The development of commercial production of ethanol from lignocellulosic materials has created the opportunity to increase the transformation of lignin streams into high-value applications. Finding applications for lignin valorization instead of combustion for energy production is essential to make biorefineries an element of sustainable development. Lignin is a complex aromatic polymer with unique characteristics. However, due to its molecular structure, lignin is an untapped resource in bioconversion technologies. Emerging strategies for lignin transformations focus on inorganic or organic catalysis or a combination of both. This thesis focuses on chemical and biological strategies to increase the value of lignin from sugarcane bagasse. Lignin obtained from alkaline treatment of steam-exploded sugarcane bagasse was submitted to an acidification process. The soluble fractions produced at different pH were comprehensively characterized, and in vitro antioxidant capacity against reactive oxygen and nitrogen species was evaluated. The soluble fraction obtained at pH 2 exhibited the highest scavenging capacities against all tested species (10.2 ± 0.7 mmol Trolox equivalent g−1 for ROO●, IC30 = 14.9 μ mL−1 for H2O2 and IC50 = 2.3 μ mL−1 for ONOO−) and the lowest polydispersity value (1.2). Biophysical data showed that the soluble fractions obtained at pH 4 and pH 2 consisted of small nanometer-sized discs with average radius and thickness of 0.31 nm made from low molecular weight polyphenolics (~400 Da). In the soluble fractions obtained at high pH larger lignin nanoparticles (average disk radius higher than 1.1 nm and disk thickness around 0.7 nm) and larger aggregates with fractal dimension of 2.8 nm were found. Phenolic and non-phenolic compounds, well-known as efficient antioxidants, were identified in all soluble fractions. The results provided, further demonstrates that acidification treatment is a promising strategy to upgrade heterogeneous lignin-enriched stream from sugarcane bagasse, such as preparations with homogeneous compositions and high antioxidant capacity. Furthermore, the potential of two fungal laccases together with a mediator to isolate low molecular weight lignin from lignocellulosic biomass was explored. These lignins were used as electron donors for activation of lytic polysaccharide monooxygenases (LPMOs). For cellulose hydrolysis a direct correlation between the low molecular weight lignin obtained with laccases and the activity of a cellulolytic cocktail containing LPMOs was found. Under the conditions tested, the co-incubation of laccases with LPMOs showed a substrate competition towards LPMOs inhibition by oxygen. Also laccase treatment may cause other modifications in presence of cellulose, rendering the material more recalcitrant for enzymatic saccharification. Finally, for the discovery of new enzymes for lignin deconstruction, the genome sequencing, annotation and secretome analysis of the marine-derived basidiomycete Peniophora sp. CBMAI 1063 grown under saline optimal conditions were performed. Omics studies showed that this fungus possesses a complete and versatile ligninolytic enzymatic spectrum, especially enzymes involved in lignin degradation. In addition, the major secreted laccase exhibited potential to lignocellulose bioconversion new technologies, promoting lignin modification, depolymerization and solubilization.