Dual-function label for raw fish pieces and preparation method thereof

Abstract

The invention discloses a visual indication of the freshness of raw fish pieces and a non-contact fresh-keeping dual-function label and a preparation method thereof, and belongs to the technical field of food packaging and preservation. The label is prepared into a fiber film by electrostatic spinning technology using bromothymol blue-alizarin as a freshness indicator and a wall material raw material, and trans-2-hexenal as a core material raw material, and the fiber film is wrapped with a transparent and breathable packaging film on the outside of the fiber film. At the same time, the present invention also provides a preparation method of the dual-function label. The label of the present invention uses bromothymol blue and alizarin as freshness indicators, and can produce significant color changes after absorbing the gas generated by the corruption of fish meat, thereby intuitively, efficiently, sensitively and accurately reflecting the freshness of raw fish pieces. At the same time, trans-2-hexenal is embedded in the label by electrostatic spinning technology, which can continue to volatilize and inhibit the growth of corrupt microorganisms during the preservation of fish pieces, thereby extending the shelf life of raw fish pieces, and has great economic value.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging and preservation, and in particular relates to a raw fish block freshness visual indication and non-contact preservation dual-function label, a preparation method of the label and a package containing the label. Background Art

[0002] With the rapid development of the food processing industry, fish such as tuna and salmon are being accepted by more and more people because of their delicious taste and rich nutrition. In order to maximize the retention of their nutritional value, eating them raw is one of the main ways to eat the above fish, such as Japanese sushi and sashimi. However, the lipids in tuna are easily oxidized during storage, causing the fish meat to spoil and affect its nutritional value and edible quality, thus adversely affecting the raw consumption of tuna. In order to more effectively ensure the food safety of raw fish, it is particularly important to observe the freshness of fish pieces in real time. In order to effectively ensure food quality and extend the shelf life of food, it is of great significance to develop new packaging materials.

[0003] With the continuous advancement of material technology, in order to ensure the quality and safety of food and extend the shelf life of packaged food, food packaging materials with unique functionality continue to emerge. Among them, smart packaging and active packaging are very important development directions of functional packaging. At present, smart packaging is mostly used to detect the freshness of food, while active packaging is mostly used to inhibit the growth of bacteria and other substances in food. For example, the prior art CN111472092B discloses a dual-indicator smart label with the function of identifying the quality of meat, as well as the preparation method and use of the label. The patent uses electrospinning technology to prepare a double-layer fiber membrane, and dissolves a hydrophobic substance and a hydrophilic substance to prepare a volatile biogenic amine sensing layer and a hydrogen sulfide sensing layer, thereby ultimately realizing the monitoring of the dual indicators of biogenic amines and hydrogen sulfide in meat, thereby improving the accuracy of smart label monitoring. Although the patent can realize the monitoring of the dual indicators of meat freshness and effectively expand the number of monitoring indicators, it is still a single monitoring and indicating function in terms of function, and has not truly achieved the purpose of having other functions other than the monitoring and indicating function, and there is still a problem of single function. In addition to their single function, current indicator labels basically provide instructions through contact, conditioned stimulation and other methods, which can easily cause contamination, damage and other adverse effects on food.

[0004] In foods with a long shelf life and sealed packaging, the use of desiccants, preservatives and other reagents is very common. However, for fresh meat with a short shelf life, especially fish slices, meat chunks and other foods, it is often rare to add desiccants, preservatives and other reagents to maintain the quality of the meat. The use of desiccants, preservatives and other reagents will affect the quality of fresh meat. For example, in sealed packaging, the use of desiccants will affect the moisture content of fresh meat due to the absorption of moisture in the meat, and the contact use of preservatives is very likely to have an adverse effect on the taste, mouthfeel and other sensory properties of the meat. Therefore, fresh meat is often stored in a temperature-controlled manner. On the one hand, this storage method will increase the storage cost, and on the other hand, the shelf life of fresh fish meat under this storage method will generally not exceed 5 days, and the shelf life cannot be further extended. Fresh fish slices often have a high market value, and the extension of the shelf life undoubtedly has a high economic value.

[0005] Trans-2-hexenal is a kind of aromatic component substance present in natural fruits and vegetables. Because of its natural safety, it has been listed in the food-grade flavoring material additive in my country. In addition to being used as a fragrance, trans-2-hexenal also has a certain antibacterial effect on fruits and vegetables such as kiwi fruit, early crisp pear, strawberry, etc. Based on the antibacterial effect of trans-2-hexenal, there is currently a report (for example, prior art CN113892517A) that uses it as a slow-release preservative. However, due to the corruption and deterioration microorganisms that cause fresh meat being completely different from fruits and vegetables, whether trans-2-hexenal is suitable for the preservation of fresh meat (especially fish) is still inconclusive. At the same time, trans-2-hexenal can also affect the Taylor cone morphology of the label fiber film, thereby changing the mechanical properties of the label fiber film, and also bringing uncertainty to its practical application in the short shelf life fresh meat such as fish. Summary of the invention

