Starch-based antibacterial slow-release intelligent film as well as preparation and application thereof

Abstract

The invention belongs to the technical field of intelligent food packaging, and particularly relates to a starch-based antibacterial slow-release intelligent film as well as preparation and application thereof, and the starch-based antibacterial slow-release intelligent film is prepared from the following raw materials in parts by weight: 3-5g of modified starch, 20% of glycerol (based on the dry weight of the modified starch), 7-11mL of pericarpium citri reticulatae essential oil Pickering emulsion and 0.5% of purple corn cob anthocyanin solution (based on the dry weight of the modified starch). The invention also provides a preparation method of the starch-based antibacterial slow-release intelligent film, and the prepared intelligent film has excellent mechanical properties, oxidation resistance, antibacterial properties and the like, can be used for detecting the freshness of pork, and has relatively high biological safety when being applied to food.

Description

Technical Field

[0001] The present invention belongs to the technical field of food intelligent packaging, and in particular relates to a starch-based antibacterial sustained-release intelligent film and a preparation method and application thereof. Background Art

[0002] With the development of the food industry, new methods of food packaging are also constantly developing. Traditional food packaging is mainly divided into plastic, glass, paper and metal materials. However, traditional packaging can only isolate microbial contamination and containers, and cannot directly provide information about food quality. Smart packaging can monitor the quality of food in real time and can effectively monitor and convey information about food quality. In order to enable smart films to provide more packaging attributes, they can be given antibacterial properties. Studies have been conducted to prepare antibacterial smart films by adding essential oils. Essential oils, as natural antibacterial agents, are rich in terpenes, alcohols, esters, aldehydes, ethers and ketones, and have broad-spectrum antibacterial properties against a variety of bacteria. The disadvantage of packaging based on polysaccharides and proteins is that they are sensitive to water. When the ambient humidity is high, the packaging will swell. This expansion will cause the dissolution of the indicator in the smart film, which will reduce the reliability of the indication. It is necessary to use a modified matrix to reduce the external migration of the indicator and maintain the good indication performance of the smart film. Summary of the invention

[0003] To achieve the above-mentioned purpose, the present invention provides a starch-based antibacterial sustained-release intelligent film and its preparation and application, which solves the problems existing in the prior art.

[0004] The technical solution adopted by the present invention is:

[0005] A starch-based antibacterial sustained-release smart film, characterized in that it is prepared from the following raw materials in parts by weight: 3-5 g of modified starch, 20% glycerol (based on the dry weight of modified starch), 7-11 mL of tangerine peel essential oil Pickering emulsion, and 0.5% purple corncob anthocyanin solution (based on the dry weight of modified starch).

[0006] Furthermore, the modified starch is prepared by preparing 8g of corn starch into a 10% suspension, adding 5% (based on the dry weight of corn starch) of pullulanase solution (2000U / g), adjusting the pH to 5.0, and then enzymolyzing for 3h to 12h at 50°C, then adjusting the pH to 11 to stop the reaction, and centrifuging and washing three times at 10000r / min in a high-speed centrifuge to obtain the modified starch.

[0007] Furthermore, the modified starch is prepared by adding distilled water to 10g corn starch to form a 10% suspension, then adding 5% to 20% esterifying agent (based on the dry weight of corn starch, 3 times N,N-dimethylformamide (DMF) dissolved) to adjust the pH to 8.5 to 9, adding NaOH dropwise to maintain the pH, and after 3 hours, adjusting the pH to 6.5 with HCL to terminate the reaction, washing three times with distilled water and ethanol, filtering, drying at 40°C, and grinding to obtain the modified starch.

[0008] In certain embodiments of the present invention, the esterification agent is selected from dodecenyl succinic anhydride (DDSA), hexadecanoic acid (PA) or 2-octenyl succinic anhydride (OSA).

[0009] In certain embodiments of the present invention, the enzymatic hydrolysis time is 3 h to 12 h, for example, 3 h, 6 h, 9 h, or 12 h.

