Method for resource utilization of fruit peel waste

Abstract

The application belongs to the technical field of agricultural and sideline product waste treatment, and particularly relates to a method for resource utilization of peel waste, which mainly comprises the following steps: 1) peels are dried, crushed, and subjected to high-pressure ultrasonic microwave acidolysis separation to obtain mixed slurry; and 2) the mixed slurry is subjected to ultrasonic dispersion, paving, natural air drying or drying to obtain biological plastic. The biological plastic obtained by the method has high mechanical properties, oxidation resistance, antibacterial properties and other multifunctional properties, and can be regarded as a biological-based plastic with great potential to replace petrochemical plastics used for food packaging.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and sideline product waste treatment technology, and specifically relates to a method for the resource utilization of fruit peel waste. Background Technology

[0002] Fruit processing and consumption generate a large amount of waste, such as fruit peels, which are generally rarely utilized or even discarded directly. These wastes contain various active ingredients, primarily including pectin, cellulose, flavonoids, and pigments. The effective resource utilization of fruit peel waste is a shared expectation and pursuit of researchers and the public. Current research on fruit peels mainly focuses on the extraction of functional active ingredients, with very little research on utilizing their high pectin and cellulose content for plastic preparation.

[0003] While the development of plastic products has brought great convenience to humankind, it has also brought numerous social and environmental problems. Due to high recycling costs, large quantities of plastic bags are discarded. Furthermore, plastic products are extremely difficult to degrade, posing a significant threat to the environment and human health. With increasing environmental awareness, the development of biodegradable and recyclable bio-based plastics (such as cellulose and pectin) has gained widespread popularity. In addition, food waste and food safety incidents caused by food spoilage have also attracted public attention; developing packaging materials that can preserve freshness and slow down the spoilage process is one effective way to address this problem.

[0004] Currently, numerous cellulose or pectin-based films have been developed with the potential to replace petrochemical plastics. However, they suffer from low mechanical strength, poor flexibility, poor water stability, lack of antioxidant or antibacterial activity, and difficulty in degradation, which hinders further development and application. Generally, the mechanical properties or water stability of the films are improved through chemical modification or physical blending with other polymers. However, this involves complex procedures and the use of toxic chemicals, which is detrimental to sustainable development. Especially in terms of bioactivity, they are often limited by poor release kinetics and potential biotoxicity. Therefore, it is of great significance to develop active packaging materials with the potential to replace petrochemical plastics in a simple, green, and sustainable manner. Summary of the Invention

[0005] To address the aforementioned problems and the shortcomings of existing technologies, this invention provides a method for the resource utilization of fruit peel waste. The aim is to provide a green, simple, and sustainable method for preparing high-strength, multifunctional bioplastics based on fruit peels. The bioplastics obtained by this method have good mechanical properties and antibacterial characteristics, and are expected to solve the aforementioned problems. Furthermore, the method allows for the recycling of pectin polysaccharides, which have high added value.

[0006] A method for the resource utilization of fruit peel waste includes the following steps:

[0007] 1) Dry and crush the fruit peel;

[0008] 2) Mix the substance obtained in step 1) with water and perform cell wall disruption under high pressure;

[0009] 3) Adjust the pH of the mixture obtained in step 2) to 1-3 using a saturated citric acid solution, then heat and stir. The advantage of the citric acid solution is that citric acid is a weak organic acid, which is beneficial for protecting bioactive substances. 4) Separate the mixture obtained in step 3) to obtain the supernatant and residue.

[0010] 5) Mix the residue from step 4) with water until it becomes uniformly viscous to obtain a cellulose-based film-forming slurry;

[0011] 6) Deaerate the slurry obtained in step 5), spread it evenly on the substrate, dry it or let it air dry, and then peel off the film to obtain bioplastic.

[0012] Preferably, the peel contains pectin and cellulose, and the peel is pulverized through a 200-mesh sieve. The raw material can be the peel of citrus fruits (oranges, lemons, tangerines, etc.), or other peels rich in pectin and cellulose (dragon fruit, bananas, watermelons, etc.).

[0013] Preferably, in step 2), the mass ratio of the obtained product to water is 1:20-50, the high-pressure environment is 2.0-3.0 MPa, and the cell wall disruption conditions are: microwave power of 400-700 W, ultrasonic power of 300-500 W, and time of 10-20 min. Rapid heating under high pressure combined with ultrasonic treatment can significantly shorten the cell wall disruption process of the pericarp and avoid damage or deterioration of the active ingredients in the cell wall caused by prolonged high temperatures.

