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Electron spin resonance spectra of γ-irradiated citrus fruit skins, skin components and stalks
International Journal of Food Science & Technology
Abstract
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 g value obtained compares well with those reported in literature (Desrosiers & McLaughlin, 1989). Several reports have suggested these free radicals to be those of semi-quinones produced by the oxidation of plant polyphenolics (Scewartz, Bolton, & Brog, 1972) or lignin (Tabner & Tabner, 1994). It is known that the polyphenols are mainly responsible for the antioxidant activity of the plant products. ...
Amritamehari churnam (AC) is an antidiabetic polyherbal formulation constituting of four herbal medicinal plants namely Phyllanthus emblica, Salacia reticulata, Tinospora cordifolia and Curcuma longa. The feasibility of using gamma irradiation at doses between 2.5 and 10 kGy to reduce microbial load and enhance shelf life of this formulation was investigated. The irradiated and non-irradiated products were stored at room temperature (25–32 °C and 50–85% R.H., 1.5 years). Acceptability of the irradiated product was assessed based on sensory, microbial, physical and chemical attributes as well as their antioxidant status. A dose 7.5 kGy was sufficient to maintain microbial quality within acceptable limit up to 18 months of storage. No significant differences in sensory properties were observed between the non-irradiated and irradiated sample. The applied dose did not cause any significant qualitative and quantitative changes in the chemical constituents, antioxidant activities as well as physical properties when measured by EPR spectroscopy.
... Both the peel and flesh parts of all the non-irradiated samples were characterized by a singlet at g = 2.004 and 2.006, respectively. Several reports have suggested these free radicals to be those of semiquinones produced by the oxidation of plant polyphenolics (Scewartz et al., 1972) or lignin (Maloney et al., 1992;Tabner and Tabner, 1994). The irradiated spectra of peel parts recorded after different drying methods exhibited a triplet at g = 2.004 with a hyperfine coupling constant (hfcc) of 3 mT. ...
... The current status of analytical detection methods for irradiated foods has been discussed in different publications. 53,[83][84][85][86][87][88][89][90][91][92] Detection methods are based on the determination of the products formed by irradiation, on physical changes such as cell membrane damage or in determining the ratio of live/dead bacteria. 45 At present there is no universal method for identifying all irradiated foodstuffs, but useful detection methods are being developed for specific foods. ...
Publisher Summary
Food irradiation is a cold process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. Although for some time a consensus has been reached in the scientific community about the wholesomeness of gamma irradiation of food, the general public remains concerned about this technology even though a number of recent reports show increasing interest in food irradiation from government regulators and industry and decreasing apprehensiveness of the public. Food irradiation is not a new technology. Today, it is approved by more than 40 countries for more than 100 irradiation food items or groups of food for consumption. This chapter discusses the action of ionizing radiation, sources of ionizing radiation, and the concepts of dose and different dose levels used in the radiation processing. It also includes disinfestations, shelf-life extension, decontamination, and advantages and disadvantages of food irradiation, with special focus on fruit and vegetable applications in the scope of irradiation. The chapter further reviews the current status of analytical methods used in the detection of irradiated fruits and vegetables under analytical detection methods and presents a summary of the applications relative to fruits and vegetable preservation.
... A sextet hyperfine structure from Mn(II) (nuclear spin I = 5/2) was clearly observed in both sugars, as shown in Fig. 4. Furthermore, a signal at g = 2.0055 ± 0.0003, which was attributed to stable free radicals, was also observed. The origin of the free radicals responsible for this ESR signal was not immediately clear and several suggestions have been proposed for its assignment, including semiquinones (Bhat, Sridhar, & Bhushan, 2007;Swartz, Bolton, & Borg, 1972), lignin (Maloney, Tabner, & Tabner, 1992;Tabner & Tabner, 1994), or oxidized fatty acids (Ikeya, Baffa, & Mascarenhas, 1989). Thus, this study was performed to clarify this problem. ...
