Thermal history indicator and method for evaluating thermal history using the same

Abstract

To make it possible to easily grasp heat history for each position.SOLUTION: A thermal history indicator indicative of thermal history when heated includes a high temperature cured material for curing the thermal history indicator when heated and temperature rises, and a color change material for changing color of the thermal history indicator by reaction during heating.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a thermal history indicator and a method for evaluating thermal history using the same. [Background technology]

[0002] Objects are heated in a variety of situations. It is sometimes desirable to know the degree of heating. For example, Patent Document 1 discloses a technique relating to a thermal history detection composition configured to be able to identify thermal history using the Maillard reaction. This thermal history detection composition can be used to determine the quality of food or the like when the food or the like is contained in a retort pouch and subjected to retort sterilization. The thermal history detection composition is contained, for example, in a bag made using a film sheet, and is contained inside the retort pouch together with the object, or is attached to the outer surface of the retort pouch. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-107226 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for knowing the thermal history at each position during heating. An object of the present invention is to make it possible to easily grasp the thermal history at each position. [Means for solving the problem]

[0005] According to one aspect of the present invention, a thermal history indicator that shows thermal history when heated includes a high-temperature curing material that hardens the thermal history indicator when heated and the temperature rises, and a color-changing material that changes the color of the thermal history indicator by reacting during heating. [Effects of the Invention]

[0006] According to the present invention, the thermal history for each position can be easily grasped. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 shows photographs of the thermal history indicators of Samples 1 and 2 and Comparative Samples 1 to 3 after heating and cooling. [Figure 2] FIG. 2 shows photographs of the thermal history indicators according to Samples 3 to 7 after heating and cooling. [Figure 3] FIG. 3 shows photographs of the thermal history indicators according to Samples 8 to 10 after heating and cooling. [Figure 4] FIG. 4 shows photographs of the thermal history indicator after heating for 4, 6, 9 or 11 minutes and then cooling. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings. The present embodiment relates to a thermal history indicator and a method for evaluating thermal history using the same.

[0009] A heating object may be heated for various purposes. Sometimes it is desired to know how the heating object has been heated. The thermal history indicator according to this embodiment is used in such cases. This thermal history indicator is heated in place of the heating object. The thermal history indicator after heating indicates information about the applied heat, and in particular indicates the thermal history, which is the cumulative amount of heat given. Based on the state of the thermal history indicator after heating, the heating state can be evaluated when the heating object is heated under the same conditions as when the thermal history indicator was heated.

[0010] The object to be heated may be, for example, food, but is not limited thereto. The purpose of heating may be, for example, sterilizing microorganisms that may be present in the food, cooking the food, etc. The heating method may be, for example, dielectric heating using microwaves or the like. Alternatively, the heating method may be heating by heat conduction, convection, or heat radiation using an oven or the like. The heating device may be a device that heats the object to be heated using steam.

[0011] The thermal history indicator according to this embodiment includes a color changer that changes color when heated and the temperature rises. The thermal history indicator according to this embodiment also has a certain size. The thermal history indicator is configured to harden at least when heated and the temperature rises. The hardening of the thermal history indicator fixes the position of the color changer. The thermal history indicator provides information about heating, such as the temperature at each position, based on the color at that position within the thermal history indicator.

[0012] The color changer changes the color of the thermal history indicator due to a reaction during heating. The color changer may be, for example, a substance whose color changes due to the Maillard reaction. In this case, the color changer includes a reducing sugar and an amino compound. The reducing sugar may include a monosaccharide. Examples of monosaccharides that can be used include xylose, ribose, and arabinose. The amino compound may include an amino acid, a peptide, and a protein. Examples of amino acids that can be used include glycine, lysine, aspartic acid, alanine, glutamic acid, histidine, and / or salts thereof. In addition to the Maillard reaction, the color changer may also be a pigment that fades due to heat, such as gardenia yellow. The color of the thermal history indicator changes depending on the thermal history, allowing the user to visually grasp the thermal history.

