Fig bacteriostatic fresh-keeping film material and preparation method of fig bacteriostatic fresh-keeping composite film

Abstract

The invention relates to a fig bacteriostatic preservative film material and a preparation method of a fig bacteriostatic preservative composite film. A film forming substance of the fig bacteriostatic preservative film material is a composition of glycerol, gelatin, water, Fmoc-F, gellan gum, dimethyl sulfoxide and a bacteriostatic agent. The invention further discloses a preparation method of the antibacterial and fresh-keeping composite film for the figs. The antibacterial and fresh-keeping composite film for the figs has high barrier property, moisture retention property and antibacterial property, the preparation process is simple, convenient and environment-friendly, and the antibacterial and fresh-keeping composite film is suitable for commercialized fresh keeping of the figs.

Description

Technical Field

[0001] The present invention relates to a fresh-keeping film and a preparation method thereof, in particular to a fresh-keeping film material for fig with antibacterial property and a preparation method of a composite film for fig with antibacterial and fresh-keeping property. Background Art

[0002] Fresh fig fruits have thin skins, no seeds, soft flesh, are sweet and refreshing, and are rich in nutrients, especially rich in trace elements, with a unique taste, and are widely welcomed by consumers. However, due to its high water content, during the express transportation process, because the transportation box has strong airtightness, the figs themselves produce a large amount of water during respiration and metabolism, and the humidity in the transportation box is high, which is extremely easy to cause phenomena such as fruit mildew, internal insect infestation, fermentation and rot, resulting in great difficulty in its fresh-keeping, seriously affecting the sales during the shelf life, and it is also very difficult for consumers to taste fresh fruits with high maturity and delicious taste. The general shelf life of fresh fig fruits is only 2 - 3 days.

[0003] As an important part of the food circulation link, food packaging, in addition to meeting basic requirements such as aesthetics and convenience, more importantly, must also have the functions of antibacterial fresh-keeping and effectively extending the shelf life of food.

[0004] Traditional plastic fresh-keeping films have many defects: some materials are easy to release harmful substances at high temperatures (such as plasticizers in PVC films), threatening human health; the proportion of non-degradable materials is high, and long-term accumulation exacerbates white pollution; it is difficult to balance air permeability and barrier property, which is easy to cause food mildew or dehydration, and most lack antibacterial activity; the heat resistance performance is limited, it is easy to melt and deform at high temperatures and is easy to crack at low temperatures, and the applicable range is limited; the viscosity stability is poor, it is easy to stick or fall off, affecting the sealing effect; in addition, although environmentally friendly film materials (such as PLA) have a relatively high price, their performance is weaker than that of traditional plastics, and it is difficult to balance cost and practicality.

[0005] Gelatin, as a product obtained by hydrolyzing and purifying collagen, mainly comes from mammalian bones and dermis tissues. Such protein-based film materials are easy to obtain raw materials and have outstanding economy, and have gradually become a research hotspot in the field of food packaging in recent years. The excellent biocompatibility and environmentally degradable characteristics can safely carry active functional components. However, its mechanical properties and thermal stability are poor after film formation, resulting in obvious technical bottlenecks in the actual application of single gelatin-based films.

[0006] In recent years, fresh-keeping materials that are natural, harmless and have good antibacterial effects have become a research hotspot. It has been found that Fmoc-F (a fluorinated amino acid derivative) has good antibacterial properties; gelatin is a natural polymer material with good film-forming property and biocompatibility; gellan gum (a natural polysaccharide) has good water solubility and gelation property, which can enhance the structural strength of the film and improve its stability. By compounding these materials to form a film material, it can not only effectively inhibit the growth of microorganisms, but also improve the storage performance of figs.

[0007] Natural bacteriostatic agents have been widely used in the preparation process of antibacterial films due to their green, natural, safe, and broad-spectrum antibacterial properties. At present, there are many studies on the antibacterial mechanism of plant compound bacteriostatic agents, and they are also recognized as food additives by the state. The generally accepted antibacterial mechanism of plant compound bacteriostatic agents is mostly as follows: the hydrophobic components in the compound bacteriostatic agent directly act on the cell membrane, and the permeability of the phospholipid bilayer of the cell membrane is greatly increased due to the inhibition of the binding of enzymes and proteins, resulting in the ultimate destruction of the cell membrane. The compound bacteriostatic agent of ε-polylysine, oregano essential oil, and cinnamon essential oil shows stronger practicability and sustainability than single bacteriostatic agents in the fields of food, medicine, daily chemicals, etc. through advantages such as synergistic effect, broad-spectrum antibacterial, and delaying drug resistance, which is an important direction for the development of future antibacterial technologies.

[0008] CN113621242A was published on November 9, 2021, and discloses a phenylalanine / gelatin-based sustained-release composite film. The film-forming substances are water, glycerol, gelatin, phenylalanine, and DMSO (dimethyl sulfoxide), which has pH responsiveness, excellent controlled-release performance, is safe and non-toxic, and has a low cost. Its defect is that this product does not have a good antibacterial and fresh-keeping effect on figs.

