CN114410077B

CN114410077B - Nano composite active packaging preservative film based on esterification modification and preparation method and application thereof

Info

Publication number: CN114410077B
Application number: CN202210091339.1A
Authority: CN
Inventors: 李立; 赵美艳; 陶宁萍; 罗琦钧; 储玉婵
Original assignee: Shanghai Ocean University
Current assignee: Shanghai Ocean University
Priority date: 2022-01-26
Filing date: 2022-01-26
Publication date: 2023-06-16
Anticipated expiration: 2042-01-26
Also published as: CN114410077A

Abstract

The invention provides a nano composite active packaging preservative film based on esterification modification, a preparation method and application thereof, wherein the method comprises the steps of carrying out esterification reaction on organic acid and carboxymethyl nano cellulose, mixing dried modified carboxymethyl nano cellulose, dried poly (adipic acid)/butylene terephthalate and a chain extender, extruding and granulating; carrying out tape casting and film forming on the mixed particles of the modified carboxymethyl nanocellulose/poly (adipic acid)/butylene terephthalate resin, and carrying out transverse and longitudinal stretching; according to the invention, an esterification method is adopted to combine and modify carboxymethyl nanocellulose by using organic acid through ester bonds, and the modified carboxymethyl nanocellulose has antibacterial and antioxidant properties, and can inhibit microbial growth in food and nutritional oxidation loss of food; the poly adipic acid/butylene terephthalate degradable material is used as the base material of the packaging material, endows the film with antibacterial and antioxidant properties, is a novel environment-friendly, safe and reliable active packaging material, and can be applied to the field of food preservation.

Description

Nano composite active packaging preservative film based on esterification modification and preparation method and application thereof

Technical Field

The invention belongs to the technical field of preservative film materials, and particularly relates to a nano composite active packaging preservative film based on esterification modification, and a preparation method and application thereof.

Background

The use of suitable packaging materials and methods minimizes the loss of food and provides safe and hygienic food, which has been the focus of food packaging. Compared with the traditional package, the active package is a brand new packaging technology. The packaging material is used as a conveying carrier to release natural antibacterial, antioxidant, enzymes and other active substances to the surface of the food, and the inner environment of the food package is changed through the controlled release of the functional components, so that the propagation of microorganisms is effectively inhibited, the spoilage of the food caused by oxidization is prevented, the nutritional value and the sensory properties of the food are ensured, and the shelf life of the food is prolonged. Accordingly, various active packaging techniques have been developed to provide better hygienic and safe food products and to reduce packaging-related environmental pollution problems. Food packaging is typically composed of common petroleum-based plastics such as polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate. These petroleum derived plastic packaging materials have good processability, low cost, and excellent mechanical and barrier (gas and liquid) properties. However, petroleum derived polymeric materials are generally not recyclable and are poorly biodegradable, potentially causing significant waste disposal and environmental pollution problems.

In addition, the nano cellulose has been paid attention to in the field of material science because of its renewable nature, excellent mechanical properties and good biocompatibility.

Regarding active packaging, there may be a safety hazard to human health because the bacteriostatic agent may migrate into the food product. Thus, research into non-migratory and natural bacteriostats is a hotspot. The use principle of the non-migration type antibacterial agent is that the high molecular polymer is modified by physical, chemical and other means, and groups with the characteristics of antioxidation, antibiosis and the like are introduced, so that the excellent lasting preservation performance can be obtained on the premise that corresponding additives are not required to be added into foods, and meanwhile, the problems of use and safety of the additives are avoided. The natural antibacterial agent can reduce the use of chemical additives in food, and has antibacterial and health promoting effects. Organic acids in natural bacteriostat are very effective for food quality and safety. The organic acid modified nano composite packaging material has great potential in improving the quality, safety and stability of food as an innovative packaging and processing technology.

Disclosure of Invention

Aiming at the defects in the prior art, the primary purpose of the invention is to provide a preparation method of a nano composite active packaging preservative film based on esterification modification.

The secondary purpose of the invention is to provide the nano composite active packaging preservative film based on the esterification modification.

The final object of the invention is to provide the application of the nano composite active packaging preservative film based on the esterification modification.

