Phycocyanin-based time and temperature indication label and preparation method thereof

Abstract

The invention relates to the technical field of intelligent labels, in particular to a phycocyanin-based time and temperature indication label which is characterized by being prepared from 8-10 parts of polyvinyl alcohol, 2.5-10 parts of zein, 1-4 parts of phycocyanin, 2-10 parts of phospholipid and 8-64 parts of ferrite. The packaging label can synchronously indicate the quality deterioration degree of a product through color difference change under the processing conditions of freezing, refrigerating and room-temperature storage of the product, and the color change trend is that the blue hue is weakened and the yellow hue is enhanced along with the increase of time and temperature. The indication label can be subjected to one-time freeze thawing forming along with the product freezing processing technology, and response to different oxidation deterioration rates can be achieved by adjusting the raw material ratio. On one hand, the synchronous responsiveness of different speed and irregular process of quality deterioration of aquatic products and products thereof caused by individual difference and batch-to-batch difference is met, and on the other hand, the change of early quality of the aquatic products and products thereof caused by lipid oxidation can be handled, and the freshness grade of the products is sensitively indicated.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent tags, and particularly relates to a time-temperature indicating tag based on phycocyanin and a preparation method thereof. Background Art

[0002] With the gradual development of the social economy and the gradual improvement of people's living standards, people are increasingly concerned about the freshness and edible safety of various foods. As is well known, there are many factors causing food spoilage and deterioration, such as biological factors (insects, parasites, microorganisms), chemical factors (endogenous enzymes in food tissues), and physical factors (light, storage temperature, water activity, oxygen concentration), etc. For some foods or food raw materials rich in fat and vitamins, under the combined action of storage environments (such as oxygen, temperature, light) and endogenous oxidants, pro-oxidant substances, etc., lipid oxidation and spoilage can occur. For example, apples, potatoes, etc. contain a large amount of tannins and phenolic substances, which are easily oxidized to black or brown under the action of oxidase. In animal meat and its products, the quality change is the result of the interactive oxidation of lipids and proteins. Especially for aquatic products and their processed products rich in unsaturated fatty acids and proteins, they are more likely to produce spoilage compared with other meats. Among them, lipid oxidation is one of the key factors for the spoilage of aquatic products, which often occurs in the early stage, and lipid oxidation cannot be avoided even under low-temperature conditions. At the same time, a large number of free radicals and aldehyde substances generated by lipid oxidation are also important reasons for accelerating the deterioration of other nutrients and emitting unpleasant odors. At present, for chilled, frozen aquatic products and their products, it is still difficult to identify the freshness from their appearance or packaging labels.

[0003] Most of the traditional methods for detecting freshness are complex to operate, while some rapid detection technologies rely on expensive instruments. Therefore, developing a visual intelligent tag that can intuitively display the freshness of aquatic products is of great significance for consumers and producers to understand the real-time freshness of aquatic products. TBARS is an index of lipid oxidation in the traditional sense, but the detection of TBARS content takes a long time and is complex to operate. Designing a tag that can visualize the lipid oxidation of aquatic products to monitor the freshness of aquatic products has good application prospects. Currently, most of the tags commonly used for visualizing the freshness of aquatic products mainly respond to total volatile basic nitrogen (TVB-N) and pH value. For example, Chinese Patent CN 202410142361.3 discloses "a method for monitoring the freshness of aquatic products by colorimetric fluorescence dual channels", the freshness indicating tag for aquatic products prepared by using pH-sensitive materials disclosed in Chinese Patent CN 201710284531.1, and the intelligent tag using natural pigments to respond to total volatile basic nitrogen disclosed in Chinese Patent CN 201610673246.4. However, the freshness indicators responded by these methods lack sensitivity to early quality deterioration compared with fatty acid oxidation. At the same time, some tags need to contact the product, and it is inevitable that pigment dissolution or other problems may occur, leading to food safety incidents.