Anthocyanin, which is soluble in water and released into sugar steam during extraction, was investigated in this study. The anthocyanin content in refined sugar, plantation white sugar, soft brown sugar and raw sugar was determined using electron spin resonance (ESR) spectroscopy, which was operated at room temperature, and compared with spectra from standard anthocyanin. The ESR spectra of red and violet anthocyanins was predominantly g≈2.0055, which corresponded to an unpaired electron located in the pyrylium ring. Signals for Fe(III) and Mn(II), which naturally occur in plants, were found in raw sugar, soft brown sugar and standard anthocyanin but were absent from refined sugar and plantation white sugar due to the refining process. In addition, the ESR results were correlated with the apparent colour of the sugar, which was determined using the method of the International Commission for Uniform Methods of Sugar Analysis and inductively coupled plasma optical emission spectroscopy.
... The nonirradiated spectra were characterized by a central line at g = 2.006, with a line width ( B pp ) of 0.54 mT as a native signal, possibly due to the photooxodation of the existing polyphenols. Several reports have suggested that these free radicals are semiquinone radicals produced by the oxidation of plant polyphenolics (Scewartz and others 1972) or lignin (Maloney and others 1992;Tabner and Tabner 1994). In the case of both the cumin samples, a sextet signal was observed showing a trace of Mn 2+ as depicted in Figure 4. ...
Changes in cumin and chili powder from India resulting from electron-beam irradiation were investigated using 3 analytical methods: electronic nose (E-nose), Fourier transform infrared (FTIR) spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The spices had been exposed to 6 to 14 kGy doses recommended for microbial decontamination. E-nose measured a clear difference in flavor patterns of the irradiated spices in comparison with the nonirradiated samples. Principal component analysis further showed a dose-dependent variation. FTIR spectra of the samples showed strong absorption bands at 3425, 3007 to 2854, and 1746 cm−1. However, both nonirradiated and irradiated spice samples had comparable patterns without any noteworthy changes in functional groups. EPR spectroscopy of the irradiated samples showed a radiation-specific triplet signal at g = 2.006 with a hyper-fine coupling constant of 3 mT confirming the results obtained with the E-nose technique. Thus, E-nose was found to be a potential tool to identify irradiated spices.Practical ApplicationIdentification of irradiated food is of paramount importance to government regulatory bodies, the food irradiation industry, and consumers as there is increasing demand for irradiated food in international trade. In this study, detection of irradiated spices was investigated with an aim to develop a simple and rapid technique using electronic nose. Fourier transform infrared analysis was performed to know the changes in functional groups after irradiation. The accuracy and validity of electronic nose detection of prior irradiation was endorsed by electron paramagnetic resonance spectroscopy.
... These side signals were first observed by Raffi et al. [23] in the achenes of irradiated strawberries. Later, similar signals were reported in different irradiated materials of plant origin and were attributed to radiation-induced cellulose radi- cals [24]. The radiation-induced side peaks of the ESR triplet spectrum were of very low intensities compared to the central ESR signal, which also appeared in the non-irradiated samples. ...
Two kinds (20 each) of gamma-irradiated (0, 5, and 10 kGy) tea samples, blended powders and packed in sachets (tea bags), were investigated using photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify their irradiation status. PSL-based rapid screening was possible for all the control samples except for one packed and two powdered samples. The irradiated samples presented a good dose-dependent PSL count except two powdered samples with very low PSL sensitivity. TL analysis provided the most reliable results, in which all the irradiated samples were identified using a well-defined high-intensity TL glow curve in a temperature range of 150–250 °C. The TL results were also confirmed by determining the TL ratio (TL1/TL2), which was <0.1 in all the non-irradiated samples and >0.1 in the irradiated ones. ESR spectroscopy was effective for only 3 packed and 6 powdered samples showing the radiation-induced cellulosic and sugar radical signals, respectively.
Figure
TL-based detection of irradiated teas
... The X-band ESR spectrum of irradiated (5-50 kGy) clematidis radix (>10 kGy), cinnamon bark (>10 kGy), phellodendron bark (>5 kGy), evodia fruit (> k5Gy), citrus unshiu peel (>10 kGy), prunella spike (>5 kGy), schizonepeta spike (>10 kGy), loranthi ramulus (>5 kGy), artemisiae capillaris herba (>10 kGy), coptis rhizome (>5 kGy), and poncirus immature fruit (>10 kGy; Fig. 2) were observed to be like cellulose radical ESR spectrum of processed plants [29]. These radicals were first reported by Raffi et al. [38] on achenes of irradiated strawberries and were detected later in the very dry part of most of the irradiated products of plant origin [27,39]. The typical cellulose radical ESR spectrum is a hyperfine triplet. ...