[0013] The high-temperature curing material, which is a material that hardens the thermal history indicator when heated to an elevated temperature, includes a cellulose compound that gels at high temperatures. Such cellulose compounds may include, for example, methyl cellulose, hydroxypropyl methyl cellulose, etc. Alternatively, the high-temperature curing material, which hardens the thermal history indicator when heated to an elevated temperature, may be a material that solidifies when heated, such as a protein.

[0014] The thermal history indicator preferably includes a high-temperature curing material that hardens the thermal history indicator at high temperatures, as well as a low-temperature curing material that hardens the thermal history indicator at low temperatures. For example, the thermal history indicator preferably includes a cellulose compound that gels at high temperatures, as well as a material that hardens the thermal history indicator in at least a portion of the temperature range where the cellulose compound does not harden. Examples of such low-temperature curing materials include polysaccharides. Examples of such polysaccharides include various polysaccharides, such as seaweed extracts, plant extracts, fruit extracts, and microbial products. More specifically, examples of such polysaccharides include gellan gum, agar, carrageenan, gum arabic, locust bean gum, pectin, and xanthan gum. Protein-based materials such as gelatin and casein may also be used as low-temperature curing materials. For example, considering that methylcellulose gels at temperatures above 50°C, low-temperature curing materials that gel at temperatures below 50°C may be used.

[0015] Even if the thermal history indicator does not contain a low-temperature curing material that hardens the thermal history indicator at low temperatures, information about heating at each position within the thermal history indicator can be obtained by checking the color tone of the thermal history indicator when it is hardened at a high temperature immediately after heating. On the other hand, if the thermal history indicator contains a low-temperature curing material that hardens even at low temperatures, the thermal history indicator that has been cooled after heating will also maintain its solid state. In other words, the position of the color-changing object is fixed even in the thermal history indicator that has been cooled after heating. With such a thermal history indicator, information about heating at each position can be obtained based on the color tone at each position in the thermal history indicator after cooling. Furthermore, by cutting the thermal history indicator after cooling, information about the temperature distribution inside the thermal history indicator can also be obtained from the color tone of the cross section.

[0016] Preferably, the thermal history indicator further includes a white powder. This white powder may be an insoluble powder. This white powder may be, for example, aluminum oxide, titanium oxide, or zinc oxide. When the thermal history indicator includes the insoluble white powder, the base color of the thermal history indicator becomes whitish. As a result, the visibility of the color change caused by heating of the thermal history indicator is improved.

[0017] The various heating-related characteristics of the thermal history indicator are adjusted to match the various characteristics of the actual heated object whose heating state is to be evaluated. For example, if the heated object is heated by dielectric heating, the electrical characteristics of the thermal history indicator are adjusted to be equivalent to the electrical characteristics of the heated object. Electrical characteristics may include dielectric constant, conductivity, etc. Furthermore, the heat transfer characteristics of the thermal history indicator are adjusted to be equivalent to the heat transfer characteristics of the heated object. For this purpose, for example, flour, starch, sodium chloride, oil, etc. may be added to the thermal history indicator. The electrical and heat transfer characteristics of the thermal history indicator do not need to match the electrical and heat transfer characteristics of the heated object, as long as there is a predetermined relationship between them so that the state of the heated object can be evaluated based on the state of the thermal history indicator.

[0018] Although not limited thereto, the thermal history indicator can be used to evaluate the thermal history of a heat treatment for sterilizing microorganisms during a food manufacturing process, for example. A thermal history indicator is installed in a heating device in place of the food, and the food is heated under the same conditions. The color change of the thermal history indicator can be confirmed to determine the heating status of the food. The thermal history indicator can evaluate the heating status for each position within the thermal history indicator. For example, the hottest point and the coldest point can also be identified. Based on this information, it can be determined whether heating is sufficient to sterilize microorganisms at all positions within the food to be heated. Furthermore, overheating of the food may cause quality deterioration. Based on the information obtained using the thermal history indicator, it can be determined whether the quality of the food has deteriorated due to overheating.

