阅读说明：本技术 一种pH响应智能控释抗菌防腐包装用保鲜剂的制备方法以及应用 (Preparation method and application of pH-responsive intelligent controlled-release antibacterial preservative packaging preservative ) 是由 刘飞 郐凌云 钟芳 陈茂深 徐菲菲 于 2021-01-20 设计创作，主要内容包括：本发明提供一种pH响应智能控释抗菌防腐包装用保鲜剂的制备方法以及应用,其特征在于,包括如下步骤：壳聚糖溶胀,含醛基化合物溶解；恒温恒压下缩合反应,得到粗产物；抽滤,乙醇洗涤,真空干燥得到醛基化合物-壳聚糖席夫碱基衍生物。本发明实现了精油随果蔬储藏时间进展的有限保鲜成分含量的精准调控,有着优异的果蔬采后抗菌与保鲜效果,且制备方法工艺简单、条件温和。(The invention provides a preparation method and application of a pH-responsive intelligent controlled-release antibacterial preservative for packaging, which is characterized by comprising the following steps: swelling chitosan, and dissolving the aldehyde group-containing compound; carrying out condensation reaction at constant temperature and constant pressure to obtain a crude product; and (3) carrying out suction filtration, washing with ethanol, and vacuum drying to obtain the aldehyde compound-chitosan Schiff base derivative. The invention realizes the accurate regulation and control of the content of the limited fresh-keeping components of the essential oil along with the storage time progress of the fruits and the vegetables, has excellent antibacterial and fresh-keeping effects after the fruits and the vegetables are picked, and has simple preparation method and process and mild conditions.)

1. A preparation method of a pH response intelligent controlled-release antibacterial preservative packaging preservative is characterized by comprising the following steps:

swelling chitosan, and dissolving the aldehyde group-containing compound;

carrying out condensation reaction at constant temperature and constant pressure to obtain a crude product;

and (3) carrying out suction filtration, washing with ethanol, and vacuum drying to obtain the aldehyde group-containing compound-chitosan Schiff base derivative.

2. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1, which is characterized by comprising the following steps: the solvent used in the swelling of the chitosan is methanol.

3. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1, which is characterized by comprising the following steps: the molecular weight of chitosan in the chitosan swelling is 50-150 KDa, and the deacetylation degree is 80-90%.

4. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1 or 3, which is characterized by comprising the following steps: the degree of deacetylation of chitosan in the chitosan swelling was 85%.

5. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1, which is characterized by comprising the following steps: the aldehyde-containing compound comprises one or more of cinnamaldehyde, citral or vanillin and other aldehyde-containing compounds.

6. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative as claimed in claim 1, which is characterized in that: the solvent adopted for dissolving the aldehyde group-containing compound is absolute ethyl alcohol, and the dosage of the aldehyde group-containing compound is-NH in chitosan₂The molar ratio of the chitosan to the aldehyde-containing compound is controlled to be 1: 1-1: 6.

7. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1 or 6, which is characterized by comprising the following steps: the dosage of the aldehyde group-containing compound is-NH in chitosan₂The molar ratio of the chitosan to the aldehyde group-containing compound is controlled to be 1: 4.

8. The preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative according to claim 1, which is characterized by comprising the following steps: the condensation reaction is carried out at constant temperature and constant pressure by placing aldehyde group-containing compound solution into a constant pressure dropping funnel, slowly dropping into swelling-completed chitosan solution at constant pressure, and stirring at 45 ℃ for reaction for 8 h.

9. The application of the preservative for pH response intelligent controlled-release antibacterial antiseptic packaging is characterized in that: the pH response intelligent controlled-release antibacterial preservative packaging preservative is separated from water contact and is placed in the same sealed environment with fruits and vegetables.

10. The application of the pH-responsive intelligent controlled-release antibacterial preservative as claimed in claim 9, wherein the pH-responsive intelligent controlled-release antibacterial preservative is characterized in that: when the pH response intelligent controlled-release antibacterial preservative for packaging is separated from water and is in contact with fruits and vegetables in the same sealed environment, the initial CO of the sealed environment₂The concentration of (A) is 5-20%.

