Stable isotope signatures (δ2 H-, δ13 C-, δ15 N-values) of walnuts (Juglans regia L.) from different regions in Germany.

Abstract

Walnuts (Juglans regia L.) are considered of high value for human nutrition and are cultivated worldwide. With globalization, however, the demand for regional products has increased. Isotopic fingerprints (δ2 H-, δ15 N- and δ13 C-values (‰)) created by means of stable isotope ratio mass spectrometry provide the possibility of tracing the geographical provenance of plant foods. Authentic walnut samples from different geographical regions in Germany could be separated from each other by means of their bulk δ2 H-values (‰) with samples from northern regions being more enriched in 2 H than samples collected from southern Germany. Next to precipitation data, the topography of the surrounding landscape of the sampling sites was taken into account for data interpretation by the creation of approximate elevation profiles. Moreover, German walnuts could be separated from French walnuts which showed significantly higher δ2 H-values (‰). Variations in annual total precipitation was reflected by the shift in δ2 H-ranges (‰) depending on the harvesting year. Additionally, organic walnuts could be well separated from conventionally produced walnuts due to their distinct δ15 N-values (‰) which could be ascribed to a cultivation practice common for organic farming. The data presented here outlined the potential of determining isotopic fingerprints of walnuts from different sites within one country for tracing their regional origin and revealing their cultivation conditions. Including topographic characteristics between the sampling locations as well as precipitation data helped to even differentiate walnuts from two adjoining countries. © 2019 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.