Retort sterilization method

Abstract

To provide a retort sterilization method capable of sterilizing by selecting a uniform sterilization temperature by numerically expressing conditions for effectively performing sterilization without damaging quality of food products from a packaging form, size of a packaging container and etc., according to a kind of the food product.SOLUTION: In a retort sterilization method for individually packaged products, depending on the heat transfer property and packaging form of the contents to be packaged, from three variables of a target Fo value (unit: minutes), a product thickness H and a come-up time (CUT) for retort sterilization, a function for calculating a reference sterilization temperature that indicates a minimum CV value (unit: minutes) is created, and an executing sterilization temperature is set within a temperature range of the reference sterilization temperature ±5°C calculated from the function to perform the retort sterilization.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a retort sterilization method carried out on individually packaged products. [Background technology]

[0002] Retort sterilization is a method of sterilization using water or steam heated to a high temperature of 100°C or higher in a pressure cooker. By selecting the sterilization temperature and time, it is possible to kill heat-resistant bacteria such as Clostridium botulinum. Therefore, it has long been used to sterilize canned products, and in recent years it has also come to be widely used to sterilize packaged products filled in containers such as pouches and cups.

[0003] In such retort sterilization, the sterilization time can be shortened by setting the sterilization temperature high, but if the temperature is too high, excessive heat will be applied only to the surface of the packaged food, damaging the quality, and if the sterilization time is too long, food components such as nutrients will be lost, also damaging the quality of the food. Therefore, retort sterilization under various conditions has been proposed depending on the type of food packed in the container and the shape of the container.

[0004] For example, an example in Patent Document 1 shows that retort sterilization of milk coffee (180 g) packed in a plastic cup with a capacity of 215 mL and an outer mouth diameter of 75 mm (estimated inner diameter of 65 mm) was performed at a sterilization temperature of 121.1°C (Fo value: 30 minutes) and a cut-up time of 15 minutes. Here, the Fo value is the heating time converted to the heating time when the sterilization temperature is 121.1°C. Specifically, Clostridium botulinum is killed after 2.4 minutes of heating at a sterilization temperature of 121.1°C, and therefore, this Fo value is used when setting sterilization conditions. Furthermore, cut-up time (CUT) is the time (minutes) required for the temperature of the heat medium in the sterilizer to reach the sterilization temperature from the treatment start temperature.

[0005] Patent Document 2 relates to rotary retort sterilization of viscous products packed in rigid containers, and in its examples it is described that retort sterilization was carried out with a cut time of 10 minutes, an Fo value of 15.5 minutes, and a sterilization temperature of 121°C. Patent Document 3 relates to static retort sterilization of cup-packed cooked rice, and describes that the general sterilization conditions are 120°C for 20 to 30 minutes.

[0006] Patent Document 4 relates to a method for producing retort porridge and does not mention CUT, but it does show that retort sterilization was carried out under various conditions, such as a sterilization temperature of 125°C and an Fo value of 19.1 minutes, or a sterilization temperature of 123°C and an Fo value of 17.9 minutes.

[0007] Additionally, Patent Documents 5 to 8 also show that various packaged foods and beverages have been subjected to retort sterilization at various temperatures. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-220207 [Patent Document 2] Japanese Patent Application Publication No. 7-194354 [Patent Document 3] Japanese Patent Application Publication No. 7-147918 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-157343 [Patent Document 5] Japanese Patent Application Publication No. 2020-80798 [Patent Document 6] Japanese Patent Application Publication No. 2019-180287 [Patent Document 7] Japanese Patent Application Publication No. 2018-166527 [Patent Document 8] Japanese Patent Application Laid-Open No. 2010-110227 Summary of the Invention [Problem to be solved by the invention]

[0009] As mentioned above, retort sterilization is carried out under various conditions depending on the type of food, etc., but the conditions are merely empirically set for each food so as not to impair its quality, based on the heating conditions that kill Clostridium botulinum as a standard, and no universal heating conditions that will not impair the quality of food have been set.

[0010] Therefore, an object of the present invention is to provide a retort sterilization method in which the conditions for effective sterilization without impairing the quality of food are mathematically formulated according to the type of food, the packaging form, the size of the packaging container, etc., and a uniform sterilization temperature can be selected to perform sterilization. [Means for solving the problem]

[0011] The inventors conducted numerous verification and evaluation tests on retort sterilization of general foods by changing the sterilization conditions, and discovered that the cooking value CV (an index at which the deterioration of food components such as nutrients is minimized), which is an index of quality change, depends on the product thickness (container size) and reaches a minimum value (smallest value) at a certain sterilization temperature, which led to the completion of the present invention.