[0010] In certain embodiments of the present invention, 5% to 20% dodecenylsuccinic anhydride (DDSA) (based on the dry weight of corn starch, dissolved in 3 times N,N-dimethylformamide (DMF)) is added, for example, 5%, 10%, 15%, 20%.

[0011] A method for preparing a starch-based antibacterial sustained-release drug, characterized in that it comprises the following steps:

[0012] (1) 10 g corn starch was added with distilled water to prepare a 10% suspension, and ultrasonic cell crusher was used for 15 min at 50% power ratio, with ultrasound on for 2 s and off for 2 s. Then, 15% dodecenyl succinic anhydride (DDSA) (based on the dry weight of corn starch, dissolved in 3 times N,N-dimethylformamide (DMF)) was added, and the pH was adjusted to 8.5-9. NaOH was added dropwise to maintain the pH. After 3 h, HCL was added to adjust the pH to 6.5 to terminate the reaction. The product was washed three times with distilled water and ethanol, filtered, dried at 40° C., and ground to obtain a product named UDSt; 0.54 g UDSt was taken to prepare a 1% suspension, gelatinized at 90° C. for 20 min, and then cooled to room temperature, 2 mL of tangerine peel essential oil was added, and emulsified and dispersed at 8000 r / min for 3 min to obtain tangerine peel essential oil Pickering emulsion, which was set aside;

[0013] (2) washing, drying, and crushing the purple corn cob, extracting it in an ultrasonic cleaner at a solid-liquid ratio of 1:10 at a power ratio of 40% and 50° C. for 40 min, filtering it, and centrifuging it in a high-speed centrifuge at 10,000 r / min for 20 min to obtain a purple corn cob anthocyanin solution for later use;

[0014] (3) Dispersing the modified starch in distilled water, stirring at 90° C. for 15 min, then adding 20% ​​glycerol (based on the dry weight of the modified starch), stirring evenly, adding the tangerine peel essential oil Pickering emulsion obtained in step (1) and 0.5% (based on the dry weight of the modified starch) of the purple corncob anthocyanin solution obtained in step (2) before ultrasonic treatment, after ultrasonic treatment for 180 s, pouring the solution into a polypropylene (PP) mold, and drying at 25° C., 40% RH for 48 h.

[0015] A starch-based antibacterial sustained-release intelligent film prepared by the above preparation method.

[0016] The application of the starch-based antibacterial slow-release smart film is characterized in that it is used to predict the freshness of pork. Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) Enzymatic hydrolysis creates pores in starch particles, which increases the water and oil absorption rate of the smart membrane;

[0018] (2) Esterification with dodecenylsuccinic anhydride (DDSA) significantly improves the water resistance of starch films. At the same time, the modified starch has higher biosafety when used in food.

[0019] (3) Esterification with dodecenylsuccinic anhydride (DDSA) creates pores on the surface of starch particles and increases the surface roughness, which significantly improves the tensile strength, water contact angle, antibacterial and antioxidant properties of the smart membrane, as well as the antibacterial area against Escherichia coli and Staphylococcus aureus, and the water vapor permeability also decreases significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1a It is the FT-IR graph of modified starch at different enzymatic hydrolysis times;

[0022] Figure 1b It is the FT-IR image of smart film prepared by modified starch with different enzymatic hydrolysis time;

[0023] Figure 2 are SEM images of modified starch granules (column 1), film surface (column 2), and cross section (column 3);

[0024] Figure 3 are SEM images of the surface (column 1) and cross section (column 2) of the modified starch film;

[0025] Figure 4 is the water contact angle diagram of the membrane;

[0026] Figure 5a Changes in L* and a*(a) of the film during storage period;

[0027] Figure 5b Plot of the change in b* versus ΔE(b) of the film during storage. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the following specific embodiments and comparative examples, the tangerine peel essential oil is provided by Guangzhou Wanhong Biotechnology Co., Ltd., dodecenylsuccinic anhydride (DDSA), pullulanase, and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) are provided by Shanghai MacLean Biochemical Technology Co., Ltd., 2-octenylsuccinic anhydride (OSA) is provided by Shanghai Jieshikai Biotechnology Co., Ltd., hexadecanoic acid (PA) is provided by Kaifeng Baichuan Huibao Spice Co., Ltd., corn starch is provided by Xinxiang Liangrun Cereal Food Co., Ltd., glycerol and N,N-dimethylformamide (DMF) are provided by Sinopharm Chemical Reagent Co., Ltd., purple corn cobs and fresh lean meat are purchased from local supermarkets, and other reagents are commercial and analytical grade reagents.

