# Comparative 1H NMR Metabolomics Between Scandinavian Propolis and Australian Propolis: The Quest to Identify Radical Scavenging Compounds

## TL;DR

This study compares the chemical composition of propolis from Scandinavia and Australia using NMR to identify compounds with antioxidant properties.

## Contribution

The study introduces a method using 1H NMR metabolomics and multivariate modeling to link propolis composition to radical scavenging activity.

## Key findings

- Scandinavian propolis has higher aromatic compounds and more consistent metabolite composition compared to Australian propolis.
- Australian propolis is richer in carbohydrates and has higher wax content with more free fatty acids.
- Ferulic acid and p-coumaric acid are key phenolic compounds associated with radical scavenging activity.

## Abstract

Propolis from
Apis mellifera
and cerumen from
Tetragonula carbonaria
are complex mixtures of beeswax, plant resins, and bee secretions whose composition varies with geography and species. Understanding these differences is important for exploring their bioactive potential. This study employs untargeted quantitative 1H NMR metabolomics to characterize
A. mellifera
propolis from Scandinavia (Denmark and Norway) and Australia, as well as cerumen from
T. carbonaria
in Australia. Hydrophilic and hydrophobic extracts were analyzed to assess compositional differences across geographical origin and bee species, and to link specific metabolites to radical scavenging activity (RSA). Principal component analysis (PCA) of the 1H NMR spectra showed a marked separation between Scandinavian and Australian propolis. Hydrophilic extracts showed that Scandinavian propolis contains higher levels of aromatic compounds, whereas Australian propolis is richer in carbohydrates. In contrast, cerumen from
T. carbonaria
exhibits higher amounts of terpenoids. Hydrophobic extracts revealed that Australian propolis has the highest wax content, with shorter chains and more free fatty acids, while Scandinavian propolis samples display uniform wax structures and the highest aromatic content. Multivariate regression using recursive weighted partial least squares (rPLS) to RSA prediction highlighted signals attributable to ferulic acid and p‐coumaric acid, which were confirmed by statistical total correlation spectroscopy (STOCSY). These findings demonstrate the utility of quantitative 1H NMR metabolomics for distinguishing botanical and geographic chemotypes of propolis and cerumen. The findings further show that Scandinavian propolis is more consistent with respect to metabolite composition compared to Australian samples, presumably reflecting differences in resin sources for foraging.

Propolis from Scandinavia and Australia was chemically characterized using 1H NMR spectroscopy and multivariate modeling. Recursive partial least squares revealed spectral features associated with radical scavenging activity, and STOCSY enabled identification of the key phenolic compounds underlying these bioactive features.