Preparation method of composite membrane based on polysaccharide and CDs

Abstract

The invention relates to a preparation method of carbon dots based on an ethanol solvent and application of the carbon dots on a composite membrane. According to the invention, the ethanol-based functionalized carbon dots CDs are synthesized by using residues left after extraction of sargassum fusiforme polysaccharide and generated waste ethanol through a hydrothermal method. The preparation method has the characteristics of greenness, environmental protection, cheap and easily available raw materials and good biocompatibility. Besides, the carbon dots can be independently used, the water vapor permeability, the oxygen permeability, the ultraviolet shielding capability, the antioxidant activity and the antibacterial activity of the albumen glue can be remarkably improved by doping the CDs into a gelatin network, and the effects are remarkably improved along with the increase of the concentration of the carbon dots. The composite film has a good application prospect in fruit preservation, and can effectively increase the commodity rate of blueberry fruits and improve the quality and flavor loss in the storage process.

Description

Technical Field

[0001] The invention relates to the technical field of composite membrane preparation, and in particular to a method for preparing a composite membrane based on polysaccharide and CDs. Background Art

[0002] At present, in order to reduce environmental pollution and burden, environmentally friendly packaging materials have gradually become the current research trend. Degradable materials, including proteins, polysaccharides, lipids, etc., are often used as film-forming matrices, supplemented with plasticizers and cross-linking agents, and semi-permeable membranes with good mechanical properties and airtightness can be prepared through processing, fusion and other processes. This type of food preservative film has been widely used in fruit and vegetable storage. Previous studies have shown that applying the film liquid to the surface of fruits and vegetables by dipping, spraying, brushing, etc. can reduce water loss and slow down the respiration rate of fruits, thereby extending the shelf life of fruits and vegetables.

[0003] In recent years, gelatin has been widely used as a cling film material for various foods, including fruits, vegetables and meat, due to its high safety, good mechanical properties, oxygen and water barrier properties, easy operation, and good preservation effect. However, gelatin has problems such as weak antioxidant and antibacterial activity. Although the infiltration of natural antibacterial substances such as bioactive polysaccharides improves the functional properties of gelatin film, the corresponding decrease in thermal stability and UV shielding ability will limit its practical application in food preservation.

[0004] Carbon dots (CDs), as a zero-dimensional nanomaterial, can not only give high strength to biofilms through intermolecular hydrogen bonding, but also destroy bacterial cell membranes through electrostatic effects, thereby enhancing the system's protection against pathogens. In addition, CDs are almost insoluble in all conventional solvents, which allows their products to be recycled and processed into packaging materials. Based on the above characteristics, CDs are considered to be an emerging renewable green packaging material. Related studies have used CDs to enhance different biopolymer matrices, such as chitosan, soy protein, cellulose, etc., to prepare green packaging materials. The addition of CDs not only enhances the mechanical properties and antibacterial activity of the composite film, but also gives it oxygen and ultraviolet barrier properties. Despite these advantages, research on integrating CDs into plastic wrap is still in its early stages. Most of the waste precursors for synthesizing CDs are forest biowaste, such as sawdust. However, there is limited exploration of the synthesis of CDs using marine biowaste.

[0005] The extraction of bioactive compounds from marine biomass is an important aspect of the marine bioeconomy. The extraction of polysaccharides from macroalgae usually uses water as the extraction medium, followed by the addition of large amounts of ethanol to precipitate the polysaccharides. This process produces a large amount of waste materials, including post-extraction residues and waste ethanol solutions (usually ethanol at a concentration of 80%). Direct disposal of these wastes can lead to resource inefficiency and environmental issues. Therefore, it is crucial to optimize the utilization of these waste resources and minimize waste generation. From the perspective of waste management and circular economy, the residues and waste ethanol solutions from polysaccharide extraction can be used as precursors for the synthesis of CDs for the development of composite membranes.

[0006] CDs were synthesized by hydrothermal method using the polysaccharide extraction residue of marine macroalgae as precursor. The obtained CDs can enhance the properties of the film, such as mechanical properties, UV blocking and antioxidant properties, and show high hydrophilicity and compatibility. Summary of the invention

[0007] In view of the above problems, the present invention provides a method for preparing a composite membrane based on polysaccharides and CDs, wherein the residue remaining after the extraction of Sargassum fusiformis polysaccharide and waste ethanol are used as precursors to prepare CDs, and composite membranes doped with different CDs concentrations are prepared using CDs.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a composite film based on polysaccharides and CDs, characterized in that it comprises the following steps:

[0009] Step 1, drying the residue remaining after extracting the Sargassum fusiformis polysaccharide for later use;

[0010] Step 2: dissolving the residue remaining after the dried Sargassum fusiformis polysaccharide is extracted with waste ethanol, centrifuging to obtain a supernatant, filtering the supernatant to obtain a filtrate, and preparing a CDs solution;

[0011] Step 3: adjusting the concentration of the CDs solution to a certain concentration to obtain a CDs sample, fully mixing the CDs sample with gelatin, polysaccharide extracted from Sargassum fusiformis and glycerol, and then performing a heat-induced cross-linking reaction to obtain a membrane solution;

[0012] Step 4: Dry the membrane solution at room temperature to obtain a membrane sample, then peel off the membrane sample and balance it at a certain temperature and humidity to obtain a composite membrane doped with CDs.

