Biomass, Volume 2, Issue 3 (September 2022) – 6 articles

Lignin is an abundant biopolymer, as well as cellulose and hemicellulose. Thus, this work aimed at isolating and characterizing the lignin from Eucalyptus spp. Sawdust—a lignocellulosic waste generated in large amounts in sawmills—to evaluate its antioxidant capacity. A biorefinery perspective was utilized: the biomass was fractionated using a sequential acid-alkaline treatment to recover the hemicellulosic carbohydrates, preserving the cellulose-rich solid fraction and isolating the lignin. The physicochemical characterization of isolated lignin was carried out using thermogravimetric (TGA), Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) analyses, while the antioxidant property was evaluated employing electron transfer and using DPPH and ABTS assays. After sequential acid-alkaline treatment, 68.15% of the hemicellulosic carbohydrates were recovered using mild acid treatment. The specific yield of lignin was 69.38%, and the remaining solid fraction contained 60.42% of cellulose. The antioxidant activity of lignin was evaluated using a DPPH radical test, and it showed an inhibition of 81.58% and IC₅₀ of 60 μg/mL. For the ABTS test, the inhibition was 99.86%, and the IC₅₀ was 7.39 µg/mL. Therefore, the lignin isolated from residual eucalyptus sawdust using sequential acid-alkaline treatment presented interesting antioxidant properties, which should be further investigated and evaluated for different applications. Full article

Plant cell walls are classified as primary and secondary walls. The primary wall is necessary for plant morphogenesis and supports cell growth and expansion. Once the growth and expansion ceases, specialized cells form secondary walls in order to give strength and rigidity to the plant. Secondary cell walls are the main constituent of woody biomass. This biomass is raw material for industrial products, food, and biomaterials. Recently, there are an increasing number of studies using biomass for biofuel production and this area has gained importance. However, there are still many unknowns regarding the synthesis and structure of complex polysaccharides forming biomass. Cellulose, being one of the main components of the cell wall, is synthesized at the plasma membrane by cellulose synthase complexes and does not require transportation. On the other hand, pectin and hemicelluloses are synthesized by enzymes located in the Golgi apparatus. Therefore, they need to be transported to the plasma membrane. Even though this transport mechanism is very important, it is one of the least understood parts of the endomembrane system. Xylan is the major hemicellulose in many biomasses and is important for renewable material production. There is limited knowledge about the cellular trafficking of xylan. In this review, we cover the current information and what we know about the vesicular transport of xylan to the cell wall. Full article

The catalytic depolymerization of alkali lignin into phenolic monomers was studied using subcritical water. In this study, subcritical water was used as the greener solvent with heterogeneous catalysts. The goal of this study was to screen for the best catalyst for the depolymerization, to optimize the reaction conditions, and to increase the yield of the phenolic monomers. The depolymerization reactions were performed at 200 and 240 °C for 5, 10, and 15 min, using subcritical water as the solvent with different catalysts. The treatment of the lignin sample with Ni-Graphene catalyst in subcritical water at 240 °C for 10 min resulted in the highest total yield of phenolic monomers, which was 41.16 ± 0.27 mg/g of alkali lignin. The catalysts also resulted the highest yield for each of the phenolic monomers guaiacol (G), vanillin (G), and homovanillic acid (G) compared to other catalysts studied. The optimized method proved to be an excellent approach to depolymerize alkali lignin. Full article

Noble metal-based materials are enormously used as a cathode material for electrocatalytic oxygen reduction reaction (ORR), which plays an important role in determining the performance of energy conversion and storage devices such as fuel cells, metal-air battery, and so on. The practicability of these energy devices is mainly related to the cost of the cathodic ORR electrocatalyst. Hence, a cost-effective and environmentally benign approach is highly demanding to design the electrocatalyst for ORR and replacing noble metal-based electrocatalyst. In this regard, biomass-derived hierarchically porous carbon-based materials have become attractive options compared to metal-based electrocatalysts due to their several advantages such as abundance in nature, economic viability, characteristic sustainability, environmental friendliness, and excellent physicochemical properties. Moreover, harsh chemicals are not being involved during their synthesis, and they intrinsically possess a variety of heteroatoms (N, P, S, etc.), which are key for augmenting the electrocatalytic activity. In the present review article, the recent progress on biomass-derived cathode electrocatalysts has been summarized for ORR including a brief account of bioresource selection, synthesis methods, and processing criteria that greatly influences the electrocatalytic activity. Full article

Due to the increased and excessive consumption of fossil fuels, sustainable alternative energy sources are badly needed to replace fossil fuels. The conversion of biomass into energy and value-added chemicals is one of the most promising potential pathways to solve this problem. Millions of tons of lignin, one of the major components of biomass, are produced annually as a byproduct of various industries, where it is treated as a low-value material. However, since it has an aromatic polymer nature, lignin is a proven source for different value-added products. Studies suggest that the selective cleavage of a specific bond of the complex lignin structure is one of the major challenges of converting lignin to a targeted product. In this study, eight different lignin depolymerization methods, both traditional and green, are reviewed. Acid and base catalytic depolymerization methods are straightforward, but due to their low selectivity and comparatively severe reaction conditions, they are expensive and not eco-friendly. Pyrolysis-based depolymerization comes with similar problems but has a higher conversion. In contrast, greener approaches, such as oxidative, microwave-assisted, super/sub-critical fluids (SCF), ionic liquid (IL), and deep eutectic solvent (DES)-based depolymerization techniques, have shown higher efficiency in terms of converting the lignin into phenolic compounds even under milder reaction conditions. SCF, IL, and DES-based approaches will likely become more popular in the future for their greener nature. Overall, depolymerization of lignin with greener technologies could make this process more economically viable and sustainable. Full article

Phycoremediation is an eco-friendly treatment for mining wastes. Copper at high concentrations is toxic for microalgae growth (bioremediation). Proteomics is a modern approach that can assist in elucidating, in detail, the highly complex metabolic mechanisms related to phycoremediation. Therefore, this study aimed to evaluate the effect of copper ions (Cu²⁺) on the metabolism of Chlorella protothecoides (UTEX 256), particularly the proteome changes. The WC culture medium supplemented with Cu²⁺ at 0.3, 0.6, and 0.9 mg/L showed a strict correlation to Cu²⁺ removal of 40, 33, and 36% of the initial content, respectively. In addition, Cu²⁺ concentrations did not affect microalgae growth—a very traditional approach to measuring toxicity. However, the proteomics data indicated that when compared to the control, reductions in protein levels were observed, and the 10 most scored proteins were related to the light-harvesting complex. Interestingly, C. protothecoides cultivated at 0.9 mg of Cu²⁺/L biosynthesized the protein Ycf3-interacting chloroplastic isoform X1 to respond to the photooxidative stress and the DNA-directed RNA polymerase III subunit RPC5 was related to the Cu²⁺ binding. Pre-mRNA-processing factor 19 and cytochrome c peroxidase proteins were observed only in the copper-containing treatments indicating the activation of antioxidant mechanisms by reactive oxygen species, which are potential environmental pollutant biomarkers. Full article