[0009] CN113508836A was published on October 19, 2021, and discloses a composite deoxidizing and fresh-keeping powder for figs, which is composed of 2% - 15% deoxidizer, 20% - 60% humidity regulator, 20% - 40% bacteriostatic agent, 1% - 15% stabilizer, and 1% - 15% acid regulator; the deoxidizer is one or a mixture of metal powder, sulfite, and ascorbic acid, the humidity regulator is one or a mixture of calcium chloride, calcium sulfate, and alumina, the bacteriostatic agent is one or a mixture of calcium propionate, calcium acetate, and sodium dehydroacetate, the stabilizer is sodium polyacrylate, and the acid regulator is one or a mixture of citric acid, tartaric acid, or phytic acid. It can reduce the growth of molds and bacteria, adjust humidity to increase hardness, protect color and flavor, inhibit the corruption of figs, and extend the fresh-keeping period of figs to 72 hours. Its defect is that the deoxidizer contains metal powder, which is harmful to the human body, and it cannot control the moisture permeability of the figs during respiration and reduce the loss of moisture. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a fig antibacterial fresh-keeping film material with good antibacterial properties, safe and non-toxic, and low cost, which can encapsulate antibacterial functional components, overcome the defects such as strong volatility and short antibacterial efficacy of antibacterial functional components, delay the diffusion rate of antibacterial functional components, so as to achieve a sustained-release and long-term effect in fig fresh-keeping and extend the shelf life of figs.

[0011] A further technical problem to be solved by the present invention is to provide a method for preparing a fig antibacterial fresh-keeping composite film using the fig antibacterial fresh-keeping film material.

[0012] The technical solution adopted by the present invention to solve its technical problems is as follows: A fig fresh-keeping composite film material, the film-forming substances are a composition of glycerol, gelatin, water, Fmoc-F, gellan gum, dimethyl sulfoxide (DMSO), and an antibacterial agent.

[0013] Further, the mass ratio of glycerol to gelatin is 1∶0.5 - 2.5. The fresh-keeping composite film made of the materials within this ratio range has better elasticity and stretching effect. If the addition amount of glycerol is less than 50% of that of gelatin, the made fresh-keeping composite film has poor extensibility and is prone to breakage; if the addition amount of glycerol is higher than 250% of that of gelatin, the effect of increasing the extensibility of the fresh-keeping composite film is not significant, but instead causes waste of resources.

[0014] Further, the mass ratio of gelatin to water is 1∶5 - 15, preferably 1∶8 - 12.

[0015] Further, the mass ratio of Fmoc-F to gelatin is 1∶10 - 50, preferably 1∶15 - 40; more preferably 1∶20 - 30.

[0016] Further, the addition amount of dimethyl sulfoxide should be ≤ 8% of the total volume of the film-forming substances, preferably 3 - 5%. As the content of DMSO increases, the light transmittance of the fresh-keeping composite film continuously increases, and the compatibility between the two film-forming bases of gelatin and glycerol also continuously enhances; but considering from the aspects of cost saving and safety, the addition amount of DMSO should be ≤ 8% of the total volume of the film-forming substances, and it is preferably controlled at 3 - 5% of the total volume of the film-forming substances.

[0017] Further, the addition amount of gellan gum is 0.1% - 0.6% of the total mass of the film-forming substances, preferably 0.2%. When the addition amount of gellan gum is 0.2% of the total mass of the film-forming substances, the physical properties of the made fresh-keeping composite film are the best and the network structure stability is the best; when the addition amount of gellan gum is too high, during the film-making process, the viscosity of the film solution is large, degassing is difficult, and the internal molecules of the made fresh-keeping composite film are prone to aggregation, which will make the molecular chains in the film arrange disorderly, making the film structure uneven and not dense, and thus causing the mechanical properties of the fresh-keeping composite film to deteriorate.

[0018] Further, the Fmoc-F is N-fluorenylmethoxycarbonyl-L-phenylalanine (i.e., fmoc-phenylalanine, abbreviated as Fmoc-LPhe, which is phenylalanine linked by the Fmoc amino protecting group.

[0019] Further, the antibacterial functional components are embedded in the fresh-keeping composite film, that is, antibacterial agents; the antibacterial agents account for 0.1% to 12% of the total mass of the film-forming material, preferably 0.5% to 10%; more preferably 0.8% to 8%, and further preferably 1.2% to 5.0%.

[0020] Further, the antibacterial functional component is one or more of a compound antibacterial agent, a dye or a drug.

[0021] Further, the antibacterial agent is ε-polylysine, oregano essential oil antibacterial agent, cinnamon essential oil antibacterial agent. Preferably, it is a compound antibacterial agent composed of a compound of ε-polylysine, oregano essential oil and cinnamon essential oil. The minimum inhibitory concentration and minimum bactericidal concentration of ε-polylysine, oregano essential oil and cinnamon essential oil are shown in the following table.

[0022] Table 1 Antibacterial zone diameters of three antibacterial substances

[0023]

[0024] The technical solution adopted by the present invention to further solve its technical problems is a method for preparing a fresh-keeping composite film for figs by using the fig antibacterial fresh-keeping film material, including the following steps:

[0025] (1) Add glycerol, F-moc-F, and dimethyl sulfoxide to water, and stir to fully mix the three.

