Preparation method and application of time-temperature indicating film with amaranth leaf extract as raw material
By preparing a time-temperature indicator membrane crosslinked with amaranth leaf extract, polyvinyl alcohol, and citric acid, the problem of cold chain monitoring during the storage and transportation of fresh meat was solved, achieving low-cost and reliable temperature fluctuation monitoring and food quality prediction.
Patent Information
- Application Number
- CN202411819133.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-11-11
- Estimated Expiration
- 2044-12-11
AI Technical Summary
The current cold chain disruptions during the storage and transportation of fresh meat are difficult to monitor effectively, affecting food quality and safety.
A time-temperature indicator film (TTI) was prepared by combining amaranth leaf extract with biodegradable thermoplastic polyvinyl alcohol (PVA) and citric acid. The effect of temperature and time was monitored by color change.
It achieves low-cost and reliable temperature fluctuation monitoring, improves the ability to predict food quality during the storage and transportation of fresh meat, and has the characteristics of mechanical strength and environmental friendliness.
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Figure CN119798730B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of food processing and preservation, and in particular to a method for preparing a time and temperature indicating membrane using amaranth leaf extract as raw material and its application. Background Technology
[0002] Indicators are used to communicate information about food quality or the surrounding environment to suppliers, retailers, and customers in real time through various signals. Temperature indicators are indirect indicators of food quality, revealing information about the external environment. They do not focus on the changes themselves, but rather provide information about the external factors (temperature abuse) that cause changes in food. Consumers can detect potential microbial growth, protein denaturation, or emulsion breakage by understanding temperature abuse. Temperature fluctuations and extreme temperatures have a significant impact on shelf life because they largely determine the microbial activity of frozen foods, refrigerated foods, and refrigerated foods in the meat and fish supply chain.
[0003] Time-temperature indicators (TTIs) show irreversible changes caused by the combined effects of temperature and time. To ensure food quality, food manufacturers also utilize them to closely monitor the temperature of their products at every stage of the supply chain. TTIs monitor cold chain temperatures through visible, irreversible colorimetric changes, reducing waste. my country is currently in a transitional period from transporting livestock and poultry to transporting meat. At present, cold chain disruptions during the storage and transportation of fresh meat still exist and are difficult to monitor, posing a potential threat to the safety of fresh meat.
[0004] Color response efficiency, colorimetric distinguishability, irreversible color change, storage stability, and apparent activation energy of total color difference change are crucial performance indicators for accurate TTI detection. The structure, light-blocking properties, mechanical properties, thickness, and biodegradability of TTI films are also important quality indicators. Therefore, there is an urgent need to develop low-cost, practical TTI films to monitor "chain breakage" phenomena during the storage and transportation of fresh meat, providing a reliable guarantee for the high-quality development of the fresh meat industry. Summary of the Invention
[0005] To address the difficulty in effectively monitoring cold chain "breaks" during the storage and transportation of fresh meat, this invention aims to provide a method for preparing a time-temperature indicator membrane using amaranth leaf extract as raw material, and its application has been tested in beef storage.
[0006] The presence of betaine in amaranth gives its leaves different colors (red, orange, or green). Among these, betaine is a nitrogen-containing, water-soluble pigment. After deposition in vacuoles, it transforms into red and yellow betaine anthocyanins. Temperature is an external factor affecting the stability of betaine; compared to refrigeration, the degradation rate constant of betaine in the extraction medium is higher at room temperature.
[0007] Therefore, this invention uses amaranth leaf extract as a key color-changing element, and co-prepares a TTI green biodegradable film with biodegradable thermoplastic polyvinyl alcohol (PVA) and citric acid, and applies it in beef storage. This film has the advantages of simple preparation, low cost, good mechanical strength, and green biodegradability, and is expected to be widely used in monitoring temperature fluctuations during the storage and transportation of fresh meat.
[0008] The technical solution of this invention is as follows:
[0009] The first objective of this invention is to provide a method for preparing a time-temperature indicating membrane using amaranth leaf extract as a raw material, the method comprising the following steps:
[0010] 1) Take amaranth leaves, homogenize the leaf tissue in ethanol, and soak overnight;
[0011] 2) After overnight filtration, the extract was filtered to remove coarse particles, centrifuged, filtered to obtain the supernatant, and the ethanol was removed by rotary evaporation. The solution was then freeze-dried to obtain amaranth leaf extract.
