Effects of synergistic fungal pretreatment on structure and thermal properties of lignin from corncob (2023)

Lignin bioconversion into polyhydroxybutyrate (PHB) has emerged as a promising valorization, however, it is suffering from inadequate conversion efficiency. Herein, an efficient strategy for addressing this challenge by employing an alkali-halophilic strain Halomonas alkalicola M2 is developed. Up to 58.5% of lignin is degraded when incubates in the non-sterilized lignin (NSL) medium under a glucose concentration of 1.055g/L, peptone concentration of 0.596g/L, and incubation time of 6.89 d, demonstrating enhanced proficiency compared to thermally sterilized lignin (TSL) method due to the improved cell growth, lignin-degrading enzyme activities, and secreted protein contents. Consequently, PHB production demonstrates a 50% increase using NSL method compared to TSL method. A separate route of enzymatic hydrolysis and fermentation (SHF) is proposed to further improve the PHB production, resulting in a record yield of PHB which is 1.89g/L. This work creatively develops a non-sterilization strategy to improve PHB production from lignin, showing great potential for promoting biological lignin valorization.

The natural biopolymers hold substantial prospects as food packaging materials due to the integrated advantages of excellent film-forming properties, biodegradability and appropriate mechanical properties. However, it remains a challenge to simultaneously endow antimicrobial, UV-shielding, water vapor and oxygen barrier properties of films. Herein, sustainable and multifunctional films were fabricated by constructing ε-polylysine (ε-PL) antimicrobial surface on the phenolated lignin/cellulose films (RCPL30). It is found that the fine control of electrostatic interactions and hydrogen bonding in anionic phenolated lignin/cellulose and cationic ε-PL is efficient for tailoring the structure and films performance. The addition of ε-PL effectively enhanced the antibacterial property, hydrophobicity, water vapor and oxygen barrier ability of the phenolated lignin/cellulose films. Antibacterial cellulose-lignin films with a high lignin content (30%) were developed. In particular, the bactericidal rate reached almost 100% when the ε-PL concentration was 3% (LRCPL30-3). The water vapor permeability and oxygen permeability of LRCPL30-3 were as low as (3.21±0.06)×10⁻¹¹gm⁻¹ s⁻¹ Pa⁻¹, (4.15±0.13)×10⁻¹⁶cm³cm/cm² s Pa, respectively. Moreover, the phenolated lignin provided an exceptional UV shielding properties (100% for UVB and 99.91% for UVA for LRCPL30-3 sample) with high thermal stability and antioxidant activities. More importantly, the as prepared LRCPL30-3 still showed high tensile strength (75.90MPa). Based on these outstanding properties, LRCPL30-3 were used for shrimp package, which effectively extended shelf-life. Overall, the study highlights the benefits of biopolymers valorization and provides evidence of potential applicability of sustainable films (specially LRCPL30-3) as candidates for active food packaging.

The grave concerns arisen as a result of environmental pollution and diminishing fossil fuel reserves in the 21st century have shifted the focus on the use of sustainable and environment friendly alternative resources. Lignocellulosic biomass constituted by cellulose, hemicellulose and lignin is an abundantly available natural bioresource. Lignin, a natural biopolymer has over the years gained much importance as a high value material with commercial importance. The present review provides an in-depth knowledge on the journey of lignin from being considered a roadblock to a bridge connecting diverse industries with widescale applications. The successful valorization of lignin for the production of bio-based platform chemicals and fuels has been the subject of intensive investigation. A deeper understanding of lignin characteristics and factors governing the biomass conversion into valuable products can support improved biomass consumption. The components of lignocellulosic biomass might be totally transformed into a variety of value-added products with the improvements in bioprocess techniques that valorize lignin. In this review, the recent advances in the lignin extraction and depolymerization methods that may help in achieving the cost-economics of the bioprocess are summarized and compared. The industrial potential of lignin-derived products such as aromatics, biopolymers, biofuels and agrochemicals are also outlined. Additionally, assessment of the recent research trends in lignin valorization into value-added chemicals has been done and present scenario of technological-industrial applications of lignin with economic perspectives is highlighted.

As sustainability gains increasing importance in addition to cost-effectiveness as a criterion for evaluating engineering systems and practices, biological processes for lignocellulose pretreatment have attracted growing attention. Biological systems such as white and brown rot fungi and wood-consuming insects offer fascinating examples of processes and systems built by nature to effectively deconstruct plant cell walls under environmentally benign and energy-conservative environments. Research in the last decade has resulted in new knowledge that advanced the understanding of these systems, provided additional insights into these systems' functional mechanisms, and demonstrated various applications of these processes. The new knowledge and insights enable the adoption of a nature-inspired strategy aiming at developing technologies that are informed by the biological systems but superior to them by overcoming the inherent weakness of the natural systems. This review discusses the nature-inspired perspective and summarizes related advancements, including the evolution from biological systems to nature-inspired processes, the features of biological pretreatment mechanisms, the development of nature-inspired pretreatment processes, and future perspective. This work aims to highlight a different strategy in the research and development of novel lignocellulose pretreatment processes and offer some food for thought.

