PH-sensitive composite fiber film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of food preservation, and provides a pH-sensitive composite fiber film as well as a preparation method and application thereof. In particular to a composite fiber film with pH-sensitive visual monitoring and antibacterial properties and application of the composite fiber film in food packaging materials. According to the invention, allicin with a green source is used as an antibacterial active substance, a small molecule compound with a cyanine-like structure is synthesized to capture the pH change in the meat preservation process, and visual monitoring is achieved through color change. The components not only have excellent antibacterial performance and high sensitivity to pH, and effectively inhibit reproduction of microorganisms on the surface of meat so as to delay deterioration, but also are safe and reliable in source, so that the usability of the fiber membrane is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of food preservation, and particularly relates to a pH-sensitive composite fiber film, a preparation method thereof, and an application thereof. Background Art

[0002] Meat products are rich in high-quality nutrients such as protein, fat, and vitamins. These nutrients not only provide a large amount of daily energy intake for humans, but also provide good growth conditions for microorganisms, making meat extremely perishable. The spoilage of meat not only affects its taste and flavor, but may also produce harmful substances, thus causing food safety problems and posing a threat to consumers' health. In order to inhibit the spoilage of meat products, extend their shelf life, and maintain their nutrition and flavor, various preservation technologies have been adopted, such as low-temperature refrigeration (-1 to 4 °C), frozen storage (below -18 °C), vacuum packaging, adding preservatives and antioxidants, dehydration preservation, radiation preservation, etc. However, refrigeration by refrigerator has high energy consumption and cannot completely prevent food spoilage. It only slows down the spoilage rate, and the optimal refrigeration temperature for different foods is different, which requires precise control. Substances harmful to health may be produced during the processes such as sun drying or salting. Chemical substances are used to delay the spoilage process of meat, but attention should be paid to using safe and compliant preservatives and cleaning them thoroughly before cooking.

[0003] In recent years, nanomaterials have developed rapidly. Due to their special structures, such as surface effect, small size effect, etc., they have shown significant advantages in meat preservation. Nano-preservation technology refers to using nanomaterials as preservatives or adding nanomaterials to food packaging to play an antibacterial and preservation role for food. Nano-composite materials prepared based on natural polymers have good mechanical properties, biocompatibility, biodegradability, chemical resistance, antibacterial properties, and gas barrier properties, and are low-cost, easy to process, and degradable, and can be used as eco-friendly materials for food packaging.

[0004] However, the current preservation films on the market have defects in terms of safety, performance limitations, cost, and consumer acceptance. Therefore, when developing and applying preservation materials, the above factors need to be comprehensively considered to seek a more safe, efficient, environmentally friendly, and cost-reasonable solution. Based on the above considerations, this patent aims to provide new ideas and methods for solving the problems existing in the current meat preservation films through innovative materials and technical means. Summary of the Invention

[0005] Object of the Invention: The technical problem to be solved by the present invention is to provide a pH-sensitive composite fiber film, a preparation method thereof, and an application thereof in view of the deficiencies of the prior art. The composite fiber film provided by the present invention is an intelligent color-changing nanofiber film, which can realize visual monitoring of the storage situation of meat, and uses the natural antibacterial agent allicin, which is safe and reliable and can effectively extend the preservation period of meat.

[0006] To solve the above technical problems, the present invention discloses a pH-sensitive composite fiber film, its preparation method and application. The specific technical solutions are as follows:

[0007] The present invention first provides the application of NIRT as a pH indicator, and the structural formula of the NIRT is shown in Formula I:

[0008]

[0009] Among them, X is any one of fluoride ion, chloride ion or iodide ion. Preferably it is iodide ion. The NIRT is a derivative of the cyanine-like structure.

[0010] Among them, the pH indicator is an indicator with pH > 5.

[0011] Preferably, when X is iodide ion, NIRT is prepared by the following method: mixing NIR and 6-hydroxy-2-naphthaldehyde in ethanol and reacting to obtain NIRT; the structural formula of the NIR is shown in Formula II:

[0012]

[0013] Preferably, the mixing molar ratio of the NIR and 6-hydroxy-2-naphthaldehyde is 1:1 to 2; for the reaction, the reaction temperature is 80 - 96 °C and the reaction time is 6 - 10 h. Preferably, the NIR and 6-hydroxy-2-naphthaldehyde are mixed, piperidine is added dropwise, refluxed in absolute ethanol, after the reaction ends, the solvent is recovered by vacuum concentration, and recrystallized with absolute ethanol to obtain pure NIRT.

[0014] In the second aspect, the present invention provides the application of NIRT as a pH indicator in the preparation of a pH-sensitive composite fiber film.

