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An electron spin resonance study of some gamma-irradiated fruits
Abstract
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.
... Different scientists reported the effectiveness of ESR spectroscopy in irradiated food of a plant origin targeting cellulose radicals. [6,7] The irradiation of food containing cellulose produces two peaks (g = 2.020 and g = 1.985) with a mutual distance of approximately 6 mT in the ESR spectrum. ESR technique can be applied easily to dried food materials without any laborious pretreatment. ...
... Similar ESR signals due to organic radicals [21] from different foods of plant origins were also reported. [6][7][8]10,13] Mainly, semiquinone radicals, which are produced by the oxidation of polyphenolic compounds in the plant matrix, are considered responsible for these results. [22,23] There was a significant difference in the intensities of the signals from different parts of the same vegetable, where the effect of different sample pretreatments was also prominent. ...
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... Some researchers (Tabner & Tabner, 1991.;Maloney, Tabner, & Tabner, 1992) carry out more detailed studies of EPR spectroscopy for seeds, stems and skins of grapes that confirm the appearance of radiation-induced signals. The spectra of irradiated grapes with doses over 6 kGy are characterized by the appearance of new lines. Central singlet line A is present in the spectra of stems, seeds and skins. Signal B c ...
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.
... 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. ...
... Increase in the signal intensity of the central line after gamma irradiation might be attributed to the presence of new lines on the 'left' and 'right' at g = 2.002. Earlier, the 'left' line which is a part of cellulosic radical triplet has been recommended to be used as a suitable detection method of irradiated dry food ingredients of plant origin (Maloney et al., 1992;Bhushan et al., 2003a,b). Hence the presence of satellite peaks observed in the present study in gamma irradiated seed coat portion can be taken as indication of radiation treatments (qualitative and quantitative) of lotus seeds. ...
Electron spin resonance (ESR) spectroscopy was used to detect the free radicals that were naturally present in lotus seeds or that were formed after employing various food processing methods (e.g., irradiation, microwave roasting, pan frying, grinding or pounding) by placing small portions of lotus seed (seed coat and cotyledon) in KCl powder in ESR quartz tubes. Spectral analysis revealed the presence of an insignificant natural abundance of free radicals and showed a sharp and clear signal at g = 2.002, more prominent in seed coat. Exposure to gamma radiation (0–30 kGy, the recommended dose for quarantine purposes) resulted in a dose-dependent increase of signal intensity at g = 2.002 with the seed coat exhibiting the presence of a weak triplet (aH = 3 mT) which can be used to authenticate irradiation treatments. Irradiated cotyledon at high doses (15 and 30 kGy) revealed significant reduction in ESR signals, attributed to an increase of free radical scavengers. Common food processing practices like microwave roasting, flame heating, grinding or pounding also generated free radicals. It is envisaged that results of the present study might be valuable for health conscious consumers who are interested in the status of free radicals in foodstuffs subjected to traditional or modern food-processing techniques. Keywords: Lotus seeds, Gamma irradiation, Electron spin resonance spectroscopy, Free radicals, Detection, Food analysis, Food composition
... The central line (main peak), which is the sum of both 'left' and 'right' lines, might have contributed to the increased signal intensity at g=2.002 in irradiated Canavalia seeds. So, the left line (satellite peak) has also been successfully applied as a detection method of irradiated foodstuffs of plant origin (MALONEY et al., 1992;DESROSIERS et al., 1995;POLONIA et al., 1995;STACHOWICZ et al., 1998). In cotyledon portion of C. cathartica seeds, insignificant levels of naturally occurring free radicals were detected (7.35±3.56 ...
ESR technique was used to detect free radicals present naturally or formed alter employing various food processing methods (irradiation, microwave roasting, pan frying and pounding) by entrapping small quantities of seed portions (seed coat and cotyledon) of Canavalia cathartica in potassium chloride powder in ESR quartz tubes. ESR signal at g=2.002 was more prominent in seed coat than the cotyledon. Application of ionising radiation (gamma and electron beam, 10 kGy) resulted in enhancement of signal at g=2.002 accompanied by a weak triplet (a(H)=3mT) in seed coat, which can be used as a suitable method of detection of irradiation. Some of the commonly employed food processing methods also generated free radicals (at g=2.002) more or less comparable to irradiation. Results of the present study might prove to be beneficial for the consumers who are interested to be acquainted with the status of lice radicals in legumes after conventional or modern food processing and preservation methods.
