High-temperature and high-humidity resistant and oil-resistant food preservation composite nanofilm and preparation method thereof

Abstract

The application belongs to the technical field of new materials of multilayer structure, and discloses a kind of high-temperature and high-humidity resistant oil-resistant food preservation composite nanometer membrane and preparation method thereof.The method comprises the following steps: (1) polylactic acid solution is electrospun to form electrospun fiber membrane; (2) on one side of the obtained electrospun membrane, antimicrobial A-containing konjac gum solution is electrostatically sprayed; (3) on the side where electrostatic spraying is completed, polylactic acid solution is electrospun again; (4) the outer side of the obtained product of step (3) is electrostatically sprayed with modified konjac gum and chitosan composite solution containing antimicrobial B.The food preservation composite nanometer membrane obtained by the application has excellent high-temperature and high-humidity resistance, and the tensile strength loss rate is less than 7% and the elongation at break loss rate is less than 11% under the conditions of 45 DEG C temperature and 95% humidity for 24 hours; meanwhile, it also has excellent antibacterial rate, and the antibacterial rate on escherichia coli can reach 99.9%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials of multi-layer structure, and relates to a food packaging material, in particular to a high-temperature and high-humidity resistant oil-resistant food preservation composite nanofilm and a preparation method thereof. BACKGROUND

[0002] Preserved food packaging materials are often used for food storage, transportation and preservation treatment, and their performance often plays a decisive role in the quality of food and is closely related to people's diet and health. Traditional metal and glass packaging materials are completely airtight and are good packaging materials, but they are not suitable for the preservation of fresh fruits and vegetables with respiratory function. Fresh fruits and vegetables, chilled meat and other physiological activities with respiratory function are urgent areas to be solved in the field of preservation, and there is strong demand in the food market. Therefore, the development of other packaging materials has always been one of the key research directions in this field.

[0003] Biobased packaging materials are a research hotspot in recent years, and they have the advantages of easy availability of raw materials, health and environmental protection, and easy preparation [1] However, existing biobased materials face the problem of a significant decrease in mechanical properties in high-temperature or high-humidity environments when preparing food packaging products, resulting in a low application value of packaging products prepared from biobased materials.

[0004] There have been many studies on high-temperature resistant products made of polymer materials, such as a large number of commercially available products in the field of building materials or medical applications. In the field of food packaging, researchers have also conducted related research. For example, CN115490965B discloses a kind of food packaging film that can be heated at high temperature and its production process. The packaging film is obtained by using a variety of high molecular materials as raw materials and adding heat-resistant agents, and has good heat resistance. However, the composition in this patent is relatively complex, and its heat resistance is measured by measuring the highest temperature without the leakage of related components. The influence of high temperature on mechanical strength is not investigated. In reality, due to weather changes, cross-border transportation or other reasons, the temperature may rise, which can easily affect the mechanical properties of the packaging material, making the packaging material easily damaged and causing the food to be exposed and deteriorated. Therefore, it is necessary to study packaging films whose mechanical properties are less affected by environmental factors such as temperature and humidity during use.

[0005] At present, according to the inventors' knowledge, there are relatively few studies in the field of food on how to make the mechanical strength of packaging films less affected by environmental factors. Only a small number of studies are limited to a small number of packaging materials, such as the development of high-temperature and high-humidity resistant edible protein films by [2] et al. However, the mechanical strength of the obtained product is low, and the application scenarios are limited.

[0006] Therefore, how to develop a packaging material with less affected mechanical strength under high temperature, high humidity and other environments by using other substrates as raw materials is urgently needed in the field.

[0007] [1]Zhu Y, Chen Q, Kong B, et al. Research Progress on Antibacterial Properties of Bio-based Nanocomposite Food Packaging Materials [J]. Chinese Journal of Food Science, 2024, 24(01): 466-474.

[0008] [2]Tu L, Zhao Q, Yue X. Development of High Temperature and High Humidity Resistant Edible Protein Film [J]. Hubei Agricultural Sciences, 2014, 53(22): 5497-5499. SUMMARY

[0009] In view of the defects of the prior art, the purpose of the present application is to provide a new material with a multi-layer structure and a preparation method thereof, which is used as a food packaging film and can still maintain good mechanical properties and good antibacterial effect under high temperature, high humidity or oil immersion environment.

