Functionalized composite membrane based on whole components of pomelo peel and application thereof

Abstract

The application belongs to the field of food packaging, and particularly relates to a functional composite film based on full-component utilization of pomelo peel and application thereof. The pomelo peel is separated into water-soluble active components (supernatant) and water-insoluble components (precipitate), and polyvinyl alcohol / supernatant films and polyvinyl alcohol / precipitate films are prepared by compounding the water-soluble active components and the water-insoluble components with polyvinyl alcohol, respectively. The polyvinyl alcohol / supernatant film has excellent antioxidant activity and flexibility, and the polyvinyl alcohol / precipitate film has excellent antibacterial property and mechanical strength. The two kinds of films can be used alone or in combination according to the preservation requirements of different foods, so as to achieve targeted preservation effect. The application realizes high-value utilization of the full components of pomelo peel, and the prepared composite film is biodegradable, and has wide application prospect in the field of food packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging, specifically relating to a functionalized composite film based on the full utilization of grapefruit peel and its application. Background Technology

[0002] The booming global food industry, while meeting human nutritional needs, also faces the dual pressures of resource waste and environmental pollution. According to the Food and Agriculture Organization of the United Nations (FAO), approximately one-third of the world's food, totaling a staggering 1.6 billion tons, is lost or wasted annually in the supply chain, with fresh fruits and vegetables suffering losses of 30% to 50% due to post-harvest spoilage. Fruit spoilage caused by vigorous respiration and microbial contamination is particularly prominent after harvest. While traditional petroleum-based plastic packaging can delay spoilage, its effectiveness is limited due to its lack of antibacterial activity and singular preservation function. Furthermore, its non-degradable nature leads to the continuous accumulation of "white pollution," posing a serious threat to the ecological environment. Therefore, developing "active packaging" that combines preservation and biodegradability is a key path to solving the synergistic problem of food waste and environmental pollution, and it drives research to shift towards the exploration of natural and sustainable resources.

[0003] Against this backdrop, the resource utilization of agricultural waste offers a new opportunity for the development of sustainable packaging materials. Fruit peels, as a major byproduct of fruit processing, are rich in cellulose, pectin, and phenolic active substances. Their conversion and utilization can achieve both sustainable development and reduce resource waste. Citrus peel waste, as one of the world's largest agricultural byproducts, shows enormous application potential due to its rich bioactive components. Grapefruit, a popular fruit, has a global annual production exceeding 5 million tons, generating over 2 million tons of grapefruit peel byproducts annually; however, the vast majority is not effectively utilized. Research shows that grapefruit peel is a complex natural treasure trove, containing water-insoluble polysaccharides such as pectin, cellulose, and hemicellulose, as well as water-soluble active ingredients such as flavonoids, phenolic acids, and vitamin C. These components possess excellent physical barrier properties, as well as antioxidant and antibacterial properties. Therefore, turning grapefruit peel into a valuable food preservation material is a highly attractive green approach.

[0004] However, current research and applications of pomelo peel mainly focus on the extraction of single active ingredients. For example, phenolic extracts are obtained from pomelo peel using methods such as organic solvent extraction, ultrasound-assisted extraction, or microwave extraction, and then incorporated as additives into film-forming matrices to impart antioxidant properties to the films. Specifically, CN 117264287 A discloses a composite film for pre-packaged vegetables and its preparation method, in which D-limonene is obtained from pomelo. Alternatively, cellulose nanocrystals are separated through chemical or enzymatic treatment to enhance the mechanical properties of the synthesized films. While these strategies have increased the added value of pomelo peel to some extent, their inherent limitations are also very obvious. The multi-step extraction and purification process is energy-intensive and complex, often requiring large amounts of organic solvents, and the residues after separation are often discarded, failing to achieve full utilization of all components. Therefore, exploring a green synthesis method for composite films based on the full utilization of pomelo peel is of great significance for developing biodegradable active packaging and the high-value transformation of pomelo peel resources. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] This invention discloses a functionalized composite film based on the full utilization of grapefruit peel components. The preparation method of the functionalized composite film includes the following steps:

[0007] (1) Preparation of supernatant and precipitate from grapefruit peel: Grapefruit peel was mixed with water and glycerol was added and stirred. The pH of the solution was adjusted to 2. After heating and stirring, the solution was centrifuged to obtain supernatant and precipitate.