[0015] Among them, polylactic acid, polycaprolactone, gelatin, NIRT and allicin are mixed in an organic solvent to obtain a mixed solution, and the mixed solution is electrospun to obtain the pH-sensitive composite fiber film;

[0016] Among them, the weight-average molecular weight of the polylactic acid is 60 - 80 kDa; the weight-average molecular weight of the polycaprolactone is 60 - 80 kDa; the weight-average molecular weight of the gelatin is 30 - 50 kDa; preferably, the weight-average molecular weight of the polylactic acid is 80 kDa; the weight-average molecular weight of the polycaprolactone is 80 kDa; the weight-average molecular weight of the gelatin is 40 kDa.

[0017] Among them, the organic solvent is any one or a mixture of methanol, hexafluoroisopropanol or acetic acid. Preferably it is a mixture of hexafluoroisopropanol and acetic acid, and the mixing volume ratio is 6 - 10:1. Preferably it is 9:1.

[0018] Among them, in the said mixed solution, the concentration of polylactic acid is 0.05 - 0.075 g / mL, the concentration of polycaprolactone is 0.05 - 0.075 g / mL, the concentration of gelatin is 0.01 - 0.03 g / mL, the concentration of NIRT is 0.03 - 0.05 g / mL, and the concentration of allicin is 0.05 - 0.15 g / mL. Preferably, the mixing mass ratio of polylactic acid, polycaprolactone and gelatin in the mixed solution is 6.5:6.5:2, the concentration of polylactic acid is 0.065 g / mL, the concentration of polycaprolactone is 0.065 g / mL, the concentration of gelatin is 0.02 g / mL, the concentration of NIRT is 0.04 g / mL, and the concentration of allicin is 0.05 - 0.15 g / mL.

[0019] Preferably, the pH-sensitive composite fiber film is prepared as follows: in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid, add 0.5 - 0.75 g of polylactic acid, 0.5 - 0.75 g of polycaprolactone, 0.1 - 0.3 g of gelatin, 0.3 g - 0.5 g of NIRT, and 0.5 g - 1.5 g of allicin, stir for 5 h, and obtain it by electrospinning. Preferably, in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid, add 0.65 g of polylactic acid, 0.65 g of polycaprolactone, 0.2 g of gelatin, 0.4 g of NIRT, and 0.5 g or 0.10 g or 0.15 g of allicin, stir until dissolved, and obtain it by electrospinning.

[0020] Among them, for the said electrospinning, the voltage is 8 - 22 kV, the flow rate is 0.2 - 1.5 mL / h, and the receiving distance is 5 - 20 cm. Preferably, the voltage is 15 kV, the flow rate is 0.5 mL / h, the receiving distance is 10 cm, the rotation speed of the roller collector is 900 r / min, the temperature is 28 °C, and the humidity is 45%.

[0021] The present invention also provides a pH-sensitive composite fiber film prepared by the application described in the second aspect. Preferably, the diameter of the pH-sensitive composite fiber film is 1000 - 1500 nm.

[0022] In the third aspect, the present invention provides the application of NIRT as a pH indicator in food preservation. Preferably, NIRT is used as a pH indicator to prepare a pH-sensitive composite fiber film for application in food preservation.

[0023] Preferably, the said food preservation is the preservation of fresh meat products. More preferably, it is any one of pork, beef or shrimp.

[0024] Beneficial effects:

[0025] The present invention provides the application of a cyanine-like structural derivative NIRT as a pH indicator. Using this application, the present invention also provides a pH-sensitive composite fiber film, which uses allicin from green sources as an antibacterial active substance, uses a small molecule compound NIRT with a cyanine-like structure to capture the pH change during meat preservation, and achieves visual monitoring through color change. These components not only have excellent antibacterial properties and high sensitivity to pH, effectively inhibit the reproduction of microorganisms on the meat surface, thereby delaying spoilage, but also have safe and reliable sources, thus improving the usability of the fiber film. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0027] Figure 1 is the synthesis route of NIRT.

[0028] Figure 2 is the 1H NMR spectrum of NIR.

[0029] Figure 3 is the 13C NMR spectrum of NIR.

[0030] Figure 4 is the mass spectrum of NIR.

[0031] Figure 5 is the 1H NMR spectrum of NIRT.

[0032] Figure 6 is the 13C NMR spectrum of NIRT.

[0033] Figure 7 is the mass spectrum of NIRT.

