Lignin, the earth’s second-most abundant biopolymer after cellulose, has long been relegated to low-value byproducts in the pulp and paper industry. However, recent advancements in valorization are transforming lignin into a sustainable and versatile feedstock for producing high-value biofuels, bioplastics, and specialty chemicals. This review explores the conversion of lignin’s complex structure, composed of syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, into value-added products. We critically assess various biochemical and analytical techniques employed for comprehensive lignin characterization. Additionally, we explore strategies for lignin upgrading and functionalization to enhance its suitability for advanced biomaterials. The review emphasizes key areas of lignin valorization, including catalytic depolymerization methods, along with the associated challenges and advancements. We discuss its potential as a feedstock for diverse products such as biofuels, bioplastics, carbon fibers, adhesives, and phenolic compounds. Furthermore, the review briefly explores lignin’s inherent properties as a UV protectant and antioxidant, alongside its potential for incorporation into polymer blends and composites. By presenting recent advancements and case studies from the literature, this review highlights the significant economic and environmental benefits of lignin valorization, including waste reduction, lower greenhouse gas emissions, and decreased reliance on non-renewable resources. Finally, we address future perspectives and challenges associated with achieving large-scale, techno-economically feasible, and environmentally sustainable lignin valorization.

Objectives: This study hypothesized that to analyse the anti-inflammatory effect of triterpenoid compound betulin in ovalbumin (OVA)-induced asthmatic mice. Methods: In this study, betulin was intraperitoneally administered in OVA-challenged and sensitized mice. The effect of betulin on inflammatory cells, lung function, reactive oxygen species (ROS) production, antioxidants status, oxidative stress markers, serum IgE level and inflammatory cytokines status in BALF was examined by enzyme-linked immunosorbent assay. The expression of tTG, TGF-β1, MMP-9 and TIMP-1 in lung tissue was scrutinized by RT-qPCR analysis, and the expression of TREM-1, p-IκB-α and NF-κBp65 proteins in lung tissue was examined by western blot analysis. Key findings: We found that the betulin treatment has effectively attenuated the proliferation of inflammatory cells, reduced the ROS generation, elevated the antioxidant enzymes and attenuated the level of oxidative markers in asthma induced mice. Moreover, reduced the level of serum IgE and pro-inflammatory cytokines, and increased the anti-inflammatory cytokine IFN-γ. Betulin treatment down-regulated the expression of MMP-9, tTG and TGF-β1 genes; moreover, betulin treatment effectively down-regulated the TREM-1, p-IκB-α and NF-κBp65 proteins level in lung. Conclusion: Betulin exhibited effective anti-asthmatic activity by attenuating the accumulation of inflammatory cells, expression of tTG, TGF-β1 and MMP-9 genes in lung tissue.

Lignin, an abundant and renewable aromatic biopolymer, represents a largely underutilized resource for the sustainable production of high-value chemicals. Among lignin-derived intermediates, protocatechuic acid (PCA) and catechol have emerged as key platform molecules due to their versatile applications in pharmaceuticals, polymers, and fine chemicals. This review provides a critical overview of microbial lignin valorization focusing on the microbial conversion of lignin-derived aromatics into PCA and catechol. It highlights recent advances in lignin depolymerization techniques, including thermochemical and biological approaches, and examines their influence on the generation of bioavailable aromatic feedstocks. We systematically discuss microbial biofunneling pathways that converge diverse lignin-derived compounds into PCA and catechol, emphasizing the role of central metabolic nodes and enzymatic transformations such as O-demethylation, hydroxylation, and decarboxylation. We treat protocatechuate decarboxylase (PCADC) as the central enzymatic bridge linking PCA and catechol. However, it should be noted that many reported microbial production strategies have been demonstrated using purified lignin-derived aromatic model compounds (e.g., ferulate, vanillate, p-coumarate, and PCA) rather than authentic lignin streams, highlighting the need for improved integration of lignin depolymerization and downstream bioconversion processes. Furthermore, the review explores state-of-the-art metabolic engineering strategies, including gene deletions, pathway rewiring, transporter engineering, and CRISPR-based regulation, to enhance product yields and selectivity. Despite significant progress, several challenges persist, including lignin recalcitrance, heterogeneity of depolymerization products, toxicity of intermediates, and limited enzyme efficiency. This review identifies key knowledge gaps and proposes future directions for integrating synthetic biology, adaptive evolution, and systems-level optimization to develop robust microbial cell factories. Overall, this work provides a strategic framework for advancing lignin bioconversion into PCA and catechol, contributing to the development of sustainable biorefineries and a circular bioeconomy.