Preparation method and application of tara gum-chitosan-polyvinyl alcohol-citral antibacterial preservative film

Abstract

The invention relates to the technical field of food antibacterial fresh-keeping packaging materials, in particular to a preparation method and application of a tara gum-chitosan-polyvinyl alcohol-citral antibacterial fresh-keeping film. Tara gum, chitosan and polyvinyl alcohol are used as film forming substrates, citral essential oil is added to serve as a multifunctional additive, and a film casting method is adopted for preparation. The raw materials used by the antibacterial preservative film prepared by the invention are safe, non-toxic and biodegradable; moreover, the preservative has good antibacterial property, can effectively inhibit growth and reproduction of microorganisms such as bacteria and molds, prolongs the shelf life, and can be applied to antibacterial preservation of foods.

Description

A method for preparing a tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film and its application. Technical Field

[0001] This invention relates to the field of antibacterial and preservative packaging materials for food, specifically to a method for preparing a tarara-chitosan-polyvinyl alcohol-citral antibacterial preservative film and its application. Background Technology

[0002] Global plastic pollution is becoming increasingly serious. The widespread use of synthetic plastics across various industries poses a significant threat to the global ecological environment. Among various food packaging materials, petroleum-based packaging materials such as polypropylene (PP), polyethylene (PE), or polyethylene terephthalate (PET) are used for food preservation packaging due to their excellent mechanical properties, good physicochemical stability, and good water vapor permeability and barrier properties. However, the widespread use of these petroleum-based materials has led to the depletion of non-renewable petroleum resources, exacerbating the energy crisis. Furthermore, traditional petroleum-based materials are difficult to degrade, while existing bio-based materials suffer from poor mechanical properties, high costs, insufficient water resistance, and a lack of effective antibacterial properties. Therefore, developing a natural, low-cost material with good mechanical properties, good biocompatibility and degradability, and antibacterial effects could effectively inhibit microbial growth, reduce foodborne illnesses and spoilage, provide high-quality and safe food, and extend its shelf life.

[0003] Tara gum alone exhibits high brittleness, low elongation at break, insufficient tensile strength and flexibility, high water vapor permeability, poor barrier properties, and a lack of significant antibacterial activity. Pure chitosan films are typically hard and brittle, with high water vapor permeability and poor water resistance, limiting their application in food preservation. While polyvinyl alcohol possesses high tensile strength and good flexibility, it is highly hydrophilic, easily soluble in water, and degrades more rapidly in the natural environment than pure polysaccharide films, lacking inherent antibacterial properties. Blending these three ingredients enhances film toughness and elongation at break, while reducing brittleness. Citral essential oil, with its lemon aroma, can serve as a natural additive and possesses strong antibacterial and free radical scavenging properties. Mixing hydrophobic citral with tara gum, chitosan, and polyvinyl alcohol improves barrier properties against oxygen and water vapor; the interaction of these four components produces a good antibacterial effect, effectively extending the shelf life of food. Summary of the Invention

[0004] To address the problems of poor mechanical properties, high cost, insufficient water resistance, poor biocompatibility and degradability, and lack of antibacterial effects in food preservation packaging materials, this invention uses tara gum, chitosan, and polyvinyl alcohol as film-forming matrices, and adds citral essential oil as a multifunctional additive, preparing the film via a casting method. This yields an antibacterial food preservation packaging film with good mechanical properties, significant antibacterial effects, and safe, non-toxic, and biodegradable properties. The specific solution provided by this invention to achieve the above objectives is as follows:

[0005] A method for preparing a tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film and its application, comprising the following steps:

[0006] Step 1: Tara gum is purified by water-soluble alcohol precipitation to obtain purified tara gum;

[0007] Step 2: Dissolve polyvinyl alcohol, chitosan and citric acid in water, and add purified tara gum while stirring to prepare mixed solution I;

[0008] Step 3: Add citral essential oil to mixed solution I, stir well to obtain mixed solution II;

[0009] Step 4: Add glycerol to mixed solution II, stir well to obtain mixed solution III, centrifuge mixed solution III to remove impurities and air bubbles, cast film using the casting method, and dry in an oven to obtain the final product.