[0010] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0011] A preparation method of a high-temperature and high-humidity resistant and oil-resistant food preservation composite nanofilm, the high-temperature and high-humidity resistant and oil-resistant food preservation composite nanofilm is a multi-layer structure, comprising a polylactic acid fiber film layer, a konjac gum antibacterial layer and a modified konjac gum and chitosan composite antibacterial layer; the preparation method comprises the following steps:

[0012] (1) electrospinning with a polylactic acid solution to form an electrospun fiber film as a first polylactic acid fiber film layer;

[0013] (2) electrostatic spraying with a konjac gum solution containing antibacterial substance A on one side of the electrospun film obtained in step (1) to form a konjac gum antibacterial layer;

[0014] (3) electrospinning with a polylactic acid solution on the side where the electrostatic spraying is completed based on the product obtained in step (2) to form a second polylactic acid fiber film layer;

[0015] (4) electrostatic spraying with a modified konjac gum and chitosan composite solution containing antibacterial substance B on the outer side of the product obtained in step (3) to form a modified konjac gum and chitosan composite antibacterial layer;

[0016] The modified konjac gum is obtained by acid hydrolysis with citric acid and then precipitating with ethanol, and then freeze-drying the precipitate;

[0017] The weight ratio of modified konjac gum to chitosan in the modified konjac gum and chitosan composite solution is 3-5:1;

[0018] The antibacterial A is a water extract of Zanthoxylum bungeanum Maxim leaves; the antibacterial B is a water extract of a mixture of Rosa rubus and grape seeds, and the weight ratio of the Rosa rubus and the grape seeds is 2:1.

[0019] In the electrospinning in steps (1) and (3), the weight ratio of the polylactic acid used is 0.8-1.2:0.8-1.2; in the electro-spraying in step (2), the weight of the konjac gum used is 0.2-0.4 times the weight of the polylactic acid used in step (1); in the electro-spraying in step (4), the total weight of the modified konjac gum and the chitosan used is 0.2-0.4 times the weight of the polylactic acid used in step (1).

[0020] Preferably, the modified konjac gum is prepared by the following method: adding konjac gum into a citric acid aqueous solution so that the weight fraction of the konjac gum is 10%, and the weight molar ratio of the konjac gum to the citric acid is 10 g:1.6 mmol; after stirring uniformly, reacting at 80℃ for 2 hours; then adding 2 times the volume of a 95% volume fraction ethanol aqueous solution, stirring uniformly, and standing to produce a precipitate, which is vacuum freeze-dried to obtain the modified konjac gum.

[0021] Preferably, the solvent in the polylactic acid solution is dichloromethane, and the weight fraction of the polylactic acid in the polylactic acid solution is 6%.

[0022] Preferably, the solvent in the konjac gum solution in step (2) is a mixed solvent of ethanol and acetic acid in a volume ratio of 5:4, and the weight fraction of the konjac gum in the konjac gum solution is 1%.

[0023] Preferably, in step (4), the solvent in the modified konjac gum and chitosan composite solution is a mixed solvent of ethanol and acetic acid in a volume ratio of 1:1, the weight fraction of the sum of the modified konjac gum and the chitosan is 1%, and the weight ratio of the modified konjac gum to the chitosan is 4:1.

[0024] Preferably, in the electrospinning in steps (1) and (3), the weight ratio of the polylactic acid used is 1:1; in the electro-spraying in step (2), the weight of the konjac gum used is 0.3 times the weight of the polylactic acid used in step (1); and in the electro-spraying in step (4), the weight of the konjac gum used on each side is 0.3 times the weight of the polylactic acid used in step (1).

[0025] Preferably, in the electrospinning in steps (1) and (3), the voltage is 15 kV, the temperature is 25℃, the receiving distance is 15 cm, and the pushing speed is 35 μL / min; and in the electro-spraying in steps (2) and (4), the voltage is 20 kV, the temperature is 25℃, the receiving distance is 15 cm, and the pushing speed is 50 μL / min.

[0026] Preferably, the preparation method of the Zanthoxylum bungeanum leaf water extract is as follows: Zanthoxylum bungeanum leaves are cut and 10 times the weight of water is added, and boiling extraction is performed for 2 hours, and the filtrate is obtained as a first filtrate; 10 times the weight of water is added to the residue, and boiling extraction is performed for 2 hours, and the filtrate is obtained as a second filtrate, and the first filtrate and the second filtrate are combined to obtain a combined filtrate; and the combined filtrate is dried by rotary evaporation to obtain the Zanthoxylum bungeanum leaf water extract.

[0027] Preferably, the weight of the antibacterial substance A is 2% of the weight of the konjac gum; and the weight of the antibacterial substance B is 2% of the total weight of the modified konjac gum and the chitosan.

[0028] The application further provides a high-temperature and high-humidity resistant oil-resistant food preservation composite nanofilm prepared by the above preparation method.

[0029] Advantages of the application

[0030] The food preservation composite nanofilm obtained by the application has excellent high-temperature and high-humidity resistance, and the loss rate of tensile strength is less than 7% and the loss rate of elongation at break is less than 11% under the conditions of 45 DEG C and 95% humidity for 24 hours; meanwhile, the food preservation composite nanofilm obtained by the application also has excellent antibacterial rate, and the antibacterial rate on Escherichia coli can reach 99.9% under the condition of 1x10 4 cfu / mL of bacterial concentration. DETAILED DESCRIPTION

[0031] It is necessary to point out here that the following examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application, and some non-essential improvements and adjustments made by skilled persons in the art according to the above application content still belong to the protection scope of the application.

