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

## TL;DR

This study identifies new phyllobilins in hops leaves, which may contribute to their antioxidant and bitter properties, offering potential for waste upcycling.

## Contribution

The discovery of new phyllobilins in hops with unique hydroxylation and potential bitterness expands their phytochemical profile.

## Key findings

- Hl-DPleB-28 and Hl-DPxB-31 were isolated and confirmed as new phyllobilins in hops.
- Hl-DPxB-31 showed high antioxidant activity comparable to quercetin.
- Hl-DPxB constitutes about 40% of HPLC peak areas in yellow leaves, indicating a role in visual senescence.

## Abstract

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.