[0012] 3) Mix the hydrochloric acid solution and ethylene glycol, and stir until homogeneous;
[0013] 4) Add polyvinyl alcohol and citric acid to the mixed solution obtained in step 3), stir until fully mixed, then heat and stir to allow polyvinyl alcohol and citric acid to react fully, then keep the temperature and let stand until the air bubbles on the top of the solution are removed; preferably, the stirring time is not less than 3 hours.
[0014] 5) Cool the mixture obtained in step 4) to room temperature, add amaranth leaf extract to the solution, and stir to evenly disperse the amaranth leaf extract in the solution;
[0015] 6) Store the solution obtained in step 5) at a refrigeration temperature below -15°C for no less than 3 hours;
[0016] 7) Freeze-dry the refrigerated solution obtained in step 6) to obtain the time-temperature indicator membrane (TTI membrane).
[0017] The storage conditions for the time and temperature indicating film described in this invention are refrigeration for later use.
[0018] Furthermore, the ethanol solution in step 1) has a concentration of 95%, and the soaking process after homogenization is carried out at 4°C.
[0019] Furthermore, the centrifugation process described in step 2) is carried out at 4°C.
[0020] Furthermore, in step 3), the hydrochloric acid aqueous solution has a pH of 1.5, and the volume ratio of hydrochloric acid solution to ethylene glycol is 4:1.
[0021] Furthermore, in step 4), the amount of polyvinyl alcohol added is 12g / 100mL, and the concentration of citric acid is 1g / 100mL; the heating process in step 4) requires heating to 90℃, rotating at 250rpm, and lasting for 2 hours.
[0022] Furthermore, the amount of amaranth leaf extract added in step 5) is 0.2-1g / 100mL, and the stirring process in step 5) is carried out at 4℃.
[0023] Furthermore, the refrigeration conditions for the solution in step 6) are below -80°C.
[0024] Furthermore, in step 7), the freeze-drying conditions are such that the vacuum degree is controlled below 0.1 m bar after pre-cooling.
[0025] The second objective of this invention is to provide a time-temperature indicator membrane made from amaranth leaf extract, wherein the time-temperature indicator membrane is prepared using the aforementioned preparation method.
[0026] Preferably, the time-temperature indicator film is formed by cross-linking ethylene glycol and citric acid to form a framework, with ethylene glycol as a film-forming aid and amaranth leaf extract as a time-temperature indicator.
[0027] Further preferred, the mass ratio of amaranth leaf extract, citric acid, and polyvinyl alcohol as raw materials is 1-2:2:24.
[0028] A third objective of this invention is to provide the application of the aforementioned time-temperature indicator film in the prediction of the shelf life of food. Preferably, the food is a temperature- and / or time-sensitive substance. The time-temperature indicator film serves as an indicator by directly observing its color change or measuring its total color difference value change. When exposed to an environment of 4-15°C, the color of the time-temperature indicator film changes from purplish-red to yellowish-brown within 0.5-8 days. When exposed to an environment of 25-35°C, the color of the time-temperature indicator film changes from purplish-red to yellowish-brown within 3-12 hours.
[0029] The beneficial effects of this invention are as follows:
[0030] This invention prepares a membrane matrix by crosslinking polyvinyl alcohol and citric acid, and then prepares and adds amaranth leaf extract to give the film the function of a time-temperature indicator. The total color difference value of this TTI film is highly sensitive to changes under food storage temperatures (4-35℃). The film exhibits irreversible color changes and a certain degree of cold storage stability. The apparent activation energy corresponding to the change in the total color difference value of the film can be changed by adjusting the amount of amaranth leaf extract added, making it applicable to the prediction of key storage indicators in various food systems. Simultaneously, the addition of amaranth leaf extract improves the film's mechanical strength, light barrier properties, smoothness, and biodegradability. The TTI film preparation process is simple and low-cost, demonstrating significant social, economic, and ecological benefits. Attached Figure Description
[0031] Figure 1 The color changes of the prepared TTI film at different temperatures are shown in Figures A, E, and F, which are the storage results at -10℃, 4℃, 15℃, 2℃, and 35℃, respectively. Figure F shows the color of the prepared film after being stored at 4-35℃ for 9 hours to 8 days and then returned to -10℃ for 1 day to check the irreversibility of the film color change.
