Food quality indicator

Abstract

A food quality indicator (100) includes an ink layer (130) configured to detect and indicate the presence of an analyte, such as a volatile organic compound (VOC), an adhesion layer (120), and a gas permeable but liquid impermeable semi-permeable layer (140), where the adhesion layer (120) is a double sided adhesion layer. The ink layer (130) includes a reactive ink (131) absorbed on the porous substrate (132) and is encapsulated between the adhesion layer (120) and the semi-permeable layer (140). The semi-transparent layer (140) may also include a coated protective layer (150) configured to prevent migration of ink from the ink layer (130). An ink (131) and a protective layer (150) for preparing a food quality indicator (100) and a method of a food quality indicator (100) are provided.

Description

Technical Field

[0001] The present invention generally relates to the field of food quality indicators and the manufacture of said food quality indicators. The present invention also relates to food packaging comprising said food quality indicators. Background Art

[0002] Many food products such as meat, poultry, fish, dairy products, fruits, vegetables, processed foods are perishable and it is difficult for consumers to detect when a particular food product has expired, especially when the food product is enclosed in packaging.

[0003] Several perishable food products are packaged in food trays using barrier films. For example, poultry is often placed in food trays with top-covering barrier films. Such food product packaging is provided for many reasons, namely, hygienic reasons, ensuring safe delivery of the product from the manufacturer to the consumer, and increasing the shelf life of the product.

[0004] The term "barrier film" means that the function of the film is to seal the food from the outside and keep the original state of the inside of the package. Therefore, it can prevent gases that have an impact on food quality, such as oxygen, carbon dioxide, nitrogen and water vapor, from penetrating into the food package.

[0005] Today, it is a basic safety requirement to provide expiry dates on food packaging so that consumers know and understand how long the food can be used. Food expiry dates are usually set during the product development phase and the calculation is based on certain assumptions, such as perishable materials are stored under certain conditions (such as refrigeration). Therefore, if the food is not stored properly, for example because the refrigerator is damaged or there is perhaps a problem with the packaging, the shelf life may not apply. However, in certain cases where the food is stored under the correct conditions, the food may still be edible beyond the recommended shelf life provided on the packaging. This may result in edible food being thrown away, thus causing additional food waste. People unconditionally believe in "best before" or "use by" dates, which do not reflect the manufacturing, packaging and storage conditions throughout the supply chain.

[0006] Many foods such as meat, pork, poultry, and processed foods produce analytes during decomposition.

[0007] Specifically, in meat, analytes are produced by lipid oxidation, Maillard reaction or Strecker degradation, which is responsible for the formation of meat flavor. Analytes produced during meat storage can produce olfactory effects, rendering the food inedible. The large number of analytes produced depends on the storage conditions and the type of packaging. The most common analytes are volatile organic compounds (VOCs), such as alcohols, amines, aldehydes, ketones, esters and sulfides, as well as volatile amines, also called biogenic amines (BA), such as ethylamine and methylamine.

[0008] The lack of real-time farm-to-table monitoring labeling in individual packages increases the risk of consuming low-quality food and food waste.

[0009] Smart packaging or "intelligent packaging" has been developed to address this issue through the development of colorimetric sensor arrays, gas sensors, time-temperature sensors, pH indicators, to name a few. Unfortunately, most smart packaging or "intelligent packaging" has not made it to the market due to the complexity of analyzing the results, the difficulty of attaching the sensor / measuring device to the food packaging, the cost, and the regulatory barriers of the components.

[0010] Color indicators printed on packaging are a promising solution, where the indicator changes color to indicate that the food has expired. However, providing a single indicator that can detect multiple analytes has been a challenge. The difficulty of printing color-changing inks on the surface of food packaging has also limited the aforementioned solutions.

[0011] Therefore, there is a need for a reliable food freshness indicator that addresses the shortcomings and deficiencies of the prior art and that can be manufactured in a cost-effective manner. Summary of the invention

[0012] Therefore, the present invention will solve or at least alleviate the problems associated with the prior art. This object is achieved by the technology set out in the attached independent claim; preferred embodiments are defined in the related dependent claims.

[0013] According to a first aspect, a food quality indicator is provided. The food quality indicator has an ink layer including ink absorbed on a porous substrate. The ink of the ink layer is configured to indicate the presence of an analyte. The food quality indicator also has an adhesive layer, which is a double-sided adhesive layer including a first side and a second side. The food quality indicator also has a semipermeable layer, which has a first surface and a second surface, and the semipermeable layer is permeable to gas but not permeable to liquid. The ink layer is arranged between the second side of the adhesive layer and the first surface of the semipermeable layer.

[0014] The advantage of providing an ink layer configured to indicate the presence of an analyte, such as a volatile organic compound (VOC), a volatile gas, a volatile amine, a biogenic amine or a volatile sulfur compound, is that it provides the end consumer with a simple, inexpensive and accurate means of continuously monitoring the quality of food. When the analyte is detected, the food quality indicator changes color successively, thereby making the consumer aware of the expiration date of the food. For example, the consumer will know whether the food has rotted or is still edible.

[0015] The ink layer is made by absorbing the ink on a porous substrate, which has the function of absorbing water-based or solvent-based reactive ink and also prevents the reactive ink from migrating into the food.

[0016] Furthermore, by encapsulating the ink layer between the adhesive layer and the semipermeable layer, the ink is protected from its surroundings, so it will take some time for the analyte to reach the ink layer. This is an advantageous feature because the food will not directly decay when the analyte is produced. The analyte can only access the ink layer by passing through the semipermeable layer. Therefore, a controlled migration of the analyte from the food to the semipermeable layer can be achieved.

[0017] According to one embodiment, the analyte must migrate through the semi-permeable layer of the food quality indicator to reach the ink layer.

[0018] Thus, a controllable and measurable migration can be obtained.

[0019] According to one embodiment, the food quality indicator further comprises a protective layer coated on the first surface of the semi-permeable layer. The protective layer is configured to prevent the ink from migrating from the ink layer.

[0020] The advantage of preventing ink migration by the protective layer is that the food monitored by the food quality indicator is further protected from contact with the ink. In addition, it is not desirable for the ink to migrate from the food quality indicator because this will affect the performance of the ink. If the ink is soiled, the ink may not effectively change color when in contact with the analyte. In addition, it may be difficult for the user to read the monitoring results from the analyte. Therefore, it is desirable to keep the ink in the encapsulation area between the adhesive layer and the semi-permeable layer for providing clear and accurate results. The analyte can only approach the ink layer by passing through the semi-permeable layer and the protective layer. Therefore, the controlled migration of the analyte from the food to the semi-permeable layer and the protective layer can be achieved.

[0021] According to one embodiment, the protective layer is gas permeable, thereby allowing the entry of analytes such as volatile organic compounds (VOCs), volatile gases, volatile amines, biogenic amines or volatile sulfur compounds.

