Antibacterial fresh food tray material and preparation method thereof

Abstract

The invention relates to the technical field of food packaging, in particular to an antibacterial fresh food tray material and a preparation method thereof. According to the bamboo parenchyma cell antibacterial fresh tray material, bamboo processing residues serve as raw materials, bamboo parenchyma cells are obtained through a water separation method, no chemical reagent or adhesive is used, and the bamboo parenchyma cell antibacterial fresh tray material is prepared in a continuous heating and hot pressing mode. According to the antibacterial fresh food tray material, glue-free forming is achieved through starch gelatinization of the antibacterial fresh food tray material and functional group change and chemical reaction among chemical components in the continuous heating and hot pressing process, and the antibacterial fresh food tray material has good oxidation resistance and antibacterial performance. When the fruit preservative is used, the rotting rate of fruits in the storage period can be reduced without adding extra antibacterial and antioxidant, and the reduction of nutrient substances in the fruits is delayed. In addition, the preparation raw materials are low in cost, environment-friendly and degradable, and the environmental and economic pressure caused by a refractory polypropylene tray material and a polylactic acid tray material with high preparation cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, and particularly to an antibacterial fresh tray material and a preparation method thereof. Background Art

[0002] On the market, polypropylene trays and polyethylene fresh-keeping films are often used to package fresh food, which is then placed on shelves or in freezers for sale. The use of a large amount of non-degradable polypropylene tray materials brings great pressure to the environment. Researchers have tried to use biodegradable thermoplastic polymer materials, such as polylactic acid, to replace polypropylene tray materials in order to relieve the environmental pressure. However, the cost of polylactic acid resin particles on the market is about 7 times that of polypropylene resin particles, resulting in high manufacturing costs and making it difficult to produce on a large scale. In addition, the problem of food spoilage caused by food microorganisms has always been difficult for people to overcome. More than 1 / 5 of the fresh food in the world is caused by spoilage every year, which not only leads to a large amount of food waste and huge economic losses, but also brings potential harm to people's bodies. Therefore, it is urgent to develop green, degradable, low-cost and antibacterial fresh tray materials.

[0003] CN106117624A discloses a fresh tray material composed of high amylose starch-cinnamaldehyde inclusion complex and starch matrix, which can slowly release cinnamaldehyde, play a good anti-corrosion and fresh-keeping role, and effectively extend the shelf life of food. Hassani F Z S A, El Bourakadi K, Merghoub N, Qaiss A, Bouhfid R, Effect ofchitosan / modified montmorillonite coating on the antibacterial and mechanicalproperties of date palm fiber trays, 2020:148 discloses a date palm fiber tray surface-modified with chitosan / modified montmorillonite-thiabendazole. The thiabendazole and lamellar montmorillonite structure in the tray can effectively inhibit the growth of Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. Although the above methods can obtain green, degradable and antibacterial tray materials, additional antibacterial agents are required to achieve antibacterial effects, and the preparation process is relatively complex. Using bamboo containing natural antibacterial compounds as raw material is one of the effective methods to solve the above problems. Tanaka A, Zhu Q C, Tan H, Horiba H,Ohnuki K, Mori Y, Yamauchi R, Ishikawa H, Iwamoto A, Kawahara H, Shimizu K,Biological Activities and Phytochemical Profiles of Extracts from DifferentParts of Bamboo ( Phyllostachys pubescens ), 2014:19 published that the ethanol extracts from the bamboo green parts 5 m and 1 m above the ground of Phyllostachys edulis have good anti-Staphylococcus aureus performance, and its natural antibacterial component may be O -hexosyl- O -deoxyhexosyl trioctacosanol. To further improve the antibacterial performance of bamboo, CN115368691A discloses a method for chemically modifying bamboo fibers to enhance their antibacterial performance.

