Experimental evidence for the processing of marine animal products and other commodities containing polyunsaturated fatty acids in pottery vessels

omega-(o-Alkylphenyl)alkanoic acids are known to form in vitro from triunsaturated fatty acids following protracted heating. These compounds have recently been identified in absorbed lipid extracts obtained from archaeological pottery vessels, providing a potentially valuable new class of indicator for the processing of commodities, such as marine oils, which contain high abundances of polyunsaturated fatty acids. Experiments were conducted to assess whether omega-(o-alkylphenyl)alkanoic acids form when pure compounds and complex triacylglycerol mixtures are heated with a fired clay. The results demonstrate that omega-(o-alkylphenyl)alkanoic acids are only produced following heating of unsaturated fatty acids (tri-, di- and monounsaturated species) or complex unsaturated fatty acyl lipids at around 270 degrees C. Heating saturated fatty acyl lipids does not yield omega-(o-alkylphenyl)alkanoic acids. Thus, when searching for evidence for the processing of marine derived animal fats in archaeological pottery vessels, it is essential that: omega-(o-alkylphenyl)alkanoic acids of carbon length C-18 and C-20 should be present, ideally with C-22 also detectable (if only in trace abundances), together with at least one of the three isoprenoid fatty acids (phytanic, pristanic or 4,8,12-tetramethyltridecanoic acid).