Determination method for foreign matter contamination in food via element concentration analysis using epma

Abstract

The purpose of the present invention is to provide a determination method for foreign matter contamination that makes it possible to easily determine when contamination occurred, namely, whether foreign matter contaminating a food contaminated the food during a production process or after the product was opened. Provided is a determination method for foreign matter contamination wherein the degree to which a trace element in a food has permeated into foreign matter contaminating the food is analyzed via an element concentration analysis method which includes a prescribed condition and in which an electron probe microanalyzer (EPMA) is used, and the timing of foreign matter contamination is determined on the basis of the results of analysis of the degree of permeation.

Description

Method for identifying foreign substances in food using elemental concentration analysis with EPMA

[0001] The present invention relates to a method for determining whether foreign matter found in food was introduced during the manufacturing process or after the product was opened, i.e., the timing of the foreign matter's introduction, by analyzing the degree of penetration of trace elements from the food into the foreign matter using an elemental concentration analysis method with an electron probe microanalyzer (EPMA), and determining the timing based on the results of the penetration analysis.

[0002] Food is something that is ingested, and therefore, its safety must be ensured. For this reason, in quality control during food manufacturing, factors that could cause contamination, such as hair, must be thoroughly eliminated. In order to thoroughly implement such quality control, it is necessary to accurately understand the actual situation of foreign matter contamination. To that end, it is important to first verify whether the foreign matter found in the food was introduced during the manufacturing process or after the product was opened, and to determine the timing of the contamination.

[0003] For example, regarding verification concerning hair, a method for determining the timing of foreign matter contamination based on the effects of heating during the manufacturing process has been investigated. Non-patent document 1 describes an investigation into whether such determination is possible based on morphological changes, since hair is made of keratin protein and undergoes morphological changes due to heat treatment. Specifically, it states that heating to 200°C to 300°C is required for morphological changes to remain, and since most hair does not undergo morphological changes with heat treatment of around 100°C, which is performed in the manufacturing process of food, it is difficult to estimate the timing of hair contamination based on heat treatment changes from morphological examination.

[0004] Furthermore, Non-Patent Document 1 discloses that when hair is heated, components inside the hair undergo changes, and catalase present in biological tissues disappears during heating, so that the presence or absence of heating can be examined based on the change in activity; and that if the hair root is present, there are cells exhibiting enzyme activity, and catalase activity can be measured. However, it is also described that, in practice, most hair that are mixed contaminants often do not have hair roots, and catalase activity itself changes under various conditions, so it is risky to comment on the presence or absence of heating.

[0005] In addition, Patent Document 1 describes a method for identifying mixed contaminants, which determines the time when contaminants are mixed in based on the analysis result of the penetration degree of food components into contaminants mixed in food, and describes that the analysis of the penetration degree of food components into contaminants is performed by an elemental concentration analysis method. Patent Document 1 describes that the elemental concentration analysis method can be measured using an electron probe microanalyzer (EPMA) apparatus. This apparatus irradiates an electron beam onto the surface of an object and detects characteristic X-rays generated therefrom, and can identify elements based on such characteristic X-rays. For example, for a cross section of hair mixed in food, the concentration distribution of sodium chloride (sodium and chlorine) in food is measured using an elemental analysis apparatus EPMA, and the mixing time of the hair can be determined from the penetration state of sodium chloride into the inside of the hair.

[0006] Japanese Unexamined Patent Publication No. 2005-83804

[0007] Gen Sato, "Method for Identification of Mixed Hair", published by Science Forum Co., Ltd., November 7, 2000 (pp. 7-8, pp. 88-91, pp. 107-108)

[0008] In the method described in Patent Document 1 above, the degree of penetration of sodium chloride contained in food into the hair is analyzed using an elemental concentration analysis method utilizing EPMA. However, some foods contain little to no sodium chloride, and in such cases, it is not possible to detect or measure the degree of sodium chloride penetration in hair contaminated with such food, making it difficult to determine the time of contamination. Furthermore, while the degree of penetration of sodium chloride into contaminated hair can be easily detected and measured using an elemental concentration analysis method utilizing EPMA because foods containing salt, for elements present in trace amounts in food, the same analytical method used for elements present in large amounts such as sodium chloride cannot be used to detect or measure the degree of penetration of such trace elements into contaminated hair, making it difficult to determine the time of contamination.

[0009] Therefore, in this field, the objective is to provide a method for identifying foreign substances that have been introduced into food, which can detect and measure the degree to which trace elements in food penetrate into foreign substances, and can determine whether the foreign substance was introduced during the manufacturing process or after the product was opened, and how the introduction occurred.

[0010] As a result of diligent research to solve the above problems, the present inventors have found that by subjecting the degree of penetration of trace elements from food into foreign matter mixed in food to an elemental concentration analysis method using EPMA with predetermined acceleration voltage, irradiation current, and measurement time conditions, it is possible to detect and measure the degree of penetration of trace elements from food into foreign matter, and based on the analysis results of the degree of penetration, it is possible to determine whether the foreign matter was mixed in during the food manufacturing process or after the product was opened.

[0011] The present invention is based on these novel findings and includes the following inventions: [1] A method for identifying foreign substances in food, which involves analyzing the degree of penetration of trace elements in food into foreign substances mixed in food using an elemental concentration analysis method utilizing an electron probe microanalyzer (EPMA), and determining the time of contamination of the foreign substance based on the analysis results of the degree of penetration, wherein the EPMA analysis conditions include the following conditions: acceleration voltage: 5kV to 25kV, irradiation current: 30nA to 200nA, measurement time per pixel: 20mSec to 60mSec. [2] The method of [1], wherein the trace element is present in an amount of 500mg or less, 400mg or less, 300mg or less, 200mg or less, or 100mg or less per 100g of food. [3] The method of [1] or [2], wherein the trace element is potassium, phosphorus, sodium, or chlorine. [4] Any of the methods of [1] to [3], wherein the EPMA analysis conditions include the following: acceleration voltage: 15 kV, irradiation current: 30 nA to 100 nA, measurement time per pixel: 20 mSec to 40 mSec. [5] Any of the methods of [1] to [4], wherein the degree of penetration of trace elements from food into foreign matter is performed based on the cross-section of the foreign matter. [6] Any of the methods of [1] to [5], wherein, in the case of food that has not been heat-treated during the manufacturing process, the timing of foreign matter contamination is determined by comparing the degree of penetration of trace elements from food into the contaminated foreign matter with the degree of penetration of said trace elements in foreign matter that has been preserved by being mixed into the food for a certain period of time to allow trace elements from food to penetrate. [7] In the case of food products that have not been heat-treated during the manufacturing process, the timing of contamination of foreign matter is determined by a preservation treatment in which a portion of the contaminated foreign matter is mixed into the food product for a certain period of time to allow trace elements from the food product to permeate into the contaminated foreign matter, and then the degree of permeation of trace elements from the food product into the contaminated foreign matter that has undergone the preservation treatment is compared with the degree of permeation of trace elements from the food product into the contaminated foreign matter that has not undergone the preservation treatment, using any of the methods in [1] to [6]. [8] The method in [6] or [7], wherein the food product is selected from the group consisting of tofu, soy milk products, milk and dairy products, noodles such as Chinese noodles, soba, udon, hiyamugi, and somen, cut vegetables, salads, and food and beverages containing one or more of these.[9] In the case of food products that have been heat-treated during the manufacturing process, the timing of foreign matter contamination is determined by comparing the degree of penetration of trace elements from the food into the foreign matter with the degree of penetration of trace elements from the food into foreign matter that has been heat-treated under conditions equivalent to the said heat treatment, using any of the methods [1] to [5] or [9].

