Andreas Rossmann

DETERMINATION OF STABLE ISOTOPE RATIOS IN FOOD ANALYSIS

Within the last few years, stable isotope analysis has gained increasing importance in authenticity control of food and food ingredients. The development of the methodology from its start in the geological sciences is reviewed, the requirements and the specific features of the technique in the area of food quality assessment are outlined, and the progress in instrumentation during the last few decades is described. Scope and limits of the analysis of stable isotope ratios to assess the quality and to determine the origin are demonstrated for foods, such as fruit juice, wine, spirits, or beer. The classical approaches investigating hydrogen, carbon and oxygen isotopes as well as strategies including elements, such as nitrogen and sulfur, are reviewed. The present state of the art and future possibilities of the methodology are discussed.

Isotopic and Elemental Data for Tracing the Origin of European Olive Oils

H, C, and O stable isotope ratios and the elemental profile of 267 olive oils and 314 surface waters collected from 8 European sites are presented and discussed. The aim of the study was to investigate if olive oils produced in areas with different climatic and geological characteristics could be discriminated on the basis of isotopic and elemental data. The stable isotope ratios of H, C, and O of olive oils and the ratios of H and O of the relevant surface waters correlated to the climatic (mainly temperature) and geographical (mainly latitude and distance from the coast) characteristics of the provenance sites. It was possible to characterize the geological origin of the olive oils by using the content of 14 elements (Mg, K, Ca, V, Mn, Zn, Rb, Sr, Cs, La, Ce, Sm, Eu, U). By combining the 3 isotopic ratios with the 14 elements and applying a multivariate discriminant analysis, a good discrimination between olive oils from 8 European sites was achieved, with 95% of the samples correctly classified into the production site.

Stable isotope ratios, major, trace and radioactive elements in emmental cheeses of different origins

Twenty Emmental cheeses from six European regions (Allgau (D), Bretagne (F), Finland, Savoie (F), Switzerland and Vorarlberg (A)) were analysed for stable isotope ratios such as 13C/12C, 15N/14N, 18O/16O, D/H and 87Sr/86Sr, as well as major (Ca, Mg, Na, K), trace (Cu, Mn, Mo, I) and radioactive elements (90Sr, 234U, 238U). The discriminating potential of these parameters was evaluated using difference tests of mean values and principal component analysis (PCA). “Finland”, “Bretagne” and “Savoie” cheeses were well separated using δ13C-, δ15N-, δ2H- and δ87Sr-values. Concentrations of molybdenum and sodium allowed the groups “Switzerland”, “Vorarlberg” and “Allgau” to be separated. 90Sr activity was highly correlated with the altitude of the production zone. Using this parameter, “Finland” and “Bretagne” were separated from “Vorarlberg” cheese. The results of the current screening test will help selecting the best tracers of origin for the remainder of the project.

Multielement (H, C, N, O, S) stable isotope characteristics of lamb meat from different Italian regions

The study focuses on the (2)H/H, (13)C/(12)C, (15)N/(14)N, (18)O/(16)O and (34)S/(32)S values of defatted dry matter (DFDM) and on the (2)H/H, (13)C/(12)C and (18)O/(16)O values of the fat fraction of meat samples from various lamb types reared in seven Italian regions, following different feeding regimes (forage, concentrate, milk). The (13)C/(12)C (r = 0.922), (2)H/H (r = 0.577) and (18)O/(16)O (r = 0.449) values of fat and DFDM are significantly correlated, the fat values being significantly lower for C and H and higher for O than for DFDM values and the differences between the two fractions not being constant for different lamb types. The feeding regime significantly affected the (13)C/(12)C, (15)N/(14)N, (18)O/(16)O and (2)H/H of fat. The DFDM (2)H/H, and (18)O/(16)O values, excluding an outlier, are significantly correlated with the corresponding values in meteoric waters, thus allowing us to trace the variability of geoclimatic factors. (15)N/(14)N is influenced by pedoclimatic conditions, whereas (34)S/(32)S is influenced by the sea spray effect and the surface geology of the provenance area. By applying stepwise linear discriminant analysis only the (2)H/H of fat was found not to be significant and 97.7% of the samples were correctly assigned to the lamb type and more than 90% cross-validated. With the feeding regime, 97.7% of the samples were both correctly assigned and cross-validated using a predictive model including (13)C/(12)C, (15)N/(14)N, (18)O/(16)O, (34)S/(32)S of DFDM and (18)O/(16)O of fat.

Coast and year effect on H, O and C stable isotope ratios of Tyrrhenian and Adriatic italian olive oils

The paper discusses the (2)H/(1)H, (18)O/(16)O and (13)C/(12)C ratios of 196 authentic Italian extra-virgin olive oils produced in 3 years on the Tyrrhenian and Adriatic coasts. The (2)H/(1)H and (18)O/(16)O ratios were linearly and positively correlated. The year of production influenced mainly (18)O/(16)O in relation to the amount of rainfall and the atmospheric humidity in the period of oil accumulation in the olives. The (2)H/(1)H ratio significantly distinguished the olive oils produced on the Adriatic coast from those on the Tyrrhenian coast in each year. This coast effect is a consequence of the different sources and isotopic compositions of the rainfall and the different climatic conditions on the two coasts. The paper contributes towards understanding the influence of climatic factors on isotopic variability and towards improving the traceability of the geographical origin of olive oils, using (2)H/(1)H as a more innovative parameter.

Humans and Camelids in River Oases of the Ica–Palpa–Nazca Region in Pre-Hispanic Times – Insights from H-C-N-O-S-Sr Isotope Signatures

Thirty years ago the use of isotope abundance ratios (IR) of bioelements in nutrition studies was a rather young discipline (Krueger and Sullivan 1984). Developed from hydrology, geochemistry, cosmo- and geochronometry isotope studies became a fertile tool also in other fields, and had an especially productive impact on archaeology, respectively, archaeometry (Koch et al. 1994; Buikstra et al. 2005).

