A water-absorbing liner with fish freshness indication function and its application

Abstract

An absorbent pad with fish freshness indication function and its application are disclosed. The absorbent pad includes a permeable layer and an absorbent layer arranged vertically, with an indicator area on one side of the absorbent layer. The permeable layer is a perforated polyethylene film used to absorb fish juices and prevent the fish from sticking to the absorbent layer after spoilage. The absorbent layer is made of wood pulp cellulose, which absorbs the fish juices while allowing them to enter the indicator area, thus enabling direct interaction between the fish juices and the indicator in the indicator area. The advantages are: the absorbent pad can absorb the juices released during the chilled storage of fish, and the color of the indicator area changes with the freshness of the fish, indicating the freshness level of the fish. The indication result is not easily affected by environmental factors and has good accuracy.

Description

Technical Field

[0001] This invention belongs to the field of food packaging, specifically relating to an absorbent liner with fish freshness indication function and its application. Background Technology

[0002] With rising living standards and increasing consumer awareness, there are higher and higher hygiene requirements for the packaging of fresh fish. Pallet packaging of fresh fish has become a common form of packaging in large chain supermarkets and fresh food distribution centers. However, fish will seep out juices during storage, which not only reduces the sensory quality and marketability of the fish, but also leads to higher relative humidity in the microenvironment, promoting microbial growth and shortening the shelf life of fresh fish.

[0003] Absorbent pads effectively absorb the juices that seep out of fish during storage. Typically, a suitably sized sheet of absorbent pad is placed at the bottom of a tray, the fish is placed on top, and then sealed with plastic wrap. However, during refrigeration, the proteins and unsaturated fatty acids in fish are acted upon by microorganisms, leading to protein decomposition and fat oxidation. This not only affects the quality of the fish but can also cause foodborne illnesses, endangering consumer safety. Therefore, real-time monitoring of the freshness of fish during transportation and storage is of significant practical importance. Currently, absorbent pads available domestically and internationally only function to absorb seepage; absorbent pads with fish freshness indicators have not yet been reported.

[0004] Currently, research on fish freshness indication both domestically and internationally mainly focuses on indicator labels and cards, which are typically placed in the headspace of tray packaging. They interact with volatile freshness markers in the headspace to indicate freshness. However, this method is indirect and suffers from problems such as unsatisfactory accuracy and susceptibility to environmental interference. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an absorbent pad with a fish freshness indicator function and its application. The absorbent pad can absorb the juices that leach out during the ice storage of fish meat, and the color of the indicator area of ​​the absorbent pad changes with the freshness of the fish meat to indicate the freshness level of the fish meat. The indication result is not easily affected by environmental factors and has good accuracy.

[0006] The technical solution of this invention is:

[0007] A water-absorbing pad with fish freshness indication function is characterized in that: the water-absorbing pad includes a permeable layer and an absorbent layer arranged vertically, and an indicator area is provided on one side of the absorbent layer; the permeable layer is a perforated polyethylene film, used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after spoilage; the absorbent layer is made of wood pulp cellulose, which absorbs the fish juice while allowing the fish juice to enter the indicator area, thereby allowing the fish juice to directly interact with the indicator in the indicator area.

[0008] The preparation process of the indicator area is as follows:

[0009] (1) Preparation of coating solution for indicator area

[0010] The indicator fixative carrier is dissolved in deionized water, and glycerol is added as a plasticizer. The mixture is stirred until homogeneous to obtain a mixed solution. The mass-to-volume ratio of the indicator fixative carrier to deionized water is 1:20 g / mL, and the mass ratio of the indicator fixative carrier to glycerol is 1:1. The indicator fixative carrier is polyvinyl alcohol, sodium alginate, or zein.

[0011] After the mixed solution has cooled, add brilliant blue solution and alizarin ethanol solution in sequence. The mass ratio of polyvinyl alcohol to brilliant blue in the brilliant blue solution and alizarin in the alizarin ethanol solution is 1000:3 and 1000:12-1000:48, respectively. Stir well to obtain the indicator area coating solution.

[0012] (2) Preparation of the indicator area of ​​the absorbent pad

[0013] Apply the solution to the indicator area at a rate of 0.1 mL / cm. 2 A uniform coating is applied to the indicator area of ​​the absorbent layer, and then dried to obtain an absorbent liner that indicates the freshness of the fish.

[0014] Furthermore, the indicator immobilizer is polyvinyl alcohol, and the mass ratio of brilliant blue to alizarin is 1:8.

