A method for directional regulation of starch-based edible film properties

Abstract

The invention discloses a method for directional regulation of starch-based edible film performance, and belongs to the technical field of food packaging. The invention prepares edible film by enzymatically modifying starch, and uses starch branching enzyme to hydrolyze starch and transglycosylate, and regulates α, 1-4 and α, 1-6 glycosidic bonds in the starch molecular structure, thereby realizing the preparation of highly branched starch-based film. Through the transformation of enzyme action process conditions, the structural basis and molecular mechanism of highly branched starch film formation are explored, and the performance optimization and dynamic regulation of edible film are realized, which lays a foundation for the application of starch film in different food fields, and provides new ideas and new means for food environmentally friendly and degradable packaging and application.

Description

Technical Field

[0001] The invention relates to a method for directionally regulating the performance of a starch-based edible film, and belongs to the technical field of food packaging. Background Art

[0002] Food packaging film wrapped on the surface of food can not only isolate microorganisms and bacteria, but also prevent the entry of foreign pollutants, thereby extending the shelf life of food. Plastic film occupies a vital position in food packaging film due to its excellent mechanical properties and good chemical stability. However, the non-degradability of plastic has caused harm to the environment, which limits the application of plastic film. The development of degradable and renewable films prepared with natural biomacromolecules as raw materials has attracted people's attention.

[0003] Starch has become one of the ideal choices for replacing plastic as a food packaging material due to its wide sources, environmentally friendly, biodegradable and renewable advantages. However, the inherent properties of starch determine that the mechanical properties and barrier properties of starch film are poor, the film is brittle, and the hydrophilicity of starch makes the starch film less stable in an environment with high relative humidity. These shortcomings seriously limit the application of starch film; and there are few studies on how to achieve directional regulation of starch film performance by changing the structure of starch itself, so it is impossible to achieve precise and multi-dimensional application of starch film in different food fields. Summary of the invention

[0004] The present invention provides a method for directionally regulating the performance of an edible film by modifying the starch structure through starch branching enzyme, which utilizes starch branching enzyme to dynamically adjust the content of α-1,4 and α-1,6 glycosidic bonds in starch to achieve dynamic changes in film performance.

[0005] The present invention provides a method for preparing an edible film, wherein starch is subjected to high-branching modification by starch branching enzyme to directionally regulate the performance of the edible film, and the method comprises the following steps:

[0006] (1) Slurry preparation

[0007] Dissolve starch in water to prepare starch milk, stir evenly at 25-50°C for later use;

[0008] (2) Gelatinization

[0009] The starch milk is heated to make the starch granules swell and collapse, forming a viscous and uniform transparent paste solution;

[0010] (3) Enzymatic hydrolysis

[0011] At 45-55°C, starch branching enzyme is added to the starch milk to catalyze the hydrolysis and transglycosidation of starch, so as to achieve enzymatic modification of the starch structure to achieve high branching;

[0012] (4) Plasticization

[0013] Adding a plasticizer to the starch emulsion after enzymatic hydrolysis in step (3) to allow the small molecule plasticizer to be incorporated between starch molecules, thereby increasing the distance between starch molecules and forming a gel solution;

[0014] (5) Casting

[0015] The gel solution obtained in step (4) is cast into a film in a polypropylene watch glass by a casting method, and the level is controlled to ensure uniform film thickness;

[0016] (6) Drying

[0017] The gel solution is dried in a horizontal vacuum drying oven, and a highly branched starch film can be obtained after drying for a certain period of time;

[0018] (7)Save

[0019] The highly branched starch film was stored in a constant temperature and humidity chamber for later use.

[0020] In one embodiment of the present invention, the type of starch in step (1) is corn starch, pea starch, tapioca starch and wheat starch.

[0021] In one embodiment of the present invention, the mass concentration of starch milk in step (1) is in the range of 3% to 5%.

[0022] In one embodiment of the present invention, the starch milk is heated in step (2) at a temperature ranging from 90 to 100° C. and a heating time ranging from 30 min to 1 h.

[0023] In one embodiment of the present invention, the amount of starch branching enzyme added in step (3) is 25-200 U / g starch on a dry basis; after adding the starch branching enzyme, the pH is adjusted to 6.0-7.5, and the reaction is carried out at 50-70°C for 3-24 hours.

[0024] In one embodiment of the present invention, the amount of starch branching enzyme added in step (3) is 25-200 U / g starch on a dry basis; after adding the starch branching enzyme, the pH is adjusted to 6.5-7.5, and the reaction is carried out at 65-70°C for more than 6 hours.