[0008] (2) Preparation of polyvinyl alcohol / supernatant composite membrane: Polyvinyl alcohol and the supernatant are mixed and stirred evenly to prepare polyvinyl alcohol / supernatant composite membrane;

[0009] (3) Preparation of polyvinyl alcohol / precipitate composite membrane: Add polyvinyl alcohol to water, add glycerin, heat and stir evenly to obtain polyvinyl alcohol solution, and then mix the polyvinyl alcohol solution with the precipitate and stir evenly to prepare polyvinyl alcohol / precipitate composite membrane.

[0010] Preferably, the grapefruit peel in step (1) is grapefruit peel powder, and the mass ratio of the grapefruit peel powder to the volume of water is 1:50.

[0011] Preferably, the glycerol is 0.5% of the total mass of grapefruit peel and water; the heating and stirring is carried out at 70°C for 0.5 h.

[0012] Preferably, in step (2), the mass of polyvinyl alcohol is 2% of the volume of the supernatant.

[0013] Preferably, in step (3), the mass ratio of polyvinyl alcohol to water is 1:50.

[0014] Preferably, the glycerol in step (3) is 2% of the total mass of polyvinyl alcohol and water;

[0015] Preferably, the heating and stirring in step (3) is carried out by heating at 90°C for 2 hours and stirring until uniform.

[0016] Preferably, the volume of the polyvinyl alcohol solution in step (3) is the same as that of the supernatant in step (1).

[0017] The application of the functionalized composite membrane of the present invention in the preparation of antibacterial products.

[0018] Preferably, the antibacterial activity is against both Gram-negative and Gram-positive bacteria.

[0019] Preferably, the Gram-negative bacteria are Escherichia coli and the Gram-positive bacteria are Staphylococcus aureus.

[0020] The beneficial effects of this invention are:

[0021] This invention separates grapefruit peel into a water-soluble active component (supernatant) and a water-insoluble component (precipitate), which are then compounded with polyvinyl alcohol (PVA) to prepare PVA / supernatant membranes and PVA / precipitate membranes, respectively. The PVA / supernatant membrane exhibits excellent antioxidant activity and flexibility, while the PVA / precipitate membrane demonstrates superior antibacterial properties and mechanical strength. Both films can be used individually or in combination to achieve targeted preservation effects for different foods. This invention realizes the high-value utilization of all components of grapefruit peel, and the prepared composite membrane is biodegradable, showing broad application prospects in the food packaging field. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of the two composite membranes of the present invention.

[0023] Figure 2 This refers to the antioxidant properties of the composite membrane.

[0024] Figure 3 The inhibitory and bactericidal effects of the two composite membranes prepared on Escherichia coli and Staphylococcus aureus were investigated. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Example 1: Separation and Composite Membrane of Active Components from Grapefruit Peel

[0027] according to Figure 1 The method for separating the active components of grapefruit peel and preparing the composite membrane in Example 1 of the present invention will be explained and described, such as... Figure 1 As shown, this method involves separating grapefruit peel into supernatant (SN) and precipitate (PP) after ultrasonic-assisted citric acid heat treatment. SN and PP are then introduced into a polyvinyl alcohol matrix membrane to prepare two composite membranes.

[0028] The specific preparation method is as follows:

[0029] Weigh 1 g of grapefruit peel powder (PPP) and add it to 50 mL of deionized water. Add 0.5% glycerol (by mass of the grapefruit peel powder solution), stir evenly at room temperature, adjust the pH of the solution to 2, heat and stir at 70°C for 0.5 h, centrifuge the resulting solution to obtain supernatant (SN) and precipitate (PP). Then, add 2 g of polyvinyl alcohol (PVA) to 100 mL of water, add 2% glycerol (by mass of the total mass of PVA and water), heat at 90°C for 2 h, stir evenly, and record as solution A. Add 2% PVA (by mass) to the supernatant (SN), stir evenly at 70°C, and record as solution B, i.e., PVA / SN film-forming solution. Then, mix solution A (the volume of solution A is equivalent to the volume of the supernatant obtained by centrifugation) into all the obtained precipitate (PP), stir evenly at room temperature (25°C), and record as solution C, i.e., PVA / PP film-forming solution. Finally, pour liquids B and C evenly into the mold and dry it in a drying oven at 50°C. After drying, peel off the two composite films to obtain a functional composite film that utilizes all components of grapefruit peel.