... 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 spectra of the central line have been attributed to the cellulose triplet signal in addition to the peroxyl radicals (Uchiyama et al., 1990;Raffi et al., 2000). The 'left' line is a part of cellulosic radical triplet and has been used as a suitable detection method of irradiated dry food ingredients of plant origin (Maloney et al., 1992;Desrosiers et al., 1995). So also, the presence of satellite peaks has been attributed to the starch signal (Chabane et al., 2001). ...
Electron spin resonance (ESR) spectroscopy was employed to detect free radicals in raw Mucuna pruriens (velvet bean) seeds after electron beam irradiation (Microtron source: 0, 2.5, 5, 7.5, 10, 15 and 30 kGy) and conventional processing (roasting, powdering and cooking). The ESR signal of irradiated seeds (g=2.0055±0.0001) was more prominent in the seed coat than cotyledon. Seed coat of irradiated samples showed dose-dependent linear increase of this signal (g = 2.0055) accompanied by a weak triplet (satellite peak; aH = 3 mT) produced exclusively by radiolysis and could be used as an indication of successful irradiation. Irradiated cotyledon portion devoid of satellite peak (triplet) showed a linear increase in signal intensity up to 10 kGy with a sharp decline at higher doses (15 and 30kGy). Stability of radiation-induced ESR signals after 6 months of storage (25 ± 1°C) revealed the presence of a weak triplet with a substantial loss of signal intensity. Thermal effects such as roasting and powdering of seeds increased the signal intensity (g = 2.0055) similar to or in greater proportion than irradiation. Phenolics in seeds, which contribute significantly to detect free radicals in vegetative parts of a plant showed a waning trend in seed coat, while it was vice versa in cotyledon. Textural studies revealed significant loss in firmness after irradiation (p
... Before irradiation, EPR spectra of pulp samples exhibit one singlet line (Fig. 1) characterized with common g ¼ 2.00487 0.0005, which is equal to that observed in skin, stone or seed samples of fresh fruits. It is attributed to free radicals of semiquinones (Swartz et al., 1972), lignin (Maloney et al., 1992) or to the oxidation products of fatty acids present in some fruits and vegetables (Ikeya et al., 1989). ...
The results of electron paramagnetic resonance (EPR) study on fresh fruits (whole pulp of pears, apples, peaches, apricots, avocado, kiwi and mango) before and after gamma-irradiation are reported using two drying procedures before EPR investigation. In order to remove water from non-irradiated and irradiated samples of the first batch, the pulp of fresh fruits is pressed, and the solid residue is washed with alcohol and dried at room temperature. The fruits of the second batch are pressed and dried in a standard laboratory oven at 40°C. The results obtained with both drying procedures are compared. All samples under study show a singlet EPR line with g=2.0048±0.0005 before irradiation. Irradiation gives rise to typical “cellulose-like” EPR spectrum featuring one intensive line with g=2.0048±0.0005 and two very weak satellite lines situated 3mT at left and right of the central line. Only mango samples show a singlet line after irradiation. The fading kinetics of radiation-induced EPR signal is studied for a period of 50 days after irradiation. When the irradiated fruit samples are stored in their natural state and dried just before each EPR measurement, the satellite lines are measurable for less than 17 days of storage. Irradiated fruit samples, when stored dried, lose for 50 days ca. 40% of their radiation-induced radicals if treated with alcohol or ca. 70% if dried in an oven. The reported results unambiguously show that the presence of the satellite lines in the EPR spectra could be used for identification of radiation processing of fresh fruits, thus extending the validity of European Protocol EN 1787 (2000). Foodstuffs—Detection of Irradiated Food Containing Cellulose by EPR Spectroscopy. European Committee for Standardisation. Brussels for dry herbs.
... 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.
... This ESR spectrum is known to be typical of non-irradiated plant materials. Although the origin of the free radicals responsible for this spectrum is not well understood, it had been opined to be semiquinones-like radicals produced by the oxidation of plant polyphenols (Swartz et al 1972) or lignin (Maloney et al 1992; Tabner and Tabner, 1994). Lignin had been shown (Abdul Khalil et al. 2006, Wanrosli et al.2007) to constitute 15.2 – 20.5% of palm frond and this may explain the observed ESR signal of the non-irradiated samples. ...
