Peach gum polysaccharide film as well as preparation method and application thereof

Abstract

The invention belongs to the field of edible films, and particularly relates to a peach gum polysaccharide film and a preparation method and application thereof. The preparation method comprises the following specific steps: adding peach gum powder into an extracting solution, heating, extracting, taking supernate after the extraction is finished, and concentrating and freeze-drying to obtain the peach gum polysaccharide, dissolving peach gum polysaccharide in deionized water, and stirring to obtain a peach gum polysaccharide solution; and uniformly mixing the peach gum polysaccharide solution with glycerol to prepare a film-forming solution, and then preparing the peach gum polysaccharide film by utilizing a solution casting method. The invention provides a preparation method for accurately regulating and controlling the molecular mass of peach gum polysaccharide and solving the problem of poor water solubility of the peach gum polysaccharide by using acid-alkali-heat synergistic treatment. By changing the molecular morphology, intermolecular force and charge state of the peach gum polysaccharide in a water solution, the peach gum film has improved elongation at break and tensile strength; the controllability is high, and the blank of the relationship between the peach gum film and peach gum molecules at present is filled; compared with the prior art, the treatment method is simple and low in cost.

Description

Technical Field

[0001] The invention belongs to the field of edible films, and in particular relates to a peach gum polysaccharide film and a preparation method and application thereof. Background Art

[0002] In recent years, white pollution caused by the non-degradability of plastics has caused serious damage to the ecological environment. Therefore, it is essential to develop a green, environmentally friendly, cost-effective and efficient packaging material. Biomass materials (such as polysaccharides, oils or proteins) are ideal for preparing packaging films due to their low cost, biodegradability and biocompatibility. However, proteins and lipids usually have higher value-added applications as food or feed ingredients. In contrast, polysaccharides are the most abundant natural polymers. Their extraction and chemical modification are relatively easy to perform, which enables them to be obtained at a relatively low price. Therefore, polysaccharides may be considered the most suitable materials for the design of new food packaging materials.

[0003] However, the common problem of polysaccharide films is that the mechanical properties are poor, and the tensile strength and flexibility cannot withstand the gravity of the articles. In order to solve the problems of poor mechanical properties and rough film surface faced by single-component films in the prior art, another substance is usually added to the polysaccharide to form a composite film, such as guar gum / casein film (CN119019722A), whey protein / pectin / clove essential oil film (CN118930917A), and zein / ethyl cellulose (CN117136996A). However, these composite films need to control the ratio between the two to achieve a stable system, and on the other hand, the components used as reinforcing materials are difficult to extract and expensive.

[0004] On the basis of polysaccharide, natural polyelectrolyte has macromolecule with ionizable groups along its main chain, has designable structure, unique composite advantage and strong intermolecular or intramolecular force, can form network structure to make film without chemical crosslinking agent, and the molecular form of this type of polyelectrolyte is usually affected by solution pH. Peach gum is an anionic acidic polysaccharide with a large amount of carboxyl groups, which is insoluble in aqueous solution due to its extremely high molecular weight, which greatly limits its application, and peach gum has poor film-forming property and is fragile. In the prior art (CN108587189A), there is a technology for preparing film by compounding zein / peach gum, but the mechanical property is very poor, and the highest elongation at break is only 7.75%, and secondly, the cost of zein is higher.

[0005] Therefore, reducing the molecular weight of peach gum to increase its water solubility and improving the film-forming properties of peach gum, especially its mechanical properties, have become two major problems that need to be solved at present. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for accurately monitoring the macromolecular morphology of peach gum by pH control method in view of the deficiencies of the prior art, so as to obtain peach gum film-forming liquid with different physical and chemical properties, and finally make the peach gum film present improved mechanical properties. The original peach gum is treated with acid and alkali to make the peach gum polysaccharide have different molecular weights, which is low in cost and easy to make; the state of the polyelectrolyte solution is changed by using the different pH of the system, so as to improve the film-forming performance, and the controllability is strong; only peach gum is used as raw material and glycerol is used as plasticizer, which is in line with the concept of green development.

[0007] In order to solve the above technical problems, the present invention discloses a method for preparing a peach gum polysaccharide film, which comprises the following specific steps:

[0008] Step 1: Add peach gum powder to the extracting solution, heat it up and extract it, take the supernatant after the extraction, concentrate and freeze-dry it to obtain peach gum polysaccharide;

[0009] Step 2: dissolving peach gum polysaccharide in deionized water, and stirring to obtain a peach gum polysaccharide solution;

[0010] Step 3: Evenly mix the peach gum polysaccharide solution and glycerol to obtain a film-forming solution, and then prepare the peach gum polysaccharide film by a solution casting method.