[0026] (2) Add gelatin and continue stirring.

[0027] (3) Add gellan gum, continue stirring, add antibacterial agents, continue stirring, and perform ultrasonic treatment at the same time.

[0028] (4) Pour into a mold, shake well, and dry to obtain the product.

[0029] Preferably, in step (1), the temperature of the stirring is 35 to 40 °C, the rotation speed during stirring is 300 to 350 rpm, and the stirring time is 5 to 8 min.

[0030] Preferably, in step (2), the temperature of the stirring is 35 to 40 °C, the rotation speed during stirring is 300 to 350 rpm, and the stirring time is 8 to 10 min.

[0031] Preferably, in step (3), the temperature of the stirring is 35 to 40 °C, the rotation speed during stirring is 300 to 350 rpm; stir for 1 to 3 min after adding gellan gum; stir for 1 to 2 min after adding the compound antibacterial agent functional component.

[0032] Preferably, in step (3), the power of the ultrasonic treatment is 100 to 200 W, and the ultrasonic treatment time is 20 to 30 min.

[0033] Preferably, in step (4), the drying temperature is 40 - 45°C, and the drying time is 24 - 48 h.

[0034] More preferably, in step (4), after drying at 40 - 45°C for 24 - 48 h, continue to dry at room temperature for 24 - 48 h.

[0035] The inventor of the present invention found that the composite film formed by the self - assembly of F - moc - F after hybridization with gelatin and gellan gum shows that: the composite film uses Fmoc - F, gelatin, and gellan gum as the main film - forming base materials, can embed bacteriostatic agents to improve the problems of the bacteriostatic agent not having a long - term bacteriostatic effect and being easily volatile in the air, slow down the diffusion rate of the bacteriostatic agent, and play a role in long - term bacteriostatic preservation during the preservation of figs, and can more effectively extend the shelf life of figs.

[0036] The present invention has the following beneficial effects: The fig fresh - keeping composite film made of the fig fresh - keeping composite film material of the present invention has good bacteriostatic effect, is green, natural, safe and non - toxic, has good biocompatibility, and the bacteriostatic effect can last for 4 - 7 days. It can not only effectively extend the shelf life of figs, but also be used for the preservation of other foods or the storage of drugs, etc. Embed functional bacteriostatic bioactive materials (such as dyes, bacteriostatic agents, drugs, etc.), and during the film - forming process, simply mix them into other film - forming substances. The method is simple and the cost is low. Description of the Drawings

[0037] Figure 1 It is the optical photograph of the fig fresh - keeping composite films of Examples 1 - 4 and Comparative Example 1 of the present invention in a transparent mold after film - forming. From left to right are the optical photographs of the fig fresh - keeping composite films of Example 1, Example 2, Example 3, Example 4, and Comparative Example 1.

[0038] Figure 2 It is the bar chart of the light transmittance of the fig fresh - keeping composite films of Examples 1 - 4 and Comparative Example 1 of the present invention.

[0039] Figure 3 It is the change curve graph (A) of the decay rate of figs treated differently during the storage period at 25°C of the fresh - keeping composite film of Example 5 of the present invention and Comparative Examples 2 - 5; the change curve graph (B) of the decay rate of figs treated differently during the storage period at 4°C.

[0040] Figure 4 It is the change (C) of the VC content of figs during the storage period at 25°C of the fresh - keeping composite film of Example 5 of the present invention and Comparative Examples 2 - 5; the bar chart (D) of the change of the VC content of figs during the storage period at 4°C.

[0041] Figure 5It is the change of total phenol content in fresh-keeping composite film of Example 5 of the present invention and figs during the storage period at 25°C in Comparative Examples 2-5 (E); the bar chart of the change of total flavonoid content in figs during the storage period at 4°C (F). In the figure: A-ε-polylysine; B-cinnamon essential oil; C-oregano essential oil; Control group (without any treatment), Plastic group (wrapped with plastic film), gentle gelatin group (wrapped with gelatin film), fgg group (wrapped with Fmoc-F-gelatin-gellan gum composite film), fggb group (Fmoc-F-gelatin-gellan gum-antibacterial agent) group.

[0042] Figure 6 It is the bar chart of the inhibitory effects of antibacterial agents ε-polylysine, cinnamon essential oil, and oregano essential oil in Examples 6-8 of the present invention on Staphylococcus aureus, Escherichia coli, and fig spoilage bacteria.

[0043] Figure 7 It is the appearance comparison photo of the fresh-keeping effect of the Fmoc-F-gelatin-gellan gum antibacterial agent fresh-keeping composite film of Example 9 of the present invention and the commercially available plastic film and phenylalanine / gelatin-based sustained-release composite film group on figs at room temperature in Comparative Examples 6-7. Detailed implementation manners

[0044] The present invention will be further described below in conjunction with examples and drawings.