Technical Field

The invention relates to the technical field of food, fruit and vegetable preservation, in particular to a preparation method and application of a preservative for pH-responsive intelligent controlled-release antibacterial preservative packaging.

Background

Fruits and vegetables are important sources of various nutrients needed by human bodies, such as vitamins, minerals, dietary fibers and the like, but because fruits and vegetables still carry out vigorous life metabolic activities after being picked, the fruits and vegetables are easy to deteriorate and decay in the transportation, sale and storage processes after being picked, and the fruits and vegetables are one of the most wasted foods. Antibacterial packaging is a promising technology to drive food safety and extend shelf life, and has shown impressive ability to extend shelf life, which is critical in the battle against global food waste. Therefore, the good antibacterial packaging material has very important significance for preventing the postharvest microbial spoilage of fruits and vegetables.

In recent years, various antibacterial agents have been generally used for preservation and freshness of picked fruits and vegetables. Compared with a chemically synthesized antibacterial agent, the natural antibacterial agent such as plant essential oil is green, safe and environment-friendly, can effectively inhibit and kill bacteria, fungi and viruses, and is becoming an important research direction in the field of postharvest storage of fruits and vegetables in recent years. The essential oil is added into the packaging material, so that on one hand, the stability of the essential oil can be improved; on the other hand, the essential oil can be preferentially and specifically released and volatilized to the surfaces of the fruits and vegetables which are most prone to microbial spoilage. However, the design of such antibacterial packages must take into consideration the release of essential oils and the spoilage of microorganisms, and the release rate is too fast or too slow to achieve the desired antibacterial effect.

In order to maximize the effect of essential oil antibacterial packaging on the antisepsis and freshness preservation of picked fruits and vegetables, researchers mainly adjust and control the aspects of packaging matrix components, inter-component combination modes, preparation processes and the like at present, so that the controllable release of active substances such as essential oil and the like in a packaging film is realized. For example, the carrier treatment of volatile active substance, i.e. increasing the tortuosity of diffusion path, can achieve the purpose of enhancing the controlled release effect and improving the stability. However, such diffusion-controlled release occurs regardless of the change in food quality, and it is still impossible to control the release of the active substance to be antibacterial according to actual needs.

Disclosure of Invention

This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.

The present invention has been made in view of the above and/or other problems associated with the prior art packaging preservatives.

Therefore, one of the purposes of the invention is to overcome the defects of the existing packaging preservative product and provide a preparation method of the pH-responsive intelligent controlled-release antibacterial preservative packaging preservative.

To solve the above technical problem, according to an aspect of the present invention, the present invention provides the following technical solutions: a preparation method of a pH response intelligent controlled-release antibacterial preservative packaging preservative is characterized by comprising the following steps:

swelling chitosan, and dissolving the aldehyde group-containing compound;

carrying out condensation reaction at constant temperature and constant pressure to obtain a crude product;

and (3) carrying out suction filtration, washing with ethanol, and vacuum drying to obtain the aldehyde group-containing compound-chitosan Schiff base derivative.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the solvent used in the swelling of chitosan was methanol.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the molecular weight of chitosan in the chitosan swelling is 50-150 KDa, and the deacetylation degree is 80-90%.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the degree of deacetylation of chitosan in the chitosan swelling was 85%.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the aldehyde-containing compound comprises one or more of cinnamaldehyde, citral or vanillin.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: compound containing aldehyde groupThe solvent adopted for dissolving the chitosan derivative is absolute ethyl alcohol, and the dosage of the aldehyde-containing compound is-NH in the chitosan₂The molar ratio of the chitosan to the aldehyde-containing compound is controlled to be 1: 1-1: 6.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the aldehyde group-containing compound is used in an amount of-NH in chitosan₂The molar ratio of the chitosan to the aldehyde group-containing compound is controlled to be 1: 4.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: and (3) condensation reaction at constant temperature and constant pressure, namely placing the aldehyde group-containing compound solution into a constant-pressure dropping funnel, slowly dropping the aldehyde group-containing compound solution into the chitosan solution after swelling at constant pressure, and stirring and reacting for 8 hours at 45 ℃.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: the pH response intelligent controlled-release antibacterial preservative for packaging is separated from water contact and is placed in the same sealed environment with fruits and vegetables.

