Method for preparing composite film through cooperation of butter flower extract and hemicellulose

Abstract

The method comprises the following steps: dissolving hemicellulose in water, adding the butter flower extract, stirring, carrying out ultrasonic degassing, immediately casting on a polytetrafluoroethylene mold after bubbles are eliminated, and drying to obtain a hemicellulose-butter flower extract composite film; the hemicellulose and the plant extract are compounded for preparation, the materials are derived from natural renewable resources, the problem that a traditional plastic preservative film is non-degradable is solved, white pollution is reduced, and the concept of sustainable development is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomass high-performance composite materials, in particular to a method for preparing a composite film by synergistically using butterbur extract and hemicellulose. BACKGROUND

[0002] In recent years, hemicellulose, as an important component of biomass resources, has attracted much attention in the fields of bioenergy, material science, and food industry. Hemicellulose is the second most abundant renewable polysaccharide in plant cell walls after cellulose, and is widely available (such as agricultural waste, wood, and herbaceous plants), meeting the demand for sustainable development. The degradation products can be converted into biofuels or high-value chemicals, reducing the dependence on fossil fuels. Hemicellulose has abundant hydroxyl and acetyl groups, which are easy to modify chemically to improve its properties such as hydrophobicity and mechanical strength. Its good biocompatibility makes it suitable for use in food packaging, medical materials, and other fields, so it is a good material for preparing films. However, the complex structure of hemicellulose still faces many challenges in practical applications: on the one hand, due to its structure composed of multiple monosaccharides (xylose, mannose, glucose, etc.) and diverse branched structures, it is difficult to extract and purify, and its uniformity is poor. On the other hand, when it is used alone to form a film, it is brittle and highly hydrophilic, so it needs to be compounded with other materials to improve its performance, but this may sacrifice its biodegradability. In addition, hemicellulose has limited antibacterial activity, and its antibacterial effect is far inferior to that of chitosan and some natural antibacterial agents such as plant polyphenols. The structural diversity of hemicellulose makes it difficult to unify its antibacterial mechanism, and its antibacterial spectrum is narrow. Hemicellulose-based antibacterial materials are prone to hydrolysis or degradation in humid environments or long-term use, leading to a rapid decline in antibacterial performance.

[0003] In existing methods of blending with hemicellulose, there are a series of limitations, such as when blending hemicellulose with inorganic or natural antibacterial agents, nanoparticles tend to agglomerate, resulting in poor dispersibility and possibly reducing the mechanical properties of the material; the release of antibacterial agents is uncontrollable, leading to short-term failure or potential toxicity. Chemical modification methods are used to improve the antibacterial properties of hemicellulose, but the modification reaction may damage the hemicellulose backbone, leading to increased brittleness of the material, and some reagents are toxic, which does not meet the requirements of green chemistry and cannot be used in applications such as food preservation and material packaging. Therefore, how to maintain the sustainability and functional adjustability of the prepared film while improving the antibacterial performance, stability, and biomass compatibility of hemicellulose has become a core issue in current research. SUMMARY

[0004] The present application addresses the problems of chemical residues, non-degradability, and single function of traditional fruit and vegetable preservation films, and proposes a method for preparing a new biodegradable composite film by compounding butterbur extract unique to the Shangri-La region with hemicellulose, based on the synergistic effect of green materials and plant active ingredients.

[0005] The application adopts butter flower extract and hemicellulose to prepare a composite film for fresh-keeping field, and the application screens and optimizes natural antibacterial and antioxidant active ingredients in the butter flower extract, screens out a synergistic regulation combined with the hemicellulose through various extraction methods of the butter flower, and optimizes a heterogeneous interface, so as to construct a composite film material with gas regulation, slow-release antibacterial and antioxidant functions.

