentration. Such findings of particle size correlated well with the morphology of the lignin macromolecules. The lignin aggregates appeared to be disaggregated from population of large aggregates to sub-population of small aggregates when the ethanol concentration was reduced. Light microscopy images analysis by ImageJ shows that the average diameter and circularity of the corresponding lignin macromolecules differs according to different ethanol concentrations. The dispersion of lignin aggregates at low ethanol concentration resulted in high availability of hydroxyl group in the soluble lignin extract. The efficacy of the lignin modification via esterification was evidenced directly via FTIR using the similar ethanol concentration of soluble lignin extract at different lignin concentrations. Conclusion This study provided the understanding of detail analysis on particle size determination, microscopic properties and structural insights of lignin aggregates at wider ethanol concentrations. The esterified lignin derived at 5 mg/mL is suggested to expand greater lignin functionality in the preparation of lignin bio-based materials.

Ultrasonic or Microwave Cascade Treatment of Medicinal Plant Waste

In this study, we present a strategy for valorizing lignocellulosic wastes (licorice root and willow bark) that result from industrial extraction of active principles using water as green solvent and aqueous NaOH solution. The wastes were submitted to severe ultrasound (US) and microwave (MW) treatments. The aim of these treatments was to extract the remaining active principles (using water as a solvent) or to prepare them for cellulose enzymatic hydrolysis to hexoses (performed in an NaOH aqueous solution). The content of glycyrrhizic acid and salicin derivatives in licorice root and willow bark wastes, respectively, were determined. The best results for licorice root were achieved by applying the US treatment for 5 min at 25 °C (26.6 mg glycyrrhizic acid/gDM); while, for willow bark, the best results were achieved by applying the MW treatment for 30 min at 120 °C (19.48 mg salicin/gDM). A degradation study of the targeted compounds was also performed and showed good stability of glycyrrhizic acid and salicin derivatives under US and MW treatments. The soluble lignin concentration prior to enzymatic hydrolysis, as well as the saccharide concentration of the hydrolyzed solution, were determined. As compared with the MW treatment, the US treatment resulted in saccharides concentrations that were 5% and 160% higher for licorice root and willow bark, respectively.

Polystyrene Sulfonate is Effective for Enhancing Biomass Enzymatic Saccharification Under Green Liquor Pretreatment in Bioenergy Poplar

Background: Water-soluble lignin (particularly lignosulfonate, LS) has been well documented for its significance on enzymatic saccharification of lignocellulose, though the promotion mechanism has not been fully understood. Much attention has been paid to natural lignin or its derivatives. The disadvantage of using natural lignin-based polymers as promoting agents lies in the difficulty in tailor-incorporating functional groups due to their complex 3D structures. To further improve our understanding on the promotion mechanism of water-soluble lignin in the bio-conversion of lignocellulose and to pursue better alternatives with different skeleton structures other than natural lignin, herein we reported a synthetic soluble linear aromatic polymer, sodium polystyrene sulfonate (PSS), to mimic LS for enhancing the efficiency of enzymatic saccharification. Results: The role of PSS played in enzymatic saccharification of pure cellulose and green liquor pretreated poplar (GL-P) was explored by analyzing substrate enzymatic digestibility (SED) under different addition dosages and various pH media, along with LS for comparison. At the cellulase loading of 13.3 FPU/g-glucan, the glucose yield of GL-P increased from 53% for the control to 81.5% with PSS addition of 0.1 g/g-substrate. It outperformed LS with the addition of 0.2 g/g-substrate by 6.3%. In the pH range from 4.5 to 6, PSS showed a positive effect on lignocellulose saccharification with the optimum pH at 4.8, where the most pronounced SED of GL-P was achieved. The underlying mechanism was unveiled by measuring zeta potential and using Quartz Crystal Microbalance (QCM) and Multi-parametric Surface Plasmon Resonance (MP-SPR). The results confirmed that the complexes of cellulase and PSS were conjugated and the negatively superchanged complexes reduced non-productive binding effectively along with the improved saccharification efficiency. The thickness of PSS required to block the binding sites of cellulase film was less than half of that of LS, and the PSS adlayer on cellulase film is also more hydrated and with a much lower shear modulus than LS adlayer. Conclusions: PSS as LS analogue is effective for enhancing the biomass enzymatic saccharification of GL-pretreated poplar. PSS exhibited a severer inhibition on the enzymatic saccharification of pure cellulose, whilst a more positive effect on bioconversion of lignocellulose (GL-P) than LS. In addition, a much lower dosage is required by PSS. The dynamic enzymatic hydrolysis indicated PSS could prolong the processive activity of cellulase. The valid data stemmed from QCM and SPR expressed that PSS bound to cellulases and the as-formed complexes reduced the nonproductive adsorption of cellulase onto substrate lignin more efficiently than LS due to its flexible skeleton and highly hydrated structure. Therefore, PSS is a promising alternative promoting agent for lignocellulose saccharification. From another perspective, the synthetic lignin mimics with controllable structures enable us to reach an in-depth understanding of the promotion mechanism of soluble lignins on enzymatic saccharification.