[0004] In order to reduce the usage amount of adhesives, hardly degradable or high-cost degradable thermoplastic polymers, the preparation of bamboo-based adhesive-free environmental protection materials has become a current research hotspot. CN106914967A discloses a preparation method of adhesive-free recombined bamboo materials. By subjecting bamboo slices or bamboo chips to cooking and softening treatment and then grinding them into fiber bundles, then heating and compressing the fiber bundles and transferring them into a forming mold, heating the forming mold to bond and form the fiber bundles therein, so as to form the adhesive-free recombined materials at one time. CN114393667A discloses a preparation method of an adhesive-free formed bamboo fiber board, which hot-presses and forms the bamboo materials, and prepares an adhesive-free formed bamboo fiber board under the conditions of without pretreatment and without adding adhesives. CN119221312A discloses a preparation method of a high-performance bamboo fiber adhesive-free formed environmental protection material. Using bamboo materials as raw materials to obtain parenchyma cells and bamboo fibers, then subjecting the parenchyma cells to steam explosion treatment and the bamboo fibers to enzyme treatment, and then hot-pressing the treated parenchyma cells and bamboo fibers to obtain a high-performance bamboo fiber adhesive-free formed environmental protection material. CN114393667A discloses a method for preparing an adhesive-free formed bamboo fiber board without separately separating bamboo fibers from bamboo materials and without pretreatment and without adding adhesives. However, some of the above methods require pretreatment of bamboo raw materials, and the preparation process is relatively complex; some remove parenchyma cells or utilize parenchyma cells in a small amount, resulting in waste of parenchyma cell resources; in most hot-pressing forming processes, when the set hot-pressing temperature is reached, the pre-laid mold is placed on the hot press plate. Preheating for a certain time at the set hot-pressing temperature, and then performing pressurization, pressure holding and cooling forming, resulting in high energy consumption during the hot-pressing forming process. Summary of the Invention

[0005] In order to solve the defects existing in the above-mentioned prior art, the present invention provides a preparation method of an antibacterial fresh food tray material, including: mixing bamboo powder with water and then standing still, collecting the upper-layer bamboo parenchyma cells; drying the bamboo parenchyma cells and spreading them out flat, spraying distilled water and then sealing and standing still to obtain a raw material; spreading the raw material in a hot-pressing mold, continuously heating from room temperature to 230°C to 250°C, then pressurizing to 10 to 16 MPa and holding the pressure for 5 to 15 minutes, and cooling to obtain the antibacterial fresh food tray material.

[0006] Bamboo materials are mainly composed of about 50% parenchyma cells, 40% fibers, 10% vessels, etc. (Liese W, Tang TK H, Properties of the bamboo culm, Bamboo: the plant and its uses, 2015:229). Among them, the parenchyma cells have large cavities and thin walls, there are a large number of pits on the cell walls, and there are a large number of starch granules in the cell cavities, and the structure is as Figure 1 shown.

[0007] During the continuous heating process of the above method of the present invention, the mold filled with moist thin-walled cells is placed on the hot press plate to fully gelatinize the starch in the thin-walled cell cavity, achieving a good bonding effect. During the high-temperature and pressurization process, the high temperature forces some chemical components of the cell wall to decompose, resulting in cracks. The lignin melts and flows, and the hemicellulose is decomposed by heat into sugar substances and forms aldehyde compounds. The two react with each other to form phenolic resin, further playing a bonding role. At the same time, the high pressure forces the cell wall structure to collapse, enabling the natural small-molecule antibacterial compounds in the bamboo cell cavity to migrate along the pits on the cell wall to the outer layer of the cell wall, exerting an antibacterial effect and obtaining a good fresh-keeping effect.

[0008] In the preparation method of the present invention, no chemical reagents and adhesives are used.

[0009] Preferably, the temperature is continuously raised to 235°C to 245°C, and then the pressure is increased to 15 to 16 MPa and held for 8 to 12 minutes.

[0010] Preferably, the bamboo powder is derived from bamboo processing residues; preferably, the bamboo powder is bamboo processing residues pulverized to 60 to 100 mesh (more preferably 80 to 100 mesh).

[0011] Preferably, the mass ratio of bamboo powder to water is 1:(10 to 15); and / or, the standing time is more than 10 minutes.

[0012] Preferably, the drying temperature is 45°C to 55°C; preferably, the drying time is more than 48 hours.

[0013] Preferably, the sealed standing time is more than 10 minutes.

[0014] Preferably, the moisture content of the raw material is 60% to 100%, preferably 98% to 100%.

[0015] Preferably, a polytetrafluoroethylene film is padded in the hot press mold.

[0016] Furthermore, the present invention provides an antibacterial fresh food tray material prepared by the above preparation method.