[0014] Preferably, in step 3), the heating and stirring conditions are: temperature 65-95℃; time 30-60 min; and stirring speed 150-500 rpm. Stirring under low pH and high temperature conditions is beneficial to accelerate pectin dissociation; excessively high pH or excessively low temperature will reduce the efficiency of pectin dissociation and will also damage or degrade the active substances contained in the cell wall.

[0015] Preferably, in step 4), the separation is carried out by centrifugation, filtration or settling.

[0016] Preferably, in step 5), the water is 10-20 times the mass of the residue, and mixing is performed by stirring and / or ultrasound. More preferably, the mixing is performed using ultrasound at a power of 300-450W for 5-10 minutes, followed by magnetic stirring until completely homogeneous. Too little water will result in poor uniform dispersion, while too much water will reduce the matrix concentration, making it difficult to form a film.

[0017] Preferably, in step 6), the slurry is spread evenly to a substrate thickness of 0.3-0.5 cm, and the drying conditions are: drying at 40-60°C until the film can be easily peeled off. Too thin or too thick a layer is detrimental to the stable formation of the film, and excessively high temperatures can cause the film to crack easily.

[0018] Preferably, the pectin polysaccharide is recovered from the supernatant in step 4) above, and the specific steps are as follows:

[0019] 7) Concentrate the supernatant obtained in step 4), add anhydrous ethanol, and precipitate.

[0020] 8) Redissolve the precipitate obtained in step 7) in water and filter it.

[0021] 9) Concentrate the solution obtained in step 8), and then freeze-dry it to obtain pectin polysaccharide;

[0022] 10) The waste liquid obtained in step 9) is rotary distilled to recover ethanol, water and citric acid solution, which can be used for the next round of bioplastics production.

[0023] More preferably, in step 7), the amount of anhydrous ethanol added is 2-4 times the volume of the concentrated supernatant.

[0024] More preferably, in step 8), the mixture is filtered through a 3.5 kDa filter membrane for 24-48 hours to filter out small molecules such as oligosaccharides, in order to further recover pectin polysaccharides.

[0025] This invention utilizes microwave-assisted ultrasonic treatment under high pressure to break down the cell walls of the pericarp, followed by citric acid heat treatment to separate pectin and cellulose. Individual components like pectin and cellulose are difficult to form films on their own, or the resulting films exhibit poor performance. This invention utilizes the pectin remaining in the fibers as a crosslinking agent, tightly entwining it with the cellulose fibers, which improves the mechanical properties of the film. Furthermore, the entire process avoids the use of harsh chemicals (such as sodium hydroxide and concentrated hydrochloric acid), preventing damage to the active substances, rapidly separating pectin and cellulose, and effectively preserving a large amount of polyphenolic active ingredients. The prepared bioplastic possesses antioxidant and antibacterial activities and is completely degradable, avoiding pollution. The pectin polysaccharides recovered in this invention have numerous RG-I domains, are rich in neutral sugar branches, and have a large molecular weight. When dissolved in water, it exhibits high viscosity and modulus, and can be mixed with edible oils to prepare stable oil-in-water emulsions with excellent rheological and emulsifying properties, resulting in higher added value compared to conventional pectin on the market.

[0026] The present invention has the following advantages and beneficial effects:

[0027] (1) This invention makes the most of the fruit peel, which not only avoids environmental pollution, but also enhances the application value of fruit peel waste.

[0028] (2) The resulting bioplastic has high mechanical strength and is completely degradable. It has antioxidant and antibacterial properties and can extend the shelf life of fruits and other items.

[0029] (3) The resulting bioplastics are recyclable, and the bioplastics can be re-formed into films after simple treatment at the end of the service life;

[0030] (4) Pectin polysaccharides can be recycled, and pectin polysaccharides have high added value;

[0031] (5) The method used does not require other film-forming agents, plasticizers or other chemical reagents. It is safe, green and simple to implement, low in cost and easy to achieve sustainable mass production. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the bioplastic prepared in Example 1 being rolled and folded;

[0033] Figure 2 A bar chart showing the DPPH scavenging rate of the bioplastic prepared in Example 1;

[0034] Figure 3 A schematic diagram of the inhibition zones of Escherichia coli and Staphylococcus aureus in the bioplastic prepared in Example 1;

[0035] Figure 4 This is a schematic diagram showing the hardness of the bioplastic prepared in Example 1 and the commercially available plastic wrap, as well as the appearance of the fruit used in the preservation test.