As a preferred scheme of the preparation method of the pH response intelligent controlled-release antibacterial preservative packaging preservative, the pH response intelligent controlled-release antibacterial preservative packaging preservative comprises the following steps: when the pH response intelligent controlled-release antibacterial preservative for packaging is separated from water and contacted with fruits and vegetables in the same sealed environment, the initial CO of the sealed environment₂The concentration of (A) is 5-20%.

The invention provides a preparation method and application of a pH-responsive intelligent controlled-release antibacterial preservative packaging preservative, which are mainly applied to the field of packaging of fruits and vegetables, wherein when the preservative is applied to the field of packaging, an aldehyde compound, namely natural antibacterial essential oil containing aldehyde groups is combined with chitosan, so that a Schiff base derivative with better antibacterial performance can be formed, and the defects that the antibacterial essential oil is easy to volatilize and unstable, and is easy to react with food components such as fat and protein to be consumed prematurely and the like can be effectively avoided; the formed imine bond has strong acid sensitivity, can be hydrolyzed only under weak acid condition, and is relatively stable under neutral and alkaline conditions. The pH response realized by the change of acid-base induced polyelectrolyte electrostatic interaction usually needs larger pH value conversion, and N atoms on a Schiff base double-bond hybrid orbit have lone-pair electrons, so that the N atoms are easy to catalyze and hydrolyze in a weak acid medium, and the reaction process is generally reversible; the invention utilizes the respiration generated in the storage process of fruits and vegetables and the acidic environment formed in the package caused by the microbial spoilage and acid production as entry points, so that the release rule of the antibacterial essential oil and the requirement for inhibiting the fruit and vegetable spoilage are basically synchronous, the substitution degree and the release regulation can be regulated by changing the molecular weight of chitosan, the deacetylation degree of chitosan and the molar ratio of chitosan to aldehyde group-containing essential oil, the precise regulation and control of the antibacterial agent are realized, the optimal antibacterial effect is exerted, and the preparation method has simple process and mild conditions.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the patents describing the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor. Wherein:

FIG. 1 is a graph showing the infrared comparison of cinnamaldehyde-chitosan Schiff base derivatives prepared in example 1 according to the present invention with raw materials.

FIG. 2 is a graph showing the release kinetics of cinnamaldehyde-chitosan Schiff base derivatives at different pH values according to example 1 of the present invention.

FIG. 3 shows cinnamaldehyde-chitosan Schiff base derivatives prepared in example 1 of the present invention at different CO concentrations₂Release kinetics of (a).

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, specific embodiments thereof are described in detail below with reference to examples of the specification.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

Example 1

The chitosan used in this example is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. M-TK-1802001, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 150KDa, the deacetylation degree of the chitosan is 90%, and cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde-1: 4. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 2

The chitosan used in this example is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. M-TK-1802001, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 150KDa, the deacetylation degree of the chitosan is 90%, and cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde is 1: 1. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 3

The chitosan used in this example is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. M-TK-1802001, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 150KDa, the deacetylation degree of the chitosan is 90%, and cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde is 1: 2. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 4

The chitosan used in this example is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. M-TK-1802001, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 150KDa, the deacetylation degree of the chitosan is 90%, and cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde 1: 6. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 5

The chitosan used in the embodiment is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. PK-200226-Sur 012, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 100KDa, the deacetylation degree of the chitosan is 80%, and the cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of the cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde-1: 4. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 6

