CN111978793B

CN111978793B - Preparation method of biological composite coating and intelligent colorimetric film material

Info

Publication number: CN111978793B
Application number: CN202010828826.2A
Authority: CN
Inventors: 龙柱; 孟亚会
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2021-07-27
Anticipated expiration: 2040-08-18
Also published as: CN111978793A

Abstract

The invention discloses a preparation method of a biological composite coating and an intelligent colorimetric film material, and belongs to the field of functional materials. The preparation method comprises the steps of taking hydroxypropyl guar gum (HPG) as a biological composite material base material, taking Cellulose Nanocrystals (CNC) as a reinforcing agent, taking a deep cosolvent (DES) as a plasticizer and a toner, taking anthocyanin (Anth) as a pH indicator, stirring at room temperature until the solution is uniformly mixed to obtain a film-forming solution, spraying the film-forming solution on the surface layer of a fruit, and drying to form a coating; and casting the film-forming solution into a film and drying to obtain the intelligent colorimetric film. The biological composite material coating and the intelligent colorimetric film prepared by the invention have the advantages of good flexibility, good barrier property, high sensitivity, good reversibility and stability and the like, and can be used as a freshness indicator of perishable fruit (such as cherries, strawberries and the like) coatings and perishable foods (such as meat, seafood and the like).

Description

Preparation method of biological composite coating and intelligent colorimetric film material

Technical Field

The invention relates to a preparation method of a biological composite coating and an intelligent colorimetric film material, belonging to the field of functional materials.

Background

Nowadays, economy develops rapidly, people's requirements for food have been transited from a saturated type to a nutritional type and a diversified type, and more attention is paid to the quality and safety of food. Due to the regional difference of the distribution of cold chain foods such as vegetables, fruits, aquatic products, meat, dairy products and the like in China and the complexity of storage and transportation, people seek the diversity of food consumption and simultaneously make the cold chain logistics of foods in China face a serious challenge. At the present stage of China, due to the facts that cold-chain logistics infrastructure is not complete enough, refrigeration conditions are not good enough, logistics speed cannot be achieved, a complete cold-chain logistics system is lacked, and when a large number of fresh foods such as meat, vegetables, fruits, aquatic products and the like are stored, transported and sold, nutritional ingredients of the foods can be lost, even rotten and deteriorated due to the fact that the fresh foods are not precooled in time, transported and packaged improperly and oscillated during transportation, and accordingly food safety problems are caused.

Fresh food is preserved and stored or enters the field of circulation, needs to have certain packing or coating, and it can reduce moisture evaporation to a certain extent, slows down corruption, maintains freshness. The packaging materials for fresh food include paper, plastic, wood, fiber and some natural materials. Taking the packaging bag as an example, the food packaging bag needs to have certain strength, low temperature resistance, good oxygen, water vapor and water barrier performance and the like in the process of cold-chain logistics. With the rapid development of cold-chain logistics, the storage of vegetables, fruits, aquatic products, meat, dairy products and the like is increased, and consumers cannot directly contact with packaged food, so that the freshness of the packaged food cannot be judged by sensory methods such as smell and the like. Therefore, how to conveniently and rapidly identify whether the food in the packaging bag (box) is rotten or not is a problem to be solved at present.

At present, although the patent of application No. 201710366626.8, "a hydroxypropyl guar gum nanocellulose composite membrane and a preparation method thereof" adopts hydroxypropyl guar gum and nanocellulose to prepare the composite membrane, the composite membrane does not have a freshness indication function, and thus, whether food is fresh or not cannot be rapidly identified at all. And while hydroxypropyl guar HPG is a suitable polymer for making biodegradable films, it is low cost, renewable, water soluble, film forming ability and high viscosity at low concentrations. However, the HPG film has low tensile strength and high hydrophilicity, and cannot meet the need for film formation; by adding Cellulose Nanocrystals (CNCs), the prepared HPG/CNCs membrane obtains higher strength, but loses corresponding flexibility and cannot meet the use requirement of the membrane.

