S21 - Session O4 - Can stable isotopes separate organic from conventional bananas?

Authors: Philippe Tixier *, Denis Loeillet, Mathieu Coulis, Thierry Lescot, Luc de Lapeyre de Bellaire

Similarly to the measurement of pesticide residues to ensure that the specifications or regulations and certifications have been met, it is essential to have methods to discriminate fruits that received organic fertilization from those that received fertilization with synthetic fertilizers. The nitrogen-15 isotopic signatures of synthetic fertilizers (resulting from fixation of nitrogen of the air) and of organic fertilizers (coming from organic matter) are very different. The objective of this study was to test whether it was possible to differentiate bananas that had received organic nitrogen from those that had received conventional fertilization. We studied the isotopic signature of bananas from seven production regions in Africa and French West Indies; in each we analyzed an organic and a conventional couple. Importantly, we were sure that in the organic situations the fertilization was only done with organic matter. In each of the 15 situations studied, we analysed 20 fruits. On each fruit, we analysed with an isotopic mass spectrometer the isotopic abundances of 15 N (reported in δ notation). The δ 15 N values of banana fruits ranged between -1.25 and 8.91‰, with a highly significant effect of the type of fertilization on δ 15 N values. Among sites, the average difference between the two types of fertilization ranged between 1.6 and 4.8‰ with a mean value of 2.83‰. These significant differences in mean δ 15 N values indicate that these measures reliably segregate banana fruits grown organically from those grown in conventional systems. The next steps will be to establish a baseline of δ 15 N values of fruit from organic systems in each region to be analyzed. To date, measurements of δ 15 N on banana fruit appear to be effective information for detecting fruit that has potentially failed to meet organic specifications and thus guide controls by certification authorities.