Investigating the formation and diagnostic value of ω‐(o‐alkylphenyl)alkanoic acids in ancient pottery

Abstract

Long-chain ω-(o-alkylphenyl)alkanoic acids (APAAs) derived from the heating of unsaturated fatty acids have been widely used for the identification of aquatic products in archaeological ceramic vessels. To date, little attention has been paid to the diagnostic potential of shorter chain (< C 20 ) APAAs, despite their frequent occurrence. Here, a range of laboratory and field experiments and analyses of archaeological samples were undertaken to investigate whether APAAs could be used to further differentiate different commodities. The results provide new insights about the conditions for the formation of APAAs and enable the proposition of novel criteria to distinguish different natural products.

A Neolithic without dairy? Chemical evidence from the content of ceramics from the Pendimoun rock-shelter (Castellar, France, 5750–5150 BCE)

“…The ratio of the two isomers of phytanic acid varied from 45 to 76% of SSR diastereoisomer. Markers of thermal transformation of animal fats (Bondetti et al, 2020;Hansel et al, 2004;Raven et al, 1997) were also detected occasionally. Traces of ω-(oalkylphenyl)alkanoic acids (APAAs) with 18 carbon atoms were detected in 3 samples (AP_0008, AP_0027, and AP_0036; Figure 4) but no C20-APAAS.…”

What do “barbarians” eat? Integrating ceramic use-wear and residue analysis in the study of food and society at the margins of Bronze Age China

“…A similar set of plant biomarkers has been identified in Bronze Age pottery vessels from the Korean Peninsula and northern Europe and reported as the first molecular and isotopic evidence of millet processing in prehistoric pottery vessels [ 57 ]. Another class of compounds identified in all ten acidified methanol extracts are isomers of the ω-(o-alkylphenyl) alkanoic acid (AAPA) with 18 carbon atoms, which are readily formed by heating a wide range of resources rich in unsaturated fatty acids precursors (C 18:x ), notably plant and aquatic resources, but also a number of terrestrial products [ 58 – 60 ]. While previous studies had shown that APAAs were formed when vessels are subjected to temperatures exceeding 270°C for at least 17 hours [ 58 ], recent experimental work has shown that these compounds are formed over just one hour of heating at 270°C, or at 200°C for 5 hours, conditions easily achieved through both boiling or roasting [ 60 , 61 ].…”

“…Another class of compounds identified in all ten acidified methanol extracts are isomers of the ω-(o-alkylphenyl) alkanoic acid (AAPA) with 18 carbon atoms, which are readily formed by heating a wide range of resources rich in unsaturated fatty acids precursors (C 18:x ), notably plant and aquatic resources, but also a number of terrestrial products [ 58 – 60 ]. While previous studies had shown that APAAs were formed when vessels are subjected to temperatures exceeding 270°C for at least 17 hours [ 58 ], recent experimental work has shown that these compounds are formed over just one hour of heating at 270°C, or at 200°C for 5 hours, conditions easily achieved through both boiling or roasting [ 60 , 61 ]. Similar experiments also show that the relative abundance of certain APAA-C 18 isomers (namely the E and H isomers—see Fig 11 ) can effectively separate three groups of food products: 1) cereals/fruits/non-leafy vegetables, 2) leafy vegetables, and 3) animal/aquatic products [ 60 ].…”

“…While previous studies had shown that APAAs were formed when vessels are subjected to temperatures exceeding 270°C for at least 17 hours [ 58 ], recent experimental work has shown that these compounds are formed over just one hour of heating at 270°C, or at 200°C for 5 hours, conditions easily achieved through both boiling or roasting [ 60 , 61 ]. Similar experiments also show that the relative abundance of certain APAA-C 18 isomers (namely the E and H isomers—see Fig 11 ) can effectively separate three groups of food products: 1) cereals/fruits/non-leafy vegetables, 2) leafy vegetables, and 3) animal/aquatic products [ 60 ]. As shown in Fig 11 , the E/H ratio associated with the ten Siwa samples ( Table 2 ) reveals a pattern generally more coherent with animal products than plants, although one cannot rule out cereals/non-leafy vegetables like millet as the source of this isomeric distribution.…”

Use of Thermally Assisted Hydrolysis and Methylation (THM-GC-MS) to Unravel Influence of Pottery Production and Post-Depositional Processes on the Molecular Composition of Organic Matter in Sherds from a Complex Coastal Settlement

“…In addition, being close to the (actual) see level, this set of ceramics has an added complexity of strong marine influences, reflected by for instance mollusks growing on potsherd surfaces. In addition, such coastal environments may be more likely to contain residues of aquatic resources that produce isoprenoid fatty acids [25][26][27].…”