[0006] In order to solve the current technical problems that fresh fish such as tuna have a short shelf life, the smart labels for preservation have a single function and do not have a preservative effect, and to achieve real-time, non-contact, and visual tracking and detection of fresh meat products during transportation, storage, processing, and sales, and to ensure the quality and safety of raw fresh meat during consumption, the present invention provides a dual-function label for raw fish pieces, a method for preparing the label, and a package containing the label. The specific technical solution is as follows:

[0007] A dual-function label for raw fish pieces, which uses bromothymol blue-alizarin as a freshness indicator and wall material raw material, and trans-2-hexenal as a core material raw material, and is prepared into a fiber membrane through electrostatic spinning technology; the outer side of the fiber membrane is wrapped with a transparent and breathable packaging film.

[0008] Preferably, the mass ratio of bromothymol blue to alizarin is: bromothymol blue:alizarin=(1-3):1.

[0009] More preferably, the mass ratio of bromothymol blue to alizarin is: bromothymol blue:alizarin=(1-2):1.

[0010] Preferably, the pH of the freshness indicator is 4-8.

[0011] Preferably, the raw fish chunks are tuna chunks.

[0012] More preferably, the encapsulation concentration of trans-2-hexenal is 2 to 3 μL / mL.

[0013] More preferably, the encapsulation concentration of trans-2-hexenal is 2.5 μL / mL, and the flow rate of the core spinning solution is 0.015 mm / min.

[0014] The second object of the present invention is to provide a method for preparing the above-mentioned dual-function label for raw fish pieces, the steps of the method are as follows:

[0015] 1) preparing a freshness indicator: dissolving bromothymol blue and alizarin in ethanol, and adjusting the pH to 4-8 to obtain a freshness indicator;

[0016] 2) Determining the minimum inhibitory concentration of trans-2-hexenal and preparing an encapsulation solution: using trans-2-hexenal to determine the minimum inhibitory concentration of aquatic spoilage bacteria; the minimum inhibitory concentration of trans-2-hexenal to aquatic spoilage bacteria is 2.5 μL / mL, and a trans-2-hexenal encapsulation solution is prepared according to the determined minimum inhibitory concentration;

[0017] 3) Preparation of a spinning fiber membrane: adding zein to a mixed solution of anhydrous ethanol and anhydrous acetic acid and stirring to dissolve, adding the freshness indicator of step (1) after dissolution, mixing to obtain a coaxial wall material spinning solution, using the trans-2-hexenal encapsulation solution obtained in step (2) as the core material spinning solution, performing an electrospinning process to obtain an electrospinning membrane;

[0018] 4) Label preparation: The electrospun membrane obtained in step (3) is dried and then cut, and then wrapped with a polyethylene film to obtain a dual-function label.

[0019] Preferably, the aquatic spoilage bacteria in step (2) include Shewanella putrefaciens, Pseudomonas fragariae, Pseudomonas fluorescens, Staphylococcus aureus and Escherichia coli.

[0020] Preferably, the concentration of corn zein after dissolution in step (3) is 30% to 40% (m / V); the volume ratio of anhydrous ethanol to anhydrous acetic acid in the mixed solution is: anhydrous ethanol: anhydrous acetic acid = 2.5:7.5; the stirring time is 1.5 to 3 hours; the specific conditions of the electrospinning treatment are: spinning distance 12 to 15 cm; positive voltage 10 to 15 kV, negative voltage -1.8 to -2 kV; wall material spinning solution flow rate 0.06 mm / min, core material spinning solution flow rate 0.015 mm / min.

[0021] Preferably, in step (4), the drying temperature is 20 to 30° C. and the drying time is 6 to 8 hours.

[0022] The third object of the present invention is to provide a package containing the dual-function label for raw fish pieces, wherein the package contains a non-contact sealed colorimetric card used together with the dual-function label for raw fish pieces.

[0023] Compared with the prior art, the beneficial effects obtained by the present invention are as follows:

[0024] (1) The present invention first prepares a bromothymol blue-alizarin mixed indicator, which reacts with volatile components produced by the corruption of tuna chunks to produce a color change, and the color change is used to monitor the freshness of raw tuna chunks. Compared with a single indicator, the composite indicator has a more sensitive and stable indicating property, and can accurately detect the freshness of raw tuna chunks.

[0025] (2) The smart label provided by the present invention utilizes electrostatic spinning technology to encapsulate trans-2-hexenal inside the label, forming a dual-function label with a core-shell structure, which adds an antibacterial function on the basis of the indication function. Compared with other smart indication labels, this indication label has the dual functions of indication and preservation, is simple and easy to use, safe and environmentally friendly, and can release antibacterial agents to form an antibacterial environment without contacting the fish pieces, effectively inhibiting the growth of spoilage microorganisms. It has been verified by experiments that it can extend the shelf life of fish pieces by at least 3 days. This smart label can not only effectively extend the shelf life of fresh fish meat and has high economic value, but also the materials used are degradable green materials, which are in line with the trend of sustainable development in food processing.