[0019] For example, measurements using probe-type temperature sensors require multiple probes to measure temperatures at multiple locations. Furthermore, thermography can obtain surface temperature distributions but cannot obtain internal temperature distributions. A thermal history indicator can obtain information about the heat applied to a heated object, which is related to the three-dimensional temperature distribution of the heated object. Compared to measurements using temperature sensors, for example, a thermal history indicator can easily grasp the thermal history of each location, making it easy to identify the hottest and coldest points.

[0020] The above-described example of use of the thermal history indicator is merely an example, and the thermal history indicator can be used for various purposes. By using the thermal history indicator, the temperature change status of the heated object during the heat treatment can be grasped. Therefore, by using the thermal history indicator, the heating conditions can be examined. Furthermore, in production lines of various items that involve heat treatment, the thermal history indicator can be heated instead of the product, and the heat treatment can be easily inspected.

[0021] In cases where objects to be heated are placed at multiple positions inside the heating device, the heating state at each position can be grasped by placing a thermal history indicator at each position.

[0022] Furthermore, it is also possible to mix live microorganisms into the thermal history indicator and examine the state of these microorganisms after heating while checking the color tone. [Example]

[0023] 1. Hardening of thermal history indicators at high temperatures The role of the substance that hardens the thermal history indicator at high temperatures in the thermal history indicator according to the above embodiment was examined. Here, methylcellulose was used as the high-temperature hardening material that hardens the thermal history indicator at high temperatures.

[0024] (1) Composition of the thermal history indicator As the thermal history indicator according to the above-described embodiment, thermal history indicators for Sample 1 and Sample 2 were prepared. Also, thermal history indicators for Comparative Sample 1 and Comparative Sample 2, which have a composition similar to Sample 1 but do not contain methylcellulose, were prepared. Also, a thermal history indicator for Comparative Sample 3, which has a composition similar to Sample 2 but does not contain methylcellulose, was prepared. The compositions of the thermal history indicators for Samples 1 and 2 and Comparative Samples 1 to 3 are shown in Table 1.

[0025] [Table 1]

[0026] The thermal history indicator of Sample 1 includes the following: The thermal history indicator of Sample 1 includes 2.0 wt% methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd.) to gel the thermal history indicator at high temperatures; 3.4 wt% gellan gum (DSP Gokyo Food & Chemical Co., Ltd.; Gelmate KA was used) to gel the thermal history indicator at low temperatures; 10.0 wt% xylose (manufactured by Wako Pure Chemical Industries, Ltd.) as a sugar for inducing the Maillard reaction; xylose also effectively improves the dispersibility of methylcellulose; 10.0 wt% glycine (manufactured by Wako Pure Chemical Industries, Ltd.) as an amino acid for inducing the Maillard reaction; 1.0 wt% aluminum oxide (manufactured by Wako Pure Chemical Industries, Ltd.) to adjust the color of the thermal history indicator. The thermal history indicator also contains 5.0% by weight of wheat flour (manufactured by Nisshin Foods Inc.) and 1.0% by weight of sodium chloride (manufactured by Nacalai Tesque Inc.) to adjust the electrical properties of the thermal history indicator. The solvent is water.

[0027] The thermal history indicator of Comparative Sample 1 does not contain methylcellulose, and the amount of wheat flour for adjusting electrical properties is reduced to 2.5% by weight, and the amount of sodium chloride is reduced to 0.5% by weight, compared to the thermal history indicator of Sample 1. The other components of the thermal history indicator of Comparative Sample 1 are the same as those of the thermal history indicator of Sample 1. That is, the thermal history indicator of Comparative Sample 1 contains 3.4% by weight of gellan gum, 10.0% by weight of xylose, 10.0% by weight of glycine, 1.0% by weight of aluminum oxide, 2.5% by weight of wheat flour, and 0.5% by weight of sodium chloride.