[0022] According to one embodiment, the analyte migrates through the semi-permeable layer and the protective layer to reach the ink layer.

[0023] According to one embodiment, the protective layer is a hydrophobic layer. The hydrophobic protective layer will cause the ink to be repelled by the protective layer. Since the protective layer is coated on the inner side of the semi-permeable layer and the ink layer is encapsulated between the adhesive layer and the semi-permeable layer, the ink layer will remain in this area.

[0024] According to one embodiment, the protective layer includes a polymer and a solvent.

[0025] According to one embodiment, the weight ratio of the polymer to the solvent of the protective layer is in the range of 0.01:2 to 0.2:0.4 (eg 0.01:1, preferably 0.15:0.56).

[0026] According to one embodiment, the polymer of the protective layer is selected from the group consisting of polydimethylsiloxane (PDMS), polyurethane, polyamide or polyethylene, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), ethyl cellulose (EC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) or any combination of the above, and the weight ratio thereof is between 0.1 and 0.5.

[0027] According to one embodiment, the solvent of the protective layer is selected from the following solvent group, the solution viscosity is between 20 and 300 cP and the boiling point is between 34.6°C and 190°C, more preferably between 50°C and 90°C, wherein the vapor pressure of the solvent is between 2.9 kPa and 170.6 kPa, preferably between 21.6 kPa and 110.6 kPa.

[0028] The advantage of the protective layer provided according to the present method is that it is hydrophobic and permeable to gas. Most substrates are highly porous substrates that are permeable to liquids and gases. It is a challenge to achieve selective diffusion on a permeable and highly permeable substrate, especially when distinguishing between gas and liquid, and the protective layer of the present invention overcomes this challenge.

[0029] According to one embodiment, the semi-permeable layer is non-transparent.

[0030] The advantage of the semi-permeable layer being non-transparent is that it provides a contrasting background for the ink layer and other parts of the food quality indicator, making the color change and the result easy to read and clear to the end consumer. Since the food quality indicator will be placed on the inside of the food packaging, it is important to easily perceive the result through the food packaging.

[0031] According to one embodiment, the semi-permeable layer is configured to be printed thereon.

[0032] An advantage of the semi-permeable layer being a material that can be printed on is that additional information can be provided on the food quality indicator, such as a text area to describe to the consumer the meaning of the change in colour of the ink layer or to provide any additional information.

[0033] According to one embodiment, the protective layer is transparent. Therefore, since the protective layer is arranged above the semi-permeable layer, any text or information printed on the semi-permeable layer is visible to the end consumer. When the food quality indicator is arranged in a food package, the semi-permeable layer is the layer arranged farthest from the barrier film top cover.

[0034] According to one embodiment, the ink layer and the semi-permeable layer have different surface areas, and thus the ink layer and the semi-permeable layer can be fastened to the second side of the double-sided adhesive layer.

[0035] According to one embodiment, the first side of the adhesive layer of the food quality indicator is configured to be attached to a barrier film of a food packaging.Thereby, the food quality indicator is attached to the food packaging in an easy manner.

[0036] According to one embodiment, the food quality indicator is configured to be attached to the inside of a food package containing a food that produces an analyte upon decomposition, such as meat, poultry, fish, dairy products, fruits, vegetables, processed foods.

[0037] According to one embodiment, the ink is made of a surfactant, a thickener, a pigment indicator, a benzopyrone compound, a solvent, and a color enhancer.

[0038] According to one embodiment, the surfactant constitutes 10% to 30% of the ink.

[0039] According to one embodiment, the surfactant is selected from the group consisting of: polyelectrolytes, hydrocolloids or any combination thereof.

[0040] According to one embodiment, the thickener constitutes 30% to 50% of the ink.

[0041] According to one embodiment, the thickener is a polymeric thickener.

[0042] According to one embodiment, the thickening agent is selected from the group consisting of cellulose polymers, carbomer polymers, carbomer derivatives, cellulose derivatives, agar, polyacrylamide, polyvinyl alcohol, alginic acid, poloxamer, polysaccharides, gelatin, pectin, or any combination thereof.

[0043] According to one embodiment, the pigment indicator is coupled to an alkoxysilane.

[0044] According to one embodiment, the alkoxysilane coupled to the pigment indicator constitutes 0.1% to 10% of the ink.

[0045] According to one embodiment, the pigment indicator is an organic pigment selected from the group consisting of diketopyrrolopyrrole, quinophthalone, azo pigment, zingiberaceae, quinacridone, indanthrone, flavonoid, pyranthrone, anthraquinone, perylene, dioxazine, peronone, thioindigo, isoindoline and isoindolone, or any combination thereof.

[0046] According to one embodiment, the alkoxysilane compound is selected from the group consisting of non-amino silane compounds, such as (3-acryloxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane or any combination thereof.

[0047] According to one embodiment, the ink is further made of a benzopyrone compound such as coumarin.

[0048] According to one embodiment, the solvent is selected from polyester resin, phenolic resin, alkyd resin, polycarbonate resin, polyamide resin, polyurethane resin, silicone resin, epoxy resin, polyethylene resin, acrylic resin, polystyrene resin, polypropylene resin or any combination thereof.

[0049] According to one embodiment, the color enhancer constitutes 0.5% to 1% of the pigment indicator.

[0050] According to one embodiment, the color enhancer is a phthalocyanine.

[0051] According to one embodiment, the porous substrate of the ink layer is selected from cellulose, paper, synthetic paper, polyolefin-based synthetic materials, thermoplastic copolyester (TPPE), low-density or high-density polyethylene, low-density or high-density polypropylene, nylon, nonwoven fabrics, fabrics or polymer films.

[0052] According to one embodiment, the pores of the porous substrate of the ink layer have a pore size between 10 μm and 100 μm and a thickness between 0.05 mm and 0.5 mm, preferably between 0.05 mm and 0.1 mm.

[0053] According to a second aspect, a method for preparing an ink for a food quality indicator is provided. The method comprises preparing a mixture by dissolving a surfactant in a solvent and adding a pigment coupled with a silane to the mixture. The mixture is then treated by ultrasound for 10-30 minutes followed by vortex mixing for 20-30 minutes. A color enhancer and a polymer thickener are added to the mixture. Thereafter, the mixture is treated by ultrasound for 10-30 minutes followed by vortex mixing for 20-30 minutes. Subsequently, a coupling agent is added to the mixture and the mixture is heated to 30-60°C.

[0054] The ink of the food quality indicator provided according to the present method has the advantage that the ink changes color in the presence of an analyte, such as a volatile organic compound (VOC), a volatile gas, a volatile amine, a biogenic amine or a volatile sulfur compound. Thus, the ink can be arranged in a food quality indicator as described above, which has several layers for protecting the ink and thus enables the migration of the analyte to the ink to be controlled when the ink is arranged inside a food packaging.