[0026] (3) The present invention uses a specific ratio of bromothymol blue-alizarin as an indicator dye, which can clearly indicate the monitoring results. At the same time, a specific concentration of trans-2-hexenal solution is used to prepare the core material, and the electrospinning technology is used for encapsulation, which not only ensures the mechanical properties of the label fiber film, but also maintains a suitable release rate of trans-2-hexenal, thereby extending the shelf life of the fish meat.

[0027] (4) The smart label used in the present invention is a pH-sensitive label that can monitor the freshness of fish meat through color changes visible to the naked eye. The smart label has the dual functions of spontaneous non-contact antibacterial function and non-destructive detection of the quality and freshness of raw tuna chunks. Producers, sellers and consumers do not need to make the smart label contact the product itself to achieve the freshness effect. Consumers only need to observe the color of the smart label to know the quality and freshness of the meat in the package, which is very convenient to use. The dual-function label can realize non-destructive, real-time, visual and rapid detection and monitoring of the freshness of raw tuna chunks during transportation, storage, processing and sales, which can overcome the shortcomings of traditional detection methods such as complex operation, long time consumption and sample destruction.

[0028] (5) The inventors found in their research that trans-2-hexenal not only has an inhibitory effect on fruit and vegetable spoilage bacteria, but also has a significant inhibitory effect on Shewanella putrefaciens, Pseudomonas fragrans, Pseudomonas fluorescens, Staphylococcus aureus and Escherichia coli, which cause tuna spoilage. And its minimum inhibitory concentration can just adapt to the electrospinning process, ensuring that trans-2-hexenal will not have an excessive negative impact on the mechanical properties of the spun fiber membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram showing the color change of dyes with different dyeing ratios under different pH conditions;

[0030] Among them, row A is the color effect diagram of the dye bromothymol blue: alizarin = 2:1, which changes with pH;

[0031] Row B is the color effect diagram of the dye bromothymol blue: alizarin = 1:1, as the pH changes;

[0032] Row C shows the color effect of the dye bromothymol blue: alizarin = 3:1 as the pH changes.

[0033] Figure 2 This is the UV-VIS curve of the bromothymol blue-alizarin indicator in Example 1.

[0034] Figure 3 This is a picture of the dual-function label prepared in Example 1 (a colorimetric card is packaged around the label).

[0035] Figure 4 The changes in the total bacterial count and volatile basic nitrogen (TVB-N) of raw tuna chunks after adding the dual-function label in Example 1 during a storage period of 10 days;

[0036] Among them, Figure a is the curve of the change of total colony count with storage time; Figure b is the curve of the change of volatile basic nitrogen with storage time.

[0037] Figure 5 The dual-function label prepared in Example 1 and the raw tuna block are stored for 1 to 10 days;

[0038] Among them, a is the color change of the indicator label blank group and the dual-function label experimental group within 1-10 days of storage;

[0039] b From left to right, the color changes of the labels of raw tuna chunks after 1-10 days of storage.

[0040] Figure 6 The visible light pictures are of raw tuna chunks in three different freshness states monitored and indicated by the label prepared in Example 1. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited by the embodiments.

[0042] Unless otherwise specified, the materials, reagents, methods, instruments, etc. used in the following examples are all conventional materials, reagents, methods, instruments in the art and can be obtained through commercial channels by those skilled in the art.

[0043] The tuna meat used in the following examples is all commercially available frozen tuna meat purchased from Jinzhou Haizhi Fresh Aquatic Product Market.

[0044] In the following examples, the acid used to adjust pH was hydrochloric acid and the base was sodium hydroxide.

[0045] In the following examples, the dye was dissolved in anhydrous ethanol, and the final concentration of the freshness indicator was 1%.

[0046] (m / v).

[0047] Before preparing the dual-function label, the effects of different dye ratios and different pH conditions on the indicator were first measured. The specific measurement process is as follows:

[0048] Bromothymol blue and alizarin were selected as indicator dyes, and anhydrous ethanol was used as solvent. The color change of the freshness indicator under pH 3-11 was measured according to the mass ratio of bromothymol blue: alizarin = (1-3): 1. The results are as follows Figure 1 As shown. Figure 1 It can be seen that under different ratio conditions, as the pH continues to increase, the color of the indicator gradually changes from yellow to blue, and the change trend is obvious.

[0049] Example 1

[0050] 1. Preparation of Freshness Indicator

[0051] 60 mg of bromothymol blue and 30 mg of alizarin were dissolved in 9 mL of ethanol solvent, the pH was adjusted to 7, and the mixture was mixed and stirred to obtain a bromothymol blue-alizarin indicator.