[0045] The phenylalanine used in the following examples is N-fluorenylmethoxycarbonyl-L-phenylalanine (i.e., fmoc-phenylalanine, abbreviated as phenylalanine), purchased from Nanjing Peptide Industry Biotechnology Co., Ltd., glycerol was purchased from Sinopharm Chemical Reagent Co., Ltd., dimethyl sulfoxide (DMSO) was purchased from Tianjin Damao Chemical Reagent Factory, gelatin, gellan gum, and antibacterial agent ε-polylysine were purchased from Shanghai Ruiyong Biotechnology Co., Ltd., and antibacterial agents cinnamon essential oil and oregano essential oil were purchased from Jiangxi Xinsen Natural Plant Co., Ltd.

[0046] Example 1

[0047] The film-forming substances in this example are: 0.0555 g of Fmoc-F, 800 μL of DMSO, 1.76 mL of glycerol, 7.84 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, and 0.02 g of compound antibacterial agent (the compound antibacterial agent is prepared from cinnamon essential oil, oregano essential oil, and ε-polylysine in a mass ratio of 7.49:7.52:7.96).

[0048] The preparation method of the Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film in this example includes the following steps:

[0049] (1) Weigh 0.0555 g of Fmoc-F, add 800 μL of DMSO, mix well on a vortex shaker, and then place it on a 45 °C ultrasonic cleaner for further dissolution for 20 min, and stir for 2 min (at 35 °C, 300 rpm).

[0050] (2) Add it to 7.84 mL of distilled water containing 1.76 mL of glycerol, mix well, and stir on a magnetic stirrer (at 35 °C, 300 rpm) for 30 min.

[0051] (3) Then add 1.1111 g of gelatin, raise the temperature to 45 °C and continue stirring for 30 min. Then add 0.02 g of gellan gum and stir on a magnetic stirrer (at 70 °C, 300 rpm) for 30 min. The mass ratio of Fmoc-F to gelatin is 1 / 20.

[0052] (4) Then add 0.02 g of the compound bacteriostatic agent and stir on a magnetic stirrer (at 60 °C, 300 rpm) for 30 min. Subsequently, carry out ultrasonic treatment for 20 min to defoam.

[0053] (5) Pour it into a 100 mm petri dish, shake well, and place it in an oven at 40 °C for drying for 24 h to form a film.

[0054] Example 2

[0055] The film-forming substances and preparation method of the Fmoc-F-gelatin-gellan gum-bacteriostatic agent fresh-keeping composite film in this example are basically the same as those in Example 1, except that the dosage of DMSO is 600 μL.

[0056] Example 3

[0057] The film-forming substances and preparation method of the Fmoc-F-gelatin-gellan gum fresh-keeping composite film in this example are basically the same as those in Example 1, except that the dosage of DMSO is 400 μL.

[0058] Example 4

[0059] The film-forming substances and preparation method of the Fmoc-F-gelatin-gellan gum-bacteriostatic agent fresh-keeping composite film in this example are basically the same as those in Example 1, except that the dosage of DMSO is 200 μL.

[0060] Comparative Example 1

[0061] The film-forming substances and preparation method of the Fmoc-F-gelatin-gellan gum-bacteriostatic agent composite film in this comparative example are basically the same as those in Example 1, except that DMSO is not added.

[0062] Measure the light transmittance of the special fresh-keeping composite film for figs obtained in Examples 1 to 4 and Comparative Example 1, and compare the effect of different DMSO addition amounts on the light transmittance of the special fresh-keeping composite film for figs. The steps for measuring the film light transmittance are as follows: Cut the prepared film into a rectangular shape the size of a cuvette, place it on one side of the small slot of an ultraviolet spectrophotometer, measure its light transmittance value at 600 nm, and use air as a control to measure two parallel samples.

[0063] Refer to Figure 1 、 2 The results show that within the visible light wavelength range, different DMSO addition amounts (0%, 2%, 4%, 6%, 8%) have a certain impact on the light transmittance of the composite film. As the DMSO addition amount increases, the light transmittance of the composite film also shows an upward trend. The light transmittance values at 600 nm are 43.7%, 55.3%, 56.1%, 58.0%, and 64.6% in sequence. When no DMSO is added, the light transmittance value of the composite film is the lowest, and the visual performance of the film is poor. As the DMSO addition amount increases, the light transmittance and visual performance continuously improve, indicating that the DMSO addition amount is closely related to the light transmittance of the composite film. However, considering cost savings and safety, the addition amount of DMSO should be reduced as much as possible.

