In the course “Footprints of Crime & Climate” in the spring of 2009, Katie Datin '11 proposed to analyze the stable isotope chemistry of hamburgers to detect whether cows ate grass or were fed corn. Free-range beef has many health benefits including less fat, fewer calories, and a higher level of omega-3 fatty acids (Clancy, 2006). The environmental benefits of pasture-raised cattle are also numerous and include decreased soil erosion, reduced water pollution, and a lessoned risk of antibiotic-resistant diseases (Clancy, 2006).
Stable isotopes of carbon and nitrogen (12C, 13C, 14N, and 15N) are tracers of diet – isotopically, you are what you eat plus a slight increase (a few parts per thousand) of the heavier isotope. Photosynthesis is carried out differently in corn than in most grasses of this region causing corn (and corn-fed animals) to have increased amounts of 13C, which is detectable.
Six students took on the project: Katie Datin '11, Liz Cranmer '09, Erik Ohlson '10, Jen Everhart '11, JohnPaul Dicks '09 and Lucia Magee '11.
They collected samples from two commercial beef suppliers and one organic meat supplier in Lancaster. The University of New Hampshire’s Stable Isotope Laboratory analyzed the samples that the students prepared during multiple lab sessions.
From graphing the data and performing the appropriate statistical tests, the students verified that meat from the organic supplier was indeed grass-fed, while cattle from the commercial suppliers were fed corn (see graph). Jahren and Kraft (2008) suggest that a carbon stable isotope value below 21 parts per thousand (‰) lower than the international standard (-21 ‰) is the dividing line between corn-fed and grass-fed cattle.
The students successfully saw an environmental science project through from conception, proposal, funding, planning, sample collecting, processing, and data analysis, to poster creation.
Jahren, A.H. & Kraft, R.A. 2008. Carbon and nitrogen stable isotopes in fast food: signatures of corn and confinement. PNAS. 105(46): 17855-17860.
Clancy, K. 2006. Greener Pastures: How grass-fed beef and milk contribute to healthy eating. Union of Concerned Scientists.