[0017] Preferably, the tensile strength of the antibacterial fresh food tray material is 1.42 to 7.88 MPa, and / or, the Young's modulus is 0.81 to 3.46 GPa, and / or, the flexural strength is 9.22 to 31.81 MPa, and / or, the flexural modulus is 1.20 to 5.58 GPa, and / or, the 24-hour water absorption rate is 13.14% to 59.50%.

[0018] More preferably, the tensile strength of the antibacterial fresh food tray material is 7.80 - 7.88 MPa, and / or the Young's modulus is 3.30 - 3.35 GPa, and / or the flexural strength is 31.50 - 31.81 MPa, and / or the flexural modulus is 5.50 - 5.58 GPa, and / or the water absorption rate in 24 h is 13.14% or less.

[0019] In the specific implementation process, the antibacterial fresh food tray material of the present invention is used as the shelf packaging for fresh food; specifically: the fresh food product is placed flat on the tray material, and then covered with polyethylene fresh-keeping film and placed on the shelf or in the freezer for fresh sales.

[0020] Preferably, the present invention also provides a method for using the above antibacterial fresh food tray material, including: placing fresh strawberries on the antibacterial fresh food tray material, then covering with a layer of polyethylene fresh-keeping film and storing in a freezer at 4°C and 80% RH.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses the residues from bamboo processing as raw materials, obtains bamboo parenchyma cells by the water separation method, does not use any chemical reagents and adhesives, and prepares the bamboo parenchyma cell antibacterial fresh food tray material by the continuously heating and pressing mode. This antibacterial fresh food tray material has the advantages of good performance, safety and no pollution, antibacterial and antioxidant, green and degradable, simple preparation process, high resource utilization rate, low cost, etc. It can not only reduce the use of plastics and synthetic resins, but also provide a new way to alleviate the oil crisis and protect the environment. When in use, it can reduce the decay rate of fruits during storage without adding additional antibacterial and antioxidant agents, delay the decline of nutrients in fruits, and improve the utilization value of bamboo parenchyma cells, which has important significance. Description of the Drawings

[0022] Figure 1 It is a scanning electron microscope (SEM) image of bamboo parenchyma cells obtained by the water separation method.

[0023] Figure 2 It is the appearance morphology diagram of the antibacterial fresh food tray materials of Examples 1 - 7.

[0024] Figure 3 It is the appearance morphology diagram of the tray material of Comparative Example 1.

[0025] Figure 4 It is the weight loss rate of strawberry fruits during storage.

[0026] Figure 5 It is the decay rate of strawberry fruits during storage.

[0027] Figure 6 It is the change in the appearance morphology of strawberry fruits during storage.

[0028] Figure 7 It shows the change in color difference of strawberry fruits during storage.

[0029] Figure 8 It shows the change in soluble solids content of strawberry fruits during storage.

[0030] Figure 9 It shows the change in titratable acid content of strawberry fruits during storage.

[0031] Figure 10 It shows the change in ascorbic acid content of strawberry fruits during storage. Detailed implementation mode

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention. In the embodiments provided in this specification, those without specific technical or conditions are carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. Those reagents or instruments without indicating the manufacturer can be obtained as conventional products through regular channels.

[0033] In the following embodiments of the present invention, the microscopic morphology was tested by scanning electron microscopy. The bamboo parenchyma cell powder obtained by the water separation method was sputter-coated with gold, and the acceleration voltage was 10 kV.

[0034] In the following embodiments of the present invention, the bamboo processing residues are specifically residues from moso bamboo processing, purchased from Hunan Fuxiang Wood Industry Co., Ltd. The bamboo processing residues are in the shape of filaments, with a starch content of 1% - 5% and a moisture content of 20% - 40%.