[0055] According to a third aspect, a method for preparing a protective layer for a food quality indicator is provided, wherein the method comprises the following steps: providing a polymer and a solvent in a weight ratio of 0.01:1, preferably 0.15:0.56, and then dissolving the polymer in the solvent at room temperature.

[0056] The advantage of the protective layer provided according to the present method is that it is hydrophobic and gas permeable. Most substrates are highly porous substrates that are permeable to liquids and gases. It is a challenge to achieve selective diffusion on a permeable and highly permeable substrate, especially when distinguishing between gases and liquids, and the protective layer of the present invention overcomes this challenge. The polymer of the protective layer is selected from the group consisting of: polydimethylsiloxane (PDMS), polyurethane, polyamide or polyethylene, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), ethyl cellulose (EC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) or any combination of the above, and the weight ratio is between 0.1 and 0.5. The solvent of the protective layer is selected from the following solution group, the solution viscosity is between 20 and 300 cP and the boiling point is between 34.6°C and 190°C, more preferably between 50 and 90°C. The vapor pressure of the solvent is between 2.9kPa and 170.6kPa, preferably between 21.6kPa and 110.6kPa.

[0057] According to a fourth aspect, a method for manufacturing an indicator of a food quality indicator is provided. The method comprises the step of providing an ink according to the above method for preparing an ink. A layer of the ink is then applied to a porous substrate to provide an ink layer. A first side of the ink layer is attached to a semi-permeable layer. A second side of the ink layer is attached to a second side of a double-sided adhesive layer.

[0058] The advantage of the present method for manufacturing an indicator of a food quality indicator is that the food quality indicator comprises several layers to protect and encapsulate the ink inside the food quality indicator so as to provide a controlled migration of an analyte, such as a volatile organic compound (VOC), a volatile gas, a volatile amine, a biogenic amine or a volatile sulfur compound, to the ink. Thus, the change in ink color is not random. It is also possible to prevent the ink from being soiled so that it does not effectively change color when in contact with the analyte. The double-sided adhesive layer enables the food quality indicator to be securely fastened to the food packaging in an easy manner.

[0059] According to one embodiment, the method further comprises the steps of providing a protective layer according to the above method for preparing a protective layer, and coating the semipermeable layer with the protective layer and then applying the ink layer to the semipermeable layer so that the protective layer is arranged between the semipermeable layer and the ink layer. The method steps related to the protective layer are only included in the method in the case where the food quality indicator is provided with a protective layer.

[0060] According to one embodiment, the last step of the method is to fasten the first side of the double-sided adhesive to the barrier film of the food packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] These and other aspects, features and advantages that can be achieved by the present invention will become apparent and elucidated from the following description of embodiments of the present invention with reference to the accompanying drawings, in which:

[0062] Figure 1 is a perspective view of a food quality indicator on a food package as the end user would see the indicator on the package;

[0063] Figure 2A-2E is a front view of a food quality indicator, which illustrates the changing process of the food quality indicator, wherein Figure 2A A food quality indicator is shown in which no analyte has been detected in the food packaging, while Figure 2E A food quality indicator is shown indicating that the food within the food package is no longer edible;

[0064] Figure 3A is an exploded perspective view illustrating a plurality of layers included in a food quality indicator according to a first embodiment of the present invention;

[0065] Figure 3B is a cross-sectional view of a food quality indicator illustrating the layers included in the food quality indicator according to the first embodiment of the present invention;

[0066] Figure 4A is an exploded perspective view illustrating a plurality of layers included in a food quality indicator according to a second embodiment of the present invention;

[0067] Figure 4B is a cross-sectional view of a food quality indicator illustrating layers included in the food quality indicator according to a second embodiment of the present invention;

[0068] Figure 5 A flow chart illustrating a method of preparing an ink according to the first or second embodiment, the ink changing color in the presence of an analyte, a volatile gas, and / or a biogas;

[0069] Figure 6 A flow chart diagram illustrating a method for preparing a protective layer for a food quality indicator according to a second embodiment; and

[0070] Figure 7 The flow chart diagram shows a method of preparing a food quality indicator according to the first or second embodiment. DETAILED DESCRIPTION

[0071] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings so that those skilled in the art can implement the present invention. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make this disclosure detailed and complete, and to fully convey the scope of the present invention to those skilled in the art. These embodiments do not limit the present invention, but the present invention is limited only by the attached patent claims. In addition, the terms used in the specific embodiments shown in the detailed description drawings are not intended to limit the present invention.

[0072] Reference Figure 1 , a food product 11 (ie a piece of meat) is shown enclosed in a food product package 10. The food product package 10 is a food tray 13 with a top cover barrier film 110.

[0073] As is well known, such food packaging 10 includes a "best before" or "use by" date to indicate the expiration date of the food. Figure 1 In the embodiment, a "best before" date 12 is provided on the barrier film 110 of the food package 10.

[0074] As an example, food 11 is illustrated as a piece of meat. In addition to a piece of meat, poultry, fish, dairy products, fruits, vegetables, processed foods, or any other type of perishable food may be shown in FIG. Figure 1 Food packaging 10.

[0075] Figure 1 A food quality indicator 100 according to the present invention is further described. The food quality indicator 100 has a reactive ink 131 absorbed on a porous substrate 132, which changes color depending on the quality of the food being monitored. Thus, a means is provided to determine whether the food 11 is edible.

[0076] The indicator 100 may be provided in the form of a label, a bag, a capsule, a hollow tube, a sheet or a tea bag.The color changing material is disposed between two substrates.

[0077] The indicator 100 should be placed in the same space as the food being monitored by the indicator 100. Figure 1 In FIG. 1 , the indicator 100 is thus attached to the barrier film 110 and is located within the area formed by the barrier film 110 and the food tray 13 .

[0078] When the food 11 is packaged, the food 11 is arranged inside the food tray 13. With the food quality indicator 100 attached to the barrier film 100, the barrier film 110 is arranged to cover the food tray 13 and provide a top cover for the food package 10.

[0079] The barrier film to which the food quality indicator 100 is attached may be made of a composition comprising at least one of the following:

[0080] - polyolefins, including low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polypropylene (PP) and biaxially-oriented polypropylene (BOPP);

[0081] - copolymers of ethylene, such as ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl alcohol copolymer (EVOH) and ethylene-acrylic acid copolymer (EAA);

[0082] - Composite materials such as amorphous silicon oxide (SiOx) and other ceramic-coated polymers;

[0083] - nanocomposite polymers, such as polymer-reinforced nanoparticles;

[0084] - substituted olefins, such as polystyrene (PS), high-impact polystyrene (HIPS, with the addition of 1,3-butadiene isomers during the polymerization of PS), oriented polystyrene (OPS), polyvinyl alcohol (PVOH), polyvinyl chloride (PVC), polyvinylidene chloride (PVdC) and polytetrafluoroethylene (PTFE);

[0085] - polyesters, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and the related copolymers PET-PEN;

[0086] - Polycarbonate (PC);

[0087] - polyamide (PA);

[0088] - Acrylonitrile, such as polyacrylonitrile (PAN) and acrylonitrile / styrene copolymers (ANS);

[0089] - regenerated cellulose;

[0090] - Polylactic acid (PLA) as a biodegradable polymer for food contact packaging;

[0091] - Plasma pretreatment of polymers.

