Food antibacterial film with photothermal effect and preparation method thereof

Abstract

The invention discloses a food antibacterial film with a photothermal effect and a preparation method thereof, and belongs to the technical field of food functional packaging. The preparation method comprises the following steps: preparing a starch layer film containing a photo-thermal agent: adding soluble starch into water to form an aqueous dispersion containing the soluble starch, adding the photo-thermal agent, heating, preserving heat, adding a plasticizer, preserving heat for a period of time, cooling, casting in a mold, and drying to obtain the starch layer film containing the photo-thermal agent; polylactic acid resin is dissolved in ethyl acetate, constant-temperature heating and stirring are carried out, and the polylactic acid layer film liquid is obtained; and preparing a starch-polylactic acid double-layer film: uniformly coating the starch layer film containing the photo-thermal agent with the polylactic acid layer film liquid to form the starch-polylactic acid double-layer film, and drying at room temperature to obtain the food antibacterial film with the photo-thermal effect. The food antibacterial film with the photothermal effect can improve the antibacterial effect, the food fresh-keeping effect and the safety, is good in mechanical performance and has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of food functional packaging, and specifically relates to a food antibacterial film with a photothermal effect and a preparation method thereof. Background Art

[0002] With the increasing severity of food safety issues, traditional food preservation methods can no longer meet the high requirements of modern consumers for food safety and freshness. Existing antibacterial technologies mainly include chemical preservatives, heat treatment, radiation sterilization, etc. However, these methods often have certain limitations. For example, chemical preservatives may have a negative impact on human health, heat treatment may lead to the loss of food nutrients, and radiation sterilization may affect the sensory quality of food. Therefore, it is particularly important to develop a new type of non-toxic and highly efficient antibacterial technology.

[0003] In recent years, the photothermal sterilization technology has gradually attracted attention. This technology uses a photothermal agent to absorb light energy and rapidly convert it into heat energy through a non-radiative mechanism under specific light conditions, generating a local high-temperature effect, thereby effectively destroying the structure of the bacterial cell membrane and its protein function. There are various types of photothermal agents, including polydopamine and edible metal oxides, etc. These materials can rapidly heat up under light irradiation, forming a local thermal effect, and then achieving the inhibition and inactivation of pathogenic microorganisms. Compared with traditional antibacterial technologies, the photothermal sterilization technology has the advantages of being fast, efficient, broad-spectrum, and non-resistant to drugs.

[0004] Although the photothermal sterilization technology shows good application prospects, it still faces some challenges in practical applications. For example, most of the existing antibacterial film materials are single-layer films, and the addition of antibacterial agents and photothermal agents may affect their physical properties, resulting in a decrease in the mechanical properties of the film, insufficient flexibility and durability. Chinese Patent with Application No. CN202311374621.1 discloses a preparation method of a photothermal-responsive chitosan fresh-keeping film, and Chinese Patent with Application No. CN202110482889.1 discloses a pectin-based nano-melanin edible photothermal antibacterial film and a preparation method thereof. However, the elongation at break of the obtained antibacterial film is relatively low, and the flexibility and durability of the film cannot meet the actual needs.

[0005] Therefore, developing a new type of double-layer film structure, one layer having a photothermal antibacterial effect and the other layer improving the mechanical properties of the film, which can effectively combine the advantages of the photothermal sterilization technology and food packaging materials, will be an important direction for future research. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a food antibacterial film with a photothermal effect and a preparation method thereof, and to develop a preparation method of a food antibacterial film that can effectively combine the photothermal sterilization technology and improve the material properties. It has a double-layer film structure, one layer has a photothermal antibacterial effect, and the other layer improves the mechanical properties of the film, meeting the antibacterial requirements of food packaging while having good flexibility and durability.

[0007] The purpose of the present invention is achieved by the following technical solutions:

[0008] The present invention provides a food antibacterial film with a photothermal effect. The food antibacterial film has a starch-polylactic acid double-layer film structure. The starch layer film contains a photothermal agent, and the polylactic acid layer film is located above the starch layer film.

