Method for constructing freshness indicating label based on volatile metabolite-driven colorimetric response

Abstract

This invention relates to a method for constructing a freshness indicator label based on a color response driven by volatile metabolic components. The method includes: providing a packaging film for food packaging, forming a first vent in the packaging film that communicates with the internal space of the packaging; providing an indicator label comprising a venting layer, a color response layer, and a transparent readability layer, forming a transverse venting channel within the venting layer, and forming a second vent on the side of the venting layer facing the color response layer that communicates with the transverse venting channel; and laminating the indicator label to the packaging film, such that the first vent communicates with the transverse venting channel, and the projections of the first and second vents in the direction perpendicular to the packaging film are staggered, allowing volatile metabolic components to enter the color response layer through the transverse venting channel and produce a color change observable by the transparent readability layer. This invention reduces the risks of liquid contact, premature local color development, and false triggering, improving the accuracy, reliability, and packaging compatibility of the label indication.

Description

Technical Field

[0001] This invention relates to the field of intelligent food packaging and freshness detection technology, specifically a method for constructing a freshness indicator label based on color response driven by volatile metabolites. Background Technology

[0002] In existing technologies, food freshness indicator labels mostly involve directly loading pH colorimetric agents, fluorescent materials, natural pigments, or composite indicators onto a film material, paper base, or fiber matrix. Upon contact with volatile amines, volatile basic nitrogen, carbon dioxide, or other metabolic gases produced by food spoilage inside the packaging, these substances undergo color or fluorescence changes, thus enabling a visual assessment of the freshness of perishable foods such as meat and seafood. For example, patent application CN115171515A discloses a label reflecting food freshness and a method for detecting food freshness. This method involves immersing a paper substrate material in a copper nanocluster solution and drying it to form a label, allowing the label to react with volatile amines produced by food spoilage and generate an observable signal. Another example is patent application CN114805875A, which discloses a low-temperature molded intelligent indicator film for visualizing pork freshness, its preparation method, and its application. This film is attached to the inside of the packaging box, and the freshness of the pork is determined by changes in color parameters. The above solution can, to some extent, enable the observation of food quality without opening the package, thus improving the problems of lag and subjectivity caused by traditional reliance on storage time, shelf life, or human sensory judgment.

[0003] However, existing freshness indicator labels typically focus on the preparation of the indicator material itself, the ratio of color developers, or the color reading method. The label structure often involves the indicator layer being directly exposed inside the packaging, or relying solely on a standard breathable sealing film for gas contact. In actual packaging, transportation, and refrigeration environments, food exudates, condensates, localized high humidity, and droplets on the inner walls of the packaging can easily come into contact with the indicator layer, leading to color developer dissolution, color background drift, uneven response areas, or misjudgments. Simultaneously, the release of volatile metabolic components inside the packaging is cumulative and spatially varied. If gases directly impact the indicator layer, problems such as localized over-coloring, unstable threshold responses, and premature triggering by low-concentration background volatiles can easily occur, thus affecting the label's correspondence with the actual spoilage process of the food.

[0004] Furthermore, existing technologies employ relatively simple gas communication methods between labels and packaging films, lacking a coordinated design for the transport paths of volatile metabolic components, air inlet locations, and color reading directions. Because the air inlet, air guide, indicator reaction, and transparent reading locations are not effectively isolated and directionally transported, after the label is attached to the packaging film, it is difficult to prevent liquids from entering the color response layer along the shortest path, and it is also difficult to ensure that volatile metabolic components undergo controllable lateral flow, buffering, and distribution before entering the indicator layer. Therefore, there is an urgent need for a method to construct a staggered, permeable, laterally permeable, and transparent reading structure between the packaging film and the indicator label, allowing volatile metabolic components inside the packaging to enter the color response layer along a predetermined path. This would reduce liquid interference and the risk of localized false triggering, while improving the response stability, readability, and packaging compatibility of the freshness indicator label. Especially in refrigerated meat and seafood packaging, exudates or condensates can easily enter the indicator layer along the shortest path formed by the vents, causing false color development triggered by non-gas-phase metabolic components. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing a freshness indicator label based on volatile metabolites driving color response, thereby addressing some of the drawbacks and shortcomings pointed out in the background art.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for constructing a freshness indicator label based on a color response driven by volatile metabolic components includes: providing a packaging film for food packaging, and forming a first vent on the packaging film that communicates with the internal space of the packaging;

[0008] An indicator label is provided, the indicator label including an air guiding layer, a colorimetric response layer and a transparent reading layer, a transverse air guiding channel is formed in the air guiding layer, and a second vent is formed on the side of the air guiding layer facing the colorimetric response layer, communicating with the transverse air guiding channel, such that the transparent reading layer is located on the side of the colorimetric response layer away from the air guiding layer;

[0009] The indicator label is laminated with the packaging film, so that the first vent is connected to the transverse air channel, and the projections of the first vent and the second vent in the direction perpendicular to the packaging film are staggered. This allows volatile metabolic components in the internal space of the packaging to enter the transverse air channel through the first vent, and then enter the color response layer through the second vent, thereby driving the color response layer to produce a color change that can be observed by the transparent readout layer.

