Long-lasting ergot lipids as new biomarkers for assessing the presence of cereals and cereal products in archaeological vessels

Jeannette J Lucejko,Maria Perla Colombini,Claudio Filippo Mangiaracina,Francesca Porta,Alessandro Vanzetti,Giuseppa Tanda,Alessandro Corretti,Erika Ribechini,Jacopo La Nasa

doi:10.1038/s41598-018-22140-z

Abstract

Cereals were very important in ancient diets, however evidence from archaeological sites of the vessels used for processing or storing cereals is comparatively rare. Micro-organisms, as well as chemical-physical effects can easily degrade cereals during the burial period. This can lead to a complete cereal decay and to serious difficulties in estimating the intensity of use of the cereals by ancient populations. Here, we present a novel biomarker approach entailing the detection of secondary lipid metabolites produced by ergot fungi (genus Claviceps), which are common cereal pests. The aim was to identify the original presence of Gramineae and to indirectly establish if vessels were used for cereal storage/processing. The fatty acid and TAG-estolide profiles of the remains from more than 30 archaeological vessels were investigated by gas chromatography/mass spectrometry (GC/MS) and high performance liquid chromatography/high resolution mass spectrometry (HPLC/ESI-Q-ToF). The detection of lipids derived from ergot in archaeological and historic contexts rests on its complex chemistry, providing a unique and relatively recalcitrant chemical signature for cereals. This research demonstrated that the combination of our innovative biomarker approach along with environmental and archaeological evidence can provide unprecedented insights into the incidence of cereals and related processing activities in ancient societies.

Highlights

Cereals played a key role in ancient times, e.g. in the Neolithic diet, their botanical and chemical remains are relatively rare at archaeological sites
This paper presents an innovative biomarker approach entailing the recognition of the exclusive lipids biosynthesized by ergot fungi of the genus Claviceps
Claviceps fungi are common pests of Gramineae[10], and they metabolically produce lipids characterized by a complex mixture of more than 70 compounds, consisting of a series of diglycerides, triglycerides and high molecular weight estolides, with ricinoleic acid (12-hydroxy-9-octadecenoic acid) being the most abundant acyl substituent[11]

Summary

Introduction

Cereals played a key role in ancient times, e.g. in the Neolithic diet, their botanical and chemical remains are relatively rare at archaeological sites. Claviceps fungi (ergot) are common pests of Gramineae[10], and they metabolically produce lipids characterized by a complex mixture of more than 70 compounds, consisting of a series of diglycerides, triglycerides and high molecular weight estolides, with ricinoleic acid (12-hydroxy-9-octadecenoic acid) being the most abundant acyl substituent[11]. Gas chromatography/mass spectrometry (GC/MS) following alkaline hydrolysis, solvent extraction and derivatization, was used as a preliminary screening approach to characterise the fatty acid profiles of the archaeological samples. Liquid chromatography coupled with high resolution tandem mass spectrometry (HPLC/ ESI-Q-ToF) was used to further investigate the lipid fraction of those samples that showed evidence of ricinoleic acid in the fatty acid profile

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