High-strength multifunctional starch / polyphenol composite packaging film and preparation method thereof

Abstract

The invention discloses a high-strength multifunctional starch / polyphenol composite packaging film and a preparation method thereof, and relates to the field of food processing. The preparation method comprises the following steps: (1) adding starch and glycerol into water, and stirring to obtain a starch suspension; (2) adding tea polyphenol into the starch suspension prepared in the step (1), and stirring to obtain a starch / tea polyphenol composite suspension; and (3) heating the starch / tea polyphenol composite suspension prepared in the step (2), extending to a mold, and drying to obtain the starch / tea polyphenol composite packaging film. The high-strength starch composite packaging film is prepared by regulating and controlling the addition amount of the tea polyphenol, the tensile strength of the starch composite packaging film is improved from 15 MPa to 19 MPa, and the starch composite packaging film also has the characteristics of good oxidation resistance, strong antibacterial activity and ultraviolet blocking, and is a multifunctional starch film.

Description

Technical Field

[0001] The invention relates to the field of food processing, and in particular to a high-strength and multifunctional starch / polyphenol composite packaging film and a preparation method thereof. Background Art

[0002] Packaging can isolate food from adverse factors in the environment (such as moisture, microorganisms, oxygen, light, dust, etc.), thereby ensuring food quality and safety. At present, food packaging made of petroleum-based plastics is widely consumed in our daily lives due to its practicality and ease of production. However, these plastics show poor degradability, causing serious harm to the ecological environment. Environmental pollution problems associated with traditional plastics have prompted the development of natural polymers as packaging materials. Among them, starch, as a natural carbohydrate polymer, has been widely developed as food packaging film.

[0003] Starch granules absorb water and then swell irreversibly at high temperatures as the crystal structure is destroyed, promoting more interactions between starch chains and water molecules, and then gelatinization occurs. Subsequently, the gelatinized starch paste is spread onto the surface of a smooth substrate to obtain a film after drying. This property gives starch good film-forming properties and green processing potential. However, pure starch films exhibit brittleness and are prone to rupture. Plasticizers (such as glycerol) are usually incorporated into films to improve the flexibility of starch films, but they reduce the interactions between starch molecules, resulting in a decrease in the stiffness and tensile strength of the film. Therefore, the tensile strength of starch films needs to be improved to meet the practical application requirements as packaging film materials.

[0004] In addition, the functional properties of food packaging have also received more and more attention. The inherent defects of films composed of a single starch cannot meet the requirements of functional food packaging (such as antioxidant properties, antibacterial activity, UV blocking, etc.). Therefore, it is necessary to develop a composite packaging film to meet the requirements of high strength, good antioxidant properties, strong antibacterial activity, UV blocking, etc.

[0005] In the prior art, there have been many studies on natural materials as packaging films, such as "Preparation and Performance Characterization of Tea Polyphenols / Starch Active Films". This document conducted single-factor experiments on preparation factors such as starch concentration, glycerol content, and film-forming liquid temperature, and optimized film-forming conditions with mechanical properties, moisture permeability, and light transmittance as evaluation indicators; on this basis, the physical and chemical properties, performance, functional activity, and functional stability of functional starch films with different TP contents were systematically characterized. However, the strength of the starch films obtained was relatively low, and the tensile strength did not exceed 15MPa, which still needs to be further improved. Summary of the invention

[0006] Technical issues

[0007] Starch film has become a packaging film with development potential due to its biodegradability and environmental friendliness. However, pure starch film is prone to rupture and has low strength. It also does not meet the requirements of functional food packaging, so it needs to be composite modified. However, the effect of improving the strength of starch film in the existing technology is not ideal. Therefore, it is necessary to develop a starch film with high strength, good antioxidant properties, strong antibacterial activity, and UV blocking.

[0008] Technical content

[0009] In view of the above-mentioned problems, the present invention proposes a multifunctional starch / polyphenol composite packaging film and a preparation method thereof. The present invention specifically selects plant-derived and readily available tea polyphenols as raw materials, incorporates them into starch film, and develops a multifunctional starch / polyphenol composite packaging film.

[0010] The present invention provides a method for preparing a high-strength and multifunctional starch / polyphenol composite packaging film, the preparation method comprising the following steps:

[0011] (1) adding starch and glycerol into water and stirring to obtain a starch suspension;

[0012] (2) adding tea polyphenols to the starch suspension prepared in step (1), and stirring to obtain a starch / tea polyphenols composite suspension;

[0013] (3) heating the starch / tea polyphenols composite suspension prepared in step (2), then stretching it onto a mold, and drying it to obtain a starch / tea polyphenols composite packaging film.