[0010] Furthermore, a temporary release chamber is formed within the transverse air guide channel. The temporary release chamber is located between the first air vent and the second air vent. An adsorption medium with a preset adsorption capacity is provided within the temporary release chamber. After the adsorption medium adsorbs volatile metabolic components to the preset adsorption capacity, volatile metabolic components exceeding the preset adsorption capacity enter the color response layer.

[0011] Furthermore, a liquid self-isolating structure is formed between the first vent and the transverse air guiding channel. The liquid self-isolating structure has a liquid receiving recess lower than the bottom surface of the transverse air guiding channel. A liquid-absorbing expansion member is provided in the liquid receiving recess. The liquid-absorbing expansion member expands after contacting the food exudate or condensate to restrict the food exudate or condensate from moving along the transverse air guiding channel toward the second vent.

[0012] Furthermore, a peripheral air distribution cavity is formed between the second vent and the color response layer. The peripheral air distribution cavity extends along the periphery of the color response layer, so that volatile metabolic components entering through the second vent enter from the periphery of the color response layer and drive the color response layer to produce a color change.

[0013] Furthermore, the temporary release chamber is sequentially formed with a background retention area and a threshold release area along the direction from the first vent to the second vent. The adsorption medium filling density in the background retention area is greater than that in the threshold release area, so that volatile metabolic components that enter the temporary release chamber and have a flux lower than a preset flux threshold are preferentially retained in the background retention area.

[0014] Furthermore, a bypass slit is formed on the side of the temporary release chamber near the second vent. After the adsorption medium adsorbs volatile metabolic components to a preset adsorption capacity, the retention effect on subsequent volatile metabolic components is reduced, allowing volatile metabolic components exceeding the preset adsorption capacity to enter the color response layer through the bypass slit.

[0015] Furthermore, the temporary release chamber is provided with a partition rib, which divides the temporary release chamber into multiple interconnected retention units. The adsorption medium is respectively disposed in the multiple retention units. Volatile metabolic components are released from the retention unit near the second vent after passing through the retention units in sequence.

[0016] Furthermore, the peripheral air distribution cavity forms air intake branches on opposite sides of the color response layer, and the ends of the two air intake branches are not connected to each other, so that volatile metabolic components diffuse from opposite sides of the color response layer toward the center.

[0017] Furthermore, a plurality of lateral guide inlets are formed between the peripheral air distribution cavity and the chromaticity response layer. The plurality of lateral guide inlets are spaced apart along the periphery of the chromaticity response layer, and the opening area of ​​the lateral guide inlets increases sequentially in the direction away from the second air vent.

[0018] Furthermore, the orientation of the plurality of lateral guide inlets is sequentially deflected along the periphery of the chromaticity response layer, so that the volatile metabolic components entering through the lateral guide inlets form a circumferentially distributed guided diffusion path on the surface of the chromaticity response layer.

[0019] This invention forms a first vent on the packaging film and a transverse air channel and a second vent within the air-guiding layer of the indicator label. The projections of the first and second vents in the direction perpendicular to the packaging film are staggered. Volatile metabolic components must pass through the first vent, the transverse air channel, and the second vent before entering the color response layer, avoiding direct impact on the color response layer. This extends the gas transport path and forms a controlled introduction process, reducing interference from local high-concentration gases, transient background gases, and liquid contact on the indication results.

[0020] This invention places a transparent reading layer on the side of the color response layer away from the air guide layer, allowing color changes to be read directly from the outside of the packaging. This avoids exposing the reading side to humid, greasy, or exudate environments, improving reading clarity and stability. Furthermore, through the peripheral air distribution cavity, the air intake branches on both sides, the lateral guide inlets with increasing area, and the deflected lateral guide inlets, volatile metabolic components are dispersed from the periphery of the color response layer and enter to form a guided diffusion path. This reduces premature local color development caused by single-point air intake, improving color uniformity, accuracy, and packaging compatibility. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the construction process of the freshness indicator label for this invention.

[0022] Figure 2 This is a schematic diagram of the misaligned lateral air guiding and liquid self-isolation structure in Embodiment 1 of the present invention.

[0023] Figure 3 This is a structural diagram of the step-by-step interception and bypass release of the temporary release chamber in Embodiment 1 of the present invention.

[0024] Figure 4 This is a verification diagram of adsorption capacity threshold and color response in Example 1 of the present invention.

[0025] Figure 5 This is a structural diagram of the peripheral air distribution chamber and the double-sided air intake branch in Embodiment 2 of the present invention.

[0026] Figure 6 This is a diagram showing the increasing lateral guide inlet area and deflection flow in Embodiment 2 of the present invention.