[0032] The raw materials used in the following examples and comparative examples are as follows:

[0033] Polylactic acid: Beijing Yongkangleye Technology Development Co., Ltd., product number PLA86;

[0034] Konjac gum: Anhui Qianshun Biological Technology Co., Ltd., product number KJ-30;

[0035] Chitosan: Nanjing Deju Biological Technology Co., Ltd., product number 3224232;

[0036] Gelatin: Jiangsu Guangrui Biotechnology Co., Ltd., item No. 01;

[0037] Modified konjac gum: konjac gum was added into an aqueous solution of citric acid so that the weight fraction of konjac gum was 10%, and the weight molar ratio of konjac gum to citric acid was 10 g: 1.6 mmol; after stirring uniformly, reaction was carried out at 80℃ for 2 hours; then 2 times volume of 95% volume fraction aqueous ethanol solution was added, and after stirring uniformly, standing was carried out, and the precipitate was vacuum freeze-dried to obtain the modified konjac gum;

[0038] Water extract of Zanthoxylum bungeanum leaves: Zanthoxylum bungeanum leaves were cut and 10 times weight of water was added, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a first filtrate; 10 times weight of water was added to the residue, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a second filtrate, and the first filtrate and the second filtrate were combined to obtain a combined filtrate; the combined filtrate was rotary evaporated and dried to obtain the water extract of Zanthoxylum bungeanum leaves;

[0039] Water extract of Rosa rugosa Thunb.: Rosa rugosa Thunb. was cut and 10 times weight of water was added, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a first filtrate; 10 times weight of water was added to the residue, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a second filtrate, and the first filtrate and the second filtrate were combined to obtain a combined filtrate; the combined filtrate was rotary evaporated and dried to obtain the water extract of Rosa rugosa Thunb.;

[0040] Water extract of grape seeds: grape seeds were taken, 10 times weight of water was added, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a first filtrate; 10 times weight of water was added to the residue, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a second filtrate, and the first filtrate and the second filtrate were combined to obtain a combined filtrate; the combined filtrate was rotary evaporated and dried to obtain the water extract of grape seeds;

[0041] Water extract of a mixture of Rosa rugosa Thunb. and grape seeds: according to a weight ratio of 2:1, Rosa rugosa Thunb. was cut and mixed with grape seeds, 15 times weight of water was added, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a first filtrate; 15 times weight of water was added to the residue, and boiling extraction was carried out for 2 hours, and the filtrate was taken to obtain a second filtrate, and the first filtrate and the second filtrate were combined to obtain a combined filtrate; the combined filtrate was rotary evaporated and dried to obtain the water extract of the mixture of Rosa rugosa Thunb. and grape seeds.

[0042] Example 1

[0043] (1) Polylactic acid was dissolved in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospinning was carried out on the polylactic acid solution to form an electrospun fiber membrane as a first polylactic acid fiber membrane layer; during electrospinning, the voltage was 15 kV, the temperature was 25℃, the receiving distance was 15 cm, and the pushing speed was 35 μL / min;

[0044] (2) Collect the electrospun film obtained in step (1); dissolve the water extract of Zanthoxylum bungeanum Maxim leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum Maxim leaves being 2% of the weight of the konjac gum; electrostatically spray the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1) to form a konjac gum antibacterial layer; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; the weight of the konjac gum used in this step is 30% of the weight of the polylactic acid used in step (1);

[0045] (3) On the basis of the product obtained in step (2), electrospinning is performed on the side where the electrostatic spraying is completed according to the method of step (1) to form a second polylactic acid fiber film layer, and the weight ratio of the polylactic acid used in this step to the polylactic acid used in step (1) is 1:1;

[0046] (4) Collect the film obtained in step (3); dissolve the water extract of the mixture of Rosa odorata and grape seeds, modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of the modified konjac gum and chitosan being 4:1, the weight fraction of the sum of the modified konjac gum and chitosan being 1%, and the weight of the water extract of the mixture of Rosa odorata and grape seeds being 2% of the total weight of the modified konjac gum and chitosan; electrostatically spray the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3) to form a modified konjac gum-chitosan composite antibacterial layer; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; when electrostatically spraying the outer sides of both sides of step (3) in this step, the total weight of the modified konjac gum and chitosan used on each side is 30% of the weight of the polylactic acid used in step (1); after spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuum pumping to obtain a composite nanometer film.

