A sustained-release starch-based fruit fresh-keeping pad and its preparation method and application

Abstract

The present invention discloses a slow-release starch-based fruit fresh-keeping pad, its preparation method and application; the slow-release starch-based fruit fresh-keeping pad is prepared by hot pressing a surface starch-based foamed board, a bottom starch-based foamed board and an SO2 gas slow-release layer in the middle layer, and sulfite is filled in the SO2 gas slow-release layer. Calculated according to the horizontal cross-sectional area of the bottom starch-based foamed board, the dosage of the sulfite is 5-25 g / m 2 ; the surface starch-based foamed board and the bottom starch-based foamed board are prepared by foaming, blanking, cutting and shaping a foaming precursor. The present invention utilizes the porous and moisture-absorbing characteristics of the starch-based material to realize the slow and controlled release of the SO2 slow-release agent under different humidity gradients, thereby achieving an excellent fresh-keeping effect on fruits, and enabling the target fruits to be fresh-keeping for 9-40 days in a normal-temperature and humid environment.

Description

Technical Field

[0001] The invention relates to a fruit fresh-keeping pad, in particular to a slow-release starch-based fruit fresh-keeping pad and a preparation method and application thereof, belonging to the field of fruit fresh-keeping. Background Art

[0002] At present, new fruit preservation technologies are emerging one after another, but due to cost and technical difficulty, the preservation methods currently used on a large scale are mainly low-temperature preservation and chemical reagent preservation. Since the coverage rate of cold chain transportation in the fruit field in my country is not high, the preservation method mainly uses chemical reagents. 2 With its trace amount and high efficiency, it can not only inhibit the activities of oxidases and microorganisms, but also inhibit food browning, discoloration and VC loss, becoming the mainstream method in chemical preservation.

[0003] SO 2 The preservation method is low-cost and quick-acting, but the method itself also has disadvantages: SO 2 The release amount is difficult to control. Large release amounts often result in bleaching of the fruit and the fruit SO 2 The residual amount will exceed the international standard; and the small release amount will not be able to play an antibacterial role. Both of these situations will directly affect the commercial value of the fruit and even harm human health. This is the reason why SO 2 The primary issue to be considered in preservation technology. 2 The main method of preservation is fumigation, which is to use a large dose of SO in a short period of time. 2 (No more than SO 2 The damage threshold to the fruit) is to treat the fruit for freshness preservation, kill most of the pathogens, and maintain the freshness preservation effect for a long time. The subsequent treatment is carried out regularly at intervals. The advantage is that the continuous freshness preservation process is omitted. The disadvantage is that the continuous freshness preservation effect of different fruits after fumigation is difficult to determine and it is easy to be contaminated again. The best SO 2 The preservation method is to first fumigate with a large dose and then treat with a low dose to maintain the preservation effect.

[0004] Chinese invention patent 201010285227.7 discloses a pollution-free grape preservation mat composed of a barrier layer, a slow-acting drug application layer, a drug-carrying layer, a fast-acting drug application layer, a release regulation layer, an adsorption layer and an anti-fog layer stacked in sequence. The multi-layered layer works together to achieve "SO 2 The effect of "fast release + slow release" is achieved. However, in actual application, the ratio of various substances in each layer is precisely adjusted to control SO 2 The operation of releasing the amount will greatly limit the use of the fresh-keeping mat.

[0005] Chinese invention patent application 201210378211.X discloses a method for realizing SO 2 With ClO 2 The design simplifies the traditional multi-layer stacked fresh-keeping mat to a certain extent and increases the single-component slow-release to a double-component slow-release, but through SO 2 Participate in the reaction to obtain ClO 2 To reduce SO 2 Drug abuse will not only make SO 2 The release dose is difficult to control, and the extent of the reaction is difficult to measure, which can easily lead to drug residues.

[0006] Existing fruit preservation pads are targeted at SO 2 A series of improvements have been made to control its release rate and the possible harm to fruits, but the results of simply modifying the method without starting from the material itself have not been ideal; the natural defects of the material itself, such as its non-degradability, lack of buffering, and the possibility that the fresh-keeping pad may become a favorable condition for promoting the growth of microorganisms in a high-humidity environment, need to be improved urgently. Summary of the invention

[0007] The object of the present invention is to provide a simple sustained-release starch-based fruit fresh-keeping pad which has buffering and antibacterial properties and can be completely degraded under natural conditions, and a preparation method thereof.

