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an Electron Spin Resonance Study of γ-irradiated Citrus Fruits
Abstract
The ESR spectra of the stalks and skins of a selection of unirradiated and γ-irradiated citrus fruits have been obtained. The spectra from the stalks and skins of unirradiated fruits exhibit only a single line, the intensity of which varies markedly from fruit to fruit. The spectra from irradiated stalks exhibit extra features which can be used to detect irradiation, particularly at higher doses. The spectra obtained from the skins of the irradiated fruits also exhibit radiation-induced features which can easily be used to detect irradiation even at the lowest dose examined (2 kGy). The spectra from the irradiated skins show a high degree of reproducibility from fruit to fruit. These observations suggest that ESR spectroscopy could form the basis of a viable test to determine the radiation history of these fruits.
... The production of either primary or secondary free radicals is indeed one of the main effects of γ-irradiation due to electron release from molecules by high-energy ionizing radiations. Whereas in aqueous environments radicals readily undergo termination reactions and, hence, have short lifetimes, in dry samples radiolytically produced radicals can be trapped within a solid matrix and they can have much longer (even many months) lifetimes (23)(24)(25)(26)(27)(28)(29)(30)(31). This allows radicals to be detected by EPR spectroscopy in dry samples and renders this technique a practical detection method of spice and herb irradiation nowadays included in international protocols (25)(26)(27)(32)(33)(34)(35)(36). ...
... In un-irradiated samples, EPR signals due to transition metal ions, such as Fe 3+ and Mn 2+ (see Figure 3), and a line centered at g ) 2.005 ( 0.001 (see Figures 3 and 4) due to organic radicals (23,24,28,30,31), attributed to quinone radicals (53), were observed. The six-line signal of Mn 2+ (26,34,35,54) centered at g ) 2.006 was easily distinguishable in the spectra of cinnamon and black pepper. ...
... For some samples (nutmeg, cinnamon, bird pepper, and black pepper), shoulders of this signal were also observed, due to signals separated by 14.5 G; in some cases weak signals at g ) 2.022 and 1.994 separated by ∼45 G were also revealed. These signals are reported in the literature for some fruits irradiated with γ-rays (23,24,55). Finally, weak signals due to the cellulose radicals (37) (signals centered at g ) 2.005 with a hyperfine splitting of ∼60 G) could be clearly distinguished in the spectra of nutmeg, oregano, basil, and parsley. ...
Nine spice and aromatic herb samples (i.e., basil, bird pepper, black pepper, cinnamon, nutmeg, oregano, parsley, rosemary, and sage) were gamma-irradiated at a dose of 10 kGy according to commercial practices. The effects of the disinfection treatment on the content of organic radicals and some nutrients (namely, vitamin C and carotenoids) in the samples were investigated by chromatographic and spectroscopic techniques. Irradiation resulted in a general increase of quinone radical content in all of the investigated samples, as revealed by electron paramagnetic resonance spectroscopy. The fate of these radicals after storage for 3 months was also investigated. The cellulose radical was clearly observed in a few samples. Significant losses of total ascorbate were found for black pepper, cinnamon, nutmeg, oregano, and sage, whereas a significant decrease of carotenoids content was observed for cinnamon, oregano, parsley, rosemary, bird pepper, and sage.
... All the non-irradiated samples showed a single central signal (g = 2.004), as reported by many workers in different foods of plant origin (Engin, Aydas, & Polat, 2011; Tabner & Tabner, 1993). The ESR signal (g = 2.005 ± 0.001) in dried plant samples is due to the1 . ...
... This might be attributed to a significant increase in intensity of the main peak in AE and WAE samples , where side peaks also exhibited a significant increase in signal intensity. The intensities of the side signals, corresponding to radiation-induced cellulose radicals, were reported in about 5% in irradiated Foeniculi fructus and 50% in irradiated citrus fruits out of the total intensity of the central ESR signal (Tabner & Tabner, 1993; Yamaoki, Tsujino, Kimura, Mino, & Ohta, 2009). ...
... It is concluded that the most suitable for EPR study of irradiated grapes are stems. The same EPR spectra are confirmed for irradiated citrus fruits (Tabner & Tabner, 1993). The irradiation of dates at doses up to 2 kGy induce radicals whose EPR spectra were similar to that described for grapes (Ghelawi, Moore, Bisby, & Dodd, 2001). ...