[0092] The thickness of the barrier film is between 10 μm and 10,000 μm, preferably between 100 μm and 1000 μm.

[0093] The barrier film is a transparent film, the light transmittance and haze of which range from 0% to 95% and from 0% to 5%, respectively, preferably from 50% to 90% and from 1% to 3%, respectively.

[0094] In the simplest form, the indicator 100 comprises the above-mentioned reactive ink 131, also referred to as ink layer 130, because the ink 131 is absorbed on a porous substrate 132 provided as a layer of the indicator 100. The ink layer 130 is sandwiched between two substrates and has the function of undergoing a systemic color change in the presence of an analyte, such as a volatile organic compound (VOC), a volatile gas, or a biogas.

[0095] The color change of the reactive ink 131 is substantially proportional to the amount of the detected analyte (e.g., VOC, volatile gas, or biogenic gas). The reactive ink 131 can detect the most common analytes, including alcohols, amines, aldehydes, ketones, esters and sulfides, volatile amines (including but not limited to methylamine and ethylamine), volatile gases (e.g., volatile fatty acids), biogenic amines, and volatile sulfur compounds.

[0096] As described above, the ink layer 130 is made by absorbing the reactive ink 131 on the porous substrate 132. The porous substrate 132 has the function of absorbing the water-based or solvent-based reactive ink 131 and preventing the reactive ink 131 from migrating into the food. The porous substrate is commercially available and physically changes size according to the size of the label 101. To name a few examples, the porous substrate is generally made of cellulose, paper, synthetic paper, polyolefin-based synthetic materials, thermoplastic copolyester (TPPE), low-density or high-density polyethylene, low-density or high-density polypropylene, nylon, nonwoven fabrics, fabrics or polymer films, which contain pore sizes between 5 μm and 100 μm.

[0097] In one embodiment of the present invention, the thickness of the ink layer 130 is generally between 0.05 mm and 0.5 mm, and preferably between 0.05 mm and 0.1 mm.

[0098] The ink layer 130 using the porous substrate 132 has the advantageous feature of strongly hindering the migration of the ink and providing a high background contrast, so that any slight color change caused by the reaction of the ink with the analyte is visible and clear. In addition, the ink layer 130 also makes it easy to integrate the protective layer 150 with the adhesive layer 120, so that the production process is simplified and scalable.

[0099] like Figure 1 As shown, the indicator 100 is a label 101 attached to a transparent barrier film 110 such that a user can see and read the indicator 100 through the barrier film 110 of the food package 10 .

[0100] Figure 2A-2E FIG. 1 shows the change process of the food quality indicator 100 perceived by the end consumer. Figure 2A-2EAs shown, the indicator 100 includes an ink layer 130 and a reference area 141. Figure 4A -B and Figure 5 As disclosed in AB, the reference area 141 is preferably part of a different layer of the indicator 100 (rather than the ink layer 130).

[0101] The indicator 100 may further include instructions 102 for explaining the ink layer 130 with respect to the reference area 141. For example, Figure 2A-2E The ink layer 130 in FIG. 1 is shown as a circular area surrounded by a reference area 141. The reference area 141 and the ink layer 130 should be placed close to each other so that the colors of the two areas can be easily compared.

[0102] As previously mentioned, the indicator 100 may further include instructions 102 for explaining the color of the ink layer 130. Such instructions 102 may be provided as printed text (e.g., in a Figure 2A-2E ), a bar code, an additional reference area, a "best before" or "use by" date, or any other relevant instructions or information that may help a user decide whether the food 11 in the food package 10 is edible.

[0103] Figure 2A The food indicator 100 according to the present invention is shown before use and / or before any analyte, volatile gas or biogas is detected. Thus, in this example, the reactive ink 131 of the ink layer 130 is white, while the reference area 141 is shown in black. The contrast difference between the ink layer 130 and the reference area 141 is high.

[0104] exist Figure 2B In the example shown in FIG. 1 , the food indicator 100 has detected some analyte, volatile gas or biogas. However, the amount detected is low, so the food is considered edible. This is shown by some dots and / or small areas of the ink layer 130 being colored a darker shade similar to the color of the reference area 141. The contrast difference between the ink layer 130 and the reference area 141 is still obvious. Therefore, the food is edible.

[0105] exist Figure 2C In, with Figure 2B , the food indicator 100 has detected some additional analytes, volatile gases or biogases compared to that shown in . This is shown by additional dots and / or small areas of the ink layer 130 being colored a darker hue similar in color to the darker hue. There is now a lower visible contrast between the ink layer 130 and the reference area 141. Therefore, the food is edible, but will soon go bad.

[0106] exist Figure 2DIn the example shown in FIG. 1 , the food indicator 100 has detected additional analytes, volatile gases or biogases. There is almost no contrast between the ink layer 130 and the reference area 141. The food is definitely not edible.

[0107] exist Figure 2E In the embodiment of the present invention, the food indicator 100 has detected an additional analyte, volatile gas or biogas. There is no contrast between the ink layer 130 and the reference area 141. The food in the monitored food package is not edible.

[0108] exist Figure 2A-2E In the embodiment, the color change has been shown with a black reference area 141 and a white ink layer 130. The invention is not limited to these colors and this arrangement. Depending on the ink 131 and on the concentration of the analyte released by the perishable product, the color of the indicator 100 can, for example, change from white to blue and finally to brown, from yellow to magenta, from orange to magenta, to name a few examples of color changes.

[0109] The reference area 141 is adapted to cooperate with the ink layer 130 comprising the ink 131 absorbed on the porous substrate 132. The reference area 141 can be divided into several reference areas with different colors, so that the development process of the food 11 can be tracked until it has rotted. For example, a white ink layer 130 can, for example, mean that the food is fresh and no analyte has been detected. A color change from white to blue may indicate that the food is still fresh, but some analyte has been detected. Therefore, an indication of the state of the food until it has rotted can be obtained. For example, a color change from orange to magenta means that the food 11 has rotted. The reference area 141 can also be provided with a text area to provide a description of the meaning of the color change of the ink layer 130.

[0110] Means for wireless communication may also be provided on the indicator 100 so that the user is informed of the status of the product monitored by the indicator 100. Thus, spoiled products may be identified at an early stage and necessary preventive measures may be taken.

