Food freshness sensor

Abstract

To provide a food freshness sensor capable of easily determining the freshness of food using an eggshell membrane or a material derived from the eggshell membrane.SOLUTION: A food freshness sensor comprises a color-changing pigment which changes color in response to substances emitted in association with food spoilage and an eggshell membrane which adsorbs the color-changing pigment or a material derived from the eggshell membrane. Polyaniline or curcumin can be suitably used as the color-changing pigment. The eggshell membrane is an inexpensive, environmentally friendly, and sustainable material. Such a food freshness sensor including the eggshell membrane and the color-changing pigment improves safety related to food freshness and quality, helps reduce food waste, and contributes to the improvement of food supply and society.SELECTED DRAWING: Figure 26

Description

[Technical Field]

[0001] The present invention relates to a food freshness sensor. [Background technology]

[0002] Conventionally, sensors that allow for easy determination of food freshness (hereinafter referred to as food freshness sensors) have been known (see, for example, Patent Document 1). For example, the food freshness sensor described in Patent Document 1 is a sensor in which an azo dye is adsorbed onto a planar medium such as paper or cloth, or dissolved and solidified in a solid medium such as agar or gelatin, and is used to detect the bacterial contamination level of fish meat. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-181192 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, eggshells of chicken eggs and other eggs are covered with a membrane called the eggshell membrane (ESM), which is primarily composed of protein. The eggshell membrane protects the egg from bacteria and separates the eggshell from the yolk. Eggshell membrane is easily available, biocompatible, and can be used as a green material that does not contain pollutants. However, while egg yolks and egg whites are widely used, the majority of eggshells and eggshell membranes are discarded.

[0005] Therefore, the present invention has been made in consideration of the above problems, and aims to provide a food freshness sensor that uses eggshell membrane or a material derived from eggshell membrane and can easily determine the freshness of food. [Means for solving the problem]

[0006] [1] A food freshness sensor according to one embodiment of the present invention is characterized by comprising a color-changing pigment that changes color due to substances released as food spoils, and eggshell membrane or an eggshell membrane-derived material that has adsorbed the color-changing pigment.

[0007] [2] In the food freshness sensor according to one aspect of the present invention, the color-changing pigment is preferably a substance that changes color under the influence of ammonia.

[0008] [3] In the food freshness sensor according to one aspect of the present invention, the color-changing dye preferably includes polyaniline.

[0009] [4] In the food freshness sensor according to one embodiment of the present invention, the color-changing pigment preferably contains curcumin.

[0010] [5] In the food freshness sensor according to one embodiment of the present invention, the eggshell membrane-derived material preferably contains an eggshell membrane-derived component and a polymer component.

[0011] [6] In the food freshness sensor according to one embodiment of the present invention, the eggshell membrane-derived material is preferably a nonwoven fabric having nanofibers containing the eggshell membrane-derived component and the polymer component. [Effects of the Invention]

[0012] The food freshness sensor of the present invention is equipped with a color-changing pigment that changes color due to substances released as food spoils, and eggshell membrane or an eggshell membrane-derived material that has adsorbed the color-changing pigment, making it a food freshness sensor that can easily determine the freshness of food using eggshell membrane or an eggshell membrane-derived material. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing FT-IR spectra of the food freshness sensor according to Example 1, eggshell membranes, and polyaniline. [Figure 2] 1 is a graph showing XRD patterns of the food freshness sensor according to Example 1, eggshell membrane, and polyaniline. [Figure 3] 1 is a graph showing TG-DTA curves and DSC curves of the food freshness sensor of Example 1, eggshell membrane, and polyaniline. [Figure 4] FIG. 1 is a diagram showing the surface shapes of the food freshness sensor and eggshell membrane according to Example 1. [Figure 5] 1 is a graph showing the results of elemental mapping of the food freshness sensor and eggshell membrane according to Example 1. [Figure 6] 1 is a table showing the color change of the food freshness sensor according to Example 1 in response to ammonia vapor. [Figure 7] 3 is a graph showing the pH responsiveness of the food freshness sensor according to Example 1. [Figure 8] FIG. 1 is a diagram showing the pH response of polyaniline. [Figure 9] FIG. 2 is a graph showing the elution of polyaniline from the food freshness sensor according to Example 1. [Figure 10] 1 is a graph showing the water characteristics of the food freshness sensor and eggshell membrane according to Example 1. [Figure 11] 1 is a photograph showing the antibacterial properties of the food freshness sensor and eggshell membrane according to Example 1. [Figure 12] 1 is a bar graph showing the biodegradability of the food freshness sensor and eggshell membrane according to Example 1. [Figure 13] FIG. 2 is a diagram showing the results of testing the function of the food freshness sensor according to Example 1 using actual food (chicken). [Figure 14] 1 is a graph showing FT-IR spectra of the food freshness sensor according to Example 2, eggshell membranes, and curcumin. [Figure 15] 1 is a graph showing XRD patterns of the food freshness sensor according to Example 2, eggshell membranes, and curcumin. [Figure 16] 1 is a graph showing TG-DTA curves and DSC curves of the food freshness sensor of Example 2, eggshell membranes, and curcumin. [Figure 17] FIG. 1 is a diagram showing the surface shapes of a food freshness sensor and eggshell membrane according to Example 2. [Figure 18]10 is a graph showing the results of elemental mapping of the food freshness sensor according to Example 2. [Figure 19] 10 is a table showing the color change of the food freshness sensor according to Example 2 in response to ammonia vapor. [Figure 20] 10 is a graph showing the pH responsiveness of the food freshness sensor according to Example 2. [Figure 21] 1 is a graph showing the UV spectrum of curcumin. [Figure 22] 1 is a photograph showing the elution of curcumin from the food freshness sensor of Example 2. [Figure 23] FIG. 10 is a diagram showing the water characteristics of the food freshness sensor and eggshell membrane according to Example 2. [Figure 24] 1 is a photograph showing the antibacterial properties of the food freshness sensor and eggshell membrane according to Example 2. [Figure 25] 1 is a bar graph showing the biodegradability of the food freshness sensor and eggshell membrane according to Example 2. [Figure 26] FIG. 10 is a diagram showing the results of testing the function of the food freshness sensor according to Example 2 using actual food (chicken). DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the food freshness sensor of the present invention will be described based on an embodiment.

[0015] [Embodiment 1] The food freshness sensor according to the first embodiment comprises a color-changing pigment that changes color due to substances released as food spoils, and eggshell membrane to which the color-changing pigment is adsorbed. The food freshness sensor is used to determine the freshness of protein-rich foods (e.g., meat or fish). The food freshness sensor may be placed directly on the surface of the food, or may be placed near the food (e.g., on the food packaging or container).

[0016] The "color-changing pigment" in this specification may be one that changes color by directly reacting with a substance released as food spoils, or one that changes color due to an environmental change (e.g., a change in pH) associated with a substance released as food spoils.

[0017] In the food freshness sensor according to the first embodiment, the color-changing dye is a substance that changes color under the influence of ammonia. Specifically, the color-changing dye in the first embodiment includes polyaniline. Polyaniline is a substance obtained by polymerizing aniline or an aniline salt, and has the attractive properties of being highly reliable, environmentally friendly, safe, and easy to manufacture. The "polyaniline" referred to in this specification is emeraldine, which changes state between emeraldine salt represented by the following chemical formula (1) and emeraldine base represented by the following chemical formula (2) due to interaction with ammonia or changes in pH, and changes color accordingly. [ka]

[0018] The food freshness sensor of embodiment 1 comprises a color-changing pigment that changes color due to substances released as food spoils, and eggshell membrane that adsorbs the color-changing pigment, and is therefore a food freshness sensor that can easily determine the freshness of food using eggshell membrane.