[0064] Example 5

[0065] The film-forming substances in this example are: 0.0555 g of Fmoc-F, 400 μL of DMSO, 1.76 mL of glycerol, 7.84 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, 0.02 g of compound bacteriostatic agent; (the compound bacteriostatic agent is prepared from cinnamon essential oil, oregano essential oil, and ε-polylysine in a mass ratio of 7.49:7.52:7.96)

[0066] The preparation method of the Fmoc-F-gelatin-gellan gum-bacteriostatic agent fresh-keeping composite film in this example includes the following steps:

[0067] (1) Weigh 0.0555 g of Fmoc-F, fully mix it with 400 μL of DMSO on a vortex shaker, and then place it on a 45°C ultrasonic cleaner for further dissolution for 20 min, and stir for 2 min (35°C, 300 rpm);

[0068] (2) Add it to 7.84 mL of distilled water containing 1.76 mL of glycerol and mix well, and stir on a magnetic stirrer (35°C, 300 rpm) for 30 min;

[0069] (3) Then add 1.1111 g of gelatin, raise the temperature to 45°C and continue to stir for 30 min, and then add 0.02 g of gellan gum and stir on a magnetic stirrer (70°C, 300 rpm) for 30 min. The mass ratio of Fmoc-F to gelatin is 1 / 20;

[0070] (4) Add 0.02 g of the compound bacteriostatic agent and stir on a magnetic stirrer (60 °C, 300 rpm) for 30 min, and then carry out defoaming by ultrasonic treatment for 20 min.

[0071] (5) Pour it into a 100 mm petri dish, shake well and place it in an oven at 40 °C for drying for 24 h to form a film.

[0072] Comparative Example 2

[0073] The preparation method of the gelatin film in this comparative example is basically the same as that of Example 5, except that: the film-forming substances do not add Fmoc-F, gellan gum and bacteriostatic agent.

[0074] Comparative Example 3

[0075] The preparation method of the Fmoc-F gelatin film - gellan gum in this comparative example is basically the same as that of Example 5, except that: the film-forming substances do not add bacteriostatic agent.

[0076] Comparative Example 4

[0077] In this comparative example, the determination was carried out with figs wrapped in plastic film.

[0078] Comparative Example 5

[0079] This comparative example is a blank control and does not use any kind of fresh-keeping film.

[0080] The fresh-keeping composite film of Example 5 was used to measure the decay rate of figs together with the composite films of Comparative Examples 2 to 3, the plastic film of Comparative Example 4, and the blank control of Comparative Example 5.

[0081] The formula for calculating the decay rate:

[0082]

[0083] Refer to Figure 3 , and the decay rate changes of figs in different treatment groups under storage conditions of 25 °C and 4 °C were experimentally compared. The results showed that the FGGB treatment group had the best effect in delaying spoilage;

[0084] At 25 °C: The decay rate of the FGGB treatment group (the Fmoc-F-gelatin-gellan gum-bacteriostatic agent fresh-keeping composite film of Example 5 of the present invention) was always the lowest, and the FGG treatment group (the Fmoc-F-gelatin-gellan gum composite film of Comparative Example 3) was the second. The decay rate of the gelatin group (the gelatin film of Comparative Example 2) reached 100% on the 4th day, the blank control group (Comparative Example 5) and the plastic film packaging control group (Comparative Example 4) reached 100% on the 5th day, and the FGG and FGGB treatment groups reached 100% on the 8th day.

[0085] At 4°C: Within 15 days, the decay rate of the blank control group (Comparative Example 5) was 38%, the decay rate of the plastic film packaging control group (Comparative Example 4) was 19%, the decay rate of the FGG treatment group (Comparative Example 3, Fmoc-F-gelatin-gellan gum composite film) was 19%, and the decay rate of the FGGB treatment group (Example 5 of the present invention, Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film) was only 9.5%, a 75% reduction compared to the blank control group (Comparative Example 5). The experiment shows that the FGGB treatment group has significant fresh-keeping advantages due to the synergistic antibacterial and slow-release mechanisms of the material system.

[0086] Determine the Vc (ascorbic acid) content of the fresh-keeping composite film of Example 5 of the present invention, the fresh-keeping composite films of Comparative Examples 2-3, the figs fresh-keeping with plastic film in Comparative Example 4, and the blank control Comparative Example 5.

[0087] Ascorbic acid content: Take 1 mL of the supernatant into a test tube, and successively add 481 mL of 0.5% o-phenanthroline, 0.5 mL of 0.4% phosphoric acid solution, 0.5 mL of 0.03% FeCl3 solution, and 1 mL of ethanol. After mixing, place it at 30°C for 1 h, and measure the absorbance at 534 nm. Draw a standard curve with ascorbic acid content solutions of different concentrations, and calculate the ascorbic acid content of the sample.

[0088] Refer to Figure 4 , The experiment shows that during storage under two temperature conditions, the Vc content of figs generally shows a downward trend, and the FGGB treatment group has a significant inhibitory effect on the loss of Vc:

[0089] At 25°C: On the 4th day, the Vc content of the control group decreased to 3.88 mg / 100 g, and the FGGB treatment group (Example 5 of the present invention, Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film) remained at 6.57 mg / 100 g, and was still 4.10 mg / 100 g on the 7th day.

[0090] At 4°C: During the storage period, the Vc decreased rapidly in the early stage. The control group (Comparative Example 5) had the largest decrease (11.94 mg / 100 g), followed by the gelatin group (gelatin film of Comparative Example 2 of the present invention) (11.09 mg / 100 g); the changes in the FGG (Comparative Example 3 of the present invention, Fmoc-F-gelatin-gellan gum composite film) and FGGB treatment groups (Example 5 of the present invention, Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film) were relatively slow. Among them, the decrease in the FGGB treatment group was 9.30 mg / 100 g, and it tended to be flat in the later stage.