[0111] The ink 131 according to the present invention is a composite of a food-grade surfactant, a food-grade thickener, a pigment indicator, a food-grade benzopyrone compound, a solvent, and a color enhancer.

[0112] The reactive ink 131 of the ink layer 130 more specifically includes:

[0113] a. A food-grade polymer surfactant that constitutes 10-30% of the total ink volume. The food-grade surfactant is selected from the group consisting of: polyelectrolytes, hydrocolloids, or any combination thereof;

[0114] b. A food grade thickener constituting 30-50% of the total ink volume. The food grade thickener is a polymer thickener. The thickener is selected from the group consisting of: cellulose polymers, carbomer polymers, carbomer derivatives, cellulose derivatives, agar, polyacrylamide, polyvinyl alcohol, alginic acid, poloxamer, polysaccharides, gelatin, pectin, or any combination thereof;

[0115] c. Alkoxysilane coupled with a pigment indicator constituting 0.1-10% of the total ink. The pigment indicator is an organic pigment selected from the group consisting of diketopyrrolopyrrole, quinophthalone, azo pigment, ginger family, quinacridone, indanthrone, flavonoid, pyranthrone, anthraquinone, perylene, dioxazine, peronone, thioindigo, isoindoline and isoindolone or any combination thereof.

[0116] The alkoxysilane compound may be selected from the group consisting of silanes not containing an amino group, such as (3-acryloxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, or any combination thereof.

[0117] The silane-coupled pigment indicator is prepared by dissolving 0.1% to 15% of the pigment in an alkoxysilane solvent and refluxing the solution at 40 to 60° C. for about 3 to 10 hours;

[0118] d. Food grade benzopyrone compounds such as coumarin.

[0119] e. Solvent dissolves components a, b, c, and d constituting 40-75% of the total amount of ink. The solvent is provided for mixing the components of the ink 131.

[0120] The clear solvent is selected from polyester resin, phenolic resin, alkyd resin, polycarbonate resin, polyamide resin, polyurethane resin, silicone resin, epoxy resin, polyethylene resin, acrylic resin, polystyrene resin, polypropylene resin or a mixture thereof, and accounts for 0.5-10% of the solvent used.

[0121] f. Color enhancer, which constitutes 0.5-1% of the pigment indicator. The color enhancer is phthalocyanine.

[0122] The ink has the functionality to undergo a systemic color change upon binding or reacting with an analyte, volatile organic compound, volatile gas, and / or biogas.

[0123] More specifically, the porous substrate 132 of the ink layer 130 includes a porous substrate selected from commercially available porous substrates, and has a pore size of 10 μm to 100 μm and a thickness of 0.05 mm to 0.5 mm, preferably 0.05 mm to 0.1 mm.

[0124] More specifically, the porous substrate 132 of the ink layer 130 is selected from a group of commercially available porous substrates, such as cellulose, paper, synthetic paper, polyolefin-based synthetic materials, thermoplastic copolyesters (TPPE), low-density or high-density polyethylene, low-density or high-density polypropylene, nylon, nonwoven fabrics, fabrics or polymer films.

[0125] The ink 131 on the porous substrate 132 of the ink layer 130 is prepared by: 1) dropcasing: dropping the ink 131 with a volume between 1 μl and 10 μl, preferably between 3 μl and 6 μl, on the porous substrate and drying under ambient conditions, or 2) dip coating: immersing the porous substrate 132 in the ink 131 solution for 10 seconds and drying under ambient conditions.

[0126] Figure 5 Included is a flow chart showing a method 200 for preparing a reactive ink 131 that changes color in the presence of an analyte, a volatile gas, and / or a biogas. A detailed description of the reactive ink 131 compounds of the ink layer 130 is provided above. The preparation includes providing a pigment and an alkoxysilane according to the above description.

[0127] Alkoxysilane coupled pigment indicators are prepared by dissolving 0.1% to 15% of the pigment in an alkoxysilane solvent and refluxing the solution at 40 to 60° C. for 3 to 10 hours. The pigment is treated with a functionalized silane to improve adhesion properties.

[0128] At least one of a food-grade polymeric surfactant, a solvent, a color enhancer, a polymeric thickener, and a food-grade benzopyrone is provided according to the specifications provided above.

[0129] The method 200 for preparing the reactive ink 131 includes the step of preparing 202 a mixture by dissolving a food-grade polymer surfactant in a solvent.

[0130] Then, the pigment coupled with the alkoxysilane is added 204 to the mixture.

[0131] The mixture is then treated 206 by sonication for 10-30 minutes and then vortex mixing for 20-30 minutes.

[0132] Color enhancer and polymer thickener are added 208 to the mixture.

[0133] Thereafter, the mixture is treated again 210 by sonication for 10-30 minutes and then vortex mixing for 20-30 minutes.

[0134] Subsequently, a coupling agent is added 212 to the mixture, and the mixture is heated 214 to 30-60°C.

[0135] In a first embodiment, ink 131 is sandwiched between two substrates to form an active ink layer 130 that changes color in the presence of an analyte, such as a volatile organic compound (VOC), volatile gas, and / or biogas.

[0136] In the simplest form, one of the two substrates is an adhesive layer 120 and the other substrate is a semi-permeable layer 140 which is permeable to gases but impermeable to liquids.

[0137] Therefore, the indicator 100 has an adhesive layer 120, an ink layer 130, and a semi-permeable layer 140. The ink layer 130 is arranged between the adhesive layer 120 and the semi-permeable layer 140. Figure 3A and Figure 3B 1. The semi-permeable layer 140 has a first surface 142 and a second surface 143. The adhesive layer 120 is a double-sided adhesive layer and is the only fastener required to fasten the layers of the indicator 100. Thus, the indicator 100 can be fixed to the barrier film 110 as a single entity. The indicator 100 is also attached to the barrier film by the adhesive layer 120.

[0138] Figure 3A FIG. 2 shows an exploded perspective view of the layers included in the food indicator 100 according to the first embodiment of the present invention. Figure 3A As shown, the width and length of the ink layer 130 are smaller than those of the double-sided adhesive layer 120 and the semi-permeable layer 140. Therefore, both the ink layer 130 and the semi-permeable layer 140 are in direct contact with the adhesive layer 120 and are fixedly attached, so that the indicator 100 is provided in the form of a single unit.

[0139] Figure 3B is a cross-sectional view of a food quality indicator 100, which shows the layers included in the food quality indicator 100 according to the first embodiment of the present invention. Figure 3B The surface area differences among the ink layer 130, the adhesive layer 120 and the semi-permeable layer 140 are omitted. Figure 3B The purpose of is to provide an illustration of how the layers of the indicator 100 are arranged on top of each other.