[0032] Figure 2 The relationship curves of ln K and 1 / T in the Arrhenius equation for the total color difference variation of the prepared TTI film and the relationship curves of ln K and 1 / T in the Arrhenius equation for the total volatile basic nitrogen (TVB-N) value of beef are shown.
[0033] Figure 3 SEM micrographs of the surface (A) and cross-section (B) of the prepared TTI film;
[0034] Figure 4 Figure A shows the thickness, light blocking properties, and mechanical properties of the prepared TTI film. Figure B shows the opacity, Figure C shows the tensile strength, and Figure D shows the elongation at break.
[0035] Figure 5 Characterization of the biodegradability of the prepared TTI film. Detailed Implementation
[0036] The present invention will be further described in detail below with reference to the embodiments. Reagents or instruments used without a specified manufacturer are considered to be conventional products that can be purchased on the market.
[0037] Example 1
[0038] 1) Amaranth leaf tissue was homogenized in 95% ethanol and then soaked overnight at 4°C;
[0039] 2) The overnight extract was filtered through gauze to remove coarse particles, centrifuged at 4°C for 15 minutes, filtered through filter paper to obtain the supernatant, and the ethanol was removed using a rotary evaporator. The solution was poured into a petri dish and freeze-dried to obtain amaranth leaf extract;
[0040] 3) Add 40 mL of hydrochloric acid aqueous solution (pH 1.5) and 10 mL of ethylene glycol to a 100 mL beaker, and stir the solution at 600 rpm at 50 °C.
[0041] 4) Add 6g of polyvinyl alcohol and 0.5g of citric acid to the solution and stir for 30 minutes. Then raise the temperature to 90℃ and stir at 250rpm for 3 hours to allow the polyvinyl alcohol and citric acid to react fully. Then keep it at 90℃ for 2 hours without stirring to remove the air bubbles on the top of the solution.
[0042] 5) After that, cover the beaker with plastic wrap and leave it at room temperature for 12 hours.
[0043] Add 0.250 g of amaranth leaf extract to the above solution and stir at 250 rpm for 2 hours at 4°C.
[0044] 6) Pour 5g of solution into a 95mL petri dish, cover the petri dish with plastic wrap and make small holes in the corners, and place the petri dish in a -80℃ refrigerator for 3 hours.
[0045] 7) Place the petri dish in a freeze dryer and freeze-dry under a vacuum of less than 0.1 m bar to prepare the PC-ALE-0.250 film. Store the film at -20°C until use.
[0046] Example 2
[0047] 1) Amaranth leaf tissue was homogenized in 95% ethanol and then soaked overnight at 4°C;
[0048] 2) The overnight extract was filtered through gauze to remove coarse particles, centrifuged at 4°C for 15 minutes, filtered through filter paper to obtain the supernatant, and the ethanol was removed using a rotary evaporator. The solution was poured into a petri dish and freeze-dried to obtain amaranth leaf extract;
[0049] 3) Add 40 mL of hydrochloric acid aqueous solution (pH 1.5) and 10 mL of ethylene glycol to a 100 mL beaker, and stir the solution at 600 rpm at 50 °C.
[0050] 4) Add 6g of polyvinyl alcohol and 0.5g of citric acid to the solution and stir for 30 minutes. Then raise the temperature to 90℃ and maintain stirring at 250rpm for 3 hours to allow the polyvinyl alcohol and citric acid to react fully. Then maintain the temperature at 90℃ for 2 hours without stirring. Remove any air bubbles from the top of the solution.
[0051] 5) Next, cover the beaker with plastic wrap and let it stand at room temperature for 12 hours. Add 0.375 g of amaranth leaf extract to the above solution and stir at 250 rpm for 2 hours at 4°C.
[0052] 6) Pour 5g of the solution into a 95mL petri dish, cover the dish with plastic wrap and poke small holes in the corners, then place the dish in a -80℃ refrigerator for 3 hours.
[0053] 7) Place the petri dish in a freeze dryer and freeze-dry under a vacuum of less than 0.1 m bar to prepare the PC-ALE-0.375 film. Store the film at -20°C until use.