Irradiation of food in the world is becoming a preferred method for their sterilization and extending their shelf life. For the purpose of trade with regard to the rights of consumers is necessary marking of irradiated foodstuffs, and the use of appropriate methods for unambiguous identification of radiation treatment. One-third of the current standards of the European Union to identify irradiated foods use the method of the Electron Paramagnetic Resonance (EPR) spectroscopy. On the other hand the current standards for irradiated foods of plant origin have some weaknesses that led to the development of new methodologies for the identification of irradiated food. New approaches for EPR identification of radiation treatment of herbs and spices when the specific signal is absent or disappeared after irradiation are discussed. Direct EPR measurements of dried fruits and vegetables and different pretreatments for fresh samples are reviewed.
... 5% for irradiated Foeniculi fructus and 50% for irradiated citrus fruits. 30,31 In general, the signal intensity ratio of the OD and FD samples was 1:6:1 and 1:7:1, respectively. However, the ideal signal intensity ratio in case of radiation-induced cellulose radicals has been reported as 1:2:1. ...
Different spices such as turmeric, oregano, and cinnamon were gamma irradiated at 1 and 10 kGy. The electron paramagnetic resonance (EPR) spectra of the nonirradiated samples were characterized by a single central signal (g = 2.006), the intensity of which was significantly enhanced upon irradiation. The EPR spectra of the irradiated spice samples were characterized by an additional triplet signal at g = 2.006 with a hyperfine coupling constant of 3 mT, associated with the cellulose radical. EPR analysis on various sample pretreatments in the irradiated spice samples demonstrated that the spectral features of the cellulose radical varied based on the pretreatment protocol. Alcoholic extraction pretreatment produced considerable improvements of the EPR signals of the irradiated spice samples relative to the conventional oven and freeze-drying techniques. The alcoholic extraction process is therefore proposed as the most suitable sample pretreatment for unambiguous detection of irradiated spices by EPR spectroscopy.
... [30,31] Different scientists have reported the variable intensities of these two radiation-specific side peaks with respect to the main ESR signal, mainly depending upon the kind of sample and its pretreatments. [32,33] The results showed that the luminescence techniques, particularly TL analysis, were more sensitive than the ESR analysis to determine the irradiation status of the unknown cinnamon samples. The practicality of TL analysis over other available methods to detect irradiated fresh mushrooms, [27] composite seasoning foods, [34] wheat, and corn [35] was also reported previously. ...
The market availability of irradiated products requires proper labeling to safeguard the consumer’s right of choice. Ten commercial cinnamon powders of different origins were investigated to confirm their irradiation history using photostimulated-luminescence, thermoluminescence, and electron spin resonance analyses. Photostimulated-luminescence analysis screened out one sample as an intermediate (700–5000 PCs) while all others were negative. Upon thermoluminescence analysis, two samples yielded weak but clear peaks in the temperature range of 150–250oC, showing the possibility of irradiation. The electron spin resonance analysis showed limited sensitivity for all the commercial samples with the absence of radiation-specific features. The applicability of these techniques was confirmed by analyzing the radiation-induced detection markers in the in-house irradiated samples. Hygienic quality parameters and physicochemical properties (moisture content, pH, Hunter’s color, and particle size) showed variable results which can affect the quality of end product and should be taken into serious considerations to ensure hygienic quality and practical applications of cinnamon powders.
... A single central signal (g=2.0040) was observed in all nonirradiated samples irrespective of sample type and pretreatment (Fig. 1). Various researchers also reported similar central signals in different foods of plant origins131415161718 and were attributed to organic (semiquinone) radicals [13,192021. Upon different sample pretreatments, the intensity of this signal was the lowest in alcoholic extracted samples while the highest in water treated samples, however qualitative appearance was the same without any change in g-value (g=2.0040). ...
