CN107856982B - Chinese chive fresh-keeping packaging film - Google Patents

Abstract

A fresh-keeping packaging film for leeks belongs to the field of film technology, and adopts the form of AA film + D film patch, that is, two pieces of A film form a fresh-keeping bag, a square hole is opened on one piece of A film, and then a square hole is pasted on the square hole. D film, the square hole is located at the root of the leek, and the D film is parallel to the leek; the D film patch accounts for 3.0-3.5% of the total area of the fresh-keeping packaging film; the A film is a fruit fresh-keeping green packaging material film with ethylene adsorption function , WVTR 10g/m ^{2 .day} , oxygen transmission rate 1300～ ^4600ml /day ^· m ² .day.atm, the water vapor transmission rate is 100‑300g/m ² .day. It can keep leeks fresh for 4 days.

Description

A kind of leek fresh-keeping packaging film

technical field

The invention relates to a fresh-keeping packaging film for chives, belonging to the technical field of films.

technical background

At present, low-temperature storage is a relatively easy preservation solution. When the entire logistics path flows according to the origin-transportation-supermarket-user, at the supermarket level, low-temperature preservation can be achieved; but if it is based on the origin-transportation-Xinfadi- Retailer wholesale-retail store-user is a logistics path, and it is difficult to achieve low temperature to the retailer level. Although the mechanical refrigeration method is a low-temperature preservation method that is being actively developed, it requires a large up-front cost investment. At present, this method has not yet been developed on the market and has not been widely used.

The effect of temperature on the preservation of leeks can be summed up in one sentence, that is, high temperature and low temperature are not conducive to the preservation of leeks, but in general, the effect of keeping leeks fresh in a low temperature environment (0-5°C) is good. Specifically, in a high temperature environment, leeks lose water seriously and are easy to wilt. The leaves are kneaded without moisture and the color gradually changes from green to yellow, and the stems have no hardness when kneaded; Conducive to the preservation of chives; in a low temperature environment (0-5 °C), the respiration of chives is inhibited, and there is basically no water loss, and the leaves kneading are more watery. Therefore, in the process of low-temperature preservation of chives, it is necessary to maintain a stable low temperature without causing chilling damage to prolong its storage period as much as possible ^[6] .

The low-temperature storage method is a kind of preservation method with relatively simple technical requirements and relatively common among various preservation methods.

According to Feng Shuangqing's research, leeks should be pre-cooled to 0 °C within 24 hours after harvesting, and then placed in an environment of 0-5 °C for low temperature preservation. There is no obvious difference from the one just put it in. I don’t think the effect is better. After harvesting leeks, put them in the environment of 15℃ for 1 day, and then put them in the environment of 0℃ for 7 days, and the commodity rate can reach 89%. Refer to The previous method, this fresh-keeping effect is also good; leeks are purchased at 15°C for 2 days, then kept at 20°C for 1 or 2 days, and then kept at any fresh-keeping temperature, the rot is very serious, which shows that this The method basically has a fresh-keeping effect of 0; in addition, adding ice to the leeks has a certain effect on reducing water loss and lowering the temperature, but it has no obvious effect on reducing the rot of the leeks ^[7] .

Modified atmosphere preservation is already the most commonly used, most advanced and highest input-output ratio of preservation methods in developed countries. At present, China is vigorously developing modified atmosphere storage, and modified atmosphere storage has sprung up in various places, but it is still far from good. meet the needs of society ^[4] .

This is the formula for the respiratory response of fruits and vegetables:

C ₆ H ₁₂ O ₆ +6H ₂ O+6O ₂ →6CO ₂ +12H ₂ O + heat + ethylene

We know that respiration increases the temperature inside the package, and that both ethylene gas and elevated ambient temperatures accelerate fruit and vegetable ripening. The principle of the controlled atmosphere preservation of leeks is that the ratio of O ₂ and CO ₂ in the fresh-keeping atmosphere changes, so as to achieve the purpose of inhibiting the respiration rate and reducing the respiration intensity of leeks, and then making the leeks higher during the storage time of the menu and keeping the freshness. Store its extension. Through modified atmosphere preservation, the respiration activity of chives will be significantly weakened, the loss of fresh weight will also be reduced, the speed of sensory quality deterioration will be reduced to the lowest speed, and the nutritional value of chives will not be affected. This advanced fruit and vegetable preservation method is non-toxic and non-polluting, and is currently the most advanced preservation technology at home and abroad ^[9] .