[0030] Embodiment 1:

[0031] A method for preparing a starch-based antibacterial sustained-release smart, characterized in that it is prepared from the following raw materials in parts by weight: 4g of modified starch, 20% glycerol (based on the dry weight of modified starch), 10mL of tangerine peel essential oil Pickering emulsion, and 0.5% purple corncob anthocyanin solution (based on the dry weight of modified starch).

[0032] The preparation method comprises the following steps:

[0033] (1) 10 g corn starch was added with distilled water to prepare a 10% suspension, and ultrasonic cell crusher was used for 15 min at 50% power ratio, with ultrasound on for 2 s and off for 2 s. Then, 15% dodecenyl succinic anhydride (DDSA) (based on the dry weight of corn starch, dissolved in 3 times N,N-dimethylformamide (DMF)) was added, and the pH was adjusted to 8.5-9. NaOH was added dropwise to maintain the pH. After 3 h, HCL was added to adjust the pH to 6.5 to terminate the reaction. The product was washed three times with distilled water and ethanol, filtered, dried at 40° C., and ground to obtain a product named UDSt; 0.54 g UDSt was taken to prepare a 1% suspension, gelatinized at 90° C. for 20 min, and then cooled to room temperature, 2 mL of tangerine peel essential oil was added, and emulsified and dispersed at 8000 r / min for 3 min to obtain tangerine peel essential oil Pickering emulsion, which was set aside;

[0034] (2) washing, drying, and crushing the purple corn cob, extracting it in an ultrasonic cleaner at a solid-liquid ratio of 1:10 at a power ratio of 40% and 50° C. for 40 min, filtering it, and centrifuging it in a high-speed centrifuge at 10,000 r / min for 20 min to obtain a purple corn cob anthocyanin solution for later use;

[0035] (3) Weigh corn starch (8 g) to prepare a 10% suspension, add 5% (based on the dry weight of corn starch) of pullulanase solution (2000 U / g), adjust the pH to 5.0 and perform enzymolysis at 50° C. for 12 h, then adjust the pH to 11 to stop the reaction, centrifuge and wash three times at 10000 r / min to obtain modified starch, weigh 4 g of the modified starch and disperse it in distilled water, stir at 90° C. for 15 min, then add 20% glycerol (based on the dry weight of the modified starch), stir evenly, add 10 mL of the tangerine peel essential oil Pickering emulsion obtained in step (1) and 0.5% (based on the dry weight of the modified starch) of the purple corn core anthocyanin solution obtained in step (2) before ultrasonic treatment, and after ultrasonic treatment for 180 s, pour the solution into a polypropylene (PP) mold and dry it at 25° C. and 40% RH for 48 h.

[0036] Embodiment 2:

[0037] The rest is the same as in Example 1, except that the enzymatic hydrolysis time in step 3 is 3 h.

[0038] Embodiment 3:

[0039] The rest is the same as in Example 1, except that the enzymatic hydrolysis time in step 3 is 6 h.

[0040] Embodiment 4:

[0041] The rest was the same as in Example 1, except that the enzymatic hydrolysis time in step 3 was 9 h.

[0042] Experimental Example 5:

[0043] A method for preparing a starch-based antibacterial sustained-release smart, characterized in that it is prepared from the following raw materials in parts by weight: 20% glycerol (based on starch dry weight), 11 mL of tangerine peel essential oil Pickering emulsion, 0.5% purple corncob anthocyanin solution (based on starch dry weight), and 5 g of modified starch.