Disclosure of Invention

In order to solve at least one of the above problems, the present invention prepares basement membranes using hydroxypropyl guar (HPG) and Cellulose Nanocrystals (CNCs); then, the deep cosolvent is used as a plasticizer and a toner, and the anthocyanin is used as a pH sensitive dye to prepare the fruit protective coating and the intelligent colorimetric material. The method comprises the steps of firstly, mixing choline chloride and biosaccharide according to a certain proportion, and then directly heating to prepare the deep cosolvent; dissolving hydroxypropyl guar gum in deionized water, adding the nano-cellulose suspension, uniformly mixing, adding different amounts of deep cosolvent and anthocyanin, stirring at room temperature until the solution is uniformly mixed to obtain a film-forming solution, and finally casting the film-forming solution into a film and drying to obtain the soft recyclable intelligent colorimetric film. Placing the pH colorimetric membrane in buffer solutions with different pH values, and observing the color change of the colorimetric membrane; soaking the fruits in the film forming solution, naturally drying to form a layer of protective film on the surfaces of the fruits, observing the putrefaction degree of the fruits and researching the anticorrosion effect of the coating; the intelligent colorimetric film is used for detecting the freshness of dairy products and meat products, observing color change and exploring monitoring effects.

The first purpose of the invention is to provide a film-forming solution, which takes hydroxypropyl guar HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth as raw materials; wherein, the deep cosolvent consists of choline chloride and biological sugar; the mass ratio of the HPG, the CNC, the DES and the Anth is 6: 200: 1-4: 1.

in one embodiment of the invention, the mass ratio of the hydroxypropyl guar HPG, the cellulose nanocrystal CNC, the deep cosolvent DES and the anthocyanin anthh is 6: 200: 2-3: 1.

in one embodiment of the invention, the mass ratio of the hydroxypropyl guar HPG, the cellulose nanocrystal CNC, the deep cosolvent DES and the anthocyanin anthh is 6: 200: 2: 1.

in one embodiment of the present invention, the deep cosolvent is prepared by directly heating choline chloride and biosaccharide under anhydrous condition.

In one embodiment of the invention, the mass ratio of the choline chloride to the biosaccharide is 20: 1-1: 6.

In one embodiment of the present invention, the mass ratio of choline chloride to biosaccharide is 2: 1.

in one embodiment of the present invention, the deep co-solvent is prepared by the following steps:

the choline chloride and the biosaccharide are mixed according to the mass ratio of 20: 1-1: 6, and stirred for 8-12 hours at the temperature of 70-90 ℃ to obtain a colorless transparent solution, namely the deep cosolvent.

choline chloride and glucose are mixed according to the mass ratio of 2:1, heated and stirred for 10 hours in an oil bath kettle at the temperature of 80 ℃ to obtain a colorless transparent solution, namely the deep cosolvent.

In one embodiment of the invention, the choline chloride is food grade.

In one embodiment of the present invention, the biosaccharide includes one or more of glucose, sucrose and microcrystalline cellulose.

In one embodiment of the present invention, the choline chloride has the following structural formula:

in one embodiment of the present invention, the structural formula of the biosaccharide (taking glucose as an example) is as follows:

in one embodiment of the present invention, the deep co-solvent has the following structural formula:

in one embodiment of the present invention, the deep co-solvent is prepared by the following steps: the choline chloride and the biosaccharide are mixed according to the mass ratio of 20: 1-1: 6, and stirred for 8-12 hours at the temperature of 70-90 ℃ to obtain a colorless transparent solution, namely the deep cosolvent.

In one embodiment of the present invention, the deep co-solvent is prepared by the following steps: mixing choline chloride and biosaccharide according to the mass ratio of 20: 1-1: 6, heating and stirring for 8-12 hours in an oil bath kettle at the temperature of 70-90 ℃ to obtain a colorless transparent solution, namely the deep cosolvent.