[0008] The hot pressing molding assembly method is adopted, and the viscosity of starch increases after it is gelatinized at high temperature when it meets water, so that the two layers of foam boards are firmly adhered together. At the same time, the starch foam material itself has the ability to absorb and hold water, which not only simplifies the assembly process, but also avoids the use of multiple reagents such as adsorbents and adhesives. The porous network structure of the starch foam material can delay SO 2 The barrier effect increases with the increase of moisture absorption, so SO 2 The release is shown as a high concentration release in a short period of time, and then gradually released at a low concentration, so as to achieve a good preservation effect. In addition, the thermoplasticity of starch allows starch materials to be blended with other substances. This feature can fundamentally improve the common problem of the preservation mat itself not being antibacterial. At the same time, the starch material is green and pollution-free and has a certain compressive strength, which is also not available in traditional preservation mat materials.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A slow-release starch-based fruit fresh-keeping pad, comprising a surface starch-based foam board, a bottom starch-based foam board and a middle layer of SO 2 The gas slow-release layer is made by hot pressing. 2The gas slow-release layer is filled with sulfite. According to the horizontal cross-sectional area of ​​the bottom starch-based foaming board, the amount of sulfite is 5-25g / m 2 The surface starch-based foam board and the bottom starch-based foam board are made from a foaming precursor after foaming, punching, cutting and shaping; the foaming precursor is prepared by pre-mixing starch, polyvinyl alcohol, nucleating agent and fiber, and then blending with plasticizer, foaming agent and water at 55-65°C for 20-25 minutes to obtain a pre-treated material, which is extruded and granulated, and dried until the moisture content drops to 13%-15%.

[0011] To further achieve the purpose of the present invention, preferably, during the hot pressing forming operation of the fresh-keeping mat, only the edges of the surface starch-based foam board and the bottom starch-based foam board are hot pressed; and the edges are sprayed with water before hot pressing.

[0012] Preferably, the sulfite is one or more of sodium pyrosulfite, potassium pyrosulfite and sodium bisulfite.

[0013] Preferably, the thickness of the bottom starch-based foam board and the surface starch-based foam board is 8-12 mm; 2 The thickness of the gas slow-release layer is 1-4 mm; the bottom starch-based foaming board and the surface starch-based foaming board are in the shape of a tile edge or a flat plate.

[0014] Preferably, the bottom starch-based foamed board or the surface starch-based foamed board is prepared by the following steps:

[0015] (1) Weighing materials:

[0016]

[0017]

[0018] (2) placing the starch, polyvinyl alcohol, nucleating agent, and fiber weighed in step (1) into a high-speed mixer and premixing at a rate of 100-200 r / min for 5-10 min at room temperature;

[0019] (3) adding the plasticizer, foaming agent and water weighed in step (1) to the material obtained in step (2), and blending at 55-65° C. at a rate of 100-200 r / min for 20-25 min to obtain a pretreated material;

[0020] (4) extruding and granulating the pretreated material obtained in step (3);

[0021] (5) drying the pellets obtained in step (4) to reduce the moisture content to 13%-15%, thereby obtaining a foaming precursor;

[0022] (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping.

[0023] Preferably, the starch is one or more of cassava starch, corn starch and potato starch or modified starches thereof; the modified starch is one or more of oxidized starch, esterified starch, cross-linked starch and hydroxypropylated starch; the plasticizer is one or more of water, glycerol and propylene glycol; the foaming agent is one or more of water, sodium bicarbonate and ethanol.

[0024] Preferably, the nucleating agent is one or more of diatomaceous earth, calcium carbonate and montmorillonite; and the fiber is one or more of dried pomegranate peel residue, dried peanut shell residue and grapefruit seed residue.

[0025] The method for preparing the sustained-release starch-based fruit fresh-keeping pad comprises the following steps:

[0026] 1) preparing a surface starch-based foamed board and a bottom starch-based foamed board: premixing starch, polyvinyl alcohol, a nucleating agent, and fibers, and then blending with a plasticizer, a foaming agent, and water at 55-65° C. for 20-25 min, extruding and granulating the obtained pretreated material, and drying until the moisture content is reduced to 13%-15% to obtain a foaming precursor, and foaming, punching, cutting, and shaping the foaming precursor to obtain a surface starch-based foamed board and a bottom starch-based foamed board;

[0027] 2) According to the horizontal cross-sectional area of ​​the bottom starch-based foam board, sulfite is added at 5-25g / m 2 Evenly set on the bottom starch-based foam board, the surface starch-based foam board, the bottom starch-based foam board and the middle layer of SO 2 The gas slow-release layer is formed by hot pressing to obtain a slow-release starch-based fruit fresh-keeping pad.