[0054] Example 3
[0055] 1) Amaranth leaf tissue was homogenized in 95% ethanol and then soaked overnight at 4°C;
[0056] 2) The overnight extract was filtered through gauze to remove coarse particles, centrifuged at 4°C for 15 minutes, filtered through filter paper to obtain the supernatant, and the ethanol was removed using a rotary evaporator. The solution was poured into a petri dish and freeze-dried to obtain amaranth leaf extract;
[0057] 3) Add 40 mL of hydrochloric acid aqueous solution (pH 1.5) and 10 mL of ethylene glycol to a 100 mL beaker, and stir the solution at 600 rpm at 50 °C.
[0058] 4) Add 6g of polyvinyl alcohol and 0.5g of citric acid to the solution and stir for 30 minutes. Then raise the temperature to 90℃ and maintain stirring at 250rpm for 3 hours to allow the polyvinyl alcohol and citric acid to react fully. Then maintain the temperature at 90℃ for 2 hours without stirring. Remove any air bubbles from the top of the solution.
[0059] 5) Next, cover the beaker with plastic wrap and let it stand at room temperature for 12 hours. Add 0.500 g of amaranth leaf extract to the above solution and stir at 250 rpm for 2 hours at 4°C.
[0060] 6) Pour 5g of the solution into a 95mL petri dish, cover the dish with plastic wrap and poke small holes in the corners, then place the dish in a -80℃ refrigerator for 3 hours.
[0061] 7) Place the petri dish in a freeze dryer and freeze-dry under a vacuum of less than 0.1 m bar to prepare the PC-ALE-0.500 film. Store the film at -20°C until use.
[0062] Comparative Example 1
[0063] 1) Add 40 mL of hydrochloric acid aqueous solution (pH 1.5) and 10 mL of ethylene glycol to a 100 mL beaker, and stir the solution at 600 rpm at 50 °C.
[0064] 2) Add 6g of polyvinyl alcohol and 0.5g of citric acid to the solution and stir for 30 minutes. Then raise the temperature to 90℃ and keep stirring for 3 hours, then keep at 90℃ for 2 hours without stirring. Remove the air bubbles from the top of the solution.
[0065] 3) Afterward, cover the beaker with plastic wrap and let it stand at room temperature for 12 hours. Without adding amaranth leaf extract, stir the above solution at 250 rpm for 2 hours at 4°C.
[0066] 4) Pour 5g of solution into a 95mL petri dish, cover the petri dish with plastic wrap and poke small holes in the corners, then place the petri dish in a -80℃ refrigerator for 3 hours.
[0067] 5) Place the petri dish in a freeze dryer and freeze-dry under a vacuum of less than 0.1 m bar to prepare the PC-ALE-0 film. Store the film at -20°C until needed.
[0068] Performance testing
[0069] The prepared films were stored at different temperatures, and the response of their total color difference to temperature and time was investigated. The feasibility of predicting TVB-N values, irreversibility of color change, cold storage stability, light blocking properties, surface morphology, mechanical properties, thickness, and biodegradability of the films obtained in Examples 1, 2, and 3 and Comparison 1 were tested respectively.
[0070] The detection method for the aforementioned indicator is as follows:
[0071] 1. Color response efficiency and colorimetric analysis of thin films
[0072] To investigate the colorimetric response of TTI films, the color changes of the films (2×2 cm) were studied at different temperatures (-10, 4, 15, 25, and 35 °C). The colorimetric values (L*, a*, and b*) of the TTI films based on their surface colors were measured using a colorimeter, and the color changes of the TTI films were captured using a camera. The colorimeter was calibrated using a white standard plate before measurement. The total color difference (ΔE) was calculated using the following formula:
[0073]
[0074] Wherein, Li*, ai*, and bi* are the chromaticity parameters of the standard white plate, while L, a, and b are the chromaticity parameters of the sample film.
[0075] 2. Dynamic modeling of chromaticity changes
[0076] To investigate the kinetic modeling of TTI thin films, the total color difference (ΔE) values as a function of time at different temperatures (-10, 4, 15, 25, and 35 °C) are shown. The chromaticity response of the time-temperature indicator F(X) is as follows:
[0077] F(X) = kdt
[0078] k is the reaction rate constant, and t is the reaction storage time. By plotting the response value F(X) against time, a straight line can be obtained; the slope of the line can be used to determine the value of k at different storage temperatures.
[0079] The temperature dependence of the reaction was calculated using the Arrhenius equation, as shown below:
[0080] In k=In(k0)-(E A / RT)
[0081] E A The value represents the activation energy of the reaction under study, and R is the universal gas constant (8.314 J mol). -1 K -1 ).