[0052] Under the condition that the mass ratio of bromothymol blue to alizarin is 2:1, the color change of the indicator under different pH conditions of 3 to 11 was measured and verified. The results are shown in Table 1. At the same time, the UV-VIS curve of the indicator under different pH conditions was measured. The results are shown in Table 1. Figure 2 shown.

[0053] Table 1 Changes of indicator RGB values ​​with pH when the dye mass ratio is 2:1

[0054]

[0055] As shown in Table 1, when the ratio of dye addition is bromothymol blue: alizarin = 2:1, the R and G values ​​generally show a downward trend, and the R value reaches the lowest point of 0 when the pH is 7-8; the G value reaches the lowest point of 0 when the pH is 10; the B value reaches the lowest point when the pH is 5, and then slowly increases and decreases. In general, the R and G values ​​vary the most in the pH range of 6-7, and the B value changes the most at pH 7-8, which shows that the dye can show obvious color changes in the range of pH 6-7 and pH 7-8. It shows that when the addition ratio of bromothymol blue to alizarin is 2:1, it has a better and more sensitive color development effect in the range of pH 6-8. In this embodiment, pH 7.0 is selected as the pH value of the dye for preparing a dual-functional label.

[0056] like Figure 2 As shown, the bromothymol blue-alizarin indicator has an absorption peak at 431nm and 616nm at pH 5, and the absorption peak at 431nm is slightly larger than the absorption peak at 616nm; bromothymol blue is an organic weak acid, and at low pH values, the main component in the solution is the yellow acid form of bromothymol blue. As the pH value increases, the concentration of the blue basic form of bromothymol blue gradually increases and causes a light green color change. As the pH value increases, a large amount of blue basic form is produced. In addition, the maximum absorption peak of the solution shifts to a higher wavelength as the pH value increases.

[0057] 2. Determination of the minimum inhibitory concentration of trans-2-hexenal and determination of the concentration of the encapsulation solution

[0058] The antibacterial effects of eight different concentrations of trans-2-hexenal solutions ranging from 0.5 μL / mL to 5 μL / mL on five major aquatic spoilage bacteria, namely Staphylococcus aureus, Shewanella putrefaciens, Pseudomonas fragrans, Pseudomonas fluorescens, and Escherichia coli, were determined, and the results are shown in Table 2. The above spoilage bacteria were all screened from spoiled raw tuna pieces.

[0059] Table 2 Minimum inhibitory concentration of five strains

[0060]

[0061] Note: “-” indicates no colony growth, “+” indicates colony growth

[0062] Table 2 shows that the inhibitory concentration of trans-2-hexenal against five strains, within the test concentration range, trans-2-hexenal has a certain inhibitory effect on the five strains, and the MIC of trans-2-hexenal against Pseudomonas fragariae, Shewanella putrefaciens, Pseudomonas fluorescens, Escherichia coli, and Staphylococcus aureus are 1.25μL / mL, 2μL / mL, 1.25μL / mL, 2.5μL / mL, and 2.5μL / mL, respectively. The minimum inhibitory concentration of trans-2-hexenal against aquatic spoilage bacteria was determined to be 2.5μL / mL.

[0063] In order to ensure the effectiveness of bifunctional labels prepared by trans-2-hexenal, the mechanical properties and air permeability of bifunctional membranes prepared by three different concentrations of trans-2-hexenal solutions of 2.5 μL / mL, 4 μL / mL and 5 μL / mL were measured. The mechanical strength of the bifunctional membrane was determined by two indicators, namely tensile strength and elongation at break. The determination method was based on the method of GB / T 1040.1-2018 "Determination of tensile properties of plastics". The air permeability was determined by water vapor permeability as an evaluation index. The determination method was based on the method used by Wu Yan et al. (Wu Yan, Qin Yuyue, Yuan Minglong, et al. Study on the performance of polylactic acid-polycaprolactone / tea polyphenol composite membrane [J]. Food Industry Science and Technology, 2014, 35(13): 144-146+223.). The specific measurement results are shown in Tables 3 and 4.

[0064] Table 3 Mechanical properties of bifunctional membranes with different concentrations of trans-2-hexenal added

[0065]

[0066] Table 4 Water vapor permeability of bifunctional membranes with different concentrations of trans-2-hexenal added

[0067]

[0068] As can be seen from Table 3, with the increase of trans-2-hexenal concentration, the tensile strength and elongation at break of the bifunctional tag showed a downward trend. This is mainly because the higher trans-2-hexenal concentration easily causes the fiber membrane to aggregate, making the prepared bifunctional indicator tag brittle and easy to break. On the other hand, the elongation at break of the bifunctional tag with an addition concentration of 2.5 μL / mL trans-2-hexenal is 50.53±4.02. a% was significantly higher than that of the trans-2-hexenal added at other concentrations, which also proved that the increase in the concentration of trans-2-hexenal would change the morphology of the Taylor cone and change the properties of the film. The dual-functional label with the addition of 2.5 μL / mL trans-2-hexenal had relatively better toughness and was more suitable for application as an indicator / preservation dual-functional label in food.