Fresh (raw roots), white (dried), and red (steamed-drid) ginseng samples were gamma-irradiated at 0 to 7 kGy. Electron spin resonance (ESR) technique was used to characterize the irradiation status of the samples, targeting the radiation-induced cellulose radicals after different sample pretreatments. All non-irradiated samples exhibited a single central signal (g=2.006), whose intensity showed significant increase upon irradiation. The ESR spectra from the radiation-induced cellulose radicals, with two side peaks (g=2.0201 and g=1.9851) equally spaced (±3 mT) from the central signal, were also observed in the irradiated samples. The core sample analyzed after alcoholic-extraction produced the best results for irradiated fresh ginseng samples. In the case of irradiated white and red ginseng samples, the central (natural) and radiation-induced (two-side peaks corresponding to cellulose radical) signal intensities showed little improvement on alcoholic-extraction. The water-washing step minimized the effect of Mn(2+), but reduced the intensity of side peaks making them difficult to indentify. The effect of different origins was negligible, however harvesting year showed a clear effect on radiation-induced ESR signals.
... These two subsignals were previously observed in irradiated fruits and spices (Raffi and Agnel 1989; de Jesus et al. 2000; Korkmaz and Polat 2001). Yamaoki et al. (2009) found that the intensities of the subsignals were approximately 5 % of the total intensity of the main signal in irradiated Foeniculi fructus, whereas Tabner and Tabner (1993), studying gamma-irradiated citrus fruits, suggested that the triplet lines have an intensity ratio of 1:2:1 and were ascribed to cellulose radicals (Raffi et al. 2000 ). The multicomponent radiation-specific ESR spectrum of crystalline sugar radical (g s1, 2.0110; g s2, 2.0008) was recorded in the irradiated (10 kGy) pak choi powder (Kwon et al. 2000). ...
Electron spin resonance (ESR) spectroscopy for the detection of irradiated food could provide complex spectra due to the presence of different nonirradiation-specific paramagnetic species in the sample. Particularly, ESR signals from naturally present Mn2+ could limit the ESR-based detection of irradiated foods of plant origin. In this study, the effects of different concentrations of Mn2+ on the radiation-specific ESR spectral features of radiation-induced crystalline sugar or cellulose radicals were examined. Soy sauce powder with Mn2+ was irradiated at 10 kGy and its effect on the identification of radiation-induced sugar (pak choi, 10 kGy) and cellulose (red pepper powder, 10 kGy) radicals was evaluated. In the blends of red pepper and soy sauce, the left (g
1 = 2.025) and central (g
2 = 2.005) peaks of the cellulose signal significantly decreased with the decline of red pepper content (R
2 = 0.9384, g
1; 0.8819, g
2). However, the right peak (g
3 = 1.988) significantly increased (R
2 = 0.9353, g
3) with an escalation in the soy sauce content. The cellulose radical signals were identifiable from the blends containing more than 50 % red pepper powder. In the blends of soy sauce and pak choi, the ESR intensity of crystalline sugar radicals significantly decreased with the decline in pak choi content (R
2 = 0.9887). However, Mn2+ signal didn’t overlap with the sugar radical signals. The ESR signals from radiation-induced crystalline sugar remained unaffected; however, the signals from cellulose radicals provided a reduced detectionability depending upon the concentration of Mn2+ in the sample.
... Electron spin resonance can be used to detect radicals produced in certain foods exposed to ionizing radiation, e.g. in the rigid matrices of bones, shells or seeds. There are a number of reports on the use of ESR for the identification of irradiated fruits: multiple fruits including grapes (Desrosiers and McLaughlin, 1989;Ratii and Agnel, 1989;Goodman et al., 1989;Tabner, 1991: Maloney et al., 1992); strawberries (Dodd et al., 1985;Raffi et al., 1988); citrus (Tabner and Tabner, 1993;Tabner and Tabner, 1994); and dates (Raffi et al., 1991;Stachowicz et al., 1992). Comparative trials in 21 laboratories showed > 90% correct identification of irradiated raisins and dried papaya (Raffi et al., 1992). ...
One variety (Aple) of Libyan dry dates (Phoenix dactylifera L.) was irradiated in a 60Co source to absorbed doses of 0.8, 1.0, 1.5 and 2.0 kGy. Unirradiated date stone contains a radical with a single line g = 2.0045, feature A. Irradiation to a dose of 2.0 kGy (the recommended dose for fruits in U.K.) induces the formation of additional radicals with signals g = 1.9895 and 2.0159, feature C. The single line having g = 2.0045 decays in both unirradiated and irradiated samples whereas the additional signals g = 1.9895 and 2.0159 remain almost unchanged over a period of time 15 months stored at room temperature and 4 degrees C.
