A method for preparing freshness indicator labels by high-voltage electrospinning and its application

Abstract

The present invention discloses a method and application of preparing a freshness indicator label by electrostatic spinning, which is obtained by the following steps: S1: adding bayberry anthocyanin to a matrix solution to obtain a spinning solution; S2: after ultrasonic filtration of the matrix solution, taking part of the solution and putting it into a 10ml syringe, fixing it on a propulsion pump, spinning using a high-voltage electrostatic spinning device under a specific voltage, receiving distance, flow rate, temperature and humidity to prepare a nanofiber membrane; S3: balancing the prepared nanofiber membrane for 48 hours, and cutting it into a specific size to prepare a freshness indicator label. The freshness indicator label prepared by the method of the present invention has a large specific surface area and porosity, and is sensitive to pH response. The bayberry anthocyanin freshness indicator label based on pullulan / polyvinyl alcohol has great application potential in the freshness monitoring and intelligent packaging of white shrimp.

Description

Technical Field

[0001] The invention belongs to the technical field of food monitoring, and in particular relates to a preparation method and application of a freshness indicator label prepared by high-voltage electrospinning. Background Art

[0002] my country suffers huge economic losses every year due to pollution of aquatic products. Due to the microorganisms carried by aquatic products themselves, they are prone to spoilage. During the spoilage process, aquatic products decompose proteins, amino acids, etc., and produce a large amount of alkaline volatile amines, such as trimethylamine (TMA), ammonia (NH3), dimethylamine (DMA), etc. These amines will increase the pH value of the aquatic products themselves and the packaging environment. Traditional packaging methods can only isolate the air outside the packaging environment and cannot monitor whether aquatic products are spoiled in real time. With the improvement of people's requirements for food safety and quality, freshness indicator labels are gradually receiving attention. It can produce color reactions by sensing changes in temperature and pH around food to distinguish the state of food (fresh, medium fresh or spoiled). At present, the most commonly used method for preparing freshness indicator labels is the casting method. The closed surface of the membrane prepared by this method will limit its pH response performance during the monitoring of food freshness.

[0003] Electrospinning is an advanced technology for preparing nanofiber membranes with high porosity and specific surface area. Due to the unique nanostructure of electrospun nanofibers, they have a high specific surface area, which enables them to carry more active substances and provide efficient catalytic performance. In theory, it can make the sensitivity and reaction time of smart packaging more sensitive and efficient, which is of certain value for improving the performance of smart indicator packaging. At present, some people have used electrospinning technology to prepare fiber membranes for pork packaging to improve antibacterial ability and extend the shelf life of pork. In the indicator cards prepared by electrospinning for detecting the freshness of meat, toxic indicators such as methyl red, bromothymol blue, bromocresol purple, etc. are added, which poses certain safety hazards. Therefore, it is very necessary to design a highly safe indicator label for food freshness detection. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method and application of preparing a freshness indicator by high-voltage electrospinning.

[0005] This is achieved specifically through the following technical solutions:

[0006] The first aspect of the present invention provides a method for preparing a freshness indicator label by high-voltage electrospinning, wherein the freshness indicator label is obtained by the following steps:

[0007] 1) Preparation of electrospinning solution: adding bayberry residue anthocyanin into a matrix solution to obtain a spinning solution;

[0008] 2) Preparation of pH colorimetric nanofiber membrane: After the matrix solution is ultrasonically filtered, part of the solution is placed in a 10 mL syringe, fixed on a propulsion pump, and spun using a high-voltage electrospinning device at a specific voltage, receiving distance, flow rate, temperature and humidity to prepare a nanofiber membrane;

[0009] 3) Preparation of freshness indicator labels: The prepared nanofiber membranes were balanced for 48 hours and cut into specific sizes to prepare freshness indicator labels.