[0069] As can be seen from Table 4, the water vapor permeability of the bifunctional tag with 2.5 μL / mL trans-2-hexenal added reached 44.657 ± 1.705 on the first day. a g / (m 2 ·d), and increased to 51.265±2.433 on the second day a g / (m 2 d) As the concentration of trans-2-hexenal increases, the water vapor permeability of the bifunctional indicator label decreases. This may be because as the concentration of trans-2-hexenal increases, the pores of the bifunctional indicator film become smaller, which is not conducive to the permeation of water vapor. This may lead to a decrease in the color change sensitivity of the bifunctional label.

[0070] Therefore, a 2.5 μL / mL trans-2-hexenal solution was selected as the encapsulation solution.

[0071] 3. Preparation of Spun Fiber Membranes and Labels

[0072] Dissolve 2g of zein (ZN) in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stir for 2.5h. When ZN is completely dissolved, add the prepared freshness indicator solution, stir evenly, and suck it into a 5mL syringe as the wall material spinning solution after ultrasonic debubbling. Then use the trans-2-hexenal solution as the core material spinning solution for electrospinning. The set distance is 12cm; the positive voltage is 10kV, and the negative voltage is -1.8kV; the wall material flow rate is 0.06mm / min and the core material flow rate is 0.015mm / min. The electrospun membrane is obtained and dried at a temperature of 30℃ for 6h; the shear size is 1.5cm×1.5cm. The obtained smart indicator membrane is tightly wrapped with a low-density polyethylene film to obtain a smart indicator label. The picture of the prepared smart indicator label under visible light is as follows Figure 3 As shown (middle part). The smart indicator label can detect gases (such as TVB-N, carbon dioxide, hydrogen sulfide, etc.) generated during the spoilage process of raw tuna chunks. Specifically, these gases will cause the pH value of the smart indicator label to change, thereby causing the indicator color to change, so that the smart indicator label can produce a color change response to the freshness of the raw tuna chunks.

[0073] 4. Preparation of single-function indicator labels

[0074] For experimental comparison, this embodiment also prepares a single-function indicator label with only an indication function. The specific method is: dissolve 2g of zein (ZN) in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stir for 2.5h. When ZN is completely dissolved, add the prepared freshness indicator solution, stir evenly, and use a syringe to inhale 5mL as the spinning solution after ultrasonic debubbling. Set the distance to 12cm; the positive voltage is 10kV, and the negative voltage is -1.8kV. Obtain an electrospun membrane, dry it at a temperature of 30°C for 6h, and cut it to a size of 1.5cm×1.5cm. Then wrap it tightly with a low-density polyethylene film, that is, a single-function indicator label.

[0075] Example 2

[0076] 1. Preparation of freshness indicator;

[0077] 60 mg of bromothymol blue and 30 mg of alizarin were dissolved in 9 mL of ethanol solvent, the pH was adjusted to 6.5, and the mixture was mixed and stirred to obtain a bromothymol blue-alizarin indicator.

[0078] 2. Determine the minimum inhibitory concentration of trans-2-hexenal;

[0079] The fresh meat product in this example is tuna fillet, and the minimum inhibitory concentration of trans-2-hexenal adopts the same parameters as in Example 1.

[0080] 3. Preparation of freshness indication / freshness preservation dual-function labels;

[0081] 1.9g of zein (ZN) was dissolved in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stirred for 2.5h. When ZN was completely dissolved, the prepared freshness indicator was added and mixed, stirred evenly, and sucked into a 5mL syringe as a wall material after ultrasonic defoaming. Then, trans-2-hexenal was used as the core material for electrospinning. The set distance was 12.5cm; the positive voltage was 11kV, and the negative voltage was -1.85kV; the wall material flow rate was 0.06mm / min, and the core material flow rate was 0.015mm / min. The obtained spinning membrane was dried at a temperature of 30℃ for 6h; the shear size was 1.5cm×1.5cm. The obtained smart indicator film was tightly wrapped with a low-density polyethylene film to obtain a smart indicator label.

[0082] Example 3

[0083] 1. Preparation of Freshness Indicator

[0084] 60 mg of bromothymol blue and 30 mg of alizarin were dissolved in 9 mL of ethanol solvent, the pH was adjusted to 7.5, and the mixture was mixed and stirred to obtain a bromothymol blue-alizarin indicator.

[0085] 2. Determination of the minimum inhibitory concentration of trans-2-hexenal

[0086] The fresh meat product in this example is tuna fillet, and the minimum inhibitory concentration of trans-2-hexenal adopts the same parameters as in Example 1.

