WO2022227701A1

WO2022227701A1 - Method for preparing oat protein and pullulan polysaccharide composite fruit and vegetable cling film by ultrasound

Info

Publication number: WO2022227701A1
Application number: PCT/CN2022/071248
Authority: WO
Inventors: 任晓锋; 梁秋芳; 马海乐; 曲文娟; 陈欢鑫; 刘宇轩; 亢利鑫; 侯婷
Original assignee: 江苏大学
Priority date: 2021-04-27
Filing date: 2022-01-11
Publication date: 2022-11-03
Also published as: CN113214514A; CN113214514B

Abstract

The present invention relates to the technical field of food packaging material preparation, and provides a method for preparing an oat protein and pullulan polysaccharide composite fruit and vegetable cling film by ultrasound. The method comprises the following steps: preparation of an oat protein/pullulan polysaccharide film-forming solution; preparation of a Nisin-loaded oat protein/pullulan polysaccharide film-forming solution; preparation of an ultrasound-treated Nisin-loaded oat protein/pullulan polysaccharide film-forming solution; and flow casting to form a film, and drying to obtain a composite film. In the preparation process of the composite film, Nisin is added to improve the mechanical properties of the composite membrane, and make the composite film have good antibacterial properties; the use of multi-mode ultrasound treatment technology is beneficial to enhancing the degree of crosslinking between the oat protein, the pullulan polysaccharide, and Nisin, and ultrasound treatment reduces the light transmittance of the composite film and improves the water barrier properties and oxygen barrier properties of the composite film. According to the present invention, strawberries are coated with the composite film for preservation, thus, the decay rate, the weight loss rate, and the hardness loss of the strawberries are significantly reduced, and the shelf life of the strawberries is prolonged.

Description

Ultrasonic preparation method of oat protein and pullulan compound fruit and vegetable fresh-keeping film

technical field

The invention relates to the technical field of preparation of food packaging materials, in particular to a method for preparing loaded Nisin by using oat protein and pullulan as raw materials, adding glycerin plasticizer and nisin (Nisin) bacteriostatic agent, and adopting an ultrasonic treatment method. Oat protein/pullulan composite film packaging material.

Background technique

At present, the global plastic production has exceeded 300 million tons. About 40% of all plastics produced are used for packaging. These plastics are not degradable and pose a serious threat to the environment. For this reason, the development of a renewable and environmentally friendly degradable film has become the research object of scholars at home and abroad. The replacement of traditional plastic packaging materials by new degradable green food packaging materials has become a future development trend.

Oatmeal, known as the "third staple food", is a full-price food with abundant yield and high nutritional value. Most of the protein content in oats is about 16%, up to 20%, ranking first among grain crops, and oat protein is recognized as a comprehensive and reasonable grain protein with amino acid ratio. Oat protein has a large yield, low price, good film-forming properties and natural degradability, making it unique in edible films. However, the mechanical properties and barrier properties of a single oat protein film have certain defects. Therefore, it is considered to add polysaccharide to prepare a composite film to solve various problems in the single-component finished film, and to adjust the proportion of the added components to improve the film performance to meet the needs of different packaging materials. needs. Pullulan is a single extracellular water-soluble microbial polysaccharide produced by the fermentation of Brachypodium. Pullulan polysaccharide food packaging film is colorless, tasteless, edible, and compared with other polymer polysaccharides, its significant advantages are good gas barrier properties, oxygen and carbon dioxide can hardly pass; It has good film formation, adhesion and oxidation resistance under the influence of temperature, pH, metal ions, etc. Glycerin is a colorless, transparent, odorless, viscous liquid with a sweet taste and hygroscopicity. It has a wide range of applications in food, and can play a role in increasing the ductility in the production of fresh-keeping coatings. Nisin, also known as nisin, has a molecular formula of C ₁₄₃ H ₂₂₈ N ₄₂ O ₃₇ S ₇ and a molecular weight of 3510. It is a kind of polypeptide compound with strong bactericidal effect extracted from the fermentation product of lactic acid streptococcus. A natural preservative and bacteriostatic agent, which can be digested into amino acids by proteolytic enzymes in the digestive tract very quickly after eating. It is the only bacteriocin allowed to be used as a preservative in food. Nisin has bacteriostatic effect on most Gram-positive bacteria G+, especially bacterial spores, such as: Staphylococcus aureus, Listeria, Clostridium botulinum, Bacillus cereus, Bacillus subtilis, etc. Nisin is non-toxic, acid-resistant, thermally stable, and has antibacterial properties. Adding Nisin to prepare a composite membrane can improve the relative properties of the membrane and broaden the application range of the composite membrane.

