Tryptophan / taurine composite material for improving oxidation resistance, preparation method and application

Abstract

The invention belongs to the technical field of new materials, and discloses a tryptophan / taurine composite material capable of improving oxidation resistance, a preparation method and application, and the composite material comprises the following components in parts by weight: 28-32 parts of chitosan, 0.048-0.055 part of tryptophan, 0.028-0.035 part of taurine, and 0.72-0.78 part of montmorillonite. The tryptophan and the taurine are loaded in the chitosan-based composite membrane, so that the oxidation resistance of the membrane is remarkably improved. The ABTS free radical scavenging rate of the composite film disclosed by the invention is increased to 73.86%. The improvement of the performance significantly enhances the ability of the film to remove active oxygen generated during the storage period of fruits and vegetables, effectively delays the oxidation process, and improves the fresh-keeping effect of fruits. The film material can keep the freshness of fruits in a high-oxidation environment, and is especially suitable for fruits and vegetables needing efficient anti-oxidation protection.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and in particular to a tryptophan / taurine composite material with enhanced antioxidant capacity, its preparation method and application. Background Technology

[0002] Currently, the existing technology has the following technical problems: Question 1: Pure chitosan membranes have limited antioxidant capacity. Chitosan relies solely on its limited number of hydroxyl and amino groups to exert its antioxidant effect, but these groups are relatively few in number and insufficient to cope with the large amount of reactive oxygen species generated during fruit storage. From a molecular structure perspective, although the hydroxyl and amino groups in chitosan molecules have some hydrogen-donating capacity and can react with free radicals, their limited number and low reactivity mean they can only capture a small number of free radicals through weak hydrogen bonding. Furthermore, the free radical scavenging rate of a single chitosan membrane is generally low, with its DPPH free radical scavenging rate typically below 15%. Therefore, chitosan molecules have limited ability to inhibit oxidation during fruit storage, and a simple chitosan membrane is insufficient to delay post-harvest browning and oxidative deterioration of fruit, making it difficult to maintain fruit flavor and quality.

[0003] Question 2: The molecular structure of pure chitosan membranes contains numerous voids, which form channels for water molecule permeation, resulting in a water vapor permeability that typically exceeds 0.4 g·m³. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 Furthermore, the chitosan membrane exhibits poor microstructural uniformity. During film formation, it is susceptible to various factors, such as solvent evaporation rate and temperature fluctuations, easily leading to the formation of localized permeation channels. From a microscopic perspective, chitosan molecules exhibit irregular aggregates with relatively large intermolecular gaps, creating rapid channels for water migration. When fruit is in storage, high water vapor permeability accelerates moisture loss, causing the peel to wrinkle and harden, severely impacting the fruit's appearance and taste. Simultaneously, in high humidity environments, rapid water migration may provide suitable conditions for microbial growth, potentially leading to excessive microbial proliferation and fruit rot.

[0004] Question 3: Currently, the preparation and modification of chitosan-based films often utilize organic acids such as acetic acid as solvents to dissolve chitosan, and enhancing their mechanical and barrier properties typically relies on glutaraldehyde or heavy metal nanoparticles (such as nano-silver) as crosslinking agents and functional additives. However, glutaraldehyde has certain cytotoxicity, and heavy metal nanoparticles may migrate from the membrane matrix into the food, potentially posing a threat to human health and causing environmental pollution, thus failing to meet the development requirements of food contact materials and green packaging. Therefore, developing non-toxic and environmentally friendly alternative strategies has become an important direction in chitosan-based film research.

[0005] The search revealed the following patent publications related to this invention's patent application: Prior art patent 1, "A Food-Derived Fruit and Vegetable Preservative, Its Preparation Method and Application Method (CN120167500A)," discloses a food-derived fruit and vegetable preservative. Its technical solution aims to simultaneously enhance the antioxidant properties and antibacterial efficiency of the preservative through the synergistic effect of its compound components. The antibacterial efficiency has been verified by quantitative data such as the E. coli inhibition rate (91.3%). However, the claimed antioxidant properties of this preservative mainly rely on theoretical explanations and post-storage observation of fruits and vegetables, lacking quantitative determination of key antioxidant indicators such as DPPH and ABTS free radical scavenging rates. Therefore, the existing experimental evidence for this patent is insufficient to fully demonstrate its clear and quantifiable protective effect against post-harvest oxidative browning of fruits. This limitation makes it difficult to provide convincing technical guarantees for addressing the post-harvest preservation needs of easily oxidized agricultural products.

