Intelligent gel label for indicating freshness of aquatic products and preparation method of intelligent gel label

Abstract

The invention belongs to the technical field of aquatic product preservation, and particularly relates to a protein-based intelligent gel label with aquatic product freshness indication and mechanical properties as well as a preparation method and application of the protein-based intelligent gel label. The preparation method comprises the following steps: mixing an ovalbumin solution with a chitosan-anthocyanin compound solution, and incubating under the action of a Ca < 2 + > ion slow release system of calcium sulfate. The intelligent gel label for indicating the freshness of the aquatic products is applied to monitoring of the freshness of the shrimps, the color of the intelligent gel label changes along with the decay degree of the shrimps, the intelligent gel label correspondingly shows different color changes under different trimethylamine concentrations, TVC values, pH values and TVB-N values, and the intelligent gel label has the advantages of being high in sensitivity, good in mechanical performance and high in stability; the food-grade safe and reliable visual monitoring of the freshness of the aquatic products is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of aquatic product preservation, and specifically relates to a protein-based smart gel label having both aquatic product freshness indication and mechanical properties, as well as a preparation method and application thereof. Background Art

[0002] During the transportation or storage of aquatic products, the growth and metabolites of food microorganisms inside the packaging may cause changes in the packaging environment, leading to food spoilage and thus food safety issues. Therefore, monitoring the freshness of aquatic meat is very important. Currently, common freshness monitoring methods include sensory evaluation, volatile basic nitrogen, and total bacterial count, while visual monitoring is one of the simplest, most convenient, and real-time intelligent methods. Intelligent packaging (Intelligent / Smart Packaging) is a new packaging technology that has emerged in the foreign food industry in the past decade. Intelligent packaging is a new technology that can automatically monitor, sense, record, and trace the internal and external environmental changes experienced by food during the circulation process, and inform and warn consumers of food safety information through visually perceptible physical changes on the packaging label.

[0003] During the spoilage process, aquatic products will produce some volatile amine gases (dimethylamine, ammonia and trimethylamine, etc.), which will cause the pH of the storage environment to change. The change can be visualized by a pH indicator, thereby achieving the effect of intelligent and visual monitoring of the freshness of meat. Patent document CN106093031A discloses a method for preparing a smart label for judging the critical freshness of aquatic products and its application. The method uses a natural pigment solution, adjusts the pH to 2-4, mixes the natural pigment solution with methylcellulose and polyethylene glycol-400, and then casts the mixture into a film to prepare a smart label. The smart label can intuitively indicate the freshness of aquatic products and can be used in conjunction with existing food packaging. It is convenient and practical. It can be combined with an electronic nose to further detect the freshness of aquatic products, and the results are reliable.

[0004] Patent document CN118994709A discloses a method for preparing an aerogel indicator label for detecting the freshness of fresh aquatic products. The method comprises the following steps: Step (1) preparing a chitosan solution: dispersing chitosan powder in deionized water, adding acid dropwise, and continuously stirring until the chitosan is just dissolved, thereby obtaining a chitosan solution having a pH of 4-5; Step (2) preparing an aerogel indicator label: adding crushed cotton linter cellulose, glycerin, and mulberry anthocyanin powder to the chitosan solution and stirring until dispersed, thereby forming a film-forming solution; adjusting the pH of the film-forming solution to 2 with acid; injecting the prepared film-forming solution into a fixed mold and freeze-forming it at low temperature; and freeze-drying it in a vacuum freeze dryer to obtain an aerogel indicator label. The color change of the aerogel indicator label produced by this method can be used to intuitively determine the freshness of the fresh aquatic product.

[0005] However, while existing technologies have developed a wide variety of smart labels for detecting the freshness of aquatic products, the color stability of smart gel labels used for food monitoring is crucial, and limited research has been conducted on the stability of smart labels for aquatic products. Therefore, the research and development of smart labels for aquatic products with excellent stability, high sensitivity, and strong mechanical properties remains a pressing challenge. Summary of the Invention

[0006] In order to solve the defects of the existing smart labels such as insufficient sensitivity, poor mechanical properties and low stability, the present invention provides a protein-based smart gel label that has both the function of indicating the freshness of aquatic products and mechanical properties. 2+ The smart gel label for indicating the freshness of aquatic products prepared by the present invention has the advantages of high sensitivity, good mechanical properties and high color stability during the shrimp freshness detection process, and can realize food-grade safe and reliable visual monitoring of the freshness of aquatic products.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a smart gel label for indicating the freshness of aquatic products, comprising the following steps:

[0009] Step S1, dissolving ovalbumin in deionized water, adjusting the pH to 6.5-7, standing for 12-24 hours, centrifuging, and collecting the supernatant to obtain an ovalbumin solution;

[0010] Step S2, adding anthocyanidin to deionized water, stirring evenly, then adding chitosan, stirring evenly, and standing for 12 to 24 hours to obtain a chitosan-anthocyanidin aqueous solution;

[0011] Step S3, mixing the ovalbumin solution prepared in step S1 with the chitosan-anthocyanidin aqueous solution prepared in step S2 to obtain a mixed solution I, then adding calcium sulfate and stirring evenly to obtain a mixed solution II;

[0012] Step S4: incubate the mixed solution II obtained in step S3, and then let it stand at a temperature of 4 to 8° C. for 12 to 24 hours.