[0019] Eggshell membrane is an inexpensive, environmentally friendly, and sustainable material, and the food freshness sensor according to embodiment 1, which uses such eggshell membrane and a color-changing dye, improves food freshness and quality safety and helps reduce food waste, thereby contributing to the improvement of food supply and society. The same applies to the food freshness sensors according to embodiments 2 and 3, which will be described later.

[0020] Furthermore, according to the food freshness sensor of embodiment 1, the color-changing pigment (polyaniline) is a substance that changes color under the influence of ammonia, so it is possible to accurately determine the freshness of foods that are rich in protein.

[0021] Furthermore, according to the food freshness sensor of embodiment 1, the color-changing pigment contains polyaniline, so that the food freshness sensor can be made non-toxic to the human body and highly stable.

[0022] [Embodiment 2] The food freshness sensor according to embodiment 2 basically has the same configuration as the food freshness sensor according to embodiment 1, but the type of color-changing pigment is different. In the food freshness sensor according to embodiment 2, the color-changing pigment includes curcumin. Curcumin can be obtained as a natural extract from turmeric and is known as a natural antibacterial agent and antioxidant. Due to interactions with ammonia and changes in pH, curcumin changes state between the structure shown in chemical formula (3) below (keto form) and the structure shown in chemical formula (4) below (enol form), resulting in a color change. [ka]

[0023] The food freshness sensor according to the second embodiment can be used in the same manner as the food freshness sensor according to the first embodiment.

[0024] The food freshness sensor of embodiment 2 uses a different type of discoloration pigment than the food freshness sensor of embodiment 1, but it is equipped with a discoloration pigment that changes color due to substances released as food spoils, and eggshell membrane that adsorbs the discoloration pigment.As a result, like the food freshness sensor of embodiment 1, it is a food freshness sensor that uses eggshell membrane and can easily determine the freshness of food.

[0025] Furthermore, the food freshness sensor according to the second embodiment makes it possible to accurately determine the freshness of foods rich in protein, since curcumin is also a substance that changes color under the influence of ammonia.

[0026] Furthermore, according to the food freshness sensor of embodiment 2, the color-changing pigment contains curcumin, so that the food freshness sensor can be made non-toxic to the human body and highly stable.

[0027] [Embodiment 3]

[0028] The food freshness sensor according to the third embodiment basically has the same configuration as the food freshness sensor according to the first embodiment, but differs in that it includes an eggshell membrane-derived material instead of eggshell membrane.

[0029] In the food freshness sensor according to the third embodiment, the eggshell membrane-derived material contains an eggshell membrane-derived component and a polymer component.Moreover, the eggshell membrane-derived material is preferably a nonwoven fabric having nanofibers containing the eggshell membrane-derived component and the polymer component.

[0030] A nonwoven fabric with nanofibers containing eggshell membrane-derived components and polymeric components can be obtained by dissolving or dispersing eggshell membranes together with polymeric components (resins) in a solution to prepare a spinning solution, and then electrospinning the spinning solution. Various polymeric components can be used, but those that can be used with water as a solvent are preferred, including polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethylene oxide (PEO), chitosan, polylactic acid (PLA), polylactic-co-glycolic acid (PLGA), polyvinylpyrrolidone (PVP), and polyurethane (PU).

[0031] Alternatively, the eggshell membrane-derived material may be a thin film of eggshell membrane dissolved or dispersed in a solution and then dried (regenerated eggshell membrane, RESM). In this case, the eggshell membrane-derived material may or may not contain polymeric components.

[0032] The color-changing dye in the food freshness sensor according to the third embodiment may be polyaniline or curcumin.

[0033] The food freshness sensor of embodiment 3 comprises a color-changing pigment that changes color due to substances released as food spoils, and an eggshell membrane-derived material that adsorbs the color-changing pigment, and is therefore a food freshness sensor that uses eggshell membrane to easily determine the freshness of food.

[0034] Furthermore, according to the food freshness sensor of embodiment 3, the eggshell membrane-derived material contains eggshell membrane-derived components and polymeric components, making it possible to produce a food freshness sensor that is easy to mass-produce and has excellent stability.

[0035] Furthermore, according to the food freshness sensor of embodiment 3, the eggshell membrane-derived material is a nonwoven fabric having nanofibers containing eggshell membrane-derived components and polymeric components, and therefore can be used as a food freshness sensor that has excellent adsorption properties for discoloration pigments and is sensitive to the state of food.

[0036] [Example] In Examples 1 to 4 shown below, food freshness sensors according to the above-described embodiments were actually manufactured, and analyzed and tested.

[0037] First, the materials and devices used in the examples will be described. Descriptions of general-purpose tools and devices will be omitted. Ethyl alcohol (anhydrous, 99.8%) was purchased from Sigma-Aldrich Japan LLC. Ammonium persulfate, aniline hydrochloride, hydrochloric acid, acetic acid (99.7%), sodium hydroxide (97%), acetone (99.5%), and aqueous ammonia (10% and 25%) were purchased from Fujifilm Wako Chemical Co., Ltd. Deionized water obtained from a Milli-Q system was used, and in the following description, unless a solvent is specifically stated, this deionized water was used. The pH buffer solutions (pH = 5 and 10) were purchased from Dojindo Laboratories, Ltd. in Kumamoto City. All reagents were used as is without purification. Turmeric powder, eggs, and chicken meat were purchased from a store in the test site (Ueda City, Nagano Prefecture).

[0038] The Fourier transform infrared spectrometer (FT-IR) used was an IRPrestige-21 manufactured by Shimadzu Corporation. The X-ray diffraction device (XRD) used was a Miniflex 300 manufactured by Rigaku Corporation. The scanning electron microscope (SEM) used was a JEOL Ltd. JSM-6010LA. The transmission electron microscope (TEM) used was a JEM-2100 manufactured by JEOL Ltd. Image J (software version 19 1.4.3.) was used as image analysis software for statistical measurements. The thermal analyzer (differential scanning calorimeter) used for the differential scanning calorimetry was Thermo plus EVO2 DSC vesta manufactured by Rigaku Corporation. The thermogravimetric analysis was performed using a thermal analyzer, TG-8120 manufactured by Rigaku Corporation.

[0039] [Example 1] In Example 1, a food freshness sensor including polyaniline and eggshell membrane (a food freshness sensor corresponding to the food freshness sensor according to Embodiment 1) was produced.

[0040] 1. Method for producing a food freshness sensor according to Example 1 1-1. Preparation of polyaniline First, 100 mL of ammonium persulfate solution (0.25 M) was added dropwise to 100 mL of 0.2 M aniline hydrochloride solution. The addition was carried out in a low temperature environment (0 to 5°C). Before the addition, each solution was cooled in a refrigerator for 1 hour. The above solution mixture was stirred for 24 hours to obtain a green polyaniline solution.

[0041] 1-2. Obtaining eggshell membrane First, egg yolk was separated from chicken eggs, and the eggshell containing the eggshell membrane was thoroughly washed with deionized water. The eggshell was then immersed in a hydrochloric acid solution (1 M) for 5 minutes. The obtained eggshell membrane was then washed with a large amount of deionized water. The eggshell membrane was air-dried and stored in a desiccator.