[0044] The preparation method comprises the following steps:

[0045] (1) 10 g corn starch was added with distilled water to prepare a 10% suspension, and ultrasonic cell crusher was used for 15 min at 50% power ratio, with ultrasound on for 2 s and off for 2 s. Then, 15% dodecenyl succinic anhydride (DDSA) (based on the dry weight of corn starch, dissolved in 3 times N,N-dimethylformamide (DMF)) was added, and the pH was adjusted to 8.5-9. NaOH was added dropwise to maintain the pH. After 3 h, HCL was added to adjust the pH to 6.5 to terminate the reaction. The product was washed three times with distilled water and ethanol, filtered, dried at 40° C., and ground to obtain a product named UDSt; 0.54 g UDSt was taken to prepare a 1% suspension, gelatinized at 90° C. for 20 min, and then cooled to room temperature, 2 mL of tangerine peel essential oil was added, and emulsified and dispersed at 8000 r / min for 3 min to obtain tangerine peel essential oil Pickering emulsion, which was set aside;

[0046] (2) washing, drying, and crushing the purple corn cob, extracting it in an ultrasonic cleaner at a solid-liquid ratio of 1:10 at a power ratio of 40% and 50° C. for 40 min, filtering it, and centrifuging it in a high-speed centrifuge at 10,000 r / min for 20 min to obtain a purple corn cob anthocyanin solution for later use;

[0047] (3) Weigh 10 g of corn starch and add distilled water to prepare a 10% suspension, then add 5% dodecenylsuccinic anhydride (DDSA) (based on the dry weight of corn starch, 3 times the amount of N,N-dimethylformamide (DMF) dissolved), adjust the pH to 8.5-9, add NaOH dropwise to maintain the pH, and after 3 hours, adjust the pH to 6.5 with HCL to terminate the reaction. Wash three times with distilled water and ethanol, filter, dry at 40°C, grind to obtain modified starch, weigh 5 g of modified starch, disperse in distilled water, stir at 90°C for 15 minutes, then add 20% glycerol (based on the dry weight of modified starch), stir evenly, add 11 mL of the tangerine peel essential oil Pickering emulsion obtained in step (1) and 0.5% of the purple corn cob anthocyanin solution obtained in step (2) (based on the dry weight of modified starch) before ultrasonic treatment, and after ultrasonic treatment for 180 seconds, pour the solution into a polypropylene (PP) mold and dry at 25°C, 40% RH for 48 hours.

[0048] Embodiment 6:

[0049] The other steps were the same as those in Example 2, except that 10% dodecenylsuccinic anhydride (DDSA) was added in step 3.

[0050] Embodiment 7:

[0051] The other steps were the same as those in Example 2, except that 15% dodecenylsuccinic anhydride (DDSA) was added in step 3.

[0052] Embodiment 8:

[0053] The other steps were the same as those in Example 2, except that 20% dodecenylsuccinic anhydride (DDSA) was added in step 3.

[0054] Comparative Example 1:

[0055] A method for preparing a starch-based antibacterial sustained-release smart, characterized in that it is prepared from the following raw materials in parts by weight: 4g corn starch, 20% glycerol (based on the dry weight of corn starch), 10mL tangerine peel essential oil Pickering emulsion, and 0.5% purple corncob anthocyanin solution (based on the dry weight of corn starch).

[0056] The preparation method comprises the following steps:

[0057] (1) 10 g corn starch was added with distilled water to prepare a 10% suspension, and ultrasonic cell crusher was used for 15 min at 50% power ratio, with ultrasound on for 2 s and off for 2 s. Then, 15% dodecenyl succinic anhydride (DDSA) (based on the dry weight of corn starch, dissolved in 3 times N,N-dimethylformamide (DMF)) was added, and the pH was adjusted to 8.5-9. NaOH was added dropwise to maintain the pH. After 3 h, HCL was added to adjust the pH to 6.5 to terminate the reaction. The product was washed three times with distilled water and ethanol, filtered, dried at 40° C., and ground to obtain a product named UDSt; 0.54 g UDSt was taken to prepare a 1% suspension, gelatinized at 90° C. for 20 min, and then cooled to room temperature, 2 mL of tangerine peel essential oil was added, and emulsified and dispersed at 8000 r / min for 3 min to obtain tangerine peel essential oil Pickering emulsion, which was set aside;