[0014] Furthermore, in step (1), the starch concentration in the starch suspension is 0.05 to 0.1 g / mL.

[0015] Furthermore, in step (1), the mass ratio of starch to glycerol in the starch suspension is 10:0.5-2.

[0016] Furthermore, in step (2), the mass ratio of starch to tea polyphenols in the starch / tea polyphenols composite suspension is 10:0.5-2.

[0017] Preferably, in step (2), the mass ratio of starch to tea polyphenols in the starch / tea polyphenols composite suspension is 10:1.

[0018] Furthermore, in step (3), the heating is performed at 80 to 90° C. for 10 to 30 minutes.

[0019] Furthermore, in step (3), the thickness of the starch / tea polyphenols composite packaging film is 0.03 to 0.05 mm.

[0020] The invention provides a high-strength and multifunctional starch / polyphenol composite packaging film prepared according to the method.

[0021] The high-strength and multifunctional starch / polyphenol composite packaging film provided by the present invention is applied in the field of food or packaging.

[0022] The present invention also provides a film-forming liquid for a high-strength multifunctional starch / polyphenol composite packaging film, wherein the film-forming liquid is prepared according to the following steps:

[0023] (1) adding starch and glycerol into water and stirring to obtain a starch suspension;

[0024] (2) adding tea polyphenols to the starch suspension prepared in step (1), heating and stirring to obtain a film-forming liquid for a high-strength multifunctional starch / polyphenol composite packaging film.

[0025] Furthermore, in step (1), the starch concentration in the starch suspension is 0.05 to 0.1 g / mL.

[0026] Furthermore, in step (1), the mass ratio of starch to glycerol in the starch suspension is 10:0.5-2.

[0027] Furthermore, in step (2), the mass ratio of starch to tea polyphenols in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film is 10:0.5-2.

[0028] Preferably, in step (2), the mass ratio of starch to tea polyphenols in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film is 10:1.

[0029] Furthermore, the heating in step (2) is performed at 80 to 90° C. for 10 to 30 minutes.

[0030] Application of the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film provided by the present invention in the field of food.

[0031] Furthermore, the application in the food field is to immerse the food in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film for 1 to 5 minutes, then take it out and dry it to obtain the packaged food.

[0032] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0033] The present invention obtains a high-strength starch composite packaging film by regulating the amount of tea polyphenols added, the tensile strength of which is increased from 15MPa to 19MPa, and the film itself has good antioxidant properties, strong antibacterial activity, and UV blocking properties, and is a multifunctional starch film. In addition, the processing process of the present invention is easy to operate, the selected raw materials are safe and non-toxic, and the obtained starch film is degradable and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1The X-ray photoelectron spectra of the starch / polyphenol composite film and starch film prepared in Example 2 and Comparative Example 1 are shown in FIG. Figure 1 a is the X-ray photoelectron spectrum of starch film and starch / tea polyphenols composite film, Figure 1 b is the peak fitting curve of the C1s fine spectrum of starch film. Figure 1 c is the C1s fine spectrum peak fitting curve of starch / tea polyphenols composite film.

[0035] Figure 2 The surface morphology of the packaging film materials prepared in Examples 1-5 and Comparative Example 1 is shown in FIG. Figure 2 a is SFs, Figure 2 b is STPFs-5, Figure 2 c is STPFs-10, Figure 2 d is STPFs-15, Figure 2 e is STPFs-20, Figure 2 f is STPFs-25.

[0036] Figure 3 The mechanical properties of the packaging film materials prepared in Examples 1-5 and Comparative Example 1 are as follows: Figure 3 a is the stress-strain curve, Figure 3 b is the tensile strength, Figure 3 c is the elongation at break.

[0037] Figure 4 is the UV-visible light transmittance of the packaging film materials prepared in Examples 1-5 and Comparative Example 1, wherein Figure 4 a is the UV-visible light transmission curve of starch / tea polyphenols composite film, Figure 4 b is the transmittance of starch / tea polyphenols composite film at a wavelength of 280 nm.