[0028] The thermal history indicator of Comparative Sample 2 does not contain methylcellulose and sodium chloride, unlike the thermal history indicator of Sample 1. The other components of the thermal history indicator of Comparative Sample 2 are the same as those of the thermal history indicator of Sample 1. That is, the thermal history indicator of Comparative Sample 2 contains 3.4% by weight of gellan gum, 10.0% by weight of xylose, 10.0% by weight of glycine, 1.0% by weight of aluminum oxide, and 5.0% by weight of wheat flour.

[0029] Compared to the thermal history indicator of Sample 1, the thermal history indicator of Sample 2 has a reduced amount of methyl cellulose to 1.0 wt %, which is used to gel the thermal history indicator at high temperatures, and also contains 5.0 wt % starch (manufactured by Wako Pure Chemical Industries, Ltd.) instead of wheat flour to adjust the electrical properties. The other composition of the thermal history indicator of Sample 2 is the same as that of the thermal history indicator of Sample 1. That is, the thermal history indicator of Sample 2 contains 1.0 wt % methyl cellulose, 3.4 wt % gellan gum, 10.0 wt % xylose, 10.0 wt % glycine, 1.0 wt % aluminum oxide, 5.0 wt % starch, and 1.0 wt % sodium chloride.

[0030] The thermal history indicator of Comparative Sample 3 does not contain methylcellulose and sodium chloride, unlike the thermal history indicator of Sample 2. The other composition of the thermal history indicator of Comparative Sample 3 is the same as that of the thermal history indicator of Sample 2. That is, the thermal history indicator of Comparative Sample 3 contains 3.4 wt% gellan gum, 10.0 wt% xylose, 10.0 wt% glycine, 1.0 wt% aluminum oxide, and 5.0 wt% starch.

[0031] (2) Method for producing a thermal history indicator A thermal history indicator with the above composition was prepared as follows. First, sodium chloride was dissolved in water to prepare a sodium chloride aqueous solution. While stirring this aqueous solution with a stirrer (manufactured by Sanshosha), a mixed powder of powdered gellan gum and powdered glycine was added to the solution. After the addition, the solution was heated to 65°C or higher using a water bath (manufactured by AS ONE Corporation) set to 90°C. Wheat flour or starch and aluminum oxide were added to the aqueous solution. The solution was transferred to a water bath (manufactured by AS ONE Corporation) set to 60°C and cooled to 60°C or lower. Once the solution was confirmed to be 60°C or lower, a mixed powder of powdered xylose and powdered methylcellulose was added to the solution. A predetermined amount of this mixed liquid was poured into a cylindrical cup with a bottom. The filled cup was then kept at 4°C for at least 1 hour. The substance in the cup hardened into a gel, completing the thermal history indicator.

[0032] (3) Heating method for thermal history indicator The thermal history indicator formed in the bottomed cylindrical cup as described above was placed horizontally with the bottom facing down and heated using a dielectric heating device. The output was set to 150 W and the heating was carried out for 5 minutes. After heating, the thermal history indicator was cooled in water at 24°C for 10 minutes. The thermal history indicator after cooling was observed.

[0033] (4) Heating results of the thermal history indicator Figure 1 shows photographs taken after the thermal history indicators of Samples 1 and 2 and Comparative Samples 1 to 3 were heated and cooled as described above. The photographs in Figure 1 show the top surfaces of the thermal history indicators in the cups, taken from above the open cups.