[0010] Further, the spinning solution is prepared by the following steps:

[0011] 1) placing polyvinyl alcohol into an aqueous solution, heating and stirring in a water bath at 90° C. for 3 h until dissolved, to obtain a polyvinyl alcohol solution with a mass fraction of 10%;

[0012] 2) dissolving pullulan in the aqueous solution, stirring at room temperature until dissolved, to obtain a pullulan solution with a mass fraction of 10%;

[0013] 3) 10% pullulan solution and 10% polyvinyl alcohol solution were mixed in a ratio of 1:2, stirred for 2 hours, and then anthocyanins accounting for 15% of the total amount of pullulan and polyvinyl alcohol were added, mixed and stirred for 1 hour, ultrasonicated for 50 minutes, and then filtered with 200 mesh gauze to obtain a spinning solution.

[0014] Furthermore, the preparation steps of the nanofiber membrane are:

[0015] 1) Use a 10mL syringe to draw an appropriate amount of solution and fix it to the propulsion pump. The parameters are set as follows: voltage 19kV; receiving distance 15cm; propulsion speed 1.0mL / hr; temperature 25℃; humidity 50%;

[0016] 2) The pH colorimetric nanofiber membrane was obtained after spinning for 1.3 h.

[0017] Furthermore, the preparation steps of the freshness indicator label are as follows: drying and balancing the prepared pH fiber membrane in an environment with a temperature of 25° C. and a relative humidity of 50% for 48 hours, cutting it into a circle with a diameter of 2 cm to prepare a freshness smart label.

[0018] The second aspect of the present invention provides a freshness indicator label obtained by the preparation method according to the above steps.

[0019] A third aspect of the present invention provides the use of a freshness indicator label in monitoring the freshness of Penaeus vannamei.

[0020] The present invention uses pullulan and polyvinyl alcohol as a membrane matrix. Pullulan is a microbial polysaccharide with good biocompatibility and degradability, but the nanofiber membrane microstructure prepared from pullulan has a beaded structure and relatively low mechanical properties. Polyvinyl alcohol has good biocompatibility and degradability, so the pullulan and polyvinyl alcohol compound can improve the mechanical properties of the nanofiber membrane; by selecting natural plant pigments as color indicators, it has the advantages of low cost and high safety. Bayberry residue anthocyanin (ATH) is a water-soluble pigment with a wide range of color changes. The freshness indicator label prepared from bayberry residue anthocyanin can respond in time according to the volatile substances generated by aquatic products during the corruption process.

[0021] The freshness indicator label prepared by the method of the present invention is sensitive to pH response due to its large specific surface area and porosity. The pullulan / polyvinyl alcohol-based waxberry residue anthocyanin freshness indicator label has great application potential in the freshness monitoring and intelligent packaging of white shrimp. As the freshness of the shrimp decreases, the freshness indicator label will undergo a corresponding color change to indicate the freshness of the shrimp in the package. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD patterns of PU-PVA, PU-PVA-10, PU-PVA-15, and PU-PVA-20;

[0023] Figure 2 The color and color difference changes of PUPA10, PUPA15 and PUPA20 in buffer solutions with different pH values;

[0024] Figure 3 The color and color difference changes of PUPA10, PUPA15 and PUPA20 under ammonia fumigation;

[0025] Figure 4 Pictures of the color changes of the labels of PUPA10, PUPA15, and PUPA20 monitored at 4°C storage conditions;

[0026] Figure 5 The color parameters of white shrimp, TVB-N and pH value of white shrimp were monitored at 4℃ for freshness indicator label. (AB) TVB-N content and pH value of white shrimp under 4℃ storage conditions; (CF) Color change parameters for monitoring white shrimp PUPA10, PUPA15 and PUPA20 under 4℃ storage conditions DETAILED DESCRIPTION

[0027] The present invention is described in further detail below in conjunction with the accompanying drawings in order to better understand the technical solution.

