Tracing the geographical origin of early potato tubers using stable hydrogen isotope ratios of methoxyl groups†

Abstract

The application of stable isotope ratio measurements has become an extremely useful tool for tracing the provenance of food products, thus ensuring that consumers receive products which comply with their labelled specifications. Recently, it has been shown that relative stable hydrogen isotope abundances (δ2H values) of wood lignin methoxyl groups have a distinct range that reflects the δ2H values of their meteoric source water. Furthermore, it has been suggested that the isotope information stored in methoxyl groups in plant matter generally might assist with determining the place of origin of plant material. We now have measured δ2H values of methoxyl groups from natural compounds in tubers of early potatoes (Solanum tuberosum) grown in different geographical locations. Tubers of early potatoes were collected from across Europe and regions close to the Mediterranean Sea between April and July 2004. The methoxyl groups from the potatoes were found to be highly depleted in 2H, relative to both their meteoric water and bulk biomass, and a systematic shift of the δ2H values between methoxyl groups and meteoric water was observed. A constant fractionation of−161±11‰. between methoxyl groups and modelled meteoric water is shown over a transaction covering the δ2H values of meteoric water from−95‰ in Northern Sweden to+25‰ in Egypt. From this information, early potato tubers from Middle Europe can be clearly distinguished from those of Mediterranean regions and from Northern Europe. Thus, we suggest that δ2H values of methoxyl groups have the potential to become an effective tool in assisting with the constraint of the geographical origin of potato tubers and other food stuffs. †Revised version of a paper presented at the 30th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 8–10 October 2007, Bayreuth, Germany.