[0027] Figure 7 This is a verification diagram of the color uniformity coefficient in Embodiment 2 of the present invention. Detailed Implementation

[0028] As attached Figure 1 As shown, in one embodiment, a packaging film for food packaging is first provided, and a first vent is formed on the packaging film, communicating with the internal space of the packaging. Subsequently, an indicator label is provided, comprising a gas-guiding layer, a color-response layer, and a transparent read-through layer arranged sequentially. A transverse gas-guiding channel is formed within the gas-guiding layer, and a second vent is formed on the side of the gas-guiding layer facing the color-response layer, communicating with the transverse gas-guiding channel. The transparent read-through layer is disposed on the side of the color-response layer facing away from the gas-guiding layer, so that the color change of the color-response layer can be read from the outside of the packaging. When the indicator label is compositely connected to the packaging film, the projections of the first and second vents in the direction perpendicular to the packaging film are staggered, thereby forming a transverse gas-guiding path between the first and second vents. During food storage, volatile metabolic components generated inside the packaging space enter the transverse gas-guiding channel through the first vent, flow along the transverse gas-guiding channel to the second vent, and then enter the color-response layer from the second vent. When the color-responsive layer comes into contact with volatile metabolic components, it produces a color response and a color change. Users can observe the color change through the transparent reading layer, thereby judging the freshness of the food.

[0029] The gas-guiding layer can be composed of a pressure-sensitive adhesive layer with die-cut grooves, a heat-sealing film layer, an elastic gasket layer, or other film layers that can maintain gas passages after lamination. The transverse gas-guiding channel can be formed by die-cutting, embossing, laser etching, or partial opening. When the indicator label is laminated with the packaging film, a sealed connection area can be formed on the outer periphery of the transverse gas-guiding channel, so that volatile metabolic components are mainly transmitted along the path formed by the first vent, the transverse gas-guiding channel, and the second vent, reducing the direct entry of outside air into the transverse gas-guiding channel. The transparent reading layer can be made of transparent polyester film, transparent polypropylene film, transparent polyethylene film, or other transparent film materials suitable for food packaging. The transparent reading layer is sealed to the periphery of the gas-guiding layer or the packaging film, and the color-response layer is located in the visible area.

[0030] Furthermore, the color-responsive layer includes a substrate and a color-developing composition loaded on the substrate. The substrate can be filter paper, cellulose membrane, nonwoven fabric, porous polymer membrane, or other porous sheet material capable of adsorbing and retaining the color-developing composition. The color-developing composition may include an indicator that produces a color change in volatile amines, volatile acids, or sulfur-containing volatile components. The indicator can be selected from one or more of bromocresol green, bromophenol blue, methyl red, methyl orange, anthocyanin, and curcumin, and can be used in conjunction with polyvinyl alcohol, chitosan, gelatin, sodium carboxymethyl cellulose, or other film-forming binders. In preparing the color-responsive layer, the color-developing composition can be dissolved or dispersed in a suitable solvent, and then loaded onto the substrate by impregnation, coating, spraying, or dropwise application. After drying, a color-responsive layer capable of changing color upon contact with volatile metabolic components is formed. When volatile metabolic components generated during food spoilage or deterioration of freshness enter the color-responsive layer, they change the acid-base or polar environment surrounding the color-developing composition, thereby causing a visible color change in the color-responsive layer.

[0031] Furthermore, a temporary storage and release chamber is formed within the transverse air-guiding channel, positioned between the first and second air vents. This allows volatile metabolic components entering through the first air vent to first pass through the temporary storage and release chamber before flowing towards the second air vent. The temporary storage and release chamber contains an adsorption medium with a preset adsorption capacity, used to temporarily adsorb the volatile metabolic components entering the transverse air-guiding channel. The adsorption medium can be activated carbon, zeolite, silica gel, cyclodextrin-modified porous materials, porous fiber carriers, or membranes loaded with adsorption materials. The adsorption medium can be placed within the temporary storage and release chamber through filling, clamping, dotting, hot pressing, or bonding. The preset adsorption capacity can be adjusted by the type of adsorption medium, the filling amount, the particle or fiber density, and the volume of the temporary storage and release chamber, and can be pre-calibrated based on the background volatile metabolic components generated during the initial storage stage of the target food. When the amount of volatile metabolic components entering does not reach the preset adsorption capacity, the adsorption medium retains them to reduce the interference of background volatile metabolic components on the color response layer. Once the adsorption medium adsorbs volatile metabolites to a preset adsorption capacity, volatile metabolites exceeding the preset adsorption capacity continue to move towards the second vent and enter the color-response layer. This causes the color-response layer to change color after the volatile metabolites reach a set accumulation level. The temporary release chamber can also sequentially form a background retention zone and a threshold release zone along the direction from the first vent to the second vent. The adsorption medium filling density in the background retention zone is higher than that in the threshold release zone, ensuring that volatile metabolites with a flux below a preset flux threshold are preferentially retained by the background retention zone. This reduces the impact of background signals generated during the initial storage stage or the slight volatilization stage of food on the judgment results, and allows volatile metabolites that have reached the preset flux threshold to continue to be transmitted to the color-response layer after entering the threshold release zone.