[0009] The present invention also provides a preparation method of a food antibacterial film with a photothermal effect, including the following steps:

[0010] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to water to form an aqueous dispersion containing soluble starch, then add a photothermal agent and heat and keep warm, then add a plasticizer to obtain a starch layer film-forming solution containing a photothermal agent, continue to keep warm, and finally cool the starch layer film-forming solution containing a photothermal agent, cast it in a mold and dry it to obtain a starch layer film containing a photothermal agent;

[0011] (2) Prepare a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, heat and stir at a constant temperature to obtain a polylactic acid layer film solution;

[0012] (3) Prepare a starch-polylactic acid double-layer film: Uniformly coat the polylactic acid layer film solution on the starch layer film containing a photothermal agent to form a starch-polylactic acid double-layer film, and dry it at room temperature to obtain a food antibacterial film with a photothermal effect.

[0013] Furthermore, in step (1), the photothermal agent is a biomimetic polymer material or an edible metal oxide with a photothermal effect.

[0014] Furthermore, the biomimetic polymer material with a photothermal effect is polydopamine, and the edible metal oxide is zinc oxide.

[0015] Furthermore, in step (1), the plasticizer is one or a combination of glycerol, D-sorbitol or propylene glycol.

[0016] Furthermore, in step (1), the water is distilled water or deionized water, and the ratio of starch to water is 8%-12% (w / v); the ratio of the photothermal agent to water is 1%-5% (w / v); the ratio of the plasticizer to water is 3%-20% (v / v).

[0017] Further, in step (1), after adding the photothermal agent, the heating temperature is 87°C - 93°C, and the heat preservation time is 10 min - 60 min; the starch layer film-forming solution containing the photothermal agent continues to be heat-preserved for 10 min - 60 min; after the film-forming solution is poured into the mold, it is dried at 35°C - 45°C.

[0018] Further, in step (2), the ratio of polylactic acid resin to ethyl acetate is 8% - 12% (w / v); the constant-temperature heating and stirring means constant-temperature water bath stirring at 55°C - 65°C for 0.5 h - 2 h.

[0019] Further, when preparing the starch-polylactic acid bilayer film in step (3), the proportion of the starch layer film-forming solution in the double-layer film-forming solution of the starch layer and the polylactic acid layer is 30% - 70% (v / v), and the thickness of the dried starch-polylactic acid bilayer film is controlled to be 100 μm - 200 μm.

[0020] The present invention also provides an application of a food antibacterial film with a photothermal effect, which is used for the functional packaging of various foods to extend the food preservation period.

[0021] Advantages and effects of the present invention:

[0022] Compared with traditional antibacterial technologies such as chemical preservatives, heat treatment, and radiation sterilization, the food antibacterial film with a photothermal effect of the present invention will not have a negative impact on human health or affect the nutritional components and sensory qualities of foods, meeting the high requirements of modern consumers for food safety; the bilayer film structure combines both the photothermal sterilization technology, which can rapidly generate local high temperatures under light irradiation conditions, significantly improving the antibacterial effect, and also improves the mechanical properties and the stability of the antibacterial effect, thereby enhancing the food preservation effect and safety, and having broad application prospects. Description of the Drawings

[0023] Figure 1 It is the heating curve of the food antibacterial film with a photothermal effect in Example 1 under near-infrared irradiation;

[0024] Figure 2 It is the heating-cooling curve of the food antibacterial film with a photothermal effect in Example 1 under five near-infrared laser on / off cycles;

[0025] Figure 3 It is the heating curve of the antibacterial film with a photothermal effect in Comparative Example 1 under near-infrared irradiation;

[0026] Figure 4 It is the heating-cooling curve of the antibacterial film with a photothermal effect in Comparative Example 1 under five near-infrared laser on / off cycles. Detailed Embodiments

[0027] The present invention will be described in detail below with reference to the embodiments.

[0028] Example 1

[0029] A food antibacterial film with photothermal effect of the present invention has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0030] A preparation method of a food antibacterial film with photothermal effect of the present invention includes the following steps:

[0031] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 10%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 2%; keep warm at 90±1°C for 30 min; add plasticizers glycerol and D-sorbitol, where the volume ratio of glycerol to water is 3.5% and the volume ratio of D-sorbitol to water is 2.5%, to form a film-forming solution; continue to keep warm for 30 min, then cool the film-forming solution, and then cast it in a mold and dry it at 40°C to obtain a starch layer film containing a photothermal agent;

[0032] (2) Prepare a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, and the mass-volume ratio of polylactic acid resin to ethyl acetate is 10%, and stir at a constant temperature of 60°C in a water bath for 1 h to obtain a polylactic acid layer film solution;

[0033] (3) Prepare a starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch layer film, control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 4.3:5.7, form a starch-polylactic acid bilayer film, dry it at room temperature, and control the thickness of the dried film to be 125±10 μm to obtain a food antibacterial film with photothermal effect.