To achieve the above primary object, the solution of the present invention is:

a preparation method of a nano-composite active packaging preservative film based on esterification modification comprises the following steps:

(1) Carrying out esterification reaction on organic acid and CMNC to obtain modified CMNC; mixing the dried modified CMNC, the dried biodegradable PBAT and the chain extender, and extruding and granulating in a double-screw extruder to obtain mixed particles of the modified CMNC/PBAT resin;

(2) And carrying out tape casting on the mixed particles of the modified CMNC/PBAT resin by a tape casting machine to form a film.

Preferably, the mass ratio of the organic acid to the CMNC is 1:1-1:5.

Preferably, the organic acid is selected from more than one of tartaric acid, citric acid, gallic acid and caffeic acid.

Preferably, in the step (1), when the organic acid and the CMNC are subjected to esterification reaction, the CMNC is heated and dissolved by dimethyl sulfoxide, then the organic acid and a catalyst are added, and the heating reaction is continued; cooling to room temperature after the reaction, adding ethanol until the precipitation is complete, freezing and centrifuging, adding ethanol, repeating the freezing and centrifuging, finally carrying out vacuum drying, and grinding to obtain the modified CMNC.

Preferably, the catalyst is p-toluenesulfonic acid, and the catalyst is added in an amount of 4wt% of CMNC.

Preferably, the temperature of the heating reaction is 90-110 ℃ and the time is 6-8h.

Preferably, the temperature of the refrigerated centrifugation is 3-5 ℃, the rotating speed is 7000-9000rpm, and the time is 10-30min.

Preferably, in step (1), the mass ratio of PBAT and modified CMNC is 9:1-7:3.

Preferably, in step (1), the drying temperature of the modified CMNC and PBAT is 50-70 ℃ and the drying time is 1-5h.

Preferably, in step (1), the chain extender is the Pasteur chain extender ADR-4388.

Preferably, in step (1), the temperatures of zones 1 to 7 in the twin-screw extruder are respectively: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and 165-175 ℃, the screw speed is 30-60rpm, preferably 40-50rpm.

Preferably, in the step (2), the temperatures of the 1 region to the 7 region in the casting machine are respectively: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and 165-175 ℃, the screw speed is 30-60rpm, preferably 40-50rpm.

To achieve the above secondary object, the solution of the present invention is:

a nano-composite active packaging preservative film based on esterification modification is prepared by the preparation method.

To achieve the final object, the solution of the present invention is:

the application of the nano-composite active packaging preservative film based on the esterification modification in the field of food preservation.

By adopting the scheme, the invention has the beneficial effects that:

the invention adopts an esterification method to modify CMNC through ester bond combination by using organic acid, and the modified CMNC has antibacterial and antioxidant properties of the organic acid and inhibits the growth of microorganisms in food and the nutritional oxidation loss of food; in addition, the PBAT degradable material is used as a base material of the packaging material for tape casting film forming, so that the esterified modified nano composite material active packaging preservative film endows the film with antibacterial and antioxidant properties, is a novel environment-friendly, safe and reliable active packaging material, and can be applied to the field of food preservation.

Drawings

Fig. 1 is a schematic diagram of the organic acid modified CMNC of the present invention.

Fig. 2 is a fourier infrared spectrum of an organic acid modified CMNC of the present invention.

FIG. 3 is an apparent view of straw mushrooms of different experimental groups according to the present invention.

FIG. 4 is a graph showing PPO changes of straw mushrooms of different experimental groups according to the present invention.

Fig. 5 is a graph showing the TPC variation of straw mushrooms of different experimental groups according to the present invention.

Fig. 6 is a graph showing the MDA change of straw mushrooms of different experimental groups according to the present invention.

FIG. 7 is a graph showing the variation of the hardness of straw mushrooms according to the present invention in different experimental groups.

Detailed Description

The invention provides an esterification-modification-based nano composite active packaging preservative film as well as a preparation method and application thereof. Tartaric acid in the organic acid is nontoxic and odorless, has antibacterial and antioxidant effects, and is widely applied to food industry. Tartaric acid is used for modifying CMNC, then the modified CMNC with antibacterial and antioxidant properties and PBAT are mixed according to different proportions and granulated, then an extrusion casting method is used for forming a film, and then a film is used for preserving fruit and vegetable foods, and experimental analysis of preservation effect is carried out.