[0028] The application of the slow-release starch-based fruit fresh-keeping pad in fruit preservation is as follows: the fruit is sealed in a container provided with the slow-release starch-based fruit fresh-keeping pad, and the slow-release starch-based fruit fresh-keeping pad is arranged at the bottom or around the container; the fruit is one or more of grapes, strawberries, and lychees.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1) Organically combine starch-based foaming materials with the field of fresh-keeping, and use the advantages of starch-based foaming materials to solve the defects of traditional fresh-keeping products.

[0031] 2) The hot pressing molding technology is used to utilize the characteristic that the viscosity of starch increases after it is gelatinized in water at high temperature, so that the two layers of foam boards are adhered to each other, thereby simplifying the preparation process of the fresh-keeping mat.

[0032] 3) All raw materials of the starch-based foamed board of the present invention are degradable, and the finished product is green and pollution-free.

[0033] 4) The starch-based foam board of the present invention is in a tile-shaped shape, which is different from the fresh-keeping paper used in the current fresh-keeping mat. It has a certain buffering performance, and the fruit can be directly placed on the fresh-keeping mat, eliminating the need for additional filling buffering materials.

[0034] 5) The starch-based foam board of the present invention has fibers with antibacterial properties added during the preparation process, which effectively solves the problem that the existing fresh-keeping mat may promote the growth of microorganisms in a high-humidity environment. It not only makes the fresh-keeping mat itself have certain antibacterial properties and thus enhances the fresh-keeping effect, but also increases the strength of the fresh-keeping mat.

[0035] 6) The starch-based foam board preparation method used in the present invention adopts a two-step preparation process, and the produced products include a foaming precursor and a foaming board. Users can choose to prepare products according to their own needs, thereby greatly reducing storage and transportation space and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the cross-sectional structure of the sustained-release starch-based fruit fresh-keeping pad of the present invention;

[0037] Figure 2 The figure is a schematic diagram of the three-dimensional structure of the sustained-release starch-based fruit fresh-keeping pad of the present invention.

[0038] Figure 3 The SO of the starch-based sustained-release fresh-keeping pad of Example 1 2 Release curve diagram.

[0039] Figure 4 The SO of the starch-based sustained-release fresh-keeping pad of Example 2 2 Release curve diagram.

[0040] Figure 5 The SO of the starch-based sustained-release fresh-keeping pad of Example 3 2 Release curve diagram.

[0041] Figure 6 The SO of the starch-based sustained-release fresh-keeping pad of Example 4 2 Release curve diagram.

[0042] The figure shows: 1. Surface starch-based foam board 2. SO 2 Gas slow-release layer 3, bottom starch-based foam board DETAILED DESCRIPTION

[0043] In order to better understand the present invention, the present invention is further described below in conjunction with the examples, but the embodiments of the present invention are not limited thereto. The specific test methods used in Examples 1-4 are as follows:

[0044] Biodegradation percentage: The starch-based foam board was cut into 2 cm × 2 cm blocks and TLC cellulose was used as the reference material (powder, particle size <20 μm). The blocks were placed in a 3 L glass compost container filled with farmland fertilizer compost for CO2 degradation. 2 The cumulative release amount was tested and the changes of the samples during the composting process were observed and recorded. The experimental conditions were set at 58±2℃, relative humidity 50%, and ventilation flow rate 100-150ml / min. (When the biodegradation rate of the reference material exceeded 70% at 45 days, it met the national standard and showed that the experimental results were effective. Therefore, it is meaningful to use the 45-day biodegradation percentage to indicate the degradation performance of the material.)

[0045] The experiment uses INSTRONT 5566 universal material testing machine to test the compression performance of the material. First, measure the thickness of the sample with a thickness gauge, then fix the sample on the sample table, make the test probe close to the surface of the sample and set the compression distance of the testing machine to 50% of the sample thickness. Set the compression speed to 5mm / min, wait for the sample height to return to stability after compression once, use a vernier caliper to measure the recovered height and then compress again. Set 5 parallels for each group of samples. The calculation formulas for compressive strength and rebound rate are as follows:

[0046]

[0047] Where F is the maximum load when the sample is compressed to 50% (N); S is the bearing area of ​​the probe (m 2 ).

[0048]

[0049] Where, h is 50% of the sample thickness (mm); h 1 is the height (mm) of the sample recovered after the first compression.