[0012] According to the present invention, in the retort sterilization method for individually packaged containerized products, the contents to be packaged are indicates conductive heat transfer, Create a function to calculate the reference sterilization temperature that indicates the minimum CV value (unit: min) from the target Fo value (unit: min) during retort sterilization according to the packaging form, The function is expressed by the following formula (1a): T base =a·ln(Fo)+b (1a) During the ceremony, T base is the standard sterilization temperature, a is the coefficient of ln(Fo), and b is the parameter CUT (unit: min) and product thickness H (unit: mm), The aforementioned There is provided a retort sterilization method characterized in that retort sterilization is performed by setting the actual sterilization temperature within a temperature range of ±5°C of the reference sterilization temperature calculated from the function.

[0013] In the retort sterilization method of the present invention, the following aspects can be suitably adopted. (A )before The contents that exhibit conductive heat transfer are solids or fluid substances with a viscosity (25°C) of 500 mPa·s or more. ( B ) The packaging form that allows constant pressure control is a pouch or cup container. (C ) Setting the actual sterilization temperature to a temperature of 121°C or higher. [Effects of the Invention]

[0014] According to the present invention, the reference sterilization temperature that minimizes quality changes of the contents is expressed by a formula, not by empirical rules, depending on the type of food contained and the packaging form of the container, so that retort sterilization can be performed while always maintaining a constant quality. Furthermore, the method of the present invention is extremely useful for designing container sizes and packaging forms, since it is possible to identify container sizes and packaging forms suitable for retort sterilization while maintaining a certain level of quality. [Brief explanation of the drawings]

[0015] [Figure 1] Diagram to explain product thickness H (packed in a pouch). [Figure 2] A diagram to explain the product thickness H (packed in a cup). [Figure 3] FIG. 1 is a diagram showing the relationship between cooking value CV (unit: min) and sterilization temperature. [Figure 4] A graph showing the relationship between the Fo value and the temperature at which the minimum CV value is obtained (CUT 5 minutes). [Figure 5] A graph showing the relationship between the Fo value and the temperature at which the minimum CV value is obtained (CUT 10 minutes). [Figure 6] A graph showing the relationship between the Fo value and the temperature at which the minimum CV value is observed (CUT 15 minutes). [Figure 7] A graph showing the relationship between the Fo value and the temperature at which the minimum CV value is observed (CUT 20 minutes). [Figure 8] A diagram plotting product thickness H on the horizontal axis and constant term b on the vertical axis (CUT 5 minutes). [Figure 9] A diagram plotting product thickness H on the horizontal axis and constant term b on the vertical axis (CUT 10 minutes). [Figure 10] A diagram plotting product thickness H on the horizontal axis and constant term b on the vertical axis (CUT 15 minutes). [Figure 11] A diagram plotting product thickness H on the horizontal axis and constant term b on the vertical axis (CUT 20 minutes). [Figure 12] 12 is a diagram showing a curve plotted with the values ​​of the coefficient c of the natural logarithm term and the constant term d read from FIGS. 8 to 11 on the vertical axis and CUT on the horizontal axis. DETAILED DESCRIPTION OF THE INVENTION

[0016] As previously mentioned, the present invention is based on the phenomenon that retort sterilization is verified by varying the sterilization temperature depending on the container contents and the container packaging format, and that the cooking value (CV), which is an index of the amount of change in content quality, depends on the product thickness H, Fo value, and CUT (come-up time) and reaches a minimum value (minimum value) at a certain temperature. That is, this phenomenon is utilized to determine a function for calculating the temperature (reference sterilization temperature) that shows the minimum CV value, and the actual sterilization temperature (effective sterilization temperature) is set according to the calculated reference sterilization temperature, and retort sterilization is performed at this temperature so that a predetermined Fo value is achieved. Therefore, before explaining how to determine the function, terms such as container contents, container packaging format, product size H, and CUT (come-up time) will be explained.

[0017] The contents to which the present invention is applied are particularly food products, as can be understood from the fact that they are subjected to retort sterilization, but can be broadly divided into those that exhibit conductive heat transfer and those that exhibit convective heat transfer.