As a non-thermal physical processing technology, ultrasound is more suitable for application in the food industry due to its green efficiency and simple operation. Research has shown that ultrasound can produce cavitation on the medium, which promotes the breaking of chemical bonds in the medium, and the cavitation effect of ultrasound. More reaction centers are exposed, and these reaction centers recombine with molecules to form various chemical bonds, thereby increasing the mechanical strength of the membrane and improving its barrier properties. At present, there is no report on the preparation of composite membrane using oat protein and pullulan, and there is no report on the ultrasonic treatment of oat protein/pullulan composite membrane.

Strawberry is a perennial herb that contains a lot of active ingredients, such as phenolic compounds, fiber, micronutrients and minerals. It has health effects such as enhancing human immunity, and has the reputation of "Queen of Fruits". However, the strawberry peel is thin and the tissue is delicate, which is vulnerable to mechanical damage and infection by external microorganisms, resulting in fruit spoilage. Most of the current methods for strawberry preservation are low-temperature refrigeration, which has good effect but high cost. Therefore, an efficient and low-cost fresh-keeping method is required to prolong the shelf life of strawberries and reduce economic losses.

The invention uses oat protein and pullulan polysaccharide as raw materials, adds glycerin plasticizer, and adds Nisin bacteriostatic agent to prepare Nisin-loaded oat protein/pullulan polysaccharide composite film, in order to solve the mechanical properties and barrier properties of single-component film In order to solve the problem of poor compatibility between the two matrix materials and meet the requirements of food packaging, the antibacterial performance of the composite film is increased, and the advanced multi-mode ultrasonic technology is adopted. At the same time, the prepared composite film is applied to strawberry fresh-keeping to achieve the effect of prolonging the shelf life of strawberry.

SUMMARY OF THE INVENTION

In order to solve the above problems, oat protein and pullulan polysaccharide were used as the matrix of the film material, glycerol was added as a plasticizer, and the physical processing method of ultrasonic treatment was used to study the effect of ultrasonic treatment on the mechanical properties of oat protein / pullulan polysaccharide composite film. The effect of composite film coating on the performance of strawberries was also investigated.

The ultrasonic preparation method of the oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film of the present invention is carried out according to the following steps:

(1) Weigh oat protein and pullulan polysaccharide and dissolve them in distilled water respectively, stir at room temperature for 1h, prepare oat protein solution and pullulan polysaccharide solution of a certain mass concentration, and adjust the pH of oat protein solution to 8;

(2) mixing oat protein solution and pullulan solution in a certain proportion, adding above-mentioned mixed solution after dissolving Nisin with a small amount of water, and slowly adding a certain amount of glycerol as plasticizer to obtain mixed solution;

(3) placing the mixed solution of step (2) in a water bath constant temperature magnetic stirrer, sealing and stirring for several hours at a certain temperature to obtain a film-forming solution;

(4) Take the film-forming solution in a sealed bag, place it in a multi-mode ultrasonic treatment equipment at room temperature and take it out after ultrasonic treatment for several times;

(5) Take the film-forming liquid and form a film by the casting method, let it stand for 10 minutes, and dry it by blasting at 60° C. for 4 hours; after the film is formed, take it out and cool it to room temperature to obtain a fresh-keeping film.

Wherein in step (1), use 5mol/L NaOH to adjust the pH of oat protein solution to 8.

Wherein the matrix concentration of avenin and pullulan in the mixed solution of step (2) is 4g/100mL-12g/100mL, and the preferred matrix concentration is 4g/100mL;

Wherein the mass ratio of oat protein and pullulan in the mixed solution of step (2) is 3:1-1:3, preferably 2:2.

Wherein the concentration of Nisin in the mixed solution of step (2) is 0.02g/100mL-0.1g/100mL, preferably the concentration of Nisin is 0.04g/100mL; with the quality of Nisin and oat protein solution, pullulan solution and Nisin Aqueous solution mass to volume ratio meter.

Wherein the amount of glycerin plasticizer added in the mixed solution of step (2) is 15%-30%, preferably 25% of the mass ratio of the solute; quality ratio meter.

Wherein the heat treatment time of the water bath described in step (3) is 10min-40min, and the preferred heat treatment time is 30min;

Wherein the heat treatment temperature of the water bath described in step (3) is 50°C-90°C, preferably the heat treatment temperature is 70°C;

Wherein the specific parameter of the ultrasonic action described in step (4) is ultrasonic time 5min-30min, preferably ultrasonic time is 10min; ultrasonic frequency 20kHz, 40kHz, 60kHz, 20/40kHz, 20/60kHz, 40/60kHz, 20/40/60kHz , the preferred ultrasonic frequency is 20/60kHz; the ultrasonic power is 40W/L-80W/L, and the preferred ultrasonic power is 50W/L.