[0004] A time-temperature indicator (TTI) is an intelligent label that can reflect time and temperature changes. The color change of the TTI caused by time and temperature changes is irreversible and easy to read, so it can be used to monitor the freshness of food. The currently developed TTIs include TTIs based on the diffusion principle, chemical polymerization reaction TTIs, microbial metabolism TTIs, and enzymatic reaction TTIs. Among them, the enzymatic reaction TTI is currently the mainstream label for early freshness visualization. Some literature has pointed out that with the accumulation of time-temperature, the TTI shows obvious color changes, from dark blue to blue-green, and finally to light yellow, which can be used to predict the spoilage process of pork. Chinese Patent CN202311179282.1 discloses a "method for rapid detection of early freshness of aquatic products based on the synergy of UV and nanoenzymes", and Chinese Patent CN 202410966723.0 discloses a method for detecting the freshness of aquatic products by using carbon dot nanoenzymes and hydrogels to respond to hypoxanthine and pH. However, the enzymatic reaction-based TTI usually requires strict storage conditions, has poor stability, and the production process is relatively complex, making it not conducive to commercialization. Chinese Patent CN202110205903.3 discloses a preparation method of a time-temperature label for monitoring pomfret during transportation, but it requires manual operation to mix two indicators in the early stage to respond, and the applicable range is limited. Therefore, it is necessary to develop a safe, stable, and sensitive color-change-based time-temperature indicating intelligent label for the freshness monitoring and indication of aquatic products and their products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the sensitivity and stability of traditional time-temperature indicator labels (TTIs) are relatively low, and there are large batch differences in the quality deterioration of aquatic products and their products during the processes of collection, fishing, processing, storage, and transportation. The shelf life of traditional packaging labels is difficult to accurately and sensitively reflect the freshness of chilled and frozen products before spoilage.

[0006] In view of the problems in the prior art, the present invention provides a time-temperature indicating label (O-TTI) that responds to lipid oxidation and its preparation method. This indicating label can be formed by one freeze-thaw cycle with the product's freezing and processing technology, and can respond to different oxidation deterioration rates by adjusting the raw material ratio. On the one hand, it meets the synchronous responsiveness of the quality deterioration of aquatic products and their products with different rates and irregular processes caused by individual differences and batch differences. On the other hand, it can cope with the early quality changes of aquatic products and their products caused by lipid oxidation and sensitively indicate the freshness level of the products.

[0007] To achieve the above object, the present invention is realized through the following technical solutions: A time-temperature indicating label based on phycocyanin, which is composed of 8-10 parts of polyvinyl alcohol, 2.5-10 parts of zein, 1-4 parts of phycocyanin, 2-10 parts of phospholipid, and 8-64 parts of ferrous salt; the packaging label synchronously indicates the degree of product quality deterioration with the change of color difference under the conditions of freezing, refrigeration, and room-temperature storage and processing of the commodity. The color change trend is that with the increase of time and temperature, the blue hue weakens and the yellow hue strengthens. The prepared indicating label is initially blue and can always maintain the initial blue color under freezing conditions. By simulating the oxidation of aquatic product lipids (such as fish oil) with phospholipids and simulating the trace metal oxides of aquatic products with ferrous salts, ferrous salts are oxidized to ferric iron in the process of electron transfer during lipid oxidation in an aerobic environment, and ferric iron can cause the color change of phycocyanin to indicate the degree of oxidation deterioration of the commodity; the functions of polyvinyl alcohol and zein are the label substrates, which belong to the materials for forming gels by freezing. On the one hand, it ensures the mechanical properties stability of the gel material during freezing and refrigeration, and on the other hand, the optimized gel network of the material is suitable for the electron chain transfer of the oxidation reaction in the aqueous environment, and the color reaction rate is controlled by the mesh pore size. Because the lipid content and types of product individuals are different, and the oxidation rate curves are different, the responsiveness of the indicating label to time-temperature can be regulated by selecting the addition ratio of ferrous salt and phospholipid. Specifically, when the feeding ratio of ferrous salt and phospholipid is different, the color difference change trend of the indicating label with environmental factors such as storage time and temperature is different. According to the change trend of commodity quality deterioration characteristic indicators, such as the change trends of physicochemical indicators TVB-N and K value for evaluating meat freshness under storage conditions, the color difference value of the indicating label and the physicochemical indicators are linearly or non-linearly fitted, and the label with the highest fitting degree is selected as the indicating label for the corresponding commodity under the response storage conditions, thereby determining its optimal material composition. Through the irreversible color change of the gel film label at different storage temperatures and times, the freshness of aquatic products with different deterioration rates and the dynamic intelligent indication of the food shelf life are realized, especially for aquatic products rich in unsaturated fatty acids and their processed products, for real-time dynamic intelligent indication in complex and variable collection, processing, storage, and transportation environments.