[0028] Embodiment 1:

[0029] Preparation of freshness indicator labels:

[0030] S1: Preparation of electrospinning solution: Add bayberry residue anthocyanin into the matrix solution to obtain the spinning solution

[0031] Specifically, the preparation of the spinning solution includes the following steps:

[0032] S11: 4 g of polyvinyl alcohol was placed in 40 mL of aqueous solution, and the solution was heated and stirred in a water bath at 90° C. for 3 h until dissolved, to obtain a polyvinyl alcohol solution with a mass fraction of 10%.

[0033] S12: Dissolve 2 g of pullulan in 20 mL of aqueous solution and stir at room temperature until dissolved to obtain a pullulan solution with a mass fraction of 10%.

[0034] S13: 10% pullulan solution and 10% polyvinyl alcohol solution were mixed in a ratio of 1:2, stirred for 2 hours, and then anthocyanins accounting for 15% of the total amount of pullulan and polyvinyl alcohol were added, mixed and stirred for 1 hour, ultrasonicated for 50 minutes, and then filtered with 200 mesh gauze to obtain a spinning solution.

[0035] S2: Preparation of pH colorimetric nanofiber membrane: A 10 mL syringe was used to draw an appropriate amount of solution, fixed to a propulsion pump, and the spinning parameters were set to perform electrospinning.

[0036] Specifically, the spinning process includes the following steps:

[0037] S21: Set the spinning parameters as follows: voltage of 19 kV; receiving distance of 15 cm; propulsion speed of 1.0 mL / hr; temperature of 25° C.; and humidity of 50%.

[0038] S22: The pH colorimetric nanofiber membrane is obtained after spinning for 1.3 h.

[0039] S3: The steps of preparing the freshness indicator label are as follows: drying and balancing the prepared pH colorimetric nanofiber membrane in an environment with a temperature of 25°C and a relative humidity of 50% for 48 hours, separating the pH colorimetric nanofiber membrane from the tin foil, and then cutting it into a circle with a diameter of 2 cm to prepare a freshness smart label.

[0040] Comparative Example 1: The preparation method is basically the same as that of the embodiment, except that during the preparation of the spinning solution, the amount of anthocyanin added is 10%.

[0041] Comparative Example 2: The preparation method is basically the same as that of the embodiment, except that during the preparation of the spinning solution, the amount of anthocyanin added is 20%.

[0042] Test example

[0043] The performance test method of the nanofiber membranes prepared with three different concentrations of anthocyanins from bayberry residue in the above examples and comparative examples is as follows:

[0044] XRD spectrum: The crystallization properties of the pH colorimetric nanofiber membrane were tested using an X-ray diffractometer with Cu-Kα radiation, with a spectral intensity of 2θ=5°-50° and a scanning rate of 2° / min.

[0045] Color change of pH colorimetric nanofiber membrane in buffer solutions with different pH values: To determine the response of pH colorimetric nanofiber membrane to pH, we prepared buffer solutions with pH values ​​of 2-12 using 0.1 M NaOH and 0.1 M HCL. The smart tag was cut into rectangles and immersed in each buffer solution with pH values ​​between 2.0 and 11.0. The color change of the smart tag under different pH buffers was observed without drying.

[0046] Use a digital camera to record the color, then use photoshop2022 software to extract the L, a, and b values, and use the formula to calculate ΔE. The formula is as follows:

[0047]

[0048] Wherein, L*, a*, b* are the chromaticity values ​​of the sample to be tested, and L0*, a0*, b0* are the chromaticity values ​​of the control sample.

[0049] Color change sensitivity of pH colorimetric nanofiber membrane to volatile ammonia (Determination of sensitivity of pH colorimetric nanofiber membrane to volatile ammonia): The pH colorimetric nanofiber membrane was cut into a circle with a diameter of 20 mm, adhered to the inner side of the culture dish, and then exposed to a 1.6 M ammonia solution for 2.5 h. The color was recorded with a digital camera every 30 min, and then photoshop2022 software was used to extract the L, a, and b values, and ΔE was calculated using the formula as follows:

[0050]

[0051] Wherein, L*, a*, b* are the chromaticity values ​​of the sample to be tested, and L0*, a0*, b0* are the chromaticity values ​​of the control sample.