Palm frond baskets have been an integral part of packaging in many countries and have formed part of the local culture such that certain agro products are assumed to be in their best when packaged in palm frond baskets, hence many resist the use of synthetic materials. Irradiation of materials requires pre-packaging; there is the need therefore to understand the effect of irradiation on the biomaterial and determine the possible parameters that can be used for identification of irradiated materials. The effect of electron beam radiation treatment on the physicochemical properties of oil palm frond basket was investigated. Irradiated baskets showed a dose dependent ESR signal intensity and retained more than 13 % of the signal 30 days post-irradiation. Irradiation had no effect on the hygroscopicity. Headspace analysis showed no significant difference in the composition of the constituents, however differences in per cent content of 2-methyl-1-penten-3one, 3-methyl-butanal, decanal, heptanes, 5-hepten-2one and dodecamethyl cyclohexasiloxane were observed. Palm frond baskets can be used as packaging material for agricultural produce meant for irradiation and ESR could be used to differentiate irradiated and non-irradiated baskets. Heptane and 2-Methyl-1-penten-3-one which increased by over 500 times post-irradiation can be candidates for identification of irradiated baskets.
... Among them, Electron Paramagnetic Resonance (EPR) suggested itself as one of the most adequate methods due to its high sensitivity to unpaired electrons present in all free radicals generated during irradiation. Generally, EPR have been used for the investigation of the hard part of foodstus, able to retain for long time (up to 1 month) the irradiation free radicals (Wieser and Regulla, 1988;Ra and Agnel, 1989;Maloney et al., 1992;Ra and Stacker, 1996;Desrosiers, 1996). ...
Fresh red alimentary pigment extracted from Monascus purpureus fungus exhibits an intense EPR line consisting of a single, narrow line, attributed to a quinone radical. When irradiated with 7 MeV electrons or 60Co γ-rays, the amplitude of this line increased with the absorbed dose following a saturation exponential dependency up to 10 kGy. During annealing treatment (isothermal heating at 100°C) the irradiation centers decay exponentially with a half-life time of 2.30 min.
... Before irradiation all samples of herbal pills (Fig. 1) exhibit only one relatively weak singlet EPR signal with g¼2.0048 7 0.0005, which is equal to that observed in dry herbs and spices. It is attributed to semiquinone free radicals produced by oxidation of polyphenolic compounds present in plants (Jezierski et al., 2002) or lignin (Maloney et al., 1992). No spectra of the excipients added to the pills were recorded. ...
The results of EPR studies on herbal pills of marigold, hawthorn, yarrow, common balm, tutsan, nettle and thyme before and after gamma-irradiation are reported. Before irradiation all samples exhibit one weak singlet EPR line with a g-factor of 2.0048±0.0005. After irradiation herbal pills could be separated in two groups according to their EPR spectra. Radiation-induced free radicals in pills of marigold, yarrow, nettle, tutsan and thyme could be attributed mainly to saccharide excipients. Tablets of hawthorn and common balm show “cellulose-like” EPR spectrum, superimposed on partly resolved carbohydrate spectrum, due to the active part (herb) and inulin, which is present in the pills as an excipient. Fading study of the radiation-induced EPR signals confirms that sugar radicals are more stable than cellulose species. The reported results show that the presence of characteristic EPR spectra of herbal pills due to excipients or active part can be used as unambiguous proof of radiation processing within 35 or more days after irradiation.
... However, as the central line is a sum of the ÔleftÕ and ÔrightÕ lines, both contributed to the increased signal at g ¼ 2.002 in irradiated coffee beans. The left line (lower field) is part of a cellulosic radical triplet and is being tested to evolve a suitable detection method for irradiated foods of plant origin (Raffi & Agnel, 1989;Maloney et al., 1992;Desrosiers et al., 1995;De Jesus et al., 1999). Figure 3 shows the comparative influence of various physical treatments (irradiation, shortterm storage and annealing) on free radical content of coffee bean varieties. ...