[0006] The technical scheme of the application is as follows: A method for preparing a composite film by synergistically using butter flower extract and hemicellulose, comprising the following steps: The hemicellulose is dissolved in water, the butter flower extract is added, stirring is performed for 30-40 min, ultrasonic degassing is performed, the film is immediately cast on a polytetrafluoroethylene mold after the bubbles are eliminated, and drying is performed to obtain a hemicellulose-butter flower extract composite film.

[0007] The mass ratio of the butter flower extract to the hemicellulose is 1:1-4.

[0008] The ultrasonic degassing power is 50-70 W, and the time is 20-30 min.

[0009] The drying is performed in an oven at 40-50 DEG C for 8-10 h.

[0010] The hemicellulose is a market-purchased finished product or is prepared according to a conventional method.

[0011] The butter flower extract is extracted from butter flower leaves, and the extraction method comprises a mechanical extrusion combined with freeze-drying method, a water extraction method and a supercritical CO2 extraction method.

[0012] The mechanical extrusion combined with freeze-drying method is specifically operated as follows: Fresh butter flower leaves are washed with tap water to remove surface dirt, and if necessary, the leaves are briefly soaked in a NaCl solution or ethanol for disinfection, then washed with deionized water and dried in the shade or at low temperature to avoid destroying active ingredients at high temperature, the dried butter flower leaves are first cut and crushed for pretreatment, the pretreated raw materials are extruded by a mechanical extruder, the extruded liquid is centrifuged to obtain a clarified liquid, the clarified liquid is freeze-dried, and finally a porous powder, i.e., the butter flower extract, is obtained.

[0013] The water extraction method adopts normal temperature extraction or heating extraction, and the specific operation is as follows: the butter flower leaves are washed and dried, ground and crushed and sieved to increase the contact area, the leaves are soaked or heated and stirred in water at normal temperature or by heating (heating extraction at 80 DEG C for 2 h), the residue is removed, if necessary, the clarified supernatant is obtained by centrifugation, the extraction liquid is concentrated by rotary evaporation under reduced pressure, and finally the butter flower extract liquid is obtained.

[0014] The supercritical CO2 extraction method is specifically operated as follows: the butter flower is subjected to low-temperature drying, crushing, grinding and other pretreatment processes, the pretreated raw material is loaded into an extraction kettle, CO2 flow is adjusted according to the volume of the kettle, and the extract discharged from the bottom of the separation kettle is collected after extraction for 1-4 hours, and the extract is further filtered to obtain an extract liquid with good compatibility.

[0015] The beneficial effects of the present application are as follows: The present application is prepared by compounding hemicellulose and plant extract, and is derived from natural renewable resources, which overcomes the non-degradable problem of traditional plastic preservative film, reduces white pollution, and meets the concept of sustainable development.

[0016] The present application utilizes the good preservation effect of butter flower itself to develop a new type of bio-based antibacterial composite film in combination with hemicellulose, so as to balance performance and sustainability, and has important significance for promoting the application of hemicellulose-based composite film material in the fields of food packaging and medical materials.

[0017] The active ingredients in the butter flower extract endow the preservative film with natural antibacterial and antioxidant properties, without the need to add chemical preservatives, thereby avoiding the risk of chemical residues and ensuring food safety; the phenol content, flavonoid content and DPPH clearance rate in the extract all exhibit strong free radical scavenging ability and antioxidant activity, and the extract has a significant inhibitory effect on a variety of common food spoilage bacteria; the beneficial ingredient acetic acid in the butter flower has antibacterial and bacteriostatic effects, and is commonly used to inhibit the growth of mold and bacteria, thereby prolonging the shelf life of food; 2-butenoic acid, 2-methyl-, is an organic acid that can inhibit microbial activity by acidifying the environment; n-hexadecanoic acid is a type of fatty acid that can be used as a surface coating or emulsifier to block oxygen and moisture; and D-limonene is a natural antibacterial agent that has an inhibitory effect on certain bacteria and fungi, while also providing aroma, thereby providing a theoretical basis and technical support for the functional application of bio-based preservative film.