[0052] Stability of pH colorimetric nanofiber membrane: The prepared pH colorimetric nanofiber membrane was stored in 4°C and 25°C environments, and the color changes of the membrane were recorded with a smartphone on the 2nd, 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, 20th, 30th, 40th, 50th, and 60th days, respectively. Then, photoshop2022 software was used to extract the L, a, and b values, and ΔE was calculated using the formula as follows:

[0053]

[0054] Wherein, L*, a*, b* are the chromaticity values ​​of the sample to be tested, and L0*, a0*, b0* are the chromaticity values ​​of the control sample.

[0055] The freshness of Penaeus vannamei was monitored using a pH colorimetric nanofiber membrane: the pH colorimetric nanofiber membrane was fixed on the top of a fresh-keeping box containing six fresh Penaeus vannamei and stored at 4°C for 6 days; the volatile basic nitrogen content and pH value of the white shrimp were measured every day, and the correlation between the color change of the colorimetric membrane and the volatile basic nitrogen content of the white shrimp was established; at the same time, the color change of the pH colorimetric nanofiber membrane was photographed with a smartphone.

[0056] Results and analysis of the above test cases

[0057] In order to screen the matrix carrier of pH indicator nanofiber membrane, the following conclusions were drawn by studying various materials: When chitosan was used as the matrix carrier of pH indicator nanofiber membrane, the viscosity of chitosan solution was large, which hindered the entanglement between molecular chains, and many droplets were generated during the spinning process, making it difficult to perform electrospinning. When sodium alginate was used as the matrix carrier of pH indicator nanofiber membrane, the sodium alginate solution had high conductivity and surface tension, and the molecular chains lacked entanglement, resulting in many droplets generated during the spinning process, making it difficult to perform electrospinning. When pure pullulan was used as the matrix carrier of pH indicator nanofiber membrane, the jet was unstable during the spinning process, a small amount of droplets were generated, and the prepared nanofiber membrane had many bead structures, and the mechanical properties of the membrane were relatively low. When pullulan was compounded with sodium hydroxymethyl cellulose to form the matrix carrier of pH indicator nanofiber membrane, the jet was unstable during the spinning process, and the formed nanofibers were relatively rough, resulting in an uneven surface of the nanofiber membrane. Pullulan and polyvinyl alcohol are compounded to form the membrane-forming material of the nanofiber membrane. Since intermolecular hydrogen bonds are formed between pullulan and polyvinyl alcohol, the performance of the pH indicating nanofiber membrane can be improved and enhanced. Therefore, pullulan and polyvinyl alcohol are finally selected as the matrix of the freshness indicator label.

[0058] 10% pullulan and 10% polyvinyl alcohol solutions were prepared respectively, and the pullulan and polyvinyl alcohol solutions were mixed in a ratio of 0% (control), 10%, 15%, and 20% (w / w) of anthocyanin in the indicator bayberry residue. The prepared pH indicating nanofiber membranes were named PUPA, PUPA10, PUPA15, and PUPA20.

[0059] Combination Figure 1 From the XRD diagram, it can be seen that with the increase of anthocyanin content, the characteristic peak shifted to the right. The addition of anthocyanin did not change the crystal structure of pullulan and polyvinyl alcohol nanofibers, proving that anthocyanin was successfully added to the pullulan and polyvinyl alcohol nanofiber membranes.

[0060] Combination Figure 2 From the color change of the pH indicator nanofiber membrane in the pH buffer solution, it can be seen that PUPA10, PUPA15, and PUPA20 are red in the buffer solution with a pH of 2, pink in the buffer solution with a pH of 3-11, and blue at a pH of 12.