Bioconversion lignocellulosic biomass (LCB) to 2,3-butanediol (2,3-BDO) is a sustainable and energy-intensive practice, but its economic feasibility has been hindered by costly pretreatment and the cumbersome fermentation process. Herein, a lignocellulolytic strain Klebsiella pneumoniae PX14 is isolated from insect gut, showing effective degradation on unpretreated LCB with rates of 51.48% for cellulose, 62.13% for hemicellulose, and 41.42% for lignin, while with a low 2,3-BDO titer of 3.26g/L. Consequently, the secretory proteins of PX14 cultured on the bamboo biomass-containing medium are extracted for the construction of an enzyme cocktail with commercial cellulase. The designed enzyme cocktail achieves efficient saccharification of the unpretreated LCB, resulting in 42.90g/L reducing sugars released, which is significantly higher than that from the secretory protein or cellulase only. These high sugars titer is also effective conversion to 2,3-BDO of 19.11g/L titer by PX14 after further optimization. For the first time, the enzyme cocktail is tried for application in simultaneous saccharification and fermentation (SSF) of 2,3-BDO from unpretreated LCB. This fed-batch SSF resulted in 47.46g/L of 2,3-BDO with 0.36g/L/h productivity under high solid loading of 20% due to the high substrate concentration tolerance of PX14. Finally, whole-genome sequencing reveals the robustness of K. pneumoniae PX14 and its molecular mechanism for such a process. These results provide a robustness strain of K. pneumoniae PX14 and its novel application in SSF of 2,3-BDO from unpretreated LCB, showing a great breakthrough in this process.

The environmental problems caused by the use of fossil fuels have increased the worldwide need for biomass use. Fungal technology provides a gentle, environmentally friendly, low-cost solution for biomass conversion and is widely used in the production of chemicals and biofuels because of its advantages in lignin degradation, saccharification, fermentation, and lipid accumulation. The causes and consequences of using fungal technology in biomass conversion must be determined, to help us to understand the proper application of fungal technologies in biomass conversion. For this purpose, we reviewed the fungal types involved in biomass conversion, the advantages and limitations of fungal technology, and strategies for improvement. We systematically reviewed the advances in how these advantages and improvement strategies can be effectively combined in the conversion of biomass into value-added products, such as alcohols, gas fuel, biodiesel, organic acids, spices, medicines, compost, and feed. The future directions based on fungi technology have also prospected. It is certain that strain screening, parameter optimization, coupling processes, and the introduction of genetic engineering throughout the application of fungal technology in biomass conversion. Fungal technology deserves more attention and further exploration as a promising sustainable biomass utilization strategy.

Bioresource Technology, Volume 272, 2019, pp. 99-104

A novel pretreatment strategy based on combination of microwave and ionic liquid [TBA][OH] was developed for enhancing enzymatic hydrolysis of Eucalyptus sawdust. The sugar yield of pretreated sample achieved 410.67 mg/g in 48 h, which suffered from optimized microwave-assisted [TBA][OH] pretreatment. The work mechanism was illuminated by chemical composition, Fourier transform infrared spectroscopy (FTIR), ¹³C cross polarization/magic-angle spinning solid state NMR (¹³C solid NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The combined effect of microwave and [TBA][OH] leads to the violent deconstruction of lignin, removal of hemicelluloses, destruction of crystalline region and an eroded, pored and irregular micro-morphology. As a green, relatively inexpensive and high efficient pretreatment, microwave-assisted [TBA][OH] pretreatment has great potential in the field of bio-refinery.

Bioresource Technology, Volume 205, 2016, pp. 159-165

In this work, corncob samples at different scales, i.e., plant scale (>1mm), tissue scale (500–100μm) and cellular scale (50–30μm), were produced to investigate the impact and mechanisms of different mechanical fragmentations on microstructure features and enzymatic hydrolysis. The results showed that the microstructure features and enzymatic hydrolysis of corncob samples, either at a plant scale or tissue scale, did not change significantly. Conversely, corncob samples at a cellular scale exhibited some special properties, i.e., an increase in the special surface area with the inner mesopores and macropores exposed to the surface; breakage of crystalline cellulose and linkages in polysaccharides; and a higher proportion of polysaccharides on the surface, which significantly enhanced enzymatic digestibility resulting in a 98.3% conversion yield of cellulose to glucose which is the highest conversion ever reported. In conclusion, mechanical fragmentation at the cellular scale is an effective pretreatment for corncob.

