ISO-FOOD ERA Chair for isotope techniques in food quality, safety and traceability Isotopes in food research
The ISO-FOOD ERA Chair for isotope techniques in food quality, safety and traceability develops advanced analytical methods of chemical analysis and complementary isotope techniques, which can uncover information that conventional techniques cannot provide, i.e. that of geographical origin, authenticity, or new and emerging contaminants in foodstuffs. Welcome Isotope techniques are used for determining isotopic ratios of elements, which cannot be obtained by conventional chemical analysis. Because of specific behaviour of isotopes in physical and chemical processes, isotope ratios of individual elements in soil, water, plant and animal tissues or molecules provide exclusive information on their origin or formation pathways. Isotope analysis is thus providing complementary information to that obtained by conventional analytical methods for determining elemental composition, toxic ionic species, organic compounds or radionuclides in the food we eat. Isotopes, on their own or combined with chemical composition, carry unique information supporting food safety and traceability and authentcity.
Isotopes are atoms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in atomic mass. Most elements have more than one natural isotope. All of them have the same chemical properties, regardless of whether they are stable or radioactive (decaying with time). Differences in their masses result in different reaction rates between heavy and light isotopes of the same element. Isotopes: tiny, yet big differences 1 1H 2 1H 3 1H
Changing isotope ratios The distribution of isotopes varies in nature, depending on the physical and (bio)chemical reactions in which they are involved - a process known as isotope fractionation. For instance during evaporation and condensation, water is always enriched with heavy isotopes ( 2 H, 18 O) compared to water vapour. The further from the source (ocean), the higher in the mountains, and the lower the temperature, the more depleted in the heavier isotope of oxygen and hydrogen is the rain or snow. This gives the precipitation in each region a distinct isotopic composition. Similar fractionation occurs during photosynthesis: plants preferentially absorb light 12 C and further fractionate it during photosynthesis. Different photosynthetic pathways are reflected in different C isotopic ratios in plants and crops. The so-called C3 photosynthesis produces plants with significantly less of the heavy carbon isotope ( 13 C) than C4 photosynthesis. Initial precipitation Later precipitation evaporation C3 C4
Authentic or fraud? Food fraud refers to the addition, tampering or misrepresentation of food, food ingredients or food packaging, or false or any other misleading statements made about a product for economic gain. Although it might not necessarily be dangerous for the consumer s health, it is illegal and results in reduced consumer confidence, economic loss, and damage to brand identity. Certificates of geographical origin or production practice (PDO protected designation of origin; PGI protected geographical indication) represent a considerable added value to the food product, therefore robust methods for fraud detection are needed. Fraud detection is a major analytical challenge: it means searching for region-specific indicators such as isotopic compositions that can differentiate between botanical origin (e.g. soy oil in olive oil), species (e.g. cow milk in goat cheese), fraudulent practices (e.g. sugar syrup in honey) or additions of illicit substances (e.g. melamine in milk). Statistical evaluation of isotopic, elemental and chemical profiles of food then reveals the accordance or deviation of analysed samples from authentic food products. Obviously, this approach depends on having the ability to compare unknown samples with a database of authentic products of known origin and year of production. Databases need to have a sufficient number of samples to have good geographic coverage and list as many parameters as possible so as to capture natural variations.
Geographical origin of food Commonly used indicators of geographical origin are the isotopic ratios of oxygen ( 18 O/ 16 O) and hydrogen ( 2 H/ 1 H) in water and organic molecules in plants and animals (e.g. cellulose, proteins, lipids). The isotopic composition of water in milk or fruit juice varies from region to region even within a small country such as Slovenia. Combined with other geographical indicators, such as the elemental fingerprint (derived from bedrock and water), isotopes are the most powerful tool for determining the geographical origin of food. To assure optimal yields, fertilisation with nitrogen is inevitable in both conventional and organic agriculture. Isotopes can help differentiate between the two production regimes: synthetic nitrate and ammonia have different isotopic compositions than sludge or organic fertilisers, and this difference can be traced to plants. In a similar way, the type of feed fed to cattle and poultry can also be traced: maize is enriched in 13 C compared to grass, and this difference is reflected in the isotopic composition of carbon in animal products, such as meat and milk. Organic or conventional? NPK > -3-4.5-3 -13-6.5 δ 18 O in rain water < -4.5 δ 18 O in cow milk Synthetic fertilisers have more light 14 N than organic fertilisers. Plants fertilised with organic fertilisers are enriched in 15 N compared with those fertilised with synthetic nitrate.
