Starch analysis is a post excavation technique used in archaeological

Archaeology

Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

 research. First applied in the 1980s, 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

Paleoclimatology

Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...

. For this reason, a broad set of methods have developed to fully analyze ancient starch.

Biology of starch

Starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 is produced in plants as a form of energy storage through the process of photosynthesis

Photosynthesis

Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

. When the plant is in need of energy, the stored starch is converted back into glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

.

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

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

.

Microscopy

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.

Low magnification

Archaeological research focused on residue adhering to artifacts

Artifact (archaeology)

An artifact or artefact is "something made or given shape by man, such as a tool or a work of art, esp an object of archaeological interest"...

 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

Residue (chemistry)

In chemistry, residue is the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group. It may also refer to the undesired byproducts of a reaction....

.

High magnification

Modern light, high powered microscope

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

s 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

Granule (cell biology)

In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

 as small as a few micrometres in diameter.

Reference collection

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

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 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.

Classification, and identification

There are two basic methods for identifying starch:

• Diagnostic tests of chemical and physical properties
• Optical properties of the granules.

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:

• Determine whether evidence for the utilization of plants is present
• Study assemblage variation
• Determine the presence of particular plant species
• Assign percentage of starch granules within a sample to a particular taxon
  Taxon
  |thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
  
  , and present quantitative data
  Numerical data
  Numerical data is data measured or identified on a numerical scale. Numerical data can be analyzed using statistical methods, and results can be displayed using tables, charts, histograms and graphs. For example, a researcher will ask a questions to a participant that include words how often, how...
  
   regarding relative abundance within the sample.

Identification of ancient starch is fairly easily for the first three levels of classification

Taxonomy

Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

, whilst the fourth level requires continued improvement in the description, classification, and identification of individual starch granules.

Starch in sediments

Starch granules retrieved from sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s are used to reconstruct the habitat

Habitat

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

s associated with human land use

Land use

Land use is the human use of land. Land use involves the management and modification of natural environment or wilderness into built environment such as fields, pastures, and settlements. It has also been defined as "the arrangements, activities and inputs people undertake in a certain land cover...

. Such studies address two areas of interest to the archaeologist:

• landscapes; specifically the reconstruction of historical plant communities at the widest scale of the environment
• specific contexts, such as settlements or activity areas; focusing on individual archaeological site
  Archaeological site
  An archaeological site is a place in which evidence of past activity is preserved , and which has been, or may be, investigated using the discipline of archaeology and represents a part of the archaeological record.Beyond this, the definition and geographical extent of a 'site' can vary widely,...
  
  s, or separate contexts within them, with the goal of identify specific human activities at a particular location.

The stages involved in the analysis of starch from sediments are; sampling

Core sample

A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...

, extraction

Extraction (chemistry)

Extraction in chemistry is a separation process consisting in the separation of a substance from a matrix. It may refer to Liquid-liquid extraction, and Solid phase extraction....

 of starch, slide mounting and viewing, and interpretation.

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.

Extraction

Most extraction techniques follow a general methodology of:

• sample preparation (sieving, drying, or soaking)
• disaggregation and deflocculation to break up the elements of the sample into single particles
• removal of undesired particles (sands, silts, minerals, organics).
• chemicals preservation of the starch granules.

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.

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.

Starch on artifacts

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:

• determine how artificats were used by combining analysis of starch with other approaches, such as the study of use-wear or additional residue types.
• reconstruction of plant use and diet.

Tool Function

Until recent years this was the primary focus of starch analysis. These studies help researchers understand a broader range of behaviorial

Human behavior

Human behavior refers to the range of behaviors exhibited by humans and which are influenced by culture, attitudes, emotions, values, ethics, authority, rapport, hypnosis, persuasion, coercion and/or genetics....

 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

Use-wear analysis

Use-wear analysis is a method in archaeology to identify the functions of artefact tools by closely examining their working surfaces and edges. It is mainly used on stone tools, and is sometimes referred to as "traceological analysis" .Using a high-powered microscope it is possible to closely study...

.

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.

Modified starch

Modified starch

Modified starch

Modified starch, also called starch derivatives, are prepared by physically, enzymatically, or chemically treating native starch, thereby changing the properties of the starch. Modified starches are used in practically all starch applications, such as in food products as a thickening agent,...

 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

Earth oven

An earth oven or cooking pit is one of the most simple and long-used cooking structures . At its simplest, an earth oven is simply a pit in the ground used to trap heat and bake, smoke, or steam food...

, 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

Arid

A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...

 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.

Preserved forms of modified starch include:

• discrete desiccated macroremains: coherent foods that are not attached to any other object and are among the most easily recognizable ancient starchy prepared foodstuffs. They can be either the intended final prepared food, like loaves of bread, or intermediate products of the food processing sequence, like starch-rich, chaffy lumps.
• attached desiccated residues: collections of starchy foodstuffs adhered to a container or vessel. The ability to identify these residues is affected by the quantity and appearance of the residue, as well as the awareness of the excavators. Residues containing obvious plant tissue are most easily recognizable, while thin smears are not as easy to recognize.
• charred residues: normally the result of accidental overcooking and can be preserved as discrete fragments or remain stuck to the cooking vessel. Due to their charred nature, these residues are very difficult to identify.