[0042] 1-3. Creating a food freshness sensor The eggshell membrane obtained as described above was immersed in a polyaniline solution and gently stirred for 1 hour. The eggshell membrane with adsorbed polyaniline was then washed three times with acetone to produce a food freshness sensor according to embodiment 1. Hereinafter, this food freshness sensor may also be referred to as "Sensor PANI-C."

[0043] 2. Structural characteristics of the food freshness sensor according to Example 1 Figure 1 is a graph showing the FT-IR spectra of the food freshness sensor, eggshell membrane, and polyaniline according to Example 1. Figure 1(a) is a graph showing the entire FT-IR spectrum, and Figure 1(b) is a graph showing the 4000 cm of Figure 1(a). -1 ~2000cm -1 Fig. 1(c) is a graph showing the range of 2000 cm in Fig. 1(a). -1 ~500cm -1 The vertical axis of Fig. 1(a) to Fig. 1(c) represents absorbance (unit: au), and the horizontal axis represents wave number (unit: cm -1 ) is shown. Figure 2 is a graph showing the XRD patterns of the food freshness sensor, eggshell membrane, and polyaniline according to Example 1. Figure 2(a) is a graph showing the entire XRD pattern, and Figure 2(b) is a graph showing an enlarged view of the XRD pattern over the range of 0° to 40°. The vertical axis of Figures 2(a) and 2(b) represents intensity (unit: au), and the horizontal axis represents 2θ (unit: degree).

[0044] First, FT-IR analysis was carried out on the food freshness sensor (sensor PANI-C) according to Example 1, eggshell membrane (ESM), and polyaniline (PANI) (see FIG. 1).

[0045] As a result, in polyaniline and sensor PANI-C, the presence of aromatic CH groups, CH3 groups, and CH2 groups resulted in a peak at 2347 cm -1 Characteristic peaks appeared at 1400, 1628, 1290, 1027, 950, 747, and 670 cm -1The characteristic peaks are due to the C=C stretching vibrations (benzenoid and quinoid rings), aromatic conjugated C-N bonds (quinoid rings and quinoid-type units similar to the electrons in polyaniline), C-H bending (out-of-plane) vibrations, and the presence of meta- and para-substituted rings. The analysis results for sensor PANI-C showed peaks common to the analysis results for eggshell membrane and polyaniline, confirming the presence of polyaniline in sensor PANI-C.

[0046] Next, XRD patterns were obtained for the food freshness sensor according to Example 1 (sensor PANI-C), eggshell membrane (ESM), and polyaniline (PANI) (see FIG. 2).

[0047] Eggshell membrane (ESM) showed an overall broad peak, indicating that the finely ordered arrangement of polypeptide chains was disrupted by hydration. The diffraction peaks at 9.96° and 22.3° were due to the arrangement, indicating the presence of amino acids in the eggshell membrane.

[0048] Polyaniline (PANI) showed characteristic peaks at 6.16°, 18.32°, 20.2°, 23.1°, 24°, and 25.6°. The peaks at 6.34° and 18.32° correspond to the organized thin layer of polyaniline and silver-polyaniline-like behavior. These peaks indicate the structural change and semi-crystalline nature of polyaniline.

[0049] On the other hand, unlike eggshell membrane, the PANI-C sensor showed peaks at 11.8°, 21.4°, 22.16°, 23.2°, 29.2°, and 32.2°, which are partially shared with polyaniline. This indicates that polyaniline was successfully adsorbed (supported) onto the eggshell membrane.

[0050] 3. Thermal stability of the food freshness sensor according to Example 1 FIG. 3 is a graph showing TG-DTA curves and DSC curves for the food freshness sensor, eggshell membrane, and polyaniline according to Example 1. FIG. 3(a) is a graph showing the TG-DTA curve, FIG. 3(b) is a graph showing the derivative of the weight loss shown in FIG. 3(a) (a graph showing the degree of weight loss at a certain temperature), and FIG. 3(c) is a graph showing the DSC curve. The vertical axis on the left side of FIG. 3(a) indicates the degree of weight loss (unit: %), the vertical axis on the right side indicates differential thermal analysis (DTA) (unit: μV), and the horizontal axis indicates temperature (unit: °C). Note that the graph in FIG. 3(a) that descends from the upper left to the lower right relates to weight loss. The vertical axis of FIG. 3(b) indicates the derivative of weight loss (unit: % / °C), and the horizontal axis indicates temperature (unit: °C). The vertical axis of FIG. 3(c) indicates heat flow (unit: mW), and the horizontal axis indicates temperature (unit: °C).

[0051] To verify the thermal stability, TG-DTA curves (see Figures 3(a) and 3(b)) and DSC curves (see Figure 3(c)) were obtained for the food freshness sensor of Example 1 (sensor PANI-C), eggshell membrane (ESM), and polyaniline (PANI).

[0052] Eggshell membrane (ESM) exhibited multistage thermal decomposition, with an initial weight loss (21%) between approximately 21 and 60°C. This is thought to be due to surface-adsorbed moisture, residual solvents, collagen denaturation, and bond breakdown. A weight loss of 27.1% was observed in the second stage of decomposition, which is thought to be due to the decomposition of organic matter contained in the eggshell membrane. A weight loss of 27.69% was observed in the third stage (approximately 500 to 600°C). An overall weight loss of 70.28% was observed during the thermal decomposition of eggshell membrane (ESM). Furthermore, DTA and differential weight loss analysis showed that eggshell membrane exhibited one endothermic peak and one exothermic peak at 100°C and 340°C. These are thought to correspond to water absorption and eggshell membrane decomposition.

[0053] Multistage thermal decomposition of polyaniline (PANI) was observed, resulting in weight losses of 14.67%, 21.76%, and 44.63%. These were attributed to the evaporation of absorbed water, the decomposition of polyaniline (thermal oxidation), and the decomposition of the products (N-phenylaniline, methane, acetylene, and carbazole). The thermal decomposition of polyaniline resulted in a weight loss of 81.06%, along with an ash content of 19.14%. DTA revealed an end peak near 100°C. Differential weight loss analysis revealed three strong peaks at 100°C, 200°C, and 300-600°C.

[0054] Multistage thermal decomposition was also observed in the food freshness sensor (sensor PANI-C) of Example 1, with weight losses of 6.91%, 47.99%, and 29.23%. These were attributed to the loss of moisture and decomposition of organic matter. For sensor PANI-C, the overall weight loss (84.13%) was observed by 550°C, and thermal decomposition was complete around 600°C, suggesting that sensor PANI-C exhibited high thermal stability. For sensor PANI-C, DTA showed an end peak between 300 and 400°C, and differential weight loss analysis showed two end peaks between 300 and 500°C.

[0055] Next, the thermal properties such as the glass transition temperature (Tg) and melting temperature (Tm) of the food freshness sensor (sensor PANI-C) according to Example 1, eggshell membrane, and polyaniline were evaluated by DSC analysis. Crystallization is one of the parameters that characterize melting behavior.

[0056] The DSC curve of eggshell membrane did not show any peaks that could be associated with the glass transition (Tg). Two endothermic peaks thought to be associated with water evaporation and eggshell membrane melting (denaturation of collagen) were observed between 75 and 168°C and between 347 and 446°C, centered at 124°C and 390°C, respectively. The results shown in the DSC curve indicate the thermal stability of eggshell membrane.

[0057] For polyaniline, two end peaks were observed at 93 to 185° C. and 196 to 247° C., centered at 125° C. and 218° C. These peaks are due to the evaporation and decomposition of water and the solvent.

[0058] For sensor PANI-C, two end peaks of 96–152°C and 262–377°C, centered at 120°C and 311°C, were observed.