[0034] Figure 8 is the pH sensitivity test chart of NIRT mixed with different pH solutions; Figure 8 a is the ultraviolet absorption spectrum chart, Figure 8 b is the color change chart of NIRT mixed with different pH solutions, Figure 8 c is the chromaticity value chart of the solution color, where the icon L represents the brightness of the color, the icon A represents the red-green chromaticity, and the icon B represents the yellow-blue chromaticity.

[0035] Figure 9 is the scanning electron microscope and diameter chart of the fiber film; Figure 9 a is the fiber film PLA / PCL / Gel, Figure 9 b is 5% Allicin,

[0036] Figure 9 c is 10% Allicin, Figure 9d is 15% Allicin.

[0037] Figure 10 It is the color change diagram of 15% Allicin in the fiber membrane at different pH values.

[0038] Figure 11 It is the appearance influence of using different fiber membranes for beef preservation.

[0039] Figure 12 It is the influence of using different fiber membranes on TVB-N, TVC and pH of beef preservation; Figure 12 a is the influence on TVB-N, Figure 12 b is the influence on TVC, Figure 12 c is the influence on pH. Specific implementation mode

[0040] The following further elaborates on this application in conjunction with the embodiments.

[0041] In the following embodiments, the NIR is 3-ethyl-1,1,2-trimethyl-1H-benz[e]indole, 3-Ethyl-1,1,2-trimethyl-1H-benz[e]indolium; the NIRT is 3-ethyl-2-[2-(6-hydroxy-2-naphthalenyl)ethenyl]-1,1-dimethyl-1H-benz[e]indole, 3-Ethyl-2-[2-(6-hydroxy-2-naphthalenyl)ethenyl]-1,1-dimethyl-1H-benz[e]indolium, and their structural formulas are as Figure 1 shown.

[0042] The weight-average molecular weight of the polylactic acid is 80 kDa; the weight-average molecular weight of the polycaprolactone is 80 kDa; the weight-average molecular weight of the gelatin is 40 kDa.

[0043] Example 1 Preparation of NIR and NIRT

[0044] The structural formula and preparation steps of NIR are as Figure 1 shown. Mix 1 mmol of 1,1,2-trimethyl-1H-benz[e]indole (0.209 g) and 2 mmol of iodoethane (0.312 g) in anhydrous acetonitrile, heat at 80 °C for 10 h, end the reaction, concentrate under vacuum to recover the solvent, obtain a gray-green solid powder, rinse the solid three times with ethylene glycol methyl ether, and filter to obtain the gray solid NIR. The 1H NMR spectrum of NIR ( Figure 2 ), 13C NMR spectrum ( Figure 3 ), and mass spectrum ( Figure 4 ) information is as follows: 11H NMR (500 MHz, Chloroform-d) δ 8.04 (s, 2H), 7.98 (s, 1H), 7.83 (s, 1H), 7.68 (s, 1H), 7.59 (s, 1H), 4.75 (s, 3H), 3.14 (s, 6H), 1.61 (s, 3H). 13 13C NMR (126 MHz, Chloroform-d) δ 194.95, 137.14, 133.61, 131.51, 130.03, 128.67, 127.77, 127.61, 122.89, 55.89, 45.62, 22.62, 16.75, 13.90. HR-MS (ESI): m / z calculated [C 28 H 26 NO] + 238.1690, found 238.16. The structural formula and preparation steps of NIRT are as follows Figure 1 shown. Dissolve 1 mmol of NIR (0.238 g) and 1 mmol of 6-hydroxy-2-naphthaldehyde (0.172 g) in ethanol, add 0.1 mL of piperidine, heat at 90 °C for 8 h. At the end of the reaction, concentrate the solvent under vacuum to recover it, obtain a brown solid powder, and recrystallize it from absolute ethanol to get a purple-red solid NIRT. The 1H nuclear magnetic resonance spectrum of NIRT ( Figure 5 ), 13C nuclear magnetic resonance spectrum ( Figure 6 ), and mass spectrum ( Figure 7 ) information is as follows: 1 1H NMR (500 MHz, DMSO-d6) δ 10.49 (s, 1H), 8.72 (s, 2H), 8.67 (s, 1H), 8.45 (s, 1H), 8.37 (m, 1H), 8.30 (s, 1H), 8.22 (s, 1H), 8.16 (s, 1H), 7.28 (d, J = 2.4 Hz, 2H), 7.25 (s, 1H), 7.23 (d, J = 2.4 Hz, 1H), 4.90 (d, J = 7.3 Hz, 2H), 3.45 (m, 1H), 1.55 (d, J = 7.2 Hz, 6H), 1.06 (t, J = 7.0 Hz, 3H). 13 13C NMR (126 MHz, DMSO-d6) δ 182.18, 159.22, 153.89, 138.85, 138.62, 135.56, 133.60, 132.07, 130.52, 129.82, 128.92, 127.71, 127.67, 127.61, 127.27, 120.38, 113.61, 110.72, 110.03, 54.18, 26.07, 14.47. HR-MS (ESI): m / z calculated [C28 H 26 NO] + 392.2009, found 392.20。