Artificial modified atmosphere and spontaneous modified atmosphere are two methods of modified atmosphere preservation. Let’s talk about artificial air conditioning first. The main principle is to use the mechanical refrigeration technology in low-temperature preservation to create a closed storage room. At the same time, the air conditioning equipment and refrigeration equipment are used together to keep the oxygen and temperature in the storage room low. state, and then maintain a suitable carbon dioxide concentration, and then regularly remove the gas in the storage warehouse that is not conducive to the preservation of leeks. ^[7] Through the above measures, the respiration intensity of chives can be effectively controlled, so as to achieve the ultimate goal of increasing the commodity rate per unit time and prolonging the shelf life. This fresh-keeping method actually comprehensively uses a variety of technologies such as reducing temperature, ventilation, reducing oxygen, and controlling carbon dioxide in a suitable range.

Next, let's take a look at spontaneous modified atmosphere preservation, which is a kind of decompression modified atmosphere preservation. Taking leeks as an example, the method is to place the leeks to be kept fresh in a single package of fresh-keeping bags, and if necessary, a vacuum method is used to reduce the air pressure in the package. The principle of preservation is that the pressure of the air in the package is greatly reduced, which greatly reduces the oxygen content in the air in the bag, and the breathing intensity of the leek is also weakened. Because of this, the process of breathing and synthesizing ethylene is inhibited. The quality of chives deteriorated.

Its advantages are that it does not produce any fresh-keeping gas, and at the same time, the investment and operating costs are low. Therefore, this method has been paid more and more attention, and it is also the focus of this research.

According to the research, under the control of other variables, the fresh-keeping effect of leeks with modified atmosphere fresh-keeping packaging is much better than that without use, which is reflected in the following aspects:

1. In terms of freshness, leeks that use modified atmosphere fresh-keeping packaging are much slower to fall in the same period of time than those that are not used;

2. In terms of sensory quality, the leaves that use the modified atmosphere fresh-keeping packaging are less yellow than those that are not used per unit time, the kneading moisture is more sufficient, and the stem hardness is higher.

According to the test results of Ma Huafeng, the fresh-keeping period of leeks packaged in polyethylene plastic bags with holes (8 holes with a diameter of 7 mm) is about 3 days under 20 °C, 4 to 5 days at 10 °C, and 0 °C. The preservation period of non-porous 0.025 mm thick polyethylene bag sealed packaging is 4 to 5 days at 20 °C, 8 to 9 days at 10 °C, and about 14 days at 0 °C ^[4] .

Finally, a fresh-keeping method to be introduced is the preservative dipping method. Taking chives as an example, the method is a chemical method that uses chemical agents to treat the surface of chives to achieve a fresh-keeping effect. At present, the preservatives used for the preservation of fruits and vegetables are generally divided into two types: antiseptic fungicides and growth inhibitors.

Although the two preservatives are both preservatives for dipping, their preservation mechanisms are different. Taking chives as an example, the main reason for the deterioration of the sensory quality of chives or even corruption is microbial infection, and the most effective way to eliminate microbial diseases on the surface of fruits and vegetables is to use antiseptics. Because the microorganisms are different, the preservatives and fungicides used are also different. Usually, there are many kinds of harmful pathogenic bacteria on the surface of leeks. Therefore, in order to achieve the preservation effect, it is best to kill several pathogenic bacteria. of antiseptic fungicides. Growth inhibitor is to reduce the respiration intensity of leek, so that the synthesis of ethylene in leek is inhibited, so as to achieve the purpose of prolonging the shelf life of leek and improving the commodity rate per unit time.

At present, gibberellin and salicylic acid are two kinds of growth inhibitors commonly used in the fresh-keeping process of leeks. The following is a brief introduction. Gibberellin can reduce the degradation rate of chlorophyll in leeks and keep the green color longer; and can inhibit to a certain extent. The formation of anthocyanins will produce less yellow color, and at the same time, it can improve the hardness of leaves and stems, and the rate of ethylene synthesis will be reduced, thereby prolonging the shelf life of leeks. Salicylic acid can improve the ability of chives to resist microbial infection.

