Pretreatment-driven intensification of ultrasound-assisted extraction of phenolic compounds from microwave-dried pea haulm biomass

Pea haulm was valorized by integrating pretreatments with ultrasound-assisted extraction after microwave-assisted hot-air drying (200 W; 40 °C, 60 °C, 80 °C). Drying severity bleached color (lightness, 76.9 to 93.4) and decreased extractables: total phenolic content (TPC, 17.2 to 14.5 mg GAE/g dry matter (DM)), total flavonoid content (TFC, 8.1 to 6.6 mg CTE/g DM), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH, 115.7 to 109.0 μmol TE/g DM), and ferric reducing antioxidant power (FRAP, 69.1 to 58.7 μmol TE/g DM). At 40 °C, pretreatments intensified extraction: high pressure maximized TPC (21.4 mg GAE/g DM) and TFC (13.7 mg CTE/g DM) with higher DPPH (132.2 μmol TE/g DM); pulsed electric field yielded the highest FRAP (77.5 μmol TE/g DM). These results showed that gentle drying (200 W_40 °C) and high-pressure pretreatment enhance ultrasound-assisted extraction of phenolic compounds from pea haulm, offering potential for sustainable production of antioxidant-rich bio-ingredients. • 200W, 40°C drying best preserves color and extractable phenolics. • HP, PEF, homogenization pretreatments intensify UAE of pea haulm bioactives. • High pressure maximizes TPC/TFC and DPPH; PEF gives highest FRAP. • Pretreatments raise surface opening (HP>PEF>homogenization). • Higher drying temp shifts proteins from α-helix to β-sheet/coil.