< preparation method of Nano composite active packaging preservative film based on esterification modification >

The preparation method of the nano composite active packaging preservative film based on esterification modification comprises the following steps:

(1) Carrying out esterification reaction on organic acid and CMNC to obtain modified CMNC; mixing dry modified CMNC, dry PBAT (purchased from Zhuhaiwantong chemical Co., ltd., trade mark A400) and chain extender uniformly, extruding and granulating in an LSSHJ-20 twin-screw extruder to obtain mixed particles of modified CMNC/PBAT resin;

(2) And casting the mixed particles of the modified CMNC/PBAT resin into a cast sheet by an LSJ-20 casting machine (Shanghai science wound rubber plastic mechanical equipment Co., ltd.), and transversely and longitudinally stretching to obtain the nano composite active packaging preservative film (namely the modified CMNC/PBAT film) based on esterification modification.

Wherein, in the step (1), the mass ratio of the organic acid to the CMNC can be 1:1-1:5, preferably 1:1.

In the step (1), the organic acid is one or more selected from tartaric acid, citric acid, gallic acid and caffeic acid.

In the step (1), as shown in fig. 1, when the organic acid and the CMNC perform esterification reaction, the CMNC is heated and dissolved by dimethyl sulfoxide, then the organic acid and the catalyst are added, and the heating (heating by using an oil bath) reaction is continued; after the reaction is finished, standing to room temperature, adding 95% ethanol, completely precipitating the reacted CMNC, freeze centrifuging, dissolving with absolute ethanol, repeating the freeze centrifuging twice, removing impurities, finally performing vacuum drying at 50 ℃, and grinding to obtain the modified CMNC (i.e. esterified modified CMNC). After the organic acid is combined with the CMNC through ester bonds, the modified CMNC has antibacterial and antioxidant properties of the organic acid, and can inhibit the growth of microorganisms in food and the loss of nutrition and oxidization of food.

Specifically, the volume of dimethyl sulfoxide is 20 times the mass of CMNC. The catalyst was p-toluenesulfonic acid, and the catalyst was added in an amount of 4wt% of CMNC. The volume of 95% ethanol used for precipitation was 2 times the volume of dimethyl sulfoxide.

The temperature of the heating reaction may be 90-110 ℃, preferably 100 ℃; the time may be 6-8 hours, preferably 8 hours.

The temperature of the refrigerated centrifugation may be 3-5 ℃, preferably 4 ℃; the rotation speed may be 7000-9000rpm, preferably 8000rpm; the time may be 10-30min, preferably 20min.

In step (1), the mass ratio of PBAT and modified CMNC is 9:1-7:3.

In the step (1), the drying temperature of the modified CMNC/PBAT is 50-70 ℃ and the drying time is 1-5h.

In the step (1), the chain extender is the Pasteur chain extender ADR-4388, and the content of the chain extender is1 weight percent of the total weight.

In step (1), the temperatures of zones 1 to 7 in the twin-screw extruder may be: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and 165-175 ℃, preferably 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃, respectively; the screw speed is 30-60r/min, preferably 40-50rpm, more preferably 50rpm.

In the step (2), the temperature of the zone 1 to the zone 7 in the casting machine may be: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and 165-175 ℃, preferably 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃, respectively; the screw speed is 30-60r/min, preferably 40-50rpm, more preferably 50rpm.

In the step (2), the average thickness of the nano composite active packaging preservative film based on the esterification modification is 40-50 mu m.

< Nano composite active packaging preservative film based on esterification modification >

The nano composite active packaging preservative film based on the esterification modification (namely the esterification modified antibacterial and antioxidant degradable preservative film) is prepared by the preparation method.

< application of Nano composite active packaging preservative film based on esterification modification >

The nano-composite active packaging preservative film based on esterification modification can be applied to the field of food preservation.

The invention will be further illustrated with reference to specific examples.

Example 1:

the preparation method of the nano-composite active packaging preservative film based on the esterification modification comprises the following steps:

(1) Preparation of modified CMNC: heating and dissolving CMNC with dimethyl sulfoxide (the volume of the dimethyl sulfoxide is 20 times of the mass of the CMNC), then adding tartaric acid and p-toluenesulfonic acid (the addition amount of the p-toluenesulfonic acid is 4wt% of the CMNC), and heating and reacting for 8 hours at 100 ℃ by using an oil bath; after the reaction is finished, standing to room temperature, adding 95% ethanol, completely precipitating the CMNC after the reaction, freezing and centrifuging at 8000rpm at 4 ℃ for 20min, dissolving with absolute ethanol, repeating twice freezing and centrifuging, removing impurities, finally performing vacuum drying at 50 ℃, and grinding to obtain the modified CMNC.