[0006] Prior art patent 2, titled "A Method for Preparing a High-Strength, Self-Lubricating Polyvinyl Alcohol Hydrogel (CN112625269B)," discloses a high-strength PVA hydrogel formed by repeated freeze-thaw cycles of PVA, hydroxypropyl cellulose, and L-tryptophan. However, due to the porous network structure within the hydrogel system and the large number of hydrophilic hydroxyl groups on the PVA molecular chains, its water vapor permeability reaches 0.5 g·m⁻¹. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 This characteristic makes the material unable to meet the moisture control requirements for fruit and vegetable storage. When used for the transportation and storage of fruits and vegetables, it cannot effectively prevent external moisture from invading and causing the fruits and vegetables to become damp and rot, nor can it inhibit the drying and deterioration caused by the loss of moisture from the fruits and vegetables themselves.

[0007] Prior art patent 3, "Composite Preservative Film and its Preparation Method and Application (CN120206905A)," discloses a composite preservative film composed of a pectin film layer and a chitosan film layer. The pectin film layer contains anthocyanins and / or anthocyanin silver ion compounds, and the chitosan film layer contains lignin. It is manufactured by a casting method. However, this patent's composite preservative film relies on anthocyanin silver ion compounds to enhance antibacterial properties. Although the silver ions are nanoscale, there is still a potential risk of metal ion migration, limiting its applicability in food contact scenarios with high safety requirements. Furthermore, the preparation process requires mixing solvents under strongly acidic or alkaline conditions (pH 2-3 or pH 13-14), which may damage the structure of some functional components. The double-layer film composite process also has strict requirements on thickness ratios, increasing the difficulty of large-scale production and limiting its widespread application in low-cost, high-safety fruit and vegetable preservation scenarios.

[0008] By comparison, the present invention patent application is fundamentally different from the aforementioned patent publications. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a tryptophan / taurine composite material with enhanced antioxidant capacity, its preparation method, and its application.

[0010] The technical solution adopted by this invention to solve its technical problem is: A tryptophan / taurine composite material for enhancing antioxidant capacity, the composite material comprising the following components in parts by weight: Chitosan 28-32 parts, tryptophan 0.048-0.055 parts, taurine 0.028-0.035 parts, montmorillonite 0.72-0.78 parts.

[0011] Furthermore, the composite material comprises the following components in parts by weight: 30 parts chitosan, 0.051 parts tryptophan, 0.0313 parts taurine, and 0.75 parts montmorillonite.

[0012] The preparation method of the tryptophan / taurine composite material as described above includes the following steps: (1) Weigh out chitosan and dissolve it in a 1% acetic acid solution. Stir with a magnetic stirrer at 600 rpm until the chitosan is completely dissolved to obtain a uniform chitosan solution. (2) The chitosan solution obtained in step (1) is thoroughly mixed with tryptophan, taurine and montmorillonite. The mixture is stirred at 600 rpm until tryptophan, taurine and montmorillonite are completely dissolved. Glycerin with a final mass concentration of 0.5% (w / v) is added as a plasticizer and Tween 80 with a final mass concentration of 0.1% (w / v) is added as a surfactant. The mixture is stirred at 600 rpm for 1 hour. The pH is adjusted to 4.5 with acetic acid. The solution is sonicated for 1 hour to remove bubbles and ensure that the solution is uniform and bubble-free, thus obtaining the tryptophan / taurine composite material.

[0013] Furthermore, in step (1), the ratio of chitosan to 1% acetic acid solution in g:mL is 30:2000.

[0014] Furthermore, in step (2), the ratio of chitosan solution, tryptophan, taurine, and montmorillonite obtained in step (1) is 500 ml: 0.051: 0.0313: 0.75.

[0015] The application of the tryptophan / taurine composite material described above in maintaining fruit freshness under high oxidizing conditions.

