阅读说明：本技术 一种新型保鲜卡及其制备方法 (Novel preservation card and preparation method thereof ) 是由 刘耀文 王玥 王毅豪 胡欣欣 程岚 陈俊冬 沈思蔚 谢娟娟 杨小 于 2020-11-30 设计创作，主要内容包括：本发明涉及一种新型保鲜卡及其制备方法,属于食品保鲜技术领域,制备方法包括以下步骤：以绿原酸提取液和柠檬烯为原料,配制保鲜溶液,再加入纤维素粉,搅拌均匀,制得粘稠状纤维素纺丝液,静电纺丝,制得纤维素电纺膜,烘干后制得保鲜活性基材层；将PVA和马铃薯淀粉混合后溶于水,加入丙三醇,在水浴条件下搅拌糊化,制得电纺液；将电纺液打印制膜于保鲜活性基材层的正反面,揭膜后制得由PVA/马铃薯淀粉复合膜包裹的保鲜卡；本发明的保鲜卡具有良好的阻隔性能,避免保鲜剂的快速挥发,延长保鲜时间,避免浪费。(The invention relates to a novel preservation card and a preparation method thereof, belonging to the technical field of food preservation, wherein the preparation method comprises the following steps: preparing a fresh-keeping solution by taking chlorogenic acid extracting solution and limonene as raw materials, adding cellulose powder, uniformly stirring to prepare a viscous cellulose spinning solution, carrying out electrostatic spinning to prepare a cellulose electrospinning film, and drying to prepare a fresh-keeping active substrate layer; mixing PVA and potato starch, dissolving in water, adding glycerol, stirring and gelatinizing under the condition of water bath to prepare electrospinning liquid; printing the electrospinning solution to form a film on the front surface and the back surface of the fresh-keeping active substrate layer, and uncovering the film to obtain a fresh-keeping card wrapped by a PVA/potato starch composite film; the preservative clamp disclosed by the invention has good barrier property, avoids quick volatilization of the preservative, prolongs the preservation time and avoids waste.)

1. A preparation method of a novel preservation card is characterized by comprising the following steps: the method comprises the following steps:

(1) preparing a fresh-keeping solution by taking chlorogenic acid extracting solution and limonene as raw materials, adding cellulose powder, uniformly stirring to prepare a viscous cellulose spinning solution, carrying out electrostatic spinning to prepare a cellulose electrospinning film, and drying to prepare a fresh-keeping active substrate layer;

(2) mixing PVA and potato starch, dissolving in water, adding glycerol, stirring and gelatinizing under the condition of water bath to prepare electrospinning liquid;

(3) and printing the electrospinning solution to form films on the front and back surfaces of the fresh-keeping active substrate layer, and uncovering the films to obtain the fresh-keeping card wrapped by the PVA/potato starch composite film.

2. The method of claim 1, wherein: in the step (1), the preparation method of the chlorogenic acid extracting solution comprises the following steps:

a, extracting a crude extract: drying and crushing honeysuckle, sieving, adding ethanol, performing ultrasonic extraction under the condition of constant-temperature water bath, performing suction filtration, centrifuging, and collecting supernatant to obtain chlorogenic acid crude extract;

b, purification: purifying with macroporous resin, loading onto column, passing the crude extract of chlorogenic acid through the column, eluting with anhydrous ethanol, collecting ethanol eluate, removing solvent from ethanol eluate, concentrating under reduced pressure to obtain paste, dissolving with anhydrous ethanol, and centrifuging to obtain supernatant as chlorogenic acid extract.

3. The method of claim 2, wherein: in the step A, the temperature of the thermostatic water bath is 55-65 ℃, the concentration of the ethanol is 60-80%, the ratio of the extraction material to the extraction liquid is 1:4-8, the pH value is 4-6, the ultrasonic frequency is 200-600W, the treatment time is 30-60min, and the extraction times are 2-5 times.

4. The method of claim 2, wherein: in the step B, the macroporous resin is DA-201 type macroporous resin, and the mass ratio of the absolute ethyl alcohol and the chlorogenic acid crude extract after decompression concentration is 1-2: 6.

5. The method of claim 1, wherein: in the step (1), the mass fraction of limonene in the fresh-keeping solution is 2-5%; the mass ratio of the cellulose powder to the fresh-keeping solution is 1: 8-10.