[0010] Further, the extraction method in step 1 is as follows: under mechanical stirring, the gelatin is slowly added to the water until it is fully dissolved into a gel-like liquid. After centrifugation to remove impurities, anhydrous ethanol is added to the gel solution under stirring to precipitate the precipitate. The precipitate is then washed with acetone and anhydrous diethyl ether, respectively, and then subjected to vacuum filtration and vacuum drying.

[0011] Further, in step 1, the ratio of water to tara gum is 1700 mL: (10.2–13.6) g. The mass ratio of the gum solution after centrifugation to remove impurities to anhydrous ethanol is 1:(1–3); the centrifugation parameters are 3500 r / min–4000 r / min for 10–20 min; the stirring time is 5–8 h; and the vacuum drying time is 2–4 days.

[0012] Furthermore, in mixed solution I, the mass concentration of polyvinyl alcohol is 0.2%–0.8%, the mass concentration of chitosan is 0.2%–0.8%, the mass concentration of citric acid is 0.2%–1.4%, and the mass concentration of tara gum is 0.2%–2%.

[0013] Furthermore, the mass concentration of essential oil in mixed solution II is 0.02% to 0.2%.

[0014] Furthermore, the mass concentration of glycerol in mixed solution III is 0.2% to 2%.

[0015] Furthermore, before membrane deposition in step 4, solution III is mixed and centrifuged at 3500 r / min for 15 min to remove air bubbles and impurities.

[0016] Furthermore, in step 4, the oven temperature is initially set at 40℃~60℃ for drying for 24h~48h.

[0017] The present invention has the following advantages:

[0018] This invention employs a casting film-forming method, using tara gum, chitosan, and polyvinyl alcohol as film-forming matrices, and hydrophobic citral essential oil as a multifunctional additive. Utilizing its synergistic effect with the three matrices, the oxygen and water vapor barrier properties of the film are significantly improved. This results in not only excellent mechanical strength but also significant antibacterial effects. Furthermore, this packaging material is safe, non-toxic, and has good biodegradability, effectively inhibiting microbial growth and thus extending the shelf life of food products. It has broad application prospects in the field of green food packaging. Figure 1 shows the tensile strength and elongation at break test results of the antibacterial food preservation film; Figure 2 shows the water vapor permeability test result of the antibacterial food preservation film; Figure 3 shows the Fourier transform infrared spectrum of the antibacterial food preservation film; Figure 4 shows the X-ray diffraction pattern of the antibacterial food preservation film; Figure 5 shows the antioxidant performance test result of the antibacterial food preservation film; Figure 6 shows the antibacterial activity test result of the antibacterial food preservation film; Figure 7 shows the biodegradability test result of the antibacterial food preservation film; Figure 8 shows the preservation performance test result of the antibacterial food preservation film on strawberries. Detailed Implementation

[0019] The technical process of the present invention will be further explained below with reference to specific embodiments:

[0020] Example 1

[0021] This embodiment provides a method for preparing a tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film and its application, specifically including the following steps:

[0022] Step 1: Purify tara gum using the water-soluble alcohol precipitation method to obtain purified tara gum; under mechanical stirring, slowly add 13g of analytical grade tara gum to 1700ml of pure water until it is fully dissolved into a gel-like liquid. Centrifuge at 3500r / min for 10min to remove impurities. After centrifugation to remove impurities, add anhydrous ethanol in an equal proportion to the gel solution under stirring to precipitate the precipitate. Wash the precipitate three times with acetone and anhydrous diethyl ether, respectively. Then, filter under reduced pressure and vacuum dry for 3 days.

[0023] Step 2: Dissolve polyvinyl alcohol, chitosan, and citric acid in 120 ml of water, and slowly add purified tara gum while stirring to prepare mixed solution I; the mass concentration of chitosan in mixed solution I is 0.4%, the mass concentration of polyvinyl alcohol is 0.4%, the mass concentration of citric acid is 1.5%, and the mass concentration of tara gum is 1.4%.