[0025] In one embodiment of the present invention, the starch branching enzyme used in step (3) refers to an enzyme with an EC number of 2.4.1.18.

[0026] In one embodiment of the present invention, the type of plasticizer in step (4) is at least one of glycerol, polyols and diols.

[0027] In one embodiment of the present invention, in step (4), after adding the plasticizer, the temperature is maintained at 90-100° C. for 30 min-1 h to allow the small molecule plasticizer to be incorporated between the starch molecules.

[0028] In one embodiment of the present invention, the pouring thickness in step (5) is 0.050 mm-0.200 mm.

[0029] In one embodiment of the present invention, the polypropylene surface dish in step (5) has an area of ​​33 cm 2 The amount of gel poured ranges from 20 to 40 g, and the thickness is 0.050 mm to 0.200 mm.

[0030] In one embodiment of the present invention, the temperature range of drying in the vacuum drying oven in step (6) is 40 to 60° C., and the drying time is 8 to 12 hours.

[0031] In one embodiment of the present invention, the temperature conditions for storage in the constant temperature and humidity chamber in step (7) are 25° C. and 50% relative humidity, and the storage time is 24 hours.

[0032] Beneficial effects of the present invention:

[0033] The present invention pre-treats starch by slurry adjustment and gelatinization to achieve the effects of disappearance of starch granule crystal structure, breaking of hydrogen bonds, dispersion into a colloidal solution in water, and convenience for enzymatic modification; then, the starch structure is qualitatively transformed by starch branching enzyme enzymatic hydrolysis to achieve the effects of increasing starch branching degree and realizing starch molecular reconstruction; then, the modified starch is plasticized, and then cast and dried to obtain an edible film.

[0034] The present invention utilizes a bioenzymatic method to regulate the high branching of starch, uses starch branching enzyme to cut the α-1.4 glycosidic bond in the starch molecule, and transfers the cut chain segment to the acceptor chain through the α-1,6 glycosidic bond to form a new branch (see Figure 1 ), the relative content of α-1,6-glycosidic bonds is increased, thereby increasing the degree of starch branching, regulating the reconstruction of glycosidic bonds inside starch molecules, thereby achieving the rearrangement of the original starch molecular structure, and laying a solid structural foundation for the preparation of highly branched starch base films.

[0035] The surface of the starch-based edible film obtained by the present invention changes from rough and porous to smooth, uniform and continuous. Compared with the film not modified by the branching enzyme, the tensile strength is significantly improved, which facilitates the application of the starch-based edible film in different food packaging fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of starch modification by starch branching enzymes.

[0037] Figure 2 Diagram of the molecular structure of amylopectin.

[0038] Figure 3 Effect of GBE modification on starch chain length distribution.

[0039] Figure 4 GBE modified starch 1 H NMR spectrum.

[0040] Figure 5 Scanning electron micrograph of starch-based films.

[0041] Figure 6 Tensile strength of corn starch films.

[0042] Figure 7 Thermogravimetric curve of corn starch film (left) and differential thermogravimetric analysis curve (right). DETAILED DESCRIPTION

[0043] In order to make the purpose, features and technical solutions of the present invention more obvious and understandable, especially to highlight the beneficial effects brought about by the synergistic effects of the various processes of the present invention, the present invention is described in more detail below through specific embodiments.

[0044] Example 1: Regulation of the structure of highly branched starch by the amount of starch branching enzyme added

[0045] Specific steps for preparing highly branched starch

[0046] (1) Slurry preparation: Pea starch was dissolved in deionized water to prepare a starch milk with a concentration of 3%, and the mixture was stirred evenly at 50° C. and stored for 30 min for later use.

[0047] (2) Gelatinization: The starch milk is heated to 95°C and kept reacting for 1 hour to make the starch granules swell and collapse, forming a viscous, uniform, transparent paste solution.

[0048] (3) Enzymatic hydrolysis: 25, 50, 100, and 200 U / g of starch branching enzyme from Geobacillus stearothermophilus were added to the starch milk at 50°C for 3 h to hydrolyze and transglycoside the starch, thereby achieving enzymatic modification of the starch structure to achieve high branching.

[0049] Example 2: Regulation of the structure of highly branched starch modified by starch branching enzyme by starch type

[0050] (1) Slurry preparation: Pea starch and corn starch were dissolved in deionized water to prepare starch milk with a concentration of 3%, and the mixture was stirred evenly at 50° C. and stored for 30 min for later use.