[0091] In summary, the FGGB treatment group can significantly reduce the loss of Vc in figs.

[0092] Determine the total phenol changes of the figs fresh-keeping with the fresh-keeping composite film of Example 5 and the figs treated as controls in Comparative Examples 2-5.

[0093] Determination method of total phenol content: Take 50 μL of the supernatant in a test tube, and sequentially add 150 μL of deionized water, 1 mL of Folin-Ciocalteu reagent, and 0.8 mL of 7.5% Na2CO3 solution. After mixing, place it at 30 °C for 1 h, and measure the absorbance at 765 nm. Draw a standard curve with gallic acid solutions of different concentrations, and calculate the TP content of the sample.

[0094] Refer to Figure 5 , at 25 °C: In the first 4 days, the total phenol content in the blank control group and the gelatin group decreased, while the plastic film, FGG (Comparative Example 3 Fmoc-F-gelatin-gellan gum composite film), and FGGB treatment group (Example 5 of the present invention Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film) remained stable; on the 4th day, the peak value was reached in each group, and the FGGB treatment group (0.82 mg / g) was significantly higher than the gelatin group (0.58 mg / g), the plastic group (0.61 mg / g), and the FGG group (0.60 mg / g).

[0095] At 4 °C: In the first 11 days, the total phenol content in the plastic film (Comparative Example 4), FGG (Comparative Example 3 Fmoc-F-gelatin-gellan gum composite film), and FGGB treatment group (Example 5 of the present invention Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film) increased, while the blank control group (Comparative Example 5) and the gelatin group (Comparative Example 2) were stable and decreased slightly; on the 11th day, the peak value of the FGGB group reached 1.14 mg / g, which was 2 times that of the blank control group and was significantly higher than other groups.

[0096] Example 6

[0097] The film-forming substance of this example is: 0.0555 g of Fmoc-F, 400 μL of DMSO, 1.76 mL of glycerol, 6.08 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, and 4 mL of ε-polylysine antibacterial agent.

[0098] The preparation method of the Fmoc-F-gelatin-gellan gum composite film with ε-polylysine as the antibacterial functional component in this example includes the following steps:

[0099] (1) Weigh 0.0555 g of Fmoc-F, fully oscillate and mix it on a vortex shaker with 400 μL of DMSO, then place it on a 45 °C ultrasonic cleaner for further dissolution for 20 min, and stir for 2 min (35 °C, 300 rpm);

[0100] (2) Add it to 7.84 mL of distilled water containing 1.76 mL of glycerol and mix well, and stir on a magnetic stirrer (35 °C, 300 rpm) for 30 min;

[0101] (3) Add 1.1111 g of gelatin, heat up to 45 °C and continue stirring for 30 min, then add 0.02 g of gellan gum and stir on a magnetic stirrer (70 °C, 300 rpm) for 30 min. The mass ratio of Fmoc-F to gelatin is 1 / 20;

[0102] (4) Add 4 ml of ε-polylysine bacteriostatic agent and stir on a magnetic stirrer (60 °C, 300 rpm) for 30 min, then place it in an ultrasonic cleaner to ultrasonically defoam for 20 min.

[0103] (5) Pour it into a 100 mm petri dish, shake well and place it in an oven at 40 °C for drying for 24 h to form a film.

[0104] Example 7

[0105] The film-forming substances in this example are: 0.0555 g of Fmoc-F, 400 μL of DMSO, 1.76 mL of glycerol, 6.08 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, and 4 ml of oregano essential oil bacteriostatic agent.

[0106] The preparation method of the Fmoc-F-gelatin-gellan gum composite film with oregano essential oil as the bacteriostatic functional component in this example is basically the same as that in Example 6, except that the bacteriostatic agent is oregano essential oil bacteriostatic agent.

[0107] Example 8

[0108] The film-forming substances in this example are: 0.0555 g of Fmoc-F, 400 μL of DMSO, 1.76 mL of glycerol, 6.08 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, and 4 ml of cinnamon essential oil bacteriostatic agent.

[0109] The preparation method of the Fmoc-F-gelatin-gellan gum composite film with cinnamon essential oil as the bacteriostatic functional component in this example is basically the same as that in Example 6, except that the bacteriostatic agent is cinnamon essential oil.

[0110] Test the growth inhibitory effects of the fresh-keeping composite films obtained in Examples 6 - 8 on Escherichia coli, Staphylococcus aureus and Phytophthora infestans on LB solid medium: The tests are carried out respectively after the fresh-keeping composite films are made and after being placed at room temperature for 24 h; Test the growth inhibitory effects of the three essential oils on Escherichia coli and Staphylococcus aureus on LB solid medium (Serial numbers Escherichia coli 1 - 3 / Staphylococcus aureus 1 - 3); The test results are shown in the following table. See also Figure 6 .

