The Application Of Starch Analysis In Archaeology

Starch is a type of secondary metabolite synthesized in plant by photosynthesis and composed of various glucose polymers. Starch granules mainly occur in the storage organs of plants, including seeds, fruits and storage roots, and provide necessary energy when seeds and roots germinate. Starch granules have taxonomic significance as starch grains from different plants may be morphologically distinguishable.Humans have exploited and used starchy plant organs as food for a long time. Starch granules may therefore be deposited on surfaces of tools when ancient people processed the starchy plants for food. In some cases, these small granules can be preserved very well and recovered by archaeologists, and hence starch analysis has a high potential for understanding human exploitation of plant resources, tools function and the nature of plant food processing in the past. Ancient starch analysis has a history of nearly 40 years in many parts of the world, including South America and Oceania.In China, Li Pan was the first person to use starch analysis, when he attempted to identify the composition of a block of flour excavated from the Dahecun site in 1974, however no further study of ancient starch was conducted after this for a long period of time. In recent years, scholars in China have paid attention to ancient starch again, but the application of this method has been hampered by a lack of systematic studies on modern reference materials and related research methodological issues.In order to resolve these questions, this thesis examined the morphological characteristics of starch grains from about 50 species of economically useful plants from China, including from the storage organs of plants from families of Poaceae, Fagaceae, Fabaceae and Dioscoreaceae. The results show that starch granules from different plants can be identified to varied taxonomic levels, including to a taxonomic subclass or genus, and in some cases to species and even to variety (e.g. Chinese yam).People often process starchy foods before eating in order to remove toxins from a plant or to improve the taste and nutrition of a plant food, resulting in morphological modification of starch granules. This thesis carried out simulation experiments in various methods of starchy food preparation and studied the resulting alteration of starch granule morphology from various food processing methods. The results demonstrate that grinding and pounding may cause breaking of starch granules and alterations of surface features, of which the degree is decided by the strength of friction appointed to the granules. Heating starch granules usually causes changes to the extinction cross of the granule, when viewed under polarized light, as the arms of the cross become wider and dark areas in the centre of the cross become larger. Experiments also indicate that the content of water in the environment affects the degree to which changes occur in starch granules after heating, and it appears that the crystal structure of starch granules is more easily damaged in an environment with excessive water. According to these experimental results, the author proposes that simulation experiments should be carried out in ancient starch analysis to improve our understanding of the nature of ancient starch and human activities, especially in relation to food processing and cooking.Based on the completed modern references studies, this thesis analyzed the starch residues extracted from artifacts unearthed from the Xishan site in Lixian county, Gansu province and from pig dental calculus of the Duzhong site in Mianchi county, in Henan province. The identification of these starch granules reveals important information about ancient plant use, methods of food preparation and pig diet. The stone tools and pottery vessels from Xishan used for this study date to the prehistoric and West Zhou dynastic periods. Numerous starch grains recovered from these artifacts were identified to various species including Job's tears (Coix lacryma jobi), wheat (Triticum sp.), barley(Hordeum sp.), oats(Avena sp.), millets (Setaria italica and Panicum milliaceum) and yam (Dioscorea opposita). Among the starches identified, some are intact and others show characteristics of damage caused by grinding and cooking, reflecting the methods of food preparation that were employed in ancient times.Duzhong is a site of the Late-Yangshao culture. A large number of animal bones were excavated from the site, including many pig mandibles with teeth intact. Starch granules were extracted from pig dental calculus. Most of these starch granules were identified to the sorghum genus(Sorghum sp.), along with wheat(Triticum sp.), other grasses(Poaceae), and tubers and acorns(Cyclobalanopsis sp.). As the starch granules recovered from dental calculus provide direct evidence of the pig's daily food, these plants identified by starch analysis are the direct evidence of ancient pig diets. These data provide new insights into pig domestication at the Duzhong site.The earliest noodles in the world have been reportedly dated to 4000 years ago, based on the discovery of alleged remains at the Lajia site in Minhe county, Qinghai province. The Lajia noodles were described as having been made by repeatedly stretching dough composed of millet flour that included millet phytolith husks within the flour, based on the analyses of starch and phytoliths from sediment recovered at the site. In order to understand this manufacturing technique we carried out simulation experiments in noodle-making and documented morphological changes in noodle starches caused by grinding and cooking. Our research demonstrates that it is not possible to stretch pure millet dough into noodles. We conclude that the husk phytoliths and starch-like granules said to be from the Lajia noodle remains may actually not have been part of the noodles themselves. Re-examination of the Lajia noodle-like remains is needed.The last part of this thesis reviews the main content presented in this thesis and discusses the present situation, problems and future orientation of ancient starch analysis.