[0050] like Figure 1 and Figure 2 As shown, the slow-release starch-based fruit fresh-keeping pad prepared by the present invention comprises a surface starch-based foaming board 1, SO 2The gas slow-release layer 2 and the bottom starch-based foaming board 3 are composed. The sulfite is evenly spread on the bottom starch-based foaming board 3, and then the surface starch-based foaming board of the same size is placed on the bottom foaming board, and then a small amount of water is sprayed on the edges of the two layers of foaming boards, and then the edges are heat-pressed with a hot press, and the two layers of starch-based foaming boards are bonded by the starch gelatinization characteristics to form a three-layer integral structure. Preferably, the thickness of the bottom starch-based foaming board 3 and the surface starch-based foaming board 1 is 8-12mm, and it is further preferred that the bottom starch-based foaming board 3 and the surface starch-based foaming board 1 have the same thickness. SO 2 The thickness of the gas slow-release layer is 1-4 mm. The fresh-keeping mat is placed at the bottom or around the fruit when in use. The shapes of the bottom starch-based foaming board and the surface starch-based foaming board are preferably tile-shaped or flat-plate-shaped.

[0051] Example 1

[0052] (1) Weighing materials: According to the mass percentage of the raw materials, weigh 82 wt% of hydroxypropyl corn starch, 6 wt% of polyvinyl alcohol, 5 wt% of glycerol, 4 wt% of water, 2 wt% of calcium carbonate, and 1 wt% of grapefruit seed residue;

[0053] (2) placing the starch, polyvinyl alcohol, calcium carbonate, and grapefruit seed residue weighed in step (1) into a high-speed mixer and premixing at a rate of 100 r / min for 10 min at room temperature;

[0054] (3) adding the glycerol and water weighed in step (1) to the material obtained in step (2), and blending at 60° C. at a rate of 180 r / min for 20 min to obtain a pretreated material;

[0055] (4) extruding and granulating the pretreated material obtained in step (3);

[0056] (5) drying the pellets obtained in step (4) to reduce the moisture content to 13% to obtain a foaming precursor;

[0057] (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping; the starch-based foamed board comprises: a surface starch-based foamed board 1 and a bottom starch-based foamed board 3, both of which are prepared by the same method and have the same shape and structure.

[0058] (7) The sulfite is sodium pyrosulfite, and the dosage of sodium pyrosulfite is 5g / m 2 The thickness of the selected surface starch-based foam board and the bottom starch-based foam board is 8mm, SO 2The thickness of the gas slow-release layer is controlled to be 1 mm, and the fresh-keeping pad is made by hot pressing. According to the test, the fresh-keeping pad has a compressive strength of 38.1 Kpa, a rebound rate of 79.72%, and a 45-day biodegradability of 96.45% (the 45-day biodegradability of the reference material is 76.80%).

[0059] (8) Strawberries were selected as fruits, and a fresh-keeping box was selected as a sealed container. A saturated KCl solution was used in advance to adjust the humidity in the box to 86% (measured by a hygrometer). The strawberries were then placed in the fresh-keeping box, and a starch-based slow-release fresh-keeping mat was placed around the strawberries. Finally, the sealed fresh-keeping box was placed at room temperature for a fresh-keeping experiment. The results showed that the fresh-keeping mat could ensure that the strawberries would not spoil within 9 days, that is, the fresh-keeping period could reach 9 days.

[0060] During the preservation experiment, SO 2 The gas detector measures SO in the closed system every 24 hours. 2 The concentration is tested until the SO 2 When the concentration is 0, the detection is stopped to obtain the SO of the starch-based sustained-release fresh-keeping pad under this embodiment. 2 Sustained release curve Figure 3 As shown in the release curve, SO 2 In the early stage of release (0-6 days), the concentration is relatively high (10-40 μl / l), and in the late stage of release (after 6 days), the concentration is relatively low (1-10 μl / l). Under the conditions of low dose of preservative and low relative humidity, the "SO 2 The effect of "fast release + slow release". The shelf life of strawberries after picking is generally 1-2 days. The shelf life of existing fruit preservation pads under the same conditions is about 3-5 days, while the starch-based slow-release preservation pad has a final shelf life of 9 days at room temperature and 86% humidity, still showing a significant preservation effect.

[0061] Example 2

[0062] (1) Weighing materials: 81 wt% of hydroxypropyl corn starch, 8 wt% of polyvinyl alcohol, 5 wt% of glycerol, 3 wt% of water, 2 wt% of montmorillonite, and 1 wt% of dried peanut shell residue;

[0063] (2) placing the starch, polyvinyl alcohol, calcium carbonate, and grapefruit seed residue weighed in step (1) into a high-speed mixer and premixing at a rate of 120 r / min for 8 min at room temperature;

[0064] (3) adding the glycerol and water weighed in step (1) to the material obtained in step (2), and blending at 60° C. at a rate of 160 r / min for 22 min to obtain a pretreated material;

[0065] (4) extruding and granulating the pretreated material obtained in step (3);

[0066] (5) drying the pellets obtained in step (4) to reduce the moisture content to 15% to obtain a foaming precursor;

[0067] (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping; the starch-based foamed board comprises: a surface starch-based foamed board 1 and a bottom starch-based foamed board 3, both of which are prepared by the same method and have the same shape and structure.