A second object of the present invention is a method for preparing the deposition solution of the present invention, comprising the steps of: uniformly mixing hydroxypropyl guar gum HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth serving as raw materials to obtain a film forming solution; wherein, the deep cosolvent is prepared by directly heating choline chloride and biosaccharide under the condition of no participation of water.

In one embodiment of the invention, the mass ratio of the hydroxypropyl guar HPG, the cellulose nanocrystal CNC, the deep cosolvent DES and the anthocyanin anthh is 6: 200: 1-4: 1.

in one embodiment of the invention, the mixing is performed by stirring (300-700rpm for 2-4h) at room temperature (20-25 ℃).

In one embodiment of the present invention, the mixing is specifically mixing uniformly at room temperature and 25 ℃ with stirring (stirring at 500rpm for 3 h).

mixing choline chloride and biosaccharide according to the mass ratio of 20: 1-1: 6, heating and stirring for 8-12h in an oil bath kettle at the temperature of 70-90 ℃ to obtain a colorless transparent solution, namely deep co-dissolution.

The third purpose of the invention is to provide a biological composite coating, which is obtained by spraying the film-forming solution of the invention on the surface layer of the fruit or directly soaking the fruit in the film-forming solution of the invention and drying.

In one embodiment of the invention, the fruit is one or more of cherry, tomato, blueberry and waxberry.

The fourth purpose of the invention is to provide an intelligent colorimetric film, which is obtained by casting the film-forming solution of the invention into a film and drying the film.

In one embodiment of the present invention, the cast film formation is 80g of the deposition solution cast on a teflon disk with a diameter of 15 cm.

The fifth purpose of the invention is the application of the intelligent colorimetric film in the freshness detection of dairy products and meat products.

In one embodiment of the invention, the prepared intelligent colorimetric film can be used as a freshness indicating film for shrimps, fish, crabs, beef, chicken and the like at the temperature of-16-50 ℃ to indicate the freshness of perishable meat products.

In one embodiment of the invention, the intelligent colorimetric film prepared at 4-50 ℃ can be used as milk, and indicates the freshness of a dairy product with short shelf life.

The sixth purpose of the invention is the application of the biological composite coating in fruit fresh-keeping.

In one embodiment of the present invention, the application is: spraying the film forming liquid on the surface of the fruit or directly soaking the fruit in the film forming liquid, and drying to obtain the biological composite coating, which can slow down the rotting degree of the fruit.

The seventh purpose of the invention is to provide a method for enhancing the colorimetric performance of the membrane, and the preparation method of the adopted membrane forming solution comprises the following steps: uniformly mixing hydroxypropyl guar gum HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth serving as raw materials to obtain a film forming solution; wherein, the deep cosolvent is prepared by directly heating choline chloride and biosaccharide under the condition of no participation of water.

The invention has the beneficial effects that:

1. the choline chloride is green and nontoxic and can be extracted from plants; the biological sugar has rich sources, is green and pollution-free, has rich anthocyanin sources, is easy to extract, is safe and non-toxic, and has lower price.

2. The deep cosolvent prepared by the invention is safe and nontoxic, can be used as a plasticizer to improve the flexibility of a film, and can also be used as a toner to enhance the color development capability of anthocyanin, so that the color change can be easily distinguished by naked eyes.

3. The biological composite material coating can slow down the rotting degree of the fruits and prolong the fresh-keeping period of the fruits

4. The intelligent colorimetric film has the advantages of high sensitivity, good reversibility and stability and the like, and can be used for detecting the freshness of dairy products and meat products.

Drawings

FIG. 1 is a flow diagram of the preparation of deep co-solvent of example 1.

FIG. 2 is a graph showing the degree of rot of blueberry and red bayberry at different times in example 3.

FIG. 3 is a graph showing the degree of decay of cherries at various times in example 3.

FIG. 4 is a graph of milk freshness versus pH and intelligent colorimetric film color change for example 5.

Detailed Description

The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.