[0018] Solids are typical examples of materials that exhibit conductive heat transfer, but viscous fluids, such as pastes with a viscosity of 500 mPa·s or more at 25°C, also exhibit conductive heat transfer. In both cases, the flow of the material does not affect heating. In addition, substances that exhibit convective heat transfer are so-called liquids, and beverages are a typical example, but substances with a viscosity of less than 500 mPa·s at 25°C are also included in the category of substances that exhibit convective heat transfer, as their flow has a significant effect on heating. Furthermore, contents in which solids are dispersed in a liquid, such as starch seaweed, curry, stew, meat sauce, beef bowl ingredients, boiled azuki beans, braised pork cubes, and stewed offal, are considered to exhibit conductive heat transfer properties.

[0019] The packaging form to which the present invention is applicable is a pouch, but may also be a cup as long as a large head space that affects heat transfer to the contents is not formed.

[0020] The product thickness H, also known as the container size H, is the length (unit: mm) of the part that determines the heat transfer rate during heat sterilization in a retort oven. For details about this product thickness, please refer to Figures 1 and 2.

[0021] That is, in the case of a pouched product whose contents are entirely or almost entirely conductive heat transfer, the thickness of the pouch when filled with the contents is thickness (container size) H, as shown in Figures 1(a) and (b).

[0022] For cup-packed products, the thickness also varies depending on the height and diameter. For example, if the height = diameter, the height or diameter becomes the product thickness H, but if the height < diameter, as shown in Figure 2(a), the height becomes the product thickness H, and if the height > diameter, the diameter becomes the product thickness H, as shown in Figure 2(b).

[0023] CUT (Come-up time) refers to the time (unit: minutes) required to reach the sterilization step (sterilization temperature ±1°C, etc.) from the start of retort sterilization. The sterilization step is the process of maintaining a constant sterilization temperature, and also includes the overshoot step (the step of temporarily exceeding the set sterilization temperature at the transition point from the lifting and lowering step to the sterilization step). For pouched products or cup-packed products with little or no headspace (HS), CUT can be set to any value.

[0024] In the present invention, when the sterilization temperature and product thickness are changed and the cooking value (CV), which is an index of the change in quality of the contents, is evaluated, this cooking value CV depends on the product thickness (container size) and is based on the phenomenon that it takes on a minimum value at a certain temperature.Based on this phenomenon, a function for calculating the sterilization temperature is created and the sterilization temperature to be actually performed is set. Such a procedure for making a function is explained in the following experiment.

[0025] <Experiment> First, contents that exhibit conductive heat transfer are suitable for conductive heat transfer without convection (viscosity of 500 mPa·s or higher). In this experimental example, a 6% aqueous solution of hydroxypropylated phosphate cross-linked starch (viscosity of approximately 800-1200 mPa·s) was selected. Pouches were selected as the containers, and the sterilization temperature and product thickness H (thickness of the pouched product) were varied. The cooking value (CV), which is an index of the degree of change in the contents due to heat deterioration, was calculated and evaluated using the following formula (Equation 1). The cut time was set to 10 minutes. The results are shown in Figure 3.

[0026] In this experiment, the pouch used had a layer structure of 12 μm PET / 15 μm Ny / 7 μm Al foil / 70 μm unstretched polypropylene from the outside in. The pouch size and filling amount were adjusted as shown in Table 1 below to achieve the product thickness H (thickness of the pouched product) to be evaluated. PET stands for polyethylene terephthalate, and Ny stands for nylon.

[0027] [Table 1]

[0028] The formula for calculating the cooking value CV is as follows:

number

[0029] As can be seen from Figure 3, the sterilization temperature at which the cooking value CV shows a minimum value varies depending on the product thickness. Therefore, to clarify the relationship between the sterilization temperature that satisfies this minimum cooking value CV and the target Fo value (the time equivalent to the heating time at 121.1), a straight line is obtained by semi-logarithmically plotting the sterilization temperature that shows the minimum CV with this Fo value on the horizontal axis (logarithmic axis).

[0030] That is, Figure 3 shows the CV curve obtained with a CUT of 10 minutes. For CV curves obtained by changing the CUT, if the sterilization temperature showing the minimum CV is plotted in a semi-logarithmic manner with the Fo value on the horizontal axis (logarithmic axis), a straight line is also obtained. 4 to 7 show straight lines obtained by performing the semi-logarithmic plot when the CUT was set to 5 minutes, 10 minutes, 15 minutes, and 20 minutes.

[0031] As can be seen from Figures 4 to 7, the sterilization temperature showing the smallest CV is the reference sterilization temperature T base This temperature is expressed in the form of the following equation (1a): T base =a·ln(Fo)+b (1a) In the formula, a represents the coefficient of ln(Fo), b indicates the constant term (intercept).

[0032] In the above formula (1a), the values ​​of the coefficient a and the constant term (intercept) b are as shown in Tables 2 to 5 below.