The beneficial effects of the present invention are:

(1) The present invention uses oat protein and pullulan polysaccharide as raw materials, adds glycerin plasticizer and Nisin bacteriostatic agent, and prepares Nisin loaded oat protein/pullulan polysaccharide composite film, which solves the problem of mechanical properties and barrier properties of single-component film. For the problem of poor performance, after adding Nisin, the light transmittance of the film material is improved, the water solubility is significantly reduced, the water blocking performance of the film is enhanced, and the oxygen permeability is slightly reduced, which is beneficial to prolong the shelf life of food.

(2) The ultrasonic processing technology used in the present invention is a physical method. Ultrasonic is a green and environmentally friendly physical processing method, which is widely used in the food industry and is a new physical processing method for preparing food packaging materials.

(3) In the process of preparing the composite membrane, the present invention uses the multi-mode ultrasonic treatment technology to increase the degree of cross-linking between avenin and pullulan, and significantly improve the mechanical properties of the membrane. After the addition of Nisin, the water solubility and oxygen permeability of the membranes were significantly reduced after ultrasonic treatment, which broadened the application prospects of the membranes.

(4) In the present invention, the prepared composite film is used to coat strawberries, which obviously reduces the rot rate, weight loss rate and hardness loss of the strawberries, and effectively prolongs the shelf life of the strawberries after the coating treatment.

Description of drawings

Fig. 1 is the structure diagram of the multi-mode ultrasonic biological treatment equipment of the present invention, wherein 1, 2, 3 are ultrasonic vibration plates, 4 is a liquid container, 5 is a water bath, 6 is a temperature probe, 7 is a circulating pump, and 8 is a computer Program controller, 9, 10, 11 are ultrasonic controllers;

Figure 2 shows the effect of matrix concentration on the mechanical properties of composite membranes;

Figure 3 shows the effect of the mass ratio of oat protein and pullulan on the mechanical properties of the composite membrane;

Figure 4 shows the effect of glycerol addition (accounting for the mass ratio of solute) on the mechanical properties of the composite membrane;

Figure 5 shows the effect of heat treatment time on the mechanical properties of the composite membrane;

Figure 6 shows the effect of heat treatment temperature on the mechanical properties of the composite membrane;

Figure 7 shows the effect of ultrasonic time on the mechanical properties of the composite membrane;

Figure 8 shows the effect of ultrasonic frequency on the mechanical properties of the composite membrane;

Figure 9 shows the effect of ultrasonic power on the mechanical properties of the composite membrane;

Figure 10 shows the effect of Nisin addition on the mechanical properties of the composite membrane;

Figure 11 is the histogram of light transmittance of different types of films, from left to right: pure oat protein film (op), pure pullulan film (pul), oat protein/pullulan composite film (op) -pul), ultrasonic oat protein/pullulan composite membrane (cs-op-pul), Nisin loaded oat protein/pullulan composite membrane (n-op-pul), ultrasonic loaded Nisin oat protein/pullulan Polysaccharide complex membrane (csn-op-pul);

Figure 12 is a histogram of water solubility of different types of membranes, from left to right: pure oat protein membrane (op), pure pullulan membrane (pul), oat protein/pullulan composite membrane (op- pul), ultrasonic oat protein/pullulan composite membrane (cs-op-pul), Nisin loaded oat protein/pullulan composite membrane (n-op-pul), ultrasonic loaded oat protein/pullulan polysaccharide Composite membrane (csn-op-pul);

Figure 13 is a histogram of oxygen permeability of different types of membranes, from left to right in the figure: control (control), pure oat protein membrane (op), pure pullulan polysaccharide membrane (pul), oat protein/pulu Orchid polysaccharide composite membrane (op-pul), ultrasonic oat protein/pullulan composite membrane (cs-op-pul), Nisin loaded oat protein/pullulan composite membrane (n-op-pul), ultrasonic loaded Nisin Oat protein/pullulan composite membrane (csn-op-pul);

Figure 14 is a graph showing the antibacterial effect of different Nisin addition amounts (0, 0.04, 0.08, 0.12, 0.2g/100mL) on Listeria. In the figure, 1, 2, 3, 4, and 5 indicate that the Nisin addition amount is 0, respectively. , 0.04, 0.08, 0.12, 0.2g/100mL composite membrane;