(2) Melt blending: mixing vacuum dried 10 weight parts of modified CMNC, blast dried 90 weight parts of PBAT (purchased from Zhuhai general chemical Co., ltd., trade mark A400) and 1 weight part of chain extender ADR-4388 (the content is 1wt% of the total weight) uniformly, adding the mixed materials into a feeder of an LSSHJ-20 twin-screw extruder, feeding the materials into the twin-screw extruder through the feeder, melting and mixing uniformly through the screw, extruding and granulating, and drying to obtain the modified mixed particles of the CMNC/PBAT resin. Wherein, the processing temperature of the twin-screw extruder is 140-175 ℃, the screw rotating speed is 50rpm, and the specific heating temperature of each zone is as follows: the processing temperatures of zones 1 to 7 were 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃ and 170 ℃, respectively.

(3) And (3) casting and forming a film: and (3) carrying out melt extrusion on the mixed particles of the modified CMNC/PBAT resin through an LSJ-20 casting machine (Shanghai science wound rubber plastic mechanical equipment Co., ltd.) to form a casting sheet, and then carrying out transverse and longitudinal stretching to obtain the nano composite active packaging preservative film based on esterification modification, wherein the thickness of the film is 40 mu m. Wherein the processing temperatures of zones 1 to 7 in the casting machine are 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃ and 50rpm respectively. The performance results are shown in table 1.

Example 2:

(2) Melt blending: mixing 20 parts by weight of modified CMNC (vacuum dried), 80 parts by weight of PBAT (purchased from Zhuhai general chemical Co., ltd., trade mark A400) and 1 part by weight of chain extender ADR-4388 (the content is 1wt% of the total weight) uniformly, adding the mixed materials into a feeder of an LSSHJ-20 twin-screw extruder, feeding the materials into the twin-screw extruder through the feeder, melting and mixing uniformly through the screw, extruding and granulating, and drying to obtain the modified mixed particles of the CMNC/PBAT resin. Wherein, the processing temperature of the twin-screw extruder is 140-175 ℃, the screw rotating speed is 50rpm, and the specific heating temperature of each zone is as follows: the processing temperatures of zones 1 to 7 were 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃ and 170 ℃, respectively.

(3) And (3) casting and forming a film: and (3) carrying out melt extrusion on the mixed particles of the modified CMNC/PBAT resin by an LSJ-20 casting machine (Shanghai science wound rubber plastic mechanical equipment Co., ltd.) to form a casting sheet, and then carrying out transverse and longitudinal stretching to obtain the nano composite active packaging preservative film based on esterification modification, wherein the thickness of the film is 40 mu m. Wherein the processing temperatures of zones 1 to 7 in the casting machine are 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃ and 50rpm respectively. The performance results are shown in table 1.

Example 3:

(2) Melt blending: mixing vacuum dried 30 weight parts of modified CMNC, blast dried 70 weight parts of PBAT (purchased from Zhuhai general chemical Co., ltd., trade mark A400) and 1 weight part of chain extender ADR-4388 (the content is 1wt% of the total weight) uniformly, adding the mixed materials into a feeder of an LSSHJ-20 twin-screw extruder, feeding the materials into a twin-screw through the feeder, melting and mixing uniformly through the screw, extruding and granulating, and drying to obtain the modified mixed particles of the CMNC/PBAT resin. Wherein, the processing temperature of the twin-screw extruder is 140-175 ℃, the screw rotating speed is 50rpm, and the specific heating temperature of each zone is as follows: the processing temperatures of zones 1 to 7 were 140 ℃, 160 ℃, 170 ℃, 175 ℃, 170 ℃ and 170 ℃, respectively.

Comparative example 1:

100 parts by weight of PBAT (available from Zhuhai Wantong chemical Co., ltd., trade name A400, china) after the forced air drying was cast into a film, and the processing temperatures of zones 1 to 7 in the casting machine were 140℃and 160℃and 170℃and 175℃and 170℃and 170℃respectively, and the screw rotational speed was 50rpm. The performance results are shown in table 1.