[0047] Example 2

[0048] (1) Dissolve polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospun the polylactic acid solution to form an electrospun fiber film as a first polylactic acid fiber film layer; during electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 35 μL / min;

[0049] (2) collect the electrospun film obtained in step (1); dissolve the water extract of Zanthoxylum bungeanum Maxim leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum Maxim leaves being 2% of the weight of the konjac gum; electrostatically spray the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1) to form a konjac gum antibacterial layer; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; the weight of the konjac gum used in this step is 40% of the weight of the polylactic acid used in step (1);

[0050] (3) on the basis of the product obtained in step (2), electrospinning is performed on the side where the electrostatic spraying is completed according to the method of step (1) to form a second polylactic acid fiber film layer, and the weight ratio of the polylactic acid used in this step to the polylactic acid used in step (1) is 2:3;

[0051] (4) collect the film obtained in step (3); dissolve the water extract of the mixture of Rosa odorata and grape seeds, modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of the modified konjac gum and chitosan being 5:1, the weight fraction of the sum of the modified konjac gum and chitosan being 1%, and the weight of the water extract of the mixture of Rosa odorata and grape seeds being 2% of the total weight of the modified konjac gum and chitosan; electrostatically spray the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3) to form a modified konjac gum-chitosan composite antibacterial layer; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; when electrostatically spraying the outer sides of both sides of step (3) in this step, the total weight of the modified konjac gum and chitosan used on each side is 40% of the weight of the polylactic acid used in step (1); after spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuum pumping to obtain a composite nanometer film.

[0052] Example 3

[0053] (1) dissolve polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospun the polylactic acid solution to form an electrospun fiber film as a first polylactic acid fiber film layer; during electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 35 μL / min;

[0054] (2)collecting the electrospun film obtained in step (1); dissolving the water extract of Zanthoxylum bungeanum Maxim leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum Maxim leaves being 2% of the weight of the konjac gum; electrostatically spraying the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1) to form a konjac gum antibacterial layer; during the electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used in this step is 20% of the weight of the polylactic acid used in step (1);

[0055] (3) on the basis of the product obtained in step (2), electrospinning is performed on the side where the electrostatic spraying is completed according to the method of step (1) to form a second polylactic acid fiber film layer, and the weight ratio of the polylactic acid used in this step to the polylactic acid used in step (1) is 3:2;

[0056] (4) collecting the film obtained in step (3); dissolving the water extract of the mixture of Rosa rugosa and grape seeds, modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of the modified konjac gum and chitosan being 3:1, the weight fraction of the sum of the modified konjac gum and chitosan being 1%, and the weight of the water extract of the mixture of Rosa rugosa and grape seeds being 2% of the total weight of the modified konjac gum and chitosan; electrostatically spraying the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3) to form a modified konjac gum-chitosan composite antibacterial layer; during the electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; when electrostatically spraying the outer sides of both sides of step (3) in this step, the total weight of the modified konjac gum and chitosan used on each side is 20% of the weight of the polylactic acid used in step (1); after the spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuum pumping to obtain a composite nanometer film.

[0057] Comparative Example 1

[0058] Compared with Example 1, the main difference is that the modified konjac gum in step (4) is replaced by konjac gum, and the specific scheme is as follows:

[0059] (1) dissolving polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospinning the polylactic acid solution to form an electrospun fiber film; during the electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0060] (2) Collect the electrospun film obtained in step (1); dissolve the water extract of Zanthoxylum bungeanum Maxim leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum Maxim leaves being 2% of the weight of the konjac gum; electrostatically spray the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1); during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used in this step is 30% of the weight of the polylactic acid used in step (1);

[0061] (3) On the basis of the product obtained in step (2), electrospinning is performed on the side on which the electrostatic spraying is completed according to the method of step (1); the weight ratio of the polylactic acid used in this step to the polylactic acid used in step (1) is 1:1;

[0062] (4) Collect the film obtained in step (3); dissolve the water extract of the mixture of Rosa rugosa Thunb and Vitis vinifera L., konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of the konjac gum to the chitosan being 4:1, the weight fraction of the sum of the konjac gum and the chitosan being 1%, and the weight of the water extract of the mixture of Rosa rugosa Thunb and Vitis vinifera L. being 2% of the total weight of the modified konjac gum and the chitosan; electrostatically spray the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3); during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used for electrostatic spraying on each side of the outer sides of both sides of step (3) is 30% of the weight of the polylactic acid used in step (1); after the spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuum pumping to obtain a composite nanometer film.