[0036] Figure 5 A bar chart comparing the hardness of the bioplastic prepared in Example 1 and the commercially available cling film, as well as the weight loss rate and hardness retention rate of the fruit in the preservation test.

[0037] Figure 6 The image shows the characterization test results of the pectin polysaccharides recovered in Example 1.

[0038] Figure 7 The rheological properties test diagrams for pectin polysaccharide and citrus peel pectin in Example 1 are shown.

[0039] Figure 8 This is a graph showing the emulsifying properties of pectin polysaccharides. Detailed Implementation

[0040] The embodiments of the present invention will be described in further detail below. It should be noted that the following embodiments are only for further illustrating the present invention, and the implementation of the present invention is not limited thereto. Some non-essential adjustments and improvements made by those skilled in the art based on the above-described inventive solutions still fall within the protection scope of the present invention.

[0041] The following fruit peels were purchased from food companies or agricultural product markets.

[0042] Example 1

[0043] A method for the resource utilization of fruit peel waste:

[0044] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 2.0MPa and subjected to ultrasonic and microwave synergistic treatment for 10min (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80℃ and a stirring rate of 300rpm for 30min. The supernatant and residue were separated by filtration. The supernatant was concentrated to a viscous consistency and then precipitated with 3 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48h and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (water being 10 times the mass of the residue) and ultrasonically treated at 300W for 5min to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a glass plate of appropriate size (0.5cm thick), dried at room temperature, and the film was peeled off to obtain the final product.

[0045] Example 2

[0046] A method for the resource utilization of fruit peel waste:

[0047] Fresh citrus peels were selected, washed, dried, and pulverized through a 100-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 3.0MPa and subjected to ultrasonic / microwave treatment for 10 minutes (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80℃ for 30 minutes at a stirring speed of 200rpm. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and then precipitated with 3 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48 hours and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (20 times the mass of the residue), and ultrasonically treated at 300W for 5 minutes to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a suitable-sized glass plate (0.5cm thick), dried at room temperature, and the film was peeled off to obtain the final product.

[0048] Example 3

[0049] A method for the resource utilization of fruit peel waste:

[0050] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 2.5MPa and subjected to ultrasonic / microwave treatment for 10 minutes (microwave intensity: 800W; ultrasonic intensity: 400W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80℃ for 30 minutes at a stirring speed of 150rpm. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and then precipitated with 3 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48 hours and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (15 times the mass of the residue), and ultrasonically treated at 300W for 5 minutes to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a glass plate of suitable size (0.5cm thick), dried at room temperature, and the film was peeled off to obtain the final product.

[0051] Example 4

[0052] A method for the resource utilization of fruit peel waste:

[0053] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 2.0MPa and subjected to ultrasonic / microwave treatment for 30min (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80℃ and a stirring rate of 400rpm for 30min. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and precipitated by adding 3 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48h and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (10 times the mass of the residue), and ultrasonically treated at 300W for 5min to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a glass plate of suitable size (approximately 0.5cm thick), dried at room temperature, and the film was peeled off to obtain the final product.

[0054] Example 5

[0055] A method for the resource utilization of fruit peel waste:

[0056] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 2.5MPa and subjected to ultrasonic and microwave treatment for 10 minutes (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 90℃ and a stirring rate of 150rpm for 60 minutes. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and then precipitated with three times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48 hours and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (10 times the mass of the residue), and ultrasonically treated at 300W for 5 minutes to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a glass plate of suitable size (0.5cm thick), dried at room temperature, and the film was peeled off to obtain the final product.

[0057] Example 6

[0058] A method for the resource utilization of fruit peel waste:

[0059] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment of 3.0MPa and subjected to ultrasonic / microwave treatment for 10 minutes (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80℃ for 30 minutes at a stirring speed of 500rpm. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and precipitated by adding 3 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5kDa filter membrane for 48 hours and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (10 times the mass of the residue) and ultrasonically treated at 250W for 10 minutes to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a glass plate of suitable size (approximately 0.5cm thick), dried at room temperature, and the film was peeled off.