Dried herbal samples consisting of root, rhizome, cortex, fruit, peel, flower, spike, ramulus, folium, and whole plant of 20 different medicinal herbs were investigated using pulsed photostimulated luminescence (PPSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify γ-ray irradiation treatment. Samples were irradiated at 0–50 kGy using a 60Co irradiator. PPSL measurement was applied as a rapid screening method. Control samples of 19 different herbs had photon counts less than the lower threshold value (700 counts 60 s−1). The photon counts of non-irradiated clematidis radix and irradiated evodia and gardenia fruits were between the lower and upper threshold values (700–5,000 counts 60 s−1). TL ratios, i.e., integrated areas of the first glow (TL1)/the second glow (TL2), were found to be less than 0.1 in all non-irradiated samples and higher than 0.1 in irradiated ones providing definite proof of radiation treatment. ESR spectroscopy was applied as an alternative rapid method. In most of the irradiated samples, mainly radiation-induced cellulosic, sugar, and relatively complicated carbohydrate radical ESR signals were detected. No radiation-specific ESR signal, except one intense singlet, was observed for irradiated scrophularia and scutellaria root and artemisiae argyi folium.
Figure
PPSL can be used as a rapid simple preliminary screening method and a combination of ESR and TL tests for a definite proof of gamma irradiation treatment of medicinal herbs.
... This g value obtained compares well with those reported in the literature (Dodd and others 1985;Desrosiers and McLaughlin 1989;Bortolin and others 2006). Several reports have suggested these free radicals to be those of semiquinones produced by the oxidation of plant polyphenolics (Scewartz and others 1972) or lignin (Maloney and others 1992;Tabner and Tabner 1994). The most important objective of identification of irradiated food is to trace the signal, which is originated only because of the radiation treatment. ...
A study of gamma-irradiated Indian medicinal plant products was carried out using electron paramagnetic resonance (EPR) spectroscopy. Improved approaches like high-power measurement, microwave saturation, and thermal behavior of the radicals were explored for detection of irradiation. Aswagandha (Withania somnifera), vairi (Salacia reticulata), amla (Emblica officinalis), haldi (Curcumin longa), and guduchi (Tinospora cordifolia) exhibited a weak singlet at g= 2.005 before irradiation. Aswagandha, immediately after radiation treatment, revealed a complex EPR spectrum characterized by EPR spectrum simulation technique as superposition of 3 paramagnetic centers. One group of signal with organic origin was carbohydrate and cellulose radical and the other was isotropic signal of inorganic origin (g⊥= 2.0044 and g∥= 1.9980). However, other products did not exhibit any radiation-specific signal after irradiation. Power saturation and thermal behavior techniques were not suitable for these products. However, amongst all the 3 approaches, high-power measurement of EPR spectra emerged as a suitable technique in identification of the irradiated aswagandha.
Practical Application: Gamma-irradiation confirms hygienic quality and improves shelf life of food and other products. However, there is a lack of international consensus over considering this as a general application and different regulations are being enforced. EPR is one of the most promising techniques to identify irradiated foodstuffs for regulatory requirements but it has many limitations. Improved approaches based on the EPR technique explained in this study may be useful to identify irradiated products and become beneficial to food regulators and food irradiation enterprises to enhance confidence in irradiation technology.
... The origin of the free radicals responsible for this EPR signal is not clear. Up to now several suggestions were made as free radicals of semi-quinones ( Swartz et al., 1972), lignin ( Maloney et al., 1992;Tabner and Tabner, 1994) or due to oxidation of fatty acids present in some vegetables ( Ikeya et al., 1989). Following European Protocol (EN 1787, 2000) after irradiation two weak satellite lines situated left and right to the naturally present one must appear. ...
The reported EPR studies on the dependence of the microwave saturation behavior as a function of temperature (up to 60 °C) and heating time of some dry plants demonstrate the possibility to distinguish naturally present from radiation induced EPR signals independently of the fact that they have equal g-factors in X- and Q-band spectra. Using these properties of the dry plants a new approach for identification of their previous radiation processing is considered. It is based on the fact that the intensity of the EPR line appearing after irradiation increases at high microwave power (for example 100 mW) and decreases at low microwave power (for example 1 mW) when the irradiated sample is recorded after thermal treatment (up to 60 °C, 60 min). The intensity of the naturally present EPR signal observed in non-irradiated samples remains, meanwhile, unchanged.