[0011] Wherein, in step 1, the concentration of the peach gum powder in the extract is 0.5-5wt%;

[0012] Preferably, in step 1, the concentration of the peach gum powder in the extract is 2 wt %.

[0013] Specifically, the extract is a mixture of deionized water, hydrochloric acid and sodium hydroxide, and the pH value of the extract is 2-10.

[0014] Wherein, in step 1, the specific temperature of the heating is 80-90°C; the specific time of the extraction is 2-8 hours;

[0015] Preferably, in step 1, the specific temperature of the heating is 90° C.; the specific time of the extraction is 4 hours.

[0016] Wherein, in step 2, the concentration of the peach gum polysaccharide solution is 0.5-5wt%;

[0017] Preferably, in step 2, the concentration of the peach gum polysaccharide solution is 2 wt %.

[0018] Wherein, in step 2, the stirring is carried out under the conditions of 30-65° C. for 2-8 hours;

[0019] Preferably, in step 2, the stirring is carried out at 45° C. for 4 hours.

[0020] Wherein, in step 3, the amount of glycerol added is 5-20% of the mass of peach gum polysaccharide;

[0021] Preferably, in step three, the amount of glycerol added is 10% of the mass of peach gum polysaccharide.

[0022] Among them, in step 3, the solution casting method, the specific steps are: the film-forming solution is poured at 0.4-0.6 g / cm 2 Evenly spread on a polyethylene plate, and dry at 30-50° C. for 10-20 hours to obtain the peach gum polysaccharide film;

[0023] Preferably, in step 3, the solution casting method comprises the following specific steps: mixing the film-forming solution at a pressure of 0.4 to 0.6 g / cm 2 The film was evenly coated on a polyethylene plate and dried at 40° C. for 15 hours to obtain the peach gum polysaccharide film.

[0024] Furthermore, the peach gum polysaccharide film prepared by the above preparation method is also within the protection scope of the present invention.

[0025] Furthermore, the application of the peach gum polysaccharide film in the preparation of packaging materials is also within the protection scope of the present invention;

[0026] Specifically, in some embodiments of the present invention, a peach gum polysaccharide film is prepared by the above-mentioned preparation method. By characterizing the mechanical properties, light transmittance and water sensitivity of the peach gum polysaccharide film, it is proved that the peach gum polysaccharide film prepared by the present invention has better mechanical properties than the current single-component polysaccharide base film, and the elongation at break can reach more than 80%, rather than only a few percent or more than ten percent. The water contact angle of all peach gum polysaccharide films is above 90°, reflecting the hydrophobicity of the material surface, with low water sensitivity, which can effectively block moisture and prevent food from getting damp or deteriorating. High-transparency packaging can show the appearance of food and enhance its attractiveness. The light transmittance of the film can reach more than 80%, and the text and pattern can be clearly seen. This proves that the peach gum polysaccharide film provided by the present invention has a good prospect for use in the preparation of packaging materials.

[0027] Beneficial effects:

[0028] 1. The present invention provides a preparation method for using acid-base-heat synergistic treatment to accurately control the molecular weight of peach gum polysaccharide and solve the problem of its poor water solubility;

[0029] 2. By changing the molecular form, intermolecular force and charge state of peach gum polysaccharide in aqueous solution, the peach gum film has improved elongation at break and tensile strength; it has strong controllability and fills the gap in the relationship between peach gum film and peach gum molecules;

[0030] 3. Compared with the prior art that uses composite membranes to solve the problem of poor mechanical properties, the present invention can achieve the purpose of improving membrane performance by regulating the molecular weight and molecular chain conformation changes of peach gum polysaccharides only through acid-base treatment. The treatment method is simple, and the peach gum polysaccharide film contains only one main component, peach gum, and has a wide source. Compared with the use of raw materials such as zein, the cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0032] Figure 1 The present invention is a flow chart of the preparation process of peach gum polysaccharide film;

[0033] Figure 2 AFM images of five peach gum polysaccharides in the examples of the present invention;

[0034] Figure 3 The mechanical properties of five peach gum polysaccharide films in the embodiments of the present invention are shown in FIG.

[0035] Figure 4 This is an experimental diagram of the stretchable length of the peach gum film prepared at a pH of 2 in an embodiment of the present invention; wherein the left figure is the state before stretching, and the right figure is the state after stretching;

[0036] Figure 5 This is a diagram showing the light transmittance performance of five peach gum polysaccharide films in the embodiments of the present invention;

[0037] Figure 6 This is a performance diagram of the water sensitivity of five peach gum polysaccharide films in the examples of the present invention. DETAILED DESCRIPTION

[0038] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0039] The peach gum particles in the following examples were purchased from Shandong Tangzheng Biotechnology Co., Ltd.