The test method comprises the following steps:

weight loss rate: at 25 ℃, the fruits required for the six groups of experiments were weighed, and the original weight was recorded as W_iThen, the fruit was weighed again every other day, recording the weight as W_tThe formula for calculating the weight loss rate (%) of fruit during storage is as follows:

tensile strength and elongation at break: the composite films were tested for mechanical strength using a BZ2.5/TNIS Zwick materials tester (Zwick, Germany) at 25 ℃ and a humidity RH of 60%. The samples were 15X 100mm in size, 50mm in grip, 50mm in draw speed, and tested at least 5 times per sample.

Water vapor transmission rate: the Water Vapor Permeability (WVP) of the membrane was measured using a Labthink W3/060 instrument (Labthink, China) at 38 ℃ and (88. + -. 1)% RH. Three measurements were made for each sample and the average value reported.

Oxygen transmission rate: the oxygen transmission rate (OP) of the film was measured at 23 ℃ and (65.2. + -. 1)% RH using a Labthink VAC-V2 apparatus (Labthink, China). The sample size was 38.48cm²The oxygen partial pressure was 0.5 MPa. Each sample was tested 3 times.

And (3) the number of times of recycling in ammonia gas detection: the film was cut into 2cm x 2cm squares before testing. Different mass fractions (w/w) of 28.7% (w/w) aqueous ammonia were mixed with distilled water in a flask having a capacity of 100mL and equilibrated at 25 ℃ for 30min to prepare an aqueous ammonia solution required for the experiment. The square film was then placed 10s above the flask mouth and the film was exposed to NH liberated from the aqueous ammonia solution in the flask₃In (1). Exposure to NH₃Previously, images of the films were taken using an RX100 III camera and color parameters of the films were measured using a portable colorimeter (Xrite2600d, MI, 101, USA). Then, at 25 ℃, the color-changing film is placedRecovering to original color after 30min in the fume hood, taking image of the film again, measuring color parameters L, a, b and Δ E of the film, Δ E [ [ (L-L ═ L-₀)²+(a*-a*₀)²+(b*-b*₀)²]^1/2。

Example 1

A method for preparing a deep co-solvent, as shown in fig. 1, comprising the following steps:

From a table look, the color of the deep cosolvent prepared in this example was found to be nearly transparent.

Example 2 preparation method optimization for deep co-solvent preparation

Adjustment 1: the glucose in example 1 was adjusted to sucrose, and the others were kept unchanged to obtain a deep co-solvent.

As a result, it was found that: the color of the prepared deep cosolvent is close to transparent.

And (3) adjustment 2: the mass ratio of choline chloride to glucose in example 1 was adjusted to 10:1, 5:1, 1:1 and 1:5, and the others were kept unchanged to obtain a deep co-solvent.

The result shows that the color of the cosolvent is deepened with the increase of the dosage of the choline chloride, the color of the film is influenced, and the film is easy to cure at normal temperature, so that the film is difficult to apply to preservation; if the amount of choline chloride is too small (1: 5 choline chloride and glucose), the time required to form a solution is long, and plasticization and hyperchromicity are poor; after the detection reagent is combined with hydroxypropyl guar gum and anthocyanin, the aim of accurately detecting freshness cannot be achieved.

And (3) adjustment: the glucose in example 1 was adjusted to microcrystalline cellulose DP200, and the others were kept unchanged to obtain a deep co-solvent.

As a result, it was found that: if the microcrystalline cellulose and the choline chloride are used for co-melting, the time is long, about 3-5 days, and the reaction rate is greatly reduced.

Example 3

A preparation method of a biological composite coating comprises the following steps:

dissolving 0.6g of hydroxypropyl guar gum in 60g of water for standby, adding 20g of nanocellulose crystals, then adding different amounts of the deep cosolvent (0,0.1,0.2,0.3,0.4g) of example 1 and 0.1g of anthocyanin, stirring at room temperature at the stirring speed of 500rpm for 3 h; obtaining a film forming solution; then, soaking fresh fruits such as blueberries, cherries, waxberries and the like in the film forming solution for 1min, taking out and naturally drying, and thus forming a biological composite coating on the surface layer of the fruits.