[0063] Comparative Example 2

[0064] Compared with Example 1, the main difference is that the konjac gum in step (2) is replaced by modified konjac gum, and the specific scheme is as follows:

[0065] (1) Dissolve polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospun the polylactic acid solution to form an electrospun fiber film; during electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0066] (2)collecting the electrospun film obtained in step (1); dissolving the water extract of Zanthoxylum bungeanum leaves and modified konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of modified konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum leaves being 2% of the weight of the modified konjac gum; electrostatically spraying the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1); during electrostatic spraying, the voltage is 20 kV, the temperature is 25℃, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used in this step is 30% of the weight of the polylactic acid used in step (1);

[0067] (3) based on the product obtained in step (2), electrospinning is performed on the side where the electrostatic spraying is completed according to the method of step (1), and the weight ratio of polylactic acid used in this step to polylactic acid used in step (1) is 1:1;

[0068] (4) collecting the film obtained in step (3); dissolving the water extract of the mixture of Rosa rugosa and grape seeds, modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of modified konjac gum and chitosan being 4:1, the weight fraction of the sum of modified konjac gum and chitosan being 1%, and the weight of the water extract of the mixture of Rosa rugosa and grape seeds being 2% of the total weight of modified konjac gum and chitosan; electrostatically spraying the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3); during electrostatic spraying, the voltage is 20 kV, the temperature is 25℃, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the total weight of modified konjac gum and chitosan used on each side of the outer sides of step (3) during electrostatic spraying in this step is 30% of the weight of the polylactic acid used in step (1); after spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent by vacuum pumping, and a composite nanometer film is obtained.

[0069] Comparative Example 3

[0070] Compared with Example 1, the main difference is that the chitosan in step (4) is replaced by gelatin, and the specific scheme is as follows:

[0071] (1) dissolving polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospinning the polylactic acid solution to form an electrospun fiber film; during electrospinning, the voltage is 15 kV, the temperature is 25℃, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0072] (2)collecting the electrospun film obtained in step (1); dissolving the water extract of Zanthoxylum bungeanum Maxim leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of the konjac gum being 1%, and the weight of the water extract of Zanthoxylum bungeanum Maxim leaves being 2% of the weight of the konjac gum; electrostatically spraying the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1); during the electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used in this step is 30% of the weight of the polylactic acid used in step (1);

[0073] (3) based on the product obtained in step (2), electrospinning is performed on the side on which the electrostatic spraying is completed according to the method of step (1), and the weight ratio of the polylactic acid used in this step to the polylactic acid used in step (1) is 1:1;

[0074] (4) collecting the film obtained in step (3); dissolving the water extract of the mixture of Rosa rugosa Thunb and Vitis vinifera L seeds, modified konjac gum and gelatin in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of the modified konjac gum to the gelatin being 4:1, the weight fraction of the sum of the modified konjac gum and the gelatin being 1%, and the weight of the water extract of the mixture of Rosa rugosa Thunb and Vitis vinifera L seeds being 2% of the total weight of the modified konjac gum and the gelatin; electrostatically spraying the electrostatic spraying solution obtained in this step on the outer sides of both sides of step (3); during the electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the total weight of the modified konjac gum and the gelatin used on each side of the outer sides of step (3) during the electrostatic spraying in this step is 30% of the weight of the polylactic acid used in step (1); after the spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuumizing to obtain a composite nanometer film.

[0075] Comparative Example 4

[0076] Compared with Example 1, the difference is that in this comparative example, a composite film is prepared by alternately stacking polylactic acid electrospun films and modified konjac gum electrospun films, and the specific scheme is as follows:

[0077] (1) preparing a polylactic acid electrospun film: dissolving polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospinning the polylactic acid solution to form an electrospun fiber film; during the electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0078] (2) Preparation of modified konjac gum-chitosan electrospun film: electrospinning is performed on the obtained polylactic acid electrospun film to cover the polylactic acid electrospun film, specifically: modified konjac gum and chitosan (weight ratio of 4:1) are dissolved in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 to form a spinning solution, and the weight fraction of solute in the solution is 10%; during electrospinning, the voltage is 12 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0079] (3) The electrospinning operation of step (1) is repeated on the film obtained in step (2);

[0080] (4) The electrospinning operation of step (2) is repeated on the film obtained in step (3);

[0081] (5) The electrospinning operation of step (1) is repeated on the film obtained in step (4);

[0082] Thus, an electrospun composite film with a 5-layer structure is obtained, and the weight ratio of the total weight of konjac gum and chitosan to the weight of polylactic acid between different layers is 3:10.

[0083] Comparative Example 5

[0084] Compared with Example 1, the main difference is that the water extract of the ink red rose and grape seed mixture is replaced by the water extract of the ink red rose, and the specific scheme is as follows:

[0085] (1) Polylactic acid is dissolved in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospinning is performed on the polylactic acid solution to form an electrospun fiber film; during electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 35 μL / min;

[0086] (2) The electrospun film obtained in step (1) is collected; the water extract of the prickly ash leaf and konjac gum is dissolved in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 to serve as an electrostatic spraying solution, and the weight fraction of konjac gum is 1%, and the weight of the water extract of the prickly ash leaf is 2% of the weight of the konjac gum; electrostatic spraying is performed on one side of the electrospun film obtained in step (1) using the electrostatic spraying solution obtained in this step; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the advancing speed is 50 μL / min; the weight of the konjac gum used in this step is 30% of the weight of the polylactic acid used in step (1);

