Boron Isotope Fractionation in Bell Pepper

Various plant compartments of a single bell pepper plant were studied to verify the variability of boron isotope composition in plants and to identify possible intra-plant isotope fractionation. Boron mass fractions varied from 9.8 mg/kg in the fruits to 70.0 mg/kg in the leaves. Boron (B) isotope ratios reported as δ11B ranged from -11.0‰ to +16.0‰ (U ≤ 1.9‰, k=2) and showed a distinct trend to heavier δ11B values the higher the plant compartments were located in the plant. A fractionation of Δ11Bleaf-roots = 27‰ existed in the studied bell pepper plant, which represents about 1/3 of the overall natural boron isotope variation (ca. 80‰). Two simultaneous operating processes are a possible explanation for the observed systematic intra-plant δ11B variation: 1) B is fixed in cell walls in its tetrahedral form (borate), which preferentially incorporates the light B isotope and the remaining xylem sap gets enriched in the heavy B isotope and 2) certain transporter preferentially transport the trigonal 11B-enriched boric acid molecule and thereby the heavy 11B towards young plant compartments which were situated distal of the roots and typically high in the plant. Consequently, an enrichment of the heavy 11B isotope in the upper young plant parts located at the top of the plant could explain the observed isotope systematic. The identification and understanding of the processes generating systematic intra-plant δ11B variations will potentially enable the use of B isotope for plant metabolism studies

Strontium isotopic signatures of natural mineral waters, the reference to a simple geological map and its potential for authentication of food

This paper presents the investigation of strontium isotope ratios of about 650 different European natural mineral waters as part of the food traceability project "TRACE" funded by the EU. Analysed 87Sr/86Sr values in the natural mineral waters range from 0.7035 to 0.7777, which indicates an influence by a great diversity of rocks from young mantle derived basaltic rocks to very old silicic continental crust. The results of the large scale investigation are used to elaborate a novel spatial prediction for strontium isotope ratios by combining the measured data with a GIS based geological map of Europe. The resulting map can be used to predict the strontium isotopic composition of groundwater and thus the composition of bio-available strontium, which is available for uptake by plants and subsequently transferred into the food chain. We also show, as an example, that the strontium isotopic composition of honey and wheat from specific sample regions within the TRACE project correlates well with that of the natural mineral water as predicted by our map. The proof of principle shown in our paper is highly relevant for geographical food authentication as it allows an assessment of the origin of food products without the immediate need for geographically authenticated materials which may not always be available. Our approach provides a cost effective first instance screening tool