[0034] Performance test:

[0035] (1) Mechanical property test:

[0036] Use a TA-XTPlusC texture analyzer to evaluate the mechanical properties of the prepared food antibacterial film with photothermal effect, including tensile strength (TS) and elongation at break (EB); before the test, balance the food antibacterial film with photothermal effect in a dryer at 25°C and a relative humidity of 57% for 12 h, then cut it into samples of 10 mm×40 mm in size and fix them at both ends of the tensile clamp, with an initial clamping distance of 20 mm and a tensile speed set at 5.0 mm / s, repeat the test 3 times, and take the average value; the calculation formulas for tensile strength and elongation at break are as follows:

[0037]

[0038] Wherein, Fmax is the maximum tension during the stretching process, L is the width of the food antibacterial film sample with photothermal effect, and W is the thickness of the food antibacterial film sample with photothermal effect;

[0039]

[0040] Wherein, L0 is the initial length of the food antibacterial film sample with photothermal effect, and L1 is the length at break of the food antibacterial film sample with photothermal effect;

[0041] Test results: The tensile strength of the food antibacterial film with photothermal effect in this example is 4.28 ± 0.21 Mpa, and the elongation at break is 249.14 ± 10.35%.

[0042] (2) Photothermal performance test:

[0043] Cut the prepared food antibacterial film with photothermal effect into samples of 1 cm × 2 cm in size, place them into 5 mL centrifuge tubes, irradiate them with a NIR (near-infrared light) irradiator, and use a near-infrared thermal imager to monitor and measure the real-time temperature of the samples; under the condition of NIR light irradiation, detect the real-time temperature of the food antibacterial film with photothermal effect and record it through a near-infrared thermal imager; perform a "switch-on - switch-off" cycle of heating the NIR irradiator for 7 min and cooling for 15 min. Under the same irradiation conditions, measure the heating-cooling curve of the food antibacterial film with photothermal effect during five laser on / off cycles of natural cooling to evaluate its photothermal stability; among them, the irradiation conditions are: NIR light irradiation time is 7 min, and the power density is 2.0 W / cm 2 ;

[0044] Test results: As Figure 1 shown, after being irradiated with near-infrared light, the temperature of the food antibacterial film with photothermal effect increases significantly with the extension of time. After irradiating for 7 min, the temperature of the film maintains at a relatively stable temperature level, and the stable maximum temperature is 46.66 ± 1.05 °C, indicating that the food antibacterial film with photothermal effect of the present invention has excellent photothermal conversion ability and can quickly convert light energy into heat energy; as Figure 2 shown, the heating-cooling curves of the food antibacterial film with photothermal effect measured during five laser on / off cycles show that the food antibacterial film with photothermal effect of the present invention has good photothermal stability.

[0045] (3) Antibacterial effect evaluation:

[0046] The antibacterial property of the packaging film is a key technical parameter for extending the storage period of packaged foods. The antibacterial activity of the prepared food antibacterial film with photothermal effect was evaluated by the dilution plate coating experiment. Among them, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used as typical representatives of Gram-negative bacteria and Gram-positive bacteria, respectively;

[0047] Test results: Under NIR light irradiation, due to the good photothermal conversion ability of polydopamine, in the petri dish using the food antibacterial film with photothermal effect, the survival rate of E. coli decreased from 80.3% without irradiation to 18.5%; the survival rate of S. aureus decreased from 78.6% without irradiation to 5.6%, indicating that the antibacterial film with photothermal effect of the present invention has a good antibacterial effect.

