Green optimisation of microwave-assisted extraction of phenolic compounds from rice straw lignocellulosic residues and LC-HRMS-based cultivar profiling.

Rice straw was valorised as a source of antioxidant phenolic compounds. Microwave-assisted extraction (MAE) was optimised using a Box-Behnken design to assess the influence of temperature, ethanol concentration, solvent volume and extraction time on yield, total phenolic content (TPC) and antioxidant capacity. Temperature and time were the key factors. Optimal conditions (80 °C, 60% ethanol, 50 mL, 40 min) produced an 18.9% yield and 796 mg GAE/100 g DW, with high antioxidant activity (FRAP 32.3; ABTS 43.2 μmol TE/g DW). LC-ESI/LTQ-Orbitrap-HRMS/MS enabled detailed profiling of phenolic compounds, with 4-hydroxybenzoic acid and quercetin-3-glucoside as major contributors. The optimised workflow was applied to eleven cultivars harvested in 2019-2020, revealing cultivar- and year-dependent differences in phenolic fingerprints and antioxidant performance. Overall, the integrated MAE-Orbitrap approach efficiently produced phenolic-rich extracts and supported comparative cultivar profiling, although further evidence on stability, safety and regulatory aspects is needed for food-related applications.