JP4113958B2 - Inspection method of irradiated food - Google Patents

Description

  The present invention relates to a method for inspecting irradiated food by determining an unknown radiation dose irradiated to food for sterilization or the like by electron spin resonance spectroscopy (hereinafter abbreviated as “ESR method”), and more specifically By changing the radiation exposure dose, observing the sequential saturation behavior of electron spins, obtaining the ESR signal intensity derived from organic free radicals induced in the food by irradiation, and applying extrapolation to the food The present invention relates to a method for inspecting irradiated food that estimates an unknown irradiation dose that has already been irradiated.

  In order to sterilize foods and to acquire the preservability that can withstand a wide range of distribution, a method of performing irradiation treatment has been put into practical use. The radiation to be used includes an electron beam and a gamma ray, but the gamma ray is generally used in the field of food irradiation since the gamma ray has a high bactericidal effect. For such irradiated foods, there are concerns about changes in components due to irradiation treatment and the health effects of radiation inducers. However, according to WHO (1988), irradiation up to 10 kGy is evaluated as safe. Since soundness has been confirmed globally, regulations that clearly specify irradiation treatment are now eliminated. In other words, the irradiation treatment is regarded as the same as cooking operations such as boiling, steaming and baking in normal food processing. Therefore, in order to distinguish foods that have not been irradiated, a display such as “Organic” or “Natura1” is intentionally performed (USDA 2003).

  Such a sterilization method by irradiation is extremely simple and effective. Therefore, the production amount of irradiated food tends to increase more and more. Therefore, inspection methods for evaluating the quality of irradiated food have been studied. A typical example is an inspection method using the ESR method. There may be a difference in ESR spectra between unirradiated food and irradiated food. For example, in the case of unirradiated food, a signal derived from an organic radical is a singlet, whereas in the case of irradiated food, a side peak appears in relation to the signal. This is because radicals are induced in food by irradiation. Therefore, if a side peak appears by looking at the ESR spectrum, it can be determined that the food sample has been irradiated. However, just because a side peak does not appear does not mean that there is no immediate irradiation. This is because the ESR spectrum varies depending on the measurement conditions, and side peaks may not be observed.

  The ESR method is established as an official method (see Non-Patent Document 1-2), for example, in the European Union (EU). However, foods to be analyzed are limited to foods containing bones or dried vegetables and dried fruits. The former measures components contained in bone tissue, and the latter measures relatively stable organic free radicals generated when cellulose is ionized by irradiation treatment by the ESR method. Thus, the reason why the ESR method is applied only to limited foods is that, as described above, characteristic ESR signals may not be observed depending on the type of food or measurement conditions.

As described above, the conventional method for inspecting irradiated food by the ESR method is not only limited to foods to be analyzed, but also a so-called qualitative method for determining the presence or absence of irradiation, and a strict quantitative method has not yet been established. . For this reason, it is not possible to quantitatively clarify how much radiation has been applied to any food to be analyzed during the irradiation process, that is, the irradiation dose. If it is possible to quantitatively measure the radiation dose of irradiated food, it will be an extremely useful technique for food safety assessment, which is the most important concern of consumers.
EN1786 Foodstuffs-detection of irradiated food containing bone-method by ESR spectroscopy, European Committee for Standardization, Belgium (1996) EN1787 Foodstuffs-detection of irradiated food containing cellulose-method by ESR spectroscopy, European Committee for Standardization, Belgium (1996)

  The problem to be solved by the present invention is to quantitatively determine the irradiation dose when a food is irradiated with radiation for sterilization etc. by measuring the food by ESR method for any food to be analyzed. Is to be able to.

  The inventors of the present invention have been able to apply the ESR method only to foods that are limited in the process of intensively studying the irradiation food inspection method using the ESR method because the ESR signal cannot be observed accurately. The cause was found to be because the ESR measurement conditions were not appropriate. More specifically, the required ESR signal may not be obtained because the signal intensity is already saturated due to the relaxation phenomenon of electron spin in the measured microwave intensity. Actually, the ESR signal was measured by changing the microwave intensity from 0.001 mW to 196 mW using the irradiated pepper as a sample. As a result, the ESR signal changed with the microwave intensity, and when the microwave intensity reached 196 mW, the signal was completely observed. A slanted baseline was exhibited. This indicates that the relaxation phenomenon of electron spin is a cause of failure to observe a correct signal.