[0024] Step 3: Add 0.02% citral essential oil to mixed solution I, stir well to obtain mixed solution II;

[0025] Step 4: Add 1.0% glycerol to mixed solution II, stir well to obtain mixed solution III. Centrifuge mixed solution III at 3500 r / min for 15 min to remove impurities and air bubbles. Lay a film using the casting method, dry at 40℃ for 48 h, cool to room temperature and peel off to obtain a Tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film, named TCPC. 0.02 .

[0026] Example 2

[0027] The difference from Example 1 is that citral essential oil is not added in step 3; all other steps and parameters are the same. The resulting film is named TCP.

[0028] Example 3

[0029] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.04 .

[0030] Example 4

[0031] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.06 .

[0032] Example 5

[0033] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.08 .

[0034] Example 6

[0035] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.10 .

[0036] Example 7

[0037] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.12 .

[0038] Example 8

[0039] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.14 .

[0040] Example 9

[0041] The difference from Example 1 is that 0.04% citral essential oil was added in step 3; all other steps and parameters remained the same. The resulting film was named TCPC. 0.16 .

[0042] Performance characterization:

[0043] Mechanical property analysis of antibacterial food preservation film

[0044] The tensile strength (TS) and elongation at break (EB) of the antibacterial food preservation films prepared in Examples 1-9 were measured to evaluate their mechanical properties. The test results are shown in Figure 1. The addition of citral oil had a certain impact on both the film thickness and mechanical properties. As can be seen from the figure, with the addition of a small amount of citral oil, the tensile strength decreased from 18.27 MPa at TCP to TCPC. 0.04 The tensile strength of the TCPC membrane was 39.75 MPa at the time of addition. With continued addition of citral oil, the tensile strength gradually decreased to 24.54 MPa. The tensile strength of the TCPC membrane was consistently higher than that of the TCP membrane, indicating better mechanical properties. Adding a small amount of citral oil can improve the tensile strength of the film because the aldehyde group of citral can form hydrogen bonds with the hydroxyl and amino groups of tara gum or chitosan, and the hydroxyl groups of polyvinyl alcohol. This hydrogen bond interaction makes the molecular network within the membrane more compact, thus improving tensile strength. As the amount of citral added increases, the tensile strength gradually decreases, which is due to the excessive addition of the molecular cross-linking network.

[0045] Water vapor permeability (WVP) analysis of antibacterial food preservation film

[0046] Antibacterial food preservation films effectively prevent water vapor transfer between the surrounding environment and packaged food. Water vapor permeability (WVP) is a key factor reflecting the water vapor barrier capacity of the film; preventing water vapor loss prevents the preserved food from drying out, losing flavor, and declining in nutrients; it also blocks external moisture from penetrating, thus preventing mold growth and spoilage due to humid environments. The water vapor permeability of the antibacterial food preservation films prepared in Examples 1-9 was tested, and the results are shown in Figure 2. The addition of a small amount of citral caused the WVP of the TCPC film to increase and then decrease compared to the TCP film.0.04 The membrane's WVP is as low as 2.55 × 10⁻⁶. -10 g·m·m -2 ·Pa -1 ·s -1 This is because the Schiff base reaction between citral and chitosan makes the membrane network structure compact, reduces pore size, and blocks water molecule permeation channels; citral contains hydrophobic olefin chains, which replace some of the hydrophilic groups on the membrane surface, reducing the membrane's permeability to water molecules. Structural analysis of antibacterial food preservation film.