[0018] The present application optimizes the design of the heterojunction interface, so that the composite film has gas regulation, slow-release antibacterial and antioxidant functions, thereby prolonging the preservation period of fruits and vegetables, and the effect is better than that of a single-function traditional film material.

[0019] The present application utilizes a variety of extraction methods, screening and synergistic regulation technologies, and precisely optimizes the combination of active ingredients and hemicellulose by utilizing the beneficial ingredients of butter flower, so as to ensure the mechanical strength, barrier property and stability of function release of the film material.

[0020] The present application develops high-value-added applications of the plant "butter flower" unique to the Shangri-La region, solves the problem of fragile leaves that are difficult to directly utilize, and realizes resource value-added by extract compounding. The film-forming material replaces direct wrapping of leaves, is convenient for industrialized production and actual use, and meets the standardized needs of transportation, storage and other links. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The microstructure of hemicellulose-ghee flower extract composite film; Figure 2 This is the standard curve of total flavonoids content in butter flower extract; Figure 3 This is the standard curve of total phenol content of butter flower extract; Figure 4 is the DPPH scavenging rate of butter flower extract at different concentrations. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below with reference to specific embodiments. However, it should be noted that the scope of protection of the present invention is not limited to these embodiments. The hemicellulose used in the embodiments of the present invention is obtained by extracting sugarcane pith, and the butter flower is a natural plant raw material picked from Shangri-La City, Diqing Tibetan Autonomous Prefecture, and the leaves bloom in summer.

[0023] Example 1 The preparation method of hemicellulose comprises the following steps: The black liquor is obtained by boiling the sugarcane pith, and the pH value of the black liquor is adjusted to 2 with 1M hydrochloric acid, centrifuged, and the pH value of the black liquor after centrifugation is adjusted to 13 with NaOH, and then adjusted to 2 with 1M hydrochloric acid, centrifuged again, and repeated 4 times until the lignin is removed. The black liquor obtained by the last centrifugation is adjusted to pH 4.5 with 1M hydrochloric acid, and then 95% ethanol with a mass concentration of 4 times the volume of the black liquor is added to precipitate hemicellulose. After precipitation is completed, it is filtered with G3 and the hemicellulose obtained is washed with acetone and ether. The washed hemicellulose is dried to obtain the desired raw material.

[0024] Comparative Example 1 Preparation method of hemicellulose cling film: 1 g of the hemicellulose extracted in Example 1 was weighed and dissolved in 48.7 g of deionized water. The mixture was heated and stirred at 90°C for 20 min until the hemicellulose was dissolved, and then glycerol (30% by weight of the hemicellulose) was added and stirred for 5 min. After stirring evenly, the mixture was ultrasonically degassed for 25 min to obtain a hemicellulose solution. The hemicellulose solution was cast on a polytetrafluoroethylene mold and dried in a 45°C oven for 8 h to obtain a pure hemicellulose film.

[0025] The pure hemicellulose film prepared in Example 1 was subjected to oxygen and carbon dioxide gas permeability performance tests. The test results showed that the oxygen permeability of the pure hemicellulose film was 98.56 cm 3 / (cm 2• d• (0.1 MPa)) and the mechanical properties of tensile strength of only 4.67 MPa and elongation at break of 9.45%, the antibacterial property of MIC of 71 μg / mL, and the antioxidant function of 41.32% (DPPH clearance rate, the same below).

