Using plant physiological stable oxygen isotope models to counter food fraud

Determination of exogenous water in grape juice through the isotopic analysis of 18O/16O

Abstract The consumption of grape juice has been growing significantly, so its quality is becoming an issue of great importance, both for the consumer and for the industry. However, identifying adulteration in juice is a great challenge and requires a reliable analytical process. The isotope ratio (18O/16O) is an important tool to determine the addition of exogenous water in beverages, however, there is no official method for juice in Brazil. This study aimed to develop and validate a method for detecting exogenous water in grape juice through isotopic analysis of 18O/16O. The development and validation of the analytical method were performed using Isotope Ratio Mass Spectrometry (IRMS). The effect of temperature and evaporation of δ18O in experimental juices was evaluated, and reference values were found for juices based on the δ 18O of musts. The influence of the juice industrial production process on 18O values was verified, and commercial juices were evaluated in relation to the values of reference regarding the addition of water. The temperature and evaporation parameters did not influence the results of the 18O of the juice, as they presented differences lower than the method uncertainty. The heat exchanger system did not influence the proposed method. The reference values for juice can come from the musts, without affecting the interpretation of the final results. Of the thirty real juices analyzed, nine had exogenous water, three proved to be reconstituted juices and eighteen were considered to have no exogenous water. The method proposed and validated in this study presented values for the limit of detection (LOD) of 0.24‰, the limit of quantification (LOQ) of 0.97‰ and measurement uncertainty of 0.71‰, proving to be effective for the detection of exogenous water in grape juice, through of the analysis of the isotopic ratio of 18O/16O by IRMS.

Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in leaf sucrose

Experimental approaches to isolate drivers of variation in the carbon-bound hydrogen isotope composition (δ² H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how ² H-fractionations in carbohydrates differ between species. We analysed, for the first time, the δ² H of leaf sucrose along with the δ² H and δ¹⁸ O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ² H of sucrose explained 66% of the δ² H variation in cellulose (R²  = 0.66), which was associated with species differences in the ² H enrichment of sucrose above leaf water ( ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0001" wiley:location="equation/pce14362-math-0001.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mtext>\unicode{x003B5}</mtext><mtext>sucrose</mtext></msub></mrow></math> : -126% to -192‰) rather than by variation in leaf water δ² H itself. ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0002" wiley:location="equation/pce14362-math-0002.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mtext>\unicode{x003B5}</mtext><mtext>sucrose</mtext></msub></mrow></math> was positively related to dark respiration (R²  = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R²  = 0.38), but only when ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0003" wiley:location="equation/pce14362-math-0003.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><msub><mi mathvariant="normal">\unicode{x003B5}</mi><mtext>sucrose</mtext></msub></mrow></mrow></math> was fixed to the literature accepted value of - 171 <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0004" wiley:location="equation/pce14362-math-0004.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>\unicode{x02212}</mo><mn>171</mn></mrow></mrow></math> ‰. No relation was found between isotopic exchange of hydrogen and oxygen, suggesting large differences in the processes shaping post-photosynthetic fractionation between elements. Our results strongly advocate that for robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizing δ² H of sugars is needed.

Differentiation of Apricots of Different Geographic Origin in Central and Southern Europe by Applying 87Sr/86Sr Analysis: Potential and Limitations

Consumers prefer food commodities of certain origins over the same products of other provenances and are willing to pay higher prices for them. Thus, it is possible to increase profit simply by giving an incorrect geographic origin to a product. To effectively control the declared geographic origin of food, the product itself has to be investigated to discover whether it actually originates from the declared origin, or if it has been mislabeled. Conventionally, control of a geographic origin is conducted by stable isotope analysis of the main elements, which has proven to be successful in numerous cases, but often reference data have to be produced anew for every harvest to control, resulting in additional costs and delays. Applying entirely geogenic parameters for the control of provenance requires reference data to be produced only once. As they do not vary between years and harvests, they can often be used for different (food) commodities. Here, we investigate whether the geographic origin of apricot samples can be controlled by their 87Sr/86Sr ratios measured by TIMS. The results show that Slovak and Hungarian apricots can be differentiated from the Wachau apricots, a well-known regional Austrian brand, and those from other regions in Austria, even though the differentiation from the latter is only partial. 87Sr/86Sr investigations can be a very potent tool; however, its success depends on the exact question that needs to be answered.

Effects of phenotypic variability on the oxygen and hydrogen isotope compositions of grains in different winter wheat varieties

Stable isotope analyses are the leading method for geographic origin determination, especially of plant-based agricultural products. Origin analysis is typically done by comparing a suspicious sample to reference materials with known geographic origin. Reference materials are usually collected at the species level, assuming different varieties of a species to have comparable isotope compositions within a given location. We evaluated whether different phenotypes that are expressed in different varieties of winter wheat (Triticum aestivum L.) influence the oxygen (δ¹⁸O) and hydrogen (δ²H) isotope composition of plant tissue water and organic compounds. We found that mean δ¹⁸O and δ²H values among winter wheat varieties did not differ significantly in leaf water, however, differed significantly in bulk dried grain tissue. The differences in bulk dried grain δ¹⁸O and δ²H values among varieties can be related to differences in phenotypic trait expression among varieties. Despite this substantial phenotypic variability, the overall variability of bulk dried grain δ¹⁸O and δ²H values among varieties was small (SD 0.54 ‰ for oxygen, 3.60 ‰ for hydrogen). We thus conclude that reference materials collected at the species level should be sufficient for geographic origin analysis of winter wheat and possibly other cereals using δ¹⁸O and δ²H values.