[0082] 3. Determination of total volatile basic nitrogen (TVB-N)
[0083] To investigate the applicability of the indicator film to beef, beef samples were placed at the same temperatures (-10, 4, 15, 25, and 35 °C) as the TTI film for a certain period of time. In a digestion tube, 15 g of beef sample was homogenized with deionized water, and 1 g of magnesium oxide powder was added to the mixture. Finally, the TVB-N values of different beef samples were determined using a nitrogen analyzer, expressed in mg / 100g.
[0084] 4. Irreversible color change test of TTI film
[0085] To check the irreversibility of TTI films, films (2×2cm) that had changed color at different temperatures (4, 15, 25 and 35°C) were placed back at -10°C for 1 day, and the color values (L*, a* and b*) were measured using an Osaka (Japan CR-400-Chroma meter) and photographed.
[0086] 5. Cold storage stability of TTI film
[0087] The stability of the TTI film was determined by making minor modifications using a prescribed method (Yar et al., 2024). In short, the stability of the PC-ALE-based film was monitored based on color changes. The film (2 × 2 cm) was stored at -15°C for 20 days, and the film color was monitored using a colorimeter at 10-day intervals.
[0088] 6. Scanning electron microscopy observation
[0089] The surface and cross-section of the indicator film were scanned using SEM. The film sample was fixed on a bronze sample stage and a thin layer of gold was sprayed onto it. The sprayed film was then fixed on the SEM sample stage, and the microstructure was observed at 10 kV.
[0090] 7. Light transmittance test
[0091] The transmittance or opacity of the thin film sample (80 × 50 mm) was measured at 600 nm using a spectrophotometer. The data were calculated using the following formula:
[0092] Opacity = A / L
[0093] Where A represents the absorbance value at 600 nm, and L represents the sample thickness (nm).
[0094] 8. Mechanical properties and thickness testing
[0095] The thickness of the indicator packaging film was measured using a digital handheld micrometer. Five measurements were taken at different locations on each film, and the average value was calculated. The tensile strength and elongation at break of the film were examined at room temperature using a texture analyzer. A 10×80 mm strip of film was placed on a 50 mm measuring fixture and tested at a speed of 50 mm / min and a tensile force of 5 kN. The TS and EAB were calculated as follows:
[0096]
[0097] Where F represents tensile strength (N); X represents sample thickness (mm); W is sample width (mm); ΔL represents the increase in distance at fracture (mm); and L represents the initial length between sample clamps (mm).
[0098] 9. Biodegradability of membranes
[0099] The biodegradation rate of the SCG-based composite film was qualitatively measured in collected soil samples. TTI film samples (2 × 2 cm) were cut and buried in the soil, and water was sprayed daily until complete degradation. The biodegradation rate of the film was calculated using the following formula:
[0100]
[0101] Where M0 represents the original weight of the sample, and M1 represents the weight after biodegradation. 2.6.12.
[0102] 10. Data Processing
[0103] All measurements of the thin film properties were repeated at least five times, and the data are expressed as mean ± standard deviation. Statistical analysis of the thin film data was performed using SPSS 16.0 software. One-way ANOVA was used to determine the differences between factors and levels. Duncan's test was used to determine the major differences between samples (p < 0.05).
[0104] The results of the indicators are as follows:
[0105] 1. Color changes of TTI at different temperatures
[0106] Figure 1 As shown in Figure AE, no significant changes were observed visually in Comparative Example 1 during storage, but the film color changed to varying degrees after the addition of amaranth leaf extract. Figure 1 (AE). For example, when the TTI films of Comparative Example 1 and Examples 1 to 3 were placed at -10°C, the color did not change for 15 days, but after 15-20 days, the TTI films of Examples 1 to 3 showed slight changes (AE). Figure 1 A). At 4°C, Examples 1 and 2 showed significant color changes within 2 days. The film of Example 3, due to its high content of amaranth leaf extract and anthocyanins, exhibited a dark red color change. Figure 1 B). At 15°C, Examples 1 and 2 changed from reddish-purple to light brown within 12 hours and to yellow within 24 hours, while Example 3 changed to brown within 24 hours and to yellow within 48 hours. Figure 1 C). At 25°C, Examples 1 and 2 changed from reddish-purple to light brown within 3 hours and to yellow within 12 hours, while Example 3 changed to brown within 9 hours and to yellow within 12 hours. Figure 1 D). At 35°C, Examples 1 and 2 turned light brown within 3 hours and yellow within 6 hours, while Example 3 turned yellow within 9 hours. Figure 1 E).