[0026] Example 2 The method for preparing the butter flower extract by mechanical extrusion combined with freeze-drying method comprises the following steps: (1) Fresh, non-diseased butter flower leaves are selected, and the rotten and impurity parts are removed. The leaf surface is washed with flowing deionized water, and the water is drained; (2) The leaves are cut into 0.5-1 cm pieces, and a tissue crusher is used for coarse crushing to increase the contact surface area; (3) Butter flower raw materials: the crushed leaves are mixed with deionized water at a mass ratio of 1:5, and a hydraulic press with a pressure of 10-15 MPa is used for 10 times of stirring to make the raw materials and the solvent preliminarily infiltrate; (4) The slurry after beating is extruded and coarsely filtered through a 200-mesh screen to remove fiber residues; (5) The filtrate after coarse filtration is centrifuged at 4°C and 10,000 rpm for 10 min, and the supernatant is taken; (6) The extract is injected into a freeze-drying tray with a liquid layer thickness of ≤1 cm, and placed in a -45°C ultra-low temperature freezer for 4h to form uniform ice crystals; (7) The frozen sample is transferred to a freeze dryer, vacuumed to 0.1 mbar, and the cold trap temperature is maintained at -50°C. When slowly warmed to -20°C, sublimation drying is performed for 24h until the ice crystals are completely removed; (8) The temperature is raised to 25°C and maintained for 8h until the extract is dried; (9) The porous extract freeze-dried block is treated by a crusher and passed through an 80-mesh screen to obtain a uniform powder, which is the butter flower extract.

[0027] Example 3 1 g of hemicellulose obtained by extraction in Example 1 is dissolved in 49 g of deionized water at 90°C and stirred for 20 min until the hemicellulose is dissolved. Then, 1 g of butter flower powder prepared in Example 2 is added to the solution in which the hemicellulose is dissolved, and the mixture is stirred for another 30 min. After the mixture is uniformly mixed, it is degassed by ultrasonic at 60W for 25 min to obtain a hemicellulose-butter flower extract mixed solution. The mixed solution is cast on a polytetrafluoroethylene mold and placed in a 45°C oven for drying for 8h to obtain a composite film.

[0028] The hemicellulose-ghee flower extract composite film prepared in Example 3 was tested for oxygen and carbon dioxide gas permeability performance, and the test results showed that the hemicellulose-ghee flower extract composite film had good gas barrier performance, wherein the oxygen permeability was 48.86 cm 3 / (cm 2 d (0.1 MPa), compared with the pure hemicellulose film of Comparative Example 1, the mechanical property increased by 23%, the antibacterial property increased by not less than 40%, and the antioxidant function increased by not less than 45%.

[0029] Example 4 The ghee flower raw material:deionized water in Example 2 was mixed according to the mass ratio of 1:7, and other process parameters were unchanged, and ghee flower extract was prepared.

[0030] Example 5 1 g of hemicellulose extracted in Example 1 was dissolved in 49 g of deionized water at 90°C, and after the hemicellulose was dissolved, 1 g of ghee flower powder prepared in Example 4 was put into the solution, and the stirring was continued for 40 min. After mixing uniformly, 50W ultrasonic degassing was carried out for 30 min, and a hemicellulose-ghee flower extract mixed solution was obtained. The mixed solution was cast on a polytetrafluoroethylene mold, and placed in a 50°C oven for drying for 8.5 h to obtain a composite film.

[0031] The hemicellulose-ghee flower extract composite film prepared in Example 5 was tested for oxygen and carbon dioxide gas permeability performance, and the test results showed that the hemicellulose-ghee flower extract composite film had good gas barrier performance; wherein the oxygen permeability was 13.79 cm 3 / (cm 2 d (0.1 MPa), compared with the pure hemicellulose film of Comparative Example 1, the mechanical property increased by 23%, the antibacterial property increased by not less than 40%, and the antioxidant function increased by not less than 45%.

[0032] Example 6 The ghee flower raw material:deionized water in Example 2 was mixed according to the mass ratio of 1:7, and other process parameters were unchanged, and ghee flower extract was prepared.

[0033] Example 7 1 g of the hemicellulose extracted in Example 1 was dissolved in 49 g of deionized water. The solution was heated and stirred at 90°C for 20 min until the hemicellulose was dissolved. 0.25 g of the butter flower powder prepared in Example 6 was then weighed and placed in the solution in which the hemicellulose had been dissolved and continued to stir for 35 min. After the mixture was evenly mixed, ultrasonic degassing was performed at 70 W for 20 min to obtain a hemicellulose-butter flower extract mixed solution. The mixed solution was cast on a polytetrafluoroethylene mold and dried in a 40°C oven for 10 h to obtain a composite membrane.