[0087] 3. Preparation of freshness indication / freshness preservation dual function labels

[0088] 1.8g of zein (ZN) was dissolved in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stirred for 2h. When ZN was completely dissolved, the prepared freshness indicator solution was added and mixed, stirred evenly, and sucked into a 5mL syringe as a wall material after ultrasonic debubbling. Then, trans-2-hexenal was used as the core material for electrospinning. The set distance was 13cm; the positive voltage was 12kV, and the negative voltage was -1.9kV; the wall material flow rate was 0.06mm / min and the core material flow rate was 0.015mm / min. The obtained spinning membrane was dried at a temperature of 28℃ for 6.5h; the shear size was 1.5cm×1.5cm. The obtained smart indicator membrane was tightly wrapped with a low-density polyethylene film to obtain a smart indicator label.

[0089] Example 4

[0090] 1. Preparation of freshness indicator;

[0091] 50 mg of bromothymol blue and 50 mg of alizarin were dissolved in 10 mL of ethanol solvent, the pH was adjusted to 7.5, and the mixture was mixed and stirred to obtain a bromothymol blue-alizarin indicator.

[0092] After the indicator was prepared, the change of the dye bromothymol blue-alizarin with pH (3-11) under equal quality conditions was measured and verified, as shown in Table 5.

[0093] Table 5 Changes of indicator R, G, B values ​​with pH when dye bromothymol blue: alizarin = 1:1

[0094]

[0095] As shown in Table 5, when the ratio of dye addition is bromothymol blue: alizarin = 1:1, the R and G values ​​first decrease and then increase, and the R value reaches the lowest point 0 when the pH is 7-8; the G value reaches the lowest point when the pH is 10; the B value reaches the lowest point when the pH is 7, and then suddenly increases and then decreases. The R, G, and B values ​​all have the largest change range in the pH range of 7-8, indicating that the color change of the dye is most obvious at pH 7-8.

[0096] In order to further study the color change of the dye under different mass ratios of bromothymol blue to alizarin with the change of pH, the color change under the mass ratio of bromothymol blue: alizarin = 3:1 and 1:2 was also measured. However, when the mass ratio was 1:2, the dye mixture could not be dissolved in the ethanol solution. The R, G, and B values ​​of the dye bromothymol blue: alizarin = 3:1 with pH change are shown in Table 6.

[0097] Table 6 Changes of indicator R, G, B values ​​with pH when bromothymol blue: alizarin = 3:1

[0098]

[0099] As shown in Table 6, when the addition ratio of bromothymol blue and alizarin is 3:1, the color change trend in solutions with different pH values ​​(3-11) is the same as when the dye addition ratio is 1:1 and 2:1. However, the change amplitude of R, G, and B values ​​under the condition of 3:1 is significantly weaker than that of 1:1 and 2:1, indicating that the color development effect of bromothymol blue and alizarin at a ratio of 3:1 is not as obvious and sensitive as the other two ratios.

[0100] Table 7 Changes of indicator R, G, B values ​​with pH when only bromothymol blue dye is added

[0101]

[0102] As shown in Table 7, the color change trend of the indicator with only bromothymol blue added in different pH value (3-11) solutions is consistent with the color change trend of the composite dye indicator, but the change range of R, G, and B values ​​is small. Not only can the three color values ​​of R, G, and B not be reduced to 0 by pH change, but the R value and G value can only be reduced to about 25 at near-limit pH, which shows that the indication effect of the indicator with only bromothymol blue added is significantly lower than that of the composite indicator, and the composite indicator has a more sensitive and stable indication property.

[0103] 2. Determination of the minimum inhibitory concentration of trans-2-hexenal

[0104] This example is directed to fresh tuna fish pieces, and the minimum inhibitory concentration of trans-2-hexenal adopts the same parameters as those in Example 1.

[0105] 3. Preparation of freshness indication / freshness preservation dual-function labels;

[0106] 2g of zein (ZN) was dissolved in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stirred for 2.5h. When ZN was completely dissolved, the prepared freshness indicator solution was added and mixed, stirred evenly, and sucked into a 5mL syringe as a wall material after ultrasonic debubbling. Then, trans-2-hexenal was used as the core material for electrospinning. The set distance was 14cm; the positive voltage was 13kV, and the negative voltage was -1.95kV; the wall material flow rate was 0.06mm / min, and the core material flow rate was 0.015mm / min. The obtained spinning membrane was dried at a temperature of 30℃ for 6h; the shear size was 1.5cm×1.5cm. The obtained smart indicator membrane was tightly wrapped with a low-density polyethylene film to obtain a smart indicator label.

[0107] Example 5

[0108] 1. Preparation of freshness indicator;

[0109] 50 mg of bromothymol blue and 50 mg of alizarin were dissolved in 10 mL of ethanol solvent, the pH was adjusted to 7.5, and the mixture was mixed and stirred to obtain a bromothymol blue-alizarin indicator.

[0110] 2. Determination of the minimum inhibitory concentration of trans-2-hexenal

[0111] This example is directed to fresh tuna pieces, and the minimum inhibitory concentration of trans-2-hexenal adopts the same parameters as those in Example 1.