Comparative example 2:

without modification of CMNC, 90 parts by weight of PBAT (available from the company of the chemical industry, ltd. In the open, bead sea, china, trade mark a 400) after forced air drying was then mixed with 10 parts by weight of unmodified CMNC dried under vacuum, the other being the same as in the foregoing example 1, wherein the contents of the respective components were in parts by weight. The performance results are shown in table 1.

Comparative example 3:

without modification of CMNC, 80 parts by weight of PBAT (available from the company of the chemical industry, ltd. In the open, bead sea, china, trade mark a 400) after forced air drying was then mixed with 20 parts by weight of unmodified CMNC dried under vacuum, the other being the same as in the foregoing example 1, wherein the contents of the respective components were in parts by weight. The performance results are shown in table 1.

Comparative example 4:

without modification of CMNC, 70 parts by weight of PBAT (available from the company of the chemical industry, ltd. In the open, bead sea, china, trade mark a 400) after forced air drying was then mixed with 30 parts by weight of unmodified CMNC dried under vacuum, the other being the same as in the foregoing example 1, wherein the contents of the respective components were in parts by weight. The performance results are shown in table 1.

The film is manufactured by an extrusion casting method, and then the mechanical property detection and the fresh-keeping effect inspection are carried out on the manufactured film.

<1> fourier infrared spectroscopy (FTIR) of tartaric acid-modified CMNC:

FTIR measurements were performed on the films in transmission mode at room temperature using a FTIR spectrometer (Nicolet iS10, thermo Fisher, USA). At 4cm ^-1 Is scanned 16 times. Each spectrum is 4000-400cm ^-1 Is acquired with the air spectrum as background correction.

Known 1755-1670cm ^-1 The stretching vibration peak is-c=o. As can be seen from FIG. 2, tartaric acid is present at 1741cm ^-1 And 1700cm ^-1 Characteristic peak at 1722cm for unmodified CMNC ^-1 Characteristic peak at 1722cm for modified CMNC ^-1 Has characteristic peak at 1700cm ^-1 New characteristic peaks appear. These results demonstrate that the tartrate-modified CMNC undergoes a chemical bond change, i.e., an ester bond is formed, during the tartaric acid-modified CMNC process.

<2> film index measurement:

(1) Oxygen Transmission Rate (OTR)

According to national standard GB/T1038-2000, cutting the sample into round shape by a special cutter, selecting a G2/132 differential pressure gas permeameter, setting the initial temperature of the test to 23 ℃, and starting to test the OTR of the sample.

(2) Mechanical strength

The Tensile Strength (TS) and Elongation At Break (EAB) of the biodegradable films were determined by a smart electronic tensile tester (Jinan XLW (EC)) using tensile testing at 25℃and 90% Relative Humidity (RH) according to ASTM-D882-12 (2012). A strip of film sample (15 mm. Times.100 mm) was placed between the jaws with an initial jaw distance of 60mm and an experimental speed of 50mm/min.

(3) Water Vapor Transmission Rate (WVTR)

The film water vapor permeability was measured by a WVTR tester (W-B-31E, labston, guangxi, china) according to the weighing method principle and GB/T1037, using a weight loss method at 38℃and 10% RH.

Table 1 results of film property tests of examples and comparative examples

As is clear from Table 1, as the amount of tartaric acid-CMNC added was increased, the mechanical strength of the composite film was increased and then decreased, and the PBAT composite film containing 10% of tartaric acid-CMNC had a maximum TS (11.25 MPa) and a maximum EAB (340.96%). In addition, the mechanical strength of the PBAT/CMNC nano composite film added with the unmodified CMNC is lower than that of the PBAT/tartaric acid-CMNC nano composite film containing the modified CMNC with the same content. The reason for this phenomenon may be that a smaller content of CMNC (< 10%) has an enhancing effect on the mechanical strength of PBAT, but as the content of CMNC increases, the compatibility of CMNC with PBAT decreases, so the mechanical strength of PBAT/CMNC nanocomposite film decreases. However, the esterified modified CMNC can enhance the compatibility of the CMNC and the PBAT, so that the mechanical strength of the PBAT/CMNC nano-composite film added with the modified CMNC is larger than that of the PBAT/tartaric acid-CMNC nano-composite film containing the unmodified CMNC in the same proportion.