Objective: To study the effects of gamma irradiation (10 and 25 kGy) on volatile oil constituents, total phenolic content, and free radical scavenging activity of cassumunar ginger rhizomes. Moreover, the effects on toxicity were investigated on both non-irradiated and irradiated samples, and accompanied by measurements of free radical content. Methods: Electron paramagnetic resonance spectroscopy (EPR) and GC-MS were used to determine free radicals and active compounds in essential oils, respectively. Toxicity was estimated using Toxi-Chromo Test. Total phenolic content and Antioxidant properties were determined using the Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, respectively. Results: Irradiation at the doses of 10 and 25 kGy significantly (P < 0.05) increased free radicals in cassumunar ginger rhizomes. However, the volatile oils, total phenolic content, antioxidant activity and toxicity were not significantly (P > 0.05) affected by the irradiation doses. Conclusion: The present results suggest that gamma irradiation at the doses up to 25 kGy can safely be used to sanitize dried cassumunar ginger rhizomes.
In this work we use paramagnetic defects induced by radiation in the fruit pulp to identify gamma-irradiated kiwi, papaya and tomato. Pulp without seed, peels or stalks are treated by alcoholic extraction in order to remove water, soluble fractions and solid residue. The ESR spectra of pulp samples of irradiated fruit is composed of species A (g = 2.0045) and species C (g = 2.0201 and g = 1.9851), which are also observed in irradiated stalks and skins. In comparison with samples which are not submitted to alcoholic extraction, species C is stable enough to be used as a dose marker. Furthermore, the species C signal can be detected perfectly even in pulp samples irradiated with doses as low as 200 Gy. Irradiation doses of fruit, exposed to 200–900 Gy of a gamma rays, were estimated with an overall uncertainty of 15% using dried pulp samples. These results indicate that radicals induced in pulp have potential to be used in the identification and absorbed dose determination of irradiated fruit.
Gamma-irradiated (0, 1, 5 and 10 kGy) spaghetti sauce samples were identified using photostimulated luminescence (PSL), thermoluminescence (TL) and electron spin resonance (ESR) techniques. PSL technique was used as a screening method for irradiated sauce samples, where the improved results of PSL method were observed for the freeze-dried and alcoholic-extracted samples. TL technique, through the density separation step of silicate minerals from irradiated samples, gave specific shape, intensity and occurrence of TL glow curve in a typical temperature range as well as TL ratio (TL 1/TL 2) to identify the irradiation treatment. The ESR method employed for the freeze-dried samples, showed radiation-specific cellulose signals for 5 and 10 kGy-treated samples, and the results were comparable with oven-dried samples. In general, TL technique was found the most sensitive and reliable for the identification of irradiated spaghetti sauces.
The safety of food irradiation is well documented; however, this technique lacks international consensus for general applicability. Validated identification methods have prime importance for the application of different regulations regarding the international trade of irradiated food. This study comprehensively investigated the potential of different available techniques for the identification of irradiated sauce samples. Liquid samples were treated with different modified methods to find the improved identification results. The presented results may be useful for different regulatory authorities to identify or monitor irradiated spaghetti sauces.
Summary In this work we use paramagnetic defects induced by radiation in the fruit pulp to identify gamma-irradiated kiwi, papaya and tomato. Pulp without seed, peels or stalks are treated by alcoholic extraction in order to remove water, soluble fractions and solid residue. The ESR spectra of pulp samples of irradiated fruit is composed of species A (g = 2.0045) and species C (g = 2.0201 and g = 1.9851), which are also observed in irradiated stalks and skins. In comparison with samples which are not submitted to alcoholic extraction, species C is stable enough to be used as a dose marker. Furthermore, the species C signal can be detected perfectly even in pulp samples irradiated with doses as low as 200 Gy. Irradiation doses of fruit, exposed to 200–900 Gy of a gamma rays, were estimated with an overall uncertainty of 15% using dried pulp samples. These results indicate that radicals induced in pulp have potential to be used in the identification and absorbed dose determination of irradiated fruit.