  In the ESR measurement conditions according to the EU official method, the microwave intensity is specified to be a constant value in order to guarantee the quantification, but this means that the ESR measurement conditions are not always appropriate. In other words, since the optimum microwave intensity varies depending on the type of food and the storage state, the microwave intensity cannot be set as a constant value. Therefore, the present inventors change the microwave intensity for each food sample and use the microwave intensity that gives the maximum value of the intensity of the signal derived from organic radicals as the optimum intensity, which depends on the type of food and the storage condition. In other words, the present inventors have learned that a good ESR signal can be obtained and have focused on this point to complete the present invention.

  That is, the present invention capable of solving the above technical problems differs from the food to be analyzed in the method for inspecting irradiated food by observing organic free radicals induced in the food by irradiation by the ESR method. Obtain the maximum value of ESR signal intensity derived from organic free radicals induced in food by irradiation by measuring the sequential saturation behavior of electron spins by ESR method for each sample irradiated by irradiation dose. A method for inspecting irradiated food, characterized in that an unknown radiation irradiation dose that has already been applied to the food is estimated by extrapolating the relationship of the maximum ESR signal intensity to the radiation irradiation dose. A method may be used in which the sample is divided into a plurality of pieces, and irradiation is performed with different irradiation doses (including the initial sample that is not irradiated, that is, the irradiation dose is zero), and ESR measurement is performed for each.

More preferably, the present invention provides a method for inspecting irradiated food by observing organic free radicals induced in the food by irradiation with an ESR method,
(A) Initial determination of the maximum value of ESR signal intensity derived from organic free radicals induced in food by irradiation by measuring the sequential saturation behavior of electron spins by ESR method for food samples to be analyzed Sample measurement step,
(B) an irradiation step for subsequently irradiating the sample with radiation;
(C) Irradiation for obtaining the maximum value of ESR signal intensity derived from organic free radicals induced in food by radiation irradiation by measuring the sequential saturation behavior of electron spins by ESR method for the irradiated sample Post-sample measurement step,
The above steps (B) and (C) are repeated as many times as necessary, and the maximum ESR signal intensity obtained in each measurement step is plotted as a relation to the radiation exposure dose, so that the food is already irradiated by extrapolation. This is a method for inspecting irradiated food, characterized by estimating an unknown radiation dose.

  Here, the measurement of the sequential saturation behavior of electron spins is performed by gradually changing the microwave intensity and measuring the ESR signal intensity derived from organic free radicals induced in the food by irradiation. The maximum ESR signal intensity in the sequential saturation curve is obtained. The ESR signal intensity is calculated by obtaining the ratio of the ESR signal intensity derived from organic free radicals induced in food by radiation irradiation and the ESR signal intensity derived from manganese ions, and the signal intensity ratio is used to calculate the signal. It is preferred to represent strength. Alternatively, the ESR signal intensity can be calculated by integrating the observed ESR signal once, applying a baseline correction, and further integrating it, and expressing the signal intensity with an organic free radical concentration proportional to the area.

  The method for inspecting irradiated food according to the present invention is the maximum ESR signal derived from organic free radicals by measuring the sequential saturation behavior of electron spins by the ESR method for samples irradiated with different known irradiation doses, respectively. Since the intensity was determined and the relationship of the maximum ESR signal intensity to the radiation exposure dose was processed by extrapolation, the radiation dose when receiving radiation treatment for sterilization etc. for any food to be analyzed It can be determined quantitatively. As described above, the method of the present invention can grasp the irradiation dose of irradiated food, which could not be clearly clarified as a numerical value, so that risk assessment can be performed from scientific basis for the safety and security that consumers most demand for food. It becomes possible.

  In particular, if the method of repeating radiation irradiation and ESR measurement multiple times is used, the same sample is repeatedly measured, so that the measurement conditions are stable, and in addition, a small automatic inspection system that is simplified by using a handling robot. There is also an effect that can be constructed.