[0034] The hemicellulose-butter flower extract composite film prepared in Example 7 was subjected to oxygen and carbon dioxide gas permeability tests. The test results showed that the hemicellulose-butter flower extract composite film had good gas barrier properties; the oxygen permeability was 53.06 cm 3 / (cm 2 •d•(0.1MPa)), compared with the pure hemicellulose membrane of comparative example 1, the mechanical properties are reduced, the antibacterial performance is improved by no less than 30%, and the antioxidant function is improved by no less than 40%.

[0035] Example 8 The method for preparing butter flower extract by water extraction comprises the following steps: (1) Select fresh, pest-free butter flower leaves, remove the rotten and impurity parts, gently rinse the surface of the leaves with running deionized water to remove the dust and impurities on the surface, and avoid rubbing to cause the loss of effective ingredients. After washing, spread them flat in a clean and ventilated place to dry in the shade. After drying, the moisture content of the raw materials must be controlled below 8%; (2) The dried butter flower leaves are crushed with a grinder and passed through a 40-mesh stainless steel sieve. The coarse particles that have not passed through the sieve need to be crushed again until they all pass through the sieve to form a uniform powder to increase the solute mass transfer efficiency; (3) Accurately weigh the butter flower powder, weigh 5 g of powder and add 100 mL of deionized water at a ratio of 1:20. Extract at room temperature and place in a constant temperature environment at 25 °C for 12 h. Stir slowly every 2 h during this period. Then heat in a 100 °C water bath and continue stirring for 1 h until the solution turns light yellow and emits a characteristic odor. (4) After dissolution, use a 100-200 mesh sieve to remove large particles of residue. If the filtrate is still turbid, centrifuge it at 4000 rpm for 10 minutes to completely separate the fine suspended matter and obtain a clear supernatant. (5) The supernatant was transferred to a rotary evaporator with a water bath temperature of 60°C and a vacuum degree of -0.08 MPa, and the volume was evaporated to 1 / 10 of the original volume (concentrated 10 times). During the process, the solution gradually became viscous and amber-colored. The butter flower extract was obtained.

[0036] Compared with normal temperature extraction (soaking in constant temperature environment of 25℃ for 12h), heating extraction (heating extraction for 2h at 80℃) can shorten the extraction time appropriately, and other steps are the same as normal temperature extraction, and the properties of butter flower extract solution obtained are similar.

[0037] Example 9 1g of hemicellulose obtained by extraction in Example 1 was dissolved in 49g of deionized water under stirring at 90℃ for 20min until the hemicellulose was dissolved. Then, the butter flower extract solution prepared in Example 8 was added, and the concentration of the butter flower extract solution was calculated to be 0.544%. 183.82g of the extract solution (about 1g of effective butter flower) was added into the solution in which the hemicellulose was dissolved, and stirring was continued for 10min. After mixing uniformly, the mixed solution was degassed by ultrasonic at 60W for 25min to obtain a hemicellulose-butter flower extract mixed solution. The mixed solution was cast on a polytetrafluoroethylene mold, and dried in an oven at 45℃ for 8h to prepare a composite film.

[0038] The composite film prepared in Example 9 was tested for oxygen and carbon dioxide gas permeability, and the test results showed that the hemicellulose-butter flower extract composite film had good gas barrier performance. The oxygen permeability was 34.26cm 3 / (cm 2 •d•(0.1MPa)), compared with the pure hemicellulose film of Comparative Example 1, the mechanical property was improved by 12%, the antibacterial property was improved by not less than 22%, and the antioxidant function was improved by not less than 40%.

[0039] Example 10 The butter flower raw material:deionized water in Example 8 was mixed according to the mass ratio of 1:10, and other process parameters were unchanged to prepare a butter flower extract solution.

