Identifying biomolecular origins of solid organic residues preserved in Iron Age Pottery using DTMS and MVA

The chemical characterisation of solid organic residues found in ceramic vessels, can provide archaeologists with valuable information about ancient diets. Although several selective analytical techniques have been applied to the analysis of specific classes of compounds, such as extractable lipids, waxes, terpenoids and protein fragments, a non-selective analytical technique is required to characterise and categorise complete solid organic residues. In this study, Direct Temperature-resolved Mass Spectrometry (DTMS) is used for the characterisation of 34 solid residues situated on vessels recovered from an indigenous settlement from the Roman period at Uitgeest – Groot Dorregeest (The Netherlands). Sample preparation is limited to grinding very small samples (5–10 μg) and suspending them in water. DTMS analysis of aliquots (1–2 μL) of this suspension gave information about a broad range of organic compounds, such as lipids, polynuclear aromatic hydrocarbons, markers for residual proteins and polysaccharides, and for newly formed complex condensed polymers. Multivariate analysis of the DTMS spectra identified five different chemotypes: groups of residues with comparable chemical characteristics. The biomolecular origin of each of these chemotypes is identified by comparison with experimentally charred reference materials. The chemotypes A₁ and A₂ consist of charred residues identified as starch-rich foods (mixed with animal or plant products), chemotype C consists of protein-rich charred animal products without starch, chemotype B contains smoke condensates from wood fires, and chemotype D consists of special protein-rich and lipid-free foods or non-food products.