[0008] A preparation method of the above-mentioned time-temperature indicating label based on phycocyanin, which is prepared by freeze-thaw cycling, includes the following steps:

[0009] (1) Weigh polyvinyl alcohol (PVA), add glycerol aqueous solution and stir to dissolve it fully to obtain a polyvinyl alcohol solution with a concentration of 8-10%;

[0010] (2) Weigh zein, add a mixed solution of glycerol with a mass fraction of 10% and ethanol with a mass fraction of 85%, and stir to dissolve it fully to obtain a zein solution with a mass fraction of 2.5-10%;

[0011] (3) Add the zein solution in step (2) to the polyvinyl alcohol solution in step (1), and the volume ratio of the two is 2:1. This ratio can not only ensure the formation and stability of the protein lyophobic sol, but also ensure the mechanical properties and mass transfer rate of the frozen gel. After sufficient mixing, the two solutions are allowed to react fully at a high temperature to obtain reaction solution I, and the temperature is cooled to room temperature for later use;

[0012] (4) Weigh phycocyanin and add distilled water and stir to dissolve it fully to obtain a phycocyanin solution with a concentration range of 1 - 4 g / L, and the light-shielded storage time does not exceed 6 h;

[0013] (5) Weigh phospholipids, add distilled water and stir to dissolve at room temperature (25 ± 2 °C) to obtain a phospholipid solution with a concentration range of 2 - 10 g / L;

[0014] (6) Weigh a certain mass of ferrous salt, add distilled water and dissolve it fully to obtain a ferrous salt solution with a concentration of 8 - 72 g / L. Exceeding or being lower than the specified concentration range is likely to cause problems such as unclear color development or insignificant color change.

[0015] (8) Add the phycocyanin solution in step (4), the phospholipid solution in step (5) and the ferrous salt solution in step (6) to the reaction solution I in step (3) in sequence according to a ratio. The ratio range is that the mass ratio of phycocyanin:phospholipid:ferrous salt is (1 - 2):(1 - 3):(4 - 32), and stir magnetically to mix evenly to obtain reaction solution II;

[0016] (9) Pour reaction solution II into a container mold, let it stand, remove the bubbles, then transfer it to a refrigerator and freeze for 24 - 48 h, and then let it stand and return to room temperature under light-shielded and room temperature conditions. The freeze-thaw process can be cycled 1 - 4 times. Finally, a time-temperature indicating label based on phycocyanin is prepared and stored at 4 °C in the dark.

[0017] Further, the dissolution temperature in step (1) is 90 - 95 °C to fully dissolve the polyvinyl alcohol solution. If the temperature is lower than 90 °C, it is easy to cause incomplete dissolution of the PVA polymer and affect the product forming; the stirring in step (2) is carried out at room temperature.

[0018] Further, step (3) reacts at 90 °C to make the two solutions react fully; the mixing is carried out under magnetic stirring at a rotation speed of 400 - 500 rpm to avoid the generation of a large number of bubbles due to too fast rotation speed.