[0040] Example 11 1g of hemicellulose obtained by extraction in Example 1 was dissolved in 49g of deionized water under stirring at 90℃ for 20min until the hemicellulose was dissolved. Then, the butter flower extract solution prepared in Example 10 was added, and the concentration of the butter flower extract solution was calculated to be 1.088%. 91.91g of the extract solution (about 1g of effective butter flower) was added into the solution in which the hemicellulose was dissolved, and stirring was continued for 10min. After mixing uniformly, the mixed solution was degassed by ultrasonic at 60W for 30min to obtain a hemicellulose-butter flower extract mixed solution. The mixed solution was cast on a polytetrafluoroethylene mold, and dried in an oven at 45℃ for 8h to prepare a composite film.

[0041] The hemicellulose-ghee flower extract composite film prepared in Example 11 was subjected to oxygen and carbon dioxide gas permeability performance tests, and the test results showed that the hemicellulose-ghee flower extract composite film had good gas barrier properties, wherein the oxygen permeability was 22.18 cm 3 / (cm 2 d (0.1 MPa), compared with the pure hemicellulose film of Comparative Example 1, the mechanical properties decreased, the antibacterial properties increased by not less than 30%, and the antioxidant function increased by not less than 45%.

[0042] Example 12 In Example 8, the ghee flower raw material: deionized water was mixed at a mass ratio of 1:30, and the other process parameters were unchanged, and a ghee flower extract solution was prepared.

[0043] Example 13 1 g of hemicellulose extracted in Example 1 was dissolved in 49 g of deionized water at 90°C, and after stirring for 20 min, the ghee flower extract solution prepared in Example 12 was added, and the concentration of the ghee flower extract solution was calculated to be 0.363%. 275.48 g of the extract solution (about 1 g of effective ghee flower) was placed in the solution in which the hemicellulose was dissolved, and stirring was continued for 10 min. After mixing uniformly, 50W ultrasonic degassing was performed for 30 min, and a hemicellulose-ghee flower extract mixed solution was obtained. The mixed solution was cast on a polytetrafluoroethylene mold, and placed in a 45°C oven for drying for 8 h, and a composite film was prepared.

[0044] The hemicellulose-ghee flower extract composite film prepared in Example 13 was subjected to oxygen and carbon dioxide gas permeability performance tests, and the test results showed that the hemicellulose-ghee flower extract composite film had good gas barrier properties; wherein the oxygen permeability was 64.1 cm 3 / (cm 2 d (0.1 MPa), compared with the pure hemicellulose film of Comparative Example 1, the mechanical properties decreased, the antibacterial properties increased by not less than 20%, and the antioxidant function increased by not less than 40%.

[0045] Example 14 The method for extracting effective components of ghee flower by supercritical CO2 includes the following steps: (1) The ghee flower leaves were gently rinsed in flowing deionized water for 3 times to completely remove the surface dust and attachments, and after washing, they were laid on multiple layers of sterile gauze and naturally dried in a cool and ventilated clean environment; (2) Using stainless steel vegetable cutter disinfected by ethanol, cut the leaves into 0.3-0.5cm uniform pieces. To obtain higher extraction yield, put the cut sample into a pre-cooled tissue grinder, add sufficient liquid nitrogen for quick freezing and then grind at 15000rpm for 60s, pass through a 60 mesh standard sieve to obtain low-temperature fine powder, which greatly increases the contact area of the material with CO2; (3) Put the pretreated raw material into the extraction kettle of the supercritical extraction device uniformly to avoid the formation of air channel or uneven filling. The loading density is strictly controlled at 0.35±0.05g / cm 3 After filling, close the extraction kettle and ensure that the sealing ring is intact. Tighten the bolts according to the equipment procedure, start the equipment, and set the system extraction parameters to 35℃, 25MPa, and CO2 flow rate of 25L / h. Extract for 2.5h. First, check the system airtightness. Introduce CO2 to slightly below the working pressure, and maintain the pressure for 10min. The pressure drop should not exceed 0.5MPa. Then, preheat the extraction kettle, separation kettle I, and separation kettle II to 35℃, 50℃, and 30℃, respectively. (4) Stir at a uniform speed. Every 30min, slowly open the discharge valve at the bottom of separation kettle I to collect the first extract. (5) Combine all the collected extracts in a clean glass settling tank, seal with sealing film, and store in a 4℃ cold environment for 30min to allow the trace amount of water to fully separate from the lipid-soluble extract. Take the upper clear oil-like extract, filter it using a 0.45μm organic microporous filter and a vacuum filtration device to further remove possible fine particles, and obtain clear CO2 extract of butter flower, with an extraction yield of 2.7%.

