Brassicaceae seed oil identified as illuminant in Nilotic shells from a first millennium AD Coptic church in Bawit,Egypt |
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Authors: | Kerlijne Romanus Wim Van Neer Elena Marinova Kristin Verbeke Anja Luypaerts Sabina Accardo Ive Hermans Pierre Jacobs Dirk De Vos Marc Waelkens |
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Institution: | (1) Centre for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium;(2) Department of Archaeology, Katholieke Universiteit Leuven, Blijde Inkomststraat 21, 3000 Leuven, Belgium;(3) Centre for Archaeological Sciences, Katholieke Universiteit Leuven, Blijde Inkomststraat 21, 3000 Leuven, Belgium;(4) Department of Gastrointestinal Research, University Hospital Leuven, Herestraat 49, 3000 Leuven, Belgium;(5) Royal Belgian Institute of Natural Sciences, Vautierstraat 29, 1000 Brussels, Belgium |
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Abstract: | Burned greasy deposits were found inside shells of the large Nile bivalve Chambardia rubens, excavated in an eight- to tenth- century AD church of the Coptic monastery of Bawit, Egypt, and supposedly used as oil lamps.
The residues were subjected to a combination of chromatographic residue analysis techniques. The rather high concentrations
of unsaturated fatty acids, as analysed by gas chromatography (GC) in the methylated extract, suggest the presence of a vegetal
oil. Analysis of the stable carbon isotopes (δ
13C values) of the methyl esters also favoured plants over animals as the lipid source. In the search for biomarkers by GC coupled
to mass spectrometry on a silylated extract, a range of diacids together with high concentrations of 13,14-dihydroxydocosanoate
and 11,12-dihydroxyeicosanoate were found. These compounds are oxidation products of erucic acid and gondoic acid, which are
abundantly present in seeds of Brassicaceae plants. Liquid chromatography coupled to mass spectrometry analysis showed low
concentrations of unaltered triglycerides, but revealed sizeable amounts of triglycerides with at least one dihydroxylated
acyl chain. The unusual preservation of dihydroxylated triglycerides and α,ω-dicarboxylic acids can be related to the dry preservation conditions. Analysis of the stereoisomers of the dihydroxylated
fatty acids allows one to determine whether oxidation took place during burning of the fuel or afterwards. The results prove
that the oil of rapeseed (Brassica napus L.) or radish (Raphanus sativus L.) was used as illuminant in early Islamic Egypt, and that not only ceramic lamps but also mollusk shells were used as fuel
containers. |
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Keywords: | Residue analysis Egyptian lamp shells HPLC-MS GC-C-IRMS GC-MS Brassicaceae seed oil |
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