[0107] The results in Table 1 also support the variation in chromaticity (ΔE) values of the TTI film at all temperatures. The color changes of the TTI film at all temperatures were observable to the naked eye. These total color differences (ΔE) are crucial for food producers, distributors, and consumers, allowing for accurate determination of food condition. These results demonstrate that TTI films with added amaranth leaf extract effectively indicate cumulative changes over temperature and time.
[0108] Table 1. ΔE values of TTI thin films at different temperatures over time
[0109]
[0110]
[0111] Numerical values are expressed as mean ± standard deviation (n = 5). Different letters in the same row indicate significant differences (p < 0.05).
[0112] 2. Irreversible color change of TTI film
[0113] Irreversibility is a crucial characteristic of TTI films. The color change observed in the irreversibility test is as follows: Figure 1 As shown in Figure F, after placing the film at -10°C for one day, it is easily observed with the naked eye that the film, which has changed color at different temperatures, does not revert to its original color or any other color. Comparison of the chromaticity values in Tables 1 and 3 also supports this conclusion. It can be confirmed that the color change of this TTI film is irreversible, and it will not revert to its original color after the temperature is lowered again.
[0114] Table 2. Color change ΔE values of TTI films after being stored at -10℃ for 1 day.
[0115]
[0116] The numerical values are expressed as mean ± standard deviation (n = 5).
[0117] 3. Storage stability test at -15℃
[0118] This study evaluated the color changes of TTI indicator films after 10 and 20 days at -15°C, as shown in Table 3. After 10 days, the color of the TTI film remained stable, with no significant changes during storage. After 20 days, slight differences appeared in the chromaticity values (increased L* and b* values, and decreased a* and ΔE values). This indicates that the prepared TTI film can be stably stored at -15°C for at least 10 days.
[0119] Table 3. Colorimetric values of TTI films stored at -15℃ for 20 days.
[0120]
[0121]
[0122] The numerical values are expressed as mean ± standard deviation (n = 5).
[0123] 4. Activation energy of TTI thin films
[0124] like Figure 2As shown, the Arrhenius equation should be used to calculate the apparent activation energy of the total color difference change. The calculated activation energies of the films in Examples 1, 2, and 3 are 115 kJ / mol, 49 kJ / mol, and 78 kJ / mol, respectively. If the difference in activation energy between food spoilage and TTI is within ±25 kJ / mol, then TTI can be used to monitor the shelf life and quality of the food in the supply chain. Therefore, the indicator film of Example 1 can be used for food systems with activation energies in the range of 90-140 kJ / mol. Examples 2 and 3 can be used for food systems with activation energies in the ranges of 24-74 kJ / mol and 53-103 kJ / mol, respectively. The measured activation energy of TVB-N in beef was 42 kJ / mol, while the activation energy of the film of Example 2 was 49 kJ / mol, indicating that the film of Example 2 can be used to track the TVB-N content in beef.
[0125] 5. Microstructure of TTI thin films
[0126] Microscopic surface morphology (in micrometers) of different composite films, such as Figure 3 As shown in the figures, the film surface and cross-section of Comparative Example 1 are smoother, defect-free, uniform, and have a dense network structure. This indicates that polyvinyl alcohol and citric acid are mixed evenly and exhibit good compatibility. The surface or cross-sectional smoothness of the films in Examples 1 and 2 is better than that of Comparative Example 1. The film roughness in Example 3 is slightly increased. This indicates that the addition of amaranth leaf extract in the range of 0.5-0.75 g / 100 mL has an effect on improving the overall smoothness of the film.
[0127] 6. Light blocking properties
[0128] Opacity is a key characteristic that represents the film's ability to act as a light barrier, since light is detrimental to food preservation to some extent. Figure 4 The results in B indicate that the addition of amaranth leaf extract significantly reduced light transmittance and increased the light blocking ability of the membrane.