Screening coffee genotypes for Cercospora coffeicola resistance in Brazil

Several efforts have been made by many researchers worldwide to develop coffee plants resistant to different Cercospora species; however, studies concerning C. coffeicola , specifically, are still incipient. In the present study, a blend of strains from this pathogen was inoculated into 18 Brazilian commercial cultivars, a coffee clone of Arabica, as well as into 41 accessions from the Germplasm Collection of Minas Gerais, to evaluate the genetic resistance ability within the population and select superior genotypes for the breeding program. After predicting genotypic values of the evaluated material, the most efficient way to select genotypes based on the data of severity to brown eye spot (BES) was also examined. Moreover, the action of defense mechanisms against C. coffeicola attacks was investigated by assessing the levels of total soluble phenolic compounds and soluble lignin in contrasting genotypes regarding disease susceptibility. Based on the results, the accession MG 1207 Sumatra demonstrated an intrinsic genetic capacity to maintain low levels of severity to brown eye spot. This genotype can thus substantially contribute to the development of new cultivars, which may lead to reduced use of pesticides. This study also evidenced that four evaluations of severity is enough to reach accuracy and efficiency for the severity of BES, thus providing expressive genetic gains. Finally, it is suggested that the levels of lignin and phenolic compounds are not associated with the resistance of coffee genotypes to brown eye spot.

Improved procedure for electro-spinning and carbonisation of neat solvent-fractionated softwood Kraft lignin

In general, the electro-spinning of lignin requires it to be functionalised and/or blended with synthetic or natural polymers. This paper reports on the use of solvent fractionated lignin-lignin blend to electro-spin BioChoice softwood Kraft lignin. The blend consisted of acetone-soluble and ethanol-soluble lignin in a binary solvent of acetone and DMSO. Solvent fractionation was used to purify lignin where the ash content was reduced in the soluble lignin fractions from 1.24 to ~ 0.1%. The corresponding value after conventional acid-washing in sulphuric acid was 0.34%. A custom-made electro-spinning apparatus was used to produce the nano-fibres. Heat treatment procedures were developed for drying the electro-spun fibres prior to oxidation and carbonisation; this was done to prevent fibre fusion. The lignin fibres were oxidised at 250 °C, carbonised at 1000 °C, 1200 °C and 1500 °C. The cross-section of the fibres was circular and they were observed to be void-free. The longitudinal sections showed that the fibres were not fused. Thus, this procedure demonstrated that solvent fractionated lignin can be electro-spun without using plasticisers or polymer blends using common laboratory solvents and subsequently carbonised to produce carbon fibres with a circular cross-section.