[10] In the case of food products that have been heat-treated during the manufacturing process, a portion of the foreign matter is heat-treated under conditions equivalent to the said heat treatment, and the degree of penetration of trace elements from the food into the heat-treated foreign matter with the degree of penetration of trace elements from the food into the non-heat-treated foreign matter, using any of the methods [1] to [5] or [9].

[11] In the case of foreign matter, the foreign matter is hair, an insect, or a part thereof, using any of the methods [1] to

[10] . All publications, patents and patent applications cited herein are incorporated herein by reference as is.

[0012] According to the present invention, it is possible to detect and measure the degree to which trace elements in food penetrate into foreign matter, and to determine whether the foreign matter mixed into the food was introduced during the food manufacturing process or after the product was opened, thereby providing a method for identifying foreign matter that has been introduced.

[0013] Figure 1 is a photographic diagram showing the results of analyzing the phosphorus concentration distribution in the cross-section of untreated hair (control) and hair mixed into yogurt (before fermentation) and stored for a predetermined period, using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the analytical conditions of <Example> or <Comparative Example> by elemental mapping method. Figure 2 is a photographic diagram showing the results of analyzing the potassium concentration distribution in the cross-section of untreated hair (control) and hair mixed into yogurt (before fermentation) and stored for a predetermined period, using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the analytical conditions of <Example> or <Comparative Example> by elemental mapping method. Figure 3 is a photographic diagram showing the results of analyzing the potassium concentration distribution in cross-sections of a control (Blank), a hair that was in contact with tofu for a predetermined time (post-opening contamination model), and a hair that was mixed into a mixture of soy milk and nigari during the manufacturing process and then incorporated into the tofu (product manufacturing contamination model), using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the analytical conditions of <Examples> by elemental mapping method. Figure 4 is a photographic diagram showing the results of analyzing the potassium concentration distribution in cross-sections of a control (Blank), a hair that was in contact with tofu for a predetermined time (post-opening contamination model), and a hair that was mixed into a container containing tofu and sealing water and stored for a predetermined period (product manufacturing contamination model), using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the analytical conditions of <Examples> by elemental mapping method. Figure 5 is a photographic diagram showing the results of analyzing the concentration distribution of sodium and chlorine in the cross-section of a strand of hair using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the analytical conditions of <Examples>, using the elemental mapping method, after preparing a 0.1 mass% saline solution, mixing the hair with the hair, and either (i) heating it at 120°C for a predetermined period and then letting it stand at an environment of approximately 20°C, or (ii) letting it stand at an environment of approximately 20°C.Figure 6 is a photographic diagram showing the results of an elemental mapping analysis using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under analysis condition A, analyzing the sodium concentration distribution in the cross-section of untreated hair (control), hair that has been in contact with Chinese noodles for a predetermined time (post-opening contamination model), and hair that has been mixed into a container in contact with Chinese noodles and stored for a predetermined period (product manufacturing contamination model). Figure 7 is a photographic diagram showing the results of an elemental mapping analysis using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under analysis condition B, analyzing the sodium concentration distribution in the cross-section of the abdomen of untreated midges (control), midges that have been in contact with Chinese noodles for a predetermined time (post-opening contamination model), and midges that have been mixed into a container in contact with Chinese noodles and stored for a predetermined period (product manufacturing contamination model). Figure 8 is a photographic diagram showing the phosphorus concentration distribution in cross-sections of untreated hair (control), hair that has been in contact with soba noodles for a predetermined time (model of contamination after product opening), and hair that has been mixed into a container in contact with soba noodles and stored for a predetermined period (model of contamination during product manufacturing). The results were obtained by analyzing the elemental mapping method using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under analysis condition C. Figure 9 is a photographic diagram showing the results of an elemental mapping analysis of the chlorine concentration distribution in cross-sections of the legs of an untreated Oriental cockroach (control), an Oriental cockroach (legs) that were in contact with shredded daikon radish from a commercially available daikon salad for a predetermined time (model of contamination after product opening), and an Oriental cockroach (legs) that were immersed in electrolyzed water used in the manufacturing process, then mixed into a bag in contact with shredded daikon radish from a commercially available daikon salad and stored for a predetermined period (model of contamination during product manufacturing), using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under analysis condition D.

[0014] The food products of this invention are various processed foods that can be served in restaurants and other establishments, and can be distributed frozen, chilled, or at room temperature.