[0019] Further, the mixing reaction time in step (3) is 15 - 20 min to avoid flocculation of zein caused by too long reaction time.

[0020] Further, the phospholipid described in step (5) is a phospholipid and its mixture with a polyunsaturated fatty acid content of not less than 25%, including but not limited to those of natural and synthetic origins, such as phospholipids derived from Antarctic krill oil ( AKO-PL ), soy lecithin (SOY-PL), egg yolk lecithin (EGG-PL), and DHA-rich phospholipids (DHA-PL) derived from squid eggs.

[0021] Further, the ferrous salt described in step (7) is a food-grade salt containing ferrous ions, including but not limited to ferrous chloride, ferrous sulfate, ferrous lactate, ferrous glycinate, and ferrous gluconate.

[0022] Further, step (8) should be carried out after the reaction solution I has been completely cooled to below 30°C, and each solution should be added in sequence to avoid the influence of too high a temperature on the stability of the reaction system.

[0023] The application of the above-mentioned phycocyanin-based time-temperature indicating label in the freshness monitoring and indication of aquatic products and their products.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) The preparation process of the O-TTI can be synchronized with the freezing process of the product processing and packaging process. The discoloration rate (time-temperature response rate) of the O-TTI can be precisely controlled by adjusting the types and ratios of raw materials. By observing the color change of the label or measuring the color difference value, the visual indication of the label can be realized. The deterioration rate of aquatic products and their products caused by environmental factors such as time and temperature is synchronously adjustable with the color difference change of the indication label in the same processing and storage environment, so as to realize the intelligent indication of the shelf life / shelf life of commodities in complex environments, without being restricted to the fixed shelf life of packaging labels.

[0026] (2) In order to make the prepared indication label consistent with the change law of the freshness of food and aquatic products, the indication label can be transferred from the frozen condition to the same environmental temperature as the food or aquatic product, such as being placed at 4°C for 0-7 days under refrigeration conditions, or being placed at 25°C for 0-3 days. Observe the color change of the indication label at the same environmental temperature as the food and aquatic products, or use a color difference meter to extract the L, a*, b* values and color difference value ΔE of the indication label. Among them, during the period of being placed at 4°C for 0-7 days, the color change law of the indication label is blue → blue-green → green; during the period of being placed at room temperature for 0-3 days, the color change law of the indication label is blue → green → brown-green. The ΔE value of the label color at each time point > 12 indicates that the perceived value of the color difference is very large, and the color change of the indication label can be clearly recognized by the naked eye. Description of the Drawings

[0027] Figure 1Examples 1-8 indicate the color changes of the indicator labels after being placed at 4 °C for 0-7 d and at 25 °C for 0-3 d; where A-H are the photos of the indicator labels of Examples 1-8 after being placed at 4 °C (left column) and 25 °C (right column) for different times, respectively.

[0028] Figure 2 It is the change in color difference value of the indicator labels in Examples 1-8 during the placement period. Among them, A is the change in ΔE value of Examples 1-5 after being placed at 4 °C for 0-7 d, B is the change in ΔE value after being placed at 25 °C for 0-72 h, C is the change in ΔE value of Examples 6-8 after being placed at 4 °C for 0-5 d, and D is the change in ΔE value after being placed at 25 °C for 0-18 h.

[0029] Figure 3 It is the discoloration photos of the fish oil mixed with FeCl2 and phycocyanin solution under different storage conditions. Among them, A is the color change of the fish oil-FeCl2-phycocyanin mixed solution after being placed at 4 °C, and B is the color change after being placed at 25 °C (the numbers in the figure represent the FeCl2 concentration, unit: Mol / L).

[0030] Figure 4 is Fe 2+ gel film, Na + gel film, and the discoloration photos of the metal-ion-free gel film. Among them, A is the color change of the Fe 2+ gel film after being placed under different conditions, B is the color change of the Na + gel film after being placed under different conditions, and C is the color change of the metal-ion-free gel film after being placed under different conditions.