[0059] It can be said that the thermal decomposition of the food freshness sensor according to Example 1 (sensor PANI-C) began at approximately 200°C and did not complete until the temperature reached 600°C. Therefore, it was confirmed that the food freshness sensor according to Example 1 has excellent thermal properties.

[0060] 4. Surface shape of the food freshness sensor according to Example 1 Figure 4 shows the surface shapes of the food freshness sensor and eggshell membrane according to Example 1. Figures 4(a) and 4(b) are SEM images of the eggshell membrane, Figure 4(c) is a histogram of the eggshell membrane, Figure 4(d) is a TEM image of the eggshell membrane, Figures 4(e) and 4(f) are SEM images of the food freshness sensor according to Example 1, Figure 4(g) is a histogram of the food freshness sensor according to Example 1, and Figure 4(h) is a TEM image of the food freshness sensor according to Example 1. The vertical axis of Figures 4(c) and 4(g) represents frequency, and the horizontal axis represents diameter (unit: nm). Figure 5 is a graph showing the results of elemental mapping of the food freshness sensor and eggshell membrane according to Example 1. Figure 5(a) is a graph relating to the eggshell membrane, and Figure 5(b) is a graph relating to the food freshness sensor according to Example 1. The vertical axis of Figure 5(a) and Figure 5(b) represents counts (×1000), and the horizontal axis represents energy (unit: keV).

[0061] To observe the surface shape, the food freshness sensor (sensor PANI-C) according to Example 1 and the eggshell membrane (ESM) were analyzed using SEM, EDS, and TEM (see FIGS. 4 and 5).

[0062] Three-dimensional network structures with an average diameter of 1.710 ± 0.335 μm were observed for the eggshell membrane and 1.723 ± 0.495 μm for the sensor PANI-C. The surface of the sensor PANI-C was uniformly coated with a large amount of polyaniline. Further magnification of the SEM image revealed the shape of the polyaniline on the eggshell membrane fibers more clearly, revealing that the polyaniline was uniformly distributed in the form of small aggregates (regular spherical morphology). Elemental mapping also revealed typical elements (C, N, O, S, Cl, and Ca for the eggshell membrane, and C, O, S, Cl, and Ca for the sensor PANI-C) on the surfaces of the eggshell membrane and sensor PANI-C. The main components of eggshell membrane fibers are proteins rich in amino acids, collagen, and glycoproteins, which provide large reactive sites for polyaniline adsorption when immersed in a polyaniline solution.

[0063] Furthermore, the degree of dispersion can be qualitatively observed using TEM. It was shown that eggshell membranes have a porous network structure that facilitates the adsorption of polyaniline. In the PANI-C sensor, polyaniline was observed to be uniformly dispersed on the surface of the eggshell membrane.

[0064] The above results confirmed that polyaniline was uniformly distributed on the surface of the eggshell membrane in the food freshness sensor of Example 1. This is thought to play an important role in the stability and reproducibility of spoilage detection.

[0065] 5. Ammonia and pH Response of the Food Freshness Sensor of Example 1 FIG. 6 is a table showing the color change of the food freshness sensor according to Example 1 in response to ammonia vapor. FIG. 7 is a graph showing the pH responsiveness of the food freshness sensor according to Example 1. FIG. 7(a) is a graph showing the pH responsiveness of the food freshness sensor according to Example 1 to steam. FIG. 7(b) is a graph showing the RGB values ​​of the colors displayed by the food freshness sensor according to Example 1 in the test of FIG. 7(a). FIG. 7(c) is a graph showing the pH responsiveness of the food freshness sensor according to Example 1 to solutions. FIG. 7(d) is a graph showing the RGB values ​​of the colors displayed by the food freshness sensor according to Example 1 in the test of FIG. 7(c). The vertical axis of FIG. 7(a) shows the total color difference (unit: ΔE), and the horizontal axis shows the type of steam (N: ammonia vapor, A: acetic acid vapor) and the number of times (1: first time, 2: second time, 3: third time). The vertical axis of FIG. 7(b) shows the magnitude of the RGB value, and the horizontal axis shows the type of steam and the number of times. The vertical axis of FIG. 7(c) shows the total color difference (unit: ΔE), and the horizontal axis shows the type of solution. The vertical axis in FIG. 7(d) indicates the magnitude of the RGB value, and the horizontal axis indicates the type of solution. Figure 8 shows the pH response of polyaniline. Figure 8(a) is a graph showing the UV spectrum of polyaniline, and Figure 8(b) is a photograph showing the appearance of polyaniline solutions at different pH levels. The vertical axis of Figure 8(a) represents absorbance (unit: au), and the horizontal axis represents wavelength (unit: nm).

[0066] The reaction to ammonia is thought to mimic the reaction to volatile compounds generated by spoilage. Spoiled food contains amino acids and nitrogen compounds, which give off a foul odor. Therefore, to confirm the suitability of the food freshness sensor (sensor PANI-C) according to Example 1 for spoilage detection, the reaction to ammonia vapor was confirmed (see Figure 6).

[0067] In the ammonia vapor detection test, detection was simulated using circular (16 mm) food freshness sensor samples, and images of each food freshness sensor were recorded as the color change occurred, and the color analysis was calculated using the Pixie program.

[0068] The change in color from the initial state (total color difference, ΔE) was measured using the following equation (1):

number

[0069] In addition, the sensitivity (S RGB ) was calculated using the following formula (2).

number

[0070] A significant and rapid color change (from green to blue) was observed in sensor PANI-C within 10 seconds of exposure to ammonia vapor. Sensor PANI-C responded to ammonia vapor with a total color difference (ΔE) of 35.01 and a sensitivity (S) of 19.64. RGB ) was shown.

[0071] The color change of the food freshness sensor is caused by the interaction between polyaniline and ammonia (NH3) generated during bacterial decomposition of food. The nitrogen atoms contained in polyaniline (emeraldine salt) react with ammonia molecules due to their properties, producing NH4 + This converts the emeraldine salt into emeraldine base, causing a color change from green to blue.

[0072] The above tests confirmed that the PANI-C sensor is effective for detecting ammonia (the color change can be detected with the naked eye and it is highly sensitive).

[0073] Important parameters for a food freshness sensor are sensitivity, real-time response, and reversibility. Therefore, a reversibility test was conducted on the food freshness sensor (sensor PANI-C) according to Example 1 (see Figures 7(a) and 7(b)). Specifically, the test involved repeatedly changing the pH for 3 minutes under different pH conditions (pH = 5 and 11). This test was conducted in the same manner as the ammonia vapor detection test, except that acid vapor (acetic acid vapor) was used to change the pH. The food freshness sensor according to Example 1 exhibited a blue color when in contact with ammonia vapor and a green color when in contact with acid vapor. Thus, it was confirmed that the food freshness sensor according to Example 1 can maintain its sensitivity even when exposed to frequent environmental changes.

[0074] Next, the response of the food freshness sensor (sensor PANI-C) according to Example 1 was evaluated using solutions of different pH values ​​(see Figures 7(c) and 7(d)). The sensitivity of the food freshness sensor (sample dimensions = 2 cm × 2 cm) to pH changes due to the solution was evaluated by immersing the food freshness sensor in 10 mL of different buffer solutions (pH = 5, 10) at room temperature (25°C) for 1 minute. Color was recorded and evaluated in the same manner as for ammonia vapor sensitivity. As a result, it was confirmed that the food freshness sensor according to Example 1 also changed color significantly in response to pH changes due to the solution.