[0034] As shown in Figure 1, the thermal history indicators of Comparative Samples 1 to 3 showed brown spots in the center, and traces of solidification after rising were observed. This is thought to be the result of the central portion of the thermal history indicator becoming liquid as it heated up and boiled over. The thermal history indicators of Comparative Samples 1 to 3 are gelled by gellan gum at room temperature, but liquefy at high temperatures, which is thought to be why they reached the state shown in Figure 1. In the thermal history indicators of Comparative Samples 1 to 3, in the state shown in Figure 1, the browned portions have now mixed and moved regardless of their position during heating. For this reason, the thermal history indicators of Comparative Samples 1 to 3 cannot provide information about heating, such as temperature distribution according to the position of the thermal history indicator.

[0035] In contrast, the thermal history indicators of Samples 1 and 2 did not show any signs of bumping, as did the thermal history indicators of Comparative Samples 1 to 3, and maintained their shape well when heated. This is thought to be because the thermal history indicators of Samples 1 and 2 contained methylcellulose, which gelled at high temperatures and maintained their solid state despite the liquefaction of gellan gum. This demonstrates that by including a substance such as methylcellulose that hardens the thermal history indicator at high temperatures, information regarding the temperature history at each position during heating can be obtained based on the color tone of the thermal history indicator.

[0036] 2. Concentrations of xylose and glycine as thermal history indicators The concentrations of xylose and glycine in the thermal history indicator according to the above embodiment were examined.

[0037] (1) Composition of the thermal history indicator As the thermal history indicator according to the above embodiment, thermal history indicators of Samples 3 to 7 were prepared, each containing different amounts of xylose as a sugar and glycine as an amino acid that cause the Maillard reaction. The compositions of the thermal history indicators of Samples 3 to 7 are shown in Table 2.

[0038] [Table 2]

[0039] The thermal history indicators of Samples 3 to 7 have almost the same composition, except for xylose and glycine. Each thermal history indicator contains 2.0 wt. % methylcellulose (Shin-Etsu Chemical Co., Ltd.) to gel the indicator at high temperatures, 3.4 wt. % gellan gum (DSP Gokyo Food & Chemical Co., Ltd.; Gelmate KA was used) and 2.5 wt. % agar (Wako Pure Chemical Industries, Ltd.) to gel the indicator at low temperatures. Each thermal history indicator also contains 1.0 wt. % aluminum oxide (Wako Pure Chemical Industries, Ltd.) to adjust the color of the indicator. Each thermal history indicator also contains 12.9 wt. % oil (Showa Sangyo Co., Ltd.) for Samples 3 and 4 and 10.0 wt. % oil (Showa Sangyo Co., Ltd.) for Samples 5 to 7 to adjust the electrical properties of the indicator. Each thermal history indicator also contains 0.7 wt. % sodium chloride (Nacalai Tesque, Inc.) to adjust the electrical properties of the indicator.

[0040] The thermal history indicators of Samples 3 to 7 contain 5.8 wt%, 6.0 wt%, 10.0 wt%, 15.0 wt%, and 20.0 wt% xylose (manufactured by Wako Pure Chemical Industries, Ltd.), respectively. The thermal history indicators of Samples 3 to 7 also contain 3.1 wt%, 6.0 wt%, 10.0 wt%, 15.0 wt%, and 20.0 wt% glycine (manufactured by Wako Pure Chemical Industries, Ltd.), respectively. The solvent is water.

[0041] (2) Method for producing a thermal history indicator A thermal history indicator with the above composition was prepared as follows. First, sodium chloride was dissolved in water to prepare a sodium chloride aqueous solution. While stirring this aqueous solution with a stirrer (manufactured by Sanshosha), a mixed powder of powdered gellan gum and powdered glycine was added to the solution. After the addition, the solution was heated to 65°C or higher using a water bath (manufactured by AS ONE) set to 90°C. Agar and aluminum oxide were added separately to the solution. The solution was transferred to a water bath (manufactured by AS ONE) set to 60°C and cooled to 60°C or lower. Once the solution was confirmed to be below 60°C, a mixture of oil and powdered methylcellulose was added. After confirming that the mixture was sufficiently mixed, xylose was added. A predetermined amount of this mixture was filled into a cylindrical cup with a bottom. The filled cup was kept warm at 4°C for at least one hour. The substance in the cup hardened into a gel, completing the thermal history indicator.