[0015] Furthermore, in step (1), when the indicator fixative carrier is dissolved in deionized water, it is heated and stirred at 95°C for 30 min; in step (2), the drying temperature is 37°C.

[0016] Furthermore, the concentration of the brilliant blue solution is 1 mg / mL, and the concentration of the alizarin ethanol solution is 1 mg / mL.

[0017] Furthermore, the length of the indicator area is 2cm and the width is 1cm.

[0018] On the other hand, the application of the aforementioned absorbent pad with fish freshness indication function in detecting fish freshness is characterized by:

[0019] Includes the following steps:

[0020] (1) Preparation of standard colorimetric cards

[0021] A water-absorbing pad with fish freshness indication function was placed in a fresh food tray. Fresh fish was placed in the center of the water-permeable layer of the water-absorbing pad with fish freshness indication function. Based on the TVB-N value of the fish at different freshness levels, the L, a, and b values ​​of the water-absorbing pad indication area under natural light were extracted as feature values. A standard colorimetric card was made based on the Lab value of the freshness grade threshold.

[0022] (2) Place the absorbent pad with fish freshness indicator function in the fresh food tray, place the fish in the center of the absorbent layer of the pad, and seal the tray; under natural light, compare the indicator area of ​​the absorbent pad with fish freshness indicator function with the standard color chart to determine the freshness of the fish during the storage stage and complete the real-time freshness detection of the fish.

[0023] Furthermore, when preparing a standard color chart based on the TVB-N value of fish meat at different freshness levels, the TVB-N values ​​were selected as 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, respectively.

[0024] Furthermore, when determining the freshness of fish during storage, a TVB-N value <15mg / 100g indicates freshness, 25mg / 100g > TVB-N value ≥15mg / 100g indicates acceptable quality, and TVB-N ≥25mg / 100g indicates spoilage.

[0025] Furthermore, under natural light, the color of the fish can be compared with that of a standard color chart to determine the freshness of the fish during storage. When the indicator area is light green as shown in the standard color chart, the fish is fresh. When the indicator area is reddish-brown as shown in the standard color chart, the fish is moderately fresh. When the indicator area is dark purple as shown in the standard color chart, the fish is spoiled.

[0026] Furthermore, based on the color change of the water-absorbing liner indicator area with fish freshness indication function, the ΔE value is extracted. Combined with the linear fitting equation y=2.1124x-7.1348, the fitting formula calculates the TVB-N value for that period.

[0027] The beneficial effects of this invention are:

[0028] (1) The absorbent pad with fish freshness indication function not only has the function of absorbing the juices that seep out during the ice storage of fish meat; the absorbent pad with fish freshness indication function can directly interact with the juices seeping out of the fish meat, so that the color of the indicator area of ​​the absorbent pad changes with the freshness of the fish meat, and finally realizes the indication of the freshness level of the fish meat; it interacts directly with the juices, rather than being placed in the headspace, so the color change speed is faster, the indication result is not easily affected by environmental factors, and the accuracy is good.

[0029] (2) Using alizarin and brilliant blue as a composite indicator can make the color change more obvious and the sensitivity higher; in particular, the color of the pad indicator area constructed by the alizarin / brilliant blue composite indicator with a mass ratio of 1:8 changes from green to brownish-red and then to dark purple, with stronger color change contrast, making it more suitable for naked-eye recognition. Attached Figure Description

[0030] Figure 1 This is a color change diagram of the absorbent pad with different proportions of indicator brilliant blue and alizarin in the coating solution of the indicator area of ​​the present invention (corresponding to Examples 1-3) as TVB-N changes;

[0031] Figure 2 These are photographs showing the color change of the indicator area of ​​the absorbent pad with different fixed carriers for the indicator in the indicator area of ​​the present invention (corresponding to Embodiments 1, 4 and 5) as TVB-N changes;

[0032] Figure 3 This is a UV full-wavelength scan of the absorbent pad of the present invention (corresponding to Example 1) after being soaked in different solvents;

[0033] Figure 4 This is a scanning electron microscope image of the absorbent pad (wood pulp cellulose-polyvinyl alcohol-indicator pad) of the present invention (corresponding to Example 1) at magnification of 3.0 kV;

[0034] Figure 5 This is a scanning electron microscope image of the wood pulp cellulose absorbent pad of the present invention at magnification of 3.0 kV;

[0035] Figure 6 This is a scanning electron microscope image of the absorbent pad (wood pulp cellulose-polyvinyl alcohol-based pad) of the present invention (corresponding to Example 1) at magnification of 3.0 kV.