[0112] 3. Preparation of freshness indication / freshness preservation dual-function labels;

[0113] 1.75g ​​of zein (ZN) was dissolved in a mixed solution of 5mL of anhydrous ethanol and anhydrous acetic acid in a ratio of 2.5:7.5 (v / v), and stirred for 2h. When ZN was completely dissolved, the prepared freshness indicator solution was added and mixed, stirred evenly, and sucked into a 5mL syringe as a wall material after ultrasonic debubbling. Then, trans-2-hexenal was used as the core material for electrospinning. The set distance was 13cm; the positive voltage was 13kV, the negative voltage was -1.95kV; the wall material flow rate was 0.06mm / min, and the core material flow rate was 0.015mm / min. The obtained spinning membrane was dried at a temperature of 25℃ for 7h; the shear size was 1.5cm×1.5cm. The obtained smart indicator membrane was tightly wrapped with a low-density polyethylene film to obtain a smart indicator label.

[0114] Example 6

[0115] The dual-function smart indicator label provided by the present invention can be used for the preservation and freshness detection of raw tuna pieces. To facilitate the detection, a colorimetric card used in conjunction with the label is prepared in this embodiment. The preparation of the colorimetric card and the process of using the dual-function label to detect fresh raw tuna slices are as follows:

[0116] S1. Preparation of dual-function colorimetric card for indication / preservation;

[0117] Take fresh raw tuna chunks for packaging, and paste the indicator / fresh-keeping dual-function label prepared in Example 1 into the packaging bag of raw tuna chunks, store the tuna chunks in a refrigerator at 4°C, and use the Kjeldahl nitrogen determination method to determine the TVB-N content of tuna chunks for different days. When the TVB-N value is lower than 15mg N / 100g, it is a high-quality product, higher than 15mg N / 100g and lower than 25mg N / 100g, it is a qualified product that can be eaten raw, and higher than 25mg N / 100g, it is an unqualified sample that cannot be eaten raw. At the same time, a blank group without adding a label and a single-function indicator label group without using trans-2-hexenal are set. The preparation process of the single-function indicator label is the same as that of Example 1.

[0118] As attached Figure 4 As shown, the TVB-N value of the blank group without label and the single-function indicator label group prepared in Example 1 exceeded 25 mg N / 100 g on the 5th day of storage. At this time, these two groups of samples are unqualified products, indicating that the tuna pieces are no longer suitable for raw consumption; the TVB-N value of the indicator / fresh-keeping dual-function label group exceeded 25 mg N / 100 g on the 8th day of storage. This is mainly because the antibacterial agent trans-2-hexenal is encapsulated by electrospinning technology, and the antibacterial agent is slowly released in a spontaneous and contactless manner to form an antibacterial environment to inhibit the growth of microorganisms in tuna meat, indirectly reducing the rate of TVB-N increase, and extending the storage period of raw tuna pieces by at least 3 days.

[0119] This is consistent with the change in the total colony count of raw tuna chunks. Due to the frozen transportation of tuna, the total colony count of the tuna chunks at 0 days of storage was 2.68±0.13lgCFU / g. On the fifth day of storage, the blank control group was 5.05±0.03lgCFU / g, and the single-function indicator label group was 4.96±0.06lgCFU / g. According to GB 10136-2015 "National Food Safety Standard for Animal Aquatic Products", the total colony count below 5lgCFU / g is qualified and can be eaten raw, and both groups exceed the limit acceptable to consumers (the error of the single-function indicator label group has exceeded the national standard). In contrast, the total colony count of tuna chunks in the indicator / fresh-keeping dual-function group exceeded this limit on the eighth day, indicating that the indicator / fresh-keeping dual-function label helps to extend the shelf life of tuna chunks, mainly because the encapsulated trans-2-hexenal has a certain inhibitory effect on bacterial growth.

[0120] The color changes of the smart indicator label were observed every day, and the color pictures of the smart indicator label changing with the storage time were recorded using a smartphone; when the raw tuna chunks were stored for 1, 2, 3, 4, 5, ..., 10 days, the collected color pictures were arranged from small to large according to the storage days, and recorded as V1, V2, V3, V4, V5, ..., V 10 , arrange the color pictures from small to large according to the number of days of storage, and make a freshness indicator color card to facilitate intuitive judgment of the freshness of tuna chunks.

[0121] like Figure 5 As shown, (a) is a picture of a blank indicator label group and a dual-function indicator / fresh-keeping label for raw tuna chunks during storage, and (b) is a picture of dual-function freshness indicator / fresh-keeping labels for raw tuna chunks stored for 1, 2, 3, 4, 5, ..., 10 days from left to right; Figure 5 It can be seen from a that the dual-function label can extend the refrigerated period of tuna fish pieces by at least 3 days, which verifies that the dual-function label has a preservation effect on tuna. Figure 5 b It can be seen that as the number of storage days increases, the visible light color of the indicator label changes from yellow to blue, indicating that when the tuna chunks gradually decay, the volatile gas reacts with the indicator in the smart indicator label, turning it blue. Under visible light, when the label shows yellow, the tuna chunks are high-quality products with a TVB-N value of less than 15 mg / 100 g; when the label shows dark blue, the TVB-N value is greater than 25 mg / 100 g, and the tuna chunks are not edible raw products.

