CHEMISTRY 1000

1. CHEMISTRY 1000 Topics of Interest #3: “Organic” Chemistry

2. “Organic” Produce Chemists use the term “organic” to describe carbon-containing compounds. Technically, that makes all produce “organic”. This presentation relates to the layperson’s definition of “organic produce” – not the chemist’s definition. • Interest in organic produce – food grown without the application of synthetic pesticides, fertilizers or hormones – is growing. Some claim that there are health benefits to eating organic produce. Others feel that it is a more environmentally friendly way to farm. Certainly, it is a more expensive way to farm and, as such, organic produce tends to cost more than conventionally grown produce. J. Chem. Ed. (2007) 84, 1244-1246 A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55, 2664-2270

3. “Organic” Produce • So, how can we tell that the grocery store’s organic produce was, in fact, grown organically? • It might carry a sticker saying that it is “certified organic”. This certification involves inspection of the farm where the produce is grown and the farming practices used. This certification costs money. • A test to determine whether produce really was grown organically is being developed in the United Kingdom. This test uses the ratio of two nitrogen isotopes (14N and 15N) in produce to determine whether natural or synthetic fertilizers were used. • How does the test work? • All living matter contains nitrogen. As produce is grown, it acquires much of its nitrogen from fertilizers. Natural fertilizers such as manure and compost tend to contain more 15N than air. Synthetic fertilizers tend to contain about the same amount of 15N as air does. J. Chem. Ed. (2007) 84, 1244-1246 A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55, 2664-2270

4. “Organic” Produce • The graphs below compare 15N/14N ratios of organic and conventionally grown produce. The x-axis shows a value, d15N, calculated by taking the difference between the 15N/14N ratio of the produce and the 15N/14N ratio of air, dividing by the 15N/14N ratio of air then multiplying by 1000‰. • d15N = 0 indicates that the 15N/14N ratio is the same as for air. • d15N > 0 indicates that the 15N/14N ratio is greater than for air. • d15N < 0 indicates that the 15N/14N ratio is less than for air.

5. It Works for Wine Too! • The same concept can be used to determine whether or not the wine in the bottle was made from grapes grown in a particular region. • The ratio of 18O : 16O in water molecules in the wine can be traced to a particular region, but this particular method can be affected by large amounts of rainfall shortly before the grapes were harvested (since rain may have a different ratio from the groundwater typically used for irrigation, and the rainwater will be taken up quickly by the grapes). • The ratio of 2H : 1H in ethanol molecules in the wine can also be traced to a given region. Because the ethanol comes from fermentation of sugar, and the sugar molecules are produced over a longer period of time, this method is more reliable. • 2H content generally increases with proximity to the equator. • 2H content generally decreases with increased altitude and with increased distance from oceans. As such, many regions have very specific 2H : 1H ratios in their grapes and, therefore, in the wine made from those grapes. T. Bigwood, M. Sharman, A. Aldus, M. J. Dennis Journal of Wine Research (1998) 9, 155-166