[0038] Figure 5 The free radical scavenging test results of the packaging film materials prepared in Examples 1-5 and Comparative Example 1 are shown in FIG. Figure 5 a is the DPPH free radical scavenging rate, Figure 5 b is the ABTS free radical scavenging rate.

[0039] Figure 6 The antibacterial ability of the packaging film materials prepared in Examples 1-5 and Comparative Example 1. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the applicant will further explain the present invention in detail below with reference to the embodiments and drawings.

[0041] Example 1

[0042] 4 g starch and 0.4 g glycerol were accurately weighed and added to 50 mL water, and then tea polyphenols (5 wt% of the mass of starch) were added and stirred at room temperature to dissolve to obtain a starch / tea polyphenol composite suspension, which was then heated at 90°C for 30 min and then cast onto a silica gel substrate and further vacuum dried to obtain a starch / tea polyphenol composite packaging film, which was recorded as STPFs-5.

[0043] Example 2

[0044] 4 g starch and 0.4 g glycerol were accurately weighed and added to 50 mL water, and then tea polyphenols (10 wt% of the mass of starch) were added and stirred at room temperature to dissolve to obtain a starch / tea polyphenol composite suspension, which was then heated at 90°C for 30 min and then cast onto a silica gel substrate and further vacuum dried to obtain a starch / tea polyphenol composite packaging film, which was recorded as STPFs-10.

[0045] Example 3

[0046] 4 g starch and 0.4 g glycerol were accurately weighed and added to 50 mL water, and then tea polyphenols (15 wt% of the mass of starch) were added and stirred at room temperature to dissolve to obtain a starch / tea polyphenols composite suspension, which was then heated at 90°C for 30 min and then cast onto a silica gel substrate and further vacuum dried to obtain a starch / tea polyphenols composite packaging film, which was recorded as STPFs-15.

[0047] Example 4

[0048] 4 g starch and 0.4 g glycerol were accurately weighed and added to 50 mL water, and then tea polyphenols (20 wt% of the mass of starch) were added and stirred at room temperature to dissolve to obtain a starch / tea polyphenols composite suspension, which was then heated at 90°C for 30 min and then cast onto a silica gel substrate and further vacuum dried to obtain a starch / tea polyphenols composite packaging film, which was recorded as STPFs-20.

[0049] Example 5

[0050] 4 g starch and 0.4 g glycerol were accurately weighed and added to 50 mL water, and then tea polyphenols (25 wt% of the mass of starch) were added and stirred at room temperature to dissolve to obtain a starch / tea polyphenol composite suspension, which was then heated at 90°C for 30 min and then cast onto a silica gel substrate and further vacuum dried to obtain a starch / tea polyphenol composite packaging film, which was recorded as STPFs-25.

[0051] Comparative Example 1

[0052] 4 g starch and 0.4 g glycerol were accurately weighed and added into 50 mL water, which was then heated at 90 °C for 30 min, then cast onto a silica gel substrate, and further vacuum dried to obtain a starch / tea polyphenols composite packaging film, recorded as SFs.

[0053] exist Figure 1 It can be clearly seen that before and after the addition of tea polyphenols, both films only contain two elements, C and O. Further peak fitting of C1s revealed that after the addition of tea polyphenols, a new OC=O group appeared, which was mainly attributed to the ester bond in the polyphenol molecular structure. And due to the large number of benzene ring structures in the tea polyphenol molecular structure, the intensity of the CC / C=C peak increased significantly. The above results show that tea polyphenols and starch films are successfully composited.

[0054] according to Figure 2 It can be seen that all films are composed of interconnected and irregular polygonal structures. The further drying process of the cast gel film involves rapid evaporation of surface water, which causes the surface of the gel film to shrink unevenly due to dehydration. Despite the presence of sunken holes on the surface, the film still exhibits good density. After the addition of tea polyphenols, the surface of the polygonal framework is rougher. Due to the significant reduction in water content, excess tea polyphenols will precipitate and form irregular particles on the surface. Despite the change in the rough surface, the density of the film surface remains almost unchanged, and there are no obvious cracks on the film surface.

[0055] exist Figure 3 As can be seen from Table 1, with the increase of tea polyphenol content, the tensile strength of the composite film first increases and then decreases. This is mainly due to the good adhesion of catechol and pyrogallol structures in the polyphenol molecular structure, which can act as cross-linking agents between starch molecular chains. However, excessive tea polyphenols form aggregates in the film, hindering the orientation arrangement of starch molecular chains (short-range regeneration), so the tensile strength is reduced. Since the cross-linking effect of polyphenols limits the movement of starch molecular chains, the elongation at break of the composite film gradually decreases.