6. The method of claim 1, wherein: in the step (1), drying the cellulose electrospun membrane at 45-55 ℃ for 3-6 min.

7. The method of claim 1, wherein: in the step (2), the mass ratio of PVA to potato starch is 1-2: 1-2.

8. The method of claim 1, wherein: in the step (2), the mass fraction of PVA in the electrospinning liquid is 0.5-1.5%; the mass fraction of glycerol in the electrospinning liquid is 0.1-1%.

9. The method of claim 1, wherein: in the step (2), the water bath temperature is 83-90 ℃, and the stirring and pasting time is 20-30 min.

10. The novel freshness card produced by the production method according to any one of claims 1 to 9.

Technical Field

The invention belongs to the technical field of food preservation, and particularly relates to a novel preservation card and a preparation method thereof.

Background

In daily life, the rotting and the deterioration of food are a great problem which troubles people, so that not only is serious economic loss caused, but also the potential safety hazard of food is brought to consumers. The existing food preservation mainly comprises a plurality of methods of placing a drying agent or a deoxidizing agent in a packaging box, low-temperature storage, controlled atmosphere storage and chemical preservation, but the methods have certain defects, such as easy poisoning caused by mistaking for children, or in the transportation process, if a drying bag is damaged, the leakage of contents can cause food pollution and can not be eaten; low temperatures cause structural failure of some food products; the cost is high or chemical reagents are subjected to monomer migration and chemical residue to cause harm to human bodies. Therefore, it is necessary to find a safe and reliable preservation method.

At present, most of drying agents and preservatives directly adopt a glue film or laminating paper which is filled with silica gel mud or various powders or particles capable of adsorbing alcohol and various fresh-keeping deoxidizing and drying chemical reagents, and the drying agents and the preservatives are soaked or mechanically filled, and then are placed in packages to play roles in keeping fresh, drying, resisting oxidation and the like. However, the method has complex manufacturing process and poor effect, and the preservative packaging bag is easy to damage to pollute food and is easy to be eaten by children by mistake.

In conclusion, a novel preservation card with good barrier property, which can avoid the rapid volatilization of the preservative, prolong the preservation time and avoid the waste and a preparation method thereof need to be researched.

Disclosure of Invention

The invention aims to provide a novel preservation card and a preparation method thereof.

The technical scheme of the invention is that the novel preservation card and the preparation method thereof comprise the following steps:

(1) preparing a fresh-keeping solution by taking chlorogenic acid extracting solution and limonene as raw materials, adding cellulose powder, uniformly stirring to prepare a viscous cellulose spinning solution, carrying out electrostatic spinning to prepare a cellulose electrospinning film, and drying to prepare a fresh-keeping active substrate layer;

(2) mixing PVA and potato starch, dissolving in water, adding glycerol, stirring and gelatinizing under the condition of water bath to prepare electrospinning liquid;

(3) and printing the electrospinning solution to form films on the front and back surfaces of the fresh-keeping active substrate layer, and uncovering the films to obtain the fresh-keeping card wrapped by the PVA/potato starch composite film.

Preferably, in the step (1), the preparation method of the chlorogenic acid extracting solution comprises the following steps:

a, extracting a crude extract: drying and crushing honeysuckle, sieving, adding ethanol, performing ultrasonic extraction under the condition of constant-temperature water bath, performing suction filtration, centrifuging, and collecting supernatant to obtain chlorogenic acid crude extract;

b, purification: purifying with macroporous resin, loading onto column, passing the crude extract of chlorogenic acid through the column, eluting with anhydrous ethanol, collecting ethanol eluate, removing solvent from ethanol eluate, concentrating under reduced pressure to obtain paste, dissolving with anhydrous ethanol, and centrifuging to obtain supernatant as chlorogenic acid extract.

Preferably, in the step A, the temperature of the thermostatic water bath is 55-65 ℃, the concentration of the ethanol is 60-80%, the ratio of the extraction material to the extraction liquid is 1:4-8, the pH is 4-6, the frequency of the ultrasonic wave is 200-600W, the treatment time is 30-60min, and the extraction times are 2-5 times;

preferably, the temperature of the thermostatic waterbath is 60 ℃, the concentration of the ethanol is 60%, the ratio of the extraction material to the liquid is 1:8, the pH is 4, the ultrasonic frequency is 200W, the treatment time is 30min, and the extraction times are 2.