[0068] (7) The sulfite is potassium pyrosulfite, and the dosage of potassium pyrosulfite is 15g / m 2 The thickness of the selected surface starch-based foam board and the bottom starch-based foam board is 10 mm, SO 2 The thickness of the gas slow-release layer is controlled to be 2 mm, and the fresh-keeping pad is made by hot pressing. According to the test, the fresh-keeping pad has a compressive strength of 39.9 Kpa, a rebound rate of 80.21%, and a 45-day biodegradation percentage of 97.28% (the 45-day biodegradation percentage of the reference material is 78.30%).

[0069] (8) Choose lychee as the fruit, use a fresh-keeping box as a sealed container, and use saturated K in advance. 2 SO 4 The solution was used to adjust the humidity in the box to 98% (measured by a hygrometer), and then the lychees were placed in the fresh-keeping box, and a starch-based slow-release fresh-keeping mat was placed at the bottom of the lychees. Finally, the sealed fresh-keeping box was placed at room temperature for a fresh-keeping experiment. The results showed that the fresh-keeping mat could ensure that the lychees would not spoil within 18 days, that is, the fresh-keeping period could reach 18 days.

[0070] During the preservation experiment, SO 2 The gas detector measures SO in the closed system every 24 hours. 2 The concentration is tested until the SO 2 When the concentration is 0, the detection is stopped to obtain the SO of the starch-based sustained-release fresh-keeping pad under this embodiment. 2 Sustained release curve Figure 4 As shown in the release curve, SO 2 The early release period (0-13 days) showed a relatively high concentration (30-120 μl / l) release, and the late release period (after 13 days) showed a relatively low concentration (1-30 μl / l) release, showing the "SO 2 The effect of "fast release + slow release". The shelf life of lychees after picking is generally 2-3 days. The shelf life of existing fruit preservation mats under the same conditions is about 5-7 days, while the starch-based slow-release preservation mat has a final shelf life of 18 days at room temperature and 98% humidity, showing a significant preservation effect.

[0071] Example 3

[0072] (1) Weighing materials: 82 wt% of hydroxypropyl corn starch, 6 wt% of polyvinyl alcohol, 5 wt% of propylene glycol, 4 wt% of ethanol, 2 wt% of calcium carbonate, and 1 wt% of dried pomegranate peel residue;

[0073] (2) placing the starch, polyvinyl alcohol, calcium carbonate, and dried pomegranate peel residue weighed in step (1) into a high-speed mixer and premixing at a rate of 150 r / min for 7 min at room temperature;

[0074] (3) adding the glycerol and water weighed in step (1) to the material obtained in step (2), and blending at 62° C. at a rate of 120 r / min for 24 min to obtain a pretreated material;

[0075] (4) extruding and granulating the pretreated material obtained in step (3);

[0076] (5) drying the pellets obtained in step (4) to reduce the moisture content to 14% to obtain a foaming precursor;

[0077] (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping; the starch-based foamed board comprises: a surface starch-based foamed board 1 and a bottom starch-based foamed board 3, both of which are prepared by the same method and have the same shape and structure.

[0078] (7) The sulfite is sodium bisulfite, and the dosage of sodium bisulfite is 15g / m 2 The thickness of the selected surface starch-based foam board and the bottom starch-based foam board is 10 mm, SO 2 The thickness of the gas slow-release layer is controlled to be 3mm, and the fresh-keeping pad is made by hot pressing. According to the test, the fresh-keeping pad has a compressive strength of 42.3Kpa, a rebound rate of 81.36%, and a 45-day biodegradation percentage of 97.37% (the 45-day biodegradation percentage of the reference material is 78.90%).

[0079] (8) Choose grapes as fruits, use fresh-keeping boxes as airtight containers, and use saturated Na 2 SO 4 The solution was used to adjust the humidity in the box to 93% (measured by a hygrometer), and then the grapes were placed in the fresh-keeping box, and starch-based slow-release fresh-keeping mats were placed around the grapes. Finally, the sealed fresh-keeping box was placed at room temperature for a fresh-keeping experiment. The results showed that the fresh-keeping mat could ensure that the grapes would not rot within 30 days, that is, the fresh-keeping period could reach 30 days.