[0016] The application of tryptophan / taurine composite materials as described above in the storage and transportation of fruits and vegetables.

[0017] The application of the tryptophan / taurine composite material as described above in reducing water loss from fruits and vegetables.

[0018] The advantages and positive effects of this invention are as follows: 1. This invention significantly enhances the antioxidant properties of a chitosan-based composite membrane by loading tryptophan and taurine onto it. The ABTS free radical scavenging rate of the composite membrane is increased to 73.86%. This performance improvement significantly enhances the membrane's ability to scavenge reactive oxygen species generated during the storage of fruits and vegetables, effectively slowing down the oxidation process and improving the preservation effect of the fruit. This membrane material can maintain the freshness of fruits under high oxidizing environments and is particularly suitable for fruits and vegetables requiring highly efficient antioxidant protection.

[0019] 2. The chitosan-based composite membrane loaded with tryptophan and taurine of this invention exhibits a significant advantage in water vapor transmission rate, with a water vapor transmission rate of 0.23 g·m⁻¹. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 The concentration was significantly lower than that of pure chitosan membrane (0.42 g·m³). -2 ·h -1 ·Pa -1 ·mm -1 ·10-3 And significantly lower than the PVA hydrogel in comparative patent 2 (0.5 g·m³). -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 This improvement effectively reduces moisture loss from fruits and vegetables during storage, delays peel wrinkling and hardening, and ensures better quality of the fruit during long-term storage. Compared to traditional membrane materials, the composite membrane of this invention has significant advantages in reducing moisture loss from fruits and vegetables, and is widely applicable to fruit and vegetable storage and transportation.

[0020] 3. The preparation method of this invention abandons the traditional high-temperature and high-pressure conditions and toxic chemical reagents, and adopts a simple, environmentally friendly, and non-toxic spraying method to prepare chitosan-based composite membranes loaded with tryptophan and taurine. This process not only avoids the use of toxic chemical crosslinking agents, but also eliminates the need for complex high-temperature and high-pressure treatments, thereby reducing the risk of environmental pollution. Compared with the complex double-layer membrane preparation method in comparative patent 3, which requires a strong acid or alkaline environment and a long time, the process of this invention is simple and efficient, suitable for large-scale production, and can reduce costs, in line with the concept of green chemistry.

[0021] 4. This invention enhances the antioxidant properties of chitosan-based membranes by loading tryptophan and taurine into a network structure, which interacts with chitosan molecules. The amino and hydroxyl groups of tryptophan and taurine can form hydrogen bonds and electrostatic interactions with the polar groups in chitosan molecules, further strengthening the overall structure of the membrane. Simultaneously, the molecular structure of tryptophan and taurine improves the membrane's antioxidant capacity and stability, significantly increasing its free radical scavenging rate. The DPPH free radical scavenging rate of chitosan-based membranes loaded with tryptophan and taurine is significantly higher than that of pure chitosan-based membranes, reaching 1.42 and 1.32 times that of pure chitosan-based membranes, respectively, effectively improving the membrane's antioxidant capacity. These combined effects result in a more stable composite membrane structure and stronger antioxidant effect, effectively solving the problem of insufficient antioxidant capacity of pure chitosan membranes in the prior art.

[0022] 5. This invention significantly improves the water vapor barrier properties of chitosan-based composite membranes by loading tryptophan and taurine. Experimental results show that the water vapor permeability of the chitosan-based composite membrane loaded with tryptophan and taurine is 0.23 g·m⁻¹. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 Compared to pure chitosan membrane (0.42 g·m³), -2 ·h -1 ·Pa -1 ·mm -1·10 -3 The membrane material exhibits significantly improved barrier properties, reducing water vapor permeability by approximately 45.2%. This improved water vapor barrier effectively prevents moisture loss from the fruit, reduces peel wrinkling and hardening, and thus slows down fruit quality deterioration. This technology provides a more ideal membrane material for fruit and vegetable storage, enhances fruit storage stability, and solves the fruit quality problems caused by excessive water vapor permeability in the prior art.

