Laboratory cooking and degradation experiments to support interpretations of absorbed lipid residues arising from the processing of broomcorn millet (Panicum miliaceum) and animal products in archaeological pottery vessels I. Molecular analysis

Plant resources were essential in prehistoric diets and their processing in pottery vessels, especially of grains, represented a crucial innovation. Lipid residue analysis of unglazed ceramics is a valuable tool for identifying ancient dietary components. While animal lipids are by far the most widely detected, increasing studies show their co-occurrence with plant lipids derived from grains or leaves. A notable observation is the broomcorn millet triterpenoid biomarker, miliacin (olean-18-en-3β-ol), presented together with acyl lipids dominated by palmitic (C 16:0 ) and stearic (C 18:0 ) acids in archaeological pottery. The co-occurrence of these lipids of contrasting sources and structures complicates interpretation of the contributing components of mixed residues due to the potentially (i) differential release and deposition rates of cereals versus animal lipids, and (ii) contrasting survival rates of triterpenoids versus acyl lipids during burial. To resolve these questions laboratory cooking and degradation experiments were conducted involving millet alone and millet/animal product mixtures. Only low concentrations of millet lipids were incorporated in replica pottery when the grains were boiled alone. Co-processing with meat enhanced miliacin incorporation, although the millet acyl lipids were completely masked by animal fats. Degradation experiments showed miliacin is highly resistant to microbial degradation. After extended degradation, the residues from the sherds dosed with millet lipids were predominately composed of miliacin, with near complete loss of acyl lipids. The degraded residues of mixed millet and animal lipids were dominated by C 16:0 and C 18:0 fatty acids alongside miliacin, suggesting that co-processing of animal products and millet would remain detectable in archaeological pottery.