[0031] Figure 5 It is the Pearson correlation coefficients between the color difference value changes of the EGG-PL, SOY-PL, AKO-PL, and DHA-PL gel labels prepared by optimizing the compounding ratio during storage at 4 °C and 25 °C and the K value and TVB-N value changes of tilapia fillets under the same storage conditions. Detailed implementation manners

[0032] The following description is only for the preferred embodiments of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0033] The following examples can be understood as separately expressing a part of the local structure or method of the present invention, or can also be understood as the combination of examples explaining the connotation of a larger scope of the structure or method of the present invention. Unless otherwise specified, all raw materials of the present invention are obtained by purchasing from the market.

[0034] In the following examples, the polyvinyl alcohol used was provided by Macklin Biochemical Technology Co., Ltd. (Shanghai, China), zein was provided by Sigma-Aldrich (Shanghai) Trading Co., Ltd., SOY-PL was provided by Beijing Bio-Top Technology Co., Ltd., EGG-PL was provided by Guangzhou Huilong Biotechnology Co., Ltd., Antarctic krill oil, AKO-PL and DHA-PL were provided by Qingdao Marine Food Nutrition and Health Innovation Research Institute.

[0035] Example 1:

[0036] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until fully dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until fully dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react fully for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 2 g / L DHA-PL solution, and 8 g / L FeCl2 solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:DHA-PL:FeCl2 is 1:1:4.

[0037] Example 2:

[0038] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until fully dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until fully dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react fully for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 2 g / L DHA-PL solution, and 0.2 mL of 8 g / L FeSO4 solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:DHA-PL:FeSO4 is 1:1:4.

[0039] Example 3:

[0040] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react fully for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 4 g / L phycocyanin solution, 6 g / L DHA-PL solution, and 64 g / L ferrous lactate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:DHA-PL:ferrous lactate is 2:3:32.

[0041] Example 4:

[0042] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react fully for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 2 g / L DHA-PL solution, and 8 g / L ferrous glycinate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:DHA-PL:ferrous glycinate is 1:1:4.

[0043] Example 5:

[0044] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 4 g / L phycocyanin solution, 6 g / L DHA-PL solution, and 64 g / L ferrous gluconate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:DHA-PL:ferrous gluconate is 2:3:32.

[0045] Example 6:

[0046] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 3 g / L Antarctic krill oil phospholipid solution, and 60 g / L ferrous lactate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin:lecithin:ferrous lactate is 2:3:30.

[0047] Example 7:

[0048] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 3 g / L egg yolk lecithin solution, and 72 g / L ferrous lactate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin: Antarctic krill oil phospholipid: ferrous lactate is 2:3:36.

[0049] Example 8:

[0050] Accurately weigh 1 g of polyvinyl alcohol, add 9 mL of distilled water, and stir magnetically at 450 r / min at 95 °C until completely dissolved. Weigh 0.125 g of zein, add it to a mixed solution of 4.875 mL of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until completely dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450 r / min at 90 °C to mix the two evenly and react for 15 min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400 r / min, respectively take 0.2 mL of 2 g / L phycocyanin solution, 3 g / L soy lecithin solution, and 60 g / L ferrous lactate solution and add them to the above mixed solution, and stir magnetically for 5 min. Pour the obtained mixed solution into a petri dish, transfer it to a -40 °C refrigerator and freeze for 20 h, and thaw at room temperature for 2 h. Finally, the mass ratio of phycocyanin: soy lecithin: ferrous lactate is 2:3:30.

[0051] As Figure 1 shown, with the prolongation of time, all 8 gel tags showed a color change from the initial blue to green. The blue of the gel tags gradually faded and turned green within 1 - 2 days of placement, and the green gradually deepened in the later stage of placement. At the same time, the ferrous chloride gel tag also showed obvious yellow in the later stage of placement.