[0046] Example 15 Dissolve 1g of hemicellulose obtained by extraction in Example 1 in 49g of deionized water, heat and stir at 90℃ for 20min until the hemicellulose is dissolved. Then, put 1g of the thick oil-like butter flower material obtained by supercritical CO2 extraction in Example 14 into the solution where the hemicellulose has been dissolved, continue stirring, and degas for 25min at 60W ultrasonic. Obtain a hemicellulose-butter flower extraction mixed solution. Pour the mixed solution into a polytetrafluoroethylene mold, place it in a 45℃ oven for drying for 8h, and obtain a composite film.

[0047] Test the oxygen and carbon dioxide gas permeability performance of the hemicellulose-butter flower extract composite film obtained in Example 15. The test results show that the hemicellulose-butter flower extract composite film has good gas barrier performance. The oxygen permeability is 22.37cm 3 / (cm 2•d• (0.1 MPa)) compared with the pure hemicellulose film of Comparative Example 1, the mechanical property is improved by 15%, the antibacterial property is improved by no less than 30%, and the antioxidant function is improved by no less than 40%.

[0048] As shown in Figure 1 , from left to right are the microstructures (SEM) of the composite films prepared in Examples 3, 9 and 15, respectively. It can be seen from the figure that the extraction method of different P. tunicosa extract has a significant influence on the micro-morphology of the film. Specifically, the film prepared by mechanical extrusion combined with freeze-drying in Example 3 and the film prepared by supercritical CO2 extraction in Example 15 both show obvious heterogeneous structure crosslinking characteristics, and the surface structure of the film is dense and uniform; while the film prepared by traditional water extraction in Example 9 shows obvious structural defects, and the surface is rough and uneven. This morphology difference may be related to the retention degree of active ingredients by different extraction methods.

[0049] The P. tunicosa extract prepared in Example 8 was used as raw material and was diluted to different concentrations for standard curve determination of total flavonoids and total phenols, and the results are shown in Figure 2 (total flavonoid content standard curve) and Figure 3 (total phenol content standard curve). As shown in Table 1, the content of active ingredients obtained by different extraction methods shows significant difference, among which the supercritical CO2 extraction method is particularly prominent, with total phenol equivalent in the extract reaching 18.2242±0.163 μg GAE / mL, which is significantly higher than the other two methods; while the mechanical extrusion combined with freeze-drying method has an advantage in total flavonoid extraction, with total flavonoid equivalent in the extract reaching 1270±12.7 μg RE / g. These data show that, compared with the traditional water extraction method, the mechanical extrusion combined with freeze-drying method and the supercritical CO2 extraction method can more effectively retain the active ingredients in P. tunicosa, which provides a material basis for the preparation of high-performance composite films.

[0050] Table 1

[0051] From the film formation mechanism, the active ingredients in P. tunicosa extract can undergo crosslinking reaction with the active groups on hemicellulose, thereby forming a dense network structure. This structure not only can effectively block gas permeation, but also can fully exert the antibacterial activity of P. tunicosa itself to block the invasion of external microorganisms. In addition, the P. tunicosa extract liquid of Example 8 was diluted to different concentrations for free radical scavenging experiment, Figure 4The DPPH free radical scavenging experiment results of the buttercup flower extract show that the buttercup flower extract has significant antioxidant activity and shows obvious concentration dependence; when the concentration of the extract reaches 10 mg / mL, the DPPH scavenging rate is as high as 76.84%, which shows excellent antioxidant performance, and this property is particularly important for the preparation of preservative films because the antioxidant activity can effectively delay the oxidation and deterioration of food and prolong the shelf life of food.