[0013] Furthermore, in actual production, sodium benzoate can be added to the supernatant obtained in step S1. This sodium benzoate can further extend the shelf life of the smart gel label without affecting the structure and effect of the gel. The amount of sodium benzoate added is such that the mass concentration of sodium benzoate in the supernatant is 0.1% (m / V).

[0014] Furthermore, the mass concentration of ovalbumin in the ovalbumin solution of step S1 is 15-20% (m / V).

[0015] Furthermore, the anthocyanin in step S2 is one or a combination of two or more of blueberry anthocyanin, roselle anthocyanin, grape anthocyanin, mulberry anthocyanin and purple sweet potato anthocyanin.

[0016] Furthermore, the mass concentration of anthocyanins in the chitosan-anthocyanin aqueous solution in step S2 is 4-6% (m / V).

[0017] Furthermore, the mass concentration of chitosan in the chitosan-anthocyanidin aqueous solution in step S2 is 10-20% (m / V), and the chitosan is acid-soluble chitosan with a deacetylation degree of ≥85%.

[0018] Furthermore, in step S3, the volume ratio of the ovalbumin solution to the chitosan-anthocyanidin aqueous solution is 1:1 to 4:1.

[0019] Furthermore, in step S3, the mass concentration of calcium sulfate in the mixed solution I is 1-2% (m / V).

[0020] Furthermore, the incubation condition in step S4 is: incubating at a temperature of 40 to 55° C. for 2 to 4 hours.

[0021] Furthermore, the present invention also provides a smart gel label for indicating the freshness of aquatic products prepared by the method for preparing the smart gel label for indicating the freshness of aquatic products.

[0022] Furthermore, the present invention provides application of the smart gel label for indicating the freshness of aquatic products in detecting the freshness of aquatic products.

[0023] Furthermore, the present invention investigates the correlation between the color change of smart gel labels and the freshness of aquatic products by measuring their TVB-N, TVC, pH, and flavor changes (particularly trimethylamine concentration) during storage. Furthermore, a method for detecting aquatic product freshness is proposed. This method employs the aforementioned smart gel label to determine the freshness of aquatic products based on the color change of the smart gel label.

[0024] The inventors have been committed to the research on the preservation of aquatic products. In the process of studying smart labels for aquatic products, the inventors found that the gel network formed by the protein / polysaccharide composite system through electrostatic interaction has a high degree of cross-linking and can form a denser spatial network structure. Ovalbumin (OVA) is a natural protein with good biocompatibility, biodegradability and strong surface activity; chitosan has good film-forming properties, as well as antibacterial and antiseptic effects and biodegradability, and is widely used in the field of preservation. Based on the characteristics of the above materials, the inventors proposed for the first time a protein-based smart gel label with both freshness indication and mechanical properties. Specifically, it is made by mixing an ovalbumin solution with a chitosan solution embedded with anthocyanins.

[0025] The detection principle of the smart gel label produced by this invention is that anthocyanins embedded in the gel display different colors depending on pH changes. The carboxyl and hydroxyl groups on the gel surface react with spoilage markers such as trimethylamine produced by aquatic products, resulting in different colors. The color changes of the smart gel label are used to determine the freshness of the aquatic product. The smart gel label exhibits a color change from light red to light brown to brown, with a ΔE value greater than 5, depending on trimethylamine concentration, TVC value, pH value, and TVB-N value. The color change of the smart gel label allows direct observation of the freshness of the aquatic product, achieving safe and reliable food-grade visual monitoring of aquatic product freshness.

[0026] Furthermore, the present invention utilizes a specific ratio of ovalbumin and chitosan to form a highly dense spatial network structure through electrostatic interaction, enhancing the mechanical properties of the smart gel label. Furthermore, the abundant carboxyl and hydroxyl groups on the gel surface react rapidly with trimethylamine, a marker of spoilage in aquatic products, thereby increasing the sensitivity of the smart gel label. Furthermore, the stable and dense network structure formed by the specific ratio of ovalbumin and chitosan not only enhances the encapsulation of anthocyanins but also improves their stability, thereby enhancing the stability of the smart gel label. This provides a highly sensitive, mechanically stable, and stable smart gel label for ensuring the freshness of aquatic products.

