Effects of chemical pre-treatments on modified starch granules: Recommendations for dental calculus decalcification for ancient starch research

Abstract

Starch granules and other plant microremains embedded in dental calculus provide information about the diet and culinary practices of past individuals. While most researchers use either hydrochloric acid (HCl) or ethylenediaminetetraacetic acid (EDTA) to demineralise samples and release embedded microremains, protocols vary significantly in regard to chemical concentration and duration. Furthermore, there are conflicting reports concerning the suitability of these chemicals for archaeological starch analyses, particularly when granules are modified (damaged) such as from food processing or enzymatic digestion. This study tests 0.5 M HCl and 0.5 M EDTA on modified modern wheat, chickpea and potato starch with direct observation of individual starch granules over 168 h, the maximum duration reported so far for full decalcification of archaeological calculus samples. While there were no observable changes to gross morphological characteristics of any granules, metric analysis indicates slight changes to average granule size in milled potato and wheat starch in all solutions. Furthermore, interactions between the chemical reagent and ions released from the calculus matrix have the potential to result in the diminished recovery of archaeological starch from HCl extractions. We recommend that of these two chemical decalcification options, EDTA is more suitable for processing archaeological dental calculus for starch microremains as it chelates ions released during decalcification of the calculus matrix that might otherwise adversely affect archaeological starch granules.