[0087] (3) On the basis of the product obtained in step (2), electrospinning is performed on the side where electrostatic spraying is completed according to the method of step (1), and the weight ratio of polylactic acid used in this step to polylactic acid used in step (1) is 1:1;

[0088] (4) Collect the film obtained in step (3); dissolve the water extract of ink red rose and modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of modified konjac gum and chitosan is 4:1, the weight fraction of the sum of modified konjac gum and chitosan is 1%, and the weight of the water extract of ink red rose is 2% of the total weight of modified konjac gum and chitosan; electrostatically spray the electrostatic spraying solution obtained in this step on both outer sides of step (3); when electrostatically spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; the weight of the sum of modified konjac gum and chitosan used on each side in this step is 30% of the weight of polylactic acid used in step (1); after completing the spraying, place it in a special container to volatilize the residual organic solvent in the obtained film material by vacuum pumping to obtain a composite nanometer film.

[0089] Comparative Example 6

[0090] Compared with Example 1, the main difference is that the water extract of ink red rose and grape seed mixture is replaced by the water extract of grape seed, and the specific scheme is as follows:

[0091] (1) Dissolve polylactic acid in dichloromethane to prepare a polylactic acid solution with a polylactic acid weight fraction of 6%, and electrospun the polylactic acid solution to form an electrospun fiber film; when electrospinning, the voltage is 15 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 35 μL / min;

[0092] (2) Collect the electrospun film obtained in step (1); dissolve the water extract of Zanthoxylum bungeanum leaves and konjac gum in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 5:4 as an electrostatic spraying solution, the weight fraction of konjac gum is 1%, and the weight of the water extract of Zanthoxylum bungeanum leaves is 2% of the weight of konjac gum; electrostatically spray the electrostatic spraying solution obtained in this step on one side of the electrospun film obtained in step (1); when electrostatically spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; the weight of konjac gum used in this step is 30% of the weight of polylactic acid used in step (1);

[0093] (3) On the basis of the product obtained in step (2), electrospun on the side where the electrostatic spraying is completed according to the method of step (1), and the weight ratio of polylactic acid used in this step to polylactic acid used in step (1) is 1:1;

[0094] (4) collecting the film obtained in step (3); dissolving grape seed water extract, modified konjac gum and chitosan in a mixed solvent composed of ethanol and acetic acid in a volume ratio of 1:1 as an electrostatic spraying solution, the weight ratio of modified konjac gum and chitosan being 4:1, the weight fraction of the sum of modified konjac gum and chitosan being 1%, and the weight of grape seed water extract being 2% of the total weight of modified konjac gum and chitosan; electrostatically spraying the outer sides of both sides of step (3) with the electrostatic spraying solution obtained in this step; during electrostatic spraying, the voltage is 20 kV, the temperature is 25°C, the receiving distance is 15 cm, and the push speed is 50 μL / min; the weight of the sum of modified konjac gum and chitosan used for each side during electrostatic spraying of the outer sides of both sides of step (3) in this step is 30% of the weight of polylactic acid used in step (1); after spraying is completed, the obtained film material is placed in a special container to volatilize the residual organic solvent in the film material by vacuum pumping to obtain a composite nanometer film.

[0095] Experimental Example 1

[0096] The mechanical properties of Examples 1-3, Comparative Example 1, Comparative Example 3, and Comparative Example 4 were tested. The tests were performed under the following three conditions: (1) after the composite nanometer film was prepared, the test was performed at 25°C, which is recorded as "0 hour"; (2) after the composite nanometer film was placed at 45°C and 95% humidity for 24 hours, the test was performed, which is recorded as "high temperature and high humidity"; (3) after the composite nanometer film was immersed in edible peanut oil and then placed at 45°C and 95% humidity for 3 hours, the test was performed, which is recorded as "oil immersion".

[0097] Tensile strength test method: 3 sections of 3 cm of the composite nanometer film were taken, 5 points on each section were randomly selected to measure the thickness, the average value was calculated, which was the thickness, and the cross-sectional area was calculated; one end of a section of the composite nanometer film was fixed, the other end was fixed to an empty mineral water bottle with a clamp, so that the entire device was perpendicular to the ground, then water was slowly added to the mineral water bottle until the elongated strip broke, the weight of the mineral water was measured, the maximum load was calculated, and the tensile strength was calculated. The tensile strength calculation formula is: tensile strength = maximum load / cross-sectional area.

[0098] Elongation at break test method: a 2.00 cm section was cut from the composite nanometer film and fixed on a vernier caliper, and then stretched appropriately until it was about to break. The length after stretching was calculated using the vernier caliper. Elongation at break = (length after stretching - length before stretching) / length before stretching.

[0099] The experimental results are shown in Table 1.