Non-traditional stable isotopes While stable isotopes of water and nutrients have been analysed for decades, the analyses of isotopic ratios of other elements ( non-traditional isotopes ) are relatively new since they require expensive state-of-the-art analytical equipment and exhaustive extraction procedures. The relative abundances of stable and radioactive isotopes of certain food contaminants, such as lead, zinc or mercury, vary between different geological sources, therefore isotopic fingerprinting of contaminants can provide information on their source. Based on the isotopic ratios of an element, for instance lead, it is possible to estimate whether the lead in the soil and crops is of natural origin (e.g. weathering of bedrock), or if it derives from anthropogenic sources. The European Commission has recently adopted the regulation of permissible levels of the most common natural (polonium, radium, uranium-238, thorium-232) and man-made radionuclides (plutonium, americium, and by-products of nuclear fission, such as cesium-137 and strontium-90) in water, food and feed. To assure consumer safety, rapid methods for determining low levels of radionuclides, and dose assessments due to intake of various foodstuffs and water for infants, children and adults have been developed. Since most foodstuffs are highly complex matrices and the concentrations of radionuclides are usually extremely low, new opportunities are being explored by combining radiochemical and mass-spectrometric methods. Radionuclides 206 Pb 204 Pb Energy spectrum of polonium radioisotopes in mussels 209 Po 210 Po
Isotopes in analytics Isotope dilution and isotope labelling Some elements are present in trace amounts and require sensitive analytical methods for their determination. The identification and quantification of molecular or ionic forms of different elements (speciation), which greatly determine their toxicity, bioavailability and behaviour, is analytically challenging. One such method is isotope dilution whereby a known amount of the same, but isotopically labelled element (or species) is added, and then the total concentration of this element (species) and its isotopic composition are measured. The initial amount of the element in the sample can then be calculated. In this way, we can assess the risk posed by potentially harmful species, such as chromium in tea. This approach can be applied to wide spectrum of essential and toxic elements, compounds and element-based nanoparticles. Radiochemical analysis and radiolabelling Radiochemical analysis is one of the most popular applications of nuclear techniques. Irradiation - bombardment with neutrons of samples in a nuclear reactor converts chemical elements into their artificial radioactive isotopes, which cannot be produced in nature. Their concentration is then analysed by α, β or γ counters; any further extraction procedure of target elements from irradiated samples, if necessary, cannot induce any contamination, therefore elements in very low concentrations can be determined. Such radiolabelling can be used for the production of radioactive tracers for tracer experiments, for instance, to determine the uptake and fate of elements or nanoparticles.? + = 50 50 Cr 53 Cr 53 50 Cr Cr Cr 53 Cr Add known amount of labelled Cr. Natural unnown amount of Cr isotopes.. Calculate original amount of Cr isotopes Measure total amount of Cr isotopes..
Analytical challenges and data quality Food analysis encompasses many metrological challenges: complex matrices and low concentrations of analysed species require new sample processing, validated methods, and stateof-the-art facilities. In the case of compound-specific isotope analyses and analysis of non-traditional stable isotopes, extraction procedures require alterations, which do not cause isotope fractionation of the target isotope in the analyte. Analysis often requires hyphenated high resolution mass spectrometric techniques with chromatographic separation. In the case of nanoparticles in food, methods have yet to be developed for their extraction and characterisation. Every day, thousands of compositional, nutritional, allergenic, isotopic, and contaminant profiles of all kinds of foods are generated worldwide. These data contain a wealth of information, however, to retrieve a custom-made, science-based analysis from millions of data, internationally coordinated databases and software for data management and processing are necessary. The task of food informatics is therefore to extract information and manage knowledge from food research. For example, the spatial databases of isotopic parameters of food are used to produce isotopic maps ( Isoscapes ) which will show the isotopic composition of authentic food products. Data management The greatest overall challenge remains establishing standardised procedures and producing suitable certified reference materials for quality control and calibration. Sampling + Processing + Measurement = Result Representative Appropriate Contamination Stability Handling Dissolution Extraction Dilution Labelling Comparison to SI units or conventional scale ± uncertainty
Capacities for tomorrow The Jožef Stefan Institute invests a great deal of effort and resources into strengthening its capacities in terms of knowledge and infrastructure. In 2015, the Department of Environmental Sciences, which hosts the ERA Chair ISO-FOOD, upgraded the Centre of Mass Spectrometry and other laboratories with state-of-the-art research equipment. This enables the development of new analytical methods required for pushing the boundaries of interdisciplinary research in environmental and food science. Moreover, recent projects funded from national sources, through EU Regional Development Funds, and the Horizon 2020 Twinning programme will enhance the use of isotopically based methodologies. Collaboration in international projects and in study programmes at the postgraduate level with the Jožef Stefan International Postgraduate School keeps contact with the European and world s leading institutions and facilitates research at the cutting edge of analytical chemistry. The ERA Chair for isotope techniques in food quality, safety and traceability develops new methods and provides education and training for food analysis and characterisation. The main research topics include: isotope and elemental fingerprinting and chemical profiling of food for determining the authenticity and geographical origin trace element speciation and fractionation determination of organic contaminants and their transformation products developing methods for detecting radionuclides at low activity concentrations nanoparticle determination and characterisation food composition databases and data management While focused on food safety, traceability and authenticity research using advanced analytical methods, attention is paid to metrology and accreditation of laboratories and methods and preparation of a repository of data and knowledge on food analysis and composition. The ERA Chair builds its sustainability in tight collaboration with national and international stakeholders from academia, science and industry. Education through research Beside performing research and training at the PhD and postdoctoral levels, the exchange of knowledge and best practices is facilitated at ISO-FOOD Exploratory Workshops, ISO-FOOD Training Courses, Summer Schools and through interlaboratory comparison exercises.
For more information please visit our web-pages: www.isofood.eu and www.environment.si. Follow us on Facebook and Twitter! General information: info@isofood.eu Contact: ERA Chair ISO-FOOD Jožef Stefan Institute Jamova cesta 39 SI-1000 Ljubljana, Slovenia ISO-FOOD received funding from the European Union s Seventh Framework Programme for research, technological development and demonstration under grant agreement No. 621329 (2014-2019). ISO Fd Food Naklada: 1000 izvodov Tekst: IJS, Odsek za znanosti o okolju Oblikovanje in ilustracija: Irena Gubanc, Mateja Škofič (Padalci) Fotografija: Miran Kambič u.d.i.a.; arhiv IJS Tisk: Graphtech