[0052] In combination with the drawings and the calculation results, it is known that the mass ratio range used for different extraction methods is 1:5-1:30, the mechanical performance is improved by 10%-30% under the condition of mechanical extrusion combined with freeze-drying, the antibacterial performance is improved by 30-60%, and the antioxidant function is improved by 40-75%; under the condition of water extraction, the antibacterial performance is improved by 20%-30%, and the antioxidant performance is improved by 40%; under the condition of supercritical CO2 extraction of buttercup flower effective components, the antibacterial effect is enhanced by 30%, and the antioxidant activity (DPPH scavenging rate) can be improved by 40%, which can be applied to the preparation of preservative films with barrier properties.

[0053] The buttercup flower extract prepared by the mechanical extrusion combined with freeze-drying method or the supercritical CO2 extraction method has complete active components, can form a composite film with a compact structure, and has good antibacterial and antioxidant functions, and has a wide application prospect in the field of food preservation packaging, and these findings provide important experimental basis and technical reference for the development of new bioactive packaging materials.

[0054] The preparation method of the hemicellulose-buttercup flower extract composite film provided by the application mixes hemicellulose with water and then mixes the hemicellulose with buttercup flower extract, freeze-dries the buttercup flower extract by the mechanical extrusion combined with freeze-drying method to prepare the hemicellulose-buttercup flower extract composite film, so that the buttercup flower extract retains good antibacterial performance and antioxidant performance, forms a natural effective preservation barrier, and combines with hemicellulose to form an excellent heterogeneous structure; the hemicellulose-buttercup flower extract composite film is prepared by the water extraction method, the water-soluble antioxidant components in the buttercup flower are effectively dissolved by the mature process of the method, so that the shelf life of fruits and vegetables is prolonged when the hemicellulose-buttercup flower extract composite film preserves the fruits and vegetables; the hemicellulose-buttercup flower extract composite film is prepared by extracting the effective components of the buttercup flower by the supercritical CO2 extraction method, the buttercup flower extract with extremely high purity is obtained by the method, and the film material is endowed with excellent barrier and mechanical properties, and has obvious advantages in detecting the antioxidant performance and stability of the film.

[0055] The above examples are only part of the implementation manners of the technical solutions of the application, and the scope of protection required by the application is not limited to the above examples, but also includes any changes, substitutions and other implementation manners easily thought of by those skilled in the art within the technical scope disclosed by the application.

Claims

1. A method for preparing a composite film by synergistically using a butter flower extract and hemicellulose, characterized in that: The following steps are involved: Hemicellulose was dissolved in water, and the butter flower extract was added, stirred for 30-40 minutes, and ultrasonically degassed. After the bubbles were eliminated, the film was immediately cast on a polytetrafluoroethylene mold and dried to obtain a hemicellulose-butter flower extract composite membrane.

2. The method for preparing a composite film by synergistically using the butter flower extract and hemicellulose according to claim 1, characterized in that: The mass ratio of the butter flower extract to hemicellulose is 1:1-4.

3. The method for preparing a composite film by synergistically using the butter flower extract and hemicellulose according to claim 1, characterized in that: The ultrasonic degassing power is 50-70W, and the time is 20-30min.

4. The method for preparing a composite film by synergistically combining the butter flower extract and hemicellulose according to claim 1, characterized in that: The drying step is to keep the temperature at 40-50° C. for 8-10 hours.

5. The method for preparing a composite film by synergistically using the butter flower extract and hemicellulose according to claim 1, characterized in that: The butter flower extract is extracted from butter flower leaves, and the extraction methods include mechanical extrusion combined with freeze drying, water extraction, and supercritical CO2 extraction.

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