[0048] Example 2

[0049] A food antibacterial film with photothermal effect of the present invention has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0050] A preparation method of a food antibacterial film with photothermal effect of the present invention includes the following steps:

[0051] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 10%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 2.5%; keep warm at 90 ± 1 °C for 30 min; add the plasticizers glycerol and D-sorbitol, where the volume ratios of glycerol, D-sorbitol to water are 3.5% respectively, to form a film-forming solution; continue to keep warm for 20 min, then cool the film-forming solution, and then cast it in a mold and dry it at 40 °C to prepare a starch layer film containing a photothermal agent;

[0052] (2) Prepare a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, and the mass-volume ratio of polylactic acid resin to ethyl acetate is 10%, and stir it in a 55 °C constant temperature water bath for 1 h to prepare a polylactic acid layer film solution;

[0053] (3) Prepare a starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch layer film, control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 1:1, form a starch-polylactic acid bilayer film, and dry it at room temperature, control the thickness of the dried film to be 110 ± 10 μm, to obtain a food antibacterial film with photothermal effect.

[0054] Example 3

[0055] The present invention relates to a food antibacterial film with a photothermal effect, which has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0056] A preparation method of a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0057] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 8%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 5%; keep warm at 88±1°C for 60 min; add the plasticizers D-sorbitol and propylene glycol, wherein the volume ratio of D-sorbitol to water is 3%, and the volume ratio of propylene glycol to water is 10%, to form a film-forming solution; continue to keep warm for 45 min, then cool the film-forming solution, and then cast it in a mold and dry it at 45°C to obtain a starch layer film containing a photothermal agent;

[0058] (2) Prepare a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, and the mass-volume ratio of polylactic acid resin to ethyl acetate is 10%. Stir at a constant temperature of 65°C in a water bath for 0.5 h to obtain a polylactic acid layer film solution;

[0059] (3) Prepare a starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch layer film, control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 3:7, form a starch-polylactic acid bilayer film, and dry it at room temperature. Control the thickness of the dried film to be 190±10 μm to obtain a food antibacterial film with a photothermal effect.

[0060] Example 4

[0061] The present invention relates to a food antibacterial film with a photothermal effect, which has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0062] A preparation method of a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0063] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 12%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 1%; keep warm at 92±1°C for 60 min; add the plasticizers glycerol and propylene glycol, wherein the volume ratio of glycerol to water is 4%, and the volume ratio of propylene glycol to water is 10%, to form a film-forming solution; continue to keep warm for 10 min, then cool the film-forming solution, and then cast it in a mold and dry it at 35°C to obtain a starch layer film containing a photothermal agent;

[0064] (2) Preparation of the polylactic acid layer film solution: Dissolve the polylactic acid resin in ethyl acetate. The mass-volume ratio of the polylactic acid resin to ethyl acetate is 8%. Stir for 1 h in a constant temperature water bath at 55 °C to obtain the polylactic acid layer film solution;

[0065] (3) Preparation of the starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch-containing layer film. Control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 5:5 to form a starch-polylactic acid bilayer film. Dry at room temperature and control the thickness of the dried film to be 110 ± 10 μm to obtain a food antibacterial film with a photothermal effect.

[0066] Example 5

[0067] A food antibacterial film with a photothermal effect according to the present invention has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0068] A preparation method of a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0069] (1) Preparation of the starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch. The mass-volume ratio of starch to water is 8%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch. The mass-volume ratio of the photothermal agent to water is 2%; keep warm at 90 ± 1 °C for 60 min; add plasticizers glycerol, D-sorbitol, and propylene glycol, where the volume ratio of glycerol to water is 3%, the volume ratio of D-sorbitol to water is 2%, and the volume ratio of propylene glycol to water is 5% to form a film-forming solution; after continuing to keep warm for 60 min, cool the film-forming solution, then cast it in a mold and dry it at 40 °C to obtain a starch layer film containing a photothermal agent;

[0070] (2) Preparation of the polylactic acid layer film solution: Dissolve the polylactic acid resin in ethyl acetate. The mass-volume ratio of the polylactic acid resin to ethyl acetate is 12%. Stir for 2 h in a constant temperature water bath at 60 °C to obtain the polylactic acid layer film solution;

[0071] (3) Preparation of the starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch-containing layer film. Control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 7:3 to form a starch-polylactic acid bilayer film. Dry at room temperature and control the thickness of the dried film to be 150 ± 10 μm to obtain a food antibacterial film with a photothermal effect.