[0075] When the UV spectrum of polyaniline solution was measured under acidic conditions (pH = 5), it showed an absorbance peak at a wavelength of 423 nm (see Figure 8(a)). On the other hand, under alkaline conditions (pH = 10), it showed an absorbance peak in the opposite direction at 450 nm. This shift is the main cause of the color change from green to blue (see Figure 8(b)). This result indicates that polyaniline containing emeraldine salt was successfully prepared.

[0076] 6. Elution, biodegradability, and antibacterial properties of the food freshness sensor according to Example 1 Fig. 9 is a diagram showing the elution of polyaniline from the food freshness sensor according to Example 1. Fig. 9(a) is a photograph showing the results of immersing the food freshness sensor according to Example 1 in a food simulant, Fig. 9(b) is a photograph showing the food freshness sensor according to Example 1 in contact with chicken for 24 hours, and Fig. 9(c) is a photograph showing the food freshness sensor according to Example 1 after contact with chicken for 24 hours and then removal. Of the photographs shown in Fig. 9(a), the photograph in the top row was taken 5 minutes after immersion, and the photograph in the bottom row was taken 10 minutes after immersion. FIG. 10 is a graph showing the water characteristics of the food freshness sensor and eggshell membrane according to Example 1. FIG. 10(a) is a graph showing water vapor transmission rate (WVTR), FIG. 10(b) is a graph showing water solubility (WS), moisture content (MC), and swelling index (SI), and FIG. 10(c) is a graph showing hydrophobicity (WCA). The vertical axis of FIG. 10(a) is water vapor transmission rate (unit: g / m 2 / day), and the horizontal axis indicates the test object. In Fig. 10(b), the vertical axis indicates percentage (unit: %), and the horizontal axis indicates the test object. In Fig. 10(b), three bar graphs are displayed for each test object, from the left, showing water solubility (WS), water content (MC), and swelling index (SI). In Fig. 10(c), the vertical axis indicates contact angle (unit: degrees). Figure 11 is a photograph showing the antibacterial properties of the food freshness sensor and eggshell membrane according to Example 1. The photographs in the upper row of Figure 11 are photographs showing the test results for gram-positive bacteria, and the photographs in the lower row are photographs showing the test results for gram-negative bacteria. Furthermore, the photographs on the left side of Figure 11 are photographs showing the test results for eggshell membrane, and the photographs on the right side are photographs showing the test results for the food freshness sensor according to Example 1. Fig. 12 is a bar graph showing the biodegradability of the food freshness sensor and eggshell membrane according to Example 1. The vertical axis of Fig. 12 shows biodegradability (weight loss after the test) (unit: %). Note that in Fig. 12, SEM images showing biodegradability are shown in each bar graph.

[0077] First, we conducted a test to examine the elution (migration) of polyaniline from the food freshness sensor (sensor PANI-C) of Example 1. To directly contact the food freshness sensor with food, it is necessary to investigate the possibility of elution from the food freshness sensor into the food. The elution of polyaniline depends not only on the properties of the materials used to manufacture the food freshness sensor, but also on its structure.

[0078] To investigate the elution of polyaniline from the food freshness sensor, the food freshness sensor of Example 1 was immersed in food simulants such as distilled water (DI water, pH = 6.4), acetic acid (3%, pH = 2.9), ethanol (50%, pH = 5.3), and ethanol (95%, pH = 5.8). The temperature was room temperature (25 ± 2°C), and the color change was examined 5 and 10 minutes after immersion (see Figure 9). As a result, no significant color change was observed in distilled water or acetic acid. On the other hand, a slight color change was observed in ethanol. This is thought to be due to the dissolution of polyaniline in ethanol.

[0079] In order to confirm the elution (migration) of polyaniline in an actual environment, the food freshness sensor according to Example 1 was brought into contact with chicken meat for 24 hours, but no elution was observed.

[0080] Next, the water characteristics of the food freshness sensor (sensor PANI-C) according to Example 1 were measured (see FIG. 10).

[0081] The water vapor transmission rate (WVTR) of the food freshness sensor was recorded according to ASTM E96 / E96M-15. The weight change due to moisture loss was recorded for a sealed sample of the food freshness sensor. The water vapor transmission rate was calculated using the following equation (3):

number

[0082] The moisture content (MC), swelling index (SI), and water solubility (WS) of the food freshness sensor were measured according to ASTM D644-99, using the following formulas (4) to (6).

number

[0083] As a result, it was confirmed that the water vapor transmission rate (WVTR), water solubility (WS), moisture content (MC), and swelling index (SI) of the food freshness sensor of Example 1 were negligible (less than 1%). These are thought to be due to physical interactions and the hydrophobicity of polyaniline. Furthermore, an increase in hydrophobicity (WCA) (from 118° to 123°) was confirmed in the food freshness sensor of Example 1 compared to eggshell membrane. This is thought to be due to the hydrophobicity of polyaniline.

[0084] Next, the antibacterial properties of the food freshness sensor (sensor PANI-C) according to Example 1 were tested (see FIG. 11). Food poisoning bacteria can harm food and pose a risk to food quality. To make a material suitable for food packaging, it is necessary to give the material antibacterial properties so that it does not harm the product and, ultimately, the human body.

[0085] The antibacterial activity of the food freshness sensor was qualitatively measured using the agar disk diffusion method according to the AATCC 147-1998 standard test, using the gram-negative bacterium Escherichia coli (E. coli) and the gram-positive bacterium B. subtilis.

[0086] As a result of the test, the food freshness sensor according to Example 1 was observed to have an antibacterial effect against gram-positive bacteria (resistance; transparent surface without an inhibition zone). The food freshness sensor according to Example 1 also exhibited antibacterial activity (sensitivity) against gram-negative bacteria. This is thought to be due to the fact that polyaniline and gram-negative bacteria bind to each other via the outer membrane of the gram-negative bacteria's cell wall, which is made of lipopolysaccharide and has a positive charge.

[0087] Next, the biodegradability of the food freshness sensor of Example 1 (sensor PANI-C) in soil was tested (see Figure 12). Specifically, the eggshell membrane and the food freshness sensor of Example 1 were buried in soil, excavated several days later, and analyzed by SEM to measure the weight loss and examine the degree of decomposition of the eggshell membrane and food freshness sensor. As a result, it was found that the food freshness sensor of Example 1 had lower decomposition potential than the eggshell membrane. This is thought to be due to the strong interaction between polyaniline and eggshell membrane, the reduced moisture content, and the smooth surface.

[0088] 7. Functional characteristics of the food freshness sensor according to Example 1 Figure 13 shows the results of testing the function of the food freshness sensor according to Example 1 using actual food (chicken). Figure 13(a) is a photograph taken immediately after placing the food freshness sensor according to Example 1, and Figure 13(b) is a photograph taken four days after the start of the test.

[0089] Finally, the actual functional characteristics of the food freshness sensor (sensor PANI-C) according to Example 1 were tested (see FIG. 13). The test was carried out using actual chicken meat.

[0090] Chicken samples were prepared by cutting them into 20g pieces and placing them in a sealed petri dish. The food freshness sensor was placed on the lid near the meat so as not to come into contact with the chicken. The samples were stored at 25°C for 4 days.

[0091] The spoilage of animal proteins due to microbial growth leads to an increase in volatile basic nitrogen compounds such as ammonia, trimethylamine, and dimethylammonium in the environment. These compounds ultimately change the pH of the environment, ultimately leading to a color change (from green to blue) of polyaniline.

