Ss Cyril and Methodius University Faculty of Electrical Engineering and Information Technologies, Skopje

Transcription

1 Ss Cyril and Methodius University Faculty of Electrical Engineering and Information Technologies, Skopje

2 Introduction Methods and standards for detection of irradiated food Physical bases of photostimulated luminescence Photostimulated luminescence response under different light conditions Conclusion

3 γ rays X rays electrons Co-60 Cs-137 maximum energy 5 MeV maximum energy 10 MeV

4 <1 kgy Inhibition of sprouting 1 kgy 10 kgy Reducing the number of pathogen microorganisms in fresh and frozen meat, poultry and sea food >10 kgy Sterilization of packed meat and hospital food

5 Treatment of food with ionizing radiation Enhancing food quality Need for techniques for detection Strengthening national regulations Achieving acceptance by consumers

6 Biological changes Radiolysis of lipids Modification of amino acids Microbiological changes Detection of changes Modification of DNA Hydrogen release Modification of carbohydrates Formation of free radicals

7 Changes in physical properties Detection of free radicals Impedance, viscosity, thermal analysis, nuclear magnetic resonance Electron-spin resonance, luminescence (chemoluminescence, thermoluminescence, photostimulated luminescence) Potatoes, pepper, fish, shrimps, eggs, spices Food containing bones, cellulose, crystal sugar, eggs, dehydrated food, spices, herbs, frozen chicken, wheat flour, shells, fresh fruits and vegetables, potatoes, food containing mineral or bioinorganic residuals

8 Physical methods Chemical methods Biological methods EN 1786 Detection of irradiated food containing bone EN 1787 Detection of irradiated food containing cellulose EN 1788 Thermoluminescence detection of irradiated food from which silicate minerals can be isolated EN Detection of irradiated food containing sugar EN 1784 Detection of irradiated food containing fat gas chromatographic analysis of hydrocarbons EN 1785 Detection of irradiated food containing fat gas chromatographic / mass spectrometric analysis of 2- Alkylcyclobutanones EN Detection of irradiated food using Direct Epifluorescent Filter EN DNA Comet Assay for the detection of irradiated foodstuffs EN Microbiological screening for irradiated food using LAL (Limulus amoebocyte lysate)/gnb (Gram negative bacteria) procedures EN Detection of irradiated food by pulsed photostimulated luminescence

9 state excited metastable ground optical stimulation Minerals accumulate radiation energy and store it in the crystal lattice. Some electrons remain trapped in the lattice. radiation measurement of released energy transformation to signal Optical stimulation gives them energy and trapped electrons are released and recombine with holes.

10 Pulsed signal with wavelengths of nm is used as a stimulation. Luminescence signal with wavelengths of nm is detected at the end of every pulse. Samples must contain enough minerals.

11 Screening method simple sample preparation testing by photostimulated luminescence Calibrated method tested samples are treated with ionizing radiation samples are tested for the second time TC project - MAK 5007 Assessing and Enabling the Implementation of Food Irradiation Technologies, funded by IAEA ( )

12 The instrument is supported with a software for computer measurements using program SUERC PPSL.

13 Samples treated with ionizing radiation High threshold Need for further tests Low threshold Unirradiated samples

14 Information necessary for the identification of the sample; Date of sampling and sampling procedure; Date of receipt; Date of test; Results; Length of storage after irradiation and before second measurement; Any points observed in the course of the test; Any operations not specified in the method or regarded as optional which might have affected the results; and A reference to the European Standard EN

15 ln N screening 10 1 kgy t (s) Irradiated paprika standard low threshold high threshold

16 Luminescence may occur under natural and artificial light stimulation on which herbs and spices may be exposed during storage, leading to false-negative results and disabling their proper identification as irradiated or unirradiated. Studying the influence of light on the photostimulated luminescence response is crucial for enhancing consumers confidence and safety.

17 Measurements are done on 4 samples: paprika, guarana, green tea and parsley. All samples are tested by PSL screening method. After that, samples are exposed to light and measurements are taken after certain periods of time.

18 ln N t (months)

19 ln N t (months) paprika guarana green tea parsley

20 ln N t (months) natural light artificial light

21 Irradiated samples kept in the dark gave a positive response. The samples kept under ambient light conditions, in plastic disposable Petri dishes, exhibited a reduction of the PSL signal, more or less pronounced depending on the type of food and type of the light condition. The observed light bleaching of the PSL signal in irradiated herbs and spices was of practical relevance since it may lead to false-negative classifications.

22 The optical bleaching of the PSL signal has been detected in all cases. The strong influence of light, natural and artificial, on the PSL signal was determined.

23 Ivana Sandeva