[0140] exist Figure 3A and Figure 3B 1, an additional layer, namely a top plastic layer 110, is shown. When the indicator 100 reaches the end consumer, the indicator 100 is attached to the top plastic layer 110, such as the barrier film 110 described above. The indicator 100 is attached in such a way that it can detect the spoilage of the food contained in the food package or container. The indicator 100 is preferably fastened to the inside of the food package or container, such as Figure 1The barrier film 110 is shown so that the food and the indicator 100 are contained in the same compartment. Thus, the indicator 100 is exposed to the food and the emitted analytes, volatile gases or biogases can be measured.

[0141] The analyte migrates through the semipermeable layer 140 to reach the ink layer 130. The semipermeable layer 140 is preferably arranged facing the monitored food 11. The adhesive layer 120 attached to the barrier membrane is therefore placed farthest from the food 11. The adhesive layer 120 is impermeable to gases.

[0142] The adhesive layer 120 of the indicator 100 includes a first surface 121 and a second surface 122, wherein the first surface 121 of the adhesive layer 120 is fixed to the top plastic layer 110, and the second surface 122 of the adhesive layer 120 is fixed to the reactive ink layer 130 and to the semipermeable layer 140. The ink layer 130 is provided between the adhesive layer and the semipermeable layer 140.

[0143] Prior to use, the first surface 121 of the adhesive layer 120 is covered by a backing layer, which is removed before attaching the adhesive layer 120 to the plastic layer 110. Thus, the function of the adhesive layer 120 is to secure the indicator 100 to the top plastic layer 110 and also to secure all layers of the indicator 100 together.

[0144] The adhesive used shall be approved for indirect contact with all types of food. The adhesive layer shall be transparent.

[0145] The double-sided adhesive substrate 120 requires high adhesive strength between the tape and the substrate surface, but also requires high transparency between the layers of the tape. Double-sided adhesives are commercially available and are tackified polyurethane foams, acrylic adhesives, rubber adhesives, and are usually backed by polyester (PET) film or PVC film.

[0146] The double-sided adhesive used is preferably AM413, TT BG40WHS445N-BG40BR of Avery Dennison. The adhesive is particularly suitable for rough or difficult-to-adhere substrates (such as rubber products) and packaging materials (such as plastic containers). The adhesive has suitable performance at low temperatures, with a minimum application temperature of -5°C and a use temperature of -40°C to 70°C.

[0147] Avery Dennison's adhesive S445N has been tested by a certified laboratory and has received a certificate of conformity. S445N complies with the European Food Regulation 1935 / 2004 / EC, German Recommendation (BfR) XXI and FDA §175.105. S445N also complies with the limit values ​​specified in 10 / 2011 / EU. S445N further complies with DIN ISO 3826-1.

[0148] Adhesive S445N can safely withstand direct contact with dry, (moist) non-fatty foods as required by relevant EU food regulations. In addition, the seams (edges) of the label material can safely withstand direct contact with a variety of foods.

[0149] When taking into account the label on the packaging, the food contact surface area to volume ratio is 6dm 2 / kg. When considering labeling directly on food, the food contact surface area to volume ratio is 2dm 2 / kg.

[0150] According to FDA regulations, the adhesive may be in direct contact with the dry food product or alternatively must be separated from the food product by a functional barrier.

[0151] The semi-permeable layer 140 of the indicator 100 is permeable only to gas and impermeable to liquid.

[0152] Preferably, the substrate for the gas-permeable semipermeable layer 140 is a woven or non-woven fiber sheet made of polyolefin, polyethylene fiber, polypropylene, polyester or plant fiber, polylactic acid (PLA), polyvinylidene fluoride (PVDF), permeable Teflon (such as stretched polytetrafluoroethylene (PTFE)), fluoroplastic, polycarbonate, cellulose (regenerated cellulose, cellulose acetate, cellulose nitrate and cellulose ester), polyethersulfone (PES), nylon or a combination of the above, and the substrate is commercially available.

[0153] The semi-permeable layer 140 provides a base for the indicator 100 and is the substrate disposed farthest from the barrier film. Figure 1 When in a food package 10), the semipermeable layer is arranged toward the food to be monitored.

[0154] An important feature of the semipermeable layer 140 is that it is gas permeable, so that analytes (such as volatile organic compounds, volatile gases and / or biogas) generated when the monitored food decomposes can move / migrate through the semipermeable layer 140 and reach the ink layer 130. Therefore, the ink 130 will react with the volatile organic compounds (VOCs), volatile gases and / or biogases, and cause the color of the ink 130 to change.

[0155] The semi-permeable layer 140 is non-transparent and its function is to provide a surface for printing the reference area 141 and / or any other text, instructions explaining the color of the ink layer 130, barcodes, additional reference areas and any other relevant instructions or information. The non-transparent semi-permeable layer increases the visibility of the information printed thereon. The semi-permeable layer 140 allows gas to pass through but hinders the migration of ink.

[0156] A particularly preferred substrate for the semipermeable layer 140 is a nonwoven spunbond polyester or polyolefin, such as those available from DuPont under the trade name In the present invention, 1059B and 1073B spunbond polyolefins (nonwoven high density polyethylene fibers) are preferred because these materials are approved by FDA, USDA and EU REACH for direct food contact.

[0157] The semi-permeable layer 140 which is permeable to gas but impermeable to liquid can also be paper, synthetic paper, thermoplastic copolyester (TPPE), polyolefin-based synthetic materials, whose permeability depends on the particle retention rate, wherein the particle retention rate is below 5 μm.

[0158] Will refer to Figure 4A and Figure 4B A second embodiment of the present invention is described. Figure 4A An exploded perspective view illustrating layers included in a food indicator 100 according to a second embodiment of the present invention is shown.

[0159] In the second embodiment, the ink 130 is sandwiched between an adhesive layer 120 and a semi-permeable layer 140, the adhesive layer 120 being the same as the adhesive layer described in the first embodiment, and the semi-permeable layer 140 being the same as the semi-permeable layer described in the first embodiment. All features described in the first embodiment are also present in the second embodiment. The reference numerals correspond.

[0160] The indicator 100 according to the second embodiment further includes a protective layer 150. The protective layer 150 is disposed between the ink layer 130 and the semi-permeable layer 140. The protective layer 150 is preferably coated on the semi-permeable layer 140.

[0161] The dimensions described for the adhesive layer 120, the ink layer 130, and the semi-permeable layer 140 are applicable to the second embodiment. All the contents described for the first embodiment are also applicable to the second embodiment.

[0162] Figure 4A The width and length of the protective layer 150 are shown to be larger than the corresponding dimensions of the ink layer 130, but smaller than the corresponding dimensions of the semi-permeable layer 140. Therefore, the ink layer 130, the protective layer 150 and the semi-permeable layer 140 are in direct contact with the second surface 122 of the adhesive layer 120 and are fixedly attached, so that the indicator 100 is provided as a single unit.

