Post-charring diagenetic alteration of archaeological lentils by bacterial degradation

Abstract

Ancient seeds recovered from archaeological contexts are typically protected from degradation through the process of low temperature charring (<300 °C). Resilient Maillard Reaction Products produced by charring are considered chemically stable, and thus, suitable for stable isotopic studies. A few high-profile reconstructions of past climate and human economies have been based on charred seeds. In this study we take a comprehensive structural, compositional, isotopic, and genetic approach to compare modern Eastern Mediterranean lentils with archaeological charred lentils recovered from Iron Age I layer Tel Dor, and five complementary southern Levantine sites ranging from the Pre-Pottery Neolithic to Persian periods. The modern lentils were charred at temperatures ranging from 100ᵒC - 400ᵒC and analyzed as a reference for the archaeological material. The modern and archaeological charred lentils were found to differ structurally, compositionally, and isotopically, challenging the notion that seed charring prevents further chemical alteration between the time of burial and recovery of the seeds. Genetic analysis of archaeological lentils revealed the presence of bacterial taxa capable of degrading chemical compounds considered stable in ambient burial conditions. We assume that microbial degradation is more likely to affect charred legumes than other seeds due to their high nitrogen content. We also acknowledge that different environments and burial conditions might promote better preservation of charred lentils. We call for the development and employment of archaeological legume screening methods that will help select seeds best suited for isotopic analyses.