International Journal of Biological Macromolecules, Volume 130, 2019, pp. 947-957

This study reports on the effects of unmodified autohydrolyzed ethanol organosolv lignin (AH EOL) and modified autohydrolyzed ethanol organosolv lignin on the structural characteristics and antioxidant properties upon incorporation of p-hydroxyacetophenone (AHP EOL). The lignin samples isolated from black liquor of oil palm fronds (OPF) were evaluated and compared using various complementary analyses; FTIR, ¹H and ¹³C NMR spectroscopy, 2D-NMR spectroscopy (HMBC and HSQC), CHN, GPC, HPLC and thermal analyses (TGA and DSC). Chemically modified organosolv lignin (AHP EOL) provided lignin with lower molecular weight (M_w), which has smaller fragments that leads to higher solubility rate in water in comparison to unmodified organosolv lignin, AH EOL (D_{AHP EOL}: 19.8% > D_{AH EOL}: 14.0%). It was evident that the antioxidant properties of modified organosolv lignin has better reducing power in comparison to the unmodified organosolv lignin. Therefore, the functionalization of lignin polymers enhanced their antioxidant properties and structural features towards a various alternative approach in lignin-based applications.

Energy Conversion and Management, Volume 199, 2019, Article 111928

Lignin is the second-most abundant biopolymer on the Earth and it is hard to valorize without pretreatment due to its inherent heterogeneity and recalcitrance. Nowadays, it is necessary to develop effective innovative methods for lignin degradation and efficient utilization. In the present study, the lignolytic bacterium Mycobacterium smegmatis LZ-K2 was isolated from rotten wood. The isolate showed high lipid production and high efficiency of lignin degradation. The lipid production of LZ-K2 grown in corn straw medium with alkali pretreatment, acid pretreatment, and without chemical pretreatment were 0.083 g/L, 0.069 g/L, and 0.072 g/L, respectively. Fatty acids (C14-C24), especially palmitic acid (C16:0; 38.9%), were also accumulated in the untreated corn straw cultures. Results confirmed that the enzyme system and Fenton reaction are the major pathways for lignin depolymerization. In addition, the presence of a critical lignin-degrading enzymes, other than cellulase and hemicellulase, was revealed by the genome analysis. Moreover, the proteome of LZ-K2 showed enzymes, mainly glucose-methanol-choline (GMC) oxidoreductases, which are involved in the Fenton reaction and β-ketoadipate pathway. Unique enzymes of oleaginous microorganisms, such as acetyl CoA carboxylase, were also identified in LZ-K2. In conclusion, the present work provides a sustainable approach for efficient conversion of lignin into biodiesel with simultaneous biological pretreatment of lignocelluloses.

International Journal of Biological Macromolecules, Volume 126, 2019, pp. 376-384

Isolation of earth abundant biopolymer, Lignin, from Dendrocalamus sinicus and their structural properties were investigated to achieve its large-scale practical applications in value-added products. Two lignin fractions (MWL, DSL) were isolated with successive treatments of dioxane and dimethylsulfoxide (DMSO) from dewaxed and ball milled bamboo (D. sinicus) sample. The two-step treatments yielded 52.1% lignin based on the total lignin content in the dewaxed bamboo sample. Spectroscopy analyses indicated that the isolated bamboo lignin was a typical grass lignin, consisting of p-hydroxyphenyl, guaiacyl, and syringyl units. The major interunit linkages presented in the obtained bamboo lignin were β-O-4′ aryl ether linkages, together with lower amounts of β-β', β-5′, and β-1′ linkages. The tricin was detected to be linked to lignin polymer through the β-O-4′ linkage in the bamboo. In addition, phenyl glycoside and benzyl ether lignin-carbohydrate complexes (LCC) linkages were clearly detected in bamboo (D. sinicus), whereas the γ-ester LCC linkages were ambiguous due to the overlapping NMR signals with other substructures. The detailed structural properties of the obtained lignin fraction together with the light-weight will benefit efficient utilization of natural polymers as a possibly large-scale bio-based precursor for making polymeric materials, biochemicals, functional carbon and biofuels, and multifunctional polymer nanocomposites.

Bioresource Technology, Volume 312, 2020, Article 123512

Five white-rot fungi Pleurotus ostreatus, Lentinus edodes, Hericium erinaceus, Pleurotus eryngii and Flammulina filiformis were studied (solid-state incubation and in vitro gas production) to determine lignin degradation and optimal duration of fermentation of corn straw. All fungi significantly decreased lignin, with optimal reductions after 28 d. Although cellulose also decreased, L. edodes and P. eryngii minimized these losses. In intro dry matter digestibility, total volatile fatty acid concentration and total gas production of fermented corn straw decreased (P<0.001) as fermentation was prolonged, with improved rumen fermentability for all fungal treatments except F. filiformis. Total gas production in L. edodes did not decrease but peaked on day 28, whereas F. filiformis reduced methane emission. In conclusion, fermentation of corn straw with P. eryngii or L. edodes for 28d degraded lignin and improved nutritional value as ruminant feed.