[0036] Figure 7 This is the standard colorimetric card for the indicator area of ​​the absorbent pad of this invention;

[0037] Figure 8 This is a schematic diagram illustrating the application of the absorbent pad of the present invention;

[0038] Figure 9 This is an evaluation chart showing the accuracy of the water-absorbing pad of the present invention in detecting fish freshness. Detailed Implementation

[0039] Example 1

[0040] (1) Preparation of coating solution for indicator area

[0041] Weigh 1g of polyvinyl alcohol and add it to 20mL of deionized water. Heat and stir at 95℃ for 30min to fully dissolve it. Add 1g of glycerol as a plasticizer and stir until the mixture is homogeneous to obtain a mixed solution. After the mixed solution cools, add 3mL of 1mg / mL brilliant blue solution and 24mL of 1mg / mL alizarin ethanol solution in sequence, and continue stirring for 30min to obtain the indicator area coating solution.

[0042] (2) Preparation of the indicator area of ​​the absorbent pad

[0043] Apply a 0.2 mL coating of the indicator area solution evenly to the indicator area (indicator area area is 2 cm²) on the wood pulp cellulose liner. 2 Place the coated gasket on a polyethylene plate and dry it in a 37°C oven.

[0044] (3) Assembly of absorbent pad with fish freshness indicator function

[0045] like Figure 8 As shown, the pad includes a permeable layer and an absorbent layer arranged vertically. An indicator area is located on one side of the absorbent layer. The indicator area is 2 cm long and 1 cm wide. The permeable layer is made of commercially available perforated polyethylene (PE) film, which is used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is a wood pulp cellulose absorbent pad, which absorbs the fish juice while allowing the fish juice to enter the indicator area, so that the fish juice can directly interact with the indicator in the indicator area. The indicator area is prepared according to step (2) to obtain an absorbent pad with the function of indicating fish freshness.

[0046] (4) Preparation of standard colorimetric cards

[0047] At a constant temperature of 4℃, the TVB-N content was measured at regular intervals. When the TVB-N content was 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, the water-absorbing liner indicator area with fish freshness indication function was photographed using an imaging device. The L, a, and b values ​​of the liner indicator area photographs were extracted as feature values ​​using Photoshop software. Based on the Lab value of the freshness grade threshold, a standard colorimetric card for the liner indicator area was created. Figure 7 As shown;

[0048] (5) Application of absorbent pads with fish freshness indication function

[0049] Place the liner inside the fresh food tray, place the fish sample in the central sample placement area of ​​the liner's permeable layer, and then seal the tray.

[0050] TVB-N was used to determine the colorimetric region corresponding to the freshness of marine fish. As the storage time of fish samples increased, the TVB-N content gradually increased. The selection criteria for the critical points in this invention were as follows: the freshness grades selected by the sensor label were: TVB-N value <15mg / 100g for freshness, 25mg / 100g > TVB-N value ≥15mg / 100g for acceptable quality, and TVB-N ≥25mg / 100g for spoilage. (National standards stipulate that when the TVB-N content is below 15mg / 100g, the fish is considered superior fresh; when the TVB-N content is between 15mg / 100g and 30mg / 100g, the fish is considered acceptable; when the TVB-N content is above 30mg / 100g, the fish sample has spoiled; while internationally, a TVB-N content above 25mg / 100g is generally considered to indicate that the food has entered the spoilage stage.)

[0051] (6) Determining the freshness of fish

[0052] Under natural light, the freshness of fish during storage can be determined by comparing its color with a standard color chart. When the indicator area is light green, the fish is fresh; when the indicator area is reddish-brown, the fish is moderately fresh; and when the indicator area is dark purple, the fish is spoiled.

[0053] An absorbent pad with fish freshness indication function is placed in a PET tray. Fresh fish is placed on the sample area of ​​the pad, and the PET tray is sealed with plastic wrap. During storage, the absorbent pad absorbs the juices exuded from the fish, and the TVB-N in the juices interacts with the coating in the indication area. Figure 1 As shown, as the TVB-N value increases, the color of the pad indicator area gradually changes from light green to dark purple under visible light.

[0054] Fish freshness assessment: Under visible light, the freshness of the fish can be judged by the color change of the indicator area on the absorbent pad that indicates fish freshness. Light green indicates fresh, reddish-brown indicates slightly fresh, and dark purple indicates not fresh.