[0015] Examples of such processed foods include, but are not limited to, retort products such as curry, stew, soup, and sauce; roux products such as curry and stew; various spice products such as wasabi paste, mustard paste, and mustard; seasoning products such as mayonnaise and dressing; dairy products such as yogurt, butter, cheese, and ice cream; dessert products such as tofu, jelly, and pudding; confectionery products such as chocolate and cookies; noodles such as Chinese noodles, soba, udon, hiyamugi, and somen; cut vegetables, salads; and beverage products such as tea, soy milk, coffee, and fruit drinks. Preferably, the food of the present invention is a food that does not contain a large amount of the element selected as the target of measurement in the elemental concentration analysis method of the present invention. Here, "large amount" in the sense of the amount of the element selected as the target of measurement contained in the food means that the element selected as the target of measurement is contained in an amount greater than 500 mg per 100 g of food. The amount of each element contained in 100 g of food can be determined by referring to, for example, the Standard Tables of Food Composition in Japan (Ministry of Education, Culture, Sports, Science and Technology). For example, preferred foods in the present invention can be selected from tofu (firm tofu, silken tofu, soft tofu, filled tofu, grilled tofu, deep-fried tofu, fried tofu, etc.), soy milk products (soy milk, processed soy milk, soy milk beverages), milk (raw milk, cow's milk, special milk, raw goat's milk, pasteurized goat's milk, raw sheep's milk, raw buffalo milk, adjusted milk, low-fat milk, non-fat milk, and processed milk), dairy products (cream, butter, butter oil, cheese, concentrated whey, ice cream, concentrated milk, skimmed concentrated milk, condensed milk, sweetened skimmed condensed milk, processed liquid milk, fermented milk (yogurt, etc.), lactic acid bacteria beverages, and milk beverages), noodles (Chinese noodles, soba, udon, hiyamugi, somen, etc.), cut vegetables, salads, and food and beverages containing one or more of these. Examples of foods and beverages containing soy milk include soy milk yogurt, and examples of foods and beverages containing milk or dairy products include processed milk or dairy products (for example, foods made by combining milk or dairy products with other ingredients (vegetable oil, defatted soy flour, etc.)), but are not limited to these.

[0016] In this invention, "foreign matter" refers to any substance that may be mixed into the above-mentioned food, but only substances that allow trace elements in the food components to penetrate, and substances that do not allow trace elements in the food components to penetrate, such as metals, are not included in the definition of "foreign matter" in this invention. Examples of "foreign matter" in this invention include, but are not limited to, hair, nails, paper, cotton products (thread, cloth), wood chips, stems, roots of plant materials, bone fragments of animal materials, thread, rope, string, insects, plastics and rubbers, etc. In this invention, "hair" is not particularly limited and can include human hair, animal hair, etc. Preferably, in this invention, "foreign matter" refers to hair, insects, or parts thereof.

[0017] This invention provides a method for determining when foreign matter was introduced into food, i.e., whether it occurred during the product's manufacturing process or after the product was opened. This is determined by analyzing the degree to which trace elements in the food penetrated the foreign matter. This analysis is performed using an elemental concentration analysis method utilizing an electron probe microanalyzer (EPMA). The EPMA uses an accelerating voltage and irradiation current to focus an electron beam in a vacuum, which is then irradiated onto minute sections (pixels) on the mirror-polished surface of a solid sample. By detecting the characteristic X-rays emitted from the sample, the type and concentration of elements contained therein can be determined. Furthermore, it is possible to analyze multiple pixels contained within a certain area for a predetermined measurement time, and display the magnitude of the elemental concentration for each pixel using different colors, thereby visually displaying the elemental concentration distribution in two dimensions (elemental mapping method).

[0018] To confirm the penetration of trace elements from food toward the center of a foreign object, or the amount of trace elements that have penetrated the food, it is preferable to irradiate the cross-section of the foreign object with an electron beam and measure the degree of penetration / concentration distribution of trace elements at that cross-section.

[0019] In the present invention, the EPMA analysis conditions include the following: Acceleration voltage: 5kV to 25kV Irradiation current: 30nA to 200nA Measurement time per pixel: 20mSec to 60mSec.

[0020] The acceleration voltage can be selected from a range of 5kV to 25kV, preferably 10kV to 20kV, and more preferably 15kV.

[0021] The irradiation current can be selected from the range of 30 nA to 200 nA, preferably 30 nA to 150 nA, and more preferably 30 nA to 100 nA.

[0022] The measurement time per pixel can be selected from a range of 20 mSec to 60 mSec, preferably 20 mSec to 50 mSec, for example, 30 mSec to 50 mSec, and more preferably 20 mSec to 40 mSec.

[0023] In the present invention, by setting the acceleration voltage, irradiation current, and measurement time per pixel of the EPMA within the above range, it is preferable that the concentration distribution of trace elements in food that have penetrated into foreign matter can be detected and measured effectively.

[0024] Particularly preferably, in the present invention, EPMA is performed under analytical conditions including the following: Acceleration voltage: 15 kV Irradiation current: 30 nA to 100 nA Measurement time per pixel: 20 mSec to 40 mSec.

[0025] In the present invention, the analysis of EPMA may be performed using a polycrystalline summing program. The polycrystalline summing program is preferable because it allows for simultaneous measurement and data processing using multiple spectrometers during analysis, summing the data measured by the multiple spectrometers, and then concentrating the summed data using a calibration curve method, thereby obtaining a high S / N (signal-to-noise ratio), i.e., clearer measurement results.

[0026] In the present invention, "trace elements in food" means elements present in amounts of 500 mg or less, 400 mg or less, 300 mg or less, 200 mg or less, or 100 mg or less per 100 g of food contaminated with foreign matter, for example, amounts of 0.5 mg to 500 mg, 1 mg to 500 mg, 3 mg to 500 mg, 5 mg to 500 mg, 10 mg to 500 mg, 50 mg to 500 mg, 60 mg to 500 mg, 70 mg to 500 mg, 80 mg to 500 mg, or 90 mg to 500 mg, preferably 100 mg to 400 mg, more preferably 100 mg to 300 mg, and even more preferably 100 mg to 200 mg. It is preferable that the trace elements to be measured are elements not present in the foreign matter, or elements present in the foreign matter in extremely small amounts. The trace elements to be measured may vary depending on the food, but examples include sodium, chlorine, potassium, phosphorus, magnesium, calcium, zinc, and iron. The amount of trace elements in food can be determined by referring to, for example, the Standard Tables of Food Composition in Japan (Ministry of Education, Culture, Sports, Science and Technology) for the amount of each element contained in 100g of food. The trace elements to be measured originate from various food components contained in the food. The penetration of various food components into foreign matter is affected by the heating temperature and time of the food, the cooking temperature and time, the storage period and temperature, pH, acidity, the degree of decomposition of food components, and the molecular size of food components. However, if the content of the element to be measured that constitutes the food components in the food is within the above range, the present invention can be applied.