Uncoated fruit was used as the control group and coated fruit was used as the experimental group, and the fruits were weighed every other day under the same experimental conditions (room temperature), weight loss was calculated, and photographed, and the rotting degree of the fruits was recorded (table 1, table 2, table 3), as shown in fig. 2 and fig. 3.

TABLE 1 weight loss rate of blueberry

TABLE 2 weight loss rate of cherries

TABLE 3 weight loss rate of waxberry

From tables 1-3, it can be seen that the weight loss rate of the fruit without the coating is greater than the weight loss rate of the fruit coated with the coating, indicating that the coating can delay the water loss of the fruit; the weight loss rate of the fruit is increased along with the increase of the amount of the cosolvent, and the water loss of the fruit in the coating is faster due to the increase of the water vapor transmission rate of the coating. As can be seen from FIGS. 2 and 3, the fruits without the coating layer showed mildew and rot after several days, the fruit coated with the coating layer showed less rot, and the fruit was kept fresh with minimal rot when the co-solvent was added in an amount of 0.2 g.

Example 4

A preparation method of an intelligent colorimetric film comprises the following steps:

dissolving 0.6g of hydroxypropyl guar in 60g of water for later use, adding 20g of nanocellulose crystals, then adding different amounts of the deep cosolvent of example 1 (0,0.1,0.2,0.3,0.4g) and 0.1g of anthocyanin, stirring at room temperature at a stirring speed of 500rpm for 3 h; obtaining a film forming solution; then casting the film-forming solution into a film (80g of the film-forming solution is cast on a polytetrafluoroethylene disc with the diameter of 15cm for film formation) and drying to obtain an intelligent colorimetric film HPG/CNC/Anth (the thickness is 52.7 +/-1.0 mu m), HPG/CNC/Anth/DES_0.1(thickness 53.0. + -. 2.0. mu.m), HPG/CNC/Anth/DES_0.2(thickness 53.1. + -. 1.3 μm), HPG/CNC/Anth/DES_0.3(thickness 53.2. + -. 1.5. mu.m), HPG/CNC/Anth/DES_0.4(thickness 53.1. + -. 1.8. mu.m).

The strength and elongation, water vapor transmission rate, oxygen transmission rate and the number of times of recycling when detecting ammonia of the intelligent colorimetric film are tested, and the test results are shown in table 4:

TABLE 4 Performance test results for Intelligent colorimetric films

As can be seen from table 4, as the content of the co-solvent increases, the tensile strength of the composite film decreases and the elongation at break increases. Due to the plastic action of the deep cosolvent, the movement among macromolecules in the composite membrane is increased, and further the elongation at break is increased. However, excessive deep cosolvent addition weakens hydrogen bonding between the biomacromolecules in the composite membrane, resulting in reduced tensile strength.

As the co-solvent content increases, the water vapor transmission rate increases and the oxygen transmission rate increases and then decreases. The co-solvent has high hygroscopicity, so that the water vapor transmission rate of the composite membrane is increased. When the addition amount of the cosolvent is small, the gaps in the composite membrane are filled, so that the internal structure of the composite membrane becomes tighter and oxygen cannot permeate easily; when the addition amount of the cosolvent is larger, the hydrogen bond effect between biological macromolecules in the composite membrane is weakened, the internal structure of the composite membrane becomes slightly loose, and the permeation of oxygen is increased.

The composite membrane without the cosolvent can be recycled for only 5 times during ammonia detection; the composite membrane containing the cosolvent can be used for 14-15 times, and the cosolvent contains chlorine ions, so that the composite membrane has a hyperchromic effect, and the using times of the composite membrane can be increased. In summary, the following steps: when the amount of the co-solvent added is 0.2g, various performances of the composite membrane are best.