... and DB pp ¼0.810 mT. Several reports have suggested these free radicals to be those of semi-quinones produced by the oxidation of polyphenolics (Scewartz et al., 1972) or lignin (Maloney et al., 1992;Tabner and Tabner, 1994). This g value obtained compares well with those reported in literature (Desrosiers and McLaughlin, 1989;Dodd et al., 1985;Bortolin et al., 2006). ...
In the present study, probably for the first time, a detailed analysis of the radiation induced radical species and thermoluminescence measurements of irradiated dog feed are reported. The EPR spectrum of non-irradiated ready-to-eat dog feed was characterized by singlet g=2.0047±0.0003. Irradiated samples exhibited a complex EPR spectrum. During high power (50.0 mW) EPR spectroscopy, a visible change in the shape of the EPR spectrum was observed and characterized by EPR spectrum simulation technique. An axially symmetric anisotropic signal with g║=2.0028 and g┴=1.9976 was identified. However, a negligible change in the matrix of irradiated edible dog chew was observed using EPR spectroscopy. Therefore, thermoluminescence study of the isolated minerals from dog chew was carried out. The composition of the poly-minerals was studied using SEM and EDX analysis and a complete verdict on identification of irradiation is proposed.
... The origin of these free radicals responsible for the EPR signal is not clear. Several reports have suggested these free radicals to be those of semi-quinones produced by the oxidation of plant polyphenolics (Scewartz, Bolton, & Brog, 1972) or lignin (Maloney, Tabner, & Tabner, 1992;Tabner & Tabner, 1994). ...
Minimal change in irradiated foods with low dose treatment makes the identification process a difficult task. Two independent physical methods, electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) detection were employed for detection of irradiation treatment on Basmati rice. EPR investigation of 0.5–2.0 kGy irradiated rice samples showed a short lived, asymmetric, dose dependent spectrum (g = 2.005), characterised by the radicals of irradiated starch. However, this signal disappears with time. The present work explores the possibility to identify irradiated rice by the relaxation characteristics and thermal behaviour of the radicals. This study reports for the first time that the different microwave saturation behaviours of the signal (g = 2.004) in irradiated and non-irradiated rice samples provide an important clue to identify radiation treatment beyond the period when the radiation specific EPR spectral lines have disappeared. TL investigation involving scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) of the poly-minerals isolated from the rice samples allowed to discriminate clearly between irradiated and non-irradiated samples even after a prolonged period of storage.
... This g value obtained compares well with those reported in the literature (Dodd and others 1985;Desrosiers and McLaughlin 1989;Bortolin and others 2006). Several studies have suggested these free radicals to be those of semiquinones produced by the oxidation of plant polyphenolics (Scewartz and others 1972) or lignin (Maloney and others 1992;Tabner and Tabner 1994). Figure 1B shows the EPR spectrum 1 d after the radiation treatment with dose 1 kGy of the skin part with an increase in signal intensity of the existing weak singlet (g = 2.0046) by a factor of 7. Raffi and others (1992) also reported similar observations where an intense signal was noticed in the spectrum of irradiated spices. ...
Low-dose gamma irradiation causes minimal changes in food matrix making identification of radiation-processed foods a challenging task. In the present study, soybean samples were irradiated with commercially permitted gamma radiation dose in the 0.25 to 1.0 kGy range for insect disinfestations of food. Immediately after irradiation electron paramagnetic resonance (EPR) spectrum of the skin part of soybean showed a triplet signal (g = 2.0046, hyperfine coupling constant hfcc = 3.0 mT) superimposed on naturally present singlet. These signals were characterized as cellulose and phenoxyl radicals using EPR spectrum simulation technique. Kernel part of the samples exhibited a short-lived, radiation-induced singlet of carbon-centered radical superimposed on naturally present sextet signal of Mn2+. A detailed study on relaxation and thermal behavior of induced radicals in skin part was carried out using EPR spectroscopy. These findings revealed that progressive saturation and thermal characteristics of the induced radicals may be the most suitable parameters to distinguish soybean subjected to radiation dose as low as 0.25 kGy from thermally treated and nonirradiated samples, even after a prolonged period of storage.
... The origin of these free radicals responsible for the EPR signal is not clear. Several reports have suggested these free radicals to be those of semiquinones produced by the oxidation of plant polyphenolics (16) or lignin (17,18). To characterize the natural signal, EPR spectra of irradiated (1 kGy) pure quinone (hydroquinone) were recorded under a similar experimental setup. ...
Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.
Food irradiation was allowed for dried seaweeds for improving microbial quality in Korea and reliable detection methods are required for the routine control in international trade. In this study, three kinds of popular dried laver (seaweeds) were electron-beam irradiated at approved 7 kGy dose, and the radiation-induced signals were detected using electron paramagnetic resonance (ESR) spectroscopy coupled with alkaline pretreatment. The influence of conventional post-irradiation sample pretreatment such as freeze drying (FD) was also compared with that of alkaline pretreatments, i.e., NaOH extraction (NE) and KOH extraction (KE). Non-irradiated samples were characterized by their ESR spectra, having singlet g-values of g = 2.006, 7 kGy-irradiated samples with FD and KE pretreatments did not exhibit any detectable irradiation-induced signals. However, all the irradiated samples treated with NaOH showed a new radiation-induced ESR signal hfcc (hyperfine coupling constant) of 2.3 mT that is different from that of the established cellulose radicals (hfcc of 3 mT). Thus, attempts have been made to understand the origin of the new signal. The improved approach of combination treatment with NaOH and ESR spectroscopy was successful in identifying irradiated dried laver.
Food irradiation can ensure the microbial safety and shelf life extension of the global supply of fresh fruit and vegetables. Reliable detection methods for irradiated foodstuffs can greatly enhance the widespread application of irradiation technology. Electron spin resonance (ESR) spectroscopy is able to directly analyze radiation-specific radicals (e.g., cellulose radicals and crystalline sugar radicals) that can serve as detection markers in irradiated foods. On the basis of these unique radiation-induced markers, the European Committee for Standardization has recommended ESR spectroscopy as a confirmatory technique for the identification of irradiated foods containing cellulose and crystalline sugar. This chapter focuses on the basic knowledge of food irradiation and the application of ESR spectroscopy in the detection of irradiated fruits and vegetables. The stability and specificity of the radiation-induced signals with respect to the shelf life of various fruit and vegetables are summarized. Recent investigations, limitations, and future research trends, particularly including different sample pre-treatments, improved detectability, and dose estimation, are also discussed.
Antioxidant property of Meyna spinosa Roxb. ex Link leaf was determined by using UV-Visible and ElectronParamagnetic Resonance (EPR) spectroscopy. Further the trace elements present in it were determined by using AtomicAbsorption Spectroscopy (AAS). The concentration of the antioxidant activity, IC50 was found to be 563.23 μg/mL and thetrace elements detected were Fe, Zn, Cu, Mo, Cr, Mn. Role of antioxidants and trace elements were discussed with referenceto the traditional knowledge. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
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.
Electron spin resonance (ESR) spectroscopy of gamma-irradiated fresh broccoli and kimchi cabbage was conducted to identify their irradiation history. Different pretreatments, such as freeze-drying (FD), oven-drying (OD), alcoholic-drying (ALD), and water-washing and alcoholic-drying (WAD) were used to lower the moisture contents of the samples prior to ESR analysis. The non-irradiated samples exhibited a single central signal (=2.0007) with clear effect of , especially in kimchi cabbage. Upon irradiation, there was an increase in the intensity of the central signal, and two side peaks, mutually spaced at 6 mT, were also observed. These side peaks with (left)=2.023 and (right)=1.985 were attributed to radiation-induced cellulose radicals. Leaf and stem in broccoli, and root and stem in kimchi cabbage provided good ESR signal responses upon irradiation. The signal noise was reduced in case of ALD and WAD pretreatments, particularly due to signals. The ALD treatment was found most feasible to detect the improved ESR spectra in the irradiated samples.
Different sea algae, such as sea tangle, seaweed and sea mustard, were gamma-irradiated at 1, 5 and 10 kGy. The influence of different sample pretreatments namely, freeze drying (FD), alcoholic extraction (AE), NaOH extraction (NOE) and KOH extraction (KOE) on the paramagnetic characteristics of the sea algae after irradiation was studied using electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of the non-irradiated samples were characterized by a single central line (g = 2.006). In the case of irradiated sea tangles, two types of paramagnetic species were identified. Sugar-like radicals were observed in the samples subjected to FD and AE. A triplet signal of the cellulose radical was identified after NOE and KOE. In case of seaweed a new radiation-induced paramagnetic centre with a hyperfine coupling (hfc) of 2.3 mT was detected after NOE and KOE. However, AE was found to be an appropriate approach to detect the radiation-induced cellulose signal for irradiated sea mustard. Thus, the importance of different sample pretreatments for EPR spectroscopy to identify and characterize detection markers in irradiated sea vegetables was demonstrated.