[0047] The film structure of the antibacterial preservation films prepared in Examples 1-9 was tested by Fourier transform infrared spectroscopy to confirm the interactions within the film components. The test results are shown in Figure 3. The spectral profiles and peaks of the nine substances were roughly the same, with no significant differences, indicating that the addition of citral essential oil did not change the basic structure of the film. The TCP film at 3340 cm⁻¹... -1 The broad peaks on both sides are attributed to the superposition of stretching vibrations of -OH groups from tara gum, chitosan, and polyvinyl alcohol, and NH groups from chitosan. The peak at 2926 cm⁻¹ is the benchmark peak for hydrogen bonding in polysaccharides. -1 The peaks around the left and right belong to the alkyl CH stretching vibrations of polyvinyl alcohol and chitosan; 1705 cm⁻¹ -1 The absorption peaks around 1020 nm may be due to the carbonyl C=O stretching vibration; the peak around 1020 nm belongs to the COC and C-OH stretching vibrations of polysaccharide glycosidic bonds, which are part of the polysaccharide chain structures of tara gum, chitosan, and polyvinyl alcohol. In the TCPC membrane, the aldehyde group -CHO of citral is effectively bonded to tara gum, chitosan, and polyvinyl alcohol -OH through hydrogen bonds. With the addition of essential oils, the hydrogen bonding of the hydroxyl groups of the polysaccharides is weakened, indicating that the membrane has good compatibility with essential oils and that the prepared membrane has a stable multi-component hydrogen-bonded cross-linked structure.

[0048] XRD analysis of antibacterial food preservation film

[0049] The crystallization characteristics of the antibacterial preservation films prepared in Examples 1-9 were analyzed using X-ray diffraction. This helps to better understand the compatibility of different components in the TCPC film. The test results are shown in Figure 4. In the TCP film, the broad peak at 19.12° indicates that the molecular chains of tara gum, chitosan, and polyvinyl alcohol are intertwined and well-compatible. This is due to the formation of hydrogen bonds between the hydroxyl groups of tara gum, the amino and hydroxyl groups of chitosan, and the hydroxyl groups of polyvinyl alcohol. The strong interaction between the matrices weakens the crystallinity of the TCP film.

[0050] Analysis of the antioxidant properties of antibacterial food preservation film

[0051] The antioxidant properties of the antibacterial preservation films prepared in Examples 1-9 were tested using the DPPH method. Antibacterial preservation packaging films with strong antioxidant capabilities can prevent rapid oxidation of food and extend its shelf life. The antioxidant properties of the films were tested using a DPPH ethanol solution to measure free radical scavenging rate; the test results are shown in Figure 5. The antioxidant properties of the TCPC film gradually increased with the addition of small amounts of citral, exceeding those of the TCP film. 0.04 The membrane exhibits the highest free radical scavenging rate because citral is a natural antioxidant, and adding a small amount enhances its free radical scavenging rate. TCPC 0.06 The membrane begins to decline sharply because when the concentration of citral exceeds the critical concentration, it will self-oxidize and generate new free radicals, which will inhibit the scavenging rate.

[0052] Antibacterial activity analysis of antibacterial food preservation film

[0053] Citral essential oil, a major component of citrus essential oils, exhibits inhibitory effects against common foodborne pathogens such as Staphylococcus aureus, Salmonella, and Escherichia coli. The antibacterial effects of different TCPC membranes were tested using Escherichia coli and Staphylococcus aureus. As shown in Figure 6, acidified chitosan containing citric acid resulted in an inhibition zone in the TCP membrane emulsion. With a small increase in citral concentration, the TCPC membrane emulsion produced a strong inhibition zone, indicating strong antibacterial activity. However, with a continuous increase in citral concentration, the inhibition zone gradually decreased, likely due to the increased volatility of high-concentration citral, leading to a decline in antibacterial activity. Therefore, appropriate addition of citral demonstrates a good antibacterial effect against Escherichia coli and Staphylococcus aureus.

[0054] Biodegradability analysis of antibacterial food preservation film

[0055] The antibacterial preservation films prepared in Examples 1-9 were buried in the soil, respectively. 0.04 Cracks appeared on the second day and the membrane completely degraded by the fourth day, indicating that the TCPC membrane with an appropriate amount of citral added degraded faster than the TCP membrane. The appropriate addition of citral essential oil indirectly accelerated the degradation rate by regulating soil microbial activity and improving the membrane's pore structure; however, excessive addition slowed down the microbial degradation rate due to the good antibacterial properties of citral essential oil.

