Sustainable valorization of pomelo peel using sequentially tailored deep eutectic solvents: A green approach to...

Pomelo peel, rich in limonene, cellulose, and lignin, holds significant potential for valorization. To overcome the limitations of conventional methods, an integrated biorefinery strategy was developed employing sequentially tailored deep eutectic solvents (DESs). Firstly, rational selection via COSMO-RS identified Menthol/Camphor as the optimal DES for limonene extraction, achieving a yield of 19.71 mg/g (94.38 % higher than n-hexane). The subsequent chemoenzymatic epoxidation of extracted limonene in choline chloride/urea hydrogen peroxide (ChCl/UHP) achieved an 88.26 % conversion rate under optimized conditions, which is comparable to conventional toluene, while more eco-friendly. Remarkably, the lipase retained 63.21 % of its initial activity after seven operational cycles. Molecular dynamics (MD) simulations elucidated that ChCl/UHP induced structural stabilization of the lipase through hydrogen-bonding interactions. For lignin separation, a ternary DES (TDES: ChCl/lactic acid/ethylene glycol, ChCl/LA/EG) effectively suppressed condensation reactions, yielding 87.15 % lignin with preserved β-O-4 linkages (83.31 % retention, 5.21-fold higher than typical acidic DES, such as ChCl/LA). The delignified residual biomass exhibited much enhanced enzymatic digestibility, achieving glucose and xylose productions that reached 2.26-fold and 2.55-fold that of raw pomelo peel, respectively. These improvements can be attributed to the destruction of lignocellulosic matrix and the removal of lignin. This strategy synergistically integrates DES-mediated extraction, enzymatic conversion, and lignin separation. The integrated process offers an environmentally benign approach to the cascade utilization of pomelo peel waste.