Summary Using electron spin resonance (ESR) free radicals, present naturally or formed after γ-irradiation of parts of coffee bean, were examined by entrapping the sample in potassium chloride powder in ESR quartz tubes. The ESR signal at g=2.002 was more prominent in the spermoderm than in the whole seed portion of the coffee beans. The γ-irradiation of coffee beans with doses of 5 or 10 kGy, normally used for decontamination, resulted in a dose-dependent increase of a signal at g=2.002 which was accompanied by a weak triplet (aH c. 3.0 mT), and which was also more prominent in the spermoderm. While short-term storage (24 h at 25 ± 0.5 °C) of irradiated beans resulted in a substantial loss of signal at g=2.002, annealing at 50 ± 0.5 °C for 16 h increased this signal intensity in greater proportion than caused by irradiation alone, suggesting that generation of free radicals in the two varieties of coffee beans is not unique to the irradiation processing alone.
... 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). ...
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 the singlet line present in most vegetable samples studied up to now is unknown. Some authors attribute it to free radicals of semi-quinone (Swartz et al., 1972) or lignin (Maloney et al., 1992) type. ...
The results from the EPR studies on fresh, air-dried and lyophilized tomato samples before and after gamma-irradiation are reported. Before irradiation fresh and air-dried tomatoes exhibit one singlet EPR line characterized with common g-factor of 2.0048±0.0005, whereas freeze-dried tomato does not show any EPR spectrum. After irradiation, a typical “cellulose-like” triplet EPR spectrum appears in all samples, attributed to cellulose free radicals, generated by gamma-irradiation. It consists of intense central line with g=2.0048±0.0005 and two weak satellite lines separated ca. 3 mT left and right of it. In air-dried and lyophilized tomatoes the “cellulose-like” EPR spectrum is superimposed by an additional partly resolved carbohydrate spectrum. Fading measurements of the radiation-induced EPR signals indicate that the intensity of the EPR spectra of air-dried and freeze-dried tomato are reduced to about 50% after 50 days, whereas those of fresh irradiated tomatoes kept at 4 °C fade completely in 15 days. The reported results unambiguously show that the presence of two satellite lines in the EPR “cellulose-like” spectra of tomato samples can be used for identification of radiation processing.
... 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.
... Recently, ESR spectra of ␥-irradiated fresh fruits have been reported [14][15][16][17]. Although previous studies have recorded the time course of signal intensities, the precise response between signal intensities and irradiation doses have not been examined [14][15][16][17][18][19][20][21][22]. Some papers have shown "cellulose-like" satellite signals in some fruits, except for the mango that has shown a singlet after irradiation [15]. ...
An electron spin resonance (ESR) spectroscopic study of radicals induced in irradiated fresh mangoes was performed. Mangoes in the fresh state were irradiated with gamma-rays, lyophilized and then crushed into a powder. The ESR spectrum of the powder showed a strong main peak at g=2.004 and a pair of peaks centered at the main peak. The main peak was detected from both flesh and skin specimens. This peak height gradually decreased during storage following irradiation. On the other hand, the side peaks showed a well-defined dose-response relationship even at 9 days post-irradiation. The side peaks therefore provide a useful means to define the irradiation of fresh mangoes.
... 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.
... 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 and 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.
The EPR spectral properties of non-irradiated and gamma-irradiated dry plants, cress seeds and mistletoe, have been studied with electron paramagnetic resonance method and the differences between non-irradiated and irradiated samples have been determined within this study. It has been shown that EPR spectra of these non-irradiated samples have very weak signal. But these plants have an intense EPR resonance line after irradiation with g value of 2.0046 ±0.0005.
In order to detect irradiated grapes by electron spin resonance(ESR)spectroscopy, 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 in the range of 0 to 10 kGy. The results showed that the ESR spectra of grape skins, grape stalks and grape seeds were 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 curves 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%). The results could provide the technical basis for the application of ESR spectroscopy in detecting irradiated grapes.
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.