[0027] Compared with the prior art, the method for preparing the smart gel label for indicating the freshness of aquatic products provided by the present invention has the following advantages:

[0028] (1) The smart gel label produced by the method for preparing aquatic product freshness indicator provided by the present invention exhibits excellent mechanical properties and is not prone to breakage during practical use. Experiments have demonstrated that the smart gel label produced by the present invention exhibits excellent properties in both hardness and viscoelasticity, facilitating its practical application in production.

[0029] (2) The smart gel label produced by the method for preparing aquatic product freshness indicator provided by the present invention exhibits high color stability. Experiments have shown that the majority of free water in the smart gel label produced by the present invention is converted into capillary water and bound water, which is more conducive to the storage of anthocyanins, a water-soluble natural indicator. Furthermore, the gel can reduce the effects of external factors on anthocyanins, thereby improving their stability.

[0030] (3) The smart gel label prepared by the preparation method of the aquatic product freshness indicator provided by the present invention has high sensitivity. In the detection of aquatic products, it complies with the national food safety standard GB 2733-2015, which stipulates that the pH value of shrimp in fresh and frozen animal aquatic products is less than 7.6 and the TVB-N value is less than 30 mg / 100 g. It has good sensing performance and can timely and effectively display the freshness of fresh and frozen animal aquatic products. It can be widely used in the field of food packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The following are actual pictures of the smart gel labels for indicating the freshness of aquatic products prepared in Examples 1 to 2 and Comparative Examples 1 to 8.

[0032] Figure 2 This is a color rendering of the smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0033] Figure 3 The graphs are rheological analysis diagrams of the smart gel labels for indicating the freshness of aquatic products prepared in Examples 1 to 2 and Comparative Examples 1 to 8.

[0034] Figure 4 This is the nuclear magnetic resonance moisture distribution diagram of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 and Comparative Examples 1 to 3.

[0035] Figure 5 This is an interaction analysis diagram of the smart gel labels for indicating the freshness of aquatic products prepared in Example 1 and Comparative Examples 1 to 3.

[0036] Figure 6This is a diagram showing the color development effect of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 under different trimethylamine concentrations.

[0037] Figure 7 This is a physical picture of the smart gel label for indicating the freshness of aquatic products prepared in Example 1, which changes with the freshness of shrimp meat at room temperature.

[0038] Figure 8 This is a graph showing the color difference, TVC value, pH value, and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 when tested with shrimp meat at room temperature.

[0039] Figure 9 This is a graph showing the composition changes of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 as shrimp meat is tested at room temperature.

[0040] Figure 10 This is a graph showing the correlation between the freshness of the aquatic product freshness indicator smart gel label prepared in Example 1 and the changes in the freshness of the shrimp meat at room temperature and the changes in the composition.

[0041] Figure 11 This is a physical picture of the smart gel label for indicating the freshness of aquatic products prepared in Example 1, which shows the change in freshness of shrimp meat during frozen storage at 4°C.

[0042] Figure 12 This is a graph showing the color difference, TVC value, pH value and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 when stored frozen with shrimp meat at 4°C.

[0043] Figure 13 This is a graph showing the composition changes of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 as shrimp meat is frozen and stored at 4°C.

[0044] Figure 14 This is a graph showing the correlation between the freshness of the aquatic product freshness indicator smart gel label prepared in Example 1 and the changes in the composition of the shrimp meat during frozen storage at 4°C. DETAILED DESCRIPTION

[0045] The present invention is further illustrated below by describing specific embodiments, but this is not intended to limit the present invention. Those skilled in the art may make various modifications or improvements based on the basic concept of the present invention, but as long as they do not deviate from the basic concept of the present invention, they are all within the scope of the present invention. Unless otherwise specified, the experimental methods used in the experiments involved in the present invention are all conventional methods; the materials used in the examples of the present invention are all food grade and are conventional commercial products. For example: ovalbumin (OVA, purity 80%), purchased from Shanghai Yuanye Biotechnology Co., Ltd.; food grade acid-soluble chitosan (CS, deacetylation degree ≥85%), purchased from Shandong Weikang Biomedicine Technology Co., Ltd. (Linyi, Shandong, China); blueberry anthocyanin (AC, purity 25%), purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number C302404; calcium sulfate hydrate (AR), purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0046] Example 1: Preparation method of a smart gel label for indicating the freshness of aquatic products

[0047] Step S1, dissolving 20 g of ovalbumin in 100 mL of deionized water, adjusting the pH to 7, standing for 24 hours, centrifuging, and collecting the supernatant to obtain an ovalbumin solution with a mass concentration of 20% (m / V);

[0048] Step S2, adding 5 g of blueberry anthocyanidins to 100 mL of deionized water and stirring evenly, then adding 10 g of chitosan, stirring evenly, and standing for 24 h to obtain a chitosan-blueberry anthocyanidin aqueous solution, wherein the mass concentration of the chitosan is 10% (m / V);

[0049] Step S3, mixing the ovalbumin solution prepared in step S1 and the chitosan-blueberry anthocyanin aqueous solution prepared in step S2 in a volume ratio of 1:1 to obtain a mixed solution I, then adding calcium sulfate with a mass concentration of 1% (m / V) to the mixed solution I, and stirring evenly to obtain a mixed solution II; the mass concentration of ovalbumin in the mixed solution II is 10% (m / V), and the mass concentration of chitosan is 5% (m / V);

[0050] Step S4: The mixed solution II was divided into 25 mL plastic cup molds, with each beaker weighing 4±0.1 g. The mixture was then placed in a water bath and incubated at 50° C. for 3 h, and then allowed to stand at 4° C. for 24 h.

