Sustainable valorization of urban fallen leaf waste via ultrasound-assisted recovery of phenolic-rich extracts: Comparative assessment of hardwood, softwood, and heterogeneous leaf biomass

초록

Despite containing high levels of functional polyphenols, fallen leaves are regarded as low-value waste in urban environments. We investigated ultrasound-assisted extraction as an approach for recovering functional polyphenolics from urban leaf biomass, with particular emphasis on biomass type. Hardwood fallen-leaf extract (HWLE), softwood fallen-leaf extract (SWLE), and heterogeneous fallen-leaf extract (HTLE) were evaluated in terms of polyphenolic recovery and functional performance. The effects of ethanol concentration (40–80%), ultrasonic amplitude (40–60%), and extraction time were initially screened based on extraction yield, followed by comparative evaluation of total polyphenol, tannin, and condensed tannin contents under selected representative conditions. The highest polyphenolic recovery among the evaluated conditions was achieved using 60% ethanol with 60% ultrasonic amplitude for 20 min. The HWLE extract exhibited the highest polyphenolic content, followed by the HTLE and SWLE extracts. However, HTLE retained substantial antioxidant and antibacterial activities despite its lower polyphenolic content relative to HWLE. Targeted LC–MS/MS analysis of HTLE identified ellagic and gallic acids as the most abundant among the quantified phenolic compounds, along with flavonols such as quercetin and kaempferol. Structural and thermal analyses further characterized the chemical heterogeneity and thermal behavior of the leaf-derived extracts. Importantly, these findings indicate that, under the conditions evaluated in this study, heterogeneous fallen-leaf biomass can retain substantial polyphenolic recovery and functional activity without prior separation into hardwood and softwood fractions. Overall, this study provides a comparative experimental basis for the potential valorization of heterogeneous urban fallen-leaf biomass as a source of functional polyphenolic compounds. © 2026 The Authors.

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