[0013] Preferably, in step 1, the specific process of drying is: placing the residue remaining after the dried Sargassum fusiformis polysaccharide is extracted in an oven at 60° C. and drying for 24 hours, so that the residue is dried to a constant weight.

[0014] Preferably, the specific process of step 2 is: the dried Sargassum fusiformis extraction residue and waste ethanol are placed in a polytetrafluoroethylene-lined reactor in a certain proportion and mixed, reacted at 200°C for 6 hours, and after the reaction, centrifuged at 12000rpm for 10 minutes to obtain a supernatant, and then the supernatant is filtered through a filter to obtain a filtrate to obtain a CDs solution.

[0015] Preferably, in step 2, the pore size of the filter is 0.22 μm.

[0016] Preferably, the specific process of step (3) is: adjusting the concentration of the CDs solution to 0.1% to 1.0% to obtain a CDs sample, and then fully mixing 100 mL of the CDs sample with 2 g of gelatin, 1 g of Sargassum fusiformis polysaccharide extract and 0.9 g of glycerol, and after mixing, heat-induced cross-linking at 50°C for 2 hours to obtain a membrane solution.

[0017] Preferably, the specific process of step (4) is: pouring the membrane solution into a culture dish, drying at room temperature for 48 hours, peeling off the prepared membrane sample, and balancing at 25°C, 50% relative temperature and humidity for 48 hours to obtain a composite membrane doped with CDs.

[0018] From the above description of the structure of the present invention, it can be seen that compared with the prior art, the present invention has the following advantages:

[0019] The present invention uses the residues remaining after the extraction of Sargassum fusiformis polysaccharide and the generated waste ethanol to prepare biowaste-derived carbon dots (CDs), and develops a multifunctional composite film by incorporating CDs into matrices such as gelatin and Sargassum fusiformis extracted polysaccharides; and when the CDs concentration is increased from 0.1% to 1.0%, the water vapor permeability, oxygen permeability, ultraviolet shielding ability, and DPPH and ABTS free radical scavenging ability of the composite film are significantly enhanced; when 1.0% CDs are incorporated into the composite film, the antioxidant ability to DPPH and ABTS is the strongest, and the free radical scavenging rate is above 80%; in practical applications, the prepared composite film maintains the hardness of blueberry fruit, reduces the decay rate by 50%, reduces the hardness loss, increases its commercial rate, and effectively prolongs the shelf life of blueberries during storage; the present invention uses marine seaweed waste to develop high-performance, environmentally friendly films, which can provide a sustainable solution to the challenge of food preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0021] Figure 1 is the oxygen permeability of the composite films doped with different carbon dots of the present invention;

[0022] Figure 2 is the water vapor permeability of the composite films doped with different carbon dots of the present invention;

[0023] Figure 3 is the DPPH free radical scavenging ability of the composite films doped with different carbon dots of the present invention;

[0024] Figure 4 is the ABTS free radical scavenging ability of the composite membranes doped with different carbon dots of the present invention;

[0025] Figure 5 is the ultraviolet transmittance of the composite films doped with different carbon dots of the present invention;

[0026] Figure 6 The effect of carbon dot-based membrane on the decay index of blueberries;

[0027] Figure 7 The effect of carbon dot-based membrane on the commercial yield of blueberries;

[0028] Figure 8 Effect of carbon dot-based films on blueberry hardness. DETAILED DESCRIPTION

[0029] The present invention will be described in further detail below.

[0030] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0031] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0032] Example 1

[0033] A method for preparing a composite film based on polysaccharide and CDs comprises the following steps:

[0034] Step 1, drying the residue remaining after extracting the Sargassum fusiformis polysaccharide in an oven at 60° C. for 24 hours to dry the residue to a constant weight;

[0035] Step 2, placing the dried Sargassum fusiformis extraction residue and waste ethanol in a polytetrafluoroethylene-lined reactor, reacting at 200° C. for 6 hours, and after the reaction, centrifuging at 12000 rpm for 10 minutes to obtain a supernatant, and then filtering the supernatant through a filter with a pore size of 0.22 μm to obtain a filtrate, thereby obtaining a CDs solution;

[0036] Step 3: adjusting the concentration of the CDs solution to 0.1% to obtain a CDs sample, and then fully mixing 100 mL of the CDs sample with 2 g of gelatin, 1 g of polysaccharide extracted from Sargassum fusiformis and 0.9 g of glycerol, and after mixing, heat-induced cross-linking was performed at 50° C. for 2 h to obtain a membrane solution;

[0037] Step 4: Pour the membrane solution into a culture dish, dry it at room temperature for 48 hours, peel off the prepared membrane sample, and balance it at 25° C., 50% relative temperature and humidity for 48 hours to obtain a composite membrane doped with 0.1% concentration of CDs.