[0051] Example 2: Preparation method of a smart gel label for indicating the freshness of aquatic products

[0052] Step S1, dissolving 20 g of ovalbumin in 100 mL of deionized water, adjusting the pH to 7, standing for 24 hours, centrifuging, and collecting the supernatant to obtain an ovalbumin solution with a mass concentration of 20% (m / V);

[0053] Step S2, adding 5 g of blueberry anthocyanidins to 100 mL of deionized water and stirring evenly, then adding 20 g of chitosan, stirring evenly, and standing for 24 h to obtain a chitosan-blueberry anthocyanidin aqueous solution, wherein the mass concentration of the chitosan is 20% (m / V);

[0054] Step S3, mixing the ovalbumin solution prepared in step S1 and the chitosan-blueberry anthocyanin aqueous solution prepared in step S2 in a volume ratio of 1:1 to obtain a mixed solution I, then adding calcium sulfate with a mass concentration of 1% (m / V) to the mixed solution I, and stirring evenly to obtain a mixed solution II; the mass concentration of ovalbumin in the mixed solution II is 10% (m / V), and the mass concentration of chitosan is 10% (m / V);

[0055] Step S4: The mixed solution II was divided into 25 mL plastic cup molds, with each beaker weighing 4±0.1 g. The mixture was then placed in a water bath and incubated at 50° C. for 3 h, and then allowed to stand at 4° C. for 24 h.

[0056] Comparative Example 1: Preparation method of a smart gel label for indicating the freshness of aquatic products

[0057] The difference from Example 1 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by 20 U / g transglutaminase, and the rest is similar to Example 1.

[0058] Comparative Example 2: Preparation method of a smart gel label for indicating the freshness of aquatic products

[0059] The difference from Example 1 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by adding 20 U / g of glutamine transferase, stirring thoroughly, and then adding calcium sulfate with a mass concentration of 1% (m / V) to achieve a synergistic effect. The rest is similar to Example 1.

[0060] Comparative Example 3: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0061] The difference from Example 1 is that calcium sulfate is not added in step S3, the incubation temperature in step S4 is set to 90° C. in a water bath for 1 hour, and the rest is similar to Example 1.

[0062] Comparative Example 4: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0063] The difference from Example 1 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by trisodium citrate with a mass concentration of 1% (m / V), and the rest is similar to Example 1.

[0064] Comparative Example 5: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0065] The difference from Example 2 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by 20 U / g transglutaminase, and the rest is similar to Example 2.

[0066] Comparative Example 6: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0067] The difference from Example 2 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by adding 20 U / g of glutamine transferase, stirring thoroughly, and then adding calcium sulfate with a mass concentration of 1% (m / V) to achieve a synergistic effect. The rest is similar to Example 2.

[0068] Comparative Example 7: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0069] The difference from Example 2 is that calcium sulfate is not added in step S3, the incubation temperature in step S4 is set to 90° C. in a water bath for 1 hour, and the rest is similar to Example 2.

[0070] Comparative Example 8: Preparation Method of Smart Gel Label for Indicating Freshness of Aquatic Products

[0071] The difference from Example 2 is that in step S3, the calcium sulfate with a mass concentration of 1% (m / V) is replaced by trisodium citrate with a mass concentration of 1% (m / V), and the rest is similar to Example 2.

[0072] Test Example 1: Determination of the color development ability of smart gel labels for indicating the freshness of aquatic products

[0073] 1. Test materials:

[0074] Smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8.

[0075] 2. Test method:

[0076] 2.1. Appearance inspection of smart gel labels:

[0077] The appearance of the smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8 were observed.

[0078] 2.2. Determination of color development ability of smart gel labels:

[0079] Solutions with pH values of 2.2, 3, 4, 5, 6, 7, and 8 were prepared respectively. Sterile cotton balls were soaked in the solutions with different pH values. The soaked cotton balls were then placed on the smart gel label for indicating the freshness of aquatic products prepared in Example 1 overnight. A colorimeter was used to record the color changes of the samples. L* represents brightness, ranging from 0 (black) to 100 (white); a* represents green (-a*) to red (+a*); and b* represents blue (-b*) to yellow (+b*). The total color difference (TCD) was calculated using the equation:

[0080]

[0081] in is the initial value of the hydrogel color

[0082] 3. Test results:

[0083] The test results are as follows Figure 1 and as shown in Table 1.