[0033] [Table 2]

[0034] [Table 3]

[0035] [Table 4]

[0036] [Table 5]

[0037] As can be seen from Figures 4 to 7 and Tables 2 to 5 above, the coefficient term a is a constant that is independent of the product thickness H (pouch thickness) or CUT, and shows a constant value of 4.3 to 4.4, but the value of the constant term (intercept) b depends on the product thickness H and CUT. That is, the standard sterilization temperature T base (The sterilization temperature at which the CV is minimal) is expressed by the function of the following formula (1). T base =F(Fo,CUT,H) (1) To be more specific, T base =a·ln(Fo)+b (1a) During the ceremony, a is a number between 4.3 and 4.4, b is a function of CUT and H and can be expressed as F(CUT, H).

[0038] Furthermore, when the product thickness H (thickness) is plotted on the horizontal axis and the constant term b on the vertical axis for each cut, the curves shown in Figs. 8 to 11 are obtained. The curves shown in FIGS. 8 to 11 can all be approximated by a logarithmic function and can be expressed by the following formula (1b). b=c·ln(H)+d (1b) The coefficient c of the natural logarithm term and the constant term d both depend on CUT and can be converted to the following equation (1c). b = fc(CUT) ln(H) + fd(CUT) (1c)

[0039] The above fc(CUT) and fd(CUT) can be expressed as follows. The values ​​of the coefficient c of the natural logarithm term and the constant term d were extracted from FIGS. 8 to 11 and are shown in Table 6 below.

[0040] [Table 6]

[0041] Next, based on the above results, a curve with CUT on the horizontal axis and c and d on the vertical axis is plotted in Figure 12. As can be seen from Figure 12, both c and d are in a linear relationship with CUT, and fc(CUT) and fd(CUT) can be expressed by the following formulas (1d) and (1e). fc(CUT)=-0.15·CUT-6.6 (1d) fd(CUT)=0.58·CUT+129.4 (1e)

[0042] Therefore, by substituting the above equations (1d) and (1e) into equation (1c), the following equation (1f) representing the constant term b can be obtained. b=-(0.15 CUT+6.6) ln(H) +0.58·CUT+129.4 (1f) Therefore, the standard sterilization temperature T base The formula (1a) showing the above is finally expressed as the following formula (1g). T base =a·ln(Fo)-(0.15·CUT+6.6)·ln(H) +0.58·CUT+129.4 (1g) In the formula, a is a number of 4.3 to 4.4.

[0043] In the present invention, the above formula (1g) is the reference sterilization temperature T baseHowever, since an approximate formula is used, it can be corrected if necessary.

[0044] In the present invention, for a product in a packaged form that can be controlled to a constant pressure and that contains a content that exhibits conductive heat transfer, such as a pouched product, the reference sterilization temperature T base Retort sterilization is performed so as to obtain the desired Fo value based on the above formula (1g). However, since the above formula (1g) uses an approximation formula and has variations, the reference sterilization temperature T calculated by the above formula is usually used. base It is desirable to carry out retort sterilization at a temperature within the range of ±5°C, especially +4°C. Even within this range, it is optimal to carry out sterilization at a temperature of 121.1°C or higher, particularly in terms of sterilization effectiveness.

[0045] Furthermore, retort sterilization itself can be carried out by a known method using a known sterilization vessel. For example, static sterilization is common, but methods such as shaking sterilization and rotation sterilization can also be used, and a shower method can also be used.

Claims

1. In the retort sterilization method for individually packaged products, The contents to be packaged exhibit conductive heat transfer, and a function is created to calculate a reference sterilization temperature that indicates the minimum CV value (unit: min) from the target Fo value (unit: min) during retort sterilization according to the packaging form. The function is expressed by the following formula (1a): T base =a・ln(Fo)+b (1a) During the ceremony, T base is the base sterilization temperature, a is the coefficient of ln(Fo), b is the parameter CUT (unit: min) and product thickness H (unit: mm), A retort sterilization method characterized in that retort sterilization is performed by setting an actual sterilization temperature within a temperature range of ±5°C of the reference sterilization temperature calculated from the function.

2. 2. The retort sterilization method according to claim 1, wherein the contents are solids or fluid substances having a viscosity (25°C) of 500 mPa·s or more.

3. 3. The retort sterilization method according to claim 1, wherein the packaging form is a pouch or a cup container.

4. The retort sterilization method according to claim 1 or 2, wherein the actual sterilization temperature is set to a temperature of 121°C or higher.

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