[0030] Example 2: Separation of active components from grapefruit peel and antioxidant properties of the composite membrane

[0031] To verify the antioxidant properties of the composite membranes obtained by the above preparation method, the dose- and time-dependent antioxidant activity of the two membranes was evaluated using a DPPH radical scavenging kit (Kit TO1143). Briefly, membrane samples at different concentrations (0, 1, 3, 5, 10, 15, and 20 mg / mL) were mixed with 1 mL of DPPH (0.1 mM) solution to form a reaction system. The mixture was then reacted in the dark for 30 minutes, and the absorbance of the solution was measured at 517 nm. For time-dependent experiments, the membrane (10 mg) was incubated in 1 mL of DPPH solution, and the absorbance was measured at 10, 20, 30, 40, 50, and 60 minutes. Figure 2As shown in Figure a, pure PVA films exhibit negligible DPPH radical scavenging activity. In contrast, the addition of SN and PP significantly enhanced the antioxidant activity of the composite films, showing a dose-dependent effect. At a film concentration of 15 mg / mL, the DPPH radical scavenging activities of PVA / SN and PVA / PP films reached 85.72% and 37.80%, respectively. This enhancement is attributed to the presence of naturally occurring bioactive compounds in SN and PP, which possess significant reducing power, enabling them to scavenge reactive oxygen species and provide hydrogen atoms. Furthermore, as... Figure 2 As shown in b, the membrane also exhibits scavenging activity that varies over time due to the gradual release of active compounds from the membrane matrix.

[0032] Example 3: Separation of active components from grapefruit peel and antibacterial properties of the composite membrane

[0033] To verify the antibacterial properties of the composite membrane, the antibacterial activity of different membranes against representative microorganisms was evaluated using the standard colony counting method: *Escherichia coli* (Gram-negative) and *Staphylococcus aureus* (Gram-positive). PVA / SN membrane (15 mg) was immersed in a bacterial suspension (1 mL, 10... 6 The PVA / PP film (15 mg) was immersed in a bacterial suspension (1 mL, 10 CFU / mL) for 2 h, while the PVA / PP film (15 mg) was immersed in the bacterial suspension (1 mL, 10 CFU / mL) for 2 h. 6 The bacterial suspension was diluted with CFU / mL for 4 h. Subsequently, 100 μL of the diluted solution was evenly spread onto Luria-Bertani (LB) agar plates. A bacterial suspension without a membrane was used as a control group. The culture dishes were incubated in a biochemical incubator at 37°C for 24 h, and bacterial growth was then observed. Figure 3 As shown, the PVA / SN film and PVA / PP film have a kill effect of up to 99.99% on foodborne bacteria Escherichia coli, which confirms that the composite film has excellent antibacterial effect.

Claims

1. A functionalized composite film based on the full utilization of grapefruit peel components, characterized in that, The method for preparing the functionalized composite membrane includes the following steps: (1) Preparation of supernatant and precipitate from grapefruit peel: Grapefruit peel was mixed with water and glycerol was added and stirred. The pH of the solution was adjusted to 2. After heating and stirring, the solution was centrifuged to obtain supernatant and precipitate. (2) Preparation of polyvinyl alcohol / supernatant composite membrane: Polyvinyl alcohol and the supernatant are mixed and stirred evenly to prepare polyvinyl alcohol / supernatant composite membrane; (3) Preparation of polyvinyl alcohol / precipitate composite membrane: Add polyvinyl alcohol to water, add glycerin, heat and stir evenly to obtain polyvinyl alcohol solution, and then mix the polyvinyl alcohol solution with the precipitate and stir evenly to prepare polyvinyl alcohol / precipitate composite membrane.

2. The functionalized composite membrane according to claim 1, characterized in that, The grapefruit peel mentioned in step (1) is grapefruit peel powder, and the mass ratio of the grapefruit peel powder to the volume of water is 1:

50.

3. The functionalized composite membrane according to claim 1, characterized in that, The glycerin is 0.5% of the total mass of grapefruit peel and water; the heating and stirring is carried out at 70°C for 0.5 h.

4. The functionalized composite membrane according to claim 1, characterized in that, In step (2), the mass of polyvinyl alcohol is 2% of the volume of the supernatant.

5. The functionalized composite membrane according to claim 1, characterized in that, In step (3), the mass ratio of polyvinyl alcohol to water is 1:

50.

6. The functionalized composite membrane according to claim 1, characterized in that, In step (3), the glycerol is 2% of the total mass of polyvinyl alcohol and water; the heating and stirring is carried out at 90°C for 2 hours.

7. The functionalized composite membrane according to any one of claims 1-7, characterized in that, The volume of the polyvinyl alcohol solution in step (3) is the same as that of the supernatant in step (1).

8. The use of the functionalized composite membrane according to any one of claims 1-7 in the preparation of antibacterial products.

9. The application according to claim 8, characterized in that, The antibacterial activity is effective against both Gram-negative and Gram-positive bacteria.

10. The application according to claim 9, characterized in that, The Gram-negative bacteria are Escherichia coli and the Gram-positive bacteria are Staphylococcus aureus.

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