Preferably, in the step B, the macroporous resin is DA-201 type macroporous resin, the mass ratio of the anhydrous ethanol and the chlorogenic acid crude extract after the reduced pressure concentration is 1-2:6, and the mass ratio of the anhydrous ethanol and the chlorogenic acid crude extract after the reduced pressure concentration is 1: 6.

Preferably, in the step (1), the mass fraction of the limonene in the preservation solution is 2-5%; the mass ratio of the cellulose powder to the fresh-keeping solution is 1: 8-10.

Preferably, in the step (1), the cellulose electrospun membrane is dried for 3-6 minutes at the temperature of 45-55 ℃.

Preferably, in the step (2), the mass ratio of PVA to potato starch is 1-2: 1-2.

Preferably, in the step (2), the mass fraction of PVA in the electrospinning solution is 0.5-1.5%; the mass fraction of glycerol in the electrospinning liquid is 0.1-1%.

Preferably, in the step (2), the water bath temperature is 83-90 ℃, and the stirring and pasting time is 20-30 min.

Preferably, the novel preservation card prepared by the preparation method.

Honeysuckle flower, the dry flower bud of honeysuckle, is sweet in taste and cold in nature, and has the effects of clearing away heat and toxic materials, dispelling wind and dissipating heat. The honeysuckle active ingredients mainly comprise flavonoids, organic acids, volatile oil and triterpenes, wherein chlorogenic acid and isochlorogenic acid of the organic acids have obvious biological activity, and have the effects of resisting bacteria, oxidation, inflammation and virus, participating in human platelet aggregation and the generation of coagulation factors and the like. Therefore, the active ingredients of the organic acids are always important indexes for measuring the extraction efficiency of the honeysuckle. Chlorogenic acid is a phenylpropanoid substance synthesized by plants in the aerobic respiration process, is prepared by condensing caffeic acid and quinic acid, is widely distributed, and contains chlorogenic acid in food and Chinese medicinal materials such as eucommia bark, honeysuckle flower and coffee bean. Chlorogenic acid has multiple effects including antibiosis, antiphlogosis, antivirus, free radical scavenging, blood sugar reduction, blood fat reduction, liver protection, gallbladder benefiting and the like.

The plant extracts containing VC, flavonoids, phenols and the like have certain nitrite removing capability, the chlorogenic acid substances belong to phenolic compounds which are divided into 3-O-caffeoylquinic acid (chlorogenic acid), 4-O-caffeoylquinic acid, 5-O-caffeoylquinic acid, 3, 4-dicaffeoylquinic acid, 3, 5-dicaffeoylquinic acid (isochlorogenic acid A), 4, 5-dicaffeoylquinic acid, 3-,4-, 5-feruloylquinic acid and the like, and the extracts not only exist in plants of Caprifoliaceae, Eucommiaceae, Compositae and other medicinal and edible dual-purpose plants, but also have certain content in fruits, vegetables, tea and other food. The nitrosation inhibiting effect of chlorogenic acid substances in removing nitrite and blocking nitrosamine synthesis is gradually enhanced along with the increase of concentration, reaction time and temperature, and is reduced along with the increase of pH value.

The chlorogenic acid substance can destroy the cell wall and membrane structure of Escherichia coli in a short time, increase cell permeability, and cause cell electrolyte, enzyme, DNA and RNA to leak out, NPN permeates into the cell membrane wall, thereby affecting the stability of cell structure and gradually killing cell.

Limonene is a highly lipophilic cyclic monoterpene, which is the major component of citrus essential oils at about 68-98% w/w. Due to its antioxidant properties and aroma characteristics. Has the effects of inhibiting bacteria, relieving cough, eliminating phlegm, relieving asthma, resisting tumor, and dissolving gallstone; can be used as essence in the flavor industry.

Limonene is a plant essential oil, is also a natural harmless preservative with good effect, and can inhibit a plurality of bacteria and fungi. The D-limonene has an inhibiting effect on food spoilage bacteria such as escherichia coli and staphylococcus aureus. In the aspect of the bacteriostasis and sterilization mechanism, the limonene is considered to be accumulated on the surface of the microorganism, so that the integrity of the film is damaged and the proton power is reduced, and the bacteriostasis and sterilization effects are achieved.