[0084] 3.1、Appearance test results of smart gel labels are as follows Figure 1 As shown:

[0085] Figure 1 Photos of smart gel labels for indicating the freshness of aquatic products made in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7, and Comparative Example 8. 5CS-Ca represents Example 1, 10CS-Ca represents Example 2, 5CS-E represents Comparative Example 1, 5CS-Ca-E represents Comparative Example 2, 5CS-H represents Comparative Example 3, 5CS-A represents Comparative Example 4, 10CS-E represents Comparative Example 5, 10CS-Ca-E represents Comparative Example 6, 10CS-H represents Comparative Example 7, and 10CS-A represents Comparative Example 8.

[0086] from Figure 1 It can be observed that the high temperature factor has a greater impact on the natural indicator anthocyanin. The protein-based gels prepared in Comparative Examples 3 and 7 are almost white. Therefore, the protein-based gel smart labels cannot be shaped by high-temperature heating treatment. At the same time, the protein-based gels obtained by alkali induction of trisodium citrate in Comparative Examples 4 and 8 are porous and uneven, so alkali induction is not an optional method. In addition, the polysaccharide mass ratio will affect the color of the gel freshness smart label. Compared with Example 2, the color display of the protein-based gel freshness smart label prepared in Example 1 will be more significant. Example 1 clearly shows the red color of anthocyanin, while Example 2 shows light brown. Therefore, Example 1 is the best embodiment.

[0087] 3.2. The color development ability of smart gel labels is shown in Table 1 and Figure 2 As shown:

[0088] Table 1 pH response changes of smart gel labels

[0089]

[0090] Figure 2 This is a color rendering of the smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0091] From Table 1 and Figure 2 It can be seen that the smart gel label for indicating the freshness of aquatic products prepared in Example 1 has a color response ΔE greater than 5 under pH changes, indicating that the smart gel label for indicating the freshness of aquatic products has good pH response capability.

[0092] Test Example 2: Mechanical Properties of Smart Gel Labels for Aquatic Product Freshness Indication

[0093] 1. Test materials:

[0094] Smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8.

[0095] 2. Test method:

[0096] The hardness and rheological properties of the smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8 were measured.

[0097] 2.1. Hardness determination of smart gel labels:

[0098] The hardness of the smart gel labels was measured using a texture analyzer. The smart gel labels for indicating aquatic product freshness, prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8, were molded into cylindrical samples with a diameter of 20 mm and a height of 10 mm using a disposable plastic beaker mold. A P-25 probe was used for compression testing, with a compressive strain of 50% and a probe speed of 1 mm / s. Hardness was measured based on the force-deformation curve.

[0099] 2.2 Rheological analysis of smart gel labels:

[0100] The rheological properties of the smart gel labels were measured using a HAAKEMARS III rheometer. The smart gel label samples for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7, and Comparative Example 8 were molded into cylindrical samples with a diameter of 20 mm and a height of 10 mm using a disposable plastic beaker mold. Dynamic oscillation sweeps were performed within the linear viscoelastic range at a frequency range of 0.1 to 20 Hz, and the complex modulus (G' and G") was recorded. The shear rate range was set to 0.1 to 100 s. -1 , determine the change of static apparent viscosity with shear rate.

[0101] 3. Test results:

[0102] The test results are shown in Table 2 and Figure 3 shown.

[0103] 3.1. The hardness test results of the smart gel label are shown in Table 2:

[0104] Table 2 Hardness results of smart gel labels

[0105]

[0106] Among them: 5CS-Ca is Example 1, 10CS-Ca is Example 2, 5CS-E is Comparative Example 1, 5CS-Ca-E is Comparative Example 2, 5CS-H is Comparative Example 3, 5CS-A is Comparative Example 4, 10CS-E is Comparative Example 5, 10CS-Ca-E is Comparative Example 6, 10CS-H is Comparative Example 7, and 10CS-A is Comparative Example 8.

[0107] 3.2. Rheological analysis results of smart gel labels Figure 3 As shown:

[0108] Figure 3 Rheological analysis graphs of smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 5, Comparative Example 6, and Comparative Example 7. 5CS-Ca represents Example 1, 10CS-Ca represents Example 2, 5CS-E represents Comparative Example 1, 5CS-Ca-E represents Comparative Example 2, 5CS-H represents Comparative Example 3, 10CS-E represents Comparative Example 5, 10CS-Ca-E represents Comparative Example 6, and 10CS-H represents Comparative Example 7.

