[Image caption: Rhodes College Students Ryan Hunt and Natalie Prodanovich worked with the GC-MS.]
McClung curators of paleoethnobotany and archaeology, Gary Crites and Timothy Baumann, are applying advanced technology in their ongoing research into the timing and route(s) of arrival of domesticated beans in southeastern North America. Collaborating on the project is Jon Russ, professor of chemistry at Rhodes College. A gas chromatograph (GC) interfaced with a mass spectrometer (MS) are being employed in an effort to identify biomarkers in modern beans that can be used to confidently identify fragments of charred, archaeologically-recovered prehistoric beans which are sometimes difficult to identify on the basis of morphology alone.
The GC separates bean material mixtures into individual molecules. The MS provides information on the type of compound based on its characteristic mass spectrum. The technique allows researchers to separate each compound in a mixture and to detect each compound individually. Initial extractions have revealed several compounds, including various fatty acids and sterols. The next focus will be determining relative concentrations of each fatty acid, the ratios of which should be unique to beans. Emphasis will also be on identifying the sterols to determine if one or more might be unique to domesticated beans.
Domesticated beans reached Eastern North America (ENA) from the Southwest soon after A.D. 1100. The earliest direct date for bean in ENA is A.D. 1115 on a specimen from New York. The earliest directly dated bean in the Southeast comes from east Tennessee and dates to A.D. 1309. Isolating biomarkers for identification of small fragments of beans from the Southeast and Mississippi Valley would make it possible to select for direct radiocarbon dating specific specimens from contexts that are potentially as early, or even earlier, than those in the Plains and Northeast. Identifying such early beans in the Southeast and lower Mississippi Valley would fundamentally change our understanding of the routes and timing of arrival of domesticated beans into Eastern North America.