[0111] The steps of the determination method of bacteriostatic performance are as follows: Pipette 100 μL of Escherichia coli bacterial suspension (about 1×10 6(CFU / mL) was evenly spread on LB solid medium with a spreader and left to stand for 5 min. Then, a sterile circular filter paper with a diameter of 6 mm was placed in the middle of the medium, and different types of essential oils were dropped onto the filter paper, or the fresh-keeping composite film was placed in the middle of the medium. After incubating upside down in an incubator at 37 °C for 24 h, the size of the inhibition zone was measured.

[0112]

[0113]

[0114] The inhibition zone experiment is a classic method in the fields of microbiology and pharmacology. Its core significance lies in evaluating the efficacy of antibacterial substances and the sensitivity of microorganisms through the intuitive antibacterial phenomenon. The table shows the antibacterial effects of 18 natural antibacterial agents against Staphylococcus aureus (Gram-positive bacterium), Escherichia coli (Gram-negative bacterium), and Phytophthora infestans. The data were measured by the inhibition zone method. The larger the value, the stronger the antibacterial effect. The antibacterial agent with the best antibacterial effect against Staphylococcus aureus is oregano essential oil (36.67 ± 0.33 mm), and the effect is significant, far exceeding other components. Cinnamon essential oil (29.00 ± 1 mm), thyme essential oil (23.67 ± 1.67 mm), and carvacrol (23.17 ± 0.83 mm) follow. The antibacterial agent with the best antibacterial effect against Escherichia coli is cinnamon essential oil (27.33 ± 2.83 mm), which is the most prominent, followed by thyme essential oil (23.83 ± 1.17 mm) and oregano essential oil (18.33 ± 1.83 mm). The antibacterial agents with the best antibacterial effect against Phytophthora infestans are cinnamon essential oil (27.67 ± 1.83 mm) and ε-polylysine (21.00 ± 0.5 mm), showing strong antibacterial activity. Curcumin (14.17 ± 2.17 mm) has a certain inhibitory effect on Phytophthora infestans, but the effect is weak, and most antibacterial agents have no inhibitory effect on Phytophthora infestans.

[0115] Example 9

[0116] The film-forming substances in this example are: 0.0555 g of Fmoc-F, 400 μL of DMSO, 1.76 mL of glycerol, 6.08 mL of distilled water, 1.1111 g of gelatin, 0.02 g of gellan gum, and 0.02 g of compound antibacterial agent.

[0117] The preparation method of the Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film in this example is similar to that of Example 8.

[0118] In this example, the Fmoc-F-gelatin-gellan gum-antibacterial agent fresh-keeping composite film with ε-polylysine, oregano essential oil, and cinnamon essential oil as antibacterial functional components was used to preserve figs.

[0119] The preparation method of the Fmoc-F-gelatin-gellan gum antibacterial and fresh-keeping composite film in this embodiment includes the following steps:

[0120] (1) Weigh 0.0555 g of Fmoc-F, fully oscillate and mix it on a vortex shaker with 400 μL of DMSO, then place it on a 45°C ultrasonic cleaner for further dissolution for 20 min, and stir for 2 min (35°C, 300 rpm);

[0121] (2) Add it to 7.84 mL of distilled water containing 1.76 mL of glycerol and mix well, and stir on a magnetic stirrer (35°C, 300 rpm) for 30 min;

[0122] (3) Then add 1.1111 g of gelatin, raise the temperature to 45°C and continue stirring for 30 min, then add 0.02 g of gellan gum and stir on a magnetic stirrer (70°C, 300 rpm) for 30 min. The mass ratio of Fmoc-F to gelatin is 1 / 20;

[0123] (4) Then add 0.02 g of the compound antibacterial agent and stir on a magnetic stirrer (60°C, 300 rpm) for 30 min, and then carry out ultrasonic treatment for 20 min to defoam.

[0124] (5) Pour it into a 100-mm petri dish, shake well and place it in an oven at 40°C for drying for 24 h to form a film.

[0125] Comparative Example 6

[0126] In this comparative example, a commercially available fresh-keeping film is used for fresh-keeping.

[0127] Comparative Example 7

[0128] In this comparative example, the phenylalanine / gelatin-based slow-release composite film disclosed in CN113621242A on November 9, 2021 is used for fresh-keeping.

[0129] The Fmoc-F-gelatin-gellan gum-antibacterial agent composite film group of the present invention: from the 1st to the 8th day, the appearance of the fig changes very slowly. On the 1st to 4th day, the fruit has bright color, regular shape, smooth surface, and almost no signs of corruption; on the 6th to 8th day, although the storage time is relatively long, the fruit only shows very slight color changes, and the overall quality remains good, without obvious decay, mildew or odor. In the Fmoc-F-gelatin-gellan gum-antibacterial agent composite film, the composite film formed by gelatin and gellan gum has a dense structure and excellent barrier properties. It can effectively hinder the exchange of oxygen, water and other substances between figs and the outside world, and greatly inhibit the respiration and water loss of the fruit, thereby maintaining the freshness and hardness of the fruit. At the same time, the antibacterial agent added to the film can continuously release effective ingredients, which has a strong inhibitory effect on mold, bacteria and other microorganisms, preventing the microorganisms from breeding and multiplying on the surface and inside the fruit, further delaying the decay and deterioration process of the figs, allowing this group of figs to maintain good quality throughout the 8-day observation period.