[0023] 6. This invention employs a simple and efficient preparation process, abandoning the use of high temperature, high pressure, and chemical reagents. Instead, it utilizes a spraying method under room temperature conditions to prepare chitosan-based composite membranes loaded with tryptophan and taurine. By controlling the pH value of the membrane solution, adding plasticizers (glycerol) and surfactants (Tween 80), and utilizing spraying technology, the membrane thickness is made uniform and the performance is stable. This process simplifies traditional processes, avoids the potential damage to components under high temperature and high pressure conditions, and does not use toxic chemical solvents, conforming to the development concept of green chemistry, and providing an environmentally friendly, safe, and efficient membrane preparation method.

[0024] 7. This invention introduces two naturally occurring molecules with clearly defined biological activities—tryptophan and taurine—into a chitosan matrix to construct an all-natural composite preservative film, avoiding the use of traditional chemical preservatives and toxic cross-linking agents. Studies have confirmed that tryptophan, as an endogenous physiological regulator, can effectively delay post-harvest fruit senescence; while taurine has been widely proven to possess strong antioxidant activity, demonstrating life-extending effects in animal models. This invention integrates these two active ingredients, enabling the composite film to effectively delay post-harvest oxidative deterioration of fruits, providing a highly efficient and environmentally friendly solution for the post-harvest fruit and vegetable supply chain. Attached Figure Description

[0025] Figure 1 This is a diagram showing the morphological appearance of walnut fruits during storage after being treated with a chitosan-based film sprayed according to the present invention. Figure 2 These are microscopic morphology images of different groups of chitosan-based films in this invention; Figure 3 Fourier transform infrared spectra of different groups of chitosan-based films in this invention; Figure 4 This is a graph showing the change in water vapor permeation over time for different groups of chitosan-based films in this invention.

[0026] Figure 5 The graph shows the DPPH and ABTS free radical scavenging rates of different groups of chitosan-based films in this invention. Figure 6 The images show the ultrastructure of walnut kernels in each group after 10 days of storage using chitosan-based membranes in this invention, where PB represents protein bodies, CW represents cell walls, and ICS represents intercellular spaces. in, Figures 1 to 4 In the above, CS-CT is a chitosan-based film without load, CS-TRP is a chitosan-based film loaded with tryptophan, CS-TAU is a chitosan-based film loaded with taurine, and CS-TRP+TAU is a chitosan-based film loaded with tryptophan and taurine. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0028] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0029] A tryptophan / taurine composite material for enhancing antioxidant capacity, the composite material comprising the following components in parts by weight: Chitosan 28-32 parts, tryptophan 0.048-0.055 parts, taurine 0.028-0.035 parts, montmorillonite 0.72-0.78 parts.

[0030] Preferably, the composite material comprises the following components in parts by weight: 30 parts chitosan, 0.051 parts tryptophan, 0.0313 parts taurine, and 0.75 parts montmorillonite.

[0031] The preparation method of the tryptophan / taurine composite material as described above includes the following steps: (1) Weigh out chitosan and dissolve it in a 1% acetic acid solution. Stir with a magnetic stirrer at 600 rpm until the chitosan is completely dissolved to obtain a uniform chitosan solution. (2) The chitosan solution obtained in step (1) is thoroughly mixed with tryptophan, taurine and montmorillonite. The mixture is stirred at 600 rpm until tryptophan, taurine and montmorillonite are completely dissolved. Glycerin with a final mass concentration of 0.5% (w / v) is added as a plasticizer and Tween 80 with a final mass concentration of 0.1% (w / v) is added as a surfactant. The mixture is stirred at 600 rpm for 1 hour. The pH is adjusted to 4.5 with acetic acid. The solution is sonicated for 1 hour to remove bubbles and ensure that the solution is uniform and bubble-free, thus obtaining the tryptophan / taurine composite material.

[0032] Preferably, in step (1), the ratio of chitosan to 1% acetic acid solution is 30:2000 g:mL.

[0033] Preferably, in step (2), the ratio of chitosan solution, tryptophan, taurine and montmorillonite obtained in step (1) is 500 ml: 0.051: 0.0313: 0.75.

[0034] The application of the tryptophan / taurine composite material described above in maintaining fruit freshness under high oxidizing conditions.