The invention has the beneficial effects that:

1) the fresh-keeping card of the invention takes the water-absorbing material to absorb the fresh-keeping agent as the fresh-keeping active base layer, and the two surfaces of the base layer are covered with the thin films, thereby avoiding the direct contact between the fresh-keeping agent and food, keeping fresh, simultaneously considering safety and sanitation, having no chemical residue after use, low cost and wide application range.

2) The film has good barrier property, avoids quick volatilization of the preservative, prolongs the preservation time and avoids waste; the invention selects food-grade paper as a substrate layer, and utilizes the characteristics of good water absorption, safety and no toxicity; then, the starch-polyvinyl alcohol composite film is selected as a material to wrap the substrate layer, and the active ingredients are slowly released by utilizing the safe, nontoxic and good barrier sealing property of the starch-polyvinyl alcohol composite film.

3) The fresh-keeping card can be used for keeping fruits and vegetables, moon cakes, candies and the like fresh, and particularly keeping foods such as the moon cakes, the cakes and the like fresh.

Drawings

FIG. 1 shows the performance indexes of strawberry preservation;

FIG. 2 is a graph of sensory scores of strawberries;

FIG. 3 is a picture of the decay of the strawberry appearance.

Detailed Description

The technical solutions of the present invention are described in further detail below, but the scope of the present invention is not limited to the following.

The invention uses chlorogenic acid extract and limonene in honeysuckle as raw materials, prepares a solution with a certain concentration as a natural preservative, uses food-grade paper with strong water absorption as a preservation active substrate layer after being soaked, and uses a starch-PVA composite film with good safety, non-toxicity and barrier property to wrap the substrate layer to prepare the preservation card for food preservation.

The invention takes the perishable strawberries as an experimental object, firstly takes the rotten degree of the experimental strawberries as an index under the condition of the same treatment time, and is compared with the common fresh-keeping method in life: comparing the fresh-keeping effects of fresh-keeping by a fresh-keeping film and cold preservation, so that the honeysuckle chlorogenic acid-limonene natural fresh-keeping card is highlighted to have an excellent fresh-keeping effect; and then setting a test, preparing solutions according to different proportions of chlorogenic acid, and preparing the fresh-keeping card.

Content of research

Experimental materials and apparatus

TABLE 1 materials and reagents

TABLE 2 Experimental instrumentation

The invention uses ultrasonic wave to assist and extract chlorogenic acid:

(1) extracting a crude extract: 500g of honeysuckle is purchased, 5g of honeysuckle is accurately weighed, dried and crushed, and then is sieved by a 45-mesh sieve and then is put into a triangular flask, and ethanol is added according to a certain proportion to be used as an extraction solvent. Extracting in constant temperature water bath according to set ultrasonic power, filtering, centrifuging, and collecting supernatant to obtain chlorogenic acid crude extract.

(note: constant temperature water bath temperature is 60 ℃, extraction solvent is 60% ethanol, ratio of extraction material to liquid is 1:8, the solution is alkaline to make chlorogenic acid partially hydrolyzed, so pH is 4, ultrasonic frequency is 200W, processing is 30min, extraction is twice)

(2) And (3) purification: purifying with DA-201 type macroporous resin, loading onto column, eluting with anhydrous ethanol, collecting ethanol eluate, removing solvent from the extractive solution at 55 deg.C in vacuum rotary evaporator, concentrating under reduced pressure to obtain paste, dissolving with 10ml anhydrous ethanol, centrifuging, and collecting supernatant as chlorogenic acid extractive solution, wherein the mass ratio of anhydrous ethanol and chlorogenic acid crude extractive solution after concentration under reduced pressure is 1: 6.

(3) And (3) determination: and drawing a standard curve of chlorogenic acid. Diluting the chlorogenic acid extracting solution with absolute ethyl alcohol according to a certain proportion, and obtaining a sample solution to be detected after constant volume. And (3) taking absolute ethyl alcohol as a blank control, measuring the absorbance at the position of 330nm, and calculating the concentration of the sample liquid to be measured through a standard curve.

Preparing a honeysuckle chlorogenic acid-limonene preservation card:

preparing a fresh-keeping solution by taking chlorogenic acid extracting solution and limonene as raw materials, adding cellulose powder, uniformly stirring to prepare a viscous cellulose spinning solution, carrying out electrostatic spinning to prepare a cellulose electrospinning film, and drying to prepare a fresh-keeping active substrate layer. The mass fraction of limonene in the preservation solution is 2%; the mass ratio of the cellulose powder to the preservation solution is 1: 8. The fiber electro-spinning membrane is dried for 4 minutes at 50 ℃.

