JPS59157565A - Measuring method of water activity of food - Google Patents

Abstract

PURPOSE:To measure the water activity (indication numeral of relative humidity indicated by food water content) of food easily by enclosing a humidity indicator consisting of a moisture absorber and a pigment in a nonpermeable container together with the food, and observing a change in color. CONSTITUTION:A moisture permeable sheet 2 carrying a sheet 3 obtained by impregnating filter paper, etc., with solution of a dye which discolores with water, e.g. a Co salt and drying it is provided on one surface of the moisture absorber 1 carrying a water soluble moisture absorptive material such as CaCl2 in filter paper, etc. Then, an opaque water-permeable colorless sheet 4 is provided thereupon to obtain the moisture indicator; one or plural (e.g. three) indicators for measuring water activity are fixed between plastic thin plates 6 and 6 having holes in the center parts by using an adhesive 7. Those humidity indicators are put in the airtight container together with the food and the state of develope or disolor of the coloring agent 3 at a specific time later is observed to detect the water activity of the food easily. Thus, optimum water activity, or water activity elapsed with the storage of the food is detected to utilize the detection result for the storage of the food, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily measuring the water activity of foods.

Here, water activity is an indicator value that allows comparison of the action of water based on relative humidity (R, H,), which is a function of water vapor partial pressure indicated by the water content of food. If the water content of a food is R, H, 75 at 50°C, then the water activity of that food is 0.75 at 20°C.

Depending on the type of food, the water activity of some foods should be kept below a certain limit, within a certain range, or above a certain limit69, and the quality of food depends on its preservation or storage. Water activity is one of the important factors. Furthermore, in the case of fresh foods (particularly fresh animal foods), the storage conditions for long-term storage are largely controlled by the water activity of the food.

Conventionally, water activity has been measured using, for example, a hygrometer using hair or a hygrometer using a moisture-sensitive element, but these measuring instruments are expensive and require skill to handle.

The present invention overcomes the shortcomings of such conventional methods and determines the moisture content of the food by sealing the food with a humidity indicator in a substantially non-porous container and observing the condition of the humidity indicator. A method for measuring the water activity of food, which is characterized by measuring the activity of the food, by using several types of humidity indicators with different indication ranges together or selectively. The maximum water activity that has elapsed since the container was sealed can be easily determined.

Foods covered by the present invention include all foods that require preservation or storage. For example, grains, seeds, potatoes, beans, vegetables, fruits, seaweed, mushrooms, meat,
These include seafood and their processed products, as well as luxury foods, confectionery, dairy products, and egg products.

The humidity indicators used in the present invention include reversible and irreversible indicators, and both can be used in the present invention.The reversible humidity indicator used in the present invention has cobalt salts as its main component. things are available. For example, a water-absorbing sheet such as a filter paper is impregnated with an aqueous solution containing cobalt salts as a main component and dried. As is well known, cobalt salts exhibit a back-colored color when dry and a pink color when absorbing moisture. Therefore, the filter paper prepared as described above, which supports cobalt salts in its structure, has a mauve color mixed with back color and pink, depending on the degree of moisture absorption.

According to this principle, it is possible to create an indicator that shows the humidity of an environment by exhibiting a pale mauve color when left in an environment with a predetermined humidity. Alternatively, cobalt salts can be used as an indicator by using a binder to form a solid solid at an appropriate concentration, and a printable sensing agent containing cobalt salts can be printed on the inside of a non-porous container to serve as an indicator. .

The irreversible humidity indicator used in the present invention consists of a moisture-absorbing material and a colorant, and as a result of the moisture absorption of the moisture-absorbent material, the colorant becomes visible or the colorant undergoes a visible color change. The moisture-absorbing material may be one in which a water-soluble hygroscopic substance is supported on a support, or it may be a super-absorbent polymer substance that itself has hygroscopic properties.