[0109] From Table 2 and Figure 3 It can be seen that under the protein-based gel freshness smart label made of polysaccharide with the same mass ratio, calcium sulfate Ca 2+The smart gel label obtained by the ion sustained-release system exhibits excellent performance in terms of hardness and viscoelasticity. Therefore, the smart gel label for indicating the freshness of aquatic products prepared in Example 1 has good mechanical properties, which facilitates the application of the smart gel label in actual production.

[0110] Experimental Example 3: Analysis of Moisture Distribution and Interaction of Smart Gel Labels for Freshness Indication of Aquatic Products

[0111] 1. Test materials:

[0112] Smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0113] 2. Test method:

[0114] The smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were subjected to moisture distribution analysis and interaction analysis.

[0115] 2.1. Determination of moisture distribution of smart gel labels:

[0116] The moisture distribution of the smart gel label was measured using a MesoMR23-060H-1 low-field nuclear magnetic resonance spectrometer. The smart gel label samples for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were molded into a disposable plastic beaker to form cylindrical samples with a diameter of 20 mm and a height of 10 mm. Magnetic resonance imaging (MRI) was used to measure the moisture distribution of the smart gel label. The samples were placed in a nuclear magnetic resonance tube and then placed in an MR-60 nuclear magnetic resonance imager for imaging analysis.

[0117] 2.2 Interaction analysis of smart gel tags:

[0118] The interaction of the smart gel labels was analyzed using a TENSOR 27 infrared spectrometer. The smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were freeze-dried to obtain test samples. The test samples were mixed with Kbr at a ratio of 1:100 and infrared spectroscopy was performed at a resolution of 4 cm. -1 , scanning range 4000~400cm -1 .

[0119] 3. Test results:

[0120] The test results are as follows Figure 4 and Figure 5 shown.

[0121] 3.1、The results of moisture distribution measurement of smart gel label are as follows Figure 4 As shown:

[0122] Figure 4 Nuclear magnetic resonance moisture distribution diagrams of smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, where 5CS-Ca is from Example 1, 5CS-E is from Comparative Example 1, 5CS-Ca-E is from Comparative Example 2, and 5CS-H is from Comparative Example 3.

[0123] The more red the color, the more free water there is. Figure 4 It can be seen that compared with Comparative Examples 1 and 2, the redness of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 is greatly reduced, indicating that the redness of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 is greatly reduced. 2+ In the ion sustained-release system, ovalbumin and chitosan form a stable dense structure, and most of the free water is converted into capillary water and bound water. Therefore, the water-soluble natural indicator anthocyanin has better storage properties in the smart gel label for indicating the freshness of aquatic products prepared in Example 1, is less affected by external factors, and is more stable.

[0124] 3.2. Interaction analysis results of smart gel tags Figure 5 As shown:

[0125] Figure 5 Interaction analysis diagram of smart gel labels for indicating the freshness of aquatic products prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, where 5CS-Ca is Example 1, 5CS-E is Comparative Example 1, 5CS-Ca-E is Comparative Example 2, and 5CS-H is Comparative Example 3.

[0126] Fourier transform infrared spectroscopy is an effective method to analyze protein-polysaccharide interactions and structural changes at the molecular level. Figure 5 It can be seen that at 1028.04cm -1 There is a characteristic peak of flavonoid tannins at 1028.04 cm-1 for anthocyanin (AC) (Boyu Chen, et al, Food Chemistry: X, 2024 (23)). Compared with Comparative Examples 1 and 2, Example 1 has a characteristic peak of flavonoid tannins at 1028.04 cm-1 for anthocyanin (AC) (Boyu Chen, et al, Food Chemistry: X, 2024 (23)). -1 The change is more obvious, and the characteristic peak of anthocyanin almost disappears, which is similar to the result of comparative example 3 after high-temperature heating treatment. This auxiliary evidence shows that the natural indicator anthocyanin is successfully embedded in the protein-based gel, which can better play the role of freshness indication.

[0127] Test Example 4: Sensitivity Test of Smart Gel Labels for Freshness Indication of Aquatic Products to Trimethylamine

[0128] 1. Test materials:

[0129] The smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0130] 2. Test method:

[0131] 0 mM (0 mmol / L), 10 mM (10 mmol / L), 20 mM (20 mmol / L), 40 mM (40 mmol / L), 60 mM (60 mmol / L), 80 mM (80 mmol / L), and 100 mM (100 mmol / L) trimethylamine solutions were prepared respectively, and then the soaked cotton balls were placed on the smart gel label for indicating the freshness of aquatic products prepared in Example 1 overnight, and the color change of the samples was recorded using a colorimeter.

[0132] 3. Test results:

[0133] The test results are as follows Figure 6 shown.