A Putative Lignin Copper Oxidase from Trichoderma reesei

The ability of Trichoderma reesei, a fungus widely used for the commercial production of hemicellulases and cellulases, to grow and modify technical soda lignin was investigated. By quantifying fungal genomic DNA, T. reesei showed growth and sporulation in solid and liquid cultures containing lignin alone. The analysis of released soluble lignin and residual insoluble lignin was indicative of enzymatic oxidative conversion of phenolic lignin side chains and the modification of lignin structure by cleaving the β-O-4 linkages. The results also showed that polymerization reactions were taking place. A proteomic analysis conducted to investigate secreted proteins at days 3, 7, and 14 of growth revealed the presence of five auxiliary activity (AA) enzymes in the secretome: AA6, AA9, two AA3 enzymes), and the only copper radical oxidase encoded in the genome of T. reesei. This enzyme was heterologously produced and characterized, and its activity on lignin-derived molecules was investigated. Phylogenetic characterization demonstrated that this enzyme belonged to the AA5_1 family, which includes characterized glyoxal oxidases. However, the enzyme displayed overlapping physicochemical and catalytic properties across the AA5 family. The enzyme was remarkably stable at high pH and oxidized both, alcohols and aldehydes with preference to the alcohol group. It was also active on lignin-derived phenolic molecules as well as simple carbohydrates. HPSEC and LC-MS analyses on the reactions of the produced protein on lignin dimers (SS ββ, SS βO4 and GG β5) uncovered the polymerizing activity of this enzyme, which was accordingly named lignin copper oxidase (TrLOx). Polymers of up 10 units were formed by hydroxy group oxidation and radical formation. The activations of lignin molecules by TrLOx along with the co-secretion of this enzyme with reductases and FAD flavoproteins oxidoreductases during growth on lignin suggest a synergistic mechanism for lignin breakdown.

Polystyrene Sulfonate with Well-Defined Structure as Lignosulfonate Analogue for Promoting Lignocellulose Enzymatic Saccharification

Background: Water-soluble lignin (particularly lignosulfonate, LS) has been well documented for its positive impact on enzymatic saccharification for lignocellulose. Even though, the promotion mechanism of LS hasn’t been fully understood. All researches paid all attentions on the natural lignin or its derivatives. Whereas the structure of natural lignin is too complex and not easily to be tailored functional groups. To further our understanding on the promotion mechanism of water-soluble lignin to enzymatic saccharification for lignocellulose and also to pursue better alternatives with different skeleton structure other than natural lignin or its derivatives, therein we reported a synthetic soluble linear aromatic polymer- sodium polystyrene sulfonate (PSS) with well-defined structure to mimic LS for enhancing the enzymatic saccharification efficiency. Results: At the cellulase loading of 10 FPU/g-glucan, the glucose yield of green liquor pretreated poplar increased from 39.8% for the control to 60.3% with PSS addition of 0.1 g/g-substrate. It outperformed LS with addition of 0.2 g/g-substrate by 4.6%. The underlying mechanism was unveiled using Quartz Crystal Microbalance and the results confirmed that the as-formed complexes of cellulase-PSS, which effectively reduced non-productive binding and eventually improving the saccharification efficiency, were only half thickness and with much lower shear moduli than those of LS. Conclusions: The synthetic lignin mimics with controllable structures offer us more opportunities to understand the promotion mechanism of soluble lignins on lignocellulose enzymatic saccharification.

Assessment of rotary drum and aerated in-vessel for composting of garden waste

For in-vessel composting of garden waste, the selection of reactor is an important factor for efficient degradation. The present study evaluates working performance of rotary drum reactor (RDR) and aerated in-vessel (AIV) for composting of garden waste. 100 kg garden waste was mixed with 10 kg cow-dung slurry and 5 kg compost and feed into both the reactors for 45 days composting period. The reactors vary in their system configuration, shape and orientation, blade design, rate of aeration, odour control, leachate production and energy requirements. Rotary drum was rotated daily six times in clockwise and anti-clockwise direction and AIV was rotated daily for 3–5 minutes using motor. Rise in temperature started within 24 hours of composting and reached 65°C and 59°C on second day itself and thermophilic phase continued for 7 and 5 days for RDR and AIV respectively. Moisture content reduction after composting period was 15.25 and 18.45 %, C/N ratio was 16.14 and 13.33, TVS reduction was 23.74 and 29.78 % and CO2 evolution rate was 6.18 and 4.14 mg/g VS/day in RDR and AIV respectively. Reduction of hemicellulose, cellulose, and lignin was more in AIV. The percentage reduction of acid insoluble lignin was 36.10 and 29.01 % and the percentage reduction of acid soluble lignin was 48.85 and 43.3% in in AIV and RDR respectively after 45 days. AIV gave better performance for composting of garden waste.