[0122] S2, verification of the dual-function visual detection effect of raw tuna block indication / freshness preservation;

[0123] Three raw tuna chunk samples of different freshness were selected, and the freshness indicator labels prepared in Example 1 were placed inside the packages of the three raw tuna chunk samples of different freshness. Within 30 seconds, the color of the smart indicator label could be clearly observed from the outside of the package as the freshness of the tuna chunk changed, and color images of the three tuna chunk samples were obtained, as shown in FIG. Figure 6 The color pictures of the three tuna chunk samples were compared with the colorimetric card prepared in S1, and it was found that the color of the first tuna chunk was similar to the picture of the colorimetric card with a storage period of 1 day. It can be preliminarily judged that the storage period of the tuna chunk is 1 day, the TVB-N value is less than 15 mg / 100g (the actual TVB-N value of the product was determined to be 11.08 mg / 100g), and the tuna chunk meat is a high-quality product. The second type of tuna chunks were found to be similar in color to the image of the color card with a storage period of 5 days. It can be judged that the storage period of the tuna chunks is 5 to 7 days, and the TVB-N value is greater than 15mg / 100g and less than 25mg / 100g (the actual TVB-N value of the product on the 5th day was determined to be 18.32mg / 100g). After the second type of tuna chunks were sealed and stored with a dual-function label for 2 days (actual storage for 7 days), the actual TVB-N value of the sample was determined to be 23.28mg / 100g. At this time, the tuna chunks are between the critical point of being edible and not edible raw. The third type of tuna chunks were found to be similar to the image of the color card with a storage period of 8 days. It can be judged that the storage period of the meat is 8 days, and the TVB-N value is greater than 25mg / 100g (the actual TVB-N value of the product was determined to be 25.24mg / 100g). The meat is not edible raw.

[0124] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention can still be modified or replaced by equivalents, and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A dual-function label for raw fish pieces, characterized in that: Bromothymol blue-alizarin is used as a freshness indicator and wall material raw material, and trans-2-hexenal is used as a core material raw material, and a fiber membrane is prepared by electrospinning technology; the outer side of the fiber membrane is wrapped with a transparent and breathable packaging film; the raw fish block is tuna fish block; the encapsulation concentration of the trans-2-hexenal is 2.5~3 μL / mL; the mass ratio of bromothymol blue to alizarin is: bromothymol blue: alizarin = (1~3): 1; the pH of the freshness indicator is 4~8.

2. The dual-function label for raw fish chunks according to claim 1, characterized in that: The flow rate of the core spinning solution was 0.015 mm / min.

3. The method for preparing the dual-function label for raw fish chunks according to any one of claims 1 to 2, characterized in that: Here are the steps: (1) Preparation of freshness indicator: dissolve bromothymol blue and alizarin in ethanol and adjust the pH to 4-8 to obtain a freshness indicator; (2) Determining the minimum inhibitory concentration of trans-2-hexenal and preparing an encapsulation solution: using trans-2-hexenal to determine the minimum inhibitory concentration of aquatic spoilage bacteria; the minimum inhibitory concentration of trans-2-hexenal to aquatic spoilage bacteria is 2.5 μL / mL, and a trans-2-hexenal encapsulation solution is prepared according to the determined minimum inhibitory concentration; (3) Preparation of spinning fiber membrane: adding zein to a mixed solution of anhydrous ethanol and anhydrous acetic acid and stirring to dissolve, adding the freshness indicator of step (1) after dissolution, mixing to obtain a coaxial wall material spinning solution, using the trans-2-hexenal encapsulation solution obtained in step (2) as the core material spinning solution, performing electrospinning treatment to obtain an electrospinning membrane; (4) Label preparation: The electrospun membrane obtained in step (3) is dried and then sheared, and then wrapped with a polyethylene film to obtain a dual-function label.

4. The preparation method according to claim 3, characterized in that: The concentration of corn alcohol-soluble protein after dissolution in step (3) is 30% to 40%; the volume ratio of anhydrous ethanol to anhydrous acetic acid in the mixed solution is: anhydrous ethanol: anhydrous acetic acid = 2.5:7.5; the stirring time is 1.5 to 3 hours; the specific conditions of the electrospinning treatment are: spinning distance 12 to 15 cm; positive voltage 10 to 15 kV, negative voltage -1.8 to -2 kV; wall material spinning solution flow rate 0.06 mm / min, core material spinning solution flow rate 0.015 mm / min.

5. The preparation method according to claim 3, characterized in that: In step (4), the drying temperature is 20-30°C and the drying time is 6-8 hours.

6. A package containing the dual-function label for raw fish chunks according to any one of claims 1-2, characterized in that: The package contains a contactless sealing colorimetric card used together with the dual-function label for raw fish pieces.

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