For the detection of the intelligent color matching film on ammonia gas with different concentrations, the test results are shown in table 5(Δ E represents the color difference between two adjacent columns):

TABLE 5 color parameters of colorimetric films at different ammonia concentrations

As can be seen from table 5, the color difference of the film was less than 5, and the color change was not easily recognized by naked eyes. When the color matching film contains the cosolvent, the color difference of the film is more than 5 under different ammonia concentrations, and the change of the color can be easily distinguished by naked eyes. Moreover, when the ammonia concentration is low (1ppm), the color difference is more than 5, and human eyes can distinguish the color change. Therefore, the cosolvent is used as a toner, so that the colorimetric film has color change which is easier to distinguish by human eyes in different ammonia concentrations, and the cosolvent can be used as an alkaline gas sensor such as ammonia.

Comparative example 2

The deep co-solvents in example 4 were adjusted to choline chloride and glycerol, and otherwise the film obtained in example 4 remained unchanged.

Comparative example 3

The deep cosolvent in example 4 was choline chloride, and the film obtained in the other example 4 was kept unchanged.

Comparative example 4

The deep co-solvent in example 4 was adjusted to glucose, and the other and example 4 remained unchanged to give a membrane.

The films of comparative examples 2-4 were subjected to the performance test, and the test results are shown in Table 6:

table 6 testing of the properties of the films obtained in comparative examples 2 to 4

Table 7 results of performance test before and after 3-month storage of the films prepared in comparative example 2 and example 4

As can be seen from table 6, the addition of choline chloride resulted in a decrease in both tensile strength and elongation at break of the composite film. When choline chloride/glycerin was used as a co-solvent, the tensile strength of the composite film was slightly increased, but glycerin was easily precipitated from the composite film during storage of the composite film, and the composite film was easily aged and embrittled (table 7). The tensile strength of the composite film is increased and the elongation at break is smaller by adding the glucose.

In addition, the color difference of the film prepared from the choline chloride/glycerol cosolvent (0.2g) of the comparative example 2 under different ammonia gas concentrations is less than 5, and the intelligent colorimetric requirement cannot be met (delta E represents the color difference between two adjacent columns).

TABLE 8 color parameters of colorimetric films at different ammonia concentrations

Ammonia gas concentration (ppm)	0	1	5	10	10²	10³	10⁴
								ΔE	-	3.31	4.52	3.60	4.47	4.34	4.41

Example 5

The application of the intelligent colorimetric film in milk preservation comprises the following steps:

weighing fresh milk with a phase volume (40mL) in a weighing bottle, respectively putting the fresh milk into the optimal intelligent colorimetric films obtained in the embodiment 4 with the size of 2cm multiplied by 2cm, and then sealing; monitoring the pH change of the milk every day by using a pH meter, and recording the pH value; photographs were taken every other day for the milk status in the measuring flask and the color change of the colorimetric film was recorded as shown in fig. 4.

As can be seen from fig. 4: with increasing storage days, the pH of the milk decreased from 6.45 (day 0) to 3.01 (day 7), at which time the milk had become too sour and spoiled for consumption. The color of the colorimetric film in the weighing bottle changes along with the change of the pH value of the milk, and the film changes from purple red to deep red. Indicating that the colorimetric film can detect the freshness of the milk.

Example 6

The application of the intelligent colorimetric film in the fresh-keeping of the white shrimps comprises the following steps:

white shrimps with the same mass (20g) were weighed, placed in a petri dish, and placed in the optimal intelligent colorimetric films obtained in example 4 with a size of 2cm × 2cm, respectively, then sealed, and stored at room temperature (25 ℃) and low temperature (4 ℃) respectively.

Every other day, white shrimp were Tested for Volatile Basic Nitrogen (TVBN) content, expressed in mg/100g according to GB 5009.228-2016 first method (where TVBN < 12, meaning fresh; 12-20, meaning slightly degraded and still edible; 20-25, meaning critical; 25, meaning completely rancid and inedible); the prawns were photographed every other day and the spoilage level of the prawns and the color change of the colorimetric film were recorded.