[0038] Example 2

[0039] A method for preparing a composite film based on polysaccharide and CDs comprises the following steps:

[0040] Step 1, drying the residue remaining after extracting the Sargassum fusiformis polysaccharide in an oven at 60° C. for 24 hours to dry the residue to a constant weight;

[0041] Step 2, placing the dried Sargassum fusiformis extraction residue and waste ethanol in a polytetrafluoroethylene-lined reactor, reacting at 200° C. for 6 hours, and after the reaction, centrifuging at 12000 rpm for 10 minutes to obtain a supernatant, and then filtering the supernatant through a filter with a pore size of 0.22 μm to obtain a filtrate to obtain a CDs solution;

[0042] Step 3: adjusting the concentration of the CDs solution to 0.5% to obtain a CDs sample, and then fully mixing 100 mL of the CDs sample with 2 g of gelatin, 1 g of polysaccharide extracted from Sargassum fusiformis and 0.9 g of glycerol, and after mixing, heat-induced cross-linking was performed at 50° C. for 2 h to obtain a membrane solution;

[0043] Step 4: Pour the membrane solution into a culture dish, dry it at room temperature for 48 hours, peel off the prepared membrane sample, and balance it at 25° C., 50% relative temperature and humidity for 48 hours to obtain a composite membrane doped with 0.5% concentration of CDs.

[0044] Example 3

[0045] A method for preparing a composite film based on polysaccharide and CDs comprises the following steps:

[0046] Step 1, drying the residue remaining after extracting the Sargassum fusiformis polysaccharide in an oven at 60° C. for 24 hours to dry the residue to a constant weight;

[0047] Step 2, placing the dried Sargassum fusiformis extraction residue and waste ethanol in a polytetrafluoroethylene-lined reactor, reacting at 200° C. for 6 hours, and after the reaction, centrifuging at 12000 rpm for 10 minutes to obtain a supernatant, and then filtering the supernatant through a filter with a pore size of 0.22 μm to obtain a filtrate, thereby obtaining a CDs solution;

[0048] Step 3, adjusting the concentration of the CDs solution to 1.0% to obtain a CDs sample, and then fully mixing 100 mL of the CDs sample with 2 g of gelatin, 1 g of polysaccharide extracted from Sargassum fusiformis and 0.9 g of glycerol, and after mixing, heat-induced cross-linking was performed at 50° C. for 2 h to obtain a membrane solution;

[0049] Step 4: Pour the membrane solution into a culture dish, dry it at room temperature for 48 hours, peel off the prepared membrane sample, and balance it at 25° C., 50% relative temperature and humidity for 48 hours to obtain a composite membrane doped with 1.0% concentration of CDs.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a composite film based on polysaccharides and CDs, characterized in that: The following steps are involved: Step 1, drying the residue remaining after extracting the Sargassum fusiformis polysaccharide for later use; Step 2, dissolving the dried Sargassum fusiformis polysaccharide extraction residue in waste ethanol (c=85%), collecting the supernatant after centrifugation, and passing the supernatant through a 0.22 μm microporous filter membrane to prepare a CDs solution; Step 3, fully mixing a CDs solution of a specific concentration with gelatin, polysaccharide extracted from Sargassum fusiformis and glycerol, and then forming a membrane solution through a heat-induced cross-linking reaction; Step 4: Dry the membrane solution at room temperature to obtain a membrane sample, then peel off the membrane sample and balance it at a certain temperature and humidity to obtain a composite membrane doped with CDs.

2. The method for preparing a composite film based on polysaccharides and CDs according to claim 1, characterized in that: In the step 1, the specific drying process is: placing the residue remaining after the extraction of Sargassum fusiformis polysaccharide in an oven at 60° C. and drying for 24 hours, and drying the residue to a constant weight.

3. The method for preparing a composite film based on polysaccharides and CDs according to claim 1, characterized in that: The specific process of step 2 is: the residue remaining after the dried Sargassum fusiformis polysaccharide is extracted and the waste ethanol are placed in a polytetrafluoroethylene-lined reactor in a certain proportion and mixed, reacted at 200°C for 6 hours, and after the reaction is completed, centrifuged at 12000rpm for 10 minutes to obtain a supernatant, and then the supernatant is filtered through a filter to obtain a filtrate to obtain a CDs solution.

4. The method for preparing a composite film based on polysaccharides and CDs according to claim 3, characterized in that: In the step 2, the pore size of the filter is 0.22 μm.

5. The method for preparing a composite film based on polysaccharides and CDs according to claim 1, characterized in that: The specific process of step (3) is as follows: the concentration of the CDs solution is adjusted to 0.1% to 1.0% to obtain a CDs sample, and then 100 mL of the CDs sample is fully mixed with 2 g of gelatin, 1 g of polysaccharide extracted from Sargassum fusiformis and 0.9 g of glycerol, and after mixing, heat-induced cross-linking is performed at 50° C. for 2 hours to obtain a membrane solution.

6. The method for preparing a composite film based on polysaccharides and CDs according to claim 1, characterized in that: The specific process of step (4) is as follows: pour the membrane solution into a culture dish, dry it at room temperature for 48 hours, peel off the prepared membrane sample, and balance it at 25° C., 50% relative temperature and humidity for 48 hours to obtain a composite membrane doped with CDs.

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