According to Zhang Yan's research, in the environment of 0 ℃, soak the roots with 100ppm GA ₃ for 15 minutes before storage, drain and wrap them in fire-absorbing paper, put them in plastic bags, and store them at 0 ℃, and they can be kept fresh for 47 days.

In addition, some researchers have also discovered many other preservation methods, which are shown as follows:

The film-coating preservation method is to coat the surface of fruits and vegetables with a layer of wax, oil or other materials. After the fruits and vegetables are dried, a colorless and transparent semi-permeable film will be formed. It is difficult for fruits and vegetables to penetrate water and other substances, so that the respiration intensity of fruits and vegetables decreases, the respiration rate decreases, and the evaporation of water in the fruits and vegetables decreases, finally achieving the purpose of prolonging the shelf life of fruits and vegetables and increasing the commodity rate. In addition, because a semi-permeable membrane is formed on the surface of fruits and vegetables, the surface of fruits and vegetables is bright in color and looks better from the outside, and the commodity value is also improved.

Zhang Enrang's team found that when using plastic wrap and controlling different temperatures (5, 10, 20, 25°C) and humidity (90%, normal humidity) to treat different varieties of chives for 7 days, the effect on the preservation effect of the three chives was observed. The experimental results showed that after 7 days of different fresh-keeping measures, the fresh-keeping effect of leek was significantly different between treatments. 5℃+normal humidity+polyethylene film and 10℃+90% humidity+polyethylene film had the best fresh-keeping effect, showing the lowest rot rate, normal color and flavor, and the least fresh weight loss; followed by 5℃+normal humidity+ Without polyethylene film, 10 ℃ + normal humidity + polyethylene film and 10 ℃ + 90% humidity + without polyethylene film; and at room temperature, whether covered with polyethylene film or not, leeks are rotten and deteriorated ^[5] .

Hou Jianshe's research found that the unsealed packaging of HDPE+CaC0 ₃ or HDPE+ molecular sieve and GBXZ plastic fresh-keeping bag under the storage condition of 2 ℃ can make the leek storage period reach 15d, the dehydration rate is about 1%, and almost no rot.

In terms of spontaneous modified atmosphere preservation, the main fresh-keeping bag material currently on the market is polyethylene (PE). As a fresh-keeping package for chives, the main disadvantage is that the water permeability is poor, and it is easy to condense, so that the chives are easily infected by bacteria and then easily rotted. Therefore, the storage period of leeks cannot be extended well at room temperature.

Active air-conditioning fresh-keeping has high requirements on the air tightness of the warehouse, and the warehouse needs to be equipped with a variety of equipment related to coordinated air conditioning at the same time, which requires high technology and automation to work together. It is an unfavorable factor limiting the large-scale application of active air conditioning.

According to research, polyethylene (PE) fresh-keeping bags are the main fresh-keeping packaging currently used in the market. PE fresh-keeping bags have high oxygen permeability, and the oxygen permeability of PE films with a thickness of about 10 microns can reach tens of thousands of ml/(m ² .atm.day), which can fully meet the needs of aerobic respiration of leeks in fresh-keeping bags. However, the moisture permeability of this film is very low, generally less than 20g/(m ² .day), and the moisture generated by the respiration of leeks cannot be quickly removed from the fresh-keeping bag, which is easy to cause moisture accumulation, resulting in RH exceeding 100%, and then the surface of the film appears Condensation phenomenon, this high humidity environment greatly increases the growth rate of bacteria, and leeks are easy to rot in this environment. Although PE plastic wrap can effectively prevent the water loss of leeks and maintain fresh weight and good properties, it also brings about the problem of rot. Therefore, we chose other plastic wraps with stronger functions to complete the experiment.

After investigation, it was found that functional films with moderate oxygen permeability and high water permeability can solve the problem of fresh-keeping leeks. The so-called functional fresh-keeping packaging is a fresh-keeping packaging material that adds a preservative or special processing to give a variety of functions on the basis of ordinary packaging. The measures currently taken are mainly to improve the water permeability and air permeability of the fresh-keeping film through physical means, and to improve its fresh-keeping ability.

SUMMARY OF THE INVENTION

The purpose of the present invention is to explore a new and effective fresh-keeping method at room temperature, prolong the fresh-keeping period of leeks at room temperature, and at the same time make leeks have good sensory quality. At the same time, it also solves the problem of condensation in the fresh-keeping bag.