[0130] Commercially available plastic film group: From the 1st to the 8th day, the figs were severely corrupted. On the 1st and 2nd day, the surface of the fruit began to show signs of slight discoloration and softening, with water-like spots in some areas; on the 3rd and 4th days, the discoloration range expanded, the fruit softened as a whole, and a small amount of mold appeared on the skin; on the 6th to 8th day, the fruit rotted over a large area, the mold increased, accompanied by a sour smell, and the fruit structure basically collapsed. Commercially available films can only provide basic physical isolation, with limited ability to block oxygen and moisture, and cannot effectively inhibit the growth of microorganisms. Figs carry microorganisms themselves, and during storage, microorganisms multiply rapidly, decomposing fruit tissues, producing a sour smell, and accelerating corruption.

[0131] Phenylalanine / gelatin-based sustained-release composite film group: On the 1st and 2nd days, the fruit had good color and shape; on the 3rd and 4th days, a small amount of discoloration spots appeared on the surface, and the fruit softened slightly; on the 6th day, the discoloration range expanded, and the fruit softened more deeply; on the 8th day, the fruit became more corrupt. The phenylalanine in the phenylalanine / gelatin-based sustained-release composite film has biological activity, which can inhibit the growth of microorganisms and delay corruption in the early stage. However, as the storage time increases, the concentration of sustained-release antibacterial substances decreases, the antibacterial effect weakens in the later stage, and the microbial reproduction accelerates, resulting in a gradual increase in the degree of fruit corruption.

Claims

1. An antibacterial fresh-keeping film material for figs, characterized in that, The film-forming substance is a composition of glycerol, gelatin, water, Fmoc-F, gellan gum, dimethyl sulfoxide, and an antibacterial agent.

2. The fig antibacterial fresh-keeping film material according to claim 1, characterized in that, The mass ratio of the glycerol to the gelatin is 1:0.5 - 2.5; the mass ratio of the gelatin to the water is 1:5 - 15, preferably 1:8 - 12; the mass ratio of the Fmoc-F to the gelatin is 1:10 - 50, preferably 1:15 - 40, more preferably 1:20 - 30; the addition amount of the gellan gum is 0.2% - 0.6% of the total mass of the film-forming substance; the addition amount of the dimethyl sulfoxide ≤ 8% of the total volume of the film-forming substance, preferably 3 - 5%.

3. The fig antibacterial fresh-keeping film material according to claim 1 or 2, characterized in that, The Fmoc-F is N-fluorenylmethoxycarbonyl-L-phenylalanine.

4. The fig antibacterial fresh-keeping film material according to any one of claims 1 to 3, characterized in that The addition amount of the antibacterial agent is 0.1% - 12% of the total mass of the film-forming substance, preferably 0.5% - 10%; more preferably 0.8% - 8%, and further preferably 1.2% - 5.0%.

5. The fig antibacterial fresh-keeping film material according to claim 4, characterized in that, The antibacterial agent is ε-polylysine, oregano essential oil antibacterial agent, cinnamon essential oil antibacterial agent; preferably a compound antibacterial agent composed of a compound of ε-polylysine, oregano essential oil, and cinnamon essential oil.

6. A method for preparing a fig antibacterial fresh-keeping composite film using the fig antibacterial fresh-keeping film material according to any one of claims 1-5, characterized in that It includes the following steps: (1) Add glycerol, F-moc-F, and dimethyl sulfoxide to water, and stir to fully mix the three. (2) Add gelatin and continue stirring. (3) Add gellan gum, continue stirring, add the antibacterial agent, continue stirring, and simultaneously perform ultrasonic treatment. (4) Pour it into a mold, shake well, and dry to obtain the product.

7. The preparation method of the fig antibacterial and fresh-keeping composite film according to claim 6, characterized in that, In step (1), the temperature of the stirring is 35 - 40°C, the rotation speed during stirring is 300 - 350 rpm, and the time of the stirring is 15 - 20 min.

8. The preparation method of the fig antibacterial and fresh-keeping composite film according to claim 6 or 7, characterized in that, In step (2), the temperature of the stirring is 35 - 40°C, the rotation speed during stirring is 300 - 350 rpm, and the time of the stirring is 8 - 10 min.

9. The preparation method of the fig antibacterial and fresh-keeping composite film according to any one of claims 6 to 8, characterized in that, In step (3), the temperature of the stirring is 65 - 70°C, the rotation speed during stirring is 300 - 350 rpm; stir for 25 - 30 min after adding the antibacterial agent; the power of the ultrasonic treatment is 100 - 200 W, and the time of the ultrasonic treatment is 15 - 20 min.

10. The preparation method of the fig antibacterial and fresh-keeping composite film according to any one of claims 6 to 9, characterized in that, In step (4), the temperature of the drying is 40 - 45°C, and the time of the drying is 24 - 48 h; preferably dry at 40 - 45°C for 24 - 48 h and then dry in a dryer for at least 2 d.

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