[0080] During the preservation experiment, SO 2 The gas detector measures SO in the closed system every 24 hours.2 The concentration is tested until the SO 2 When the concentration is 0, the detection is stopped to obtain the SO of the starch-based sustained-release fresh-keeping pad under this embodiment. 2 Sustained release curve Figure 5 As shown in the release curve, SO 2 The early release period (0-12 days) showed a relatively high concentration (30-150 μl / l) release, and the late release period (after 12 days) showed a relatively low concentration (1-30 μl / l) release, showing the "SO 2 The effect of "fast release + slow release". The shelf life of grapes after picking is generally 2-7 days. The shelf life of existing fruit preservation pads under the same conditions is about 10-13 days, while the starch-based slow-release preservation pad has a final shelf life of 30 days at room temperature and 93% humidity, showing a very significant preservation effect.

[0081] Example 4

[0082] (1) Weighing materials: 81 wt% of hydroxypropyl corn starch, 6 wt% of polyvinyl alcohol, 5 wt% of water, 4 wt% of propylene glycol, 2 wt% of diatomaceous earth, and 2 wt% of dried pomegranate peel residue;

[0083] (2) placing the starch, polyvinyl alcohol, calcium carbonate, and dried pomegranate peel residue weighed in step (1) into a high-speed mixer and premixing at a rate of 150 r / min for 8 min at room temperature;

[0084] (3) adding the glycerol and water weighed in step (1) to the material obtained in step (2), and blending at 58° C. at a rate of 150 r / min for 23 min to obtain a pretreated material;

[0085] (4) extruding and granulating the pretreated material obtained in step (3);

[0086] (5) drying the pellets obtained in step (4) to reduce the moisture content to 13%-15%, thereby obtaining a foaming precursor;

[0087] (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping; the starch-based foamed board comprises: a surface starch-based foamed board 1 and a bottom starch-based foamed board 3, both of which are prepared by the same method and have the same shape and structure.

[0088] (7) The sulfite is sodium pyrosulfite, and the amount of sodium pyrosulfite is 25g / m 2 The thickness of the selected surface starch-based foam board and the bottom starch-based foam board is 12mm, SO 2The thickness of the gas slow-release layer is controlled to be 4 mm, and the fresh-keeping pad is made by hot pressing. According to the test, the fresh-keeping pad has a compressive strength of 54.2 Kpa, a rebound rate of 84.72%, and a 45-day biodegradation percentage of 95.20% (the 45-day biodegradation percentage of the reference material is 75.40%).

[0089] (8) Choose grapes as fruits, use fresh-keeping boxes as airtight containers, and use saturated Na 2 SO 4 The solution was used to adjust the humidity in the box to 93% (measured by a hygrometer), and then the grapes were placed in the fresh-keeping box, and a starch-based slow-release fresh-keeping mat was placed at the bottom of the grapes. Finally, the sealed fresh-keeping box was placed at room temperature for a fresh-keeping experiment. The results showed that the fresh-keeping mat could ensure that the grapes would not rot within 40 days, that is, the fresh-keeping period could reach 40 days.

[0090] During the preservation experiment, SO 2 The gas detector measures SO in the closed system every 24 hours. 2 The concentration is tested until the SO 2 When the concentration is 0, the detection is stopped to obtain the SO of the starch-based sustained-release fresh-keeping pad under this embodiment. 2 Sustained release curve Figure 6 As shown in the release curve, SO 2 The early release period (0-20 days) showed a relatively high concentration (50-400 μl / l) release, and the late release period (after 20 days) showed a relatively low concentration (1-50 μl / l) release, showing the "SO 2 The effect of "fast release + slow release". The shelf life of grapes after picking is generally 2-7 days. The shelf life of existing fruit preservation pads under the same conditions is about 15-18 days, while the starch-based slow-release preservation pad has a final shelf life of 40 days at room temperature and 93% humidity, showing a very significant preservation effect.