[0035] Example 1 This example provides an antibacterial fresh food tray material, and its preparation method is as follows: 1) Collect bamboo processing residues and dry them to constant weight; 2) Crush the dried bamboo processing residues obtained in step 1) with a pulverizer to a particle size of 100 mesh to obtain bamboo powder; 3) Add 10 times the volume of pure water to the bamboo powder obtained in step 2), stir evenly and let stand for 10 min, and collect the floating substances on the upper layer, which are bamboo parenchyma cells; 4) Dry the bamboo parenchyma cells obtained in step 3) at 50 °C for 48 h, and place them in a constant temperature and humidity chamber at 20 °C and 60% RH for standby; 5) Weigh 25 g of the bamboo thin-walled cells obtained in step 4), spread them evenly, spray atomized distilled water evenly 3 - 5 cm above the material, mix and stir, then seal and let stand for 10 min to prepare a raw material with a moisture content of 100%. 6) Spread the raw material obtained in step 5) evenly on a hot-pressing mold lined with a polytetrafluoroethylene film. 7) Place the mold obtained in step 6) on the lower platen of a hot press and bring the upper platen into contact with the upper surface of the mold. Continuously heat from room temperature to 230 °C, then apply pressure up to 10 MPa and hold the pressure for 5 min. After cooling, an antibacterial fresh food tray material is obtained, and the obtained material is abbreviated as 230 - 10 - 5.

[0036] Example 2 This example provides an antibacterial fresh food tray material, and the only difference in its preparation method from Example 1 is that: 7) Place the mold obtained in step 6) on the lower platen of a hot press and bring the upper platen into contact with the upper surface of the mold. Continuously heat from room temperature to 230 °C, then apply pressure up to 16 MPa and hold the pressure for 15 min. After cooling, an antibacterial fresh food tray material is obtained, and the obtained material is abbreviated as 230 - 16 - 15.

[0037] Example 3 This example provides an antibacterial fresh food tray material, and the only difference in its preparation method from Example 1 is that: 7) Place the mold obtained in step 6) on the lower platen of a hot press and bring the upper platen into contact with the upper surface of the mold. Continuously heat from room temperature to 240 °C, then apply pressure up to 16 MPa and hold the pressure for 5 min. After cooling, an antibacterial fresh food tray material is obtained, and the obtained material is abbreviated as 240 - 16 - 5.

[0038] Example 4 This example provides an antibacterial fresh food tray material, and the only difference in its preparation method from Example 1 is that: 7) Place the mold obtained in step 6) on the lower platen of a hot press and bring the upper platen into contact with the upper surface of the mold. Continuously heat from room temperature to 240 °C, then apply pressure up to 10 MPa and hold the pressure for 10 min. After cooling, an antibacterial fresh food tray material is obtained, and the obtained material is abbreviated as 240 - 10 - 10.

[0039] Example 5 This example provides an antibacterial fresh food tray material, and the only difference in its preparation method from Example 1 is that: 7) Place the mold obtained in step 6) on the lower platen of a hot press and bring the upper platen into contact with the upper surface of the mold. Continuously heat from room temperature to 250 °C, then apply pressure up to 13 MPa and hold the pressure for 5 min. After cooling, an antibacterial fresh food tray material is obtained, and the obtained material is abbreviated as 250 - 13 - 5.

[0040] Example 6 This embodiment provides an antibacterial fresh food tray material. The only difference in its preparation method from that of Embodiment 1 is as follows: 7) Place the mold obtained in step 6) on the lower platen of the hot press, bring the upper platen into contact with the upper surface of the mold, continuously heat from room temperature to 250 °C, then apply pressure to 16 MPa and hold the pressure for 10 min, and an antibacterial fresh food tray material is obtained after cooling. The obtained material is abbreviated as 250-16-10.

[0041] Embodiment 7 This embodiment provides an antibacterial fresh food tray material. The only difference in its preparation method from that of Embodiment 1 is as follows: 7) Place the mold obtained in step 6) on the lower platen of the hot press, bring the upper platen into contact with the upper surface of the mold, continuously heat from room temperature to 240 °C, then apply pressure to 16 MPa and hold the pressure for 10 min, and an antibacterial fresh food tray material is obtained after cooling. The obtained material is abbreviated as 240-16-10.

[0042] Comparative Example 1 This comparative example provides a tray material. The only difference in its preparation method from that of Embodiment 1 is as follows: 7) Wait for the hot press to heat up to 240 °C, place the mold obtained in step 6) on the hot press and keep it preheated without pressure for 10 min, then apply pressure to 16 MPa and hold the pressure for 10 min, and a tray material is obtained after cooling.

