Researchers in the University of Oxford’s Department of Chemistry have re-investigating the molecular composition of a puzzling residue found in bronze jars excavated from a sixth century BCE Greek shrine in Paestum, to work out what it actually is.
The research is the first biomolecular evidence that the residue once contained honey, most likely in the form of honeycomb. The researchers hope this work will inspire further re-analysis of materials held in museum collections where sampling is limited and earlier tests proved inconclusive.
The shrine was originally discovered in 1954 with the bronze jars containing an orange-brown sticky substance. Archaeologists assumed the residue was honey but over 30 years, three different teams analysed the residue but couldn’t find honey and concluded that the jars contained some sort of animal or vegetable fat.
In the new study, the researchers used analytical techniques including mass spectrometry for proteins and small molecule compositional analysis, to determine its molecular makeup. This enabled the identification of sugars, organic acids, and royal jelly proteins that would have remained undetected using a single method.
Professor James McCullagh, Director of Oxford’s Mass Spectrometry Research Facility in the Department of Chemistry who co-led the project, said: "The application of multiple analytical techniques was key to the success of this study. By applying several mass spectrometry and spectroscopic approaches we were able to reveal a comprehensive picture of the residue’s molecular composition — enabling us to distinguish between contaminants, degradation products, and original biomarkers."
The team used X-ray photoelectron spectroscopy to analyse the surface of the residue and found copper corrosion products closely associated with it, said lead author Dr Luciana da Costa Carvalho, a postdoctoral researcher in the department. "Copper ions are naturally biocidal, and we believe their presence may have helped protect the sugar markers in this area from microbial decay." The study ‘A Symbol of Immortality: Evidence of Honey in Bronze Jars Found in a Paestum Shrine Dating to 530-510 BCE’ has been published in the Journal of the American Chemical Society.
The paper notes: "While the presence of other commodities, other bee products (e.g., propolis), plant oils, or milk, cannot be excluded from the original composition of the Paestum residue, our findings significantly expand the analytical toolkit available for investigating chemically complex archeological residues. By integrating TSP-GC/MS, AEC-MS, proteomics, and spectroscopy (FTIR and XPS), we have revealed the chemical complexity of the archeological residue and demonstrated the feasibility of detecting nonlipid biomarkers."
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