[0092] As a result of the test, it was confirmed that the food freshness sensor according to Example 1 changed color from green to light blue as the chicken spoiled. The total color difference (ΔE) was 24.16, which was far above the threshold (ΔE=5) generally considered to be detectable by the naked eye.

[0093] From the above test results, it was confirmed that the food freshness sensor (sensor PANI-C) according to Example 1 was successfully produced, and that the food freshness sensor can be used to easily determine the freshness of food.

[0094] [Example 2] In Example 2, a food freshness sensor including curcumin and eggshell membrane (a food freshness sensor corresponding to the food freshness sensor according to Embodiment 2) was produced.

[0095] 1. Method for producing a food freshness sensor according to Example 2 1-1. Preparation of curcumin A mixture of turmeric powder (20 g) and ethanol (200 ml) was magnetically stirred in an air atmosphere at 70°C for 3.5 hours. After cooling to room temperature, the mixture was vacuum filtered, and the filtrate was used as the extract (curcumin solution). The extraction rate of curcumin from turmeric was 4.2%.

[0096] 1-2. Obtaining eggshell membrane First, chicken eggshells were soaked in deionized water for 2 hours. Then, the eggshell membranes were manually collected from the soaked eggshells. The collected eggshell membranes were washed three times with deionized water.

[0097] 1-3. Creating a food freshness sensor The food freshness sensor of Example 2 was obtained by immersing eggshell membranes in a curcumin solution, stirring for 1 hour, and then drying in an oven at 70°C. The prepared food freshness sensor was stored in a desiccator. Hereinafter, this food freshness sensor may be referred to as "Sensor E-Cot."

[0098] 2. Structural characteristics of the food freshness sensor according to Example 2 14 is a graph showing the FT-IR spectra of the food freshness sensor, eggshell membrane, and curcumin according to Example 2. Fig. 14(a) is a graph showing the entire FT-IR spectrum, and Fig. 14(b) is a graph showing the FT-IR spectrum at 4000 cm of Fig. 14(a). -1 ~2000cm -1 14(c) is an enlarged graph showing the range around 2000 cm in FIG. 14(a). -1 ~500cm -1 14(a) to 14(c), the vertical axis represents absorbance (unit: au), and the horizontal axis represents wavenumber (unit: cm -1 ) is shown. Fig. 15 is a graph showing XRD patterns of the food freshness sensor, eggshell membrane, and curcumin according to Example 2. The vertical axis of Fig. 15 represents intensity (unit: au), and the horizontal axis represents 2θ (unit: degree).

[0099] First, FT-IR analysis was performed on the food freshness sensor (sensor E-Cot) according to Example 2, eggshell membrane (ESM), and curcumin (CUR) (see FIG. 14).

[0100] In the FT-IR spectrum of the food freshness sensor (sensor E-Cot) according to Example 2, -1 The additional vibration (bending) corresponds to the CH3 asymmetric stretching vibration, and is approximately 1423 cm -1 The peaks correspond to the CH bending and are at approximately 1589 and 1516 cm -1It was observed that the high intensity peaks correspond to the amide I vibration and the amide II vibration, respectively. Furthermore, it was confirmed that the food freshness sensor according to Example 2 had peaks common to curcumin and eggshell membrane. Therefore, it is considered that the adsorption (support) of curcumin to the eggshell membrane was successful.

[0101] Next, XRD patterns were obtained for the food freshness sensor of Example 2 (sensor E-Cot), eggshell membrane (ESM), and curcumin (CUR) (see FIG. 15).

[0102] From the XRD pattern of the food freshness sensor of Example 2 (sensor E-Cot), it was confirmed that the degree of crystallinity in the food freshness sensor of Example 2 was increased compared to eggshell membrane due to the adsorption of curcumin. This is thought to be due to the fact that curcumin molecules tend to align with other curcumin molecules, and therefore the area of ​​high crystallinity in the food freshness sensor of Example 2 increased compared to eggshell membrane.

[0103] 3. Thermal stability of the food freshness sensor according to Example 2 FIG. 16 is a graph showing the TG-DTA curves and DSC curves of the food freshness sensor, eggshell membranes, and curcumin according to Example 2. FIG. 16(a) is a graph showing the TG-DTA curves, FIG. 16(b) is a graph showing the derivative of the weight loss shown in FIG. 16(a) (a graph showing the degree of weight loss at a certain temperature), and FIG. 16(c) is a graph showing the DSC curves. The vertical axis on the left side of FIG. 16(a) indicates the degree of weight loss (unit: %), the vertical axis on the right side indicates differential thermal analysis (DTA) (unit: μV), and the horizontal axis indicates temperature (unit: °C). Note that the graph in FIG. 16(a) that descends from the upper left to the lower right relates to weight loss. The vertical axis of FIG. 16(b) indicates the derivative of weight loss (unit: % / °C), and the horizontal axis indicates temperature (unit: °C). The vertical axis of FIG. 16(c) represents the heat flow (unit: mW), and the horizontal axis represents the temperature (unit: °C).

[0104] To verify the thermal stability, TG-DTA curves and DSC curves were obtained for the food freshness sensor of Example 2 (sensor E-Cot), eggshell membrane (ESM), and curcumin (CUR) (see Figure 16).

[0105] Multistage thermal decomposition was observed in the food freshness sensor (Sensor E-Cot) of Example 2. First, initial decomposition (12% of the weight loss) was observed around 50°C. This is thought to be due to the loss of physically adsorbed water, bond denaturation, and collagen denaturation. 57% of the weight loss was observed in the second stage of decomposition, which is thought to be due to organic matter. A weight loss of 98% was observed throughout all stages of thermal decomposition of the food freshness sensor of Example 2. Furthermore, DTA and differential weight loss analysis of the food freshness sensor of Example 2 showed an end peak in the differential value of weight loss around 300 to 500°C. It is thought that full-scale thermal decomposition of the food freshness sensor of Example 2 began at approximately 200°C and was not complete until 600°C.

[0106] Next, the melting behavior (crystallization) of the food freshness sensor of Example 2 (sensor E-Cot), eggshell membrane, and curcumin was evaluated by DSC analysis.

[0107] In the food freshness sensor (Sensor E-Cot) according to Example 2, an endothermic peak not related to the glass transition temperature (Tg) was observed around 50°C, which is thought to be related to the degradation of collagen within the membrane resulting from the breaking of hydrogen bonds and rearrangement of the helical structure to a random chain arrangement.

[0108] From the above results, it can be said that the thermal decomposition of the food freshness sensor according to Example 2 began at approximately 200°C and did not complete until the temperature reached 600°C. Therefore, it was confirmed that the food freshness sensor according to Example 2 has excellent thermal properties.

[0109] 4. Surface shape of the food freshness sensor according to Example 1 Figure 17 shows the surface shapes of the food freshness sensor and eggshell membrane of Example 2. Figures 17(a) and 17(b) are SEM images of the eggshell membrane, Figure 17(c) is a histogram of the eggshell membrane, Figure 17(d) is a TEM image of the eggshell membrane, Figures 17(e) and 17(f) are SEM images of the E-Cot sensor, Figure 17(g) is a histogram of the E-Cot sensor, and Figure 17(h) is a TEM image of the E-Cot sensor. The vertical axis of Figures 17(c) and 17(g) represents frequency, and the horizontal axis represents diameter (unit: nm). Fig. 18 is a graph showing the results of elemental mapping of the food freshness sensor according to Example 2. The vertical axis of Fig. 18 represents counts (x1000), and the horizontal axis represents energy (unit: keV).

