Unlocking lignin valorization and harnessing lignin-based raw materials for bio-manufacturing

Lignin, an energy-rich and adaptable polymer comprising phenylpropanoid monomers utilized by plants for structural reinforcement, water conveyance, and defense mechanisms, ranks as the planet's second most prevalent biopolymer, after cellulose. Despite its prevalence, lignin is frequently underused in the process of converting biomass into fuels and chemicals. Instead, it is commonly incinerated for industrial heat due to its intricate composition and resistance to decomposition, presenting obstacles for targeted valorization. In contrast to chemical catalysts, biological enzymes show promise not only in selectively converting lignin components but also in seamlessly integrating into cellular structures, offering biocatalysis as a potentially efficient pathway for lignin enhancement. This review comprehensively summarizes cutting-edge biostrategies, ligninolytic enzymes, metabolic pathways, and lignin-degrading strains or consortia involved in lignin degradation, while critically evaluating the underlying mechanisms. Metabolic and genetic engineering play crucial roles in redirecting lignin and its derivatives towards metabolic pathways like the tricarboxylic acid cycle, opening up novel avenues for its valorization. Recent advancements in lignin valorization are scrutinized, highlighting key challenges and promising solutions. Furthermore, the review underscores the importance of innovative approaches, such as leveraging digital systems and synthetic biology, to unlock the commercial potential of lignin-derived raw materials as sustainable feedstocks. Artificial intelligence-driven technologies offer promise in overcoming current challenges and driving widespread adoption of lignin valorization, presenting an alternative to sugar-based feedstocks for bio-based manufacturing in the future. The utilization of available lignin residue for synthesis of high-value chemicals or energy, even alternative food, addresses various crises looming in the food-energy-water nexus.