An example of the inspection method according to the present invention is shown in the flowchart of FIG. The present invention is basically a method for inspecting irradiated food by observing organic free radicals induced in the food by irradiation by the ESR method. Typically, the inspection is performed according to the following procedure.
(A) First, a sample is collected and adjusted for the food to be analyzed.
(B) The sequential saturation behavior of electron spin is measured for the initial sample by the ESR method.
(C) Subsequently, the sample is subjected to radiation irradiation treatment with a predetermined irradiation dose.
(D) For the sample after irradiation, the sequential saturation behavior of electron spin is measured by the ESR method.
(E) It is determined whether or not the radiation irradiation process has reached a predetermined number of times. If the required number of measurements has not been reached, the process returns to (c).
(F) From the sequential saturation behavior of electron spins measured by the ESR method, the maximum value of ESR signal intensity derived from organic free radicals induced in each sample by radiation irradiation is obtained.
(G) Plot the maximum of those ESR signal intensities as a relationship to radiation dose
(I) Estimating an unknown radiation exposure dose that has already been applied to food by obtaining an extrapolated value by extrapolation. This completes the inspection.

  The food sample is appropriately adjusted so as to be suitable for ESR measurement according to its type and properties. If it does not affect the ESR measurement, it may be granular or powdered. For those that are affected by anisotropy, it is preferable that the particle size be made uniform by passing through an appropriate sieve (for example, about 200 mesh). For samples containing a lot of moisture, the measurement temperature is set such as freezing or low temperature in order to avoid the influence of moisture content. If necessary, a reduced pressure or an inert gas atmosphere can be used.

  Sequential saturation behavior of electron spin is measured by measuring the ESR signal intensity derived from organic free radicals induced in food by irradiation by gradually changing the microwave intensity, and creating a sequential saturation curve .

  As for the initial sample, basically, as in the conventional case, it is an indicator that a sharp single line signal with a g value of 2 obtained by ESR measurement is strong, and that a new signal appears in the vicinity of the signal with a g value of 2. The presence or absence of irradiation treatment can be determined. This new signal appears as a twin peak. However, since the signal on the low magnetic field side is unstable and often cannot be observed, it has been reported that it is useful to use the signal on the high magnetic field side to detect the presence or absence of irradiation. In the method of the present invention in which is appropriately set, this irradiation induction signal can be observed as a twin peak. Therefore, the presence or absence of the irradiation process can be determined based on the presence or absence of a newly appearing twin peak signal.

  The sample is irradiated with radiation at a known irradiation dose, and ESR measurement is performed on the sample after the irradiation. The measurement of the sequential saturation behavior of electron spin by the ESR method is performed by measuring the ESR signal intensity derived from organic free radicals induced in the food by irradiation with radiation by changing the microwave intensity as described above. Create a saturation curve. This irradiation and ESR measurement are alternately repeated as many times as necessary. Here, as the radiation irradiation, gamma ray irradiation with cobalt 60 is preferable. The maximum value of the signal intensity is obtained from the sequential saturation curve thus obtained. Note that the microwave intensity at which the maximum value of the signal intensity is obtained in the sequential saturation curve varies depending on the irradiation dose irradiated.

  As described above, the signal intensity of a sharp single line having a g value of 2 is increased by irradiation. This is a signal derived from organic free radicals. The signal intensity increased as the irradiation dose was increased. As a result of measuring the signal intensity up to 50 kGy irradiation, a proportional relationship was obtained between the irradiation dose and the signal intensity. Therefore, by plotting the maximum ESR signal intensity obtained from the sequential saturation curve by each ESR measurement as a relation to the radiation exposure dose and obtaining the extrapolated value by extrapolation, the unknown radiation exposure that has already been irradiated to the food The dose can be estimated.

  The maximum ESR signal intensity used for plotting as a relationship to radiation dose may be a direct representation of the observed spectrum signal intensity in height. However, since a transition metal ion in the sample (specifically, a manganese ion that always appears in vegetable foods) is observed as a signal in food samples, the peak of the organic free radical with the transition metal ion as a marker is observed. A method of determining the ratio and making it the maximum ESR signal strength is preferred. This is because the peak ratio is defined on the same spectrum and can be treated as a constant constant. Incidentally, in the EU official method, a certain microwave intensity is specified in order to guarantee the quantitative property, but as can be seen from the analysis by sequential saturation, correct measurement is impossible with such a method.

  In irradiated food samples, as described above, new induced organic free radicals are observed as side peak signals, so it is difficult to express the signal intensity as high. Therefore, when quantifying irradiation-induced organic free radicals, a signal observed as a spectrum (a signal derived from an organic free radical and a side peak signal in the vicinity thereof) is integrated once, subjected to baseline correction, and further integrated. Thereby, the signal intensity can be expressed as an area. By expressing the signal intensity by area, it can be grasped as an absolute quantity.