[0110] The food freshness sensor (sensor E-Cot) of Example 2 and eggshell membrane were analyzed using SEM, EDS, and TEM (see FIGS. 17 and 18).

[0111] The results confirmed that the eggshell membrane had a woven three-dimensional network structure with an average diameter of 1.6±0.44 μm. In the food freshness sensor (Sensor E-Cot) of Example 2, a smooth fiber morphology without aggregation was observed due to curcumin adsorption, but no significant change in diameter was observed (1.6±0.42 μm). Further magnification of the SEM image revealed the shape of the curcumin on the eggshell membrane fibers more clearly, revealing that the curcumin was uniformly distributed in a regular spherical shape.

[0112] As a result of analyzing elemental mapping (not shown) of the food freshness sensor according to Example 2, it was observed that typical elements (C, O and S) were uniformly distributed on the surface.

[0113] Furthermore, TEM observation confirmed that curcumin was uniformly dispersed (with minimal aggregation) on the eggshell membrane in the food freshness sensor of Example 2. This is thought to play an important role in the stability and reproducibility of spoilage detection.

[0114] 5. Ammonia and pH Response of the Food Freshness Sensor of Example 2 FIG. 19 is a table showing the color change of the food freshness sensor according to Example 2 in response to ammonia vapor. FIG. 20 is a graph showing the pH responsiveness of the food freshness sensor according to Example 2. FIG. 20(a) is a graph showing the pH responsiveness of the food freshness sensor according to Example 2 to steam, FIG. 20(b) is a graph showing the pH responsiveness of the food freshness sensor according to Example 2 to a solution, and FIG. 20(c) is a graph showing the RGB values ​​of the color displayed by the food freshness sensor according to Example 2 in the test of FIG. 20(b). The vertical axis of FIG. 20(a) shows the total color difference (unit: ΔE), and the horizontal axis shows the type of steam (N: ammonia vapor, A: acetic acid vapor) and the number of times (1: first time, 2: second time, 3: third time). The vertical axis of FIG. 20(b) shows the total color difference (unit: ΔE), and the horizontal axis shows the type of solution. The vertical axis of FIG. 20(c) shows the magnitude of the RGB value, and the horizontal axis shows the type of solution. Figure 21 shows the pH responsiveness of curcumin. Figure 21(a) is a graph showing the UV spectrum of curcumin, and Figure 21(b) is a photograph showing the appearance of curcumin solutions at various pH levels. The vertical axis of Figure 21(a) represents absorbance (unit: au), and the horizontal axis represents wavelength (unit: nm). The pH of the curcumin solutions in Figure 21(b) is, from left to right, pH = 10, 7, and 5.

[0115] First, to confirm the suitability of the food freshness sensor (sensor E-Cot) of Example 2 for spoilage detection, its response to ammonia vapor was confirmed (see FIG. 19). The test method and formulas used were the same as those in Example 1, so a detailed explanation will be omitted.

[0116] As a result, a significant and rapid color change (from yellow to orange to red) was observed within 10 seconds of exposure to ammonia in the food freshness sensor of Example 2 (Sensor E-Cot). While a total color difference (ΔE) of greater than 5 is perceptible to the naked eye, the food freshness sensor of Example 2 exhibited a total color difference (ΔE) of 69.59.

[0117] The above test confirmed that the food freshness sensor according to Example 2 is effective in detecting ammonia.

[0118] Next, a test on reversibility was carried out on the food freshness sensor (sensor E-Cot) according to Example 2 (see FIG. 20(a)). The test method was the same as in Example 1, so a description thereof will be omitted.

[0119] As a result, the food freshness sensor according to Example 2 exhibited a reddish color when exposed to ammonia vapor (ΔE = 69.59, 66.52, and 62.23, respectively), and maintained a yellow color when exposed to acid vapor (ΔE = 12.25, 21.40, and 19.05, respectively). The food freshness sensor according to Example 2 maintained the same color even after multiple interactions (three times) with acidic and basic vapors. Thus, it was confirmed that the food freshness sensor according to Example 2 can maintain its sensitivity even when exposed to frequent environmental changes.

[0120] Next, the reaction of the food freshness sensor (sensor E-Cot) according to Example 2 was evaluated using solutions of two different pH values ​​(pH = 5, 10) (see Figures 20(b) and 20(c)). The test method was the same as that of Example 1, and therefore a detailed description is omitted.

[0121] As a result, the food freshness sensor (Sensor E-Cot) of Example 2 showed a clear color change (yellow to red) in the solution. Compared to the initial state, the food freshness sensor of Example 2 showed a total color difference (ΔE) of 85.80 in alkaline solution and a total color difference (ΔE) of 20.82 in acidic solution.

[0122] The UV spectrum of curcumin (see Figure 21(a)) shows an absorbance peak at a wavelength of 420 nm. At pH values ​​of 5, 7, and 10, absorbance peaks appear at 430, 429, and 420 nm, respectively. These absorbance peak shifts cause curcumin to change color from yellow to reddish (see Figure 21(b)). Curcumin is usually predominantly in the keto form, and exists as the enol form under alkaline conditions (keto curcumin is yellow, while enol curcumin is reddish).

[0123] 6. Elution, biodegradability, and antibacterial properties of the food freshness sensor according to Example 2 Fig. 22 is a set of photographs showing the elution of curcumin from the food freshness sensor of Example 2. Of the photographs shown in Fig. 22, the photograph in the upper row was taken 5 minutes after immersion, and the photograph in the lower row was taken 10 minutes after immersion. Figure 23 shows the water characteristics of the food freshness sensor and eggshell membrane according to Example 2. Figure 23(a) is a graph relating to water vapor transmission rate (WVTR), Figure 23(b) is a graph relating to water solubility (WS), moisture content (MC) and swelling index (SI), and Figure 23(c) is a photograph relating to hydrophobicity (WCA). The vertical axis of Figure 23(a) is water vapor transmission rate (unit: g / m 2 / day), and the horizontal axis indicates the test object (ES: eggshell membrane, ESCUR: food freshness sensor according to Example 2). The vertical axis of Figure 23(b) indicates percentage (unit: %), and the horizontal axis indicates the test object. In Figure 23(b), three bar graphs are displayed for each test object, from the left, relating to water solubility (WS), moisture content (MC), and swelling index (SI). Figure 24 is a photograph showing the antibacterial properties of the food freshness sensor and eggshell membrane of Example 2. The photographs in the upper row of Figure 24 are photographs showing the test results for eggshell membrane, and the photographs in the lower row are photographs showing the test results for the food freshness sensor of Example 2. Furthermore, the photographs on the left side of Figure 24 are photographs showing the test results for gram-negative bacteria, and the photographs on the right side are photographs showing the test results for gram-positive bacteria. Figure 25 is a bar graph showing the biodegradability of the food freshness sensor and eggshell membrane according to Example 2. The vertical axis of Figure 25 represents biodegradability (weight loss after the test) (unit: %). Note that Figure 25 also shows an SEM image showing biodegradability.

[0124] First, a test was conducted on the elution (migration) of curcumin from the food freshness sensor (sensor E-Cot) according to Example 2 (see FIG. 22). The test method was the same as in Example 1, so a description thereof will be omitted.

[0125] For the E-Cot sensor, a slight color change was observed in ethanol (50% and 95%). Furthermore, in acetic acid, a significant color change was observed after 5 minutes, and an even greater color change was observed after 10 minutes. This is likely due to the solubility of curcumin in ethanol and acetic acid. No significant change was observed in water.