[0091] Example 5

[0092] In order to prove that the starch-based sustained-release fresh-keeping pad material of the invention has antibacterial properties that ordinary fresh-keeping pad materials on the market do not have (all without adding preservatives), the fresh-keeping pads in Examples 1, 2, 3, and 4 are now used without adding preservatives. Two common fruit fresh-keeping pads on the market (without preservatives added) are purchased, and the total number of mold colonies in the environment in which they are placed is measured using the natural sedimentation method to measure the antibacterial properties of the fresh-keeping pad material itself. The two commercially available fresh-keeping pads were purchased from Miyuan New Materials Technology Co., Ltd., using food PE film / non-woven fabric film materials, and super absorbent resins are made into absorbent pads for packaging. The excellent water absorption properties of super absorbent resins are combined with the moisture permeability of non-woven fabrics to achieve the purpose of water absorption. At the same time, preservatives can be added to the pads, and the barrier properties of the film materials can be used to delay SO2 The two fresh-keeping pads are made of PE film and non-woven fabric film, respectively, with a size of 155mm×95mm. The specific antibacterial experimental operation steps are as follows: open the prepared Bengal red culture medium plate and place it on a saturated Na 2 SO 4 After the solution is humidified (93%), the plate is placed in a fresh-keeping box for 30 minutes for sampling. After sampling, the plate is collected and placed in a mold incubator (25°C) for 72 hours. Finally, the mold colonies on the plate are counted. Five parallels are set under each experimental condition, and the final result is the average. The total mold colony count (y) is calculated as follows:

[0093]

[0094] Among them, A is the number of mold colonies on the plate; S is the plate area (m 2 );t is the exposure time of the plate (min).

[0095] Table 1 Antibacterial performance test of different fresh-keeping pads (without preservatives added)

[0096]

[0097]

[0098] From the experimental data of the blank group in Table 1, it can be seen that under high humidity, the total number of mold colonies in the closed environment showed a natural upward trend (210→236), but the increase was slow; while in Examples 1 to 4 of the starch-based foamed board with antibacterial fiber added, the total number of mold colonies showed an obvious downward trend over time (183→131, 157→105.157→105, 131→52), showing good antibacterial performance. From the antibacterial experimental data of the two commercially available fresh-keeping mats (183→262), it can be seen that the fresh-keeping mats showed antibacterial performance in a short period of time, which may be due to the water absorption effect of the fresh-keeping mats, which caused the relative humidity in the environment to decrease, causing the mold growth environment to change, and then causing the mold growth rate to slow down; in the subsequent period, the number of mold colonies increased significantly and showed a trend of exceeding the blank control group, which may be that the fresh-keeping mat itself acted as a medium for mold growth, resulting in aggravated mold growth. By comparing the entire antibacterial experiment, it can be concluded that the starch-based fresh-keeping pad prepared in the embodiment has better solved the disadvantage that the traditional fresh-keeping pad (without adding preservatives) promotes the growth of microorganisms in a high humidity environment. In the above analysis, "→" means that the change trend has not changed in the middle, and it is only in one direction of rising / falling.

[0099] Example 6

[0100] The fresh-keeping pads in Examples 1, 2, 3, and 4 and the two fresh-keeping pads purchased in Example 5 were used to 4 different amounts of sodium metabisulfite on the purchased Kyoho grapes that had been previously saturated with sodium 2 SO 4 The solution was used to adjust the humidity (93%) in a sealed fresh-keeping box for preservation, and a blank control experiment was conducted. The actual preservation effect is shown in Table 2.

[0101] Table 2 Test on the preservation effect of different fresh-keeping pads on Kyoho grapes

[0102]

[0103] As can be seen from Table 2, the storage time of Kyoho grapes under normal temperature and high humidity is about 3 days. Without using preservatives, it can be seen that the preservation effects of the commercially available fresh-keeping pad and the starch-based sustained-release fresh-keeping pad in the embodiment are almost the same, and even the fresh-keeping pad using a non-woven film (commercially available fresh-keeping pad 2) has a preservation effect that is 1 day longer than that of Examples 1 and 2. As the amount of preservative used increases, the fresh-keeping effect of the commercially available fresh-keeping pad gradually declines compared to the starch-based sustained-release fresh-keeping pad in the embodiment. When the amount of preservative used is 25g / m 2 In the experimental group, the preservation effect in the embodiment is significant. Due to the commercially available preservation pad group, the preservation time of the preservation pad in Example 4 is almost twice that of the commercially available preservation pad. In general, the preservation effect of the commercially available preservation pad is maintained by its own good water absorption effect, but the preservation effect of water absorption is only effective for a very short time; when the preservative is added, the commercially available preservation pad cannot achieve the ideal sustained release effect, that is, "fast release + slow sustained release". For example, the commercially available preservation pad 1 uses PE film (strong barrier properties) and can only achieve a slow sustained release effect, and the commercially available preservation pad 2 uses non-woven fabric film (poor barrier properties) and can only achieve a fast release effect; while the starch-based sustained-release preservation pad can achieve an ideal preservation effect by improving the material itself, which greatly increases the preservation time.