[0072] Example 6

[0073] The present invention relates to a food antibacterial film with a photothermal effect, which has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0074] A preparation method of a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0075] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 10%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 2%; keep warm at 90±1°C for 30 min; add the plasticizer glycerol, and the volume ratio of glycerol to water is 3% to form a film-forming solution; after continuing to keep warm for 30 min, cool the film-forming solution, then cast it in a mold, and dry it at 35°C to prepare a starch layer film containing a photothermal agent;

[0076] (2) Prepare a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, and the mass-volume ratio of polylactic acid resin to ethyl acetate is 12%. Stir at a constant temperature of 65°C in a water bath for 1 h to prepare a polylactic acid layer film solution;

[0077] (3) Prepare a starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch layer film, control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 4.5:5.5 to form a starch-polylactic acid bilayer film, dry it at room temperature, and control the thickness of the dried film to be 150±10 μm to obtain a food antibacterial film with a photothermal effect.

[0078] Example 7

[0079] The present invention relates to a food antibacterial film with a photothermal effect, which has a starch-polylactic acid bilayer film structure. The starch layer film contains the photothermal agent polydopamine, and the polylactic acid layer film is located above the starch layer film.

[0080] A preparation method of a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0081] (1) Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 10%; add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 2%; keep warm at 90±1°C for 10 min; add the plasticizer D-sorbitol, and the volume ratio of D-sorbitol to water is 8% to form a film-forming solution; after continuing to keep warm for 30 min, cool the film-forming solution, then cast it in a mold, and dry it at 40°C to prepare a starch layer film containing a photothermal agent;

[0082] (2) Preparation of the polylactic acid layer film solution: Dissolve the polylactic acid resin in ethyl acetate. The mass-volume ratio of the polylactic acid resin to ethyl acetate is 8%. Stir for 1 h in a constant temperature water bath at 60 °C to obtain the polylactic acid layer film solution;

[0083] (3) Preparation of the starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch-containing layer film. Control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 5:5 to form a starch-polylactic acid bilayer film. Dry at room temperature and control the thickness of the dried film to be 150 ± 10 μm to obtain a food antibacterial film with a photothermal effect.

[0084] Example 8

[0085] A food antibacterial film with a photothermal effect according to the present invention has a starch-polylactic acid bilayer film structure. The starch layer film contains a photothermal agent, the edible metal oxide zinc oxide, and the polylactic acid layer film is located above the starch layer film.

[0086] A method for preparing a food antibacterial film with a photothermal effect according to the present invention includes the following steps:

[0087] (1) Preparation of the starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch. The mass-volume ratio of starch to water is 10%; Add the edible metal oxide zinc oxide to the aqueous dispersion containing soluble starch. The mass-volume ratio of the photothermal agent to water is 1.2%; Keep warm at 90 ± 1 °C for 30 min; Add the plasticizer propylene glycol. The volume ratio of propylene glycol to water is 20% to form a film-forming solution; After continuing to keep warm for 45 min, cool the film-forming solution, and then cast it in a mold and dry it at 40 °C to obtain the starch layer film containing a photothermal agent;

[0088] (2) Preparation of the polylactic acid layer film solution: Dissolve the polylactic acid resin in ethyl acetate. The mass-volume ratio of the polylactic acid resin to ethyl acetate is 10%. Stir for 1 h in a constant temperature water bath at 60 °C to obtain the polylactic acid layer film solution;

[0089] (3) Preparation of the starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch-containing layer film. Control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 6:4 to form a starch-polylactic acid bilayer film. Dry at room temperature and control the thickness of the dried film to be 125 ± 10 μm to obtain a food antibacterial film with a photothermal effect.