[0060] Example 7

[0061] A method for the resource utilization of fruit peel waste:

[0062] Fresh lemon peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of lemon peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment (2.0 MPa) and subjected to ultrasonic / microwave treatment for 10 minutes (microwave intensity: 600 W; ultrasonic intensity: 500 W). The pH of the mixture was adjusted to 2 using a saturated citric acid solution. Then, the mixture was stirred at 80°C and a stirring rate of 200 rpm for 30 minutes. The supernatant and residue were separated by filtration or centrifugation. The supernatant was concentrated to a viscous consistency and precipitated by adding 4 times its volume of anhydrous ethanol. The precipitate was collected and redissolved in water. The mixture was filtered through a 3.5 kDa filter membrane for 48 hours and freeze-dried to obtain pectin polysaccharide. The residue was mixed with an appropriate amount of water (10 times the mass of the residue) and ultrasonically treated at 300 W for 5 minutes to form a cellulose-based film slurry. After degassing, the slurry was poured onto a glass plate of suitable size (approximately 0.5 cm thick) and allowed to dry at room temperature before peeling off the film.

[0063] Comparative Example 1

[0064] A method for the resource utilization of fruit peel waste:

[0065] Select fresh citrus peels, wash and dry them, then pulverize them through a 200-mesh sieve. Weigh 10g of citrus peel powder and mix it with deionized water at a ratio of 1:25 (m / v). Place the mixture in a high-pressure environment of 2.0-3.0MPa and treat it with ultrasound and microwave for 10min (microwave intensity: 600W; ultrasound intensity: 500W). Adjust the pH of the mixture to 2 using 1mol / L hydrochloric acid solution. Then, stir at 80℃ and a stirring rate of 300rpm for 30min. Separate the supernatant and residue by filtration or centrifugation. Mix the residue with an appropriate amount of water (water is 10 times the mass of the residue) and treat it with ultrasound at 250W for 10min to form a cellulose-based film-forming slurry. After degassing, pour it onto a glass plate of appropriate size (thickness 0.5cm). After air-drying or baking at room temperature, the film is difficult to peel off and difficult to form.

[0066] Comparative Example 2

[0067] A method for the resource utilization of fruit peel waste:

[0068] Fresh citrus peels were selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of citrus peel powder was weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture was placed in a high-pressure environment (2.0-3.0 MPa) and subjected to ultrasonic / microwave treatment for 10 minutes (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture was adjusted to 10 using a 1mol / L sodium hydroxide solution. Then, the mixture was stirred at 80℃ for 30 minutes at a stirring speed of 300 rpm. The supernatant and residue were separated by filtration or centrifugation. The residue was mixed with an appropriate amount of water (10 times the mass of the residue), and ultrasonically treated at 250W for 10 minutes to form a cellulose-based film-forming slurry. After degassing, the slurry was poured onto a suitable-sized glass plate (0.5cm thick) and air-dried or oven-dried at room temperature. The resulting film was difficult to peel off and form.

[0069] Comparative Example 3

[0070] A method for the resource utilization of fruit peel waste:

[0071] Fresh sugarcane bagasse is selected, washed, dried, and pulverized through a 200-mesh sieve. 10g of sugarcane bagasse powder is weighed and mixed with deionized water at a ratio of 1:25 (m / v). The mixture is placed in a high-pressure environment of 2.0MPa and subjected to ultrasonic and microwave treatment for 10min (microwave intensity: 600W; ultrasonic intensity: 500W). The pH of the mixture is adjusted to 2 using a saturated citric acid solution. Then, the mixture is stirred at 80℃ and a stirring rate of 300rpm for 30min. The supernatant and residue are separated by filtration or centrifugation. The residue is mixed with an appropriate amount of water (10 times the mass of the residue) and ultrasonically treated at 250W for 10min to form a cellulose-based film-forming slurry. After degassing, the slurry is poured onto a glass plate of appropriate size (0.5cm thick) and dried at room temperature or by baking. The resulting film is difficult to peel off and difficult to form.

[0072] The preparation methods disclosed in Comparative Examples 1-3 are difficult to form complete membranes.

[0073] Test case

[0074] Determination of DPPH free radical scavenging rate:

[0075] The DPPH free radical scavenging ability and antioxidant capacity were determined using a micro DPPH free radical scavenging ability assay kit (BC4750, Solarbio). Figure 2 As shown, the clearance rate increases with increasing bioplastic concentration, reaching 70.07% at 50 mg / mL. The specific steps are as follows:

[0076] 1. Grind the bioplastic (film) prepared in Example 1 in a mortar (or grind it in a pulverizer) and pass it through a 50-mesh sieve; weigh 0.01g, 0.02g, 0.03g, 0.04g, and 0.05g of samples respectively, add 1mL of the extraction solution in the kit, soak in a water bath at 40℃ for 30min, centrifuge at 10000rpm for 10min at room temperature, take the supernatant, and place it on ice for testing.