[0027] In making a determination based on the elemental concentration analysis method using EPMA described above, for foods that have been heat-treated during the manufacturing process, for example, a portion of the foreign matter mixed in the food is heat-treated under conditions equivalent to the heat treatment in the manufacturing process, and the degree of penetration of trace elements from the food into the heat-treated foreign matter is compared with the degree of penetration of trace elements from the food into the foreign matter that has not been heat-treated. Specifically, the foreign matter mixed in the food is first cut in half using a cutter or the like. Next, one of the cut pieces of foreign matter is heat-treated under conditions equivalent to the sterilization conditions of the food in which it was mixed, for example, retort heat treatment, in the same way as in the manufacturing process. After that, electron beams are irradiated onto the cross-sections of the retort-heat-treated foreign matter and the other foreign matter that has not been heat-treated, and the degree of penetration of trace elements from the food into each foreign matter is measured and compared.

[0028] Furthermore, in the case of food products that are not heat-treated during the manufacturing process, a portion of the foreign matter found in the food is subjected to a preservation treatment in which trace elements from the food permeate into the foreign matter that has been mixed into the food for a certain period of time. The degree of permeation of trace elements into this foreign matter is then compared to the degree of permeation of trace elements from the food into foreign matter that has not undergone this preservation treatment. Specifically, similar to the food products that are heat-treated during the manufacturing process described above, the foreign matter found in the food is first cut in half using a cutter or the like. Next, one half of the cut foreign matter is mixed into the same food product that the foreign matter was originally found in for a certain period of time to undergo a preservation treatment in which trace elements from the food permeate into the foreign matter. After that, the degree of permeation of trace elements from the food into the preserved foreign matter and the cross-section of the other foreign matter that has not undergone the preservation treatment are irradiated with an electron beam, and the degree of permeation of trace elements from the food into each foreign matter is measured and compared.

[0029] Furthermore, the timing of contamination by foreign matter can be determined by methods other than comparing the degree of penetration of trace elements into the food in the two cut pieces of foreign matter described above.

[0030] Specifically, first, various data based on the relationship between the foreign object found in the food and the food itself, as well as the food's manufacturing conditions, are prepared in advance. For example, a foreign object control sample is prepared by pre-preparing an object of the same type as the foreign object and mixing it into a specific food product, then performing retort heat treatment. When the foreign object that was found in the specific food product is obtained, the degree of penetration of trace elements from the food into the foreign object is measured, and the results are compared with the aforementioned foreign object control sample. This allows for a quicker and more accurate determination of when the foreign object was introduced into the food, without requiring the hassle of reprocessing, such as cutting a hair in half and subjecting one half to retort heat treatment.

[0031] Furthermore, even in foods that have not been heat-treated during the manufacturing process, by preparing a foreign object of the same type as the foreign object beforehand as a foreign object control sample, which has been preserved by being mixed in for a certain period of time to allow trace elements to permeate the food, the timing of foreign object contamination can be determined using the same method as described above.

[0032] The aforementioned comparison can be performed by visually observing the elemental concentration distribution, the presence or absence of elemental parts, etc., using a standard computer-based elemental mapping method, either with the naked eye or a fluorescence microscope. According to the elemental mapping method, as the concentration of an element increases, it is represented in the order of purple, blue, green, yellow, red, and white, allowing for a clear understanding of the degree of penetration.

[0033] Furthermore, such comparisons can also be made by measuring the amount of specific elements detected in the EPMA chart.

[0034] By comparing the above, the timing of contamination of the food with foreign matter is determined. If the treated foreign matter and the untreated foreign matter, or the foreign matter in the food compared to the foreign matter control sample, have nearly the same elemental concentration, it is determined that there is a high probability that the foreign matter in the food was introduced during the food manufacturing process. On the other hand, if the elemental concentration of the untreated foreign matter, or the foreign matter in the food compared to the foreign matter control sample, is low, or if there is almost no elemental concentration distribution, it is determined that the foreign matter in the food was introduced after the product was opened.

[0035] In other words, regarding the determination of when foreign matter was introduced into the food, if there is a large difference in the elemental concentration distribution between the treated foreign matter and the untreated foreign matter, or between the foreign matter control sample and the foreign matter found in the food, it is highly likely that the foreign matter was introduced into the food after the product was opened. Conversely, if the difference in elemental concentration distribution is small, it is highly likely that the foreign matter was introduced into the food during the food manufacturing process.

[0036] Furthermore, if a foreign object found in food was introduced during the food manufacturing process, even if the aforementioned treatment is applied to the foreign object, no significant change will be observed in the degree to which trace elements in the food penetrate the foreign object.

[0037] Furthermore, in the elemental concentration analysis method using EPMA, when measuring the degree of penetration of trace elements in food, it is preferable, and more preferable, to set the measurement conditions, such as the size of the foreign matter used for comparison and the measurement area, to be the same so as not to significantly affect the measurement results. The present invention will be described in more detail below with reference to examples.

[0038] Example 1: Elemental concentration analysis using EPMA to determine the degree of trace element penetration in hair mixed with yogurt (1) Sample preparation A commercially available Caspian Sea yogurt starter culture was mixed with milk in a lidded container sterilized with boiling water to make yogurt (before fermentation). Human hair was mixed into the yogurt, which was then sealed and stored in a refrigerator (below 10°C) for 1 day, 3 days, 7 days, 14 days, or 24 days. After the predetermined period, the hair was removed from the yogurt, and the yogurt adhering to the surface was wiped off. From the resulting sample, a sample for elemental concentration analysis of the sample cross-section was prepared by the method described below. For control, untreated (i.e., not in contact with yogurt) human hair was used, and a sample for elemental concentration analysis was prepared in the same manner.

[0039] (2) Preparation of samples for elemental concentration analysis of sample cross-sections Each of the samples prepared above was submerged in photopolymerizable resin, the resin was cured with an ultraviolet irradiation device, the sample was encapsulated to prepare a cured composite resin, then the cross-section of the sample was surfaced using a cutter knife, sandpaper or the like. Next, gold vapor deposition was performed using a gold vapor deposition apparatus to prepare samples for elemental concentration analysis of each sample cross-section.

[0040] (3) Measurement of elemental concentration distribution Each of the samples for elemental concentration analysis prepared above was fixed to a sample stage for an elemental analyzer such that the cross-section of the sample faced upward. Next, the concentration distributions of phosphorus and potassium in the cross-section of the sample in each sample for elemental concentration analysis were measured under the following analysis conditions using an electron probe microanalyzer (EPMA, apparatus name: JXA-isp100, manufactured by JEOL Ltd.).

[0041] Analysis conditions: <Examples> Acceleration voltage: 15 kV Irradiation current: 100 nA Measurement time per pixel: 40 mSec

[0042] <Comparative Examples> Acceleration voltage: 15 kV Irradiation current: 30 nA Measurement time per pixel: 20 mSec

[0043] (4) Measurement results of elemental concentration distribution The concentration distributions of phosphorus and potassium in the cross-section of each sample were analyzed by an elemental mapping method as shown in FIG. 1 and FIG. 2, and the concentration distribution of each element in the cross-section was measured.