Electron spin resonance (ESR) spectroscopy was used to detect the free radicals that were naturally present in lotus seeds or that were formed after employing various food processing methods (e.g., irradiation, microwave roasting, pan frying, grinding or pounding) by placing small portions of lotus seed (seed coat and cotyledon) in KCl powder in ESR quartz tubes. Spectral analysis revealed the presence of an insignificant natural abundance of free radicals and showed a sharp and clear signal at g=2.002, more prominent in seed coat. Exposure to gamma radiation (0–30kGy, the recommended dose for quarantine purposes) resulted in a dose-dependent increase of signal intensity at g=2.002 with the seed coat exhibiting the presence of a weak triplet (aH=3mT) which can be used to authenticate irradiation treatments. Irradiated cotyledon at high doses (15 and 30kGy) revealed significant reduction in ESR signals, attributed to an increase of free radical scavengers. Common food processing practices like microwave roasting, flame heating, grinding or pounding also generated free radicals. It is envisaged that results of the present study might be valuable for health conscious consumers who are interested in the status of free radicals in foodstuffs subjected to traditional or modern food-processing techniques.
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.
An improved detection of radiation-induced paramagnetic faults was developed to identify the irradiation status of basil and clove. The effectiveness of different sample pretreatments, including freeze-drying (FD), oven-drying (OD), alcoholic-extraction (AE), and water-washing and alcoholic-extraction (WAE), were examined. All non-irradiated samples showed a single central signal (=2.006), whereas radicals representing two additional side peaks (=2.023 and =1.986) with a mutual distance of 6 mT were detected in the irradiated samples. AE and WAE produced the best results for irradiated clove in terms of intensities of radiation-specific ESR signals and their ratios to the central signal. However, FD provided the highest intensities of radiation-specific ESR signals for basil, whereas their ratios to the major signal were better in the cases of AE and WAE. Signal noise, particularly due to signals, was observed, whereas it decreased in AE and WAE pretreatments. Based on our results, AE and WAE can improve the detection conditions for radiation-specific ESR signals in irradiated samples.
Using electron spin resonance (ESR) spectroscopy with both experimental
and theoretical approaches, we revealed the γ-radiation induced
radicals in two glucose polymers, cellulose and starch. Before
irradiation, ESR signals are silent in both the glucose polymers. After
irradiation, a singlet signal at g=2.0 appeared in both the glucose
polymers. The twin peaks were invisible in the starch sample. We
identified the twin peaks to be a part of triplet signal and analyzed
the molecular structure of the cellulose radical. Through theoretical
simulations, we revealed, for the first time, that the triplet signal
was due to hyperfine interactions of unpaired electron with two protons
in the cellulose radical. The third peak within the triplet is
overlapped by the free radical at g=2.0. We further found that the
cellulose radical does not remain at the rigid limit or the static
state, but undergoes axial rotations around C-C and C-H
bonds. We concluded that the triplet ESR signal reflects the cellulose
radical.
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.
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).
A major factor hampering the introduction of ionizing radiation as an alternative quarantine treatment to chemical fumigation for fruit and vegetables is the lack of reliable, simple and inexpensive post-treatment methods to confirm this low dose irradiation treatment. Considering this purpose, thermoluminescence (TL) measurements of the wind blown dust naturally adhered to the surface of table grapes, was surveyed. Two doses, 0.5 and 1.0 kGy, were studied, applied to the main Chilean table grape export varieties: Thompson Seedless and Flame Seedless.TL measurements were carried out over 78 days for Thompson Seedless and 62 days for Flame Seedless varieties, both stored at 1 ± 1°C (usual handling of this fruit). TL response fading of dust samples stored at room temperature was also followed over 125 days. The TL response values obtained from the irradiated samples exceeded at least 3 times the highest ones obtained from the unirradiated counterparts. The treatment, even for the lower γ-radiation dose applied, could be properly detected well above the shipping and marketing time for this Chilean export fruit (2–8 weeks). This method also has the advantage of using relatively inexpensive equipment.
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.
ESR signals were recorded from irradiated papaya at liquid nitrogen temperature (77 K), and freeze-dried irradiated papaya at room temperature (295 K).Two side peaks from the flesh at the liquid nitrogen temperature indicated a linear dose response for 3–14 days after the γ-irradiation. The line shapes recorded from the freeze-dried specimens were sharper than those at liquid nitrogen temperature.
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.
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.
This review gives a brief outline of the principles of the EPR detection method for irradiated foods by food type. For each food type, the scope, limitations and status of the method are given. The extensive reference list aims to include all which define the method, as well as some rarely cited works of historical importance.
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.
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.
Statutory Instruments 1990 The Food (Control of Ir-radiation) Regulations, 2490 Food Irradiation and the Chemist
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