[0055] I. Leakage Analysis of Brilliant Blue / Alizarin Indicator

[0056] To determine whether the brilliant blue / alizarin indicator was fixed to the indicator area of ​​the freshness indicator absorbent pad, a release test was conducted on the pad's indicator area. The test results are as follows: Figure 3 As shown; by Figure 3 It was found that after 12 hours, the absorbance values ​​of the UV-Vis absorption curves of water, 75wt% ethanol, and 100wt% ethanol, which had respectively immersed the indicator area of ​​the liner, were close to 0, and the resulting filtrate was clear and transparent, indicating that there was almost no indicator in the filtrate. These results indicate that the brilliant blue / alizarin sensing indicator has been stably fixed on the indicator area of ​​the liner with almost no leakage.

[0057] II. Determination of water volume in absorbent pads with fish freshness indication function

[0058] As absorbent pads for aquatic product packaging, measuring their absorbency is crucial, as it reflects their maximum moisture absorption capacity. The absorbency of the absorbent pad in Example 1, which indicates fish freshness, was measured to have an average absorbency of 0.0204 g / cm². 2 .

[0059] III. Accuracy Evaluation of Absorbent Liners with Fish Freshness Indication Function

[0060] A water-absorbing liner with a fish freshness indicator function was applied to monitor the freshness of three different batches of small yellow croaker to verify the effectiveness of the liner's indicator area in monitoring fish freshness. The color change of the liner's indicator area was as follows: Figure 9 As shown, with the increasing storage time of the small yellow croaker, the color of the indicator area on the absorbent pad of the first batch of samples gradually changed from light green to reddish-brown, and then to dark purple. Based on the color change of the indicator pad, the ΔE value was extracted, and combined with the linear fitting equation y = 2.1124x - 7.1348, the TVB-N content was further quantitatively calculated. When the indicator pad turned reddish-brown, the calculated TVB-N was 18.13 mg / 100g; when the indicator pad turned dark purple, the calculated TVB-N was 27.56 mg / 100g. To further verify the accuracy of the indicator results, the TVB-N content of the samples was determined according to the national standard method. When the pad was reddish-brown, the measured TVB-N content was 18.04 ± 0.63 mg / 100g. After a period of continued storage, the color of the pad completely turned dark purple, and the actual measured TVB-N content at this time was 27.91 ± 1.30 mg / 100g. A significance analysis was performed between the calculated values ​​and the values ​​measured using the national standard method. The results showed no significant difference, proving that the monitoring results of the indicator area of ​​the absorbent liner are accurate and reliable. Subsequently, the same method was used to measure and analyze two other batches of samples, and the results showed that the actual measured values ​​were not significantly different from the TVB-N calculated based on the linear fitting equation. In summary, the absorbent liner with fish freshness indication function prepared by this invention can effectively monitor the freshness of fish.

[0061] Example 2

[0062] (1) Preparation of coating solution for indicator area

[0063] Weigh 1g of polyvinyl alcohol and add it to 20mL of deionized water. Heat and stir at 95℃ for 30min to fully dissolve it. Add 1g of glycerol as a plasticizer and stir until the mixture is homogeneous to obtain a mixed solution. After the mixed solution cools, add 3mL of 1mg / mL brilliant blue solution and 48mL of 1mg / mL alizarin ethanol solution in sequence, and continue stirring for 30min to obtain the indicator area coating solution.

[0064] (2) Preparation of the indicator area of ​​the absorbent pad

[0065] Apply a 0.2 mL coating of the indicator area solution evenly to the indicator area (indicator area area is 2 cm²) on the wood pulp cellulose liner. 2 The coated pad is placed on a polyethylene plate and dried in a 37°C oven to prepare an absorbent pad with fish freshness indication function.

[0066] (3) Assembly of absorbent pad with fish freshness indicator function

[0067] like Figure 8 As shown, the pad includes a permeable layer and an absorbent layer arranged vertically. An indicator area is located on one side of the absorbent layer. The indicator area is 2 cm long and 1 cm wide. The permeable layer is made of commercially available perforated polyethylene (PE) film, which is used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is a wood pulp cellulose absorbent pad, which absorbs the fish juice while allowing the fish juice to enter the indicator area, so that the fish juice can directly interact with the indicator in the indicator area. The indicator area is prepared according to step (2) to obtain an absorbent pad with the function of indicating fish freshness.

[0068] (4) Preparation of standard colorimetric cards

[0069] At a constant temperature of 4℃, the TVB-N content was measured at regular intervals. When the TVB-N content was 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, the water-absorbing liner indicator area with fish freshness indication function was photographed using a photographic device. The L, a, and b values ​​of the liner indicator area photograph were extracted as feature values ​​using Photoshop software. Based on the Lab value of the freshness grade critical point, a standard colorimetric card of the liner indicator area was made.