[0044] FIG. 1 shows the measurement results of the phosphorus concentration distribution in the cross-section of each sample. When analyzed under the conditions of <Examples>, the presence of phosphorus was confirmed throughout the entire interior of hair that had been stored in yogurt for a predetermined period of time. Further, when comparing hair stored for 1 day and hair stored for 3 days, it was confirmed that more phosphorus was present inside the hair of the sample stored for 3 days.

[0045] Further, when comparing the sample stored for 3 days with samples stored for 7 days, 14 days, or 24 days, no significant difference was found in the amount of phosphorus inside the hair among these samples.

[0046] Almost no presence of phosphorus was confirmed inside untreated hair (i.e., hair not brought into contact with yogurt).

[0047] Furthermore, when analyzed under the conditions of <Comparative Example>, almost no presence of phosphorus was confirmed in the cross-section of any sample. It has been confirmed that good results can be obtained when similarly measuring concentration distribution for elements that are present in an amount of approximately 500 mg or more per 100 g of food under the conditions of <Comparative Example> (data not shown). However, since phosphorus is a trace element contained in yogurt in an amount of approximately 100 mg / 100 g (Standard Tables of Food Composition in Japan 2020 (8th revised edition), Ministry of Education, Culture, Sports, Science and Technology), it was confirmed that under the conditions of said <Comparative Example>, it is difficult to detect phosphorus that has permeated from yogurt into the interior of contaminated hair.

[0048] Figure 2 shows the measurement results of potassium concentration distribution in the cross-section of each sample. When analyzed under the conditions of <Example>, the presence of potassium was confirmed inside hair that had been stored in yogurt for a predetermined period.

[0049] It was also confirmed that the longer the storage period, the greater the amount of potassium present inside the hair.

[0050] Almost no presence of potassium was confirmed inside untreated hair (i.e., hair not contaminated in yogurt).

[0051] Furthermore, when analyzed under the conditions of <Comparative Example>, almost no presence of potassium was confirmed in the cross-section of any sample. Since potassium is a trace element contained in yogurt in an amount of approximately 170 mg / 100 g (Standard Tables of Food Composition in Japan 2020 (8th revised edition), Ministry of Education, Culture, Sports, Science and Technology), it was confirmed that under the conditions of said <Comparative Example>, it is difficult to detect potassium that has permeated from yogurt into the interior of contaminated hair.

[0052] These results suggest that, for hair found in yogurt, it is possible to determine the period of contamination based on the degree of phosphorus and potassium penetration or concentration distribution within the hair, and whether or not the hair was introduced during the manufacturing process. Specifically, if phosphorus and potassium penetration into the hair is confirmed, and / or if a large amount of phosphorus and potassium is found inside the hair, it suggests that the hair has been present for a long time and is likely to have been introduced during the manufacturing process. On the other hand, if phosphorus and potassium penetration into the hair is not confirmed, and / or if a large amount of phosphorus and potassium is not found inside the hair, it suggests that the hair has been present for a short time and is unlikely to have been introduced during the manufacturing process.

[0053] Example 2: Elemental concentration analysis using EPMA to determine the degree of trace element penetration in hair mixed into tofu (1) Sample preparation Assuming contamination during manufacturing, human hair was mixed into a mixture of soy milk and nigari (magnesium chloride), heated in a microwave oven to make homemade tofu, which was stored in a refrigerator (below 10°C) for 7 days. Also, assuming contamination after opening the product, human hair was brought into contact with commercially available tofu and left to stand at room temperature for 20 minutes. After the predetermined period, the hair was removed from the tofu, and the tofu and / or moisture adhering to the surface was wiped off. From the obtained samples, samples for elemental concentration analysis of the sample cross-section were prepared using the method described in Example 1 (2) above. For the control, a sample for elemental concentration analysis was prepared in the same manner without including human hair.

[0054] (2) Measurement of elemental concentration distribution Using the elemental concentration analysis samples prepared above, the potassium concentration distribution in the cross-section of the sample was measured using the method described in Example 1 (3) and the analytical conditions in <Example>.

[0055] (3) Measurement results of elemental concentration distribution The concentration distribution of potassium in the cross-section of each sample was analyzed using an elemental mapping method as shown in Figure 3, and the concentration distribution of potassium in the said cross-section was measured.

[0056] Figure 3 shows the measurement results of the potassium concentration distribution in the cross-section of each sample. When analyzed under the conditions of <Examples>, the presence of potassium was confirmed inside the hair mixed with tofu. Furthermore, when comparing the case where the hair was in contact with tofu for 20 minutes (post-opening contamination model) with the case where it was mixed with a mixture of soy milk and nigari (product manufacturing contamination model), the presence of potassium was confirmed throughout the hair, including inside, in the product manufacturing contamination model, and a larger amount of potassium was also confirmed.

[0057] Potassium is a trace element found in tofu at an amount of approximately 110 mg to 150 mg / 100 g (Standard Tables of Food Composition in Japan 2020 (8th Revised Edition), Ministry of Education, Culture, Sports, Science and Technology). Under the conditions of the above <Example>, it was confirmed that potassium that had penetrated from the tofu into the hair was detectable.

[0058] These results suggest that, regarding hair found in tofu, it is possible to determine the period of contamination based on the degree of potassium penetration or concentration distribution within the hair, and whether or not the hair was introduced during the manufacturing process. Specifically, if potassium penetration into the hair is confirmed, and / or if a large amount of potassium is found inside the hair, it suggests that the hair has been present for a long time and is likely to have been introduced during the manufacturing process (the tofu production stage). On the other hand, if potassium penetration into the hair is not confirmed, and / or if a large amount of potassium is not found inside the hair, it suggests that the hair has been present for a short time and is unlikely to have been introduced during the manufacturing process.

[0059] Example 3: Elemental concentration analysis using EPMA to determine the degree of trace element penetration in hair mixed with tofu (sealed water) (1) Sample preparation Assuming contamination during manufacturing, human hair was mixed into a commercially available container containing tofu and sealed water, and stored in a refrigerator (4°C) for 1 or 7 days. Also, assuming contamination after opening the product, human hair was brought into contact with commercially available tofu and left to stand at room temperature for 20 minutes. After the predetermined period, the hair was removed from the tofu, and the tofu and / or moisture adhering to the surface was wiped off. From the obtained samples, samples for elemental concentration analysis of the sample cross-section were prepared using the method described in Example 1 (2) above. For the control, a sample for elemental concentration analysis was prepared in the same manner without including human hair.