[0032] In one embodiment, a bypass slit is formed on the side of the temporary release chamber near the second vent. This bypass slit can be formed by an elastic diaphragm, a compressible septum, a partially unbonded area, or a gap at the end of a separator rib. After the adsorbent medium adsorbs volatile metabolic components to a preset adsorption capacity, its retention effect on subsequent volatile metabolic components decreases, allowing these components to move through the bypass slit to the second vent and further into the color response layer. In some embodiments, the adsorbent medium can be an expandable adsorption composite material, which, after reaching the preset adsorption capacity, acts on the bypass slit and increases its effective passage area. Separators can also be provided within the temporary release chamber, dividing it into multiple interconnected retention units. The adsorbent medium is disposed within each of these retention units. Adjacent retention units can be interconnected through gaps at the ends of the separator ribs, lateral notches in the separator ribs, or connecting gaps above the separator ribs, allowing volatile metabolic components to pass sequentially between the multiple retention units. After volatile metabolic components enter the temporary release chamber, they flow sequentially along multiple retention units, where they are adsorbed step-by-step by the corresponding adsorption medium. Once the adsorption medium in each retention unit reaches its corresponding adsorption state, the volatile metabolic components are released from the retention unit closest to the second vent, thus entering the color-response layer. This structure can delay the direct action of background volatile metabolic components on the color-response layer and establish a correspondence between the color changes in the color-response layer and the changes in food freshness.

[0033] Furthermore, a liquid self-isolating structure is formed between the first vent and the transverse air guiding channel. This structure traps liquid entering near the first vent, preventing it from entering the transverse air guiding channel along with volatile metabolic components. The liquid self-isolating structure has a liquid-receiving recess, the bottom of which is lower than the bottom of the transverse air guiding channel. This allows food exudate or condensate to preferentially enter the liquid-receiving recess after reaching the first vent, instead of flowing directly to the second vent. A liquid-blocking step, a deflection channel, or a hydrophobic and breathable barrier can be formed between the liquid-receiving recess and the transverse air guiding channel, allowing gaseous volatile metabolic components to pass through while blocking liquid water or food exudate. A liquid-absorbing expansion member is installed within the liquid-receiving recess. This member can be made of water-absorbing resin, liquid-absorbing fiber, or other materials capable of absorbing liquid and expanding in volume. When food exudate or condensate enters the liquid-receiving recess, it comes into contact with the liquid-absorbing expansion element. The expansion element absorbs the liquid and expands, occupying the connecting area between the liquid-receiving recess and the transverse gas-guiding channel, thereby blocking the movement of liquid to the second vent. This reduces the risk of liquid entering the color-response layer while maintaining the gas-phase transfer of volatile metabolic components, preventing liquid wetting from causing erroneous color changes or response distortion in the color-response layer.

[0034] Furthermore, a peripheral air distribution cavity is formed between the second vent and the color response layer. This cavity extends along the periphery of the color response layer, allowing volatile metabolic components entering through the second vent to first enter the peripheral air distribution cavity and then proceed into the color response layer from its periphery. The peripheral air distribution cavity can be formed by the gap between the transparent reading layer, the air guiding layer, and the periphery of the color response layer, or by an annular or semi-annular gasket positioned on the outer periphery of the color response layer. This prevents volatile metabolic components from concentrating on a localized area of ​​the color response layer, allowing them to disperse along its periphery, thus improving the uniformity and readability of the color change. The peripheral air distribution cavity can form air intake branches on opposite sides of the color response layer, with the ends of these branches not connected. This allows the volatile metabolic components entering the peripheral air distribution cavity to flow along the air intake branches on both sides and diffuse from the opposite sides of the color response layer towards the center. This structure allows the chromaticity response layer to gradually develop color towards the center after being driven by volatile metabolic components on both sides, reducing the response deviation caused by unilateral air intake.

[0035] In one embodiment, multiple lateral inlets are formed between the peripheral air distribution cavity and the color response layer. These lateral inlets are spaced apart along the periphery of the color response layer, allowing volatile metabolic components to enter the color response layer through multiple locations. The lateral inlets can be circular holes, elongated holes, slits, or partial notches, and can be formed by die-cutting, punching, embossing with slots, or partial non-bonding. Along the direction away from the second vent, the opening area of ​​the lateral inlets increases sequentially, reducing the air intake resistance at locations farther from the second vent, thereby compensating for the flux attenuation of volatile metabolic components during flow within the peripheral air distribution cavity. The opening area of ​​the lateral inlets can be increased by increasing the orifice diameter, increasing the slit width, extending the opening length, or increasing the number of local openings. This improves the problem of insufficient air intake in areas far from the second vent, allowing the color response layer to obtain a relatively balanced gas phase input along different locations along its periphery. Multiple lateral guide inlets are sequentially deflected along the periphery of the chromaticity response layer, causing volatile metabolic components entering through these inlets to form a circumferentially distributed guided diffusion path on the surface of the chromaticity response layer. This guided diffusion path expands the contact area between the volatile metabolic components and the chromaticity response layer and promotes the distribution of volatile metabolic components along the surface of the chromaticity response layer, thereby improving the continuity of color changes and the stability of readings.

[0036] Example 1:

[0037] This embodiment provides a method for constructing a freshness indicator label based on volatile metabolites driving colorimetric response, applicable to the freshness indication of refrigerated fish samples. The food packaging uses a composite packaging film, and the storage environment is refrigerated at 4°C. A first vent, with a diameter of 0.8 mm, is formed on the packaging film, communicating with the internal space of the packaging. An indicator label is also provided, comprising a gas-conducting layer, a colorimetric response layer, and a transparent readability layer. The gas-conducting layer uses a die-cuttable pressure-sensitive adhesive layer. A transverse gas-conducting channel, 1.2 mm wide and 0.18 mm deep, is formed within the gas-conducting layer on the side facing the colorimetric response layer, communicating with the transverse gas-conducting channel. The second vent, with a diameter of 0.6 mm, is formed on this side.