[0042] (3) Heating method for thermal history indicator The thermal history indicator prepared as described above was heated and cooled in the same manner as in the case of samples 1 and 2, and the thermal history indicator after cooling was observed.

[0043] (4) Heating results of the thermal history indicator Figure 2 shows photographs taken after the thermal history indicators of Samples 3 to 7 were heated and cooled as described above. The photographs in Figure 2 show the top surfaces of the thermal history indicators in the cups.

[0044] In all cases, no traces of bumping were observed, as was observed in the above-mentioned Comparative Samples 1 to 3. It was also confirmed that the browning process differed depending on the concentration of xylose and glycine. In all cases, it was confirmed that the sample functioned as a thermal history indicator.

[0045] 3. Monosaccharides and amino acids as thermal history indicators The types of monosaccharides and amino acids and their concentrations in the thermal history indicator according to the above embodiment were examined.

[0046] (1) Composition of the thermal history indicator For the thermal history indicator according to the above embodiment, ribose, arabinose, and xylose were used as monosaccharides that induce the Maillard reaction. Glycine and lysine hydrochloride were used as amino acids that induce the Maillard reaction. Thermal history indicators Samples 8 to 10 were prepared using different combinations of these. The compositions of the thermal history indicators for Samples 8 to 10 are shown in Table 3.

[0047] [Table 3]

[0048] The thermal history indicators of Samples 8 to 10 have almost the same composition, except for the monosaccharides and amino acids. Each thermal history indicator contains 2.0 wt% methylcellulose (Shin-Etsu Chemical Co., Ltd.) to gel the indicator at high temperatures, 3.4 wt% gellan gum (DSP Gokyo Food & Chemical Co., Ltd.; Gelmate KA was used) and 2.5 wt% agar (Wako Pure Chemical Industries, Ltd.) to gel the indicator at low temperatures. Each thermal history indicator also contains 1.0 wt% aluminum oxide (Wako Pure Chemical Industries, Ltd.) to adjust the color of the indicator. Each thermal history indicator also contains 12.9 wt% oil (Sample 8) and 10.0 wt% oil (Showa Sangyo Co., Ltd.) to adjust the electrical properties of the indicator. Each thermal history indicator also contains 0.7 wt% sodium chloride (Nacalai Tesque, Inc.) to adjust the electrical properties of the indicator.

[0049] The thermal history indicator of sample 8 contains 5.0 wt% ribose (manufactured by Wako Pure Chemical Industries, Ltd.), 5.0 wt% arabinose (manufactured by Wako Pure Chemical Industries, Ltd.), and 10.0 wt% glycine (manufactured by Wako Pure Chemical Industries, Ltd.) to induce the Maillard reaction. The thermal history indicator of sample 9 contains 10.0 wt% ribose and 10.0 wt% glycine to induce the Maillard reaction. The thermal history indicator of sample 10 contains 10.0 wt% xylose (manufactured by Wako Pure Chemical Industries, Ltd.) and 10.0 wt% lysine hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd.) to induce the Maillard reaction. The solvent is water.

[0050] (2) Method for producing a thermal history indicator Thermal history indicators of the above composition were prepared in the same manner as in the case of samples 3-7.

[0051] (3) Heating method for thermal history indicator The thermal history indicators prepared as described above were heated and cooled in the same manner as in the case of samples 1 to 7, and the thermal history indicators after cooling were observed.

[0052] (4) Heating results of the thermal history indicator Figure 3 shows photographs taken after the thermal history indicators of Samples 8 to 10 were heated and cooled as described above. The photographs in Figure 3 were taken of the top surfaces of the thermal history indicators in the cups.

[0053] In all cases, no traces of bumping were observed, as was observed in the above-mentioned Comparative Samples 1 to 3. It was also confirmed that the browning process differed depending on the type and concentration of monosaccharides and amino acids. In all cases, it was confirmed that the samples functioned as thermal history indicators.