Mixing PVA powder and potato starch in proportion to prepare 150mL of solution, stirring for 30 minutes under the condition of water bath at 85 ℃ for gelatinization to prepare electrospinning liquid, wherein the mass fraction of PVA in the electrospinning liquid is 1%; the mass fraction of glycerol in the electrospinning liquid is 0.5%; and printing the electrospinning solution to form films on the front and back surfaces of the fresh-keeping active substrate layer, and uncovering the films to obtain the fresh-keeping card wrapped by the PVA/potato starch composite film.

Design of preservation experiment

Fresh strawberries were purchased, eight ripe, non-damaged, uniform fruits were selected and immediately brought back to the laboratory for experimentation.

Firstly, setting different experimental conditions for each group of experimental strawberries, namely a membrane-free group, a PVA group, a preservation card group and a PE group, recording the rotting degree of the strawberries under different storage conditions every two days, and comparing the preservation effects under different storage conditions;

secondly, chlorogenic acid solutions with different concentrations and potato starch and PVA with different proportions are prepared to influence the preservation effect of the strawberries at normal temperature, and the optimal proportion is explored.

The specific experimental scheme is as follows: preparing chlorogenic acid solution with concentration of 0%, 2%, 4% 10ml each, and preparing into fresh-keeping card by using a treatment group containing distilled water as control group with concentration of 3 parallel groups. The tested strawberries were randomly divided into 5 groups, 5 per experimental group, 3 replicates. The strawberry and the preservation card are respectively placed and stored in a normal-temperature ventilation environment, indexes such as rot rate, titratable acid and the like of fruits are measured on days 0, 2, 4, 6 and 8, each test is repeated for 3 times, and the results are averaged to evaluate the preservation effect.

Test index

(1) PVA/potato starch material Performance testing

Tensile strength: cutting the PVA/potato starch composite film into standard sample strips, performing a tensile test by using a PT-1198 type tensile tester, and calculating according to a formula (2-1) to obtain the tensile strength.

σ_t＝F_max/A₀ (2-1)

Young's modulus: the slope of the initial line of the stress-strain curve is obtained from the equation (2-2).

Impact strength: and (3) carrying out an impact test by using an SGN-500P type impact tester by using a cantilever beam method to obtain the impact strength.

Thickness: the thickness of the PET film was measured by a thickness meter by a five-point test method.

Barrier properties: the water vapor transmission rate and the oxygen transmission rate of the composite membrane are tested to characterize the barrier property of the composite membrane.

(2) Paper-based substrate Material Performance testing

Water absorption: the water absorption performance of the food-grade paper is tested by a Cobb water absorption tester and a Bob method.

Tensile strength: the paper is cut into standard sample strips, a PT-1198 type tension tester is used for carrying out a tension test, and the tensile strength is obtained by calculation according to a formula (2-3).

Thickness: the thickness of the paper was measured by a thickness gauge in a five-point method.

(3) Calculation of weight loss ratio

Weighing strawberries of each experimental group and the control group respectively before processing with honeysuckle green orthoacid, weighing the strawberries of each group every 3 days after processing and refrigerating, and calculating the weight loss rate by a weighing method. Calculated by the formula (2-4).

Weight loss rate (mass before treatment-mass after treatment)/mass before treatment x 100% (2-4)

(4) Titratable acids

Weighing 10 g of strawberry pulp, placing the strawberry pulp in a grinding body, mashing the strawberry pulp uniformly, and adding distilled water to a constant volume of 100 ml. And filtering the juice, taking 20ml of filtrate, adding 3-5 drops of phenolphthalein indicator, and titrating with 0.001mol/L NaOH solution until the solution is red and the color does not fade for 30 seconds, thus obtaining the titration end point. The amount of NaOH solution was recorded and the strawberry pulp titratable acid (%) was calculated according to equation (2-5). Each set of tests was repeated 3 times and the average was taken.

(5) Sensory evaluation

And evaluating the quality of the strawberries from three aspects of appearance, color and taste by adopting a grading standard. Every two days.