[0058] (2) washing, drying, and crushing the purple corn cob, extracting it in an ultrasonic cleaner at a solid-liquid ratio of 1:10 at a power ratio of 40% and 50° C. for 40 min, filtering it, and centrifuging it in a high-speed centrifuge at 10,000 r / min for 20 min to obtain a purple corn cob anthocyanin solution for later use;

[0059] (3) Weigh 4 g corn starch and disperse it in 50 mL distilled water, stir at 90° C. for 15 min, then add 20% glycerol (based on the dry weight of corn starch) and stir evenly; before ultrasonication, add 10 mL of tangerine peel essential oil Pickering emulsion and 0.5% purple corncob anthocyanin solution (based on the dry weight of corn starch), after ultrasonic treatment for 180 s, pour the solution into a polypropylene (PP) mold and dry it at 25° C. and 40% RH for 48 h.

[0060] Example 9

[0061] The rest is the same as Example 2, except that 10% hexadecanoic acid (PA) is added in step 3.

[0062] Example 10

[0063] The other steps were the same as those in Example 2, except that 10% 2-octenylsuccinic anhydride (OSA) was added in step 3.

[0064] The film prepared with corn starch was recorded as St (Comparative Example 1), the membranes prepared with modified starch hydrolyzed with pullulanase solution for 3h, 6h, 9h and 12h were recorded as PLSt-3, PLSt-6, PLSt-9 and PLSt-12 respectively; the membranes prepared with modified starch with 5%, 10%, 15% and 20% of dodecenylsuccinic anhydride (DDSA) esterifying agent were recorded as DASt-5, DASt-10, DASt-15 and DASt-20 respectively, the membrane prepared with modified starch with 10% of hexadecanoic acid (PA) esterifying agent was recorded as PASt-10, and the membrane prepared with modified starch with 10% of 2-octenylsuccinic anhydride (OSA) esterifying agent was recorded as OSAt-10.

[0065] 1. Characterization of modified starch and structural analysis of membranes

[0066] Figure 1a The following are FT-IR images of modified starches at different enzymatic hydrolysis times. Both corn starch and modified starch show typical starch absorption peaks, which indicates that enzymatic hydrolysis does not produce new groups. -1 The absorption peak at 2922cm is related to the stretching vibration of the OH group of starch molecules. -1 The stretching vibration of CH and CH2 groups causes the asymmetric stretching vibration of COC and the symmetric stretching vibration of COC, which causes the 1071cm -1 and 1152cm -1 Strong absorption. 1047 / 1022cm -1 With 1022 / 995cm -1 The peak intensity ratio of 1047 / 1022 cm represents the order of the double helix structure and the order of the starch molecules, respectively. -1 The higher the ratio, 1022 / 995cm -1 The lower the ratio, the higher the molecular order. Corn starch and modified starch hydrolyzed for 12 hours at 1047 / 1022cm -1 and 1022 / 995cm -1 The ratios are 0.95, 1.02 and 1.06, 0.99, respectively, which indicates that the modified starch has a higher order.

[0067] Figure 1bFT-IR images of smart membranes prepared by modified starch with different enzymatic hydrolysis times. As shown in the figure, the spectra of all membranes have similar absorption peaks. This is because the substances in the membranes are starch, tangerine peel essential oil, and anthocyanins, and the groups of modified starch and corn starch are not significantly different, as shown in Figure 1(a). At 3411cm -1 The strong absorption peak is the stretching vibration peak of OH, 2932cm -1 is the stretching vibration peak of CH, 1639cm -1 These are the stretching vibration peaks of CC. 1733, 1684, 1365, 1276 cm -1 The strong absorption of the essential oils is related to the C=O, C=C, and CN stretching vibration peaks of the essential oils. The addition of purple corn cob anthocyanins results in an absorption peak at 3411 cm -1 、2932cm -1 、1639cm -1 and 1120-980cm -1 This is related to the interaction between anthocyanins and starch.