First of all, in order to make the screening results accurate and reliable, before the formal screening, I set up an observation stage for preliminary screening and membrane function verification; in the observation stage, the author chose AE and DE series films as the observation objects; in the formal film selection stage, the author first did AE series functional film; Next, I did a screening experiment of two series of fresh-keeping bags, DV film and AA film + D film patch.

Each group of laboratory experiments is similar. Taking the AE series as an example, we first use our self-made high oxygen permeability functional film E and a high moisture permeability film A, according to the respiration rate at room temperature, according to our proposed multi-functional According to the integrated design theory, calculate the required areas of E and A two functional films, heat splicing into N groups of EA dual-function integrated fresh-keeping bags, and compare with the naked group to evaluate the fresh-keeping effect of the dual-function integrated fresh-keeping bags on chives.

In order to achieve the above object, the present invention proposes a method for integrating two functional thin films to solve this problem.

A fresh-keeping packaging film for leek of the present invention is characterized in that it adopts the form of AA film + D film patch, that is, two pieces of A film form a fresh-keeping bag, a square hole is opened on one piece of A film, and then a square hole is pasted on the square hole. Combined with the D film, the square hole is located at the root of the leek, and the D film is parallel to the leek. The D-film patch accounts for 3.0-3.5% of the total area of the fresh-keeping packaging film.

The A film is a green packaging material film for fruit preservation with ethylene adsorption function, WVTR 10g/m ² .day, and oxygen transmission rate 1300-4600ml/day·m ² ; its preparation can be found in Patent ZL2010105224424. The preparation method includes the following steps:

(1) Preparation of molecular sieve: at room temperature, add pseudo-boehmite to water, stir and mix evenly; then add a template agent (generally used, such as diethylamine, triethylamine, etc.) and silica sol, until the gel is formed; put the gel into a stainless steel autoclave, heat it to 200-250 ℃ in a closed manner, and perform constant temperature crystallization for 48 hours under its own pressure; after the crystallization is complete, wash with deionized water and dry; Roast at ~700°C for 4-6 hours to completely remove the template agent, and pulverize to a particle size of 5-100 microns to obtain the original molecular sieve powder, and the Si/Al (molar ratio) in the molecular sieve is 5-100. (2) Film preparation: 100-90 parts of polyethylene or polypropylene resin and 0.5-10 parts of molecular sieve are uniformly mixed, melt-blended on a twin-screw extruder, and then blown into a film.

D film is a highly moisture-permeable fresh-keeping film, and its composition is that the dry raw materials are composed of loofah fiber, natural cellulose powder, polyvinyl alcohol and EVA, and their mass ratio (dry weight) in the packaging material is 5-50% respectively , 40-85%, 0-5% (preferably 1-5%), 5-15%. Its oxygen transmission rate is 1×10 ⁴ -1×10 ⁵ ml/m ² .day.atm, and the water vapor transmission rate is 100-300g/m ² .day. The preparation can be found in ZL 2014102260959. Dissolve polyvinyl alcohol and EVA resin in water, the amount of water is 40-60 times of the total mass of polyvinyl alcohol and EVA resin, then add loofah fiber and natural cellulose powder, soak and swell for 10-24 hours, then use a ball mill or colloid Grinding for 5-10 hours, so that the suspension of loofah fibers and natural fibers with a fiber length of 1-10 microns is cast on a tape casting equipment to obtain a fully degradable cellulose-based packaging material with antibacterial properties.

Not any film can achieve the object of the present invention. In order to make the screening results accurate and reliable, an observation stage was set up before the formal screening for preliminary screening and membrane function verification; in the observation stage, AE, DE and other series of films were selected as the observation objects; in the formal film selection stage, AE and DV films were first made Screening experiments of two series of fresh-keeping bags with AA film + D film patch.

Each group of laboratory experiments is similar. First, according to the respiration rate at room temperature, according to the proposed multi-functional integrated design theory, calculate the required areas of the two functional films E and A, and thermally spliced into N groups of EA dual-functional integration The fresh-keeping bag was compared with the naked group to evaluate the fresh-keeping effect of the dual-function integrated fresh-keeping bag on chives.

Description of drawings

Fig. 1 is the appearance structure diagram after packing the leek of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the following examples.