[0090] Comparative Example 1

[0091] A method for preparing an antibacterial film with a photothermal effect, which is different from Example 1 in that the photothermal agent uses a nano mixed solution of silver ions-polyphenol substances, includes the following steps:

[0092] (1) Preparation of a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, with the mass-volume ratio of starch to water being 10%; add a nano-hybrid solution containing silver ions - polyphenol substances as the photothermal agent to the aqueous dispersion containing soluble starch, with the mass-volume ratio of the photothermal agent to water being 2%; keep it warm at 90 ± 1 °C for 30 min; add plasticizers glycerol and D-sorbitol, where the volume ratio of glycerol to water is 3.5% and the volume ratio of D-sorbitol to water is 2.5%, to form a film-forming solution; after continuing to keep it warm for 30 min, cool the film-forming solution, then cast it in a mold and dry it at 40 °C to prepare a starch layer film containing a photothermal agent;

[0093] (2) Preparation of a polylactic acid layer film solution: Dissolve polylactic acid resin in ethyl acetate, with the mass-volume ratio of polylactic acid resin to ethyl acetate being 10%, and stir it in a 60 °C constant temperature water bath for 1 h to prepare a polylactic acid layer film solution;

[0094] (3) Preparation of a starch-polylactic acid bilayer film: Uniformly coat the polylactic acid layer film solution on the dried starch layer film, control the volume ratio of the starch layer film-forming solution to the polylactic acid layer film-forming solution to be 4.3:5.7, to form a starch-polylactic acid bilayer film, dry it at room temperature, and control the thickness of the dried film to be 125 ± 10 μm to obtain an antibacterial film with a photothermal effect.

[0095] Photothermal performance test:

[0096] Cut the antibacterial film with a photothermal effect prepared in this comparative example into 1 cm × 2 cm samples, place them in 5 mL centrifuge tubes, irradiate them with a NIR (near-infrared light) light irradiator, and use a near-infrared thermal imager to monitor and measure the real-time temperature of the samples; under the condition of NIR light irradiation, detect the real-time temperature of the prepared antibacterial film with a photothermal effect and record it with a near-infrared thermal imager. Perform a "switch-on-off" cycle of heating the NIR light irradiator for 7 min and cooling for 15 min. Under the same irradiation conditions, measure the heating-cooling curve of the composite film in five laser on / off cycles of natural cooling to evaluate its photothermal stability. Among them, the irradiation conditions are: NIR light irradiation time is 7 min, and the power density is 2.0 W / cm 2 .

[0097] Test results: As Figure 3 shown, after being irradiated with near-infrared light, the temperature of the antibacterial film with a photothermal effect in this comparative example increases with the extension of time. After irradiating for 7 min, the highest temperature of the film is 35.78 ± 2.98 °C, showing a certain temperature fluctuation, which is about 10 °C lower than the highest temperature (average value) of the food antibacterial film with a photothermal effect in Example 1. As Figure 4As shown in the figure, the heating-cooling curves of the antibacterial film with photothermal effect measured in five laser on / off cycles indicate that the antibacterial film with photothermal effect in this comparative example also has inferior photothermal stability compared to Example 1, fully demonstrating that the food antibacterial film prepared by the present invention has more excellent photothermal conversion ability, can quickly convert light energy into heat energy and is more stable, which is more conducive to food preservation. In addition, compared with heavy metal photothermal materials such as silver ions, it has better safety and can be widely used in the preparation of food preservative films.

[0098] Comparative Example 2

[0099] A preparation method of a food antibacterial film with photothermal effect, which is different from Example 1 in that it is a single-layer starch film containing a photothermal agent, and includes the following steps:

[0100] Prepare a starch layer film containing a photothermal agent: Add soluble starch to distilled water to form an aqueous dispersion containing soluble starch, and the mass-volume ratio of starch to water is 10%. Add the polymer photothermal agent polydopamine to the aqueous dispersion containing soluble starch, and the mass-volume ratio of the photothermal agent to water is 2%; Keep it warm at 90 ± 1 °C for 30 min; Add plasticizers glycerol and D-sorbitol, where the volume ratio of glycerol to water is 3.5%, and the volume ratio of D-sorbitol to water is 2.5%, to form a film-forming solution; After continuing to keep it warm for 30 min, cool the film-forming solution, then cast it in a mold and dry it at room temperature, controlling the thickness of the dried film to be 125 ± 10 μm to obtain a single-layer food antibacterial film with photothermal effect.