[0070] (5) Application of absorbent pads with fish freshness indication function

[0071] An absorbent pad with fish freshness indication function is placed in a PET tray. Fresh fish is placed on the sample area of ​​the pad, and the PET tray is sealed with plastic wrap. During storage, the absorbent pad absorbs the juices exuded from the fish, and these juices interact with the indication area of ​​the pad. Figure 1 As shown, as the TVB-N value increases, the color of the pad indicator area gradually changes from the initial light green to grayish-purple; when the TVB-N value is higher than 24.90 mg / 100g, the color completely turns grayish-purple and remains unchanged.

[0072] Example 3

[0073] (1) Preparation of coating solution for indicator area

[0074] Weigh 1g of polyvinyl alcohol and add it to 20mL of deionized water. Heat and stir at 95℃ for 30min to fully dissolve it. Add 1g of glycerol as a plasticizer and stir until the mixture is homogeneous to obtain a mixed solution. After the mixed solution cools, add 3mL of 1mg / mL brilliant blue solution and 12mL of 1mg / mL alizarin ethanol solution in sequence, and continue stirring for 30min to obtain the indicator area coating solution.

[0075] (2) Preparation of the indicator area of ​​the absorbent pad

[0076] Apply a 0.2 mL coating of the indicator area solution evenly to the indicator area (indicator area area is 2 cm²) on the wood pulp cellulose liner. 2 The coated pad is placed on a polyethylene plate and dried in a 37°C oven to prepare an absorbent pad with fish freshness indication function.

[0077] (3) Assembly of absorbent pad with fish freshness indicator function

[0078] like Figure 8 As shown, the pad includes a permeable layer and an absorbent layer arranged vertically. An indicator area is located on one side of the absorbent layer. The indicator area is 2 cm long and 1 cm wide. The permeable layer is made of commercially available perforated polyethylene (PE) film, which is used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is a wood pulp cellulose absorbent pad, which absorbs the fish juice while allowing the fish juice to enter the indicator area, so that the fish juice can directly interact with the indicator in the indicator area. The indicator area is prepared according to step (2) to obtain an absorbent pad with the function of indicating fish freshness.

[0079] (4) Preparation of standard colorimetric cards

[0080] At a constant temperature of 4℃, the TVB-N content was measured at regular intervals. When the TVB-N content was 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, the water-absorbing liner indicator area with fish freshness indication function was photographed using a photographic device. The L, a, and b values ​​of the liner indicator area photograph were extracted as feature values ​​using Photoshop software. Based on the Lab value of the freshness grade critical point, a standard colorimetric card of the liner indicator area was made.

[0081] (5) Application of absorbent pads with fish freshness indication function

[0082] An absorbent pad with fish freshness indication function is placed in a PET tray. Fresh fish is placed on the sample area of ​​the pad, and the PET tray is sealed with plastic wrap. During storage, the absorbent pad absorbs the juices exuded from the fish, and these juices interact with the indication area of ​​the pad. Figure 1 As shown, as the TVB-N value increases, the color of the pad indicator area gradually changes from the initial dark green to brown, and when the TVB-N value exceeds 24.90 mg / 100g, the color turns into dark purple.

[0083] Depend on Figure 1 It was observed that when the pad indicator area was prepared using a sensor indicator solution with a brilliant blue / alizarin mass ratio of 1:16 (Example 2), the color of the pad indicator area gradually changed from the initial light green to grayish-purple as the TVB-N value increased; when the TVB-N value was higher than 24.90 mg / 100g, the color completely turned grayish-purple and remained unchanged. When the pad indicator area was prepared using an indicator solution with a brilliant blue / alizarin mass ratio of 1:8 (Example 1), the color of the pad indicator area gradually changed from the initial light green to reddish-brown; with the increase of TVB-N content, it eventually turned dark purple. When the pad indicator area was prepared using an indicator solution with a brilliant blue / alizarin mass ratio of 1:4 (Example 3), the color of the pad indicator area gradually changed from the initial dark green to brown; when the TVB-N value exceeded 24.90 mg / 100g, the color turned dark purple.

[0084] By comparing the color changes of the pad indicator areas in Examples 1-3, it can be found that the color changes of the pad indicator areas prepared with an indicator solution of Brilliant Blue / Alizarin in a ratio of 1:8 are more regular and distinct, and the color contrast of the pad indicator areas is strongest when the TVB-N content is at different freshness grade thresholds.