[0129] 7. Mechanical properties and thickness
[0130] All TTI films had thicknesses ranging from 0.20 to 0.22 mm, and the introduction of amaranth leaf extract did not significantly alter the film thickness. Figure 4 A). Compared to Comparative Example 1, the introduction of amaranth leaf extract significantly improved the tensile strength of the TTI film. Figure 4 C) and elongation at break ( Figure 4 D). This indicates that the addition of amaranth leaf extract not only imparts TTI function to the film but also significantly improves the film's mechanical properties and enhances its mechanical strength.
[0131] 8. Biodegradability of membranes
[0132] In the material selection process, biodegradability is a particularly important factor to consider. Compared to Comparative Example 1, the addition of amaranth leaf extract significantly improved the biodegradability of the film, exhibiting a concentration-dependent effect. After one week, the weight loss of the Comparative Example 1 film was approximately 15%, while the weight loss of the film with added amaranth leaf extract reached 19%-24%. After three weeks, the weight loss of the Comparative Example 1 film was 43%, while the weight loss of the film with added amaranth leaf extract reached 47%-57%. Figure 5 The results showed that the introduction of amaranth leaf extract significantly enhanced the biodegradability of the film and improved its environmental friendliness.
[0133] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
[0134] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material, characterized in that, The method includes the following steps: 1) Take amaranth leaves, homogenize the leaf tissue in an ethanol solution, and soak overnight; 2) After overnight filtration, the extract was filtered to remove coarse particles, centrifuged, filtered to obtain the supernatant, and the ethanol was removed by rotary evaporation. The solution was then freeze-dried to obtain amaranth leaf extract. 3) Mix the hydrochloric acid solution and ethylene glycol, and stir until homogeneous; 4) Add polyvinyl alcohol and citric acid to the mixed solution obtained in step 3), stir until fully mixed, then heat and stir to allow polyvinyl alcohol and citric acid to react fully, then keep the temperature and let stand until the air bubbles at the top of the solution are removed. 5) Cool the mixture obtained in step 4) to room temperature, add amaranth leaf extract to the solution, and stir to evenly disperse the amaranth leaf extract in the solution; 6) Store the solution obtained in step 5) at a temperature below -15°C for at least 3 hours; 7) Freeze-dry the refrigerated solution obtained in step 6) to obtain the time and temperature indicator membrane.
2. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 1) The ethanol solution concentration is 95%, and the soaking process after homogenization is carried out at 4°C.
3. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 2) The centrifugation process is carried out at 4°C.
4. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 3) The hydrochloric acid aqueous solution has a pH of 1.5, and the volume ratio of hydrochloric acid solution to ethylene glycol is 4:
1.
5. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 4) The amount of polyvinyl alcohol added is 12 g / 100 mL, and the concentration of citric acid is 1 g / 100 mL; Step 4) The heating process needs to be heated to 90°C, rotated at 250 rpm, and lasted for 2 hours.
6. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, The amount of amaranth leaf extract added in step 5) is 0.2-1 g / 100 mL, and the stirring process in step 5) is carried out at 4°C.
7. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 6) The solution is refrigerated at -80°C or below.
8. The method for preparing a time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 1, characterized in that, Step 7) The freeze-drying conditions are that the vacuum degree is controlled below 0.1 m bar after pre-cooling.
9. A time-temperature indicating membrane using amaranth leaf extract as raw material, characterized in that, The time and temperature indicating film is prepared by the preparation method described in any one of claims 1 to 8.
10. The time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 9, characterized in that, The time-temperature indicator film is formed by cross-linking polyvinyl alcohol and citric acid to form a framework, and amaranth leaf extract is used as a time-temperature indicator.
11. The time-temperature indicating membrane using amaranth leaf extract as raw material according to claim 10, characterized in that, The mass ratio of amaranth leaf extract, citric acid, and polyvinyl alcohol as raw materials is 1-2:2:
24.
12. The application of the time-temperature indicating film of claim 9 in the preparation of food shelf-life prediction.
13. The application according to claim 12, characterized in that, The food is a temperature- and / or time-sensitive substance. The time-temperature indicator film serves as an indicator by directly observing its color change or measuring its total color difference value change. When exposed to an environment of 4-15°C, the color of the time-temperature indicator film changes from purplish-red to yellowish-brown within 0.5-8 days. When exposed to an environment of 25-35°C, the color of the time-temperature indicator film changes from purplish-red to yellowish-brown within 3-12 hours.