The chitosan used in this example was selected from Zhejiang gold Chitosan pharmaceutical Co., Ltd, production batch No. M-TK-2004001, 3.0g of chitosan was placed in a three-necked flask, 50mL of methanol was added, and the mixture was swollen overnight at room temperature, wherein the molecular weight of chitosan was 100KDa and the degree of deacetylation of chitosan was 85%, and cinnamaldehyde was dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde-1: 4. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 7

The chitosan used in this example is selected from Zhejiang gold Chitosan pharmaceutical industry Co., Ltd, production batch No. M-TK-2004002, 3.0g of chitosan is placed in a three-neck flask, 50mL of methanol is added, and the mixture is swelled overnight at room temperature, wherein the molecular weight of the chitosan is 100KDa, the deacetylation degree of the chitosan is 90%, and cinnamaldehyde is dissolved in 30mL of absolute ethanol to obtain an absolute ethanol solution of cinnamaldehyde; the molar ratio of the synthetic raw materials is chitosan: cinnamaldehyde-1: 4. Transferring the cinnamaldehyde solution into a constant-pressure dropping funnel, slowly dropping the cinnamaldehyde solution into the swollen chitosan solution under constant pressure, and stirring and reacting for 8 hours at the temperature of 45 ℃. And carrying out suction filtration and washing on the obtained product. And Soxhlet extracting with anhydrous ethanol for 12h, and vacuum drying at 50 deg.C to obtain yellow cinnamaldehyde-chitosan Schiff base derivative powder.

Example 8

The yellow cinnamaldehyde-chitosan schiff base derivative powder obtained in example 1 was subjected to IS10FT-IR infrared spectroscopy, and the infrared spectroscopy (FTIR) results thereof were shown in FIG. 1.

As can be seen from FIG. 1, the yellow powder obtained in example 1 was 1634cm^-1The C ═ N stretching peak appeared, confirming the formation of schiff-basified chitosan derivatives. In the FT-IR spectrum of chitosan, 1597cm^-1The peak is an amino N-H deformation vibration peak, and the disappearance of the peak after the Schiff base reaction is due to-NH₂Reaction with CHO in cinnamaldehyde results in a reduction in N-H; in the FT-IR spectrum of cinnamaldehyde, 1680cm^-1The peak at (a) is a C ═ O stretching vibration peak, which corresponds to the aldehyde group of free cinnamaldehyde. The spike disappears after the schiff base reaction, indicating that the ungrafted free cinnamaldehyde has been substantially removed during the alcohol wash and sufficient extraction. From the infrared spectrum analysis, the yellow powder prepared in example 1 was a chitosan type schiff base derivative.

Example 9

The release kinetics of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 was measured at different pH, and the specific test method was: the release rate of cinnamaldehyde over time of cinnamaldehyde-chitosan schiff base derivatives in buffer solutions with different pH values is shown in FIG. 2:

as can be seen from fig. 2, the material finally showed 80% cinnamaldehyde release after being placed in acidic buffer solutions with pH values of 3 and 5 for 96h, the release rate was fast first and slow later, and finally, the material tended to be in equilibrium, while the material gradually released slowly under neutral pH conditions, and the final cumulative release amount was only less than 20%, and thus, the release rate and cumulative release amount of cinnamaldehyde under acidic conditions were higher than those under neutral conditions. Therefore, the release of cinnamaldehyde on the cinnamaldehyde-chitosan schiff base derivative presents obvious pH sensitivity, the release effect of the cinnamaldehyde-chitosan schiff base derivative under an acidic condition is obviously better than that under a neutral condition, and the release degree of the cinnamaldehyde-chitosan schiff base derivative is related to the breakage degree of the schiff base bond.