[0051] (2) Gelatinization: The starch milk is heated to 95°C and kept reacting for 1 hour to make the starch granules swell and collapse, forming a viscous, uniform, transparent paste solution.

[0052] (3) Enzymatic hydrolysis: 25 U / g of starch branching enzyme from Geobacillus stearothermophilus was added to the starch milk at 50°C for 3 h to hydrolyze and transglycoside the starch, thereby achieving enzymatic modification of the starch structure to achieve high branching.

[0053] Example 3: Regulation of the structure of highly branched starch by starch branching enzyme modification time

[0054] (1) Slurry preparation: Pea starch was dissolved in deionized water to prepare a starch milk with a concentration of 3%, and the mixture was stirred evenly at 50° C. and stored for 30 min for later use.

[0055] (2) Gelatinization: The starch milk is heated to 95°C and kept reacting for 1 hour to make the starch granules swell and collapse, forming a viscous, uniform, transparent paste solution.

[0056] (3) Enzymatic hydrolysis: 25 U / g of starch branching enzyme from Geobacillus stearothermophilus was added to the starch milk at 50°C for 3 h, 6 h, and 9 h, respectively, to hydrolyze and transglycoside the starch, thereby achieving enzymatic modification of the starch structure to achieve high branching.

[0057] Control group 1:

[0058] Step (1) and step (2) are the same as in Example 1;

[0059] In step (3), deionized water was used instead of GBE enzyme, and the reaction was carried out at a constant temperature of 50° C. for 3 h.

[0060] Control group 2:

[0061] Step (1) and step (2) are the same as those in Example 1; step (3) of Example 1 is omitted.

[0062] The following tests were performed on Examples 1-3 and the control group:

[0063] 1. Determination of branch chain length distribution

[0064] The chain length distribution of the samples was determined by high performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD). The chromatographic analysis conditions were: ultrapure water, 0.25 M NaOH, 1 M NaAC solution ternary gradient elution, chromatographic column CarboPacPA 200, flow rate 0.5 mL / min, column temperature 30 °C, and injection 20 μL.

[0065] Amylopectin is a highly branched polysaccharide that is connected by α-1,4 glycosidic bonds to form the main chain of glucose and by α-1,6 glycosidic bonds to form the side chains. Its structure is as follows Figure 2 The chain length distribution refers to the fact that after the α-1,6 glycosidic bonds of starch are cut by debranching enzymes, a series of linear short chains with different degrees of polymerization (DP) are obtained, i.e., glucan chains of different lengths. The content of glucan chains with different degrees of polymerization is then analyzed by high-performance anion exchange chromatography.

[0066] Table 1 and Figure 3 The chain length distribution of the enzymatic hydrolyzate obtained in Example 1 is shown in Table 1. In order to further analyze the fine branch structure of highly branched corn starch (i.e., the specific proportion of glucan chains of different lengths), the branched starch side chain segments cleaved by the debranching enzyme were classified according to their lengths, namely DP 3-12, DP 13-24, DP 25-36, and DP>36. The content of each segment is shown in Table 1 and Figure 1 shown.

[0067] Table 1 Branched chain segment content of pea starch treated with different amounts of starch branching enzyme

[0068]

[0069] Different letters on the same column of data in Table 1 indicate that the means between groups are significantly different at the p < 0.05 level.

[0070] Depend on Figure 3 It can be seen that the chain length distribution of pea starch is close to normal distribution, among which the content of DP<13 and DP 13-24 segments is relatively high. After GBE treatment, the segment structure of the modified starch has changed, but it is still close to normal distribution as a whole. After modification, the content of segments DP<13 and DP 24-36 gradually increases with the increase of enzyme addition, and the content of DP 12-24 and DP>36 gradually decreases. This result shows that GBE tends to hydrolyze the longer molecular segments in amylopectin as a whole and reconnect the cut molecules, resulting in a decrease in the long chain content and an increase in the short chain content.

[0071] 2. Determination of α-1,6-glycosidic bond content

[0072] H NMR Spectrometer (1 H NMR) was used to study the branching degree of starch. The highly branched starch samples after enzymatic hydrolysis were freeze-dried, then ground and sieved. The highly branched starch was dissolved in heavy water (D2O) to obtain a 20 mg / mL solution, and then placed in a boiling water bath for 30 min. The gelatinized sample was freeze-dried for 72 h and then redissolved in heavy water (20 mg / mL) for hydrogen nuclear magnetic resonance spectrometer. (1 HNMR) detection.