As can be seen from table 1, the OTR of the nanocomposite film increased with the addition of CMNC and tartaric acid-CMNC, respectively, and the PBAT/tartaric acid-CMNC nanocomposite film with the modified CMNC was smaller than the OTR of the PBAT/CMNC nanocomposite film with the same content of unmodified CMNC. Regarding the film WVTR, since CMNC has hydrophilicity, but PBAT has poor hydrophilicity, as the addition amount of CMNC increases, the WVTR of the PBAT mixed film increases. And the hydroxyl number is reduced after the esterification modification of the CMNC, and the hydrophilicity is weakened, so that the PBAT/tartaric acid-CMNC nano-composite film with the modified CMNC is smaller than the WVTR of the PBAT/CMNC nano-composite film with the unmodified CMNC.

<3> application of straw mushroom preservation:

four experimental groups were set up, one in the bare group (no film package), one in the PBAT film package of comparative example 1, and one in the PBAT/tartaric acid-CMNC film of example 3 and the PBAT/CMNC film package of comparative example 4, each set up in three parallels. The freshly picked straw mushrooms in the market are evenly divided into 4 parts, each part has the weight of 500+/-2 g, the 4 parts are packaged in film bags, and then stored at the constant temperature of 16 ℃, and the straw mushrooms in each bag are taken for index measurement at intervals of 0h, 24h, 48h, 72h and 96 h.

(1) Appearance of straw mushroom

Fig. 3 is an apparent view of straw mushrooms during fresh keeping. With the extension of the storage time, the straw mushrooms are gradually autolyzed. The brown rot and strong ammonia odor of the exposed group of straw mushrooms appear after 24 hours of storage, the surfaces of the straw mushrooms shrink after 48 hours of storage, become sticky, the surfaces of the straw mushrooms are seriously mildewed, and the edible value of the straw mushrooms is completely lost. The straw mushrooms of the PBAT/tartaric acid-CMNC package group have the slowest autolysis speed. After 96 hours of storage, the appearance of the straw mushrooms in the PBAT/tartaric acid-CMNC package group is best compared with the other 3 groups of straw mushrooms.

(2) Polyphenol Oxidase (PPO) and Total Phenol Content (TPC)

PPO plays a key role in catalyzing the phenol hydroxylation process. PPO is the main cause of volvariella volvacea browning. Enzymatic browning is also related to the structure and integrity of cell membranes. FIG. 4 illustrates that PPO activity of straw mushrooms increases and decreases with increasing storage time. The PPO activity of the naked group straw mushrooms is highest before 96 hours (P < 0.05). The PPO activity of the straw mushrooms packaged by the PBAT/tartaric acid-CMNC film does not obviously increase before being stored for 72 hours. PPO activity was highest in all other groups at 24 h. Research results prove that the PBAT/tartaric acid-CMNC film can effectively inhibit PPO activity of straw mushrooms. As shown in fig. 5, TPC for the naked and packaged straw mushrooms was increased and then gradually decreased. TPC of straw mushrooms in the PBAT/tartaric acid-CMNC film group was highest before 96 h. These results can be explained by the fact that PPO can oxidize phenol. The PPO activity of straw mushrooms in the PBAT/tartaric acid-CMNC film group was low (FIG. 4). The accumulated phenolics exhibit antioxidant activity, which may help to reduce browning in mushrooms by maintaining film integrity.

(3) Malondialdehyde (MDA)

MDA is one of the major products of membrane lipid peroxidation, and its content is generally used as an indicator of lipid peroxidation, reflecting the extent of membrane lipid peroxidation. As can be seen from fig. 6, as the storage time of the straw mushrooms is prolonged, the MDA content of the straw mushrooms is gradually increased. During the storage and fresh-keeping period, the MDA content of the straw mushrooms in the PBAT/tartaric acid-CMNC film group is minimum, which indicates that the membrane lipid peroxidation degree of the straw mushroom cell membranes in the PBAT/tartaric acid-CMNC film group is minimum and the peroxidation damage to the straw mushroom cell membranes is minimum. This result is consistent with the appearance of the fruiting body of straw mushroom shown in figure 3. The PBAT/tartaric acid-CMNC film has the strongest autolysis inhibition effect on straw mushrooms.