[0045] The chromaticity change data and ultraviolet absorption spectra of the NIRT solution at different pH values were tested. The specific test method was as follows: NIRT was dissolved in an ethanol solution to prepare a 5 g / L NIRT ethanol solution, and aqueous solutions with different pH values were prepared using sodium hydroxide and hydrochloric acid. Equal volumes were mixed and the chromaticity changes and corresponding ultraviolet absorption spectra were tested using a colorimeter. The results are as Figure 8 shown. The absorption spectra of the NIRT solution at different pH values shifted to higher wavelengths as the pH value changed ( Figure 8 as shown in a), and the color showed an obvious change from red to blue-violet to light yellow ( Figure 8 as shown in b). The color change was mainly attributed to the transformation of its chemical structure. In addition, there were significant differences in the color brightness L, red-green chromaticity A, and yellow-blue chromaticity B values between different films ( Figure 8 as shown in c). The above results indicate that NIRT has significant pH sensitivity.

[0046] Example 2

[0047] Weigh 0.65 g of polylactic acid, 0.65 g of polycaprolactone, and 0.2 g of gelatin, stir them in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid until dissolved, and prepare a blank fiber film on an electrospinning device with a voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 10 cm, and a roller rotation speed of 900 r / min, denoted as PLA / PCL / Gel.

[0048] Weigh 0.65 g of polylactic acid, 0.65 g of polycaprolactone, 0.2 g of gelatin, 0.4 g of NIRT, and 0.5 g of allicin, stir them in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid until dissolved, and prepare a fiber film on an electrospinning device with a voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 10 cm, and a roller rotation speed of 900 r / min, denoted as 5% Allicin.

[0049] Weigh 0.65 g of polylactic acid, 0.65 g of polycaprolactone, 0.2 g of gelatin, 0.4 g of NIRT, and 1 g of allicin, stir them in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid until dissolved, and prepare a fiber film on an electrospinning device with a voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 10 cm, and a roller rotation speed of 900 r / min, denoted as 10% Allicin.

[0050] Weigh 0.65 g of polylactic acid, 0.65 g of polycaprolactone, 0.2 g of gelatin, 0.4 g of NIRT, and 1.5 g of allicin. Stir them in a mixed solution of 9 mL of hexafluoroisopropanol and 1 mL of acetic acid until dissolved. Prepare a fibrous membrane on an electrospinning device with a voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 10 cm, and a roller rotation speed of 900 r / min, denoted as 15% Allicin. As Figure 9 shown, the diameters of the prepared fibrous membranes PLA / PCL / Gel, 5% Allicin, 10% Allicin, and 15% Allicin are 870 nm, 1015 nm, 1119 nm, and 1344 nm respectively.

[0051] Place the 15% Allicin fibrous membrane prepared above in solutions with different pH values and observe the color changes. As Figure 10 shown, the 15% Allicin fibrous membrane shows an obvious change from orange-red to blue-violet at different pH values, indicating that the fibrous membrane is also sensitive to pH.

[0052] Example 3

[0053] Use the fibrous membrane prepared in Example 2 for meat preservation, including the following steps:

[0054] Cut fresh beef into relatively uniform sizes, clean and disinfect it with 0.2% sodium hypochlorite, wrap it with the fibrous membrane prepared in Example 2, and store it in a 4°C refrigerator. Additionally, store fresh beef without wrapping it with any fresh-keeping film in a 4°C refrigerator as a control group (Control).

[0055] Evaluate the beef preservation results through three indicators: pH, total volatile basic nitrogen (TVB-N), and total viable count (TVC). pH, color, TVB-N, and TVC are indicators that change significantly during meat storage. Therefore, in this invention, the pH value of beef during storage was monitored, the color change of the meat was observed, and TVB-N was determined according to GB / T 5009.44, and TVC was determined according to GB 4789.2.