[0056] Table 1

[0057]

[0058] according to Figure 4 The results show that pure starch film has a high transmittance in the wavelength range of 200-800nm. After adding tea polyphenols, the transmittance in the ultraviolet region (200-400nm) is significantly reduced and is positively correlated with the amount of tea polyphenols added. This is mainly due to the presence of a large number of benzene rings in the molecular structure of polyphenols. In addition, the composite film still maintains a high transmittance in the visible light region (>60%). The above results show that the introduction of tea polyphenols can effectively enhance the ultraviolet shielding effect of the composite film and retain the light transmittance of the starch film.

[0059] The antioxidant capacity of the packaging film materials prepared in Examples 1-5 and Comparative Example 1 was evaluated by the scavenging rate of two free radicals (DPPH and ABTS). Figure 5 The results show that the single-component starch film has a low free radical scavenging rate and does not have significant antioxidant capacity. With the addition of tea polyphenols, the free radical scavenging rate of the composite film gradually increases. The phenol structure in the polyphenol molecular structure can release hydrogen protons in the solution to capture free radicals.

[0060] from Figure 6 The results show that the single-component starch film has no obvious inhibition zone, while with the increase of tea polyphenol concentration, the inhibition zone against the four bacteria gradually increases, showing a certain antibacterial activity. The increase in the inhibition zone is closely related to the polyphenol content. Polyphenols can be released from the composite film and further directly bind to the peptidoglycan layer of Gram-positive bacteria, interfering with their biosynthesis by destroying their cell walls. For Gram-negative bacteria, it may induce oxidative stress caused by the production of H2O2, resulting in subsequent loss of bacterial activity or even death.

[0061] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a high-strength and multifunctional starch / polyphenol composite packaging film, characterized in that: The preparation method comprises the following steps: (1) adding starch and glycerol into water and stirring to obtain a starch suspension; (2) adding tea polyphenols to the starch suspension prepared in step (1), and stirring to obtain a starch / tea polyphenols composite suspension; (3) heating the starch / tea polyphenols composite suspension prepared in step (2), then extending it onto a mold, and drying it to obtain a starch / tea polyphenols composite packaging film; In step (1), the starch concentration in the starch suspension is 0.05-0.1 g / mL, and the mass ratio of starch to glycerol in the starch suspension is 10:0.5-2; In step (2), the mass ratio of starch to tea polyphenols in the starch / tea polyphenols composite suspension is 10:0.5-2.

2. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of starch to tea polyphenols in the starch / tea polyphenols composite suspension is 10:

1.

3. The preparation method according to claim 1, characterized in that: The heating in step (3) is performed at 80 to 90° C. for 10 to 30 minutes.

4. The preparation method according to claim 1, characterized in that: The thickness of the starch / tea polyphenols composite packaging film in step (3) is 0.03-0.05 mm.

5. A high-strength and multifunctional starch / polyphenol composite packaging film prepared according to the preparation method according to any one of claims 1 to 4.

6. Use of the high-strength and multifunctional starch / polyphenol composite packaging film of claim 5 in the field of food or packaging.

7. A film-forming liquid for a high-strength multifunctional starch / polyphenol composite packaging film, characterized in that: The film-forming solution is prepared according to the following steps: S1. Add starch and glycerol into water and stir to obtain a starch suspension; S2. Add tea polyphenols to the starch suspension prepared in step (1), heat and stir to obtain a film-forming liquid for a high-strength multifunctional starch / polyphenol composite packaging film. In step S1, the starch concentration in the starch suspension is 0.05-0.1 g / mL, and the mass ratio of starch to glycerol in the starch suspension is 10:0.5-2; In step S2, the mass ratio of starch to tea polyphenols in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film is 10:0.5-2.

8. The membrane-forming solution according to claim 1, characterized in that: In step (2), the mass ratio of starch to tea polyphenols in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film is 10:

1.

9. Application of the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film according to claim 7 or 8 in the food field.

10. The use according to claim 9, characterized in that The application in the food field is to immerse the food in the film-forming liquid of the high-strength multifunctional starch / polyphenol composite packaging film for 1 to 5 minutes, then take it out and dry it to obtain the packaged food.

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