[0073] use1 H NMR was used to determine the relative content of α-1,6-glycosidic bonds in starch samples before and after modification. The results are as follows: Figure 4 As shown. The chemical shifts of α-1,6-glycosidic bonds and α-1,4-glycosidic bonds are 4.97ppm and 5.37ppm respectively. The relative content of α-1,6-glycosidic bonds can be obtained according to the peak areas of the corresponding absorption peaks of α-1,4-glycosidic bonds and α-1,6-glycosidic bonds in the sample. The results showed that after the starch in Example 3 was modified by branching enzyme, its relative content of α-1,6-glycosidic bonds increased significantly with the extension of modification time, indicating that starch branching enzyme modification can significantly increase the branching degree of starch.

[0074] Example 4: Regulation of the performance of highly branched starch films by the amount of starch branching enzyme added

[0075] (1) Plasticization: 30% glycerol based on the dry starch basis was added to the starch lactolysate obtained in step (3) of Example 1, and the mixture was reacted at 95° C. for 30 min to allow the small molecule plasticizer to be incorporated between the starch molecules to increase the distance between the starch molecules.

[0076] (2) Casting: 20 g of gel solution was cast on a polypropylene surface dish by the casting method to form a film, and the level was controlled to ensure uniform film thickness.

[0077] (3) Drying: After drying in a horizontal vacuum drying oven at 60°C for 8 hours, a highly branched starch film can be obtained.

[0078] (4) Storage: The dried film was taken out from the vacuum drying oven and stored in a constant temperature and humidity chamber at 25° C. and a relative humidity of 50% for 24 h.

[0079] Example 5: Effect of starch branching enzyme on the performance of different types of highly branched starch films

[0080] (1) Plasticization: 30% glycerol based on the dry starch basis was added to the starch lactolysate obtained in step (3) of Example 2, and the mixture was reacted at 95° C. for 30 min to allow the small molecule plasticizer to be incorporated between the starch molecules, thereby increasing the distance between the starch molecules.

[0081] (2) Casting: 20 g of gel solution was cast on a polypropylene surface dish by the casting method to form a film, and the level was controlled to ensure uniform film thickness.

[0082] (3) Drying: After drying in a horizontal vacuum drying oven at 60°C for 8 hours, a highly branched starch film can be obtained.

[0083] (4) Storage: The dried film was taken out from the vacuum drying oven and stored in a constant temperature and humidity chamber at 25° C. and a relative humidity of 50% for 24 h.

[0084] Example 6: Effect of starch branching enzyme modification time on the performance of highly branched starch films

[0085] (1) Plasticization: 30% glycerol based on the dry starch basis was added to the starch lactolysate obtained in step (3) of Example 3, and the mixture was reacted at 95° C. for 30 min to allow the small molecule plasticizer to be incorporated between the starch molecules, thereby increasing the distance between the starch molecules.

[0086] (2) Casting: 20 g of gel solution was cast on a polypropylene surface dish by the casting method to form a film, and the level was controlled to ensure uniform film thickness.

[0087] (3) Drying: After drying in a horizontal vacuum drying oven at 60°C for 8 hours, a highly branched starch film can be obtained.

[0088] (4) Storage: The dried film was taken out from the vacuum drying oven and stored in a constant temperature and humidity chamber at 25° C. and a relative humidity of 50% for 24 h.

[0089] Control group 3:

[0090] No plasticizer was added, and the rest was the same as in Example 6.

[0091] The following tests were performed on Examples 4-6 and Control Group 3:

[0092] 1. Scanning electron microscopy observation

[0093] The sample was sliced ​​and glued to the sample stage, and a layer of gold powder was sprayed evenly on the surface. It was observed at a voltage of 3.0 kV. The results are shown in Figure 5 .

[0094] Figure 5 It is the scanning electron microscope observation result of each group of starch-based film. It can be seen from the inter-group comparison results of control group 3 and embodiment 6 that, whether or not starch branching enzyme modification is added, the addition of glycerol improves the plasticity of starch molecules, and the attraction between the spacing polymer molecules between starch molecules increases the softness of starch materials, so that the surface of starch film is gradually smooth. The intra-group comparison of control group 3 and embodiment 6 shows that, whether or not there is a plasticizing effect of glycerol, after the modification of starch branching enzyme, the surface of starch film changes from rough and porous to smooth and uniform continuous surface, and this phenomenon occurs significantly with the extension of amylase modification time. The substantial reduction of cavities and rough surfaces is conducive to the improvement of film performance. It is speculated that the chain structure of starch molecules is reorganized after modification by branching enzyme, making the surface structure of starch film more compact and smooth.