(4) Hardness of

Hardness is related to the ripeness of fruits and vegetables. Aging of mushrooms results in a soft texture, characterized by softening of the mushroom tissue. Softening may be due to degradation of the cell wall by bacterial enzymes and increased endogenous autolysin activity after harvesting. In the present invention, the hardness of straw mushrooms decreases during storage (fig. 7). Straw mushrooms packed with PBAT/tartaric acid-CMNC film were stiffer than other groups, especially after 48h storage. After 96h storage, the PBAT/tartrate-CMNC group reached 3.93N. The change in hardness is typically associated with starch oxidation, which increases sugar content and moisture loss and reduces swelling pressure. These results demonstrate that the PBAT/tartaric acid-CMNC film is effective in maintaining straw mushroom hardness.

The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments. Those skilled in the art will appreciate that, in light of the principles of the present invention, improvements and modifications can be made without departing from the scope of the invention.

Claims

1. A preparation method of a nano-composite active packaging preservative film based on esterification modification is characterized by comprising the following steps of: the method comprises the following steps:

(1) Esterifying the organic acid and the carboxymethyl nanocellulose to obtain modified carboxymethyl nanocellulose; mixing the dried modified carboxymethyl nanocellulose, the dried poly (adipic acid)/butylene terephthalate and a chain extender, and extruding and granulating in a double-screw extruder to obtain mixed particles of the modified carboxymethyl nanocellulose/poly (adipic acid)/butylene terephthalate resin;

(2) Carrying out tape casting on the mixed particles of the modified carboxymethyl nanocellulose/poly (adipic acid)/butylene terephthalate resin by a tape casting machine to form a film;

in the step (1), the organic acid is selected from more than one of tartaric acid, citric acid, gallic acid and caffeic acid;

in the step (1), when the organic acid and the carboxymethyl nanocellulose are subjected to esterification reaction, the carboxymethyl nanocellulose is heated and dissolved by dimethyl sulfoxide, then the organic acid and a catalyst are added, and the heating reaction is continued; cooling to room temperature after reaction, adding ethanol until precipitation is complete, freezing and centrifuging, adding ethanol, repeating freezing and centrifuging, finally vacuum drying, and grinding to obtain modified carboxymethyl nanocellulose;

the catalyst is p-toluenesulfonic acid, and the addition amount of the catalyst is 4wt% of carboxymethyl nanocellulose;

the temperature of the heating reaction is 90-110 ℃ and the time is 6-8h;

the temperature of the freeze centrifugation is 3-5 ℃, the rotating speed is 7000-9000rpm, and the time is 10-30min;

in the step (1), the temperatures of the 1 region to the 7 region in the double-screw extruder are respectively as follows: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and the screw rotation speed is 30-60rpm;

in the step (2), the temperatures of the 1 region to the 7 region in the casting machine are respectively as follows: 135-145 ℃, 155-165 ℃, 165-175 ℃, 170-180 ℃, 165-175 ℃ and the screw rotation speed is 30-60rpm.

2. The preparation method of the nano-composite active packaging preservative film based on esterification modification, which is disclosed by claim 1, is characterized by comprising the following steps: in the step (1), the mass ratio of the organic acid to the carboxymethyl nanocellulose is 1:1-1:5.

3. The preparation method of the nano-composite active packaging preservative film based on esterification modification, which is disclosed by claim 1, is characterized by comprising the following steps: in the step (1), the mass ratio of the poly (adipic acid)/the butylene terephthalate to the modified carboxymethyl nanocellulose is 9:1-7:3.

4. The preparation method of the nano-composite active packaging preservative film based on esterification modification, which is disclosed by claim 1, is characterized by comprising the following steps: in the step (1), the drying temperature of the modified carboxymethyl nanocellulose and the modified carboxymethyl cellulose are respectively 50-70 ℃ and the drying time is respectively 1-5h.

5. The preparation method of the nano-composite active packaging preservative film based on esterification modification, which is disclosed by claim 1, is characterized by comprising the following steps: in the step (1), the chain extender is a basf chain extender ADR-4388.

6. The nano composite active packaging preservative film based on esterification modification is characterized in that: which is obtained by the production process according to any one of claims 1 to 5.

7. The use of the nano-composite active packaging preservative film based on esterification modification as set forth in claim 6 in the field of food preservation.