Examples of water-soluble hygroscopic substances include water-absorbing salts (for example, water-soluble salts of alkali metals, alkaline earth metals, magnesium, etc.), cynic acid, hygroscopic surfactants, aliphatic polyhydric alcohols, etc. However, it is not limited to these materials.1 Also, sheet-like supports are convenient for supporting these water-soluble hygroscopic substances, such as filter paper, Japanese paper, fabrics, non-woven fabrics, or fired-swollen materials. Items that have the ability to retain liquid within themselves, such as vermiculite or Noguichi light; items that have a small ability to retain liquid, such as western paper, cardboard, and coated paper; or items that have no ability to retain liquid at all, such as plastic plates and glass plates. If the water-soluble hygroscopic substance is solid, it is necessary to impregnate the support with it as an aqueous solution and then dry it. If it is a liquid, impregnate the support with an appropriate amount. If the support has little or no liquid holding capacity, the water-soluble hygroscopic substance can be applied to the surface of the substrate using a suitable binder and, if necessary, dried.

At this time, it is also possible to mix and apply a filler as appropriate.

When the hygroscopic material is a highly water-absorbing polymer substance having hygroscopic properties, it can itself be used as the hygroscopic material of the present invention, but this material may further carry a water-soluble hygroscopic substance. This super absorbent polymer material is commercially available in the form of powder or beads, and it is convenient to use a suitable binder to tightly adhere it to the surface of a sheet material. . Examples of such superabsorbent polymer substances include saponified vinyl acetate-acrylic methyl copolymers, starch-acrylic copolymers, and vinyl alcohol-acrylic acid copolymers.

Coloring agents do not necessarily have to be colored substances themselves;
Substances that develop, fade, or change color when in contact with water or a water-soluble solution of a water-soluble substance (A Glue 76), and substances that are themselves colored substances and cause migration by water or an aqueous solution of a water-soluble substance (A-Glue 76). It can be divided into Group B).

For example, a solid pH indicator can be used as the substance of group A, and in this case, an acidic or alkaline substance compatible with the indicator is supported on the moisture absorbent material.

In addition, a water-permeable sheet carrying a pH indicator is attached to one side of the sheet-shaped moisture absorbing material, and a sheet carrying an appropriate acidic or alkaline substance that develops, discolors, or fades the pH indicator is attached to the other side. Alternatively, a mixture of a solid pH indicator and a compatible solid acidic or alkaline substance may be used as the colorant.

Typical examples of Group B substances include water-soluble dyes (
It is preferable that the material supporting it does not have strong dyeing properties.

When using a substance of group A above as a coloring agent, the release of water by the hygroscopic material can be determined by directly observing the coloring, fading, or discoloration of the surface of the support on which it is supported, i.e., around the indicator. You can know that the humidity has reached the humidity specified by the indicator, but if a B group substance is used as a coloring agent,
A water-permeable, colorless (even light-colored), and opaque sheet-like material, such as filter paper, is provided in close contact with the upper surface of the support on which it is supported. The dye dissolved in water (or aqueous solution) is observed to bleed onto the top surface of the opaque sheet and color it. When using Group A substances, a water-permeable, colorless (or light-colored) and opaque sheet-like material is placed in close contact with the layer carrying the coloring agent, and the appearance of color on the surface is observed. Of course, this is a good thing.

Among the colorants that can be used, group A colorants include, in addition to the above-mentioned pH indicators, oxidation-reduction indicators, and substances that develop or change color due to dioxidation reaction that reacts at room temperature. It is used in a mixed state with a solid powder such as a reducing substance or a diazo component or a coupling component (these are called toning components), or the toning component is present inside or on the surface of the moisture-absorbing and water-retaining material. Alternatively, a colorant-carrying sheet may be placed on one side of a sheet-shaped moisture absorbent material, and a toning component-carrying sheet may be placed on the other side in close contact with each other.