[0060] (2) Measurement of elemental concentration distribution Using the elemental concentration analysis samples prepared above, the potassium concentration distribution in the cross-section of the sample was measured using the method described in Example 1 (3) and the analytical conditions in <Example>.

[0061] (3) Measurement results of elemental concentration distribution The concentration distribution of potassium in the cross-section of each sample was analyzed using an elemental mapping method as shown in Figure 4, and the concentration distribution of potassium in the said cross-section was measured.

[0062] Figure 4 shows the measurement results of the potassium concentration distribution in the cross-section of each sample. Comparing the case where the sample was in contact with tofu for 20 minutes (post-opening contamination model) with the case where human hair was mixed into a container containing tofu and sealed water (product manufacturing contamination model), it was confirmed that in the product manufacturing contamination model, potassium was present throughout the hair, even inside, and in a larger quantity. Furthermore, it was confirmed that the amount of potassium present inside the hair increased with the length of the contamination period.

[0063] These results suggest that, regarding hair found in containers containing tofu and sealed water, it is possible to determine the period of contamination of the hair based on the degree of potassium penetration or concentration distribution within the hair, and whether or not the hair was introduced during the manufacturing process. Specifically, if potassium penetration into the hair is confirmed, and / or if a large amount of potassium is found inside the hair, it suggests that the hair has been present for a long time and that it is highly likely to have been introduced during the manufacturing process (before the container was sealed). On the other hand, if potassium penetration into the hair is not confirmed, and / or if a large amount of potassium is not found inside the hair, it suggests that the hair has been present for a short time and that it is unlikely to have been introduced during the manufacturing process.

[0064] Example 4: Elemental concentration analysis of trace elements other than phosphorus and potassium in hair using EPMA (1) Sample preparation In order to verify whether it is possible to measure the degree of penetration or concentration distribution in hair for trace elements other than phosphorus and potassium, a 0.1 mass% saline solution was prepared, and human hair was mixed in there. (i) It was heated at 120°C for 15 minutes and then immersed in an environment of about 20°C for half a day, or (ii) it was immersed in an environment of about 20°C for half a day. After the predetermined period had elapsed, the hair was removed from the saline solution, and the moisture adhering to the surface was wiped off. From the obtained sample, a sample for elemental concentration analysis of the sample cross-section was prepared by the method described in Example 1 (2) above.

[0065] (2) Measurement of elemental concentration distribution Using the elemental concentration analysis samples prepared above, the concentration distributions of sodium and chlorine in the cross-section of the sample were measured using the method described in Example 1 (3) and the analytical conditions in <Example>.

[0066] (3) Measurement results of elemental concentration distribution The concentration distribution of potassium in the cross-section of each sample was analyzed using an elemental mapping method as shown in Figure 5, and the concentration distribution of sodium and chlorine in the same cross-section was measured.

[0067] Figure 5 shows the measured concentration distributions of sodium and chlorine in the cross-section of each sample. The presence of both elements was confirmed throughout each sample, even inside the hair strands.

[0068] These results confirm that, similarly, the degree of penetration or concentration distribution in hair can be measured for trace elements other than phosphorus and potassium by analyzing them under the conditions described in the above <Examples>. This demonstrates that various trace elements in food can be used to determine when hair contamination occurred in the food.

[0069] Example 5: Elemental concentration analysis using EPMA to determine the degree of penetration of trace elements in hair mixed into chilled ramen (1) Sample preparation Assuming contamination during manufacturing, human hair was mixed into the ramen noodles of commercially available chilled ramen in a plastic container with a snap-on lid that is distributed refrigerated (below 10°C) (contact with the ramen noodles themselves, not with the soup, etc.), the snap-on lid was closed, and the container was stored in a refrigerator (below 10°C) for 72 hours (3 days). After the predetermined period, the hair was removed from the chilled ramen, and the moisture adhering to the surface was wiped off. A sample for elemental concentration analysis of the sample cross-section was prepared from the obtained sample using the method described in Example 1 (2) above. For controls, untreated human hair (i.e., not in contact with ramen noodles) and, assuming contamination after opening the product, human hair that had been placed in contact with the ramen noodles after opening the lid of the chilled ramen container was used and left at room temperature (20-28°C) for 20 minutes were used, and similarly, samples for elemental concentration analysis were prepared.

[0070] (2) Measurement of elemental concentration distribution The samples prepared above for elemental concentration analysis were fixed to the sample stage of the elemental analyzer so that the cross-section of the sample was facing upwards. Next, the concentration distribution of sodium was measured for the cross-section of each elemental concentration analysis sample using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the following analysis condition A. Since alkaline water (lye water, water containing salts such as sodium chloride) is used in the manufacture of Chinese noodles, sodium was selected as the element to be measured.

[0071] Analysis conditions A: Acceleration voltage: 15kV, Irradiation current: 30nA, Measurement time per pixel: 20mSec

[0072] (3) Elemental concentration distribution measurement results Figure 6 shows the results of analyzing and measuring the sodium concentration distribution in the cross-section of each sample using an elemental mapping method. When analyzed under the above conditions, the presence of sodium was confirmed throughout the entire interior of hair (product manufacturing contamination model) that had been stored on Chinese noodles for a predetermined period of time.

[0073] In untreated hair (i.e., hair not in contact with Chinese noodles) and in human hair that had been in contact with Chinese noodles and left at room temperature (20-28°C) for 20 minutes (a model of contamination after product opening), the presence of sodium was hardly detected.

[0074] Sodium is a trace element present in Chinese noodles at an amount of approximately 66 mg / 100g (Standard Tables of Food Composition in Japan 2020 (8th Revised Edition), Ministry of Education, Culture, Sports, Science and Technology). It was confirmed that, even if only in contact, sodium that had penetrated from the surface of the Chinese noodles into the inside of the hair contaminated with the noodles could be detected under the above conditions.

[0075] These results demonstrate that even in foods containing sodium as a trace element, such as Chinese noodles, it is possible to detect and measure the degree of sodium penetration or concentration distribution within foreign matter found within the food. Based on the degree of sodium penetration or concentration distribution, it is possible to determine when the foreign matter was introduced.