[0052] As Figure 2As shown, the change in color difference of the 8 gel tags placed under different conditions gradually increases with the passage of time. And regardless of whether it is at 4°C or 25°C, the color difference ΔE of the gel tags is greater than 5, indicating that the naked eye can distinguish the color change of the gel tags; the color difference of the gel tags prepared with FeCl2 is greater than that of other ferrous ion gel tags during placement, indicating that its color change is the most obvious.

[0053] Example 9:

[0054] Prepare 0.1M FeCl2 solution and 3mg / ml phycocyanin solution respectively. Take 0.6ml of 3mg / ml phycocyanin solution, add 0.1ml of fish oil extracted from sturgeon milt, and add 0, 0.4, 0.8, 1.2, 1.6ml of 0.1M FeCl2 solution respectively. After making up to 5ml, vortex and mix well. Place at 25°C and 4°C for 6 days respectively, and observe the change of the system color. As Figure 3 As shown, the solutions prepared with different concentrations of FeCl2, fish oil and phycocyanin showed different degrees of changes during placement. The solutions prepared with higher concentrations of FeCl2 (0.012M and 0.016M) showed color changes, but at the same time caused the flocculation of phycocyanin, making the solution unstable, indicating that the system prepared with fish oil is not suitable for indicating the change of freshness.

[0055] Example 10:

[0056] Accurately weigh 1g of polyvinyl alcohol, add 9ml of distilled water, and stir magnetically at 450r / min at 95°C until fully dissolved. Weigh 0.125g of zein, add it to a mixed solution of 4.875ml of glycerol (w = 10%) and 85% ethanol, and stir magnetically at room temperature until fully dissolved. Add the zein solution to the polyvinyl alcohol solution, stir magnetically at 450r / min at 90°C to mix the two evenly and react fully for 15min to obtain a polyvinyl alcohol / zein mixed solution. After cooling to room temperature, under the condition of magnetic stirring at a speed of 400r / min, add 0.2ml of 2g / L phycocyanin solution and 3g / L EGG-PL solution to three test tubes. In addition, add 60g / L of ferrous lactate to tube 1, 60g / L of sodium chloride solution to tube 2, and add the same volume of water to tube 3 as a control. After magnetically stirring the mixed solutions of the three sample tubes for 5min, pour them into a petri dish, and further transfer them to a -40°C refrigerator for freezing for 20h, and thaw at room temperature for 2h to prepare three gel films. Observe their color changes at 25°C for 24h and 4°C for 7 days respectively. As Figure 4 As shown, among the three gel films, only the gel film containing Fe 2+ showed a color change from blue to green, and Na +The gel films and the gel films without metal ions remained blue throughout the storage period, indicating that the change in the color of the gel films during storage was due to the oxidation of Fe 2+ to Fe 3+ .

[0057] Effect verification:

[0058] (1) Determination of TVB-N and K value of fish meat:

[0059] Fresh tilapia (500 g ± 50 g) was purchased from Nanbin Farmers' Market, Yazhou District, Sanya City, Hainan Province. After hitting the head, the skin and bones were removed, and ice was covered on the fish meat and sent to the laboratory for determination within 30 min. The automatic Kjeldahl distillation method (GB 5009.228-2016) was used to determine the total volatile basic nitrogen (TVB-N); the K value was determined with reference to SC / T 3048-2014. 2 g of the sample was weighed, homogenized with 10% perchloric acid solution, centrifuged at 8000 rpm for 10 min at 4 °C, the precipitate was extracted again with 5% perchloric acid solution, repeated twice, the supernatant was combined, the pH was adjusted to 6.5 and filtered, and then analyzed by high performance liquid chromatography.