[0100] Table 1

[0101]

[0102] As shown in Table 1, Examples 1-3 and Comparative Example 1, in step (4), when the konjac gum is replaced by modified konjac gum, the tensile strength and elongation at break decrease significantly, both in high temperature and humidity and in oil immersion. Meanwhile, as shown in Table 1, Examples 1-3 and Comparative Example 3, in step (4), when the chitosan is replaced by gelatin, the same situation occurs.

[0103] In addition, as shown in Comparative Example 4, when the composite film is prepared by alternately stacking the polylactic acid electrospun film and the modified konjac gum electrospun film, the mechanical strength and the maintenance of the mechanical strength are significantly worse than those of the composite nanofilm obtained by the present application, both at 0 time, in high temperature and humidity, and in oil immersion.

[0104] Therefore, it is crucial to use polylactic acid as the inner layer material of the composite nanofilm and to use modified konjac gum and chitosan to form the outer electrospun layer of the composite nanofilm of the present application for maintaining the mechanical strength.

[0105] Experimental Example 2

[0106] The antibacterial performance of Examples 1-3, Comparative Example 2, Comparative Example 5, and Comparative Example 6 was tested.

[0107] After the Escherichia coli was cultured to the late logarithmic growth phase, the culture solution was centrifuged, and the bacterial pellet was washed with PBS for 3 times. Then the bacterial pellet was resuspended in PBS, and the bacterial concentration was adjusted to 1x10 4 cfu / mL (calculated according to the plate count method) as the working solution. A composite nanofilm with a length and width of 1 cm was placed in the working solution and treated at 25°C, 150 rpm for 4 hours. Then the bacterial concentration was measured by the plate count method, and the antibacterial rate was calculated according to the bacterial concentration before and after treatment.

[0108] The experimental results are shown in Table 2.

[0109] Table 2

[0110]

[0111] As shown in Examples 1-3 and Comparative Example 2, when the konjac gum is replaced by modified konjac gum in step (2), the antibacterial property of the obtained composite nanofilm decreases significantly. The reason may be that the release of the water extract of Zanthoxylum bungeanum leaves is poorer for modified konjac gum than for konjac gum, which makes it difficult to form a good synergistic effect between the water extract of Zanthoxylum bungeanum leaves and the water extract of the outer antibacterial substance of the composite nanofilm, which is the mixture of the water extract of Rosa rubus and the water extract of Vitis vinifera. Meanwhile, as shown in Examples 1-3, Comparative Example 5 and Comparative Example 6, there is a synergistic effect between the water extracts of Rosa rubus and Vitis vinifera in terms of antibacterial property, and the antibacterial property of the composite nanofilm will decrease significantly after removing one of the water extracts.

[0112] Experimental Example 3

[0113] The composite nanofilm obtained in Example 1 was used to test the effect of packaging juicy peaches. Juicy peaches with consistent maturity, uniform size, and a weight of 180-200 g were taken, and the peaches were completely wrapped and packaged using the film obtained in Example 1, as the experimental group (10 peaches); peaches that were not packaged were used as the control group (10 peaches). The experimental group and the control group were stored at 4°C for 30 days, and the respiratory intensity, enzyme activity, sugar-acid ratio, hardness, and malondialdehyde were examined. The respiratory intensity of the peaches in the experimental group was significantly lower than that of the control group, and the respiratory peak of the control group was on the 14th day (69.21 mL·(kg·h -1 )), while the respiratory peak of the experimental group was delayed to the 26th day (45.15 mL·(kg·h -1 )); after 30 days, the polyphenol oxidase enzyme activity of the experimental group was 180 U·g -1 , which was significantly lower than the polyphenol oxidase enzyme activity of the control group (330 U·g -1 ); after 30 days, the sugar-acid ratio of the experimental group was 35.2, which was significantly higher than the sugar-acid ratio of the control group (22.3); after 30 days, the hardness of the peaches in the experimental group decreased by 15%, while the hardness of the peaches in the control group decreased by 46%; the malondialdehyde content of the experimental group was 0.12 μmol˙kg -1 , and the malondialdehyde content of the control group was 0.58 μmol˙kg -1 . It can be seen that the composite nanofilm obtained in Example 1 has a good fresh-keeping effect on juicy peaches. The experiment showed that the juicy peaches packaged with the composite nanofilm still had good commercial value when stored at +4°C for 30 days, and the storage method was significantly higher than the traditional 5-day cold storage period.