[0163] Figure 4B FIG. 1 shows a cross-sectional view of a food indicator 100 according to a second embodiment of the present invention. Figure 4B The dimensions of the layers are omitted in FIG. 1 , and all layers of the indicator 100 are shown to have the same width and length. Figure 4BThe purpose of is to provide an illustration of how the layers of the indicator 100 are arranged on top of each other.

[0164] exist Figure 4A and Figure 4B An additional layer is shown in FIG. 1 , namely the top plastic layer 110. As described above, the indicator 100 is fixed to the top plastic layer 110, such as a barrier film 110, when it reaches the end consumer.

[0165] The purpose of having the protective layer 150 is to hinder the migration of ink from the ink layer 130 and the semi-permeable layer 140. The protective layer 150 is permeable to gas and thus acts as a functional barrier.

[0166] The protective layer 150 allows only gas to diffuse through the protective layer 150. The analyte migrates through the semi-permeable layer 140 and the protective layer 150 to reach the ink layer 130. The ink and liquid are prevented from diffusing through the material of the protective layer 150.

[0167] The protective layer 150 is a chemically and mechanically stable hydrophobic layer and serves as a functional barrier. The protective layer 150 is made of a composite material including a polymer and a solvent.

[0168] The polymer is one selected from the following materials: polydimethylsiloxane (PDMS), polyurethane, polyamide, polyethylene, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), ethyl cellulose (EC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) and a combination thereof, and the weight ratio thereof is between 0.1 and 0.5.

[0169] The solvent is selected from a series of solvents with a viscosity between 20 and 300 cP. Preferably, the boiling point of the selected solvent is between 34.6°C and 190°C, preferably between 50°C and 90°C. In addition, the solvent is also selected from a series of solvents with a vapor pressure between 2.9 kPa and 170.6 kPa, preferably between 21.6 kPa and 110.6 kPa. Therefore, rapid drying is achieved.

[0170] Figure 6 is a flow chart illustrating a method 250 for preparing a protective layer 150. The method includes the steps of providing 252 a polymer and a solvent in a weight ratio ranging from 0.01:2 to 0.2:0.4 (e.g., about 0.01:1, preferably about 0.15:0.56), and dissolving 254 the polymer in the solvent at room temperature.

[0171] After the protective layer 150 is made, the protective layer 150 is coated on the semipermeable layer 140. The protective layer 150 is coated on the semipermeable layer 140 using a standard printing method such as screen printing, flexographic printing, digital printing, and gravure printing. After the coating is completed, the active substrate is immediately dried quickly in a heating element at 80° C. for 1 second to 5 minutes, particularly 3 to 30 seconds. This will be further described below.

[0172] The protective layer 150 may be transparent or not. If the protective layer 150 is transparent, information may be printed on the semi-permeable layer 140 .

[0173] The additional protective layer 150 makes the indicator 100 safer because the ink from the ink layer 130 is prevented from migrating through the protective layer 150. Thus, an additional barrier is provided between the ink and the food being monitored.

[0174] Figure 7 The flowchart of FIG. 3 shows a method 300 for manufacturing the indicator 100 according to the first or second embodiment of the present invention. A detailed description of the different layers of the indicator 100 has been provided above.

[0175] The reference area 141 or text may be printed on the semi-permeable layer 140 .

[0176] The method 300 comprises the step of providing 306 an ink according to the method 200 for preparing the ink 131. The ink 131 is applied 308 on and absorbed by the porous substrate 132. Thus, an ink layer 130 is provided. The ink layer 130 has a first side 133 and a second side 134. The first side 133 of the ink layer 130 is attached 310 to the first surface 142 of the semi-permeable layer 140. The second side 134 of the ink layer 130 is attached 312 to the second side 122 of the double-sided adhesive layer 120.

[0177] The method 300 may also include providing 302 a protective layer 150 according to the method 250 for preparing the protective layer 150, and coating 304 the first surface 142 of the semi-permeable layer 140 with the protective layer 150, and then attaching the ink layer 130 to the semi-permeable layer 140 such that the protective layer 150 is disposed between the semi-permeable layer 140 and the ink layer 130. Thus, an additional barrier is provided that prevents the ink 131 from migrating from the ink layer 130 to the protective layer 150, and subsequently migrating to the food 11 and the food packaging 10.

[0178] The method 300 also includes a final step of attaching 314 the first side 121 of the double-sided adhesive layer 120 to the barrier film 110 of the food package 10 .

[0179] The indicator 100 provided in the form of a label can be attached to the barrier film 110 for the food package 10 by combining the indicator 100 with the barrier film 110 in a roll-to-roll or mechanically pressed manner. Preferably, the double-sided adhesive layer 120 is protected by a liner before application.

[0180] Furthermore, the invention has mainly been described with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

[0181] In the claims, the term "comprises / comprising" does not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims, these may be advantageously combined, and the inclusion in different claims does not mean that a combination of features is not feasible and / or disadvantageous. Furthermore, reference to the singular does not exclude the plural. The terms "a", "an", "first", "second" etc. do not exclude a plurality. The reference signs in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

1. A food quality indicator (100), comprising: an ink layer (130) comprising an ink (131) absorbed on a porous substrate (132) configured to indicate the presence of an analyte, an adhesive layer (120), wherein the adhesive layer (120) is a double-sided adhesive layer comprising a first side (121) and a second side (122), a semipermeable layer (140) comprising a first surface (142) and a second surface (143), wherein the semipermeable layer (140) is permeable to gas but impermeable to liquid, The ink layer (130) is encapsulated between the second side (122) of the adhesive layer (120) and the first surface (142) of the semi-permeable layer (140).

2. The food quality indicator (100) according to claim 1, wherein the analyte migrates through the semi-permeable layer (140) to reach the ink layer (130).

3. The food quality indicator (100) according to claims 1 to 2, further comprising a protective layer (150) coated on the first surface (142) of the semi-permeable layer (140), wherein the protective layer (150) is configured to prevent the ink (131) from migrating from the ink layer (130).

4. The food quality indicator (100) according to claim 3, wherein the protective layer (150) is permeable to gas.

5. The food quality indicator (100) according to claims 3 to 4, wherein the analyte migrates through the semi-permeable layer (140) and the protective layer (150) to reach the ink layer (130).

6. The food quality indicator (100) according to claims 3 to 5, wherein the protective layer (150) is a hydrophobic layer.

7. The food quality indicator (100) according to claims 3 to 6, wherein the protective layer (150) comprises a polymer and a solvent.

8. The food quality indicator (100) according to claim 7, wherein the weight ratio of the polymer to the solvent of the protective layer (150) is in the range of 0.01:2 to 0.2:0.4, such as 0.01:1, preferably 0.15:0.

56.