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.
SummaryEPR studies of free radicals generated in roasting process of peanut, almond, walnut and apricot are reported separately for the kernels and flakes. The raw flakes exhibit a weak singlet EPR signal, whereas raw kernels are EPR silent. Two different EPR signals are recorded in the course of roasting. One in flakes with g = 2.0040, which is independent of temperature and time of roasting and is attributed to C-centered free radical. The same C-centered (g = 2.0040) free radical is recorded at high temperature (>140 °C) and for extended time (>20 min) of roasted kernels connected with burning of the material. However, an O-centered (g = 2.0048) free radical of ‘lipid’ type appears in kernels at roasting temperature of 100–140 °C and short time (5–20 min). On the contrary, free radical concentration in kernels and flakes increases with increase in roasting temperature and decreases with the time after that. The kinetics of the decay of free radicals concentration in flakes and kernels is followed at room temperature under the storage environment (air or argon).
It seems that the consumer acceptance of irradiated foods goes through the capacity of laboratories to facilitate control of the trade and detect if a product without labeling has been irradiated or not. This chapter describes the analytical artilleries of food control laboratories. It consists of validated methods for food irradiation detection such as electron spin resonance (ESR) spectroscopy of bones, crystalline cellulose, and dried fruits; thermo- and photostimulated-luminescence (TL and PSL, respectively); gas chromatography (GC) analysis of hydrocarbons and 2-alkylcyclobutanones; bacteriological approaches such as direct epifluorescence filter technique (DEFT) and limulus amoebocyte lysate-gram negative bacteria (LAL-GNB) methods; and biochemical designed method such as the comet assay also known as single cell gel electrophoresis. The author also presents some nonvalidated methods like the luminescence and radiolytic products formed from biomacromolecules such as lipids, carbohydrates, proteins, and nucleic acids. At the end of the chapter, the author presents some new applications of theses analytical techniques, for example, the detection of irradiated ingredients present in low amounts in nonirradiated complex foods. It is thus clear that detection of irradiated food (regarded as extremely difficult 16 years ago) is now possible thanks to standardized analytical methods used in food-control laboratories. This edition first published 2013 © 2013 Blackwell Publishing and the Institute of Food Technologists.
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 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, pears 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 of refrigerated strawberries allows one to assert whether or not the fruit has been irradiated under commercial conditions required to inactivate the moulds responsible for food loss.
A reliable method is needed to determine if foods have been irradiated and are in compliance with respect to the allowable absorbed radiation dose. Several approaches for the identification of irradiated foods are under development worldwide. These include measurement of o-tyrosine, radiolytically generated hydrocarbons from lipids and chemiluminescence or thermoluminescence, and the use of electron spin resonance (ESR) to measure free radicals trapped in calcified tissues. This paper describes the efforts being undertaken at the FDA to develop analytical procedures to monitor and identify foods that have been treated with ionizing radiation. In particular, it focuses on the use of an ESR approach to measure radiation-induced free radicals trapped in calcified tissues and the use of a capillary gas chromatography (GC)-based procedure to determine radiolytically generated hydrocarbons formed by the radiolysis of lipids in various foods.
Summary Detection of irradiated spices by electron spin resonance (ESR) measurements was not successful in the past because a central line of unknown origin was detected in the ESR-spectra of both irradiated and unirradiated samples. Identification of irradiated samples by measuring the increase in intensity of this signal after irradiation is limited because the signal intensity decreases over a period of some weeks of storage and reaches the range of unirradiated samples. By changing the measurement conditions (low microwave power) we could detect two additional lines on both sides of the main signal. This line pair appears only in the spectra of irradiated spices. A similar line pair was found in the spectra of irradiated nutshells and possibly derives from cellulose radicals in the sample. For some spices, especially paprika, the identification of irradiated samples by detecting these additional lines was possible even after relatively long periods of storage.
