Study On Identification Of Irradiated Food By Electron Spin Resonance Spectrometry

The safety of agricultural products and food is a major livelihood issue. With global trade integration, the theme of the development of food tends to be more healthy, safety, sanitary and nutrition, food irradiation technology, for its distinctive feature, plays an irreplaceable role in making sure food hygiene, safety, reducing pollution and residues, and ensuring environmental safety. China is the world's largest country in food irradiation, every year the amount of food by irradiation accounts for 1/4 of global amount, the food irradiation facilities and total amount of irradiated food are advanced in the world. However, in recent years with increasing demand for production, consumption and international trade of irradiated food, The European Union and some developed countries developed a variety of settings on technical barriers to trade by their technology advantages in food irradiation testing which gave a negative influence to our country's export of produce. The Qixian'⁶⁰Co accident'happened in Henan which caused the mass hysteria and the'irradaition gate'which caused by Chef Kang brand of ready-to-eat noodles in labeling of irradaition on flavoring bags all caused extensive concern of the whole society in the safety of irradiated food. Therefore, it is very important and of practical significance to study on an easy and fast method to identify the irradiated food and unirradiated food, and also measure or determine the irradiation dose.In this paper, plant-based foods were chosen for experiments and the electron spin resonance (ESR) technique was used as a detecting method. Different kinds of foods were irradiated as different doses which in order to build the relationship between the ESR spectrums and different doses in the same food and the relationship between the ESR spectrums and the same dose in different foods. Moreover, features of ESR spectrum in different parts of food were also studied. We studied the influencing factors which produced the ESR signal intensity and revealed the relation in irradiation dose and ESR intensity and we also discussed the ESR signal attenuation change in storage period. In addition to this, this paper take the lead in detecting the ESR spectum of food which irradiated by different type of rays (γrays and EB), ultimately, we preliminarily established a national criterion for detection of irradiated plant-based foodstuffs by use of ESR. This paper also take the lead in estimation of the initial absorbed dose in irradiated food by using the dose-additive method, and this provide theory on the determination model of the irradiation dose. The main content of this paper and results showed as follows:1. Sunflower seeds, walnuts, pistachios and hazelnut were used as experimental materials which were irradiated to different doses. We studied the relationship between ESR intensity, irradiation dose, and correlation R². The results showed that ESR spectrum of irradiated samples was obviously different from that of non-irradiated samples, and the ESR signal intensity was positively related with the irradiation dose. After irradiation the ESR intensity and spectrum shape all had changed and we could identify whether or not four kinds of food had been irradiated. The appearance of the two weak satellite lines which situated left and right to the intense singlet line in walnut and pistachio nut samples proved the existence of the cellulose radical. The detection limit of walnut was 1 kGy, the detection limit of the remaining three kinds of samples was even lower than 1 kGy. 2. Four kinds of spices (paprika, mustard powder, curry powder and ginger powder) were used as test materials to study the feature changes of ESR spectrum and the ESR intensity in the range of 0 to 15 kGy and to research on the variation of ESR intensity in the storage period of 220 days. The results showed that the ESR spectroscopy of four kinds of spices was obviously different before and after irradiation, the intensity of ESR signal increased with the increasing of the irradiation dose. The ESR intensity of all samples decreased during the storage time, even after 220 days ESR method could also be used to identify the other three kinds of irradiated samples except mustard powder.3. The grape skins, grape stalks and grape seeds were used as test materials to study the feature changes of ESR spectrum and the relationship between ESR intensity and irradiation dose. The results showed that the ESR spectroscopies of grape skins, grape stalks and grape seeds was obviously different before and after irradiation, the intensity of ESR signal increased with the increasing of the absorbed dose. The grape stalks which had the minimum detection limit (0.25 kGy) could be used as an ideal experimental material to identify whether or not grapes had been irradiated. By comparing the dose effect curves of grape skins, grape stalks and grape seeds it was concluded that grape stalk curve showed the most accurate (R²=0.9943). The ESR intensity of three kinds of irradiated samples all decreased during the storage time (15 d), grape skins showed severest attenuation (attenuation 80%).4. The white pepper powder, paprika powder, cumin powder and pistachios were used as test materials to study the feature changes of ESR spectrum a?nd the relationship between ESR intensity and irradiation dose in different doses, the shape variation of ESR spectrum inγ-rays and electron beams was also compared. The results showed that the ESR spectrum of 4 kinds of irradiated samples was obviously different before and after irradiation, the intensity of ESR signal increased with the increasing of the absorbed dose. The dose above 432 Gy could be detected in white pepper powder and pistachios, the dose above 875 Gy could be detected in paprika powder and cumin powder. The ESR intensity of all samples decreased during the storage time (200 d), even after 200 days the ESR method could also be used to identify 4 kinds of irradiated samples. The same dosage ofγ-rays and electron beams has no significant influence on the shape of ESR spectrum, however, the difference of irradiation mechanism caused slight impact on ESR intensity.5. The cumin was studied as experimental material to investigate the feature changes of ESR spectrum and the relationship between ESR intensity and irradiation dose and the initial absorbed dose of cumin was assessed by using the dose-additive method. The results showed that even after 220 days ESR method could also be used to identify whether or not the cumin has been irradiated. The dose additive method can be used for a reliable evaluation of the absorbed dose in cumin and the deviation between the initial dose and the dose estimated by using 3rd degree polynomial function at different storage times (10, 20 and 30 days) after initial irradiation is all less than 1 kGy, the estimated doses of samples using the 3rd polynomial function are more close to the actual doses than using the exponential function. The ESR technique could be used as a qualitative and quantitative method to indentify irradiated cumin.