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Electron paramagnetic resonance (EPR) spectroscopy

Identification

Key words EPR spectroscopy, food control, paramagnetic centre, colour centres, free radical, irradiation control
Latest version 2012/10/08
Completed by UTCN

How does it work?

Primary objective EPR is used in food technology for determining the composition of food products, quality and process control, and chemical composition control.
Working principle Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance (ESR) spectroscopy, is a technique for detecting and measuring chemical species with one or more unpaired electrons (paramagnetic transition metal and lanthanide ions, organic and inorganic free radicals, colour centres).

The physical concept of EPR is related to the unpaired electron spin of paramagnetic species present in a sample. By interacting with an external magnetic field (Bo), the electronic spin behaves within certain limits and aligns itself either parallel or unparalleled to the field. Each alignment has a specific energy. The resonance of the unpaired electron in the magnetic field (its jump between the two energy levels) can be obtained by either varying the electromagnetic waves frequency while holding the magnetic field constant, or doing the reverse. In practice, it is usual to vary the magnetic field and maintaining constant the frequency. Usually, EPR spectra are obtained with electromagnetic waves from the 9÷10 GHz range (microwaves) and magnetic fields of 3,000÷4,000 Gauss [2-6].

Images
Additional effects -
Important process parameters Paramagnetic character [7]
Important product parameters Dimension

What can it be used for?

Products EPR spectroscopy is able to analyse only samples containing chemical species with unpaired electrons (paramagnetic species), from products such as:
  • frozen raw meat (beef, pork, poultry and fish)
  • seeds of fruits (dates and figs) f.i. < 10-12 mol/l
  • dried mushrooms
  • gelatine and macaroni
Operations Raw material and final product quality control, process control, detection and measurement of free radicals and antioxidants
Solutions for short comings The EPR spectroscopy is a fast method, don't need a preliminary preparation of the samples before measurements and it’s easy to use. EPR spectroscopy matches with the needs of the food industry since it offers solutions for important problems such as the detection and measurement of free radicals (as result of decomposition processes, heat treatments and radio-sterilisation processes), detection and measurement of irradiated products or the study of antioxidants. EPR spectroscopy is the only method to detect the paramagnetic species [8-10].

Some applications of the the EPR spectroscopy in food industry are:

  • chemical characterization of the free radical molecules, some transition metal and rare-earth ions (Cu2+, Mn2+, V4+, Fe3+, Gd3+, Eu3+, etc.) of food products (i.e, tea, wine, vegetable oils)
  • detection and measurement of free radicals (ROS = reactive oxygen species) in food products
  • flavour stability control (i.e., for beer).
  • irradiation control of food products
  • antioxidant activity detection [1-4]

What can it NOT be used for?

Products Food samples without paramagnetic species.
Operations None, as long as they result in paramagnetic species.
Other limitations A limitation is related to the dimensions of the sample. Thus, it is difficult to accomplish the requirement to have a homogeneous and constant magnetic field in the sample holder area for samples bigger than a few 10-100 millimetres.
Risks or hazards There are no risks associated with the use of the EPR spectroscopy in food industry.

Implementation

Maturity EPR spectroscopy has a long tradition in food science at laboratory scale, especially related to the food irradiation control. EPR devices are available in lab and on an industrial scale.
Modularity /Implementation The implementation of EPR spectroscopy in food industry at a large scale is expected. For this purpose, bench top EPR equipments are available. This type of equipment fulfils important criteria such as ease-of-use, turn-key-operation, high sample throughput, automatic reporting of results and low price of equipment. Bench top EPR spectrometers can be used as in-line equipments [11].
Consumer aspects -
Legal aspects The EU norms define the food irradiation control via EPR spectroscopy in CODEX General Standard for Irradiated Foods, CODEX STAN 106 - 1983, rev.1-2003 by:
  • EN 1786:1996.Foodstuff - Detection of irradiated containing bone by ESR spectroscopy
  • EN 1787:2000.Foodstuff - Detection of irradiated food containing cellulose by ESR spectroscopy
  • EN 13708:2001. Foodstuff - Detection of irradiated food containing crystalline sugar by ESR spectroscopy
Environmental aspects The use of the EPR spectroscopy does not generate environmental problems.

Further Information

Institutes IRTA, INRA
Companies Bruker, Magnettech, Active Spectrum, JEOL
References 1. Lund A, Shiotani M., Shimada S., Principles and Applications of EPR Spectroscopy, Springer Verlag 2011

2. Gudjondottir M., Belton P.S., Webb G.A., Magnetic Resonance in Food Science: Challenges in a Changing World, RSC Publishing, 2009

3. Desrosiers M.F., Current status of the EPR method to detect irradiated food, Applied Radiation and Isotopes, 47, 11-12 (1996) 1621-1628

4. Duliu O.G, Ferdes M. and Ferdes O.S., EPR study of some irradiated food enzymes, Journal of Radioanalytical and Nuclear Chemistry 260, 2 (2011) 273-277, DOI: 10.1023/B:JRNC.0000027095.19005.e7

5. Waclaw Stachowicz W., Strzelczak-Burlinska G., Michalik J., Wojtowicz A., Dziedzic-Goclawska A., Ostrowski K, Application of electron paramagnetic resonance (EPR) spectroscopy for control of irradiated food, Journal of the Science of Food and Agriculture, 58, 3 (1992) 407-415, DOI: 10.1002/jsfa.2740580316

6. Poulet S.A., Wichard T., Ledoux J. B. Ledoux, Lebreton B., Marchetti J., Dancie C., Bonnet D., Cueff A., Morin P., Pohnert G., Influence of diatoms on copepod reproduction. I. Field and laboratory observations related to Calanus helgolandicus egg production, Inter Research MEPS 308:129-142 (2006)-doi :03354/meps308129

7. Stasko A., Polovka M., Brezova V., Biskupic S., Malık F., Tokay wines as scavengers of free radicals (an EPR study), Food Chemistry 96 (2006) 185–196

8. Levêque P.P., Godechal Q., Gallez B., EPR Spectroscopy and Imaging of Free Radicals in Food, Israel Journal of Chemistry, 48, 1 (2008) 19-26

9. Bors W, Kazazic S.P., Michel C., Kortenska V.D., Stettmaier K., Klasinc L., Methoxyphenols: Antioxidant principles in food plants and spices: Pulse radiolysis, EPR spectroscopy, Int.J.Quant.Chem., 90, 2 (2002) 969-979

10. Stopka P., Krizova N., Vrchotova P., Babikova A., Trizka L., Balik J., Kiselakova M., Antioxidant Activity of Wines and Related Matters Studied by EPR Spectroscopy, Czech J. Food Sci. 26 (2006) S49–S54

11. Prasuna CP, Chakradhar RP, Rao JL, Gopal NO., EPR as an analytical tool in assessing the mineral nutrients and irradiated food products-vegetables, Spectrochim Acta A Mol Biomol Spectrosc. 71(3) (2008) 809-813

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Created by Hte irta on 8 October 2012, at 12:31