[0038] When laminating the indicator label to the packaging film, the projections of the first and second vents perpendicular to the packaging film are offset by 8mm, creating a transverse airflow path between them. A transparent reading layer, made of transparent polyester film, is positioned on the side of the color-response layer opposite to the airflow layer, allowing users to observe color changes in the color-response layer from the outside of the packaging. A sealed connection area is formed around the outer periphery of the airflow layer, ensuring that volatile metabolic components generated inside the packaging primarily enter the transverse airflow path through the first vent and then through the second vent into the color-response layer.

[0039] like Figure 2 As shown, the first vent is located on the packaging film side, and the second vent is located on the side of the air-guiding layer facing the color-response layer, and is connected to the transverse air-guiding channel. The two vents do not coincide in the vertical projection direction, but are connected in a staggered manner through the transverse air-guiding channel. The figure further illustrates the layering relationship of the packaging film, air-guiding layer, color-response layer, and transparent reading layer, as well as the structural state where the liquid-containing recess is set lower than the bottom surface of the transverse air-guiding channel. Therefore, volatile metabolic components can enter the color-response layer along the transverse path, while exudate or condensate preferentially falls into the liquid-containing recess, reducing the possibility of liquid entering the second vent along the gas path.

[0040] The color-responsive layer comprises a porous cellulose membrane and a color-developing composition loaded onto the porous cellulose membrane. The color-developing composition includes bromocresol green and polyvinyl alcohol (PVA) as a film-forming material. During preparation, bromocresol green is dispersed in a solution containing PVA, coated onto the surface of the porous cellulose membrane, and then dried. This allows the color-responsive layer to produce a visible color change upon contact with volatile amine metabolites generated from refrigerated fish samples.

[0041] A temporary release chamber is formed within the transverse air guide channel, located between the first and second air vents. The temporary release chamber is 10 mm long and 3 mm wide. Along the direction from the first to the second air vent, the temporary release chamber sequentially forms a background retention zone and a threshold release zone. The background retention zone is filled with 0.018 g of activated carbon fiber, and the threshold release zone is filled with 0.010 g of activated carbon fiber. The adsorption medium density in the background retention zone is greater than that in the threshold release zone, ensuring that low-flux volatile metabolic components generated during the initial stage of refrigeration are preferentially adsorbed and retained by the background retention zone.

[0042] A partition rib is installed within the temporary release chamber, dividing it into multiple interconnected retention units. Adjacent retention units are connected by communication gaps at the ends of the partition ribs, and activated carbon fibers are disposed within each retention unit. After volatile metabolic components enter the temporary release chamber, they pass through the multiple retention units sequentially and are adsorbed step-by-step by the activated carbon fibers within each retention unit, preventing background volatile metabolic components from directly impacting the color response layer.

[0043] A bypass slit is formed on the side of the temporary release chamber near the second vent. The bypass slit is formed by a local unbonded area near the second vent. After the activated carbon fiber adsorbs volatile metabolic components to a preset adsorption capacity, its retention effect on subsequent volatile metabolic components decreases, allowing volatile metabolic components exceeding the preset adsorption capacity to enter the second vent through the bypass slit and further enter the color response layer.

[0044] like Figure 3 As shown, the temporary storage and release chamber is arranged sequentially along the gas phase transfer direction, comprising a background retention zone, a threshold release zone, and a bypass slit. Separating ribs ensure that volatile metabolic components are progressively distributed across multiple retention units. The background retention zone contains a large mass of adsorbent medium, preferentially retaining low-flux volatile metabolic components. The threshold release zone is located at its rear end, used to continue buffering and guiding release after the background retention zone approaches saturation. The bypass slit is located near the second vent. When the adsorbent medium reaches its preset adsorption capacity, its retention effect on subsequent volatile metabolic components decreases, allowing them to enter the second vent through the bypass slit. This diagram clarifies the sequential relationship between temporary storage, retention, threshold release, and bypass exit.

[0045] The preset adsorption capacity is determined by the following formula:

[0046]

[0047] In the formula, This indicates the preset adsorption capacity of the adsorbed medium in the temporary storage and release chamber, in mg. This indicates the mass of the adsorption medium placed in the temporary release chamber, in grams. This represents the adsorption capacity of a unit mass of adsorption medium for the target volatile metabolic component, expressed in mg / g. This formula indicates the retention capacity of the temporary release chamber for background volatile metabolic components, determined by the mass of the adsorption medium and the unit adsorption capacity. In this embodiment, the mass of activated carbon fiber filling the background retention zone... The adsorption capacity of activated carbon fiber for trimethylamine is 0.018g. If we take 22 mg / g, then substituting it into the equation, we get:

[0048] mg

[0049] The background retention zone has a preset adsorption capacity of 0.396 mg for trimethylamine. When the cumulative amount of trimethylamine entering the temporary release chamber does not exceed 0.396 mg, trimethylamine is preferentially retained by the background retention zone; when the cumulative amount exceeds 0.396 mg, the subsequent volatile metabolites enter the threshold release zone and are released to the second vent.