[0056] Test chart of the preservation performance of antibacterial plastic wrap on strawberries

[0057] Fresh strawberries were sealed in containers using the antibacterial preservation films prepared in Examples 1-9. As shown in Figure 8, the strawberries in commercially available polypropylene cups began to rot on the third day, with obvious fungal colonies appearing on the strawberry surface. However, the TCPC film, crosslinked with tara gum, chitosan, polyvinyl alcohol, and citral, did not show significant deterioration on the third day, which may be attributed to the antibacterial and antioxidant activity of the TCPC film. With the addition of citral, TCPC...0.16 Colonies began to appear on the membrane on day 6, TCPC 0.08 Membrane, TCPC 0.10 Membrane TCPC 0.12 Membrane and TCPC 0.14 Colonies began to appear on the membrane on day 13, TCPC 0.06 Microbial colonies appeared on the membrane on day 17. This is because the high content of citral essential oil disrupts the intermolecular forces between the membrane matrix, accelerates water loss and respiration in strawberries, and provides usable nutrients for mold growth. TCPC 0.02 The mold appeared on the membrane only one day later than the group without essential oils. This is because the low concentration of essential oils was insufficient to create a good antibacterial environment, and the low concentration could not effectively alter the membrane structure or improve its preservation performance. On day 26, TCPC... 0.04 The membrane showed no signs of rotting or bacterial colonies, while the rest of the membrane had completely rotted. At this concentration, citral essential oil can release sufficient antibacterial components to inhibit mold growth on the strawberry surface; it can also form a dense membrane structure, maintaining suitable gas exchange and good moisture barrier properties, thus delaying the strawberry's own respiration and decay, resulting in the longest shelf life. These findings indicate that adding an appropriate amount of citral can significantly extend shelf life.

Claims

1. A method for preparing a tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film and its application, characterized in that, Includes the following steps: Step 1: Purify tara gum using the water-soluble alcohol precipitation method to obtain purified tara gum; Step 2: Dissolve polyvinyl alcohol, chitosan, and citric acid in water, and add the purified tara gum while stirring to obtain mixed solution I; Step 3: Add citral essential oil to mixed solution I, and stir evenly to obtain mixed solution II; Step 4: Add glycerol to mixed solution II, and stir evenly to obtain mixed solution III. Centrifuge mixed solution III to remove impurities and air bubbles, cast film using the casting method, and dry in an oven to obtain the final product.

2. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film according to claim 1, characterized in that... The purification method in step 1 is as follows: under mechanical stirring, slowly add the strychnine resin to the water until it is fully dissolved into a gel-like liquid. After centrifugation to remove impurities, add anhydrous ethanol to the gel solution under stirring to precipitate the precipitate. Then wash the precipitate with acetone and anhydrous diethyl ether respectively, and then perform vacuum filtration and vacuum drying.

3. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial preservation film according to claim 2, characterized in that, The ratio of water to tarara is 1700mL:(10.2~13.6)g.

4. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film according to claim 2, characterized in that, The mass ratio of the gel solution after centrifugation to anhydrous ethanol is 1:(1~3); the centrifugation parameters are 3000r / min~4000r / min for 10min~20min; the stirring time is 5h~8h; and the vacuum drying time is 2~4 days.

5. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial preservative film according to claim 1 are characterized in that... In mixed solution I, the mass concentrations of polyvinyl alcohol are 0.2%–0.8%, chitosan is 0.2%–0.8%, citric acid is 0.2%–1.4%, and tara gum is 0.2%–2%.

6. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film according to claim 1, characterized in that, The essential oil concentration in mixed solution II is 0.02%–0.2% by mass.

7. The preparation method and application of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film according to claim 1, characterized in that, The mass concentration of glycerol in mixed solution III is 0.2%–2%.

8. A method for preparing a tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film and its application, characterized in that, The antibacterial food preservation film is prepared using the method described in any one of claims 1 to 7, which is as follows.

9. The preparation method of the tara gum-chitosan-polyvinyl alcohol-citral antibacterial food preservation film according to claim 8 and its application.

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