Six-month size variation in maize starch with different glycerin concentrations

Abstract

Starch granule analysis allows archaeologists to identify botanic resources utilized by ancient peoples, informing about past foodways and subsistence strategies. As a relatively new archaeometric technique, not many studies have been done over the viability of starch granules over time or the proper microscope slide preservation techniques. Starch granules are noted for their visible cross-hatching fissures (extinction cross), which are most visible through a polarized light microscopy. This is a pilot study in measuring starch granule changes over a period of time based on varying glycerin to water ratios. In order to study changes starch samples (particularly size), 100 randomly selected starch granules were measured. The first measurements were taken in mid- March and then taken again six months later in September. Four solutions were made with glycerin-to-water ratios varying from: 10%, 30%, 50%, and 70%. These solutions included the same amount of maize starch and Lycopodium spores (as a control). The four solutions were put on twelve corresponding slides. Starch concentration with lycopodium was also measured through total lycopodium count on one slide. Over the course of six-months there were significant changes among starch granule size and shape, with the average size dramatically increasing over time in all glycerin concentrations. It appears some starch granules underwent gelatinization likely due to taking in water within the solution. There is variation in the six-month random sampling, but it appears the 50% glycerin-to-water solution had the greatest size growth, followed the 70% concentration, then 30% concentration, and finally the 10% concentration. This study informs archaeologists that long-term storage of starch residues creates dramatic differences in the morphological characteristics of the starch granules and therefore must be used cautiously.