[0126] Next, the water characteristics of the food freshness sensor (sensor E-Cot) and eggshell membrane according to Example 2 were measured (see FIG. 23). The test method and formulas used were the same as those in Example 1, so a description thereof will be omitted.

[0127] As a result, the water vapor transmission rate (WVTR), water solubility (WS), moisture content (MC), and swelling index (SI) of the food freshness sensor of Example 2 were negligible (less than 1%). This is likely due to physical interactions and the hydrophobicity of curcumin. Furthermore, the interaction (WCA) between the food freshness sensor of Example 2 and eggshell membrane with water (a droplet) was measured at residence times of 100, 300, 500, 700, 900, and 1000 ms. For the food freshness sensor of Example 2, a constant contact angle was observed within 500 ms, followed by a decrease in the contact angle (from approximately 110° to approximately 106°). This is likely due to the hydrophilic nature of the eggshell membrane.

[0128] Next, the antibacterial properties of the food freshness sensor (Sensor E-Cot) and eggshell membrane of Example 2 were tested (see Figure 24). The test method was basically the same as in Example 1, but Staphylococcus aureus was used as the gram-positive bacterium.

[0129] As a result, a transparent surface was observed on the sample in the case of gram-negative bacteria, suggesting that the food freshness sensor of Example 2 has antibacterial properties. Furthermore, compared to the case of eggshell membrane, the food freshness sensor of Example 2 did not have an inhibition region against gram-positive bacteria, and a transparent surface was confirmed. This is thought to be because the amount of curcumin adsorbed on the surface of the food freshness sensor of Example 2 was small. From the above results, it is thought that the food freshness sensor of Example 2 is resistant to both gram-negative and gram-positive bacteria.

[0130] Next, the biodegradability of the food freshness sensor (sensor E-Cot) and eggshell membrane in soil was tested (see FIG. 25). The test method was the same as in Example 1, so a detailed description will be omitted.

[0131] As a result, a decrease in biodegradability was observed in the food freshness sensor of Example 2 (sensor E-Cot) compared to eggshell membrane, which is thought to be due to the hydrophobicity and antibacterial properties of curcumin.

[0132] 7. Functional characteristics of the food freshness sensor according to Example 2 Figure 26 shows the results of testing the functionality of the food freshness sensor according to Example 2 using actual food (chicken). Figure 26(a) is a photograph taken immediately after the placement of the food freshness sensor according to Example 2, Figure 26(b) is a photograph taken four days after the start of the test, Figure 26(c) is a graph showing the color change of the food freshness sensor, and Figure 26(d) is a graph showing the RGB values ​​of the color displayed by the food freshness sensor according to Example 2 in the test of Figure 26(c). The vertical axis of Figure 26(c) shows the total color difference (unit: ΔE), and the horizontal axis shows the number of days (unit: days) since the start of the test. The vertical axis of Figure 26(d) shows the magnitude of the RGB value, and the horizontal axis shows the number of days (unit: days) since the start of the test.

[0133] Finally, the actual functional characteristics of the food freshness sensor (sensor E-Cot) according to Example 2 were tested (see FIG. 26). The test method was the same as in Example 1, so a description thereof will be omitted.

[0134] As a result of the test, the food freshness sensor of Example 2 (Sensor E-Cot) changed from yellow to red over a four-day period. Within 12 hours of the start of the test, the food freshness sensor of Example 2 detected an initial change in pH in the environment. Furthermore, at the end of the test, four days later, the food freshness sensor of Example 2 showed a significant color change visible to the naked eye (ΔE=62.70).

[0135] From the above test results, it was confirmed that the food freshness sensor (sensor E-Cot) according to Example 2 was successfully produced, and that the food freshness sensor can be used to easily determine the freshness of food.

[0136] [Example 3] Example 3 describes an example of actually creating a food freshness sensor according to embodiment 3, in which the eggshell membrane-derived material is a nonwoven fabric having nanofibers containing eggshell membrane-derived components and polymer components.

[0137] First, lemon juice was extracted by physically squeezing half a lemon. The lemon juice was centrifuged for 30 minutes and then filtered. The filtrate was used as the lemon extract. Next, a polymer (PVA) was added to the lemon extract (10%, w / w) and stirred at 90°C for 3 hours. Eggshell membrane (15%) was then added and stirred again for 6 hours to obtain a spinning solution. The spinning solution was electrospun at a voltage of 17 kV and a flow rate of 0.3 mL / h. To obtain uniform, bead-free nanofibers, the tip-collector distance (TCD) was maintained at 15 cm, a temperature of 25°C, and a humidity of 40%.

[0138] It was confirmed that by adsorbing a discoloration pigment to the eggshell membrane-derived material prepared by the above method using the method described in Examples 1 and 2, it is possible to create a food freshness sensor equipped with eggshell membrane-derived material made of nonwoven fabric.

[0139] [Example 4] Example 4 describes an example in which a food freshness sensor according to embodiment 3 was actually produced in which the eggshell membrane-derived material was recycled eggshell membrane (RESM).

[0140] First, the eggshell membrane was washed with deionized water and dried at room temperature for 12 hours. The eggshell membrane was then cut into small pieces and placed in an alkaline solution containing NaOH, urea, and HO in a weight ratio of 7:8:80, followed by stirring for 10 minutes. The membrane was then frozen, thawed, and vigorously stirred at room temperature to obtain a clear solution. The solution was then dripped into a PTFE dish and incubated in a 60°C water bath for approximately 24 hours, after which it was washed 10 times with pure water. Finally, the regenerated eggshell membrane grown in the PTFE dish was removed with tweezers and collected, followed by drying in a vacuum oven at 40°C for 24 hours.

[0141] It was confirmed that by adsorbing a discoloration pigment to the eggshell membrane-derived material prepared by the above method using the method described in Examples 1 and 2, it is possible to create a food freshness sensor equipped with eggshell membrane-derived material, which is recycled eggshell membrane.

[0142] Although the present invention has been described based on the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments. The present invention can be embodied in various forms without departing from the spirit of the present invention, and for example, the following modifications are also possible.

[0143] (1) In the above embodiments and examples, the discoloration pigment was polyaniline or curcumin, but the present invention is not limited thereto. The discoloration pigment may be any pigment that changes color due to a substance released as food spoils. Examples of discoloration pigments that can be used include anthocyanin, alizarin, shikonin, betalain, phenolphthalein, bromocresol purple, bromocresol green, methyl orange, and methyl red.

[0144] (2) In Examples 1 and 2, chicken meat was used as the food, but the present invention is not limited to this. The food freshness sensor of the present invention can be used to determine the freshness of foods other than chicken meat (meat other than chicken, such as animal meat, fish, etc.) as long as the food is rich in protein.

Claims

1. A color-changing pigment that changes color due to substances released as food spoils; A food freshness sensor comprising an eggshell membrane or an eggshell membrane-derived material having the color-changing pigment adsorbed thereon.

2. 2. The food freshness sensor according to claim 1, wherein the color-changing pigment is a substance that changes color under the influence of ammonia.

3. 3. The food freshness sensor of claim 2, wherein the color-changing dye comprises polyaniline.

4. 3. The food freshness sensor of claim 2, wherein the color-changing pigment comprises curcumin.

5. The food freshness sensor according to claim 1, wherein the eggshell membrane-derived material contains an eggshell membrane-derived component and a polymer component.

6. The food freshness sensor according to claim 5, wherein the eggshell membrane-derived material is a nonwoven fabric having nanofibers containing the eggshell membrane-derived component and the polymer component.

Images