[0061] Combination Figure 3 , the pH indicator nanofiber membrane was fumigated with ammonia, and the color of PUPA10, PUPA15, and PUPA20 membranes changed from pink to blue-green at 30 minutes; to green at 60 minutes; to yellow-green at 90 to 120 minutes; and to yellow at 150 minutes. Among them, the color change of PUPA15 membrane was the most obvious visually.

[0062] Combination Figure 4 and Figure 5 By comparing the results and combining the color parameter control, when the safety threshold of TVB-N value of white shrimp is 30mg / 100g, when the storage time is 4d, the TVB-N value of shrimp increases from 2.15 to 31.45mg / 100g, exceeding the safety threshold, and the pH value increases from 6.05 to 7.93. The white shrimp has been corrupted and deteriorated. At this time, the color of PUPA10 and PUPA20 is consistent with that on the third day, and the color of PUPA15 changes to green. PUPA15 has a good indicator of the corruption of shrimp, and the visible color change is consistent with the degree of corruption determined by the above chemical indicators.

[0063] The freshness indicator label based on pullulan / polyvinyl alcohol and bayberry residue anthocyanins has great application potential in shrimp freshness monitoring and smart packaging, and provides a reference for the application of natural anthocyanin indicator film in food shelf life monitoring.

Claims

1. A method for preparing a freshness indicator label by high-voltage electrospinning, characterized in that: Prepared by the following method: 1) Preparation of electrospinning solution: adding bayberry residue anthocyanin into a matrix solution to obtain a spinning solution; the preparation of the spinning solution comprises the following steps: 1-1) Add polyvinyl alcohol to the aqueous solution, heat and stir in a 90°C water bath for 3 hours until dissolved, to prepare a polyvinyl alcohol solution with a mass fraction of 10%; 1-2) dissolving pullulan in an aqueous solution, stirring at room temperature until dissolved, to prepare a pullulan solution with a mass fraction of 10%; 1-3) 10% pullulan solution and 10% polyvinyl alcohol solution were mixed in a ratio of 1:2, stirred for 2 hours, and then anthocyanins accounting for 15% of the total dry matter of pullulan and polyvinyl alcohol were added, mixed and stirred, ultrasonicated, and filtered with 200 mesh gauze to obtain a spinning solution 2) Preparation of pH colorimetric nanofiber membrane: After ultrasonic filtration of the spinning solution prepared in step 1), a portion of the solution is placed in a syringe, fixed on a propulsion pump, and spinning is performed using a high-voltage electrospinning device to prepare a nanofiber membrane; 3) Preparation of freshness indicator labels: The nanofiber membrane prepared in step 2) is balanced for 48 hours and then cut into a specific size to obtain a freshness indicator label.

2. A method for preparing a freshness indicator label by high voltage electrospinning according to claim 1, characterized in that In step 2), the nanofiber membrane is prepared by the following steps: 1) Use a 10mL syringe to draw an appropriate amount of solution and fix it to the propulsion pump. The parameters are set as follows: voltage 19 kV; receiving distance 15 cm; propulsion speed 1.0mL / hr; temperature 25℃; humidity 50%; 2) The nanofiber membrane was obtained by spinning for 1.3 h.

3. A method for preparing a freshness indicator label by high voltage electrospinning according to claim 1, characterized in that In step 3), the freshness indicator label is specifically prepared as follows: the prepared nanofiber membrane is dried and balanced in an environment with a temperature of 25°C and a relative humidity of 50% for 48 hours, the nanofiber membrane is separated from the tin foil on the high-voltage electrospinning device, and then cut into a circle with a diameter of 2 cm to prepare a freshness indicator label.

4. A method for preparing a freshness indicator label by high voltage electrospinning according to claim 1, characterized in that In step 1-3), the mixing and stirring time is 1 hour, and the ultrasonic time is 50 minutes.

5. A freshness indicator label prepared by the method of any one of claims 1 to 4.

6. Use of the freshness indicator label as claimed in claim 5 in monitoring the freshness of Penaeus vannamei.

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