[0085] Example 4

[0086] (1) Preparation of coating solution for indicator area

[0087] Weigh 1g of sodium alginate and add it to 20mL of deionized water. Heat and stir at 95℃ for 30min to dissolve it completely. Add 1g of glycerol as a plasticizer and stir until the mixture is homogeneous to obtain a mixed solution. After the mixed solution cools, add 3mL of 1mg / mL brilliant blue solution and 24mL of 1mg / mL alizarin ethanol solution in sequence, and continue stirring for 30min to obtain the indicator area coating solution.

[0088] (2) Preparation of the indicator area of ​​the absorbent pad

[0089] Apply a 0.2 mL coating of the indicator area solution evenly to the indicator area (indicator area area is 2 cm²) on the wood pulp cellulose liner. 2 The coated pad is placed on a polyethylene plate and dried in a 37°C oven to prepare an absorbent pad with fish freshness indication function.

[0090] (3) Assembly of absorbent pad with fish freshness indicator function

[0091] like Figure 8 As shown, the pad includes a permeable layer and an absorbent layer arranged vertically. An indicator area is located on one side of the absorbent layer. The indicator area is 2 cm long and 1 cm wide. The permeable layer is made of commercially available perforated polyethylene (PE) film, which is used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is a wood pulp cellulose absorbent pad, which absorbs the fish juice while allowing the fish juice to enter the indicator area, so that the fish juice can directly interact with the indicator in the indicator area. The indicator area is prepared according to step (2) to obtain an absorbent pad with the function of indicating fish freshness.

[0092] (4) Preparation of standard colorimetric cards

[0093] At a constant temperature of 4℃, the TVB-N content was measured at regular intervals. When the TVB-N content was 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, the water-absorbing liner indicator area with fish freshness indication function was photographed using a photographic device. The L, a, and b values ​​of the liner indicator area photograph were extracted as feature values ​​using Photoshop software. Based on the Lab value of the freshness grade critical point, a standard colorimetric card of the liner indicator area was made.

[0094] (5) Application of absorbent pads with fish freshness indication function

[0095] An absorbent pad with fish freshness indication function is placed in a PET tray. Fresh fish is placed on the sample area of ​​the pad, and the PET tray is sealed with plastic wrap. During storage, the absorbent pad absorbs the juices exuded from the fish, interacting with the coating of the indication area. Figure 1 As shown, with the continuous increase of TVB-N value, the initial color of the pad indicator area under visible light is light green, and then turns brown; when the TVB-N content exceeds 25mg / 100g, the color of the indicator area is grayish-purple; as the TVB-N content continues to increase, the color of the pad indicator area no longer changes.

[0096] Example 5

[0097] (1) Preparation of coating solution for indicator area

[0098] Weigh 1g of zein and place it in 20mL of deionized water. Heat and stir at 95℃ for 30min to fully dissolve it. Add 1g of glycerol as a plasticizer and stir until well mixed to obtain a mixed solution. After the mixed solution cools, add 3mL of 1mg / mL brilliant blue solution and 24mL of 1mg / mL alizarin ethanol solution in sequence, and continue stirring for 30min to obtain the indicator area coating solution.

[0099] (2) Preparation of the indicator area of ​​the absorbent pad

[0100] Apply a 0.2 mL coating of the indicator area solution evenly to the indicator area (indicator area area is 2 cm²) on the wood pulp cellulose liner. 2 The coated pad is placed on a polyethylene plate and dried in a 37°C oven to prepare an absorbent pad with fish freshness indication function.

[0101] (3) Assembly of absorbent pad with fish freshness indicator function

[0102] like Figure 8 As shown, the pad includes a permeable layer and an absorbent layer arranged vertically. An indicator area is located on one side of the absorbent layer. The indicator area is 2 cm long and 1 cm wide. The permeable layer is made of commercially available perforated polyethylene (PE) film, which is used to permeate the fish juice produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is a wood pulp cellulose absorbent pad, which absorbs the fish juice while allowing the fish juice to enter the indicator area, so that the fish juice can directly interact with the indicator in the indicator area. The indicator area is prepared according to step (2) to obtain an absorbent pad with the function of indicating fish freshness.

[0103] (4) Preparation of standard colorimetric cards

[0104] At a constant temperature of 4℃, the TVB-N content was measured at regular intervals. When the TVB-N content was 6mg / 100g, 8mg / 100g, 15mg / 100g, 16mg / 100g, 19mg / 100g, 23mg / 100g, 25mg / 100g, and 29mg / 100g, the water-absorbing liner indicator area with fish freshness indication function was photographed using a photographic device. The L, a, and b values ​​of the liner indicator area photograph were extracted as feature values ​​using Photoshop software. Based on the Lab value of the freshness grade critical point, a standard colorimetric card of the liner indicator area was made.

