Transformation of Onion Peel Waste Into Value‐Added Compounds via Sequential Biorefining

ABSTRACT Onion peel is a prominent agricultural byproduct generated worldwide, requiring effective waste‐management strategies while enabling the production of value‐added chemicals and materials. Onion peel contains various bioactive compounds, valuable extractives, and carbohydrate‐rich structural components. This work reports the sequential separation and value addition of the significant components of onion peel. A two‐stage extraction removed various extractives selectively by choosing appropriate solvent systems with controlled polarity. Initially, non‐polar lipophilic extractives were recovered by using n ‐heptane as a solvent. A binary solvent system consisting of water and biomass‐derived dimethyl isosorbide (DMI) in a 70:30 (v/v) ratio was found to be effective for extracting flavonoid‐rich compounds from onion peel. Acid hydrolysis transformed the extracted residue component into levulinic acid (LA), a prominent platform chemical. A 24.7 wt% maximum LA yield was obtained under optimized conditions (140°C, 4 h). The humin byproduct was preliminarily evaluated as an adsorbent for methylene blue removal from water. The present study demonstrates the potential of sequential biomass valorization approaches for improving the utilization of onion peel biomass.