  The inspection method of irradiated food by such a procedure is suitable for automation. As the inspection system, for example, a handling robot is arranged between the ESR measurement device and the gamma ray irradiation device. The inspection is completed simply by looking at the sample tube containing the sample with a handling robot and moving the sample tube back and forth between the ESR measurement device and the gamma ray irradiation device. When measuring the sequential saturation behavior of electron spin, the ESR signal intensity can be measured by changing the microwave intensity by program control on the ESR measuring device side, and the gamma ray irradiation dose can be controlled by a handling robot. This is because it can be easily performed by controlling the time during which the tube is inserted into the gamma irradiation apparatus.

  In the examples, black pepper was used as a sample. The granular black pepper was squeezed between medicine wrapping papers and lightly crushed with a pestle to make a powder, which was used as a sample for measurement. This is because, when pulverized by a mill having a metal blade, the signal intensity may be increased due to oxidation by oxygen in the air. 300 mg of this sample was weighed and placed in an ESR sample tube (made of 99.9% quartz glass), and ESR measurement was performed. Here, there was no substantial difference in signal between the case where the sample tube was air-excluded under reduced pressure or filled with inert gas, and the case where such treatment was not performed. The sample was put in a sample tube in compressed air, and lightly capped and subjected to splitting.

  ESR measurement was performed using an ESR spectrometer (JES-FE1XG, manufactured by JEOL Ltd.). The frequency of the microwave used for the measurement is X band (9.3 GHz). The resonant magnetic field was 250 mT and 340 mT. The sweep magnetic field is 500 mT. Since the measurement sweep magnetic field is wide as described above, detection of transition metal ions and organic free radicals (free electrons) is possible.

  An example of an ESR spectrum for a sample not irradiated with radiation is shown in FIG. The obtained ESR signal has three components. First, it is a sharp and strong signal when the g value indicated by P1 is 2.0. This is an organic free radical. The second is a six-line signal centered at g = 2.0 shown by P2. This was identified as a manganese ion because its ultrafine structure constant was about 7.4 mT. The signal of g = 4.0 indicated by P3 is an iron ion. Thus, organic free radicals and transition metal ions can be observed regardless of the type of food. Since the six lines derived from manganese ions of P2 are derived from manganese clusters in photosynthesis, any food can be observed as long as it is a vegetable food.

  Next, an example of the ESR spectrum for the irradiated sample is shown in FIG. The obtained ESR signal has four components. In addition to the signals P1, P2 and P3, side peak signals S1 and S2 appeared as the fourth. S1 and S2 are signals that appear at symmetrical positions in the vicinity of both sides (low magnetic field side and high magnetic field side) of P1 due to organic free radicals, and are spectra specific to the irradiated sample. Therefore, if side peaks (S1 and S2) appear in the observed ESR spectrum, it can be determined that the sample has been irradiated.

  In the examples, all ESR measurements were performed at room temperature (20 ° C.). It is said that the smaller the value of the magnetic field modulation width, the less the noise and the more reproducible signal intensity can be obtained. However, in the food sample, 1 × 10 G is sufficient for the magnetic uplifting modulation width.

  In order to examine the sequential relaxation behavior of the electron spin in the sample, the measurement was performed by changing the microwave intensity stepwise from 1 mW to 196 mW to obtain the signal intensity derived from the organic radical. Here, for the signal intensity, the height of the ESR signal derived from the organic radical is represented by the manganese ion intensity (height) in the sample as a standard. That is, sample signal intensity (height) ÷ manganese signal intensity (height) = sample signal intensity ratio. Taking the microwave intensity on the horizontal axis and the above signal intensity ratio on the vertical axis, the relaxation behavior of the electron spin can be obtained from the successive saturation curve.

  FIG. 4 shows an example of the sequential saturation behavior of the sample. When the microwave intensity is changed, a saturation phenomenon occurs. For example, a decrease in the signal indicated by P1 due to the microwave intensity is a typical example. In FIG. 4, at a microwave intensity of 1 mW, P1 is a sharp and strong signal. However, P1 is almost halved at B microwave intensity of 16 mW, and P1 is hardly observable at C microwave intensity of 196 mW.