[0077] 2. Preheat the spectrophotometer for at least 30 minutes, adjust the wavelength to 515 nm, zero the instrument with anhydrous ethanol, and measure its absorbance.

[0078] 3. Mix the supernatant with "Reagent 3", "Reagent 1" and "Working Solution" in the kit according to the instructions, vortex to mix, and let stand at room temperature in the dark for 30 minutes. Measure the absorbance at 515 nm. Each test tube should have a control tube.

[0079] 4. Calculate according to the formula: DPPH free radical scavenging rate (%) = [[A blank - (A determination - A control)] ÷ A blank] × 100%.

[0080] Antibacterial performance test

[0081] The antibacterial activity was determined by the disc diffusion method, which was used to detect Escherichia coli (10⁻⁶) and saturate it with a 10⁻⁶ mol / L ... 7 CFU / mL), Staphylococcus aureus (10 7 After spreading CFU / mL onto the culture medium, circular films (the bioplastic prepared in Example 1) cut to a diameter of 1.5 cm were attached to the culture medium and incubated at 37°C for 24 hours. The inhibition zones were then observed. Figure 3 As shown, the presence of the inhibition zone indicates that bacteria cannot grow normally near the bioplastic prepared in this invention, which also demonstrates its antibacterial properties.

[0082] Hardness and freshness test

[0083] The results were determined using a texture analyzer (Paul Technologies, TA.XTC-20).

[0084] At room temperature, mangoes, bananas, and avocados from the same batch (with similar ripeness or color) were selected, and their initial weight and initial hardness were recorded. They were placed separately in the bioplastic prepared in Example 1 (experimental group) and commercially available plastic wrap (control group). The mangoes, bananas, and avocados were stored separately without mixing. After 6 days, the bioplastic and plastic wrap were opened, and the changes in the appearance of the mangoes, bananas, and avocados were observed. The final weight and final hardness were recorded. In the experimental group, the mangoes, bananas, and avocados showed slight changes in ripeness compared to before the experiment, with minimal changes and no rotting. In the control group, the mangoes, bananas, and avocados showed significantly increased ripeness compared to before the experiment, with a darker, blacker color and obvious rotting. Figure 4 As shown in Figure 5, the weight loss rate and firmness retention rate of the fruit before and after the experiment were calculated based on their weight and firmness. The experimental group showed a significantly lower weight loss rate and a higher firmness retention rate than the control group. The bioplastic prepared in this invention exhibits significantly better preservation effects than commercially available food preservation films.

[0085] Weight loss rate: (Initial weight - Final mass) / Initial weight × 100%

[0086] Hardness retention rate: Final hardness / Initial hardness × 100%

[0087] Testing of pectin polysaccharide structure

[0088] The pectin polysaccharides recovered in Example 1 were characterized, such as... Figure 6 Based on the high efficiency anion exchange chromatogram (a), gel permeation chromatogram (b), nuclear magnetic resonance hydrogen spectrum (c), and two-dimensional nuclear magnetic resonance HSQC spectrum (d) of pectin, its RG-I configuration and rich neutral sugar side chains can be identified.

[0089] Rheological property testing of pectin polysaccharides

[0090] Preparation of pectin polysaccharide emulsions: The pectin polysaccharides recovered in Example 1 were diluted with water to prepare 1.0%, 2.0%, and 4.0% solutions, respectively; commercially available citrus peel pectin was also diluted with water to prepare 1.0%, 2.0%, and 4.0% solutions. Tests yielded the following results: Figure 7 The rheological property test diagram shown is as follows. Figure 7 In Figure 'a', the viscosity curve of the pectin solution is shown, and in Figures 'bd' and 'd', the storage modulus (G′) and loss modulus (G″) of the pectin solution are shown. RPP represents pectin fructose, and CP represents commercially available citrus peel pectin. The figures demonstrate that the pectin polysaccharides recovered in this invention have higher viscosity and shear-thinning properties than commercially available citrus peel pectin. They also have higher moduli and exhibit "solid-like" properties (G′ > G″), showing potential for self-gel formation.