[0056] The appearance of beef preservation under different fibrous membranes is as Figure 11 shown. Appearance is an important indicator to measure meat freshness and directly affects consumers' willingness to buy meat. The results show that the brightness of all beef samples decreases with the extension of storage time, which may be because the interaction between myoglobin and oxygen in the meat increases the production of methemoglobin, thus reducing the brightness. As time goes by, it gradually changes from red to brown, which may be due to the rapid production of cherry-red oxymyoglobin by the oxygen in the meat barrel. Figure 11 The circled parts in

[0057] Under the action of enzymes and bacteria, the protein in meat is decomposed to produce alkaline nitrogen, called TVB-N, which is an important indicator for evaluating the freshness of meat. As Figure 12 shown in Figure a, during storage, the TVB-N values of all beef samples increased over time. The control group showed obvious deterioration on the 6th day, with a TVB-N value of 15.22 mg / 100 g, exceeding the specified limit (GB / T 5009.44, 15.00 mg / 100 g). The PLA / PCL / Gel group also showed consistent results. In contrast, the treatment with different concentrations of allicin fiber films added with NIRT significantly delayed the production of TVB-N in beef on the 9th, 12th, and 15th days, which was significantly lower than that of the control group and the PLA / PCL / Gel group.

[0058] The TVC value of meat samples can accurately predict microbial contamination during storage. If the TVC value exceeds 6 log10 CFU / g, the meat is considered spoiled (GB 4789.2). In the experiment, the TVC values of all beef samples increased with the extension of storage time, but at different rates. As Figure 12 shown in Figure b, the control group and the PLA / PCL / Gel group increased the fastest and exceeded the national standard value on the 6th day, indicating that the meat had spoiled. The colony growth of the experimental groups added with NIRT and allicin was significantly delayed, indicating that the fiber films added with NIRT and allicin had an inhibitory effect on microorganisms during storage and hindered the rapid development of microorganisms.

[0059] The pH value is considered a key parameter for evaluating meat quality. During storage, the pH value showed varying degrees of increase, mainly due to the presence of meat spoilage microorganisms and the production of endogenous alkaline substances such as ammonia and amines, which promoted protein degradation. As Figure 12 shown in Figure c, the pH values of the control group and the PLA / PCL / Gel group reached the level of spoiled meat (pH 6.8) on the 6th day. In contrast, the pH increase of the different concentrations of allicin fiber film groups added with NIRT was relatively slow, delaying the growth level of microorganisms. In addition, from Figure 12 Figure c, it can be seen that during the storage of meat, the pH will show a certain degree of increase. The fiber film of the present invention can change color (from orange-red to blue-violet) with the increase of pH, thus realizing the visual monitoring of meat spoilage. At the same time, due to the cyanine-like structure of NIRT, a certain degree of antioxidant effect is retained. Therefore, the fresh-keeping effect of the combination of NIRT and allicin added is more significant than that of allicin added alone.

[0060] The present invention provides a pH-sensitive composite fiber film, a preparation method thereof, and an idea and method for application. There are many methods and ways to specifically implement this technical solution. The above description is only a preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be implemented by using the prior art.

Claims

1. Application of NIRT as a pH indicator, the structural formula of the NIRT is shown in Formula I: in, X is any one of a fluoride ion, a chloride ion or an iodide ion.

2. The use according to claim 1, characterized in that: The pH indicator is an indicator of pH>5.

3. Application of NIRT as pH indicator in the preparation of pH-sensitive composite fiber films.

4. The use according to claim 3, characterized in that: Polylactic acid, polycaprolactone, gelatin, NIRT and allicin are mixed in an organic solvent to obtain a mixed solution, and the mixed solution is subjected to electrostatic spinning to obtain the pH-sensitive composite fiber film.

5. The use according to claim 4, characterized in that: The weight average molecular weight of the polylactic acid is 60-80 kDa; the weight average molecular weight of the polycaprolactone is 60-80 kDa; the weight average molecular weight of the gelatin is 30-50 kDa; and the organic solvent is any one or more combinations of methanol, hexafluoroisopropanol or acetic acid.

6. The use according to claim 4, characterized in that: In the mixed solution, the concentration of polylactic acid is 0.05-0.075 g / mL, the concentration of polycaprolactone is 0.05-0.075 g / mL, the concentration of gelatin is 0.01-0.03 g / mL, the concentration of NIRT is 0.03-0.05 g / mL, and the concentration of allicin is 0.05-0.15 g / mL.

7. The use according to claim 4, characterized in that: The electrostatic spinning has a voltage of 8 to 22 kV, a flow rate of 0.2 to 1.5 mL / h, and a receiving distance of 5 to 20 cm.

8. Application of NIRT as pH indicator in food preservation.

9. The use according to claim 7, characterized in that: NIRT is used as a pH indicator to prepare a pH-sensitive composite fiber film for food preservation.

10. The use according to claim 7, characterized in that: The food preservation is the preservation of fresh meat products.

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