[0054] 4. Evaluation of thermal history using thermal history indicators Evaluation of thermal history during heating using the thermal history indicator according to the above embodiment was studied.

[0055] (1) Method For the evaluation, thermal history indicators prepared using the composition and preparation method of Sample 6 described above were used. These thermal history indicators were heated using a dielectric heating device as in the above example. The output was set to 150 W. The heating time was set to 4 minutes, 6 minutes, 9 minutes, or 11 minutes. After heating, the indicators were cooled, and then the thermal history indicators were observed.

[0056] (2) Results Figure 4 shows photographs of the thermal history indicator after heating for 4, 6, 9, or 11 minutes and then cooling. The photographs on the left are of the top surface of the thermal history indicator in the cup. The photographs on the right are of the cross section of the thermal history indicator cut vertically through the center.

[0057] It can be seen that as the heating time increases, the area in the thermal history indicator that turns brown expands and the color becomes darker. In other words, as the heating time increases, the area in the thermal history indicator that becomes high temperature expands and the temperature also rises. It can be seen that by using the thermal history indicator, it is possible to grasp the thermal history, such as the position where the temperature of the thermal history indicator rises during heating and the manner of the temperature rise.

[0058] More specifically, for example, in the cross-sectional photograph on the right column for a 4-minute heating time, the center of the thermal history indicator, indicated by the solid arrow, begins to change color after 4 minutes of heating, and the color gradually darkens, indicating that this position is the hottest point. Also, in the cross-sectional photograph on the right column for a 11-minute heating time, the upper corner of the thermal history indicator, indicated by the hollow arrow, shows no progress in discoloration even after 11 minutes of heating, indicating that this position is the coldest point. For example, if the target object to be heated is food and it is heated for 11 minutes, if no deterioration in quality occurs in the central portion indicated by the solid arrow and sufficient sterilization of microorganisms occurs in the corner portion indicated by the hollow arrow, it becomes clear that the heating has achieved its purpose.

[0059] In this way, it has become clear that the use of this thermal history indicator makes it possible to grasp the state of temperature change of the heated object during heat treatment. Therefore, it is understood that the use of the thermal history indicator makes it possible to examine heating conditions, etc. Furthermore, it is understood that in a production line that includes heat treatment, by heating the thermal history indicator instead of the product, it is possible to inspect the heat treatment, etc.

[0060] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

Claims

1. A thermal history indicator having a three-dimensional shape and showing the thermal history of each position when heated, a high-temperature curing material that cures the thermal history indicator when heated to an elevated temperature; a low-temperature curing material that cures the thermal history indicator in at least a part of a temperature range that is not cured by the high-temperature curing material; a color change substance that changes the color of the thermal history indicator by a reaction during heating; Includes a thermal history indicator.

2. The thermal history indicator according to claim 1 , wherein the high-temperature curing material that cures the thermal history indicator is a cellulose compound.

3. The thermal history indicator of claim 2 , wherein the cellulose compound that hardens the thermal history indicator is methyl cellulose or hydroxypropyl methyl cellulose.

4. The thermal history indicator of claim 1 , wherein the color change substance comprises at least a reducing sugar and an amino compound.

5. 5. The thermal history indicator according to claim 1, wherein the low-temperature curing material that cures the thermal history indicator is a polysaccharide.

6. The thermal history indicator according to claim 5 , wherein the polysaccharide that hardens the thermal history indicator includes at least one of gellan gum, agar, carrageenan, gum arabic, locust bean gum, pectin, and xanthan gum.

7. 7. The thermal history indicator of claim 1, further comprising an insoluble white powder.

8. Installing a thermal history indicator according to any one of claims 1 to 7 in a heating device; evaluating the state of heating by the heating device based on the change in color tone of the thermal history indicator; A method for evaluating thermal history, including:

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