[0134] Volatile basic nitrogen mainly consists of ammonia and amines (trimethylamine and dimethylamine), and trimethylamine can be detected and analyzed with the help of GC-MS to determine the changes in its content over time during storage. Figure 6 This is a diagram showing the color development of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 at different trimethylamine concentrations. Figure 6 As can be seen, as the trimethylamine concentration increases, the gel surface changes from pink to dark gray and finally to dark brown. When the trimethylamine concentration is above 20 mM, the hydrogel surface begins to appear dark gray. When the trimethylamine concentration is above 40 mM, a color change is observable to the naked eye (the difference between ΔE values is greater than 5). When the trimethylamine concentration is above 60 mM, the smart gel label for indicating the freshness of aquatic products prepared in Example 1 clearly displays different colors over time (the difference between ΔE values is greater than 12). Therefore, the smart gel label for indicating the freshness of aquatic products prepared in Example 1 demonstrates excellent sensitivity to trimethylamine.

[0135] Test Example 5: Application of Smart Gel Label for Freshness Indication of Aquatic Products at Room Temperature

[0136] 1. Test materials:

[0137] The smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0138] 2. Test method:

[0139] The smart gel label for indicating the freshness of aquatic products prepared in Example 1 was observed as the freshness of the shrimp meat changed at room temperature. The color difference, TVC value, pH value, and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 were tested at room temperature. The Pearson correlation coefficient between the indicators was calculated using Origin. The Pearson correlation factor was used to assess whether a linear relationship existed between the two indicators. This allowed for a better analysis of the correlation between the changes in the freshness of the shrimp meat at room temperature and changes in its composition.

[0140] 3. Test results:

[0141] The test results are as follows Figures 7 to 10 shown.

[0142] (1) The smart gel label for indicating the freshness of aquatic products prepared in Example 1 changes with the freshness of shrimp meat at room temperature. Figure 7 shown.

[0143] (2) The color difference, TVC value, pH value and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 were detected with shrimp meat at room temperature. Figure 8 shown.

[0144] (3) The results of the composition change of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 as the shrimp meat is tested at room temperature are as follows: Figure 9 shown.

[0145] (4) The correlation results between the freshness of the aquatic product indicated by the smart gel label prepared in Example 1 and the change of the shrimp meat freshness at room temperature and the change of the composition are as follows: Figure 10 shown.

[0146] Depend on Figures 7 to 10 It can be seen that as shrimp are stored at room temperature, the shrimp meat gradually turns red. After the shrimp dies, on the one hand, the lack of oxygen in the muscle produces reduced myoglobin, and on the other hand, astaxanthin gradually oxidizes and turns red. The smart gel label for indicating the freshness of aquatic products prepared in Example 1 gradually changes from red to dark gray as the freshness changes.

[0147] After 12 hours of storage at room temperature, the color change can be observed with the naked eye (the difference between ΔE>5). At the same time, the shrimp meat was analyzed for its components. After 12 hours of storage at room temperature, the TVB-N content was close to 30mg / 100g. When stored at room temperature for 12 to 24 hours, the pH was>6 and the TVC>6lgCFU / g. According to GB 2733-2015 National Food Safety Standard for Fresh and Frozen Animal Aquatic Products and related literature (Sheng Chen, et al, International Journal of Biological Macromolecules, Volume 283, 2024, 137754), the shrimp meat can be judged to be stale or inedible after being placed at room temperature for 12 hours. In addition, methyl mercaptan and ethanol began to appear as freshness changed, and trimethylamine increased exponentially. Through correlation processing, it was found that there was a good correlation between ΔE and other indicators. The results reflect that the responsiveness of the smart gel tag is well correlated with the changes in the freshness components of shrimp stored at room temperature.

[0148] Test Example 6: Application of Smart Gel Labels for Freshness Indication in Aquatic Products Frozen Storage at 4°C

[0149] 1. Test materials:

[0150] The smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0151] 2. Test method:

[0152] The smart gel label for indicating the freshness of aquatic products prepared in Example 1 was observed as the freshness of shrimp meat changed during frozen storage at 4°C. The color difference, TVC value, pH value, and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 were tested as the shrimp meat was frozen and stored at 4°C. The Pearson correlation coefficient between the indicators was calculated using Origin. The Pearson correlation factor was used to assess whether a linear relationship existed between the two indicators. This allowed for a better analysis of the correlation between the change in freshness of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 and the change in composition during frozen storage at 4°C.

[0153] 3. Test results:

[0154] The test results are as follows Figures 11 to 14 shown.

[0155] (1) The smart gel label for indicating the freshness of aquatic products prepared in Example 1 shows the change in the freshness of shrimp meat during frozen storage at 4°C. Figure 11 shown.

[0156] (2) The color difference, TVC value, pH value and TVB-N value of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 were tested with shrimp meat frozen at 4°C. Figure 12 shown.

[0157] (3) The results of the composition change of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 during frozen storage of shrimp meat at 4°C are as follows: Figure 13 shown.