[0060] (2) Optimization of the addition ratio of gel film components:

[0061] Taking the gel films prepared with ferrous lactate and EGG-PL as an example, gel films with different mass ratios were prepared (EGG-PL: ferrous lactate = 1:6 - 1:14). The gel films with different mass ratios were placed at 25 °C for 18 h and at 4 °C for 5 d, and the color difference value (ΔE) of the gel films was measured and photographed at regular intervals during this period. During the monitoring at 25 °C, the color difference value showed an overall upward trend, so a linear fitting was performed on the color difference value. During the monitoring at 4 °C, the color difference value showed a trend of faster growth in the early stage and slower growth in the later stage, so an exponential growth type non-linear fitting was performed on the color difference value. The results are shown in Table 1.

[0062] Table 1: Summary table of fitting equations for the color difference values of gel films prepared by compounding AKO-PL (A), EGG-PL (B), SOY-PL (C) and ferrous lactate in different proportions during storage at 4 °C and 25 °C

[0063]

[0064] As can be seen from Table 1, under the linear fitting at 25°C, in the equation, a represents the magnitude of the change rate of the color difference value, and b represents the magnitude of the initial color difference value. Except for EGG-PL:ferrous lactate = 1:6, the a values of the other concentration groups do not change much, indicating that the change rates of the color difference values are close. When EGG-PL:ferrous lactate = 1:10, the b value is the largest, that is, the initial change of the color difference value at this concentration is the largest, and the color difference value of this concentration group is the largest during the response period. Therefore, when EGG-PL:ferrous lactate = 1:10, it can better indicate the response during the 25°C period. Under the exponential growth non-linear fitting at 4°C, the α value in the equation represents the level with the largest color difference value, and the β value is inversely proportional to the change rate of the color difference value. When EGG-PL:ferrous lactate = 1:6, the β value is the largest, indicating that the change rate of the color difference value of this concentration group is the smallest. Except for this concentration group, the β values of the other groups are close. The groups with the largest α values are EGG-PL:ferrous lactate = 1:10 and 1:12, indicating that the color difference levels of these two concentration groups are the largest during the response period. Therefore, when EGG-PL:ferrous lactate = 1:10 and 1:12, it can better indicate the response during the 4°C period. In summary, when preparing the gel film with EGG-PL and ferrous lactate, when EGG-PL:ferrous lactate = 1:10, the response effect of the gel film during the 25°C and 4°C periods is better. Therefore, this is determined as the best concentration ratio of EGG-PL and ferrous lactate. (3) Screening gel labels according to the response correlation between the color difference change of the gel film and the fish freshness indicators (TVB-N, K value):

[0065] Select the four gel films of AKO-PL, EGG-PL, SOY-PL, and DHA-PL with the optimized best compounding ratio, and conduct Pearson correlation analysis on the change of their color difference values and the changes of TVB-N and K values during the storage of fish. The obtained results are as Figure 5 shown. As can be seen from the figure, at 4°C, the gel film with the best correlation with the K value and TVB-N of tilapia is SOY-PL, and its Pearson correlation coefficients are 0.971 and 0.968 respectively, which can be used as the indication labels for the K value and TVB-N of the tilapia freshness indicator. Secondly, the correlation between AKO-PL and the K value and TVB-N is also relatively good, and DHA-PL and EGG-PL are the second. At 25°C, the correlations between the four gel films and the K value of tilapia are all good, but the correlations with TVB-N are poor, all less than 0.9. It can be seen that the prepared gel film can well respond to the freshness of tilapia. The SOY-PL gel film shows the best correlation with tilapia, especially the good correlation with the K value.

[0066] All aspects, embodiments, and features of the present invention should be considered illustrative in all respects and do not limit the present invention. The scope of the present invention is only defined by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will appreciate other embodiments, modifications, and uses.

[0067] In the preparation method of the present invention, the order of each step is not limited to the listed order. For those of ordinary skill in the art, without creative efforts, the changes in the sequence of each step are also within the protection scope of the present invention. In addition, two or more steps or actions can be carried out simultaneously.