The results of a co-trial organized by the Community Bureau of Reference on the use of Electron Spin Resonance spectroscopy for the identification of irradiated food in 21 laboratories are presented. The trial was qualitative on beef and trout bones, sardine scales, pistachio nut shells, dried grapes, and papaya, and quantitative on poultry bones. There was no difficulty in identifying irradiated meat bones, dried grapes, and papaya. In the case of fish bones there is a need for further kinetic study on different species. Identification of irradiation in pistachio nuts is more complicated and additional research is needed before further trials. All laboratories were able to distinguish between chicken bones irradiated at 1 to 3 kGy or 7 to 10 kGy although there was a partial overlap between the results.
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 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.
Electron spin resonance (ESR) spectroscopy has been used to examine components from γ-irradiated fish, meat and fruit produce in order to identify areas in which the technique may be of use in detecting an irradiation history.
Results show that, in the studied samples of the flesh of meat, fish and fruit, stable radical species are not formed on irradiation, thus indicating that ESR will have no applications for determining a radiation history of such specimens. However, stable ESR signals are obtained in components where radical centres can be stabilised within a crystalline or protein matrix. Thus bone from meat or fish yields a characteristic ESR signal at levels likely to be used commercially, although signal intensity appears to be related to the degree of crystallinity of the hydroxyapatite. This would be a complicating factor in determining quantitative radiation exposure measurements. Similarly a radiation-induced ESR signal can be observed in scampi shell. The signal appears to be associated with the chitin component and thus cooking, either before or after irradiation, can result in a major decrease in signal intensity as a result of chitin degradation. Several radical species were observed in irradiated animal fat, one of which had spectral parameters similar to those obtained from organic peroxy radicals. These species were of limited stability restricting any practical ESR determination to within a few days of treatment. Stable free radical centres are produced in the seeds of fruit, but their spectra generally resemble those of the naturally occurring melanin-type pigments. Since the concentrations of the latter may vary considerably as a result of natural factors such as exposure to sunlight, ESR has limited applications in the diagnosis of an irradiation history in such materials. With irradiated grapes a weak spectral component that was not present in unirradiated specimens was observed in the seeds. It is possible, therefore, that the ESR method could be useful for detecting irradiated grapes.
SummaryA multinational co-trial was organized to determine if electron spin resonance (ESR) spectroscopy could be used to monitor foods exposed to ionizing radiation. The bones of chicken legs, frog legs and pork rib bones were prepared and distributed as unknowns to the participating laboratories. In every instance, non-irradiated bones were correctly identified as such. Moreover, irradiated bones were not only correctly identified, but relatively good estimates of the absorbed dose were obtained. An intercomparison of the different approaches used by each laboratory is discussed, and recommendations for future trials are presented.
The ESR spectra of the seeds, pits, shells, and skins of a variety of irradiated fruits and vegetables were measured. All spectra, control and irradiated, contained a single resonance with a g-factor of 2.00. Additional resonances due to Mn2+ were observed for the drupelets of blackberries and red raspberries. An unusual radiation-induced radical was observed for irradiated mango seed; however, the signal decayed completely within a few days. It was concluded that only in a few specialized cases could the ESR resonances observed be suitable for postirradiation monitoring or dosimetry.
ESR provides an excellent method for the identification of irradiated foods containing bone or calcified cuticle, even in the absence of unirradiated controls. It also shows promise for strawberries.
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.
The results of an intercomparison, organized by the Community Bureau of Reference (Commission of the European Communities), on the use of Electron Spin Resonance spectroscopy for the identification of irradiated food are presented. A qualitative intercomparison was carried out using beef and trout bones, sardine scales, pistachio nut shells, dried grapes and papaya. Protocols are proposed for meat bones, fish bones (with some restrictions) and fruits such as dried grapes and papaya. The protocol for pistachio nuts and fruits such strawberries is more complicated and further research is needed prior the organization of future intercomparisons. A quantitative intercomparison on poultry bones was also organized. Laboratories were able to distinguish between chicken bones irradiated at 1 to 3 kGy or 7 to 10 kGy.
Can we Tell if Our Food Has Been Irradiated
- Swallow A.J.
Electron Spin Resonance Inter-comparison Studies on Irradiated Foodstuffs. EUR No 13630
- J J Raffi
Electron Paramagnetic Resonance Identification of Food Treated with Ionizing Radiation
- Raffi J.J.
Identification of γ-irradiated Foods
- J C Evans