Example 10

The determination of antibacterial activity of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 is carried out by the following specific steps: diluting activated Escherichia coli and Staphylococcus aureus to 1 × 10⁵CFU/mL to prepare a bacterial suspension, preparing 3mg/mL solution of yellow cinnamaldehyde-chitosan Schiff base derivative powder, cinnamaldehyde and chitosan, sucking 1mL of the solution and mixing with 4mL of the bacterial suspension, measuring the change of the colony number of escherichia coli and staphylococcus aureus by adopting a colony counting method, recording the influence of the yellow cinnamaldehyde-chitosan Schiff base derivative powder, cinnamaldehyde and chitosan on the change of the colony number of the escherichia coli and staphylococcus aureus, and recording the number of the escherichia coli and staphylococcus aureus after the experiment is finished in tables 1 and 2.

TABLE 1 influence of yellow cinnamic aldehyde-chitosan Schiff base derivative powder, cinnamic aldehyde, chitosan on the number of Escherichia coli

TABLE 2 influence of powder of cinnamic aldehyde-chitosan Schiff base derivatives, cinnamic aldehyde, chitosan on the number of Staphylococcus aureus

Example 11

The yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 was subjected to different initial CO₂Measuring the accumulative release amount of cinnamaldehyde at different concentrations to obtain cinnamaldehyde-chitosan Schiff base derivatives at different concentrations of CO₂The simulated cinnamaldehyde release kinetics in the high humidity acidic microenvironment is shown in figure 3.

Example 12

The preservation and freshness performance of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in the example 1 on strawberries is measured, wherein the preservation and freshness performance tests comprise decay rate, hardness and total number of bacterial colonies, and the specific experimental method comprises the following steps:

fresh strawberries were divided into 4 groups (5 per group, about 110g) and placed in sealed transparent PVC plastic containers. 0.1, 0.2 and 0.4g of cinnamaldehyde-chitosan schiff base derivatives and a blank control group (only strawberry was added) were added to 4 groups, respectively. Sealing, and storing in a constant temperature and humidity incubator at 25 deg.C and 50% RH. The strawberry quality index was observed every 2 days.

The rotting rate is as follows: the strawberry is observed at different storage time, the rot index of the strawberry is calculated by combining the strawberry morphological change (mildewing, rotten plaque and skin tissue softening), and the calculation method of the rot index comprises the following steps: the decay index (decay number + softening number 0.5)/total number, calculated as the decay index, is reported in table 3.

Hardness: measuring the hardness of the strawberries in different storage times by adopting a texture analyzer, wherein the type of a probe is P/50, and the speed before measurement is 1.00 mm/s; the testing speed is 1.00 mm/s; the measured speed is 1.00 mm/s; the compression amount was 30% and the trigger force was 5g, and the measured hardness data at different times are recorded in table 4.

Total number of colonies: the total number of colonies contained in strawberries stored for different periods of time was determined according to the standard GB 4789.2-2016, and the specific determination method is as follows: taking 10g of strawberries (sampling from the tops of the strawberries by using a sterile knife to ensure that the positions sampled each time are as consistent as possible) and 90g of sterile normal saline in a sterile sampling bag, patting for 2-3 min, then carrying out 10-fold serial dilution, selecting 2-3 appropriate diluents, taking 1mL of the diluents, pouring the diluents into a sterile plate, adding about 15mL of melted plate counting agar (the temperature is lower than 46 ℃), turning the plate over after the diluents are solidified, and observing the total number of colonies after culturing for 24h at 37 ℃. The results of the measurement are shown in table 5:

TABLE 3 rotting rates of stored strawberries at different times

TABLE 4 hardness of stored strawberries at different times

TABLE 5 Total number of colonies of strawberries stored at different times

As can be seen from tables 3, 4, and 5, the addition of the yellow cinnamaldehyde-chitosan schiff base derivative powder obtained in example 1 significantly inhibited decay of strawberries, maintained hardness of strawberries, and reduced growth of microorganisms attached to and growing on strawberries, as compared to the blank control group.