TABLE 3 strawberry sensory index evaluation criteria

Table 4: mechanical property of different proportion fresh-keeping card

Table 5: water vapor permeability of different proportion fresh-keeping card

In fig. 1a-e, the performance indexes of the strawberry in the preservation process are shown as follows: (a) weight loss rate, (b) titratable acid, (c) soluble solid, (d) Vc content, and (e) hardness. Fig. 1a depicts the weight loss of all samples after 13 days of the first storage, which is due to the fact that strawberries are rich in a large amount of water and increase in water loss due to transpiration, and after a large amount of water loss, the strawberries are withered and softened locally, and simultaneously, the hydrolysis of enzymes is intensified, and the aging of strawberry cells is accelerated, so that the commodity value is reduced. The water loss rate of the experimental group is obviously lower than that of the control group, when the 13 th day is reached, the weight loss of the strawberries is 14.85 percent, the weight loss of the freshness card group is only 10.39 percent, and the water retention performance is stronger than that of the film-free group. Figure 1e shows a graph of the change in strawberry firmness over time in a 13 day storage experiment. This is because the adherence of the cell wall, cell transfer material and turgor pressure are all affected by strawberry respiration. The hardness value of the strawberries is higher than the initial value at 3d because the strawberries are not completely mature during picking, and then the strawberries begin to decline, and the obvious decline trend of the experimental group is more delayed than that of the control group. The acidity of the strawberries is increased and then decreased due to the fact that the ripeness of the picked strawberries is 7-8, the titratable acid value is decreased integrally after the strawberries are fully ripe, the film-free group is most obviously decreased, the acidity of the experimental group is decreased slowly compared with that of the control group, particularly, the acidity of the strawberries of the fresh-keeping card is obviously higher than that of the film-free group, the acidity value is 0.59% at 13d and is 141.89% of that of the film-free group, and the titratable acid decrease rate of the strawberries can be effectively delayed. As can be seen from fig. 1d, after the storage time of the strawberries is prolonged, the Vc content measured by the non-membrane group and the experimental group is reduced as a whole, which is caused by the external oxidation, self-respiration and microbial infection and decay in the storage process of the strawberries. It is clear from the figure that the Vc of the strawberry in the crisper group is more slowly reduced than that in the non-film group, the Vc content of the strawberry in the crisper group at 13d is 48.39mg/100g, while the Vc content of the strawberry in the non-film group is only 35.22mg/100g, and the Vc consumption of the strawberry in the non-film group is obviously slower than that of the strawberry in the film group. Meanwhile, the PVA membrane group is reduced more slowly than a non-membrane group, because the PVA membrane group can isolate part of oxygen to avoid the consumption of strawberry Vc. In addition, the soluble solid content of the strawberries is an important index reflecting the sugar content of the strawberries and is also an important component for judging the nutritional value of the strawberries. Figure 1c is the effect of different treatment groups on soluble solids of strawberries. As can be seen from the figure, the soluble solid content of strawberries generally decreases with time, because strawberries need to maintain respiration by decomposing their own nutrients during storage, and the soluble solids are the main target to be consumed during respiration. The overall reduction of the soluble solids of the strawberries without any treatment added to the membrane-free group is most obvious, the soluble solids of the strawberries are only 4.2 at the 13 th day and 40% at the 1 st day, the reduction trend is obvious (P is less than 0.05), and the value of the soluble solids of the PVA membrane group is slightly higher than that of the soluble solids of the membrane-free group, because the PVA membrane group can isolate the strawberries from being infected and decayed by external microorganisms. In addition, the content of the crisper group at 13d reaches 8.4, which is 200.51% of that of the film-free group, and the graph shows that the whole curve of the crisper decreases slowly compared with the film-free group, which indicates that the crisper group can delay the consumption of soluble solids of the strawberries compared with the film-free group.

From tables 4 and 5, it can be seen that the composite film has good comprehensive performance, and when the composite film is primarily applied to strawberry preservation, sensory evaluation of strawberries shows that the sensory evaluation value of strawberries is reduced integrally along with the increase of storage time of strawberries. The no-film and PVA film groups showed a marked decline (P <0.05), gradually decayed from 5d, darkened, more specks and developed alcoholic smell, gradually lost commercial value after 7d and completely lost commercial value at 13 d. The descending trend of the preservation card and the PE is slower, the preservation card is integrally superior to other groups, the sense is good, and the preservation effect is obvious. As can be seen from FIG. 3, the decay of strawberries is obviously increased along with the storage time, and the treatment groups except the freshness card all have mould infection with different degrees after 7d, while the freshness card has softened spots on the surface, becomes dark in luster and has no obvious mould growth.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.