Example 1

The OTR of the A membrane material is 1300ml/M2.day.atm, and the WVTR is 10g/M2.day.

Preparation of D membranes: WVTR 50g/M2.day, OTR 10 ⁴ ml/M2.day.atm.

AA+D film patch series (two large A films are first attached together to form a bag, then a hole is cut on a bag, and the D film is attached, the total area of the two A films is 500cm ² , the patch The area of D is 16cm ² ; the weight of leek is about 150g for one sample. The appearance structure is shown in Figure 1 .

AA film + 4×4cm D film patch is the most suitable modified atmosphere fresh-keeping bag for leek preservation, in which AA film accounts for 96.9% of the total area, and 4×4cm D film patch accounts for 3.1% of the total area.

The fresh-keeping package can make the shelf life of the chives at room temperature reach 4 days, the chives are still fresh after being kept fresh for 4 days, the leaves are not obviously yellowed, the kneading water is sufficient, the hardness of the stem is sufficient, and the water loss rate is lower than 12.8%.

In terms of sensory quality, due to its high moisture permeability, D film is stronger than that of A film, and the moisture inside all bags is more easily discharged. The leeks are not easy to cause water accumulation and rot, but they are also particularly easy to be fresh due to water loss. The weight decreased significantly, and the leaves as a whole were dry and dehydrated, the hardness of the stems on the sensory quality was reduced, and the leaves were kneaded without moisture. Although the A film also has high moisture permeability, it is still much worse than the D film, which will not cause the leeks to dehydrate. From the data point of view, the multifunctional film with A film is better in terms of maintaining fresh weight. Due to the high oxygen permeability and carbon dioxide permeability of E film, the carbon dioxide concentration in the fresh-keeping bag with E film is kept at a very low standard.

Other ratios of D film experimental table (headspace gas and weight loss)

Claims (1)

1. A Chinese chive preservative packaging film is characterized in that a form of AA film and D film paster is adopted, namely a preservative bag is composed of two films A, a square hole is formed in one film A, then a film D is attached to the square hole, the position of the square hole is located at the root position of the Chinese chive, and the film D is parallel to the Chinese chive; d, the film patch accounts for 3.0-3.5% of the total area of the preservative packaging film;

wherein the film A is a fruit fresh-keeping green packaging material film with the function of adsorbing ethylene, and WVTR 10g/m ²Day, oxygen transmission rate of 1300 to 4600ml/day m ²(ii) a The D film is a high moisture-permeable fresh-keeping film with the oxygen transmission rate of 1 multiplied by 10 ⁴-1×10 ⁵ml/m ²Day. atm, the water vapor transmission rate is 100-300g/m ².day；

The preparation method of the film A comprises the following steps:

(1) and preparing the molecular sieve: adding pseudo-boehmite into water at room temperature, and stirring and mixing uniformly; then adding template agents of diethylamine or triethylamine and silica sol until gel is formed; putting the gel into a stainless steel autoclave, heating to 200-250 ℃ in a sealed manner, and crystallizing for 48 hours at a constant temperature under the self pressure; after crystallization is completed, washing with deionized water and drying; finally, roasting for 4-6 hours at 500-700 ℃ to completely remove the template agent, and crushing to 5-100 micron particles to obtain raw powder of the molecular sieve, wherein the Si/Al molar ratio in the molecular sieve is 5-100;

(2) and preparing a film: uniformly mixing 100-90 parts of polyethylene or polypropylene resin and 0.5-10 parts of molecular sieve, then carrying out melt blending on a double-screw extruder, and blowing to form a film;

the film D is a high moisture-permeable fresh-keeping film, which comprises dry raw materials of loofah sponge fiber, natural cellulose powder, polyvinyl alcohol and EVA, and the mass ratios of the raw materials in the packaging material are respectively 5-50%, 40-85%, 0-5% and 5-15%; dissolving polyvinyl alcohol and EVA resin in water, wherein the amount of water is 40-60 times of the total mass of the polyvinyl alcohol and the EVA resin, then adding loofah sponge fiber and natural cellulose powder, soaking and swelling for 10-24 hours, then treating for 5-10 hours by using a ball mill or a colloid mill, so that the fiber length of the loofah sponge fiber and the natural fiber is 1-10 microns of suspension, and casting on casting molding equipment to obtain the cellulose-based packaging material with antibacterial property and complete degradation.

Images