Supercritical Fluids for Higher Extraction Yields of Lipids from Archeological Ceramics

Abstract

The extraction and study of organic residues from ceramics has been a subject of interest for the last 50 years in archeology and archeological science. Lipids are among the best-preserved organic substances in archeological contexts and can provide information about the diets of ancient populations as well as past environments. Here, we present a method which demonstrates significantly improved extraction of lipids from archeological pots by replacing liquid organic solvents with supercritical fluids. Optimization of the procedure using response surface methodology (RSM) approach showed that, on our system, optimal conditions for supercritical extraction of lipids from synthetic fired clay ceramics could be achieved using carbon dioxide with 16 vol % of cosolvent EtOH-HO (95:5 v/v) in 90 min at a flow rate of 2.3 mL/min, for a pressure of 30 MPa and a temperature of 50 °C. For all reference and archeological samples included in this study, lipid yields obtained by supercritical fluid extraction under these optimal conditions were systematically higher than by conventional solvent extraction. This study also highlighted a variability of the ratio of unsaturated versus saturated fatty acids depending on the extraction method. This can have important implications in the identification of the residue(s). The increased extraction efficiency provided by supercritical fluids, as well as their minimally destructive nature, enable new and refined approaches to residue analysis and dating of archeological ceramics.

Tutorial on lipidomics

“…Although these methods improve the extraction efficiency of certain lipid compounds, the sample processing throughput is still unsatisfactory. Therefore, in recent years, scientists have also been studying the use of solidphase extraction, microwave-assisted extraction, supercritical fluid extraction, and other technologies to extract lipids from samples in order to increase the throughput of sample processing through automation [112][113][114]. In conclusion, the current sample processing in lipid analysis is still using traditional liquid-liquid extraction methods especially for quantitative lipidomics, because these extraction methods have a better extraction efficiency for most lipid compounds.…”

Lipids in Archaeological Pottery: A Review on Their Sampling and Extraction Techniques

“…Last but not least, an innovative extraction technique based on the use of supercritical fluids has been recently explored by Devièse et al [ 108 ]. As reported by the same authors, supercritical fluid extraction (SFE) has not yet been widely explored in the field of archaeological science, but the results of this pilot study are very promising.…”

“…In fact, only small portions of solvents are combined with the supercritical fluid in order to change its polarity. Devièse et al [ 108 ] optimized the extraction of lipids from pottery by the SFE method using water and ethanol as cosolvents, which are less toxic than extraction solvents conventionally used in solid–liquid extraction. Regarding the extraction performance, the SFE allowed the authors to detect, in laboratory-made ceramic samples, higher quantities of lipids than those obtained by using a conventional solvent-based extraction (chloroform:methanol, 2:1 by volume) protocol.…”

Something fishy in the Great Lakes? A reappraisal of early pottery use in north-eastern North America

“…Without knowing the extent of these complex and varied post-depositional degradation processes, it is wholly unrealistic to expect that organic residues can be reliably classified on the basis of their fatty acid distributions. The method of extraction may also affect the distribution of fatty acid liberated from the sample (Regert et al 1998; Correa-Ascencio & Evershed 2014; Deviese et al 2018).…”