Example 13 the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 was tested for its preservative and freshness-keeping properties against broccoli, and the preservative and safety properties against strawberries were tested for decay rate, hardness, and colony count, according to the following experimental methods:

fresh broccoli was divided into 4 groups (150 g each) and placed in sealed transparent PVC plastic containers. Chitosan, cinnamaldehyde-chitosan schiff base derivatives and blank control (only broccoli was added) were added to 4 groups, respectively. Sealing, and storing in a constant temperature and humidity incubator at 25 deg.C and 50% RH. Observing and measuring the broccoli quality index every 2 days.

The rotting rate is as follows: the broccoli is observed at different storage time, the strawberry rot index is calculated by combining the strawberry morphological change (mildew, rotten plaque and skin tissue softening), and the calculation method of the rot index comprises the following steps: the decay index (decay number + softening number 0.5)/total number, calculated as the decay index, is reported in table 6.

Chlorophyll content: measuring the chlorophyll content of broccoli in different storage time periods, weighing 1.0g of sample, placing the sample in a mortar, adding 15mL of anhydrous acetone solution for grinding, carrying out high-speed centrifugation for 10min, taking supernatant, measuring the light absorption value at 663nm, calculating the chlorophyll mass ratio, and expressing the result in mg/g.

Total number of colonies: the total number of colonies of broccoli in different storage time is determined, 10g of broccoli and 90g of sterile normal saline are taken from a sterile working table and are beaten for 2-3 min in a sterile sampling bag, then 10-fold serial dilution is carried out, 1mL of 2-3 suitable diluents are selected and poured into a sterile plate, then about 15mL of melted plate counting agar (the temperature is lower than 46 ℃) is added, the plate is turned over after solidification, and the total number of colonies is observed after 24 hours of culture at 37 ℃. The results of the measurement are shown in table 8:

TABLE 6 decay index of broccoli at different storage times

TABLE 7 chlorophyll content of broccoli at different storage times

TABLE 8 Total number of colonies of broccoli at different storage times

Analysis was performed on the data:

as can be seen from the data in tables 1 and 2, the inhibitory rates of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 to escherichia coli and staphylococcus aureus under the condition of pH 5 can respectively reach 86.17% and 93.65%, in addition, the total number of bacterial colonies is significantly reduced from neutral to weak acid, the yellow cinnamaldehyde-chitosan schiff base derivative powder has a significant bacteriostatic effect on escherichia coli and staphylococcus aureus compared with a blank experimental group without any component, and the yellow cinnamaldehyde-chitosan schiff base derivative powder has a significant advantage on the bacteriostatic effect on escherichia coli and staphylococcus aureus compared with cinnamaldehyde and chitosan.

As can be seen from FIG. 3, in a highly humid and slightly acidic system without direct contact with the aqueous phase, the release rate of cinnamaldehyde in the cinnamaldehyde-chitosan Schiff base derivative is dependent on CO in the closed cavity₂Increasing in concentration, i.e., increasing with increasing acidity of the environment; with the lapse of time, the concentration of cinnamaldehyde released by the yellow cinnamaldehyde-chitosan schiff base derivative powder is firstly released rapidly, the concentration of effective components in the environment is improved, and then the effective components are released slowly, so that the concentration of the effective components is ensured; when the cinnamaldehyde-chitosan Schiff base derivative is used as the preservative, the preservative is quickly released into air at the initial stage and dispersed in the air to realize the effect of quickly increasing the effective concentration when the setting is finished and the preservation process is carried out, then the effective components are slowly released to maintain the stability of the concentration, the release curve has the tendency of being quick first, slow second and stable last, and the actual requirements of fruit and vegetable preservation are met.

As can be seen from tables 6, 7 and 8, the addition of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 significantly inhibited the decay of broccoli, inhibited the reduction of chlorophyll, and reduced the growth of microorganisms attached to and growing on broccoli, compared to the blank control group.

