Valorization of pomegranate peel waste through pyrolysis-liquid-assisted ultrasound extraction: antioxidant, antibacterial and targeted phytochemical characterization

Background: Pomegranate (Punica granatum L.) peel is a phenolic-rich processing by-product, but its valorization commonly relies on conventional solvents. This study examined an integrated approach in which pomegranate peel pyrolysis liquid (PP-PL) was repurposed as the extraction medium for ultrasound-assisted extraction (UAE) of the same biomass. The methodological originality lies specifically in using biomass-derived PP-PL in UAE. Results: PP-PL-assisted extract (PP-E) and an aqueous control extract (AQ-E), prepared from the same peel batch under identical UAE conditions, were compared. The apparent gravimetric recovery of PP-E was 202.5 g kg−1. PP-E showed approximately two-fold higher total phenolic and flavonoid contents than AQ-E. In vitro agar well diffusion screening revealed the largest inhibition zone for PP-E against Staphylococcus aureus at 80 g L−1 (22.65 ± 1.50 mm), whereas AQ-E produced no detectable inhibition zones against the tested strains at the same concentration. PP-E achieved DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS+ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical-scavenging values of 92.42 ± 0.25% and 97.00 ± 0.17%, respectively, and showed pronounced total antioxidant capacity and iron(III) ion (Fe3+)- and copper(II) ion (Cu2+)-reducing capacities. Targeted liquid chromatography–tandem mass spectrometry (LC–MS/MS) using authentic standards quantified six phenolics, with ellagic acid as the predominant analyte (2015.10 mg kg−1 extract). Conclusion: Integration of pomegranate peel pyrolysis with PP-PL-assisted UAE generated an extract exhibiting in vitro antioxidant properties and antibacterial potential in agar well diffusion screening, providing an alternative route for pomegranate peel valorization. This strategy supports the further development of biomass-derived extraction media for recovering value-added compounds from agro-industrial residues.