[0050] A liquid self-isolating structure is formed between the first vent and the transverse air guiding channel. This structure includes a liquid-receiving recess, the bottom of which is 0.5 mm lower than the bottom of the transverse air guiding channel. A liquid-absorbing expansion element, made of cross-linked sodium polyacrylate absorbent resin sheet, is installed within the liquid-receiving recess. When exudate or condensate from the refrigerated fish sample reaches the vicinity of the first vent, it preferentially enters the liquid-receiving recess and contacts the liquid-absorbing expansion element. After absorbing the liquid, the expansion element expands, occupying the connecting area between the liquid-receiving recess and the transverse air guiding channel, thereby blocking the movement of liquid towards the second vent while allowing gaseous volatile metabolic components to continue entering the transverse air guiding channel.

[0051] To determine whether the chromaticity response layer produces a visually readable color change, the color difference response value is used for evaluation. The color difference response value is determined by the following formula:

[0052]

[0053] In the formula, This indicates the overall color difference of the chromaticity response layer before and after the response; This represents the brightness value of the chromaticity response layer in the Lab color space before the response. This indicates the red and green hue values ​​of the chromaticity response layer in the Lab color space before the response. This indicates the yellow-blue tint value of the chromaticity response layer in the Lab color space before response; This represents the brightness value of the chromaticity response layer in the Lab color space after the response. This represents the red and green hue values ​​of the chromaticity response layer in the Lab color space after the response. This represents the yellow-blue hue value of the chromaticity response layer in the Lab color space after the response. In this embodiment, the value measured before the response... It is 72.4. It is -5.8. It was 18.6; measured after the response. It is 61.2. It is 2.1. Substituting the value into the equation, we get:

[0054]

[0055] This indicates that the color response layer has produced color changes that are perceptible to the naked eye.

[0056] like Figure 4 As shown, the cumulative amount of trimethylamine gradually increases in the early detection stage, but before exceeding the preset adsorption capacity of 0.396 mg, it is mainly in the background retention stage, and the increase in overall color difference is relatively limited. When the detection stage enters the later stage, the cumulative amount of trimethylamine exceeds the preset adsorption capacity, and the temporary release chamber changes from the retention state to the threshold release state, and the overall color difference increases significantly, reaching about 15.5. This figure shows the corresponding relationship between the adsorption capacity threshold and the color response results, which can illustrate that the color change in this embodiment is not directly triggered by the initial background volatile metabolites, but occurs after the volatile metabolites accumulate to a set level.

[0057] During the storage of refrigerated fish samples, volatile amine metabolites generated inside the packaging enter the transverse air guiding channel through the first vent, and then pass through the liquid self-isolating structure and the temporary release chamber. Initially, background volatile metabolites are trapped by the background trapping zone and the adsorption medium in multiple retention units. When the volatile metabolites accumulate to a set level, the adsorption medium reaches its preset adsorption capacity and its trapping effect on subsequent volatile metabolites decreases. These subsequent volatile metabolites then enter the color response layer through the bypass gap and the second vent, causing a color change in the color response layer, which is then displayed through the transparent reading layer.

[0058] Therefore, in this embodiment, a transverse air guiding path is formed by the staggered arrangement of the first and second air vents. A step-by-step interception and threshold release structure is formed by the temporary release chamber, background interception area, threshold release area, multiple retention units and bypass gaps. Liquid self-isolation is achieved by the liquid containment recess and liquid absorption expansion component. This can reduce the interference of initial background volatiles and liquid wetting on the color response layer, so that the color change of the color response layer corresponds to the change in freshness of the refrigerated fish meat sample.

[0059] Example 2:

[0060] This embodiment provides a method for constructing a freshness indicator label based on volatile metabolites driving colorimetric response, applicable to the freshness indication of refrigerated chicken breast samples. The food packaging uses a composite packaging film, and the storage environment is refrigerated at 4°C. A first vent, with a diameter of 0.7 mm, is formed on the packaging film, communicating with the internal space of the packaging. An indicator label is also provided, comprising a gas-conducting layer, a colorimetric response layer, and a transparent readability layer. The gas-conducting layer uses a die-cuttable pressure-sensitive adhesive layer, forming a transverse gas-conducting channel with a width of 1.0 mm and a depth of 0.15 mm. A second vent, with a diameter of 0.6 mm, is formed on the side of the gas-conducting layer facing the colorimetric response layer, communicating with the transverse gas-conducting channel.

[0061] When laminating the indicator label to the packaging film, the projections of the first and second vents in the direction perpendicular to the packaging film are offset by a distance of 6mm. This allows volatile metabolic components generated inside the packaging to enter the transverse air guide channel through the first vent and flow along the transverse air guide channel to the second vent. A transparent reading layer is located on the side of the color-response layer opposite to the air guide layer. The transparent reading layer is made of transparent polyester film, allowing color changes in the color-response layer to be read from the outside of the packaging.