[0035] The application of tryptophan / taurine composite materials as described above in the storage and transportation of fruits and vegetables.

[0036] The application of the tryptophan / taurine composite material as described above in reducing water loss from fruits and vegetables.

[0037] Specifically, the relevant preparation and testing methods are as follows: (I) A method for preparing a tryptophan / taurine composite material with enhanced antioxidant capacity, comprising the following steps: Step 1) Weigh 30g of chitosan (CS) and dissolve it in 2000mL of 1% acetic acid solution. Stir with a magnetic stirrer at 600rpm until the chitosan is completely dissolved to obtain a homogeneous chitosan solution.

[0038] Step 2) Thoroughly mix 500 ml of the chitosan solution obtained in Step 1) with 0.75 g of montmorillonite, stirring at 600 rpm until the montmorillonite is completely dissolved. Add 0.5% (w / v) glycerol as a plasticizer and 0.1% (w / v) Tween 80 as a surfactant, stirring at 600 rpm for 1 hour. Adjust the pH to 4.5 with acetic acid. Sonicate the solution for 1 hour to remove air bubbles, ensuring the solution is homogeneous and bubble-free. Obtain the composite membrane, denoted as CS-CT.

[0039] Step 3) Thoroughly mix 500 ml of the chitosan solution obtained in Step 1) with 0.051 g of tryptophan and 0.75 g of montmorillonite. Stir at 600 rpm until the tryptophan and montmorillonite are completely dissolved. Add 0.5% (w / v) glycerol as a plasticizer and 0.1% (w / v) Tween 80 as a surfactant. Stir at 600 rpm for 1 hour. Adjust the pH to 4.5 with acetic acid. Sonicate the solution for 1 hour to remove air bubbles and ensure the solution is homogeneous and bubble-free. Obtain the composite membrane, denoted as CS-TRP.

[0040] Step 4) Thoroughly mix 500 ml of the chitosan solution obtained in Step 1) with 0.0313 g of taurine and 0.75 g of montmorillonite. Stir at 600 rpm until the taurine and montmorillonite are completely dissolved. Add 0.5% (w / v) glycerol as a plasticizer and 0.1% (w / v) Tween 80 as a surfactant. Stir at 600 rpm for 1 hour. Adjust the pH to 4.5 with acetic acid. Sonicate the solution for 1 hour to remove air bubbles and ensure the solution is homogeneous and bubble-free. Obtain the composite membrane, denoted as CS-TAU.

[0041] Step 5) Thoroughly mix 500 ml of the chitosan solution obtained in Step 1) with 0.051 g tryptophan, 0.0313 g taurine, and 0.75 g montmorillonite. Stir at 600 rpm until the tryptophan, taurine, and montmorillonite are completely dissolved. Add 0.5% (w / v) glycerol as a plasticizer and 0.1% (w / v) Tween 80 as a surfactant. Stir at 600 rpm for 1 hour. Adjust the pH to 4.5 with acetic acid. Sonicate the solution for 1 hour to remove air bubbles, ensuring the solution is homogeneous and bubble-free. Obtain the composite membrane, denoted as CS-TRP+TAU.

[0042] (II) Detection of tryptophan / taurine composite membrane: (1) Determination of DPPH free radical scavenging ability Prepare a 0.1 mM DPPH ethanol solution (store protected from light). Weigh 25 mg of the chitosan-based film sample (i.e., the film prepared in step (I) and all subsequent films). Add 5 mL of the above DPPH ethanol solution, vortex to mix, and react in the dark for 30 minutes. Measure the absorbance (A2) at 517 nm using a spectrophotometer. Use pure DPPH ethanol solution (A1) and 95% ethanol as the control and blank reference, respectively. Perform six parallel measurements for each group. The DPPH free radical scavenging rate is calculated as follows: DPPH free radical scavenging rate (%) ×100.