[0105] (5) Application of absorbent pads with fish freshness indication function

[0106] An absorbent pad with fish freshness indication function is placed in a PET tray. Fresh fish is placed on the sample area of ​​the pad, and the PET tray is sealed with plastic wrap. During storage, the absorbent pad absorbs the juices exuded from the fish, and these juices interact with the indication area of ​​the pad. Figure 1 As shown, with the continuous increase of TVB-N value, the initial color of the pad indicator area under visible light is grass green, and then turns brown; when the TVB-N content exceeds 25mg / 100g, the pad color turns purple; as the TVB-N content continues to increase, the color of the indicator pad no longer changes.

[0107] Depend on Figure 2 It can be seen that the color of the indicator area changes with the increase of TVB-N value. The indicator area of ​​the pad made with polyvinyl alcohol (Example 1) as a carrier is initially light green. As the storage time of the fish increases, when the TVB-N value rises to 21.16 mg / 100g, the color of the indicator area turns red. When the TVB-N is 24.90 mg / 100g, the color of the indicator area turns reddish-brown; when the TVB-N content exceeds 35.90 mg / 100g, the color remains dark purple. The indicator area of ​​the pad made with sodium alginate (Example 4) as a carrier is initially light green, then turns brown; when the TVB-N content exceeds 25 mg / 100g, the indicator area is grayish-purple; as the TVB-N content continues to increase, the color of the indicator area no longer changes. The pad indicator area made with zein (Example 5) as a carrier was initially grass green, and then turned brown; when the TVB-N content exceeded 25 mg / 100g, the pad color turned purple; as the TVB-N content continued to increase, the color of the indicator pad no longer changed.

[0108] By comparing the color changes of the indicator areas of the three groups of pads in Examples 1, 4 and 5, it can be found that the indicator areas of the pads prepared with polyvinyl alcohol, sodium alginate and zein as indicator carriers all showed good color-changing ability. Among them, the color change of the freshness indicator absorbent pad prepared with polyvinyl alcohol as carrier was more regular and distinct, and the color contrast of the pad indicator area was the strongest when the TVB-N content was at different freshness grade thresholds.

[0109] Comparative Example 1

[0110] Weigh 1g of polyvinyl alcohol and add it to 20mL of deionized water. Heat and stir at 95℃ for 30min to fully dissolve it. Add 1g of glycerin as a plasticizer and stir until well mixed to obtain a mixed solution. Apply 0.2mL of the mixed solution evenly to the indicator area (indicator area is 2cm²) on the wood pulp cellulose liner. 2 The coated pad is placed on a polyethylene plate and dried in an oven at 37°C to prepare an absorbent pad.

[0111] Images of wood pulp cellulose (the wood pulp cellulose used in the embodiments of this invention), wood pulp cellulose-polyvinyl alcohol (Comparative Example 1), and wood pulp cellulose-polyvinyl alcohol-sensing indicator pad (Example 1) under scanning electron microscopy at an accelerating voltage of 3.0 kV are shown below. Figures 4-6 As shown. When the image magnification is 200, by Figure 4 It can be seen that the wood pulp cellulose liner has a disordered and chaotic fibrous structure. For example... Figure 5 As shown, after adding polyvinyl alcohol to the wood pulp cellulose liner, a film-like substance appeared between the fibrous materials. This is mainly due to the aggregation of polyvinyl alcohol on the surface of the wood pulp fibers, thereby coating them. And compared to... Figure 5 compared to, Figure 6 After adding a sensing indicator during the padding preparation process, the smooth film structure between the fibrous materials changed. This may be because the addition of the sensing indicator altered the original ordered structure of the wood pulp cellulose-polyvinyl alcohol substrate. Compared to single wood pulp fibers, Figure 6 The fibers exhibited are thicker and have a rougher surface, demonstrating that the sensing indicator—polyvinyl alcohol—was successfully immobilized on the surface of the wood pulp cellulose. Overall, Figure 6 It still exhibits a loose porous structure, and because polyvinyl alcohol contains a large number of hydrophilic hydroxyl groups, it has a strong affinity for water and can attract more water molecules. This will also help the pad absorb and conduct water quickly, which is beneficial to improving the sensitivity of the freshness monitoring process.