[0091] Pectin polysaccharide emulsification performance test

[0092] In Example 1, the recovered pectin polysaccharide and commercially available citrus peel pectin were prepared into 0.5%, 1.0%, 1.5%, and 2.0% solutions respectively with water. These solutions were then mixed with an equal amount of corn germ oil and homogenized using a high-speed homogenizer at 14000 rpm for 2 minutes to obtain emulsions. After standing for 30 days, visual and microscopic images of the emulsions on the first and third days are shown below. Figure 8 As shown in the figure, RPP represents pectin fructose, and CP represents commercially available citrus peel pectin. The commercially available pectin emulsion experienced severe stratification and demulsification, while the emulsion prepared from the pectin polysaccharide prepared in Example 1 still maintained good stability.

[0093] Table 1 compares the performance of the bioplastic prepared in Example 1 with that of commercially available food preservation film.

[0094]

[0095] This invention maximizes the utilization of fruit peels, not only avoiding environmental pollution but also enhancing the application value of fruit peel waste. The resulting bioplastic has high mechanical strength and is completely biodegradable, possessing antioxidant and antibacterial properties, which can extend the shelf life of fruits and other products. The resulting bioplastic is recyclable; after its service life, the bioplastic can be easily processed to form a film again. Pectin polysaccharides can be recovered, and these polysaccharides have high added value. The method used requires no other film-forming agents, plasticizers, or other chemical reagents, making it safe, green, simple, and easy to implement at low cost, facilitating sustainable mass production.

[0096] The above embodiments are preferred embodiments of the present invention, mainly demonstrating and describing the main features and basic principles of the present invention. However, the implementation of the present invention is not limited to the above embodiments. Any modifications, alterations, substitutions, combinations, or simplifications made by those skilled in the art without departing from the spirit and scope of the present invention should be considered within the scope of the present invention.

Claims

1. A method for the resource utilization of fruit peel waste, characterized in that, The steps are as follows: 1) Dry and crush the fruit peel; 2) Mix the substance obtained in step 1) with water and perform cell wall disruption under high pressure; 3) Adjust the pH of the mixture obtained in step 2) to 1-3 using a saturated citric acid solution, then heat and stir. 4) Separate the mixture obtained in step 3) to obtain the supernatant and residue; 5) Mix the residue from step 4) with water until it becomes uniformly viscous to obtain a cellulose-based film-forming slurry; 6) Degas the slurry obtained in step 5), spread it evenly on the substrate, dry it or let it air dry, and then peel off the film to obtain the bioplastic. In step 2), the mass ratio of the obtained substance to water is 1:20-50, the high pressure environment is 2.0-3.0 MPa, and the cell wall breaking conditions are: microwave power of 400-700 W, ultrasonic power of 300-500 W, and time of 10-20 min. The pectin polysaccharides were recovered using the supernatant from step 4) above. The specific steps are as follows: 7) Concentrate the supernatant obtained in step 4), add anhydrous ethanol, and precipitate. 8) Redissolve the precipitate obtained in step 7) in water and then filter it. 9) Concentrate the solution obtained in step 8), and then freeze-dry it to obtain pectin polysaccharide; 10) The waste liquid obtained in step 9) is rotary distilled to recover ethanol, water and citric acid solution, which can be used for the next round of bioplastics production.

2. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, The peel contains pectin and cellulose, and the peel is crushed through a 200-mesh sieve.

3. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, In step 3), the heating and stirring conditions are: temperature 65-95℃, time 30-60 min, and stirring speed 150-500 rpm.

4. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, In step 4), separation is achieved by centrifugation, filtration, or settling; in step 5), water is used at 10-20 times the mass of the residue, and mixing is achieved by stirring and / or ultrasound.

5. The method for resource utilization of fruit peel waste according to claim 4, characterized in that, Step 5) The mixing is performed using an ultrasonic power of 300-450 W for 5-10 min, followed by magnetic stirring until completely homogeneous.

6. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, In step 6), the slurry is spread evenly to a substrate thickness of 0.3-0.5cm, and the drying conditions are: dry at 40-60℃ until the film can be easily peeled off.

7. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, In step 7), the amount of anhydrous ethanol added is 2-4 times the volume of the concentrated supernatant.

8. The method for resource utilization of fruit peel waste according to claim 1, characterized in that, In step 8), the filter is passed through a 3.5 kDa filter membrane for 24-48 hours.

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