[0076] Example 6: Elemental concentration analysis using EPMA to determine the degree of trace element penetration in insects (abdomen of midges) found in chilled ramen (1) Sample preparation Assuming contamination during manufacturing, midges (dead) were mixed into the ramen noodles of commercially available chilled ramen in a plastic container with a snap-on lid that is distributed refrigerated (below 10°C) (they were in contact with the ramen noodles themselves, not with the soup, etc.), the lid was put on, and the container was stored in a refrigerator (below 10°C) for 72 hours (3 days). After the predetermined period, the midges were removed from the chilled ramen, and the moisture adhering to the surface was wiped off. From the obtained sample, a sample for elemental concentration analysis of the sample cross section was prepared by the method described below. For control, we used untreated midges (dead) (i.e., not in contact with the Chinese noodles) and midges (dead) that had been opened to simulate contamination after the product was opened. These midges were then placed in contact with the Chinese noodles after opening the lid of the chilled Chinese noodles container and left at room temperature (20-28°C) for 20 minutes. Samples for elemental concentration analysis were prepared in the same manner.

[0077] (2) Preparation of samples for elemental concentration analysis of sample cross-sections The midges prepared above were submerged in photopolymerized resin, and the resin was cured using an ultraviolet irradiation device to create a composite resin in which the sample was embedded and cured. Next, the cross-section of the abdomen of the sample was prepared using a cutter knife or sandpaper. Then, gold deposition was performed using a gold deposition device to prepare samples for elemental concentration analysis of each sample cross-section.

[0078] (3) Measurement of elemental concentration distribution The samples prepared above for elemental concentration analysis were fixed to the sample stage of the elemental analyzer so that the cross-section of the sample was facing upwards. Next, the concentration distribution of sodium was measured for the cross-section of each elemental concentration analysis sample using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the following analysis condition B.

[0079] Analysis conditions B: Acceleration voltage: 15kV, Irradiation current: 30nA, Measurement time per pixel: 20mSec

[0080] (4) Elemental concentration distribution measurement results Figure 7 shows the results of analyzing and measuring the sodium concentration distribution in the cross-section of each sample using an elemental mapping method. When analyzed under the above conditions, the presence of sodium was confirmed inside the midge (product manufacturing contamination model) that was stored on Chinese noodles for a predetermined period of time.

[0081] In untreated midges (i.e., those not in contact with Chinese noodles) and midges that were in contact with Chinese noodles and left at room temperature (20-28°C) for 20 minutes (a model of contamination after product opening), the presence of sodium was hardly detected.

[0082] As mentioned above, sodium is a trace element in Chinese noodles. However, under the conditions described above, it was confirmed that sodium that had penetrated from the surface of the Chinese noodles into the inside of the midge that had been mixed in could be detected, even though it was merely in contact with the noodles.

[0083] These results demonstrate that even in foods containing sodium as a trace element, such as Chinese noodles, and even in foreign objects such as insects (midges), it is possible to detect and measure the degree of sodium penetration or concentration distribution within the foreign object found in the food. Based on the degree of sodium penetration or concentration distribution, it is possible to determine when the foreign object was introduced.

[0084] Example 7: Elemental concentration analysis using EPMA to determine the degree of penetration of trace elements in hair mixed into soba noodles (1) Sample preparation Assuming contamination during manufacturing, human hair was mixed into the noodles of commercially available chilled soba noodles in a plastic container with a snap-on lid that is distributed refrigerated (below 10°C) (contact with the soba noodles themselves, not with the soup, etc.), the snap-on lid was closed, and the container was stored in a refrigerator (below 10°C) for 72 hours (3 days). After the predetermined period, the hair was removed from the chilled soba noodles, and the moisture adhering to the surface was wiped off. From the obtained sample, a sample for elemental concentration analysis of the sample cross-section was prepared using the method described in Example 1 (2) above. For controls, untreated human hair (i.e., not in contact with soba noodles) and, assuming contamination after opening the product, human hair that had been placed in contact with the soba noodles after opening the lid of the chilled soba container was used and left at room temperature (20-28°C) for 20 minutes were used, and similarly, samples for elemental concentration analysis were prepared.

[0085] (2) Measurement of elemental concentration distribution The samples prepared above for elemental concentration analysis were fixed to the sample stage of the elemental analyzer so that the cross-section of the sample was facing upwards. Next, the phosphorus concentration distribution was measured for the cross-section of each elemental concentration analysis sample using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the following analysis condition C.

[0086] Analysis conditions C: Acceleration voltage: 15kV, Irradiation current: 100nA, Measurement time per pixel: 40mSec

[0087] (3) Elemental concentration distribution measurement results Figure 8 shows the results of analyzing and measuring the phosphorus concentration distribution in the cross-section of each sample using an elemental mapping method. When analyzed under the above conditions, the presence of phosphorus was confirmed throughout the entire interior of hair (product manufacturing contamination model) that had been stored on soba noodles for a predetermined period of time.

[0088] Phosphorus was detected in both untreated hair (i.e., hair not in contact with soba noodles) and human hair that had been in contact with soba noodles and left at room temperature (20-28°C) for 20 minutes (model of contamination after product opening). However, the amount was smaller compared to human hair stored for 72 hours (3 days) (model of contamination during product manufacturing).

[0089] In soba noodles, phosphorus is a trace element present in amounts of approximately 80 mg / 100g (Standard Tables of Food Composition in Japan 2020 (8th Revised Edition), Ministry of Education, Culture, Sports, Science and Technology). It was confirmed that, even if merely in contact with the hair, phosphorus that had penetrated from the surface of the soba noodles could be detected under the above conditions.

[0090] These results demonstrate that even in foods containing phosphorus as a trace element, such as soba noodles, it is possible to detect and measure the degree of phosphorus penetration or concentration distribution within foreign matter found within the food. Based on the degree of phosphorus penetration or concentration distribution as a trace element, it is possible to determine when the foreign matter was introduced.

[0091] Example 8: Elemental concentration analysis using EPMA to determine the degree of trace element penetration in insects (legs of a black cockroach) found in a radish salad (1) Sample preparation Assuming contamination during manufacturing, the legs of a black cockroach (dead) were immersed in electrolyzed water used in the manufacturing process. Then, the legs were mixed into shredded radish (not in contact with the vegetable itself, but not with the dressing, etc.) of a commercially available refrigerated (below 10°C) packaged radish salad, and stored in a refrigerator (below 10°C) for 48 hours (2 days). After the predetermined period, the black cockroach legs were removed from the radish salad, and the moisture adhering to the surface was wiped off. From the obtained sample, a sample for elemental concentration analysis of the sample cross-section was prepared by the method described below. For control, we used the legs of an untreated cockroach (dead) (i.e., not immersed in electrolyzed water and not in contact with the shredded radish in the commercially available radish salad) and the legs of a cockroach (dead) that, simulating contamination after opening the product, were not immersed in electrolyzed water but were in contact with the shredded radish in the commercially available radish salad and left in a refrigerator (below 10°C) for 48 hours (2 days). Samples for elemental concentration analysis were prepared in the same manner.