Global spatial distributions of nitrogen and carbon stable isotope ratios of modern human hair

RATIONALE Natural stable carbon (δ(13)C) and nitrogen isotope ratios (δ(15)N) of humans are related to individual dietary habits and environmental and physiological factors. In forensic science the stable isotope ratios of human remains such as hair and nail are used for geographical allocation. Thus, knowledge of the global spatial distribution of human δ(13)C and δ(15)N values is an essential component in the interpretation of stable isotope analytical results. METHODS No substantial global datasets of human stable isotope ratios are currently available, although the amount of available (published) data has increased within recent years. We have herein summarised the published data on human global δ(13)C andδ(15)N values (around 3600 samples) and added experimental values of more than 400 additional worldwide human hair and nail samples. In order to summarise isotope ratios for hair and nail samples correction factors were determined. RESULTS The current available dataset of human stable isotope ratios is biased towards Europe and North America with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ(13)C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ(15)N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production. CONCLUSIONS There are still a large proportion of countries, especially in Africa, where there are no available data for human carbon and nitrogen isotope ratios. Although the interpretation of modern human carbon isotope ratios at the global scale is quite possible, and correlates with the latitude, the potential influences of extrinsic and/or intrinsic factors on human nitrogen isotope ratios have to be taken into consideration.

Determination of the 13C contents of organic acids and sugars in fruit juices: an inter-comparison study

Abstract The determination of the repeatability (r) and reproducibility (R) of the ( 13 C / 12 C ) measurement in sugars and organic acids contained in different fruit juices was conducted on an international basis involving 17 laboratories. The mean values of r‰ (R‰) for acids and sugars are, respectively, equal to 0.58 (1.75) and 0.34 (0.71) and the relatively large values observed for R of acid determinations are related to the preparation step. However, the least significant difference computed for several pairs of natural and spiked juices indicate that the 13 C method can be applied for detecting fruit juice adulteration.

Improved detection of sugar addition to apple juices and concentrates using internal standard 13C IRMS

Abstract In order to improve the detection of sugar addition in apple juice using isotopic methods, malic acid has been defined as a suitable internal standard for the determination of the carbon 13 content. After a clean-up step, sugars and organic acids were separated from each other by an anion exchange process, and pure malic acid was isolated by preparative reversed-phase liquid chromatography (LC). This method has been applied to the stable isotope analysis of apple juice samples of different origins and years. A correlation between the carbon isotope ratios of sugars and malic acid has been observed, and cutoff points concerning the difference of δ 13 C values between those metabolites have been defined. In the case of the addition of sugar from C4 plants (such as corn and cane), it has been demonstrated that the detection limit can be as low as 5% whereas it is often higher than 10% while using the conventional carbon 13 method on the whole juice.

Special Issue dedicated to Professor Hanns-Ludwig Schmidt on the occasion of his 85th birthday

This Special Issue of Isotopes in Environmental and Health Studies honours Hanns-Ludwig Schmidt, a pioneer of stable isotope science. H.-L. Schmidt has had a most distinguished career in isotope research. It started with the synthesis of radioactive tracer compounds and led to a wide range of fundamental, methodical and applied research on the stable isotope composition of the main elements of the biosphere, principally 13C/12C, 15N/14N, 2H/1H, 18O/16O and 34S/32S. That career has been an awe inspiringly long one, 55 years [1] and counting, as is documented by his contribution to a review on the causes and implications of in vivo isotope fractionations [2] in this Special Issue. Young stable isotope researchers may wonder how such a career could have unfolded, what circumstances and coincidences – academic and other – influenced and guided it, and which interactions with colleagues and students accompanied and enriched it. For that reason H.-L. Schmidt was asked by the Editors of this Special Issue to contribute a personal account of his career. After some hesitation with regard to the appropriateness of such a contribution, H.L. Schmidt agreed and presented us with a concise and lively account of his walks of life with isotopes [1]. H.-L. Schmidt and his students and co-workers have contributed many fundamental findings to several fields of basic and applied stable isotope research, in plant biochemistry, human and animal physiology and ecology, environmental science, archaeology, paleoscience, forensics and food authenticity proofing. That diversity is also reflected in the contributions to this Special Issue by colleagues and by former students and co-workers [2–13]. Schmidt’s own work included early studies on photosynthetic carbon isotope discrimination [14,15], which provides clues on the affiliation of plant species to photosynthetic types, and on limitations of discrete steps in the transfer of CO2 from the air to RuBisCO in both C3 and C4 plants, and on the enzymatic mechanisms underlying post-photosynthetic carbon isotope discrimination phenomena. The occurrence of interand intra-molecular isotope distribution in natural compounds was known at least since the famous paper of Abelson and Hoering [16]. Schmidt and his group provided a theoretical framework explaining such phenomena by connecting observations with specific enzyme reactions during synthesis and degradation processes in autotrophic or heterotrophic organisms [2,17–21]. One such finding with wide implications was the heterogeneous carbon isotope pattern in glucose [22] with a 13C enrichment in the positions C-3 and C-4 which is caused by an equilibrium isotope effect on the aldolase reaction [23]. This pattern, also detectable in leaf soluble sugars and transitory starch [24], is responsible for the 13C depletion of acetogenic lipids and the relationship between δ13C values of the fermentation products ethanol or acetic acid and that of the source sugar ([10] and literature cited therein), and contributes to the 13C enrichment of dark-respired CO2 in plants ([25, see also [9,11]) and in connection with further isotope effects