[0095] 2. Mechanical properties

[0096] The film was cut into rectangular sample strips of 20×80 mm, the distance between the two racks was set to 20 mm, and the stretching speed was set to 20 mm / min to measure the mechanical strength of the starch-based film.

[0097] The results are as follows Figure 6 As shown, with the increase of enzyme addition, the tensile strength of the starch film shows a trend of first increasing and then decreasing, reaching a peak value when the enzyme addition is 25U / g, and then starting to show a downward trend; compared with the original starch film (the product of the control group 1 is made into a film according to the method of Example 6), its tensile strength increased by 100.09%, 69.58%, 49.75%, and 9.68%, respectively. Combined with the chain length distribution results, GBE tends to hydrolyze the longer molecular segments in the branched starch as a whole, and reconnect the cut molecules, resulting in a decrease in the long chain content and an increase in the short chain content. The increase in high branching increases the short-range order of starch crystals, thereby increasing the tensile strength of the starch film.

[0098] 3. Thermodynamic properties

[0099] The detection was performed using TGA 8000. About 3 mg of starch film was loaded into a crucible plate and then heated from 30°C to 500°C at a heating rate of 15°C under a nitrogen atmosphere with a gas flow rate of 20 mL / min.

[0100] The results are as follows Figure 7 As shown in the figure, the degradation temperature of starch-based films after GBE treatment gradually decreases with the increase of enzyme addition amount. After starch is modified by GBE enzyme, the linear chains of debranched starch are rearranged after gelatinization, but its crystalline area is smaller than that of native starch, resulting in a lower decomposition temperature. In addition, the decrease in thermal stability may be related to the weakened molecular interaction between starch chains and starch amorphous crystal structure.

[0101] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing an edible film, characterized in that: The following steps are involved: (1) Slurry preparation Dissolve starch in water to prepare starch milk, stir evenly at 25-50℃ for later use; (2) Enzymatic hydrolysis The starch milk is heated to make the starch granules swell and collapse to form a viscous and uniform transparent paste solution, and then the temperature is lowered to 45-55°C. A starch branching enzyme is added to the starch milk to catalyze the hydrolysis and transglycosidation of the starch, so as to achieve enzymatic modification of the starch structure to achieve high branching; (3) Plasticization Adding a plasticizer to the starch emulsion after enzymatic hydrolysis in step (2) to allow the small molecule plasticizer to be incorporated between starch molecules, thereby increasing the distance between starch molecules and forming a gel solution; (4) Casting The gel solution obtained in step (3) is cast into a film in a polypropylene watch glass by a casting method, and the level is controlled to ensure uniform film thickness; (5) Drying The gel solution is dried in a horizontal vacuum drying oven, and a highly branched starch film can be obtained after drying for a certain period of time; (6) Save The highly branched starch film is stored in a constant temperature and humidity chamber for later use; Wherein, the amount of starch branching enzyme added in step (2) is 25-200 U / g starch on a dry basis; after adding the starch branching enzyme, the pH is adjusted to 6.0-7.5, and the reaction is carried out at 50-70°C for 3-24 hours.

2. A method for preparing an edible film according to claim 1, characterized in that: The types of starch in step (1) are corn starch, pea starch, tapioca starch and wheat starch.

3. A method for preparing an edible film according to claim 1, characterized in that: The mass concentration of starch milk in step (1) is in the range of 3% to 5%.

4. A method for preparing an edible film according to claim 1, characterized in that: The temperature range of heating the starch milk in step (2) is 90-100° C. and the heating time is 30 min-1 h.

5. A method for preparing an edible film according to claim 1, characterized in that: The type of plasticizer in step (3) is at least one of glycerol, polyols and diols.

6. A method for preparing an edible film according to claim 1, characterized in that: In the step (3), after adding the plasticizer, the temperature is maintained at 90-100° C. for 30 min-1 h to allow the small molecule plasticizer to be incorporated between the starch molecules.

7. A method for preparing an edible film according to claim 1, characterized in that: The pouring thickness in step (4) is 0.050 mm to 0.200 mm.

8. A starch-based edible film obtained by the method according to any one of claims 1 to 7.

9. Use of the starch-based edible film according to claim 8 in food packaging.

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