Analytical strategies for discriminating archeological fatty substances from animal origin

Abstract

Mass spectrometry (MS) is an essential tool in the field of biomolecular archeology to characterize amorphous organic residues preserved in ancient ceramic vessels. Animal fats of various nature and origin, namely subcutaneous fats of cattle, sheep, goats, pigs, horses, and also of dairy products, are those most commonly identified in organic residues in archeological pottery. Fats and oils of marine origin have also been revealed. Since the first applications of MS coupled with gas chromatography (GC) in archeology at the end of 1980s, several developments have occurred, including isotopic determinations by GC coupled to isotope ratio MS and identification of triacylglycerols (TAGs) structure by soft ionization techniques (ESI and APCI). The combination of these methods provides invaluable insights into the strategies of exploitation of animal products in prehistory. In this review, I focus on the analytical strategies based upon MS that allow elucidation of the structure of biomolecular constituents and determination of their isotopic values to identify the nature of animal fat components preserved in highly complex and degraded archeological matrices.

Organic Residues in Archaeology: The Highs and Lows of Recent Research

“…Modern reference fats fall within well-defined areas on a scatter plot of δ 13 C 18:0 against δ 13 C 16:0 , reflecting the different metabolic processes by which different organisms synthesize these two acids (5,32,68). Results can also be plotted as ∆ 13 C vs δ 13 C 16:0 (where ∆ 13 C = δ 13 C 18:0 -δ 13 C 16:0 ), a method which eliminates minor local variations in isotopic values by using ∆ 13 C, while still incorporating the variations in δ 13 C 16:0 produced by the presence of marine fats or C 4 plants (67).…”

“…This is due to the processes of degradation and dissolution that occur during burial and, in some cases, alteration of the fats during the lifetime of the vessel, for example during cooking. These processes tend to deplete diagnostic biomarker compounds that are characteristic of particular fats (3)(4)(5)(63)(64)(65)(66)(67) preventing the unique identification of degraded fatty material.…”

“…Continuing research in this area is steadily increasing understanding of the strengths and weaknesses of compound specific carbon stable isotope analysis and providing solutions to some of the problems encountered (5,32). The measurement of hydrogen isotopic values, while technically challenging, may provide a new level of discrimination in the identification of archaeological fats, already showing success in distinguishing horse milk and adipose fats (5,32).…”

“…The measurement of hydrogen isotopic values, while technically challenging, may provide a new level of discrimination in the identification of archaeological fats, already showing success in distinguishing horse milk and adipose fats (5,32). Nevertheless, the interpretation of isotopic data from residues should always be carried out with full reference to the results of molecular analysis and to faunal and other evidence from the site.…”

“…Comprehensive reviews of the field are available in the literature and present a more detailed view of the research published in the last 10 years (1)(2)(3)(4)(5). In particular this chapter does not address advances in the field of ancient DNA research as applied to archaeological residues as this is a separate field outside the scope of this review (1).…”