Characterization of Phyllobilins in Hops: Antioxidant and Potentially Bitter Senescence-Related Metabolites

Hops is of high relevance to the food sector, and increasingly valued as medicinal plant. Its complex phytochemistry includes phenolic compounds and bitter prenylated polyketides, but phyllobilins─bioactive linear tetrapyrroles from chlorophyll catabolism─remain underexplored. In this work, several dioxobilin-type phylloleucobilins (DPleBs) and phylloxanthobilins (DPxBs) were identified in yellowish leaves of common hops (Humulus lupulus). Isolation from 107 g of leaves yielded 0.24 mg of Hl-DPleB-28 and 0.80 mg of Hl-DPxB-31. Structural elucidation via UV/vis, HR-MS², and NMR confirmed those as new phyllobilins, featuring an unusual hydroxylation motif, indicating an uncharacterized metabolic pathway. Hl-DPxB constituted about 40% of HPLC peak areas at 420 nm in yellow leaves, suggesting its significant role in the visual senescence of hops. Hl-DPxB-31 possessed high antioxidative activity, comparable to quercetin. A virtual tool predicted over 60% bitterness probability. These findings expand the phytochemical profile of hops and highlight potential for upcycling leaf waste.