[0068] The water absorption rate WAC and oil absorption rate OAC of corn starch are 80% and 200% respectively. After enzymatic hydrolysis, the WAC and OAC of modified starch are significantly improved. After 12h of enzymatic hydrolysis, the water absorption rate WAC and oil absorption rate OAC of modified starch increased to 240% and 260% respectively, because the starch exposed more hydroxyl groups after enzymatic hydrolysis, and the porous structure was conducive to capturing and retaining oil droplets, as shown in Table 1.

[0069] Table 1. Water absorption rate WAC and oil absorption rate OAC of corn starch and modified starch with different enzymatic hydrolysis time

[0070] Membrane Type St PLSt-3 PLSt-6 PLSt-6 PLSt-12 WAC water absorption (%) 80±20 120±10 140±10 200±20 240±10 OAC oil absorption rate (%) 200±10 210±5 220±10 240±10 260±15

[0071] 2. Membrane morphology analysis:

[0072] The surface and cross-sectional microscopic images of the membrane are shown in Figure 2. Figure 2 As shown. Compared with St, the surfaces of PLSt-3, PLSt-6, PLSt-9, and PLSt-12 are rougher, and the adhered essential oil particles are larger and more, because the porous structure has a high adsorption effect on oil. The cross-sections of St and PLSt-3 can be divided into two parts: honeycomb holes and dense and uniform, and obvious fractures can be observed at the edge of St. Modified starch has a high water and oil adsorption capacity, which makes the cross-sections of PLSt-6 and PLSt-9 have fewer holes and are uniform overall. PLSt-12 shows a uniform texture and is honeycomb-shaped.

[0073] The SEM images of the membranes are shown in Figure 3As shown in the figure. The surface of the St film is rough, with essential oil particles attached, and the cross-section has uniform holes due to the evaporation and surface aggregation of the essential oil emulsion during drying. The surfaces of DASt-5, DASt-10, DASt-15, and DASt-20 have a rougher surface due to the esterification of dodecenyl succinic anhydride, and more essential oil particles are attached.

[0074] 3. Film thickness, tensile strength and elongation at break

[0075] The thickness, tensile strength and elongation at break of the film are shown in Table 2. The thickness of St is 0.221 mm, and the thicknesses of DASt-5, DASt-10, DASt-15 and DASt-20 are 0.227 mm, 0.237 mm, 0.244 mm and 0.251 mm respectively. The long hydrophobic chain of dodecenyl succinic anhydride in the modified starch increases the repulsion between starch molecules, resulting in an increase in thickness.

[0076] The tensile strength and elongation at break of the membrane were tested as follows: the membrane samples were cut into a size of 15 mm × 130 mm, and a horizontal computer tensile tester (WAL-300B, Hangzhou Qingtong Bo Ke Automation Technology Co., Ltd.) was used to measure the tensile strength and elongation at break of the membrane samples at a moving speed of 100 mm / min, and the readings were taken directly from the instrument.

[0077] The elongation at break of St is 3.00%, the components in the DASt-5 film are evenly distributed, the network structure is more complete, and the tensile strength is 15.68MPa. As shown in Table 2, the tensile strength and elongation at break of all modified starch smart films are higher than St, and the modified starch improves the mechanical properties of the film.

[0078] Table 2. Film thickness, tensile strength, and elongation at break

[0079]

[0080]

[0081] 4. Water contact angle of membrane

[0082] Figure 4 This is the water contact angle image of the membrane.

[0083] The method for detecting the water contact angle of the membrane is as follows: the film is cut into pieces of size 10 mm × 50 mm, and then a deionized water droplet is injected on the surface of the film using a special syringe, and then the water contact angle of the membrane is measured using a contact angle meter (FCA2000A, Shanghai Aifeisi Precision Instrument Co., Ltd.), and the reading is directly taken from the instrument.

[0084] The water contact angles of St, DASt-5, DASt-10, DASt-15, and DASt-20 were 53.87°, 60.52°, 61.64°, 71.68°, and 74.05°, respectively. The hydrolysis antennae of the modified starch smart film were all higher than those of St, mainly because dodecenyl succinic anhydride was hydrophobic, and the adhesion of essential oil particles on the surface reduced the affinity for water molecules.