[0062] The color-responsive layer is a circular porous cellulose membrane with a diameter of 12 mm. A color-developing composition, including bromophenol blue, chitosan, and film-forming aids, is loaded onto the circular porous cellulose membrane. During preparation, the color-developing composition is uniformly coated onto the circular porous cellulose membrane and dried to form a color-responsive layer that can react colorimetrically with volatile amine metabolites produced by refrigerated chicken breast samples.

[0063] A peripheral air distribution cavity is formed between the second vent and the color response layer. The peripheral air distribution cavity extends along the periphery of the color response layer and has a width of 0.8 mm. Volatile metabolic components entering through the second vent first enter the peripheral air distribution cavity, and then enter the color response layer from the periphery side, so that the volatile metabolic components do not directly concentrate and impact the central area of ​​the color response layer.

[0064] like Figure 5 As shown, the projections of the first vent and the second vent in the direction perpendicular to the packaging film are staggered. The transverse air guide channel connects the internal space of the packaging with the second vent, and the second vent is then connected to the peripheral air distribution cavity set around the periphery of the color response layer. Figure 5 The diagram also shows the air intake branches formed by the peripheral air distribution chamber on opposite sides of the color response layer. Volatile metabolic components enter through the second vent and are guided to the left and right sides of the color response layer, and then diffuse from the sides towards the center. This structure allows the gas to be distributed peripherally before entering the color response layer, reducing premature local color development caused by single-point air intake.

[0065] The peripheral gas distribution chamber forms two air intake branches on opposite sides of the color response layer, located on the left and right sides of the layer, respectively, with their ends not connected. Volatile metabolic components enter the peripheral gas distribution chamber and are distributed into the two air intake branches, diffusing from opposite sides of the color response layer towards the center. This allows the sides of the color response layer to receive gas phase input first, gradually producing continuous color development towards the center.

[0066] Multiple lateral inlets are formed between the peripheral air distribution cavity and the color response layer, and these lateral inlets are spaced apart along the periphery of the color response layer. In this embodiment, each air intake branch has four lateral inlets, which are slit-shaped. Along the direction away from the second vent, the opening widths of the four lateral inlets are 0.30mm, 0.40mm, 0.50mm, and 0.60mm respectively, and the opening height of each lateral inlet is 0.20mm, thus relatively increasing the air intake area away from the second vent.

[0067] like Figure 6 As shown, the peripheral air distribution chamber is unfolded into a channel structure extending along the gas phase migration direction. The second vent is located on the inlet side, and multiple lateral guide inlets are arranged sequentially in a direction away from the second vent. The opening width of each lateral guide inlet increases progressively, and the opening area of ​​the distal lateral guide inlet is larger than that of the proximal lateral guide inlet, so that the distal region can still obtain effective air intake after the gas flux decays. Figure 6 The diagram also shows the state in which the lateral guide inlets are deflected in sequence, and the volatile metabolic components enter the surface of the color response layer to form a circumferentially distributed guide diffusion path, thereby expanding the contact range with the color response layer.

[0068] The opening area of ​​the side guide inlet is determined by the following formula:

[0069]

[0070] In the formula, This represents the opening area of ​​the i-th side guide inlet, in mm². This represents the opening width of the i-th side guide entrance, in mm; This represents the opening height of the i-th side guide inlet, in mm; i represents the sequence number of the side guide inlet along the direction away from the second vent. This formula is used to determine the actual air intake area at the corresponding position based on the width and height of the side guide inlet.

[0071] In the first side guide inlet near the second vent It is 0.30mm. Substituting the value as 0.20mm, we get:

[0072]

[0073] In the fourth side guide inlet, located away from the second vent. It is 0.60mm. Substituting the value as 0.20mm, we get:

[0074]

[0075] As can be seen from the above data, the opening area of ​​the fourth lateral guide inlet is larger than that of the first lateral guide inlet. The position farthest from the second vent can obtain lower air intake resistance, thereby compensating for the flux attenuation of volatile metabolic components during the flow of the peripheral air distribution cavity, so that different positions around the chromaticity response layer can obtain a relatively balanced gas phase input.

[0076] The orientation of the multiple lateral guide inlets is sequentially deflected along the periphery of the chromaticity response layer. In this embodiment, along the direction away from the second vent, the deflection angles of the four lateral guide inlets relative to the radial direction of the chromaticity response layer are 15°, 25°, 35°, and 45°, respectively. After volatile metabolic components enter the surface of the chromaticity response layer through the lateral guide inlets, they not only diffuse into the interior of the chromaticity response layer but also generate a deflection-guided diffusion effect along the surface of the chromaticity response layer, thereby expanding the contact area between the volatile metabolic components and the chromaticity response layer.

[0077] To evaluate the color uniformity at different detection locations on the colorimetric response layer, a color uniformity coefficient is used for characterization. This color uniformity coefficient is determined by the following formula:

[0078]

[0079] In the formula, R represents the color uniformity coefficient between different detection locations in the colorimetric response layer; Δ Δ represents the minimum color difference value among multiple detection locations. This represents the maximum color difference value among multiple detection locations. The closer R is to 1, the more uniform the color rendering is across different locations in the chromaticity response layer. ΔE is the color difference value before and after the chromaticity response layer's response, which can be obtained from the Lab color parameters.