Claims

1. A method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm, characterized in that: The high temperature, high humidity and oil resistant food preservative composite nanofilm is a multilayer structure, comprising a polylactic acid fiber film layer, a konjac gum antibacterial layer, and a modified konjac gum chitosan composite antibacterial layer; the preparation method comprises the following steps: (1) electrospinning a polylactic acid solution to form an electrospun fiber membrane as a first polylactic acid fiber membrane layer; (2) electrostatically spraying a konjac glucomannan solution containing an antibiotic substance A on one side of the electrospun membrane obtained in step (1) to form a konjac glucomannan antibacterial layer; (3) Based on the product obtained in step (2), electrospinning is performed on the side where the electrostatic spraying is completed using a polylactic acid solution to form a second polylactic acid fiber film layer; (4) electrostatic spraying is carried out on the outside of step (3) gained product with modified konjac glucomannan and chitosan composite solution containing antibiotic B to form modified konjac glucomannan chitosan composite antibacterial layer; The modified konjac gum is obtained by acidolysis with citric acid, precipitation with ethanol, and freeze-drying the precipitate. In the composite solution of modified konjac gum and chitosan, the weight ratio of modified konjac gum to chitosan is 3 to 5:1; The antibacterial substance A is an aqueous extract of Zanthoxylum bungeanum leaves; the antibacterial substance B is an aqueous extract of a mixture of dark red roses and grape seeds, with the weight ratio of dark red roses to grape seeds being 2:1; When carrying out electrostatic spinning in step (1) and step (3), the weight ratio of polylactic acid used is 0.8~1.2:0.8~1.2; When step (2) carries out electrostatic spraying, the weight of used konjac glucomannan is 0.2~0.4 times of the weight of polylactic acid used in step (1); When step (4) carries out electrostatic spraying, the total weight of used modified konjac glucomannan and chitosan is 0.2~0.4 times of the weight of polylactic acid used in step (1).

2. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: The modified konjac glucomannan is prepared by the following method: adding konjac glucomannan to a citric acid aqueous solution so that the weight fraction of the konjac glucomannan is 10% and the weight molar ratio of the konjac glucomannan to the citric acid is 10g:1.6mmol; stirring evenly, reacting at 80°C for 2 hours; then adding 2 times the volume of a 95% ethanol aqueous solution, stirring evenly, standing to produce a precipitate, and vacuum freeze-drying the precipitate to obtain the modified konjac glucomannan.

3. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: The solvent in the polylactic acid solution is dichloromethane, and the weight fraction of polylactic acid in the polylactic acid solution is 6%.

4. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: The solvent of the konjac glucomannan solution in step (2) is a mixed solvent that ethanol and acetic acid mix according to a volume ratio of 5:4, and the weight fraction of konjac glucomannan in the konjac glucomannan solution is 1%.

5. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: In step (4), the solvent in the modified konjac gum and chitosan composite solution is a mixed solvent in which ethanol and acetic acid are mixed in a volume ratio of 1:1, the weight fraction of the sum of modified konjac gum and chitosan is 1%, and the weight ratio of modified konjac gum and chitosan is 4:

1.

6. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: When carrying out electrostatic spinning in step (1) and step (3), the weight ratio of polylactic acid used is 1:1; When step (2) carries out electrostatic spraying, the weight of konjac glucomannan used is 0.3 times the weight of polylactic acid used in step (1); When step (4) carries out electrostatic spraying, the weight of konjac glucomannan used on every side is 0.3 times the weight of polylactic acid used in step (1).

7. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 6, characterized in that: When electrospinning is performed in steps (1) and (3), the voltage is 15 kV, the temperature is 25° C., the receiving distance is 15 cm, and the propulsion speed is 35 μL / min; when electrostatic spraying is performed in steps (2) and (4), the voltage is 20 kV, the temperature is 25° C., the receiving distance is 15 cm, and the propulsion speed is 50 μL / min.

8. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: The preparation method of the water extract of Zanthoxylum bungeanum leaves is as follows: chopping the Zanthoxylum bungeanum leaves, adding 10 times the weight of water, boiling and extracting for 2 hours, and collecting the filtrate to obtain a primary filtrate; adding 10 times the weight of water to the filter residue, boiling and extracting for 2 hours, collecting the filtrate to obtain a secondary filtrate, combining the primary filtrate and the secondary filtrate to obtain a combined filtrate; and subjecting the combined filtrate to rotary evaporation and drying to obtain the obtained product. The preparation method of the water extract of the mixture of dark red rose and grape seed is as follows: chopping the dark red rose according to the weight ratio, mixing it with grape seeds, adding 15 times the weight of water, boiling and extracting for 2 hours, and collecting the filtrate to obtain a primary filtrate; adding 15 times the weight of water to the filter residue, boiling and extracting for 2 hours, and collecting the filtrate to obtain a secondary filtrate, combining the primary filtrate and the secondary filtrate to obtain a combined filtrate; and subjecting the combined filtrate to rotary evaporation and drying to obtain the obtained product.

9. The method for preparing a high temperature, high humidity and oil resistant food preservative composite nanofilm according to claim 1, characterized in that: The weight of the antibacterial substance A is 2% of the weight of the konjac gum; the weight of the antibacterial substance B is 2% of the total weight of the modified konjac gum and chitosan.

10. A high temperature, high humidity and oil resistant food preservation composite nanofilm, characterized in that: The food preservative composite nanofilm is prepared by the preparation method according to any one of claims 1 to 9.

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