[0043] Test Example 1 Perform microscopic morphology tests on the tray materials prepared in the above embodiments and comparative examples. The scanning electron microscope (SEM) images of bamboo parenchyma cells obtained by the water separation method are as Figure 1 shown. The test results of the embodiments are as Figure 2 shown. It can be seen from the figure that with the increase of temperature, pressure and time, there are certain dark carbonized areas on the surface of the tray materials, but the overall color is relatively uniform, the surface is flat and smooth without cracks, and the appearance morphologies of the materials obtained with different hot pressing parameters are not significantly different. The test results of Comparative Example 1 are as Figure 3 shown. It can be seen from the figure that the carbonized area on the surface of this material is large, the carbonization effect is obvious, it is dark black, and there are obvious cracks, and a complete tray material cannot be formed, and the strength is low, and it cannot be cut by a laser cutting machine.

[0044] Test Example 2 Test the physical and mechanical properties of the tray materials of Embodiments 1 to 7 and Comparative Example 1 according to GB / T 1447—2005 "Test Methods for Tensile Properties of Fiber Reinforced Plastics", GB / T 1449—2005 "Test Methods for Flexural Properties of Fiber Reinforced Plastics" and GB / T 17657—2022 "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Decorated Wood-Based Panels", as shown in Table 1.

[0045] Table 1 Physical and Mechanical Property Test Results of the Tray Materials

[0046] As can be seen from Table 1, the density of the tray materials in Examples 1-7 is 0.79-1.17 g·cm -3 , appropriately increasing the hot pressing pressure and prolonging the hot pressing time are beneficial to increasing the density of the tray materials; the tensile strength and Young's modulus of the tray materials in Examples 1-7 are 1.42-7.88 MPa and 0.81-3.35 GPa respectively, and the flexural strength and modulus are 9.22-31.81 MPa and 1.20-5.58 GPa respectively. Appropriately increasing the hot pressing pressure and prolonging the hot pressing time can improve the mechanical properties of the tray materials; the 24-hour water absorption rate of the tray materials in Examples 1-7 is 13.14-59.50%. Appropriately shortening the hot pressing time is beneficial to improving the water resistance of the tray materials.

[0047] Generally speaking, Example 7 (240-16-10) has the highest density, the best mechanical properties and water resistance, while Example 1 (230-10-5) has the worst comprehensive performance. Specifically, compared with Example 1 (230-10-5), the density, tensile strength, Young's modulus, flexural strength and flexural modulus of Example 7 (240-16-10) are increased by 48%, 455%, 310%, 245% and 365% respectively, and the 24-hour water absorption rate is reduced by 78%.

[0048] Comparative Example 2 This comparative example provides a polypropylene tray material, and its preparation method is as follows: 1) Use a cryogenic grinder to crush food-grade polypropylene resin particles, pass through a 100-mesh sieve, and place them in an oven at 50°C for drying for 24 hours; 2) Weigh 60 g of the polypropylene powder obtained in step 1); 3) Preheat the double-platen hot press to 170°C, and evenly spread the polypropylene powder on the hot press mold lined with polyethylene terephthalate film; 4) Place the mold obtained in step 3) on the hot press, first melt it without pressure for 10 minutes, then apply pressure to 10 MPa and hold for 5 minutes, then apply pressure to 20 MPa and hold for 5 minutes, release the pressure, and cool to obtain the polypropylene tray material.

[0049] Comparative Example 3 This comparative example provides a polylactic acid tray material, and its preparation method is as follows: 1) Use a cryogenic grinder to crush food-grade polylactic acid resin particles, pass through a 100-mesh sieve, and place them in an oven at 50°C for drying for 24 hours; 2) Weigh 60 g of the polylactic acid powder obtained in step 1); 3) Preheat the double-plate hot press to 170 °C, and evenly spread the polylactic acid powder on the hot press mold lined with polyethylene terephthalate film. 4) Place the mold obtained in step 3) on the hot press. First, melt it without pressure for 10 min, then apply a pressure of 10 MPa and hold for 5 min, then apply a pressure of 20 MPa and hold for 5 min, relieve the pressure, and cool to obtain the polylactic acid tray material.