[0080] In this embodiment, color difference values ​​were detected at the left, right, and center positions of the color response layer, respectively, and the corresponding ΔE values ​​were measured to be 13.8, 14.6, and 12.9, respectively. It is 12.9, Δ Substituting 14.6, we get:

[0081]

[0082] like Figure 7As shown, the overall color difference at the three detection positions on the left, right and center of the color response layer is in a similar range. The color difference value at the right detection position is 14.6 and the color difference value at the center detection position is 12.9. These two values ​​are used to calculate the color uniformity coefficient R. Figure 7 By displaying the color difference at different locations using column height, average color difference line, and balanced color rendering area, it can be shown that the color response layer does not exhibit significant color rendering deviation due to excessive unilateral strength or insufficient central strength under the effects of dual-sided air intake, far-end area compensation, and deflection-guided diffusion.

[0083] In this embodiment, the staggered connection between the first and second vents forms a transverse air guiding path. The volatile metabolic components entering through the second vent are dispersed to the periphery of the color response layer by the peripheral air distribution cavity. The two-sided diffusion towards the center is achieved by the air intake branches on both sides. The increased opening area of ​​the distal lateral guide inlet compensates for the flux attenuation. The sequentially deflected lateral guide inlets form a guiding diffusion path, thereby improving the uniformity, continuity, and reading stability of the color change of the color response layer.

Claims

1. A method for constructing a freshness indicator label based on color response driven by volatile metabolites, characterized in that, include: A packaging film for food packaging is provided, wherein a first vent is formed on the packaging film communicating with the internal space of the packaging; An indicator label is provided, the indicator label including an air guiding layer, a colorimetric response layer and a transparent reading layer, a transverse air guiding channel is formed in the air guiding layer, and a second vent is formed on the side of the air guiding layer facing the colorimetric response layer, communicating with the transverse air guiding channel, such that the transparent reading layer is located on the side of the colorimetric response layer away from the air guiding layer; The indicator label is laminated with the packaging film, so that the first vent is connected to the transverse air channel, and the projections of the first vent and the second vent in the direction perpendicular to the packaging film are staggered. This allows volatile metabolic components in the internal space of the packaging to enter the transverse air channel through the first vent, and then enter the color response layer through the second vent, thereby driving the color response layer to produce a color change that can be observed by the transparent readout layer.

2. The construction method according to claim 1, characterized in that, A temporary storage and release chamber is formed within the transverse air guide channel. The temporary storage and release chamber is located between the first air vent and the second air vent. An adsorption medium with a preset adsorption capacity is provided in the temporary storage and release chamber. After the adsorption medium adsorbs volatile metabolic components to the preset adsorption capacity, the volatile metabolic components exceeding the preset adsorption capacity enter the color response layer.

3. The construction method according to claim 1, characterized in that, A liquid self-isolating structure is formed between the first vent and the transverse air guiding channel. The liquid self-isolating structure has a liquid receiving recess lower than the bottom surface of the transverse air guiding channel. A liquid-absorbing expansion member is provided in the liquid receiving recess. The liquid-absorbing expansion member expands after contacting the food exudate or condensate to restrict the food exudate or condensate from moving along the transverse air guiding channel toward the second vent.

4. The construction method according to claim 1, characterized in that, A peripheral air distribution cavity is formed between the second vent and the color response layer. The peripheral air distribution cavity extends along the periphery of the color response layer, so that volatile metabolic components entering through the second vent enter from the periphery of the color response layer and drive the color response layer to produce a color change.

5. The construction method according to claim 2, characterized in that, The temporary release chamber is formed sequentially with a background retention area and a threshold release area along the direction from the first vent to the second vent. The adsorption medium filling density in the background retention area is greater than that in the threshold release area, so that volatile metabolic components that enter the temporary release chamber and have a flux lower than a preset flux threshold are preferentially retained in the background retention area.

6. The construction method according to claim 2, characterized in that, A bypass slit is formed on the side of the temporary release chamber near the second vent. After the adsorption medium adsorbs volatile metabolic components to a preset adsorption capacity, volatile metabolic components exceeding the preset adsorption capacity enter the color response layer through the bypass slit.

7. The construction method according to claim 2, characterized in that, The temporary release chamber is provided with a partition rib, which divides the temporary release chamber into multiple interconnected retention units. The adsorption medium is respectively disposed in the multiple retention units. Volatile metabolic components are released from the retention unit near the second vent after passing through the retention units in sequence.

8. The construction method according to claim 4, characterized in that, The peripheral air distribution cavity forms air intake branches on opposite sides of the color response layer. The ends of the two air intake branches are not connected to each other, so that volatile metabolic components diffuse from opposite sides of the color response layer toward the center.

9. The construction method according to claim 4, characterized in that, Multiple lateral guide inlets are formed between the peripheral air distribution cavity and the color response layer. The multiple lateral guide inlets are spaced apart along the periphery of the color response layer, and the opening area of ​​the lateral guide inlets increases sequentially in the direction away from the second air vent.

10. The construction method according to claim 9, characterized in that, The orientation of the plurality of lateral guide inlets is sequentially deflected along the periphery of the chromaticity response layer, so that volatile metabolic components entering through the lateral guide inlets form circumferentially distributed guided diffusion paths on the surface of the chromaticity response layer.

Images