[0040] Example 1: Preparation of peach gum polysaccharide film

[0041] Figure 1 The following is a flow chart of the preparation process of peach gum polysaccharide film. The specific steps are as follows:

[0042] S1. Grind the peach gum particles into powder and pass through a 100-mesh sieve to obtain peach gum powder, which is then stored in a drying dish for later use;

[0043] S2. Mix deionized water with hydrochloric acid and sodium hydroxide to obtain extracts having pH values ​​of 2, 4, 6, 8, and 10, respectively;

[0044] S3. 2 g (dry weight) of peach gum powder was added to 98 g of the extract to obtain a 2% (mass ratio) peach gum mixture, and all the mixtures were extracted at 90°C for 4 hours; the supernatant was concentrated and freeze-dried to obtain five kinds of peach gum polysaccharides (PGP), respectively named PGP-2, PGP-4, PGP-6, PGP-8, and PGP-10;

[0045] S4. Dissolve five kinds of PGP in deionized water, stir at 45 ° C for 4 hours, and obtain a 2% (mass ratio) peach gum polysaccharide solution; then add 10% glycerol by mass of peach gum polysaccharide to the peach gum polysaccharide solution, stir for 2 hours, and obtain a uniform film-forming solution;

[0046] S5. About 32 g of the five film-forming solutions were poured onto a polyethylene plate with a diameter of 9 cm, and then the samples were dried at 40°C for 15 hours to obtain five peach gum polysaccharide films (PGPF), which were named PGPF-2, PGPF-4, PGPF-6, PGPF-8, and PGPF-10.

[0047] Example 2: Characterization of peach gum polysaccharide film properties

[0048] 1. Molecular properties of PGP powder and characterization of its state in aqueous solution

[0049] By hydrolyzing peach gum with different pH solutions, peach gum polysaccharides with different molecular weights can be obtained. The molecular weight and conformation of the polysaccharide can be accurately determined by tandem detection using high performance liquid size exclusion chromatography coupled with laser light scattering and differential detector (HPSEC-MALLS-RI). Table 1 shows the molecular characteristics of PGP extracted from five different pH extracts. It can be seen from Table 1 that with the increase of extraction pH, the Mw of PGP gradually increases. This shows that alkali can more effectively destroy the intermolecular forces and polymer structure of peach gum, making it easier for polysaccharides to degrade. In addition, alkaline conditions increase the electrostatic repulsion between peach gum molecules, stretch the molecular chains, and the radius of gyration R g Acid and alkali promote the partial hydrolysis of peach gum polysaccharides to a certain extent, which can effectively increase the utilization rate.

[0050] Table 1 Molecular properties of PG powder extracted by five different pH extraction solutions

[0051]

[0052] PGP powder was prepared into 10 μg / ml aqueous solution, and the morphology of five kinds of PGP in aqueous solution was characterized by atomic force microscopy (AFM). Figure 2The AFM images of five kinds of PGP, among which a is peach gum polysaccharide prepared at pH 2, b is peach gum polysaccharide prepared at pH 4, c is peach gum polysaccharide prepared at pH 6, d is peach gum polysaccharide prepared at pH 8, and e is peach gum polysaccharide prepared at pH 10. These peach gum polysaccharides of different molecular weights are aggregated or dispersed in aqueous solution under the influence of charge state and intermolecular forces. Since there are many carboxyl groups on the PGP molecule, the change of pH leads to the change of ionization level, which leads to the change of molecular structure. Under lower pH conditions, the carboxyl groups on the PGP molecular chain do not undergo ionization and show their original high-branched structure. Irregular spherical structures were observed in the PG-10 sample. The results may be due to the ionization of PGP molecules by carboxyl groups under alkaline conditions, resulting in ionization and elongation of molecular chains, weak intermolecular binding and strong electrostatic repulsion. As the pH value increases, the electrostatic repulsion between molecules increases, and more weak interactions are formed between molecules, thereby promoting distribution. PG-6 and PG-8 show a cross-linked network structure.

[0053] 2. Characterization of mechanical properties of PGPF

[0054] The mechanical properties of five PGPFs were tested respectively, and the tensile strength and elongation at break were measured by SC-100N electronic universal testing machine. The specific steps are as follows: the film material is cut into 60mm×10mm rectangular strips, and the thickness of all rectangular strips of film material is measured. The weighing sensor is 1000N, the original clamping distance is 40mm, and the speed is 10mm / min. The Young's modulus is calculated according to the formula E=(F·L) / (A·△L), where F is the external force; A is the cross-sectional area or the cross-sectional area perpendicular to the force; △L is the change in length; and L is the original length.