The ESR spectra of the stalks and skins of a number of non-irradiated and γ-irradiated citrus fruits suggest that ESR spectroscopy could be used to establish the irradiation history. Two major spectral changes occur up on irradiation. Two additional features appear and are only observed in irradiated specimens (Features B and D, the latter separated by c. 5.9mT) and these are accompanied by an increase in the intensity of the main central signal (Feature A). Observations on the stability of Features A and D indicate that they arise from different radicals. Experiments on the meso- and exo-carps indicate that Features B and D are located mainly in the former and Feature A mainly in the latter.
This item deals with identification of irradiated foodstuffs by means of Electron Paramagnetic Resonance (EPR). EPR is the
most accurate method for such routine applications since radicals are stabilized for a long time in all (part of) foods which
are in solid and dry state; consequently, EPR can be applied to meat and fish bones, fruit and relative products (from vegetal
origin), seafoods, etc.
The ESR spectra of the flesh of a selection of unirradiated and γ-irradiated citrus fruits have been obtained. When dried, the flesh from unirradiated fruits gives rise to virtually no ESR spectrum. However, the flesh of irradiated fruits exhibit a strong spectrum with radiation induced features which show a high degree of reproducibility within the fruits examined. These features have been previously observed in spectra from the intact skin and skin components of irradiated citrus fruits. It is believed that this is the first time that radicals have been observed by ESR in the flesh of irradiated fruits.
This article's purpose primarily is to review the scientific literature on the development of analytical methods for the identification of irradiated foods over the past decade. The main modalities currently being employed or developed (e.g. physical vs. chemical vs. biological) are introduced, and their advantages and disadvantages discussed. Radiation/free radical chemistry and electron spin resonance (ESR) spectroscopy are presented in the most depth. Some recent food irradiation/ESR research from the authors' laboratories is included. Finally, it is hoped that this review will shed some light on the current status and prospects for food irradiation practices world-wide.
A collaborative study on the use of the half-embryo test for the detection of irradiated citrus fruit was undertaken. Collaborative samples of seeds removed from citrus fruit, which were irradiated with doses of 0, 0.2 and 0.5 kGy, were examined by 12 participating laboratories. The percentage of correct identifications, whether irradiated or unirradiated, was 92% of 48 samples after 4 days incubation and 98% after 7 days incubation. Only one sample, irradiated with 0.2 kGy, was incorrectly identified. This collaborative study shows that irradiated citrus fruit can be identified using the half-embryo test and that the test can be applied in practice.
An electron paramagnetic resonance (EPR) spin probe study of irradiated wheat seeds was performed depending on irradiation dose. The structural changes in the membrane integrity were followed using aqueous solutions of 4-hydroxy-TEMPO (TANOL) spin probe and a line broadening material. In the studies dry seed embryos were kept in these solutions for 150 min. The spectra were recorded at various times of air drying process. The simulation of these spectra indicated a decrease in the water content of the embryos depending on the increasing irradiation dose. This indicates the increase in the permeability of the membranes as a result of the radiation damage. From the decay curves it is possible to determine about irradiation dose, however, this approach is not very successful at close irradiation doses.
ESR spectra of the hard seed cover and kernel coating of irradiated orange and tangerine fruits were obtained under different sample drying conditions to analyze the effect of treatment on ESR line at g = 2.0033 (line A). The spectra shows almost the same lines that appear in stalks, achenes, seeds and skins of fresh fruit. The peak-to-peak intensity of the line A of the spectra shows a linear variation with dose in the range studied (up to 5 kGy) under controlled sample preparation. Q-band ESR spectra shows that this line is composed for three different lines from different species. A1, A2 and A3. The A2 and A3 lines are associated with dose but grow also during drying of the sample and are probably due to 'cellulosic' components of the seed cover. The A1 line appears only when sample is dried and is probably associated with the quinones of the internal kernel coat.