[0092] (2) Preparation of samples for elemental concentration analysis of sample cross-sections The cockroach legs prepared above were submerged in photopolymerized resin, and the resin was cured using an ultraviolet irradiation device to create a composite resin in which the sample was embedded and cured. Next, the cross-section of the sample leg was smoothed using a cutter knife or sandpaper. Then, gold deposition was performed using a gold deposition device to prepare samples for elemental concentration analysis of each sample cross-section.

[0093] (3) Measurement of elemental concentration distribution The samples prepared above for elemental concentration analysis were fixed to the sample stage of the elemental analyzer with the cross-section of the sample facing upwards. Next, the chlorine concentration distribution was measured for the cross-section of each elemental concentration analysis sample using an elemental analyzer EPMA (instrument name: JXA-isp100, JEOL Ltd.) under the following analysis condition D. In the manufacture of commercially available packaged cut vegetables / salads, electrolyzed water is generally used to sterilize raw vegetables, and this electrolyzed water contains sodium hypochlorite at a concentration of approximately 80 ppm. Therefore, since chlorine is contained in the electrolyzed water at a concentration of approximately 38 ppm, chlorine was measured as a trace element in this test.

[0094] Analysis conditions: <Example D> Acceleration voltage: 15kV Irradiation current: 30nA Measurement time per pixel: 20mSec

[0095] (4) Elemental concentration distribution measurement results Figure 9 shows the results of analyzing and measuring the chlorine concentration distribution in the cross-section of each sample using an elemental mapping method. When analyzed under the above conditions, the presence of chlorine was confirmed throughout the entire interior of a cockroach leg (product manufacturing contamination model) that had been immersed in electrolyzed water and stored for a predetermined period on shredded radish from the commercially available radish salad.

[0096] The presence of chlorine was confirmed inside both the untreated (i.e., uncontacted with electrolyzed water and the shredded radish in the commercially available radish salad) legs of the American cockroach and the legs of the American cockroach that were not immersed in electrolyzed water but were in contact with the shredded radish in the commercially available radish salad and left in a refrigerator (below 10°C) for 48 hours (2 days) (model of contamination after product opening). However, the amount was smaller compared to the model of contamination during product manufacturing.

[0097] These results confirm that, even if the cockroach was only in contact with the shredded radish in a commercially available radish salad, chlorine that had penetrated from the surface of the shredded radish could be detected on its leg under the above conditions.

[0098] These results confirm that even in foods containing chlorine as a trace element, such as packaged cut vegetables / salads, and even in foreign objects such as insects (cockroach legs), it is possible to detect and measure the degree of penetration or concentration distribution of trace elements within the foreign object found in the food. It was also shown that, by utilizing these trace elements, the time of contamination of the foreign object can be determined based on the degree of penetration or concentration distribution within the foreign object.

[0099] The results above confirm that it is possible to detect and measure the degree of penetration or concentration distribution of foreign substances mixed into food by utilizing various trace elements in food, and that the method for determining the timing of contamination of food with foreign substances according to the present invention is applicable to a wide variety of foods and foreign substances.

Claims

1. A method for identifying foreign substances in food, which involves analyzing the degree of penetration of trace elements from food into foreign substances mixed into food using an elemental concentration analysis method with an electron probe microanalyzer (EPMA), and determining the time of contamination based on the analysis results of the degree of penetration, wherein the EPMA analysis conditions include the following: acceleration voltage: 5kV to 25kV, irradiation current: 30nA to 200nA, measurement time per pixel: 20mSec to 60mSec.

2. The method according to claim 1, wherein the trace element is an element present in an amount of 500 mg or less per 100 g of food.

3. The method according to claim 2, wherein the trace element is potassium, phosphorus, sodium, or chlorine.

4. The method according to claim 1, wherein the EPMA analysis conditions include the following: acceleration voltage: 15 kV, irradiation current: 30 nA to 100 nA, and measurement time per pixel: 20 mSec to 40 mSec.

5. The method according to claim 1, wherein the degree of penetration of trace elements from food into a foreign object is analyzed based on the cross-section of the foreign object.

6. The method according to claim 1, wherein, in the case of food that has not been heat-treated during the manufacturing process, the timing of contamination of foreign matter is determined by comparing the degree of penetration of trace elements in the food into the foreign matter with the degree of penetration of said trace elements in foreign matter that has been mixed into the food for a certain period of time and subjected to a preservation treatment that allows trace elements from the food to penetrate.

7. The method according to claim 1, wherein, in the case of food that has not been heat-treated during the manufacturing process, the timing of foreign matter contamination is determined by preserving a portion of the contaminated foreign matter by mixing it into the food for a certain period of time to allow trace elements from the food to permeate into the contaminated foreign matter, and then comparing the degree of permeation of trace elements from the food into the contaminated foreign matter that has undergone the preservation treatment with the degree of permeation of trace elements from the food into the contaminated foreign matter that has not undergone the preservation treatment.

8. The method according to claim 6, wherein the food is selected from the group consisting of tofu, soy milk, milk and dairy products, noodles, cut vegetables, salads, and food and beverages containing one or more of these.

9. The method according to claim 1, wherein, in the case of food that has been heat-treated during the manufacturing process, the timing of contamination of foreign matter is determined by comparing the degree of penetration of trace elements from the food into the foreign matter with the degree of penetration of trace elements from the food into foreign matter that has been heat-treated under conditions equivalent to the said heat treatment.

10. The method according to claim 1, wherein, in the case of food products that have been heat-treated during the manufacturing process, the timing of contamination is determined by heat-treating a portion of the contaminated foreign matter under conditions equivalent to the heat-treating process, and comparing the degree of penetration of trace elements from the food product into the heat-treated contaminated foreign matter with the degree of penetration of trace elements from the food product into the non-heat-treated contaminated foreign matter.

11. The method according to claim 1, wherein the foreign matter is hair, an insect, or a part thereof.

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