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Abstract

This thesis presents a framework for converting agricultural residues into value-added aromatic compounds through an integrated waste-to-value process that combines chemical and biological upgrading. Oat and faba bean husks were selected as feedstocks for developing a sequential approach leading to vanillin and vanillylamine production. The study began with the optimisation of an ethanol–water organosolv pretreatment using a Box–Behnken design to maximise lignin recovery and purity. The optimum conditions, 156.8 °C with cellulose and lignin residence times of 6.0 h and 3.4 h, respectively, yielded distinct sulfur-free fractions suitable for downstream valorisation. To evaluate the oxidative conversion stage, lignin depolymerisation was first optimised using Kraft lignin as a model substrate under alkaline conditions with CuSO₄ and H₂O₂. Statistical modelling identified temperature, base concentration, and catalyst loading as key variables, and the optimised parameters of 115 °C, 1.5 M KOH, and 4 wt % CuSO₄ produced 0.348 mg mL⁻¹ of vanillin, establishing a reproducible process that will be adapted to organosolv lignin in future work. In parallel, a metagenomically derived ω-transaminase was expressed in E. coli to confirm its ability to convert vanillin to vanillylamine. Reactions using commercial vanillin and IPA as the amine donor showed consistent product formation, with retention times of 2.07–2.20 min and concentrations between 0.003 and 0.009 mg mL⁻¹, the highest yield obtained at 0.5 mMIPTG and 5 µL vanillin. Together, these studies establish each stage of the envisioned waste-to-value pathway i.e. from biomass fractionation and lignin oxidation to enzymatic amination, whilei dentifying key conditions for efficient conversion. The findings demonstrate the technical feasibility of integrating chemical and biocatalytic steps to produce renewable aromatics and set the groundwork for developing an end-to-end process that links agricultural waste streams to high-value chemical products such as vanillin and vanillylamine.