TVBN and color difference values (table 9) the results show: the fifth day at 4 ℃ and the first day at 25 ℃, the TVBN content is more than 25, and the shrimp cannot eat the food, at this time, the colorimetric film changes color, and the color difference value is proved to be distinguishable by human eyes, so that the colorimetric film can indicate the freshness of the shrimp.

TABLE 9 white shrimp TVBN content and color Difference value of colorimetric film Δ E

Example 7 sensitivity

Five kinds of smart colorimetric films (HPG/CNC/Anth, HPG/CNC/Anth/DES) of example 4 having a size of 2cm × 2cm were applied_0.1、HPG/CNC/Anth/DES_0.2、HPG/CNC/Anth/DES_0.3、HPG/CNC/Anth/DES_0.4) Placing on a white plate respectively, and sucking a buffer solution with the pH of 12 by using a dropper; a drop of buffer solution was applied to the surface of each of the five colorimetric membranes, and the response time of the colorimetric membrane was recorded.

When the DES of the deep cosolvent is 0, the response time is about 6 s; when DES is 0.1 and 0.2, response time is about 1-2 s; the response time is about 2-3 s when the DES is 0.3 and 0.4, which shows that the intelligent colorimetric film prepared in example 4 has good sensitivity.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. The film forming liquid is characterized in that hydroxypropyl guar HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth are used as raw materials;

wherein, the deep cosolvent consists of choline chloride and biological sugar; the preparation method of the deep cosolvent comprises the following steps: mixing choline chloride and biosaccharide according to a mass ratio of 2:1, stirring for 8-12h at 70-90 ℃ to obtain a colorless transparent solution, namely a deep cosolvent;

the mass ratio of the hydroxypropyl guar HPG to the cellulose nanocrystal CNC to the deep cosolvent DES to the anthocyanin Anth is 6: 200: 1-4: 1;

the biological sugar comprises one or two of glucose and sucrose.

2. A method for preparing the deposition solution according to claim 1, comprising the steps of:

uniformly mixing hydroxypropyl guar gum HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth serving as raw materials to obtain a film forming solution; wherein, the deep cosolvent is prepared by directly heating choline chloride and biosaccharide under the condition of no participation of water.

3. A biocomposite coating, wherein the biocomposite coating is obtained by spraying the deposition solution of claim 1 on the surface of a fruit or directly immersing the fruit in the deposition solution of claim 1, and drying.

4. An intelligent colorimetric film obtained by casting the deposition solution according to claim 1 into a film and drying the film.

5. Use of the intelligent colorimetric film of claim 4 in the detection of freshness of dairy and meat products.

6. The use according to claim 5, wherein the use is at 4-50 ℃ for the intelligent colorimetric film of claim 4 to be used as milk, indicating the freshness of dairy products with short shelf life.

7. The use of claim 5, wherein the smart colorimetric film of claim 4 can be used as a film for indicating freshness of shrimps, fish, crabs, beef and chicken at-16-50 ℃ to indicate the freshness of perishable meat products.

8. The use of the biocomposite coating of claim 3 in the preservation of fruit, wherein the biocomposite coating is prepared by spraying the deposition solution of claim 1 on the surface of fruit or directly immersing the fruit in the deposition solution of claim 1, and drying to obtain the biocomposite coating, which can reduce the rotting degree of fruit.

9. A method for enhancing the colorimetric performance of a membrane is characterized in that the preparation method of the adopted membrane forming solution comprises the following steps: uniformly mixing hydroxypropyl guar gum HPG, cellulose nanocrystal CNC, deep cosolvent DES and anthocyanin Anth serving as raw materials to obtain a film forming solution;

the mass ratio of the HPG, the CNC, the DES and the Anth is 6: 200: 1-4: 1;

the biological sugar comprises one or two of glucose and sucrose.