[0055] Figure 3 The mechanical properties of five PGPFs are shown in Figure 1, where a is Young's modulus, b is tensile strength, and c is elongation at break. Figure 3 It can be seen that the peach gum polysaccharide films after acid and alkali treatment show different elongation at break and mechanical properties, especially the film made of peach gum polysaccharide treated with an extract of pH 2, whose elongation at break can reach more than 90% ( Figure 4 The experimental diagram of the stretchable length of peach gum film prepared at pH 2, the left picture is the state before stretching, and the right picture is the state after stretching), with greatly improved flexibility. In addition, compared with the neutral treatment group, the film prepared by alkaline-treated peach gum polysaccharide showed enhanced tensile strength. Peach gum packaging films with different flexibility and strength have a variety of application scenarios.

[0056] 3. Characterization of light transmittance of PGPF

[0057] The light transmittance of five PGPFs was tested by 759S UV-Vis spectrophotometer. The film samples were cut into 10mm×50mm rectangular strips and placed in a quartz cuvette so that the film was close to the inner wall of the cuvette. The samples were scanned at a full wavelength of 200-800nm ​​by 759S UV-Vis spectrophotometer. Figure 5 is a diagram of the light transmission performance of five PGPFs, where a is the transmittance of the five PGPFs between 200 and 800 nm, and b is a physical diagram of the five PGPFs; Figure 5 It can be seen that all peach gum films show good light transmittance, reaching more than 80%. Figure 5 As shown in b, the presence of the film will not interfere with the readability of the pattern and text, thereby meeting the transparency requirements of the food packaging film, and can better display the appearance of the food and increase its appeal.

[0058] 4. Characterization of water sensitivity of PGPF

[0059] The water sensitivity of five PGPFs was characterized by a video optical contact angle meter (OCA20). The film samples were cut into 6 cm × 1 cm rectangular strips and then pasted on a glass slide, which was placed horizontally on the table of the meter. The instrument was then adjusted so that the micro-injector was located directly above the rectangular strip, and a drop of ultrapure water (5 μL) was quickly dripped onto the film surface while the camera button was pressed. Figure 6 is a performance diagram of the sensitivity of five PGPFs to water, wherein a is the contact angle value (WCA) of the five PGPFs, b is the contact angle image of the five PGPFs, and c is the water vapor transmission rate value (WVP) of the five PGPFs; Figure 6 It can be seen that acid and alkali treatments destroyed the self-interaction of the peach gum molecular chains, exposing more carboxyl and hydroxyl groups, thereby increasing the binding between molecules and water and enhancing the surface wettability of the membrane material. As the pH value decreases or increases, the WCA value of the membrane gradually decreases and the hydrophilicity increases. WVP is the water transfer between the membrane and the surrounding environment and is related to the moisture resistance of the membrane. Membranes with a higher affinity for water molecules restrict more water and allow these molecules to diffuse through the membrane, thereby increasing WVP.

[0060] The present invention provides a peach gum polysaccharide film and a preparation method and application thereof. There are many methods and approaches to realize the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be realized by existing technologies.

Claims

1. A method for preparing peach gum polysaccharide film, characterized in that: The specific steps are: Step 1: Add peach gum powder to the extracting solution, heat it up and extract it, take the supernatant after the extraction, concentrate and freeze-dry it to obtain peach gum polysaccharide; Step 2: dissolving peach gum polysaccharide in deionized water, and stirring to obtain a peach gum polysaccharide solution; Step 3: Evenly mix the peach gum polysaccharide solution and glycerol to obtain a film-forming solution, and then prepare the peach gum polysaccharide film by a solution casting method.

2. The preparation method according to claim 1, characterized in that: In step 1, the concentration of the peach gum powder in the extract is 0.5-5wt%.

3. The preparation method according to claim 2, characterized in that: The extract is a mixture of deionized water, hydrochloric acid and sodium hydroxide, and the pH value of the extract is 2-10.

4. The preparation method according to claim 1, characterized in that: In step 1, the specific temperature of the heating is 80-90° C.; the specific time of the extraction is 2-8 hours.

5. The preparation method according to claim 1, characterized in that: In step 2, the concentration of the peach gum polysaccharide solution is 0.5-5wt%.

6. The preparation method according to claim 5, characterized in that: In step 2, the stirring is carried out at 30-65° C. for 2-8 hours.

7. The preparation method according to claim 1, characterized in that: In step 3, the amount of glycerol added is 5-20% of the mass of peach gum polysaccharide.

8. The preparation method according to claim 1, characterized in that: In step 3, the solution casting method comprises the following specific steps: mixing the film-forming solution at a pressure of 0.4 to 0.6 g / cm 2 The film is evenly coated on a polyethylene plate and dried at 30-50° C. for 10-20 hours to obtain the peach gum polysaccharide film.

9. A peach gum polysaccharide film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the peach gum polysaccharide film described in claim 9 in preparing packaging materials.

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