[0158] (4) The correlation results between the change in freshness and composition of the smart gel label for indicating the freshness of aquatic products prepared in Example 1 during frozen storage at 4°C are as follows: Figure 14 shown.

[0159] from Figures 11 to 14 As can be seen, while the shrimp meat barely changed color over time at 4°C, the smart gel tag gradually changed from red to dark gray, achieving a visible color change by the third day (difference in ΔE > 5). Compositional analysis of the shrimp meat revealed a TVB-N content of nearly 30 mg / 100 g and a pH > 6 after the third day of storage at 4°C. TVC increased with storage time, and GC-MS results revealed the appearance and rise of acetone and ethanol, with particularly pronounced increases in trimethylamine and ethanol. Correlation analysis revealed a strong correlation between ΔE and other indicators, demonstrating that the shrimp meat gradually became inedible after the third day of storage. These results demonstrate a strong correlation between the responsiveness of the smart gel tag and the changes in freshness components of shrimp stored at 4°C.

[0160] Test Example 7: Stability Determination of Smart Gel Labels for Aquatic Product Freshness Indication

[0161] 1. Test materials:

[0162] The smart gel label for indicating the freshness of aquatic products prepared in Example 1.

[0163] 2. Test method:

[0164] The smart gel label for indicating the freshness of aquatic products prepared in Example 1 was stored in a sealed environment at 4°C and 25°C, respectively. The color change of the smart gel label was observed on day 0, 10, 20, 30, 40, 50, and 60, and the color difference ΔE compared with the original white plate was expressed.

[0165] 3. Test results:

[0166] The test results are shown in Table 3.

[0167] Table 3 Stability determination of smart gel labels for indicating freshness of aquatic products

[0168]

[0169] As shown in Table 3, the smart gel label for indicating the freshness of aquatic products prepared in Example 1 of the present invention had a ΔE difference of less than 2 after storage at 4°C and 25°C for 60 days, indicating no significant color difference. This indicates that the smart gel label for indicating the freshness of aquatic products prepared in Example 1 has high stability.

[0170] In addition, during the research process, the inventors found that the smart gel labels prepared in Reference Example 1 using agarose, chitosan, and anthocyanin as raw materials; and using hydroxycarboxymethyl starch, chitosan, and anthocyanin as raw materials, were stored under the same conditions of 4°C and 25°C. Basically, after 30 days of storage, the △E difference of the gel standard was greater than 4, or even close to 5, and color change began to appear. The smart gel label prepared in the present invention using ovalbumin, chitosan, and anthocyanin as raw materials had a stability of at least greater than 60 days.

[0171] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing a smart gel label for indicating the freshness of aquatic products, characterized in that: The following steps are involved: Step S1, dissolving ovalbumin in deionized water, adjusting the pH to 6.5-7, standing for 12-24 hours, centrifuging, and collecting the supernatant to obtain an ovalbumin solution; Step S2, adding anthocyanidin to deionized water, stirring evenly, then adding chitosan, stirring evenly, and standing for 12 to 24 hours to obtain a chitosan-anthocyanidin aqueous solution; Step S3, mixing the ovalbumin solution prepared in step S1 with the chitosan-anthocyanidin aqueous solution prepared in step S2 to obtain a mixed solution I, then adding calcium sulfate and stirring evenly to obtain a mixed solution II; Step S4: incubate the mixed solution II obtained in step S3, and then let it stand at a temperature of 4 to 8° C. for 12 to 24 hours.

2. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, characterized in that: The mass concentration of ovalbumin in the ovalbumin solution in step S1 is 15-20% (m / V).

3. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: The anthocyanin in step S2 is one or a combination of two or more of blueberry anthocyanin, roselle anthocyanin, grape anthocyanin, mulberry anthocyanin and purple sweet potato anthocyanin.

4. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: The mass concentration of anthocyanins in the chitosan-anthocyanin aqueous solution in step S2 is 4-6% (m / V).

5. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: The mass concentration of chitosan in the chitosan-anthocyanidin aqueous solution in step S2 is 10-20% (m / V), and the chitosan is acid-soluble chitosan with a deacetylation degree of ≥85%.

6. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: In step S3, the volume ratio of the ovalbumin solution to the chitosan-anthocyanidin aqueous solution is 1:1 to 4:

1.

7. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: In step S3, the mass concentration of calcium sulfate in the mixed solution I is 1-2% (m / V).

8. The method for preparing the smart gel label for indicating the freshness of aquatic products according to claim 1, wherein: The incubation conditions in step S4 are: incubating at a temperature of 40 to 55° C. for 2 to 4 hours.

9. The smart gel label for indicating the freshness of aquatic products, prepared by the method for preparing the smart gel label for indicating the freshness of aquatic products according to any one of claims 1 to 8.

10. Use of the smart gel label for indicating the freshness of aquatic products as claimed in claim 9 in detecting the freshness of aquatic products.

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