[0112] The above are merely specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An absorbent liner with fish freshness indication function, characterized in that: The absorbent pad includes a permeable layer and an absorbent layer arranged vertically, with an indicator area on one side of the absorbent layer. The permeable layer is a perforated polyethylene film used to permeate the fish juices produced by the fish meat and to prevent the fish meat from sticking to the absorbent layer after it spoils. The absorbent layer is made of wood pulp cellulose, which absorbs the fish juices while allowing them to enter the indicator area, thus enabling the fish juices to interact directly with the indicator in the indicator area. The preparation process of the indicator area is as follows: (1) Preparation of coating solution for indicator area The indicator fixative carrier was dissolved in deionized water, and glycerol was added as a plasticizer. The mixture was stirred until homogeneous to obtain a mixed solution. The mass-to-volume ratio of the indicator fixative carrier to deionized water was 1:20 g / mL, and the mass ratio of the indicator fixative carrier to glycerol was 1:

1. The indicator fixative carrier was polyvinyl alcohol. After the mixed solution has cooled, add brilliant blue solution and alizarin ethanol solution in sequence. The mass ratio of polyvinyl alcohol to brilliant blue in the brilliant blue solution and alizarin in the alizarin ethanol solution is 1000:3 and 1000:12-1000:48, respectively. Stir well to obtain the indicator area coating solution. (2) Preparation of the indicator area of ​​the absorbent pad Apply the solution to the indicator area at a rate of 0.1 mL / cm. 2 The material is evenly applied to the indicator area of ​​the absorbent layer and dried to obtain an absorbent liner that indicates the freshness of the fish.

2. The absorbent liner with fish freshness indication function according to claim 1, characterized in that: The mass ratio of brilliant blue to alizarin is 1:

8.

3. The absorbent liner with fish freshness indication function according to claim 1, characterized in that: When the indicator fixative carrier is dissolved in deionized water in step (1), it is heated and stirred at 95°C for 30 min; when drying in step (2), the drying temperature is 37°C.

4. The absorbent liner with fish freshness indication function according to claim 1, characterized in that: The concentration of the brilliant blue solution is 1 mg / mL, and the concentration of the alizarin ethanol solution is 1 mg / mL.

5. The absorbent liner with fish freshness indication function according to claim 1, characterized in that: The indicator area is 2cm long and 1cm wide.

6. The application of an absorbent pad with fish freshness indication function as described in claim 1 in detecting fish freshness, characterized in that: Includes the following steps: (1) Preparation of standard colorimetric cards A water-absorbing pad with fish freshness indication function was placed in a fresh food tray. Fresh fish was placed in the center of the water-permeable layer of the water-absorbing pad with fish freshness indication function. Based on the TVB-N value of the fish at different freshness levels, the L, a, and b values ​​of the water-absorbing pad with fish freshness indication function under natural light were extracted as feature values. A standard color chart was made based on the L, a, and b values ​​of the freshness grade threshold. (2) Place the absorbent pad with fish freshness indicator function in the fresh food tray, place the fish in the center of the absorbent layer of the pad, and seal the tray; under natural light, compare the indicator area of ​​the absorbent pad with fish freshness indicator function with the standard color chart to determine the freshness of the fish during the storage stage and complete the real-time freshness detection of the fish.

7. The application of the absorbent pad with fish freshness indication function according to claim 6 in detecting fish freshness, characterized in that: When preparing a standard color chart based on the TVB-N value of fish meat at different freshness levels, the TVB-N values ​​were selected as 6 mg / 100g, 8 mg / 100g, 15 mg / 100g, 16 mg / 100g, 19 mg / 100g, 23 mg / 100g, 25 mg / 100g, and 29 mg / 100g, respectively.

8. The application of the absorbent pad with fish freshness indication function according to claim 6 in detecting fish freshness, characterized in that: When determining the freshness of fish during storage, a TVB-N value <15mg / 100g indicates freshness, 25mg / 100g > TVB-N value ≥15mg / 100g indicates acceptable quality, and TVB-N ≥25mg / 100g indicates spoilage.

9. The application of the absorbent pad with fish freshness indication function according to claim 6 in detecting fish freshness, characterized in that: Under natural light, the freshness of fish during storage can be determined by comparing its color with a standard color chart. When the indicator area is light green, the fish is fresh; when the indicator area is reddish-brown, the fish is moderately fresh; and when the indicator area is dark purple, the fish is spoiled.

10. The application of the absorbent pad with fish freshness indication function according to claim 6 in detecting fish freshness, characterized in that: Based on the color change of the water-absorbing liner indicator area with fish freshness indication function, the ΔE value is extracted. Combined with the linear fitting equation y=2.1124 x-7.1348, the fitting formula calculates the TVB-N value for that period.

Images