The international commerce of vegetable products is often dependent on the quarantine protections that are imposed by the importing countries because of the fear of contamination by fruit flies. The use of ionizing radiation as a treatment for these products can be used to remove this problem and a real proof of irradiation can contribute to the implementation of the international commerce. ESR measurement on the pulp of vegetable products can be used as a proof of irradiation using the species introduced in cellulose that are found uniquely in irradiated products. The stability of these species are compatible with the life of the products analyzed. The pulp signal intensity is sufficient to identify products irradiated with doses as low as 100 Gy for some fruits.
The ESR spectra of the seeds, skins and stalks of unirradiated and γ-irradiated Cape black grapes have been obtained. In the spectra of all parts of the grape a single line (g ca. 2.004) is observed both before and after irradiation. New spectral features are observed after irradiation with doses of between 2 and 10 kGy. Some of these features decline in intensity over a period of several days. However, in the case of stalks, new spectral features are readily observed over the shelf-life of the fruit and in samples irradiated to a dose of only 2kGy.
Electron spin resonance spectra of the m‐dinitrobenzene anion radical and several of its derivatives have been examined under a variety of conditions in order to study the alternating linewidth effect and, for the first time, the associated dynamic second‐order frequency shifts. More detailed information about the molecular motions was obtained in this way than is otherwise possible. The m‐dinitrobenzene anion, the 3,5‐dinitromesitylene anion, the 3,5‐dinitrophenolate dianion, and the 3,5‐dinitrobenzoate dianion radicals were obtained by electrolytic generation in solvents such as tetrahydrofuran (THF), 1,2‐dimethoxyethane (DME), and N,N‐dimethylformamide (DMF). Except for the benzoate dianion in DMF, the data are well represented by a two‐state model with two 14N splitting constants, aI and aII. The two different splittings probably arise because the nitro groups are complexed with the solvent or with cations. Even the spectra showing a rapid exchange between the two states have values of aI and aII that are approximately the same as those found for the single species that are obtained in the presence of alkali‐metal cations, and which correspond to the static limit. The correlation times τc observed in the spectra showing the alternating linewidth effect were in the range from 0.4–0.9×10−9 sec, while those corresponding to the static limit are greater than about 10−6 sec. Spectra of the 3,5‐dinitrobenzoate dianion radical obtained in DMF with and without added water could not be analyzed by a two‐state model; a more appropriate model is probably one in which the carboxylate group in addition to the two nitro groups can interact with the solvent or the cations. A few spectra were carefully studied to obtain data on the g‐tensor and electron‐nuclear anisotropic dipolar interactions as well as those arising from modulations of the isotropic splittings, and this complete analysis made it possible to estimate values of the spectral densities for the latter interaction. In most cases studied in this way, it was found that there was complete out‐of‐phase correlation of the splittings at the two nitrogen nuclei.
The ESR spectra of the seeds, skins and stalks of unirradiated and γ-irradiated Chilean white grapes have been obtained and the results compared to those previously reported for Cape black grapes. The high degree of reproducibility of the spectra obtained from the stalks of different varieties of grapes suggest that ESR spectroscopy could form the basis of a viable test to determine their irradiation history. The condition of the stalk prior to irradiation has been found to have little effect on the resulting spectra. The spectra from the stalks, skins and seeds of unirradiated and γ-irradiated apples, peers and cherries have also been examined. Although most of the spectra from irradiated components exhibit extra features, they are sometimes short-lived and restrict the development of ESR as a viable test.
The electron spin resonance spectrum of achenes, pips, stalks and stones from irradiated fruits (strawberry, raspberry, red currant, biberry, apple, pear, fig, french prune, kiwi, water-melon and cherry) always displays, just after γ-treatment, a weak triplet (a(h) ~ 30 G) dus to a cellulose radical; its left line (lower field) can be used as an identification test of irradiation, at least for strawberries, raspberries, red currants or bilberries arradiated in ordewr to improve their storage time.
TABNER features are first observed in the ESR spectrum. spin resonance spectra of dinitrobenzene anion radicals
- Brian J Tabne1i
- Viv1ese~a
BRIAN J. TABNE1I and VIv1Ese~a A. TABNER features are first observed in the ESR spectrum. spin resonance spectra of dinitrobenzene anion radicals.
An ESR study of some γ-irradiated fruits
- Maloney
Food Irradiation and the Chemist
- Stevenson
ESR identification of irradiated strawberries
- Raffi