[0050] Test Example 3 According to the methods of Bondet V, B williams W, Berset C, Kinetics and mechanisms of antioxidant activity using the DPPH free radical method, 1997: 609-615. and Liu N, Chen X, Park H, Liu C, Liu C, Meng X, Yu L, Effect of MW and concentration of chitosan on antibacterial activity of Escherichia coli, 2006: 60-65., the DPPH free radical scavenging rate and the optical density OD of Staphylococcus aureus bacterial solution were respectively tested for the tray materials of Example 7, Comparative Example 2 and Comparative Example 3. The blank refers to the pure bacterial solution sample without adding the tray material during the test. The test results are shown in Table 2.

[0051] Table 2 Test results of antioxidant and antibacterial properties

[0052] As can be seen from Table 2, the DPPH free radical scavenging rate of Example 7 is 41.19%, which is significantly higher than that of Comparative Example 2 (5.06%) and Comparative Example 3 (1.40%). This indicates that bamboo parenchyma cells are rich in natural antioxidant components (such as phenols and flavonoids), and can effectively scavenge DPPH free radicals.

[0053] In terms of the effect of inhibiting Staphylococcus aureus, the optical density OD value of Example 7 is always the lowest, and the antibacterial effect is the best. This may be because bamboo parenchyma cells contain natural antibacterial components (such as bamboo quinone and phenolic compounds), which migrate to the surface layer of the cell wall of bamboo parenchyma cells during the continuous heating and pressurization stage, directly inhibiting the growth of bacteria. At the same time, its biomass porous structure may adsorb bacteria or release antibacterial substances, enhancing the continuous antibacterial ability. While the OD values of Comparative Example 2 and Comparative Example 3 are higher and increase with time, and the antibacterial property is poor.

[0054] Generally speaking, Example 7 has good antibacterial and antioxidant properties.

[0055] Test Example 4 The total migration amount of Example 7 was tested according to GB 31604.8-2021 "National Food Safety Standard - Determination of Total Migration Amount of Bamboo and Wood Materials and Products for Food Contact". The total migration amount of Example 7 was 6.583 mg / dm 2 , which is lower than the national standard requirement (10 mg / dm 2 ), and it belongs to safe bamboo and wood materials for food contact.

[0056] Example 8 The antibacterial fresh produce tray material prepared in Example 7 was used to package fresh strawberries. The specific steps are as follows: 1) Place 12 fresh strawberries flat on the tray material, and then wrap them with polyethylene food wrap; 2) Place the packaged strawberry tray obtained in step 1) in a freezer at 4°C and 80% RH for 12 days. The nutritional indicators of the strawberry fruits were detected every 3 days.

[0057] Comparative Example 4 In this comparative example, the polypropylene tray material prepared in Comparative Example 2 was used to package fresh strawberries, and the steps were the same as those in Example 8.

[0058] Comparative Example 5 In this comparative example, the polylactic acid tray material prepared in Comparative Example 3 was used to package fresh strawberries, and the steps were the same as those in Example 8.

[0059] Test Example 5 1. The weight loss rate of strawberry fruits during storage, as Figure 4 shown.

[0060] As the storage time increased, the weight loss and shrinkage of strawberry fruits gradually became more serious. Therefore, the weight loss rates of strawberry fruits packaged in the three types of trays all increased continuously, and the increase in the weight loss rate of strawberry fruits in Example 8 was the most obvious. The reason for the relatively high weight loss rate of strawberry fruits in Example 8 is that the bamboo parenchyma cell tray material contains a large amount of hydrophilic components such as cellulose and hemicellulose, which are easy to absorb the water released by the transpiration of strawberry fruits. Generally speaking, after 12 days of storage, the weight loss rate of strawberry fruits in Example 8 was still lower than 5%, and good commerciality was still maintained.

[0061] 2. The decay rate of strawberry fruits during storage, as Figure 5 shown.

[0062] With the increase of storage time, the decay rate of strawberry fruits on the three tray materials gradually increased, and the decay rate of strawberry fruits in Comparative Example 5 was the highest. On the 12th day of storage, the decay rate of Comparative Example 5 reached 75%, which was significantly higher than that of Comparative Example 4 (67%) and Example 8 (58%). In addition, in the early stage of storage, no decay was found in the strawberry fruits of Example 8, and obvious decay did not occur until 6 days after storage. This is mainly because the bamboo parenchyma cell tray material has good antibacterial properties.

[0063] 3. Changes in the appearance and morphology of strawberry fruits during storage, such as Figure 6 shown.