[0101] Mechanical property test:

[0102] Use a TA-XTPlusC texture analyzer to evaluate the mechanical properties of the single-layer food antibacterial film with photothermal effect prepared in this comparative example, including tensile strength (TS) and elongation at break (EB); Before the test, place the prepared composite film in a dryer at 25 °C and a relative humidity of 57% to equilibrate for 12 h; Then cut the film into samples with a size of 10 mm × 40 mm and fix them at both ends of the tensile clamp. The initial clamping distance is 20 mm, and the tensile speed is set to 5.0 mm / s. Repeat the test 3 times and take the average value. The calculation formulas for tensile strength and elongation at break are the same as those in Example 1;

[0103] Test results: The tensile strength of the single-layer food antibacterial film with photothermal effect in this comparative example is 4.58 ± 0.29 Mpa, and the elongation at break is 152.13 ± 8.32%. Higher requirements are placed on the flexibility and durability of food packaging films. The elongation at break (average value) of the food antibacterial film with photothermal effect prepared in Example 1 of the present invention is nearly 64% higher than that of this comparative example, and the tensile strength also remains at a relatively high level, having more excellent mechanical properties, and the flexibility and durability can meet the application requirements.

[0104] Through the above embodiments, the double-layer film structure of the food antibacterial film with photothermal effect of the present invention effectively combines the advantages of photothermal sterilization technology and food packaging materials, can rapidly generate local high temperature under light irradiation conditions, significantly improve the antibacterial effect, and is non-toxic and harmless, meeting the high requirements of modern consumers for food safety; in addition, the double-layer composite structure of the food antibacterial film with photothermal effect of the present invention not only enhances the mechanical properties of the film, but also improves the stability of the antibacterial effect, overcomes the deficiencies of the existing single-layer film, and has broad application prospects.

Claims

1. A food antibacterial film with photothermal effect, characterized in that: The food antibacterial film is a starch-polylactic acid double-layer film structure, the starch layer film contains a photothermal agent, and the polylactic acid layer film is located on the starch layer film.

2. A method for preparing the food antibacterial film with photothermal effect according to claim 1, characterized in that: The following steps are involved: (1) Preparing a starch layer film containing a photothermal agent: adding soluble starch to water to form a water dispersion containing the soluble starch, then adding a photothermal agent and heating and keeping the temperature, then adding a plasticizer to obtain a starch layer film-forming liquid containing the photothermal agent, continuing to keep the temperature, and finally cooling the starch layer film-forming liquid containing the photothermal agent, casting it in a mold and drying it to obtain a starch layer film containing the photothermal agent; (2) preparing a polylactic acid layer film liquid: dissolving a polylactic acid resin in ethyl acetate, heating and stirring at a constant temperature to obtain a polylactic acid layer film liquid; (3) Preparation of starch-polylactic acid double-layer film: The polylactic acid layer film liquid is evenly coated on the starch layer film containing the photothermal agent to form a starch-polylactic acid double-layer film, and then dried at room temperature to obtain a food antibacterial film with photothermal effect.

3. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: The photothermal agent in step (1) is a biomimetic polymer material or an edible metal oxide having a photothermal effect.

4. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 3, characterized in that: The bionic polymer material with photothermal effect is polydopamine, and the edible metal oxide is zinc oxide.

5. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: In step (1), the plasticizer is one or a combination of glycerol, D-sorbitol or propylene glycol.

6. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: In step (1), the water is distilled water or deionized water, the ratio of starch to water is 8%-12% w / v; the ratio of photothermal agent to water is 1%-5% w / v; the ratio of plasticizer to water is 3%-20% v / v.

7. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: After adding the photothermal agent in step (1), the heating temperature is 87°C-93°C, and the insulation time is 10min-60min; the starch layer film-forming liquid containing the photothermal agent is further kept warm for 10min-60min; after the film-forming liquid is cast into the mold, it is dried at 35°C-45°C.

8. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: In step (2), the ratio of polylactic acid resin to ethyl acetate is 8%-12% w / v; constant temperature heating and stirring refers to stirring in a constant temperature water bath at 55° C.-65° C. for 0.5 h-2 h.

9. The method for preparing a food antibacterial film with photothermal effect as claimed in claim 2, characterized in that: When preparing the starch-PLA double-layer film in step (3), the proportion of the starch layer film-forming liquid in the starch layer and the PLA double-layer film-forming liquid is 30%-70% v / v, and the thickness of the starch-PLA double-layer film after drying is controlled to be 100 μm-200 μm.

10. An application of the food antibacterial film with photothermal effect as claimed in claim 1, characterized in that: Used for functional packaging of various foods to extend the shelf life of food.

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