title: Olive oil or lard?: distinguishing plant oils from animal fats in the archeological record of the eastern Mediterranean using gas chromatography/combustion/isotope ratio mass spectrometry.
abstract: Distinguishing animal fats from plant oils in archaeological residues is not straightforward. Characteristic plant sterols, such as β-sitosterol, are often missing in archaeological samples and specific biomarkers do not exist for most plant fats. Identification is usually based on a range of characteristics such as fatty acid ratios, all of which indicate that a plant oil may be present, none of which uniquely distinguish plant oils from other fats. Degradation and dissolution during burial alter fatty acid ratios and remove short-chain fatty acids, resulting in degraded plant oils with similar fatty acid profiles to other degraded fats. Compound-specific stable isotope analysis of δ(13)C(18:0) and δ(13)C(16:0), carried out by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), has provided a means of distinguishing fish oils, dairy fats, ruminant and non-ruminant adipose fats, but plant oils are rarely included in these analyses. For modern plant oils where C(18:1) is abundant, δ(13)C(18:1) and δ(13)C(16:0) are usually measured. These results cannot be compared with archaeological data or data from other modern reference fats where δ(13)C(18:0) and δ(13)C(16:0) are measured, as C(18:0) and C(18:1) are formed by different processes resulting in different isotopic values. Eight samples of six modern plant oils were saponified, releasing sufficient C(18:0) to measure the isotopic values, which were plotted against δ(13)C(16:0). The isotopic values for these oils, with one exception, formed a tight cluster between ruminant and non-ruminant animal fats. This result complicates the interpretation of mixed fatty residues in geographical areas where both animal fats and plant oils were in use.
authors.affiliation: Division of Archaeological, Geographical and Environmental Sciences, University of Bradford, Richmond Road, Bradford BD7 1DP, UK. v.j.steele1@bradford.ac.uk
authors.forename: Valerie J
authors.initials: VJ
authors.lastname: Steele
authors.forename: Ben
authors.initials: B
authors.lastname: Stern
authors.forename: Andy W
authors.initials: AW
authors.lastname: Stott
mesh_terms: D000818:Animals; D001106:Archaeology; D002247:Carbon Isotopes / Q000032:analysis; D005223:Fats / Q000032:analysis*; D005227:Fatty Acids / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D019083:Mediterranean Region; D000069463:Olive Oil; D010938:Plant Oils / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D005223:Fats; D005227:Fatty Acids; D000069463:Olive Oil; D010938:Plant Oils