[0068] Finally, it should be noted that the specific embodiments described herein are only examples of the present invention and do not limit the implementation manners of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways for substitution. It is not necessary and impossible to list all implementation manners here. And these obvious changes or variations derived from the essence of the present invention still fall within the protection scope of the present invention. Interpreting them as any additional restrictions is contrary to the spirit of the present invention.

Claims

1. A time-temperature indicator label based on phycocyanin, characterized in that: The packaging label is composed of 8 to 10 parts of polyvinyl alcohol, 2.5 to 10 parts of zein, 1 to 4 parts of phycocyanin, 2 to 10 parts of phospholipids, and 8 to 64 parts of ferrous salt. The packaging label indicates the degree of deterioration of the product quality by color difference changes when the product is stored in freezing, refrigeration, or room temperature. The color change trend decreases with the increase of time and temperature, and the blue hue decreases and the yellow hue increases.

2. A method for preparing the phycocyanin-based time-temperature indicator label according to claim 1, characterized in that Prepared by freeze-warming cycles, including the following steps: (1) Weigh polyvinyl alcohol, add glycerol aqueous solution and stir to fully dissolve it to obtain a polyvinyl alcohol solution with a concentration of 8-10%; (2) weighing zein, adding a mixed solution of 10% by mass of glycerol and 85% by mass of ethanol, stirring to fully dissolve it, and obtaining a zein solution with a mass fraction of 2.5-10%; (3) adding the zein solution in step (2) to the polyvinyl alcohol solution in step (1) at a volume ratio of 2:1, mixing the two solutions thoroughly, reacting the two solutions at high temperature to obtain a reaction solution I, and cooling the solution to room temperature for standby use; (4) Weigh phycocyanin, add distilled water and stir to fully dissolve it to obtain a phycocyanin solution with a concentration range of 1-4 g / L, and store it away from light for no more than 6 hours; (5) Weigh phospholipids, add distilled water and stir to dissolve at room temperature to obtain a PC solution with a concentration range of 2-10 g / L; (6) Weigh a certain amount of ferrous salt, add distilled water to fully dissolve it, and obtain a ferrous salt solution with a concentration of 8-72 g / L; (8) adding the phycocyanin solution of step (4), the phospholipid solution of step (5) and the ferrous salt solution of step (6) to the reaction solution I of step (3) in order according to a ratio, wherein the mass ratio of phycocyanin:phospholipid:ferrous salt is (1-2):(1-3):(4-32), and mixing them evenly by magnetic stirring to obtain a reaction solution II; (9) Pour the reaction solution II into the container model, let it stand and remove bubbles, then transfer it to a refrigerator and freeze it for 24-48 hours, then let it stand in a dark place and at room temperature and return to room temperature. The freezing-warming process can be repeated 1-4 times to finally obtain a phycocyanin-based time-temperature indicator label, which is then stored in a dark place at 4°C.

3. The preparation method according to claim 2, characterized in that: The dissolving temperature of step (1) is 90-95°C, so that the polyvinyl alcohol solution is fully dissolved; and step (2) is carried out under stirring at room temperature.

4. The preparation method according to claim 2, characterized in that: Step (3) reacts at 90° C. to allow the two solutions to react fully; and mixes under magnetic stirring at a rotation speed of 400-500 rpm.

5. The preparation method according to claim 2, characterized in that: The mixing reaction time of step (3) is 15-20 minutes.

6. The preparation method according to claim 2, characterized in that: The phospholipids described in step (5) are phospholipids with a polyunsaturated fatty acid content of not less than 25% and mixtures thereof.

7. The preparation method according to claim 2, characterized in that: The ferrous salt described in step (7) is a food grade salt containing ferrous ions.

8. The preparation method according to claim 2, characterized in that: In step (8), the reaction solution I should be completely cooled to below 30° C. before each solution is added in sequence.

9. Use of the phycocyanin-based time-temperature indicator label according to claim 1 in monitoring and indicating the freshness of aquatic products and their products.

Images