Starch analysis is a post excavation technique used in archaeological research. First applied in the 1980s,[1] starch analysis has became an invaluable tool to paleobotanists and archaeologists alike. Starch is ubiquitous in the archaeological record and can provide answers to a large number of archaeological questions: ranging from dietary analysis to environmental reconstruction. For this reason, a broad set of methods have developed to fully analyze ancient starch.[2]
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Starch is produced in plants as a form of energy storage through the process of photosynthesis. When the plant is in need of energy, the stored starch is converted back into glucose.[3]
Starch granules can be classified as simple, compound, or semi-compound depending on how they are formed in the plant. The variants react to several stains in different ways, which is useful during the identification stage. The most popular staining agents are variants of iodine.[4]
Starch granules are usually under 100 micrometres in size, and are, therefore, best observed under compound microscopes equipped with various lighting conditions and magnifications from x200 to x800.[5]
Low magnification
Archaeological research focused on residue adhering to artifacts start at lower magnifications, commonly using a stereoscope. Most data obtained at this stage is qualitative, an important first stage to fuller analysis. Magnifications of between x10 and x50 are sufficient to locate target residues, describe features and confirm internal structures of the identified residues.[6]
High magnification
Modern light, high powered microscopes have an internal light source, allowing illuminaton with both transmitted and reflected light. These microscopes can provide a magnification of up to x1000: good enough to provide clear images of starch granules as small as a few micrometres in diameter.[7]
The reference collection provides the key to identifying the plant origin of the starch residues. The starch reference collection is built with regard to a range of factors, including whether starch morphology varies with season, growth or environmental conditions. The most important factor is the potential range of plants materials appropriate to the research being undertaken. Collecting and preparing reference material assists with observation of the variability of starch production, and identifying the different morphologies specific to plant species.[8]
There are two basic methods for identifying starch:
It is unclear whether these tests are useful to archaeologists, because they often result in destruction of the morphological integrity of the individual starch granules.
There are four levels of classification:
Identification of ancient starch is fairly easily for the first three levels of classification, whilst the fourth level requires continued improvement in the description, classification, and identification of individual starch granules.[9]
Starch granules retrieved from sediments are used to reconstruct the habitats associated with human land use. Such studies address two areas of interest to the archaeologist:
The stages involved in the analysis of starch from sediments are; sampling, extraction of starch, slide mounting and viewing, and interpretation.[10]
Sampling
Sampling a sediment core or sratigraphic profile to gather information about an environment requires a detailed understanding of the way the sediments were formed.[11]
Extraction
Most extraction techniques follow a general methodology of:
Slide mounting and viewing
Starch granules are mounted onto a slide, using a variety of mounting medias including, but not limited, to water, glycerol, and glycerine jelly. It is important that the material is dried thoroughly before being mounted to ensure that no further degradation of the sample occurs. The slide is then viewed, as appropriate, for identification and counting.[13]
Interpretation
After the starch granules have been examined, the findings are then recorded and interpreted with respect to the research questions that are being investigated.
Artifacts collect starch granules and protect them from decay due to microorganisms, thus providing excellent conditions for long-term preservation. Two types of analysis are commonly performed:
Tool Function
Until recent years this was the primary focus of starch analysis. These studies help researchers understand a broader range of behaviorial questions, as well as determining the specific function of a particular artifact. Starch analysis also assists researchers in identifying potential tool functions that may have been overlooked by simple use-wear analysis.[15]
Plant Use
Most studies have focused on stone artifacts, mainly those used in food preparation. There is increasing awareness of the value of starch analysis to investigate other artifacts; including craft activities involving the preparation of adhesives, medicines, and other nonfood items.[16]
Modified starch is created when the morphological or physico-chemical structure of native starch is disrupted in some way, such as in food preparation. The most common way to modify starch is to apply heat. Cooking pits, hearths, and ovens that may have come into contact with starchy material yield modified starches.
Modified starch is only likely to be preserved under specific conditions, such as arid regions because of its susceptibility to organic decay. Studies of ancient modified starch aid understanding of ancient food technology, variations in cuisine among different social groups, as well as provide an understanding the function of ancient food-processing equipment.[17]
Preserved forms of modified starch include:
Torrence, Robin (2006), Ancient Starch Research, Walnut Creek, CA: Left Coast Press Inc., ISBN 1-59874-018-0