[0043] (2) Determination of ABTS free radical scavenging ability A stock solution was prepared by mixing ABTS (7 mM) and potassium persulfate (2.4 mM) at a volume ratio of 2:1. After activation in the dark for 12-16 h, the solution was diluted to A734nm = 0.70 ± 0.10. 25 mg of chitosan-based film sample was weighed and added to 5 mL of the above DPPH ethanol solution. After vortexing and mixing, the sample was reacted in the dark for 30 min. The absorbance at 734 nm was measured using a spectrophotometer (A2), with pure ABTS dilution as a control (A1). Each group was measured in parallel six times. The ABTS free radical scavenging rate was calculated using the formula: ABTS free radical scavenging rate (%) ×100%.

[0044] (3) Measurement of membrane water vapor transmission rate Take several 50mL glass bottles and fill each with 30mL of ultrapure water. Use a micrometer to measure the thickness (mm) of the chitosan-based film at three different locations. Then, cover the bottle opening with the film to be tested and seal the edges of the glass bottle with waterproof sealing film. Place the sealed glass bottles in a silica gel desiccator (0% relative humidity, 25℃) and record the mass of the glass bottles at 0, 6, 12, 24, 36, and 48 hours. Each group should be tested three times. Water vapor transmission rate (WVP) is calculated using the formula: WVP (g·m³ / g) = WVP / (g·m³ / g) -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 ) .

[0045] In the formula, Δm is the mass difference of the glass bottle (g), reflecting the mass of water vapor passing through the membrane; d is the average thickness of the membrane (mm); and S is the area of ​​the glass bottle opening (m²). 2 ); t is the test time interval (h); ΔP is the water vapor pressure difference across the film at 25℃, which is fixed at 3169Pa.

[0046] (4) Scanning electron microscopy (SEM) test The microstructure of the thin film surface was observed using a G300 scanning electron microscope (Carl Zeiss, Germany). After being fixed with conductive adhesive and vacuum sputtered with gold, the chitosan-based thin film samples underwent morphological analysis at an accelerating voltage of 10 kV.

[0047] (5) Fourier transform infrared spectroscopy (FTIR) test The powder sample of the thin film was scanned using a NyiICOLETiSSOFT-IR Fourier transform infrared spectrometer (4000 cm⁻¹). -1 -400cm -1 Within the wavenumber range, chemical structures are analyzed by changes in characteristic absorption peaks.

[0048] (III) Applications of tryptophan / taurine composite membranes: Step 1) Prepare composite membrane solutions for the four experimental groups CT, CS-TRP, CS-TAU, and CS-TRP+TAU according to the tryptophan / taurine composite membrane preparation steps described above.

[0049] Step 2) Take 130 fresh walnuts that are uniform in size, undamaged, and free from pests and diseases, remove the green husk, pre-cool them in a cold storage at a temperature of (4±1)℃ for 48 hours, and then randomly divide them into four groups.

[0050] Step 3) Use a spray gun to evenly spray the composite membrane solution of the four experimental groups onto the surface of the four groups of walnuts. Specific parameters are set as follows: spray flow rate 3.8 L / h, feeding pressure 1.8 kg / cm². 2 The voltage is 7.5kV, the current is 60mA, and the vertical distance between the spray gun and the walnut is kept at 25cm.

[0051] Step 4) After the composite membrane solution is formed, the walnut samples of each group are stored in a constant temperature and humidity incubator at 25±0.5℃ and 85-95% relative humidity.

[0052] Step 5) During the storage of fresh walnuts, observe the walnuts every other day and measure the color and browning of the kernels. Take 6 walnuts from each group and record the results.

[0053] The relevant test results are as follows: like Figure 1 As shown, walnut samples treated with chitosan-based films exhibited different morphological changes during storage. The CS-CT group showed the most severe fatty acid oxidation on day 10 of storage, with obvious browning and oil spots appearing on the kernel surface. This may be related to the insufficient oxygen barrier properties of the chitosan film, leading to the continuous oxidation of unsaturated fatty acids in the kernel during storage. In contrast, the oxidation levels of walnut kernels in the CS-TRP and CS-TAU groups were reduced, while the CS-TRP+TAU group maintained the best morphology, showing only slight browning. This indicates that the combined loading of tryptophan and taurine significantly enhanced the antioxidant properties of the film, effectively delaying the oxidative rancidity of the walnut kernels.

