Synergistic CCD-ANN optimization of organosolv–DES biphasic delignification for high-yield lignin isolation from banana inflorescence bract

The efficient fractionation of lignocellulosic biomass into its primary constituents (cellulose, hemicellulose, and lignin) is pivotal for the advancement of sustainable biorefineries. In this study, banana inflorescence bract (BIB), an underutilized agro-waste was explored as a potential feedstock through an integrated pretreatment strategy. The process combined organosolv pretreatment with a subsequent deep eutectic solvent (DES)-based post-delignification step to enhance delignification and improve cellulose accessibility. Initially, the organosolv process parameters were optimized using a one-variable-at-a-time (OVAT) approach and further refined through central composite design (CCD)-based response surface methodology (RSM) and an artificial neural network integrated with a genetic algorithm (ANN-GA). The optimized ANN-GA model predicted and achieved a delignification of 64.77 ± 0.32 % (w/w) under the conditions of 1:12 (w/v) solid-to-liquid ratio at 75 °C for 120 min. To recover residual lignin, DES-based post-delignification treatment was conducted. The lignin fractions extracted from both organosolv and DES liquors were characterized using FT-IR, ¹H NMR spectroscopy, particle size analysis, and antioxidant activity assays. Furthermore, enzymatic saccharification of the pretreated biomass yielded 41.95 ± 0.10 % (w/w) and 57.97 ± 0.21 % (w/w) of fermentable sugars from organosolv-treated and DES-treated solid residues respectively, indicating improved cellulose digestibility. In addition, the solvents used in this study were recycled and reused for three successive treatment cycles, achieving a recovery of 85 % for ethanol and 83.33 % for DES that could enhance the environmental and economic feasibility of the process. Hence, this study underscores the potential of BIB as a viable, sustainable feedstock for biocatalytic applications and lignin valorization in modern biorefineries.