[0085] 5. Antioxidant and antibacterial properties of the membrane

[0086] The detection method of the inhibition area of ​​Escherichia coli and Staphylococcus aureus is as follows: The inhibition zone method is used to determine the antibacterial ability of the membrane against Escherichia coli and Staphylococcus aureus. A membrane sample with a diameter of 15 mm is placed on an agar culture dish evenly smeared with 50 μL of bacterial solution, and incubated at 37°C for 15 hours. The inhibition area around the membrane sample is measured to evaluate the antibacterial ability of the membrane.

[0087] The detection method of 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) scavenging rate is as follows: 0.2g of film was crushed at a speed of 5000r / min, and then oscillated in 20mL of water for 12h. After centrifugation, 1mL of supernatant was mixed with DPPH ethanol solution, incubated in the dark for 30min, and then the absorbance was measured at 517nm. The DPPH scavenging rate was calculated according to the following formula.

[0088]

[0089] In the formula and are the absorbance of the sample and blank group, respectively.

[0090] Table 3 shows the inhibition zone areas and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) clearance rates of different films. As shown in Table 3, the 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) clearance rates of St and DASt-5, DASt-10, DASt-15, and DASt-20 are 84.58%, 90.36%, 92.00%, 88.37%, and 87.85%, respectively. The inhibition area of ​​the modified starch film against the two bacteria is higher than that of St.

[0091] Table 3. Inhibition zone area and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) clearance rate of different membranes

[0092]

[0093] 6. Actual testing of pork

[0094] Table 4 and Figure 5a , Figure 5bIt is the TVB-N of pork during storage, the pH change and the image of the membrane and the color parameter corresponding to the membrane. TVBB-N is one of the important indicators for judging the quality of pork. It is generally believed that pork begins to rot when TVBB-N>15mg / 100g, and TVB-N>30mg / 100g is considered to be completely rotten and inedible. As shown in Table 4, pork is fresh within 1d, TVB-N<15mg / 100g; at 2d, TVB-N is 20.12mg / 100g, and it has begun to rot; at 3d, TVBN-N is 32.37mg / 100g, which is completely inedible. pH is also one of the indicators for judging the quality of pork. It is generally believed that the pH of fresh pork is between 5.80-6.20, and the pH of rotten pork is>6.20. As shown in Table 4, the pH of pork is 5.76 and 6.10 at 0d and 1d, respectively, which belongs to fresh pork. Starting from 2d, pH>6.20, and gradually rotten occurs.

[0095] Tables 5 and 6 are the equations and correlation coefficients of the linear fitting and polynomial fitting of the membrane ΔE versus TVB-N and pH, respectively. When fitting ΔE versus TVB-N, DASt-5 showed the highest correlation, and the correlations of the two fittings were both greater than 0.99. When fitting ΔE versus pH, DASt-5 still had the highest correlation, and the correlations of the two fitting methods were greater than 0.97. The fitting results show that the change in ΔE of DASt-5 during pork storage is highly correlated with the quality of pork and can be used to predict changes in freshness.

[0096] Table 4 TVB-N, pH changes and membrane images during storage of pork

[0097]

[0098] Table 5 Linear and polynomial fitting parameters of ΔE and TVB-N

[0099]

[0100] Table 6 Linear and polynomial fitting of ΔE and pH

[0101]

[0102] In summary, enzymatic hydrolysis produces pores in starch granules. The water and oil absorption rates of the smart membrane prepared by modified starch hydrolyzed by pullulanase increased by 160% and 60%, respectively. Compared with St, the tensile strength of PLSt-12 increased by 27.33% and the water contact angle increased by 35.23°. DDSA esterification causes pores on the surface of starch granules and increases the surface roughness. The tensile strength, water contact angle, antibacterial, antioxidant and water vapor permeability of DASt-5 are significantly improved compared with St. Its tensile strength increased by 39.13%, water contact angle increased by 6.65°, 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) scavenging rate increased by 5.78%, and the antibacterial areas against Escherichia coli and Staphylococcus aureus were 210.55 mm 2 and 285.05mm 2 .