[0064] 4. Changes in the color difference of strawberry fruits during storage, such as Figure 7 shown.

[0065] As can be seen from Figure 6 and 7 , with the extension of storage time, the appearance quality of strawberry fruits on the three tray materials deteriorated from good to bad, and decay gradually occurred, and the color generally changed from bright red to dark red. Among them, the color difference of Comparative Example 4 fluctuated greatly, probably because of the decay and mildew phenomenon of turning from red to yellow and then to white. The color difference of strawberry fruits in Comparative Example 5 and Example 8 was generally on the rise, and the relative rise of Example 8 was slower. Generally speaking, Example 8 could better maintain the appearance quality of strawberry fruits during storage.

[0066] 5. Changes in the soluble solid content of strawberry fruits during storage, such as Figure 8 shown.

[0067] 6. Changes in the titratable acid content of strawberry fruits during storage, such as Figure 9 shown.

[0068] 7. Changes in the ascorbic acid content of strawberry fruits during storage, such as Figure 10 shown.

[0069] As can be seen from Figure 8 , 9 and 10, with the extension of storage time, the carbohydrate and acid substances in strawberry fruits on the three tray materials decreased in consumption, and the ascorbic acid content first increased and then decreased. Among them, the strawberry fruits in Example 8 always had the highest nutrient content throughout the storage period, and the decrease range was small. This is mainly because the bamboo parenchyma cell tray material used in Example 8 has an antioxidant effect, which can delay the decline of nutrient substances in strawberry fruits during storage and effectively delay the senescence rate of strawberry fruits during storage.

[0070] In addition, the hardness changes of strawberry fruits in Example 8, Comparative Example 4 and Comparative Example 5 during storage were also compared and analyzed, as shown in Table 3.

[0071] Table 3 Changes in the hardness of strawberry fruits

[0072] As can be seen from Table 3, with the extension of the storage time, the hardness of the strawberry fruits in Example 8, Comparative Example 4, and Comparative Example 5 gradually decreased because the cell wall substances of the strawberries were gradually degraded. Generally speaking, there were no significant differences in the changes in the hardness of the strawberry fruits in Example 8, Comparative Example 4, and Comparative Example 5.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an antibacterial fresh-keeping tray material, characterized in that Including: Mix bamboo powder with water and let it stand, then collect the upper-layer bamboo parenchyma cells; dry the bamboo parenchyma cells and spread them out, spray distilled water and seal for standing to obtain the raw material; spread the raw material in a hot pressing mold, continuously heat up to 230°C - 250°C, then apply pressure up to 10 - 16 MPa and hold the pressure for 5 - 15 minutes, and cool to obtain the antibacterial fresh food tray material.

2. The preparation method according to claim 1, wherein, Continuously heat up to 235°C - 245°C, then apply pressure up to 15 - 16 MPa and hold the pressure for 8 - 12 minutes.

3. The preparation method according to claim 1, characterized in that, The bamboo powder is derived from bamboo processing residues; preferably, the bamboo powder is bamboo processing residues ground to 60 - 100 mesh.

4. The preparation method according to claim 1, characterized in that, The mass ratio of bamboo powder to water is 1:(10 - 15); and / or, the standing time is more than 10 minutes.

5. The preparation method according to claim 1, characterized in that, The drying temperature is 45°C - 55°C; preferably, the drying time is more than 48 hours.

6. The preparation method according to claim 1, wherein The sealing and standing time is more than 10 minutes.

7. The preparation method according to claim 1, wherein The moisture content of the raw material is 60% - 100%, preferably 98% - 100%.

8. The preparation method according to claim 1, characterized in that, A polytetrafluoroethylene film is padded in the hot pressing mold.

9. The antibacterial fresh food tray material prepared by the preparation method according to any one of claims 1 - 8.

10. The antibacterial fresh food tray material according to claim 9, characterized in that, The tensile strength of the antibacterial fresh food tray material is 1.42 - 7.88 MPa, and / or, the Young's modulus is 0.81 - 3.46 GPa, and / or, the flexural strength is 9.22 - 31.81 MPa, and / or, the flexural modulus is 1.20 - 5.58 GPa, and / or, the water absorption rate in 24 hours is 13.14% - 59.50%.

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