Ultrasound-assisted extraction of bioactive phenolic compounds from walnut green husk: Phytochemical characterization and multi-endpoint Caenorhabditis elegans bioactivity screening for food-relevant applications.

This study optimized phenolic extraction from walnut green husk (Juglans regia L.) and established a screening framework for evaluating bioactivity of agricultural byproduct extracts toward food ingredient development. Indirect ultrasound-assisted extraction with 80% ethanol yielded maximum phenolic content (477 mg/100 g fresh weight), 8.7-fold higher than water extraction. Principal component analysis confirmed solvent polarity as the primary factor in extraction selectivity. HPLC-DAD-MS identified thirteen compounds dominated by naphthoquinones (31%) and tetralones (24%). Caenorhabditis elegans whole-organism screening demonstrated significant bioactivities: oxidative stress resistance, thermal tolerance, proteotoxicity alleviation, and metabolic modulation. This approach supports the use of C. elegans screening as a rapid bioassay for evaluating bioactivity of agricultural byproduct extracts, with scalable extraction methodology (food-grade solvent, ambient temperature, 10 min) suitable for industrial valorisation.