Typical colorants of group B are water-soluble dyes as described above, and other water-insoluble dyes and pigments that can easily flow with water can also be used.

A specific example of the structure of these indicators will be explained below with reference to the drawings. The humidity indicator shown in FIG.
A water-permeable sheet (2) carrying . At this time, the coloring agent is present inside the water-permeable sheet in FIG. 1(a), and on the surface in FIG. 1(b)K.

FIG. 2 shows a sample in which a colorant is present on the surface of the moisture absorbent material (1). Figure 3 shows a case in which the coloring agent itself is colored, such as a water-soluble dye (group B), and Figure 3 (a) shows a case in which the colorant is colored by itself, such as a water-soluble dye. A moisture permeable sheet (2) carrying a colorant (3) on one side of the material (1).
) and a water-permeable, colorless or light-colored opaque layer (4).
Figure (B) uses a hygroscopic material (1) in which a colorant (3) and a water-soluble hygroscopic substance are supported on the same support, and a water-permeable, colorless or light-colored opaque layer (4). things that are in close contact,
Figure 3 (c) has a structure in which a colorant (3) is sandwiched between a hygroscopic material (1) carrying a water-soluble hygroscopic substance and a water-permeable colorless or light-colored opaque layer (4). It is.

Figure 4 shows the case where the coloring agent is a substance (A group) that causes coloring, fading, or discoloration when it comes into contact with water or an aqueous solution of a water-soluble substance. Alternatively, it has a structure sandwiched between a layer (5) carrying a color-changing substance and a moisture-permeable sheet (2) carrying a coloring agent.

Fig. 5 shows a humidity indicator as shown in Fig. 3 (b), which is sandwiched between two thin plastic plates (6) with a hole in the center and fixed with adhesive (7). The figure shows several humidity indicators, each indicating a different humidity, sandwiched between two thin glass plates with holes. 0.6.0.7.0.8) indicates the water activity of the food necessary for these humidity indicators to develop color. That is, if 0.6 and 0.7 are colored, this indicates that the water activity of the food in which they were sealed was approximately 7.

The humidity indicator assembled as described above is sealed together with the food whose water activity is to be measured in a substantially non-porous container, which can be shaped into a box, cone, bag, etc. can be selected as appropriate. The state (change in color) of a humidity indicator after a certain period of time when it is sealed in a container with food and kept at storage humidity.
By observing the , the water activity of the food at the storage humidity can be determined. It is convenient if all or part of the container is made of a transparent material so that the humidity indicator can be observed from the outside of the container.

If the humidity indicator cannot be observed from the outside, open the container, remove the humidity indicator, and observe the change in color of f-t. Humidity indicators do not change color instantaneously, so there is no problem in measuring with this method.

The water activity of food measured in this way serves as a guideline for measures to be taken when preserving or storing the food. For example, recently, oxygen absorbers containing iron powder as the main ingredient have been used to preserve food in an oxygen-free state. The moisture needed for this purpose is contained in the oxygen absorber, and the moisture is required in the food to preserve it. There is a type M, and the former type is suitable for foods with a water activity of approximately 70% or less, and the latter type is suitable for foods with a water activity of 70% or more. By measuring , the above selection becomes extremely easy. In addition, processed marine products (for example, fish string, salted salmon, etc.) may be stored at room temperature, but it can be determined whether they should be frozen or not, based on their water activity values.

In other words, the water activity value obtained in Example 1 indicates that it is necessary to freeze this salted salmon for long-term storage, and the value obtained in Example 2 indicates that it is necessary to freeze this salted salmon for long-term storage. It can be seen that the oxygen absorber containing iron as a main component used to maintain the oxygen state should be of a type in which water is mixed into the oxygen absorber.

Example 1 Using an aqueous solution of IJ Ant Blue For (colorant), a calcium chloride aqueous solution with a concentration shown in Table 1 was added.
Make a liquid. Filter papers were immersed in these aqueous solutions, taken out and dried to obtain moisture absorbing materials made of colored filter papers containing calcium chloride as shown in Table 1.