[0054] like Figure 2 As shown, the CS-CT group membrane surface is relatively smooth and uniform, without obvious pores and bubbles, but there are some irregular aggregates of varying sizes, which may be due to the aggregation of chitosan particles; the CS-TRP group membrane surface has some irregular undulations and texture changes compared to the CS-CT group, which may be due to the interaction between tryptophan loading and chitosan molecules; the CS-TAU group surface is smooth and uniform, with only a few fine groove-like textures, indicating that taurine is well dispersed in the chitosan matrix and has a certain degree of effect on the microstructure of the membrane; the CS-TRP+TAU group surface exhibits a relatively complex texture, with the groove-like structure being more pronounced in the CS-TAU group, which may be due to the combined effect of tryptophan and taurine causing changes in the arrangement and interaction of chitosan molecules, thereby affecting the microstructure of the membrane surface.

[0055] like Figure 3As shown, on day 10 of storage, the nucleolar cell structure in the CS-CT group showed significant degeneration, with large protein aggregates and significantly enlarged intercellular spaces. The CS-TRP group had fewer vacuolated areas in its nucleolar cells compared to the CS-CT group, with clearer intracellular structures and slightly enlarged intercellular spaces. The cell boundaries in the CS-TAU group were relatively clear, but some areas still showed enlarged intercellular spaces. The nucleolar cell structure in the CS-TRP+TAU group was closest to that of day 0, with the smallest enlargement of intercellular spaces and significantly improved cell membrane integrity compared to the CS-CT group. This indicates that the synergistic effect of tryptophan and taurine can effectively delay ultrastructural damage to nucleolar cells during storage. In contrast, the patent "A food-derived fruit and vegetable preservative, its preparation method and usage method (CN120167500A)" only qualitatively describes the antioxidant performance of this preservative based on the appearance of browning, without observing the ultrastructure of fruit tree cells or measuring antioxidant properties such as ABTS free radical scavenging rate. This invention observed the ultrastructure of cells in each group during storage, providing more convincing evidence of the antioxidant properties of chitosan-based membranes loaded with tryptophan and taurine.

[0056] like Figure 4 As shown, at 3350cm -1 Near the CS-CT group, the hydroxyl stretching vibration peak of the chitosan-based films was relatively broad, while the peak of the chitosan-based films loaded with tryptophan or taurine (CS-TRP, CS-TAU, CS-TRP+TAU) was relatively narrower, while the peak of the chitosan-based films loaded with tryptophan or taurine was narrower, at 3357 cm⁻¹. -1 3355cm -1 3353cm -1 The shift in the direction of higher wavenumbers indicates that the addition of tryptophan and taurine disrupts the hydrogen bonding between chitosan molecules; furthermore, the CS-TRP group and the CS-TRP+TAU group showed a shift at 1560 cm⁻¹. -1 The stretching vibration peak of the amide II band in the vicinity shows a certain degree of shift towards higher wavenumbers compared to the CS-CT group, indicating that tryptophan or the combined effect of tryptophan and taurine may weaken the electrostatic interactions of the chitosan-based film. These structural changes may have a significant impact on the mechanical and barrier properties of the film.

[0057] like Figure 5 As shown, the water vapor transmission rate of each group of chitosan-based films exhibits a highly linear relationship with time. The correlation coefficient (R0) of the water vapor transmission rate of each group of chitosan-based films shows a highly linear relationship with time. 2 The correlation coefficient (R) between the CS-CT group and the CS-TRP group was relatively high. 2 () greater than 0.99.

[0058] like Figure 6As shown, the CS-CT group film exhibited the lowest antioxidant activity, with DPPH and ABTS radical scavenging rates of 12.19% and 63.61%, respectively. The ABTS radical scavenging rates of the CS-TRP and CS-TAU groups were 73.86% and 70.66%, respectively, representing increases of 16.1% and 11.1% compared to the CS-CT group. Furthermore, the DPPH and ABTS radical scavenging rates of the CS-TRP+TAU group reached 16.64% and 71.20%, respectively, both significantly higher than the CS-CT group without tryptophan and taurine loading, and also higher than the CS-TAU group loaded with taurine only. This indicates that tryptophan loading and the combined loading of tryptophan and taurine can effectively enhance the antioxidant properties of the film. In particular, the CS-TAU group film showed no significant difference in DPPH radical scavenging rate compared to the CS-CT group, but its ABTS radical scavenging rate was significantly higher than that of the CS-CT group, indicating that taurine has a certain selectivity in scavenging specific free radicals.