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A starch-based antibacterial sustained-release smart film, characterized in that: The invention is prepared from the following raw materials in parts by weight: 3-5g of modified starch, 20% of glycerol (based on the dry weight of modified starch), 7-11mL of tangerine peel essential oil Pickering emulsion, and 0.5% of purple corncob anthocyanin solution (based on the dry weight of modified starch).

2. A starch-based antibacterial sustained-release smart film according to claim 1, characterized in that: The modified starch is prepared by preparing 8g of corn starch into a 10% suspension, adding 5% (based on the dry weight of corn starch) of pullulanase solution (2000U / g), adjusting the pH to 5.0, performing enzymolysis at 50°C for 3h to 12h, then adjusting the pH to 11 to stop the reaction, and washing by centrifugation at 10000r / min in a high-speed centrifuge for three times to obtain the modified starch.

3. The starch-based antibacterial sustained-release smart film according to claim 1, characterized in that: The modified starch is prepared by adding 10g of corn starch to distilled water to form a 10% suspension, then adding 5% to 20% of dodecenyl succinic anhydride, hexadecanoic acid or 2-octenyl succinic anhydride (based on the dry weight of corn starch and dissolved in 3 times of N,N-dimethylformamide), adjusting the pH to 8.5 to 9, adding NaOH dropwise to maintain the pH, adjusting the pH to 6.5 with HCL after 3 hours to terminate the reaction, washing three times with distilled water and ethanol, filtering, drying at 40°C, and grinding to obtain the modified starch.

4. A starch-based antibacterial sustained-release smart film according to claim 2, characterized in that: The enzymatic hydrolysis time is 3 h to 12 h, for example 3 h, 6 h, 9 h, 12 h.

5. A starch-based antibacterial sustained-release smart film according to claim 3, characterized in that: The adding of 5% to 20% dodecenylsuccinic anhydride (based on the dry weight of corn starch, dissolved in 3 times of N,N-dimethylformamide), for example, 5%, 10%, 15%, 20%.

6. The method for preparing a starch-based antibacterial sustained-release smart film according to claim 4 or 5, characterized in that: The following steps are involved: (1) 10 g corn starch was added with distilled water to prepare a 10% suspension, and ultrasonic cell crusher was used for 15 min at 50% power ratio, with ultrasound on for 2 s and off for 2 s. Then, 15% dodecenyl succinic anhydride (based on the dry weight of corn starch and dissolved in 3 times of N, N-dimethylformamide) was added, and the pH was adjusted to 8.5-9. NaOH was added dropwise to maintain the pH. After 3 h, HCL was added to adjust the pH to 6.5 to terminate the reaction. The product was washed three times with distilled water and ethanol, filtered, dried at 40° C., and ground to obtain a product named UDSt; 0.54 g UDSt was taken to prepare a 1% suspension, gelatinized at 90° C. for 20 min, and then cooled to room temperature, 2 mL of tangerine peel essential oil was added, and emulsified and dispersed at 8000 r / min for 3 min to obtain tangerine peel essential oil Pickering emulsion, which was set aside; (2) washing, drying, and crushing the purple corn cob, extracting it in an ultrasonic cleaner at a solid-liquid ratio of 1:10 at a power ratio of 40% and 50° C. for 40 min, filtering it, and centrifuging it in a high-speed centrifuge at 10,000 r / min for 20 min to obtain a purple corn cob anthocyanin solution for later use; (3) Dispersing the modified starch in distilled water, stirring at 90° C. for 15 min, then adding 20% ​​glycerol (based on the dry weight of starch), stirring evenly, adding the tangerine peel essential oil Pickering emulsion obtained in step (1) and 0.5% (based on the dry weight of modified starch) of the purple corncob anthocyanin solution obtained in step (2) before ultrasonic treatment, after ultrasonic treatment for 180 s, pouring the solution into a polypropylene (PP) mold, and drying at 25° C., 40% RH for 48 h.

7. A starch-based antibacterial sustained-release intelligent film prepared by the preparation method of claim 6.

8. An application of the starch-based antibacterial sustained-release smart film as claimed in claim 7, characterized in that: Used to predict the freshness of pork.

Images