Table 1 These calcium chloride-containing colored filter papers (hygroscopic material) are layered with untreated filter paper as an opaque layer, and as shown in Figure 5, they are sandwiched between two plastic sheets with a hole in the center and brought into close contact with each other to control humidity. Indicator wo') (ツ7'c.N[L
1-N [L 6 pairs of indicators were made, and each pair was left in a space with a relative humidity (RH) of 40%, 60, 70, 80, and 90% for 3 days to remove the untreated filter paper. The coloring was observed and the results are shown in Table 2.

Table 2 A set of the same humidity indicators was placed in a bag made of vinylidene chloride together with salted salmon so that the filter paper side of the humidity indicator did not touch the salted salmon, and the bag was sealed. This is 3
When observed after a day, color development of the humidity indicator as shown in Table 3 was observed.

This indicates that the water activity of this salt salmon is 0.8. It turns out that freezing is necessary to preserve this salted salmon for a long time.

Table 3 Example 2 Ikg of tsukudani was placed in an airtight container with a transparent lid. Water activity below sail 6 is blue, 0.65 is mauve, 0.7
The reversible humidity indicator, which changes color to pink, was packaged in a transparent air-permeable packaging material, attached to the lid of the container described above, and the container was sealed and left indoors.

After U hours, the humidity indicator inside the container is mauve;
Therefore, it was shown that the water activity of this tsukudani was about 0.65. Please note that this tsukudani is measured using a hygrometer AH-1 manufactured by Shibaura Electronics.
The relative humidity I measured was 62 degrees. Based on this measurement value, in order to make this tsukudani an oxygen-free state using an oxygen absorber whose main component is iron powder, it is necessary to use a type of oxygen absorber that contains water in the oxygen absorber. I understand that.

[Brief explanation of the drawing]

Figure 1 (A) and (B), Figure 2, Figure 3 (A), (B) and (C), Figure 4, Figure 5 (B), and Figure 6 (B) are from the book. A sectional view showing a specific example of the humidity indicator of the invention, FIG. 5(a) and FIG. 6(a) are plan views of the same. l: Moisture-absorbing material 2: Moisture-permeable sheet 3: Color agent 4: Opaque layer 5: Layer carrying a chemical that develops, discolors, or fades the color agent 6: Plastic thin plate 7: Adhesive Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 (A) (A)

Claims (1)

[Claims] 1. A food product characterized in that the food product is sealed together with a humidity indicator in a substantially non-porous container, and the water activity of the food product is measured by observing the state of the humidity indicator. water activity measurement method. 2. The water activity measuring method according to claim 1, wherein the humidity indicator is an irreversible humidity indicator. 3. A patent in which the humidity indicator is an irreversible humidity indicator consisting of a moisture-absorbing material and a coloring agent, and as a result of the moisture absorption of the moisture-absorbing material, the coloring agent visibly becomes uniform or the coloring agent undergoes a visible change. Claim 1 or 2
Water activity measurement method in section. 4. The water activity measuring method according to claim 1, 2 or 3, wherein the hygroscopic material comprises a water-soluble hygroscopic substance and a support supporting the hygroscopic substance. 5. In the humidity indicator, the support constituting the moisture absorbing material is in the form of a sheet, and the sheet support supports a water-soluble hygroscopic substance as well as a colorant, and the upper surface of the sheet support is The water activity measuring method according to any one of claims 1 to 4, which is an irreversible humidity indicator configured by placing a water-permeable white or light-colored opaque sheet in close contact with the water activity indicator. . 6. The water activity measuring method according to claim 1, wherein the humidity indicator is a reversible humidity indicator. 7. According to any one of claims 1 to 6, a part of the non-breathable container is made entirely of a transparent material, and the state of the humidity indicator is observed from the outside. Water activity measurement method described.