[0059] As shown in Table 1, the CS-CT group of films exhibited the highest water vapor permeability, at 0.42 g·m⁻¹. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 The water vapor transmission rate of the CS-TRP and CS-TAU group membranes was not significantly different from that of the CS-CT group, while the water vapor transmission rate of the CS-TRP+TAU group membrane was significantly lower than that of the CS-CT group, reaching 0.23 g·m³. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 The water vapor permeability decreased by 45.24% compared to the CS-CT group, indicating that the chitosan-based film loaded with tryptophan and taurine can effectively improve the water vapor barrier capacity of the film. This may be attributed to the optimization of the film's microstructure and the enhancement of intermolecular interactions. Furthermore, compared to the polyvinyl alcohol hydrogel in the prior art CN112625269B, the water vapor permeability of this sample is 0.5 g·m⁻¹. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 The WVP of the CS-TRP+TAU composite membrane prepared by this invention is only 0.23 g·m³. -2 ·h -1 ·Pa -1 ·mm -1 ·10 -3 The barrier properties are improved by approximately 54%.

[0060] Table 1. Water vapor transmission rate values ​​of chitosan-based films in different groups

[0061] Meanwhile, based on the above-mentioned detection results and the preparation methods of CS-CT, CS-TRP, CS-TAU, and CS-TRP+TAU, it can be seen that tryptophan and taurine have a synergistic effect in the method of the present invention, which can synergistically improve the relevant properties of the prepared composite membrane. In particular, tryptophan and taurine with a mass ratio of 0.051:0.0313 have a significant synergistic effect, which can significantly improve the relevant properties of the prepared composite membrane.

[0062] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A tryptophan / taurine composite material for enhancing antioxidant capacity, characterized in that: The composite material comprises the following components in parts by weight: Chitosan 28-32 parts, tryptophan 0.048-0.055 parts, taurine 0.028-0.035 parts, montmorillonite 0.72-0.78 parts.

2. The tryptophan / taurine composite material according to claim 1, characterized in that: The composite material comprises the following components in parts by weight: 30 parts chitosan, 0.051 parts tryptophan, 0.0313 parts taurine, and 0.75 parts montmorillonite.

3. The method for preparing the tryptophan / taurine composite material as described in claim 1 or 2, characterized in that: Includes the following steps: (1) Weigh out chitosan and dissolve it in a 1% acetic acid solution. Stir with a magnetic stirrer at 600 rpm until the chitosan is completely dissolved to obtain a uniform chitosan solution. (2) The chitosan solution obtained in step (1) is thoroughly mixed with tryptophan, taurine and montmorillonite. The mixture is stirred at 600 rpm until tryptophan, taurine and montmorillonite are completely dissolved. Glycerin with a final mass concentration of 0.5% (w / v) is added as a plasticizer and Tween 80 with a final mass concentration of 0.1% (w / v) is added as a surfactant. The mixture is stirred at 600 rpm for 1 hour. The pH is adjusted to 4.5 with acetic acid. The solution is sonicated for 1 hour to remove bubbles and ensure that the solution is uniform and bubble-free, thus obtaining the tryptophan / taurine composite material.

4. The preparation method according to claim 3, characterized in that: In step (1), the ratio of chitosan to 1% acetic acid solution is 30 g to 2000 mL.

5. The preparation method according to claim 3 or 4, characterized in that: In step (2), the ratio of chitosan solution obtained in step (1) to tryptophan to taurine to montmorillonite (ml:g:g:g) is 500:0.051:0.0313:0.

75.

6. The application of the tryptophan / taurine composite material as described in claim 1 or 2 in maintaining the freshness of fruit under high oxidizing conditions.

7. The application of the tryptophan / taurine composite material as described in claim 1 or 2 in the storage and transportation of fruits and vegetables.

8. The use of the tryptophan / taurine composite material as described in claim 1 or 2 in reducing water loss from fruits and vegetables.

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