By combining the data in tables 3, 4, 5, 6, 7 and 8 in examples 12 and 13, the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in the invention has good effects of inhibiting the rot of fruits and vegetables, maintaining the freshness of fruits and vegetables and reducing the microbial pollution in the process of preserving fruits and vegetables, and the rot index of the blank group of strawberries and broccoli reaches 30% after 2-4 days at room temperature, namely the strawberry and broccoli lose the commercial property. The decay index of the strawberries and the broccoli after being stored for 6 days at room temperature is only about 20% due to the addition of the cinnamaldehyde-chitosan schiff base derivatives, and the cinnamaldehyde-chitosan schiff base derivative powder prepared by the method has the obvious effect of prolonging the shelf life of fruits and vegetables.

Example 14

The degree of substitution of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in examples 1 to 7 was measured in the following manner: and (3) carrying out element analysis and determination on the sample by adopting an element analyzer to obtain the carbon-nitrogen ratio of the powder particles, and further calculating by using the following formula to obtain the substitution degree of the product. The substitution degree was calculated by elemental analysis of C/N, and the measured substitution degree data are shown in Table 9.

DS is the degree of substitution of the product; DD is the degree of deacetylation of chitosan; mc and Mn are the relative atomic masses of carbon and nitrogen atoms respectively; nc is the number of carbon atoms in a substituent molecule; r is the carbon-nitrogen ratio in the substituent.

TABLE 9 degree of substitution data for the products of examples 1-7

Examples	Degree of substitution
		Example 1	0.26
Example 2	0.13
		Example 3	0.20
Example 4	0.28
		Example 5	0.29
Example 6	0.36
		Example 7	0.39

As can be seen from table 9, the substitution degree of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in example 1 was the highest, and the substitution degree data of the yellow cinnamaldehyde-chitosan schiff base derivative powder prepared in examples 1 to 4 was obtained, and the molar ratio of chitosan to cinnamaldehyde was 1:4, which is the preferred ratio of chitosan to cinnamaldehyde; according to the substitution degree data of the yellow cinnamaldehyde-chitosan schiff base derivative powders prepared in the examples 1 and 5 to 7, the difference of the substitution degree between the examples 7 and 6 is smaller than that between the examples 6 and 5, the increase of the substitution degree is smaller, and the deacetylation degree of the example 6 is 85% which is the preferable deacetylation degree of the present invention in consideration of the cost and the complexity of the treatment process required for the deacetylation degree to be increased to 90%.

As can also be seen from fig. 2, when other preparation parameters are the same and pH is equal to or greater than 3, the lower the pH, the faster the release rate of the aldehyde group, and the pH of the acidic solution generated after dissolution of carbon dioxide and other acids generated during preservation of fruits and vegetables is not lower than pH3, it can be concluded that the response release rate of the aldehyde group compound during preservation of fruits and vegetables increases with the decrease of pH, and the pH of the solution such as water vapor during preservation and water vapor generated in the enclosed space by respiration of fruits and vegetables possibly generated during preservation of fruits and vegetables tends to decrease with the progress of preservation, and therefore the release rate of the aldehyde group compound tends to increase with the progress of preservation.

As can be seen from fig. 3, when other preparation parameters are the same, the release rate of the aldehyde compound decreases with the decrease of pH, and in the preservation process of fruits and vegetables, the cumulative effect of respiration of fruits and vegetables leads to the trend of increasing the concentration of carbon dioxide in the closed space as the preservation process proceeds, so that the release rate of the aldehyde compound increases with the increase of preservation time in the preservation process of fruits and vegetables.

According to the conclusion obtained by combining the above fig. 2 and fig. 3, the cinnamaldehyde-chitosan schiff base derivative prepared in the invention can be in direct contact with air or water vapor in the air in the internal environment of fruit and vegetable preservation, and as the preservation time of fruit and vegetable increases, the release rate of aldehyde group compounds tends to increase, and the content of aldehyde group compounds in the sealed environment also tends to increase.

Meanwhile, in the embodiments 1 to 7, a plurality of cinnamaldehyde-chitosan Schiff base derivatives are selected, which shows that the preparation method adopted by the invention has a good production adaptation function for a plurality of chitosans, and the raw material sources adopted by the invention comprise a plurality of or even all chitosan types.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.