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.
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.
Welcome
Isotopes:
tiny, yet big
differences
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.
1
1
H
2
1
H
3
1
H
ap
o ra ti o
n
C4
ev
C3
al p
recipitat
io
te
r pr
io
ecipitat
n
In
it i
La
Similar fractionation occurs during photosynthesis: plants
preferentially absorb light 12C 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 (13C) than C4 photosynthesis.
n
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 (2H, 18O) 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.
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 (18O/16O) and hydrogen (2H/1H) 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 13C compared to
grass, and this difference is reflected in the isotopic composition of carbon in animal products, such as meat and milk.
NPK
> -3
-4.5 — -3
-13
-6.5
δ O in rain water
18
< -4.5
δ O in cow milk
18
Synthetic fertilisers have more
light 14N than organic fertilisers.
Plants fertilised with organic
fertilisers are enriched in 15N
compared with those fertilised
with synthetic nitrate.
Organic or
conventional?
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
Pb
Pb
206
204
Energy spectrum of polonium
radioisotopes in mussels
Po
209
Po
210
Isotopes in
analytics
Isotope dilution and isotope labelling
Radiochemical analysis and radiolabelling
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 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.
?
+
Add known amount
of labelled Cr.
Cr 53Cr
Cr 53Cr
50
50
Natural unnown
amount of Cr isotopes.
Measure total amount
of Cr isotopes.
.
.
l
cu
Cal
at
eo
to
pe
s
Cr 53Cr
50
=
rigin
is
Cr
al amount of
o
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.
The greatest overall challenge remains establishing standardised procedures and producing suitable certified reference materials for quality control and calibration.
Sampling
+
Representative
Appropriate
Contamination
Stability
Handling
Processing
Dissolution
Extraction
Dilution
Labelling
+
Measurement
Comparison to SI
units
or conventional
scale
=
Result
± uncertainty
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
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.
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.
Education
through
research
For more information please visit our web-pages:
www.isofood.eu and www.environment.si.
Follow us on Facebook and Twitter!
General information: [email protected]
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