9. The food quality indicator (100) according to claims 7 to 8, wherein the polymer of the protective layer (150) is selected from the group consisting of polydimethylsiloxane (PDMS), polyurethane, polyamide or polyethylene, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), ethyl cellulose (EC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) or any combination thereof, and the weight ratio thereof is between 0.1 and 0.

5.

10. A food quality indicator (100) according to claims 7 to 9, wherein the solvent of the protective layer (150) is selected from the group of solvents having a viscosity between 20 and 300 cP and a boiling point between 34.6°C and 190°C, more preferably between 50 and 90°C, wherein the vapor pressure of the solvent is between 2.9 kPa and 170.6 kPa, preferably between 21.6 kPa and 110.6 kPa.

11. The food quality indicator (100) according to any one of the preceding claims, wherein the semi-permeable layer (140) is non-transparent.

12. The food quality indicator (100) according to any one of the preceding claims, wherein the semi-permeable layer (140) is configured to be printed thereon.

13. The food quality indicator (100) according to claims 3 to 11, wherein the protective layer (150) is transparent.

14. The food quality indicator (100) according to any one of the preceding claims, wherein the ink layer (130) and the semi-permeable layer (140) have different surface areas so that the ink layer (130) and the semi-permeable layer (140) can be fastened to the second side (122) of the double-sided adhesive layer (120).

15. The food quality indicator (100) according to any one of the preceding claims, wherein the first side (121) of the adhesive layer (120) of the food quality indicator (100) is configured as a barrier film (110) attached to a food packaging (10).

16. A food quality indicator (100) according to any one of the preceding claims, wherein the food quality indicator (100) is configured to be attached inside a food package (10) containing a food (11) that produces an analyte upon decomposition, such as meat, poultry, fish, dairy products, fruits, vegetables, processed foods.

17. The food quality indicator according to any one of the preceding claims, wherein the ink (131) comprises a surfactant, a thickener, a pigment indicator, a benzopyrone compound, a solvent and a color enhancer.

18. The food quality indicator according to claim 17, wherein the surfactant constitutes 10% to 30% of the ink (131).

19. The food quality indicator according to claims 17 to 18, wherein the surfactant is selected from the group consisting of: polyelectrolytes, hydrocolloids or any combination thereof.

20. The food quality indicator according to claim 17, wherein the thickener constitutes 30% to 50% of the ink (131).

21. A food quality indicator according to claims 17 and 20, wherein the thickener is a polymeric thickener.

22. The food quality indicator (100) according to claims 17 and 20 to 21, wherein the thickener is selected from the group consisting of: cellulose polymers, carbomer polymers, carbomer derivatives, cellulose derivatives, agar, polyacrylamide, polyvinyl alcohol, alginic acid, poloxamer, polysaccharides, gelatin, pectin or any combination thereof.

23. The food quality indicator (100) according to claim 17, wherein the pigment indicator is coupled with alkoxysilane.

24. The food quality indicator (100) according to claims 17 and 23, wherein the alkoxysilane coupled to the pigment indicator constitutes 0.1% to 10% of the ink (131).

25. The food quality indicator (100) according to claims 17, 23 to 24, wherein the pigment indicator is an organic pigment selected from the group consisting of: diketopyrrolopyrrole, quinophthalone, azo pigment, zingiberaceae, quinacridone, indanthrone, flavonoid, pyranthrone, anthraquinone, perylene, dioxazine, peronone, thioindigo, isoindoline and isoindolone or any combination thereof.

26. The food quality indicator (100) according to claims 17, 23 to 25, wherein the alkoxysilane compound is selected from the group consisting of: non-amino silane compounds, such as (3-acryloxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane or any combination thereof.

27. The food quality indicator (100) according to claim 17, wherein the ink (131) further comprises a benzopyrone compound, such as coumarin.

28. The food quality indicator (100) according to claim 17, wherein the solvent is selected from polyester resin, phenolic resin, alkyd resin, polycarbonate resin, polyamide resin, polyurethane resin, silicone resin, epoxy resin, polyethylene resin, acrylic resin, polystyrene resin, polypropylene resin or any combination thereof.

29. The food quality indicator (100) according to claims 17 and 23 to 25, wherein the color enhancer constitutes 0.5% to 1% of the pigment indicator.

30. The food quality indicator (100) according to claims 17 and 29, wherein the color enhancing agent is phthalocyanine.

31. The food quality indicator according to any one of the preceding claims, wherein the porous substrate (132) of the ink layer (130) is selected from cellulose, paper, synthetic paper, polyolefin-based synthetic materials, thermoplastic copolyesters (TPPE), low-density or high-density polyethylene, low-density or high-density polypropylene, nylon, nonwoven fabrics, fabrics or polymer films.

32. A food quality indicator according to any one of the preceding claims, wherein the pores of the porous substrate of the ink layer (130) have a pore size between 10 μm and 100 μm, and a thickness between 0.05 mm and 0.5 mm, preferably between 0.05 mm and 0.1 mm.

33. A method (200) for preparing an ink (131) for a food quality indicator (100) according to claims 1 to 32, the method (200) comprising the following steps: - preparing (202) a mixture by dissolving a surfactant in a solvent; - adding (204) a silane-coupled pigment to the mixture; - treating the mixture by sonication for 10-30 minutes followed by vortex mixing for 20-30 minutes (206); - adding (208) a colorant and a polymer thickener to the mixture; - treating the mixture by sonicating the mixture for 10-30 minutes followed by vortex mixing for 20-30 minutes (210); - adding (212) a coupling agent to the mixture; and - The mixture is heated (214) to 30-60°C.

34. A method (250) for preparing a protective layer (150) for a food quality indicator (100) according to claims 1 to 33, the method (250) comprising the following steps: (a) providing (252) a polymer and a solvent in a weight ratio of 0.01:1, preferably 0.15:0.56; and (b) dissolving (254) the polymer in the solvent at room temperature.

35. A method (300) for manufacturing an indicator (100) of a food quality indicator (100) according to claims 1 to 34, the method (300) comprising the following steps: - providing (306) an ink (131) according to said method (200) for preparing said ink (131); - applying (308) a layer of ink (131) to the porous substrate (132) to provide an ink layer (130); - attaching (310) the first side (133) of the ink layer (130) to the semi-permeable layer (140); - attaching (312) the second side (134) of the ink layer (130) to the second side (122) of the double-sided adhesive layer (120).

36. The method (300) according to claim 35, further comprising the steps of: - providing (302) a protective layer (150) according to said method (250) for preparing said protective layer (150); - coating (304) the semi-permeable layer (140) with the protective layer (150) and then applying the ink layer (130) to the semi-permeable layer (140) so that the protective layer (150) is arranged between the semi-permeable layer (140) and the ink layer (130).

37. The method (300) according to claims 35 to 36, comprising attaching (314) the first side (121) of the double-sided adhesive layer (120) to a barrier film (110) for a food packaging (10).

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