  FIG. 5 shows an example of a sequential saturation curve. When the signal intensity (height) of P1 is obtained by changing the microwave intensity, a saturation curve is obtained sequentially. A plurality of such sequential saturation curves were obtained by changing the radiation dose. In the present invention, the maximum value of the signal intensity of P1 is obtained from this sequential saturation curve. For irradiation, gamma rays from cobalt 60 were used. The dose was determined by adjusting the distance from the radiation source and the irradiation time. The position (magnetic field) where the signal intensity of P1 is maximum differs depending on the sample. This indicates that it is necessary to set an appropriate microwave intensity in the ESR measurement of a food sample. In the present invention, the appropriate microwave intensity is set at a position where the signal intensity of P1 is maximized. It is decided.

  As the radiation irradiation dose increases, the maximum value of the signal intensity of P1 tends to increase. Therefore, the maximum value of the signal intensity of P1 is obtained for each successive saturation curve obtained by changing the radiation irradiation dose. Here, the value obtained by dividing the signal intensity (height) of P1 in the ESR spectrum by the manganese signal intensity (height) is defined as the maximum ESR signal intensity. This maximum ESR signal intensity is plotted against the radiation dose, and an extrapolation point is obtained by extrapolation. An example of the extrapolation method is shown in FIG. Connect the measurement points with a straight line and extend to find the point where the signal strength ratio is zero. In FIG. 6, since it crosses the base line at a position of about −25 kGy, it can be estimated that the sample has already been irradiated with about 25 kGy.

  It can test | inspect similarly about food samples other than black pepper. As other experimental examples, examples of observable P3 include white pepper, green tea (sencha, matcha, hojicha), black tea, ginseng, etc., and examples where P3 cannot be observed include flour. (This is because wheat flour does not contain iron). In the ESR measurement of wheat flour, an organic free radical signal can be observed, but the signal intensity tends to be unstable. In wheat flour, a wide signal is observed near g = 2.0, and it is observed overlapping with six lines of manganese ions. This wide signal affects not only the structure line of manganese ions, but also the signal intensity of organic free radicals with a g value of 2. The crystal structure in wheat, that is, the anisotropy due to the starch component, is an effect on the ESR signal, and this is the factor that made the signal intensity unstable. However, a reproducible signal was obtained when the grain sizes of the flour were made uniform by passing through a 200 mesh node.

  In this embodiment, measurement is performed in the X band as described above. In such an X-band measurement, it is impossible to separate complicated overlapping signals around the g value of 2. However, by measuring in the W band, there is a possibility that detailed signal observation around the g value 2 can be carried out. According to this, it is possible to separate a wide signal such as wheat and perform twin peak observation. Conceivable.

The flowchart which shows the typical example of this invention method. Explanatory drawing which shows an example of the ESR spectrum of an unirradiated sample. Explanatory drawing which shows an example of the ESR spectrum of the irradiated sample. Explanatory drawing which shows the sequential saturation behavior of a signal. Explanatory drawing which shows the example of a sequential saturation curve. Explanatory drawing of an extrapolation method.

Claims (1)

In the inspection method of irradiated food, which observes organic free radicals induced in food by irradiation by electron spin resonance spectroscopy (ESR method),
(A) Initial determination of the maximum value of ESR signal intensity derived from organic free radicals induced in food by irradiation by measuring the sequential saturation behavior of electron spins by ESR method for food samples to be analyzed Sample measurement step,
(B) an irradiation step for subsequently irradiating the sample with radiation;
(C) Irradiation for obtaining the maximum value of ESR signal intensity derived from organic free radicals induced in food by radiation irradiation by measuring the sequential saturation behavior of electron spins by ESR method for the irradiated sample Post-sample measurement step,
Comprising
In the measurement of the sequential saturation behavior of electron spins in the steps (A) and (C) above, the ESR signal intensity derived from organic free radicals induced in the food by irradiation by changing the microwave intensity gradually. Is calculated by integrating the observed ESR signal once, applying baseline correction, and further integrating, and sequentially generating a saturation curve from the obtained ESR signal intensity to obtain the maximum ESR signal intensity,
The steps (B) and (C) above are repeated as many times as necessary, and the maximum ESR signal intensity obtained in each measurement step is plotted as a relationship to the radiation exposure dose. A method for inspecting irradiated food, characterized by estimating the radiation exposure dose.

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