Claims

1. A sustained-release starch-based fruit fresh-keeping pad, characterized in that: The surface starch-based foam board, the bottom starch-based foam board and the middle SO2 gas slow-release layer are formed by hot pressing. The SO2 gas slow-release layer is filled with sulfite. According to the horizontal cross-sectional area of ​​the bottom starch-based foam board, the amount of sulfite is 5-25g / m 2 The surface starch-based foam board and the bottom starch-based foam board are made by foaming, punching, cutting and shaping the foaming precursor; The foaming precursor is prepared by pre-mixing starch, polyvinyl alcohol, a nucleating agent, and fibers, and then mixing with a plasticizer, a foaming agent, and water at 55-65° C. for 20-25 minutes, extruding and granulating the obtained pre-treated material, and drying until the moisture content is reduced to 13%-15%; The bottom starch-based foam board or the surface starch-based foam board is prepared by the following steps: (1) Weighing materials: (2) placing the starch, polyvinyl alcohol, nucleating agent, and fiber weighed in step (1) into a high-speed mixer and premixing at a rate of 100-200 r / min for 5-10 min at room temperature; (3) adding the plasticizer, foaming agent and water weighed in step (1) to the material obtained in step (2), and blending at 55-65° C. at a rate of 100-200 r / min for 20-25 min to obtain a pretreated material; (4) extruding and granulating the pretreated material obtained in step (3); (5) drying the pellets obtained in step (4) to reduce the moisture content to 13%-15%, thereby obtaining a foaming precursor; (6) The foaming precursor obtained in step (5) is foamed, punched, and cut through a wave-shaped die head to obtain a starch-based foamed board after shaping.

2. The sustained-release starch-based fruit fresh-keeping pad according to claim 1, characterized in that: When the fresh-keeping pad is subjected to hot pressing and forming operation, only the edges of the surface starch-based foaming board and the bottom starch-based foaming board are subjected to hot pressing; before hot pressing, the edges are subjected to water spraying treatment.

3. The sustained-release starch-based fruit fresh-keeping pad according to claim 1, characterized in that: The sulfite is one or more of sodium pyrosulfite, potassium pyrosulfite and sodium bisulfite.

4. The sustained-release starch-based fruit fresh-keeping pad according to claim 1, characterized in that: The thickness of the bottom starch-based foam board and the surface starch-based foam board is 8-12 mm; the thickness of the SO2 gas slow-release layer is 1-4 mm; the shape of the bottom starch-based foam board and the surface starch-based foam board is tile-shaped or flat.

5. The sustained-release starch-based fruit fresh-keeping pad according to claim 1, characterized in that: The starch is one or more of cassava starch, corn starch and potato starch or modified starch thereof; the modified starch is one or more of oxidized starch, esterified starch, cross-linked starch and hydroxypropylated starch; the plasticizer is one or more of water, glycerol and propylene glycol; the foaming agent is one or more of water, sodium bicarbonate and ethanol.

6. The sustained-release starch-based fruit fresh-keeping pad according to claim 1, characterized in that: The nucleating agent is one or more of diatomaceous earth, calcium carbonate and montmorillonite; the fiber is one or more of dry pomegranate peel residue, dry peanut shell residue and grapefruit seed residue.

7. The method for preparing the sustained-release starch-based fruit fresh-keeping pad according to any one of claims 1 to 6, characterized in that The steps include: 1) preparing a surface starch-based foamed board and a bottom starch-based foamed board: premixing starch, polyvinyl alcohol, a nucleating agent, and fibers, and then blending with a plasticizer, a foaming agent, and water at 55-65° C. for 20-25 min, extruding and granulating the obtained pretreated material, and drying until the moisture content is reduced to 13%-15% to obtain a foaming precursor, and foaming, punching, cutting, and shaping the foaming precursor to obtain a surface starch-based foamed board and a bottom starch-based foamed board; 2) According to the horizontal cross-sectional area of ​​the bottom starch-based foaming board, sulfite is evenly arranged on the bottom starch-based foaming board at 5-25g / m2, and the surface starch-based foaming board, the bottom starch-based foaming board and the middle layer of SO2 gas slow-release layer are hot-pressed to prepare a slow-release starch-based fruit preservation pad.

8. Use of the sustained-release starch-based fruit fresh-keeping pad according to any one of claims 1 to 6 in fruit fresh-keeping, characterized in that: The fruits are placed in a sealed container provided with the slow-release starch-based fruit fresh-keeping mat, and the slow-release starch-based fruit fresh-keeping mat is arranged at the bottom or around the container; the fruits are one or more of grapes, strawberries and lychees.

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