Figure 15 shows the effect of different coatings on the rot rate of strawberries, from top to bottom in the figure: unpackaged treatment control group (control), pe film packaging treatment group (pe), and op-pul film film-forming solution coating treatment group (op-pul), n-op-pul film-forming liquid coating treatment group (n-op-pul), csn-op-pul film-forming liquid coating treatment group (csn-op-pul);

Figure 16 shows the effect of different coatings on the appearance of strawberries, from left to right in the figure: unpackaged control group (control), pe film packaging treatment group (pe), and op-pul film-forming liquid coating treatment group (op-pul), n-op-pul film-forming liquid coating treatment group (n-op-pul), csn-op-pul film-forming liquid coating treatment group (csn-op-pul);

Figure 17 shows the effect of different coatings on the weight loss rate of strawberries, from top to bottom in the figure: unpackaged treatment control group (control), pe film packaging treatment group (pe), op-pul film film-forming liquid coating treatment group (op-pul), n-op-pul film-forming liquid coating treatment group (n-op-pul), csn-op-pul film-forming liquid coating treatment group (csn-op-pul);

Figure 18 shows the effect of different coatings on the hardness of strawberries, from top to bottom in the figure: unpackaged treatment control group (control), pe film packaging treatment group (pe), and op-pul film-forming solution coating treatment group (op-pul), n-op-pul film-forming liquid coating treatment group (n-op-pul), csn-op-pul film-forming liquid coating treatment group (csn-op-pul).

Detailed ways

Terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art unless otherwise specified. The present invention will be described in further detail below in conjunction with specific embodiments and with reference to data. It should be understood that these examples are intended to illustrate the invention only and not to limit the scope of the invention in any way.

Fig. 1 is the multi-mode ultrasonic biological treatment equipment of the present invention, this equipment is equipped with a computer program controller 8, can set ultrasonic working parameters (ultrasonic power density, frequency, pulse working time, intermittent time and total processing time) to control respectively Three

ultrasonic controllers

9, 10, 11 are respectively connected to three

ultrasonic vibration plates

1, 2, and 3 of different frequencies, which can realize single frequency/two frequencies/three frequencies ultrasonic treatment; put the solution to be treated into the liquid Single-frequency/dual-frequency/multi-frequency ultrasonic treatment is performed in the device 4, and the circulating pump 7 is started to circulate the solution. The automatic control of the solution temperature is realized through the water bath 5 and the temperature probe 6 .

Experimental Materials:

Oat protein purity ≥80%, purchased from Lanzhou Waterless Biotechnology Co., Ltd.; Pullulan was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Nisin was purchased from Shandong Fengtai Biotechnology Co., Ltd.; glycerol was purchased from analytical pure in Sinopharm Group Chemical Reagent Co., Ltd.

The method for measuring the mechanical properties of the film materials prepared in the examples of the present invention is as follows: cut the film into a 20mm×60mm strip, measure its tensile strength (TS) and elongation at break (EAB) with a physical property analyzer, and test The speed is 1mm/s and the clamping distance is 30mm.

Tensile strength calculation formula: TS=F/(d×W)

In the formula: TS—tensile strength (MPa); F—maximum tension (N) when the film breaks; d—film thickness (mm); W—film width (mm).

Calculation formula of elongation at break: EAB=(LL ₀ )×100/L ₀

In the formula: EAB—elongation at break (%); L—the distance between the marking lines when the film breaks (mm); L0—the distance between the original marking lines of the film (mm).

Example 1: Optimization of matrix concentration in the preparation of oat protein/pullulan composite membrane

(1) Prepare avenin solution and pullulan polysaccharide solution with a mass concentration of (4, 6, 8, 10, 12) g/100 mL (wherein the pH of the avenin solution is adjusted to 8), and the same mass concentration of avenin The solution and pullulan solution were mixed in equal volumes.

(2) after adding the 25% glycerin plasticizer that accounts for the mass percentage of the solute (oat protein and pullulan), place it in a water-bath constant temperature magnetic stirrer and seal and stir for 30min, and the water-bath temperature is 70° C. to obtain uniform oat Protein/pullulan film-forming solution.

(3) Due to the different concentrations of the film-forming liquid, different amounts of the film-forming liquid were drawn and cast on a disposable plastic plate to form a film, and the amount of solute in the plate was controlled to be 0.6 g. It was placed in a drying dish with a relative humidity of ₄₃ % ₍ a saturated K2CO3 solution was placed in the drying dish).

The matrix concentration was optimized for tensile strength and elongation at break, and the results are shown in Figure 2. It can be seen from Figure 2 that with the increase of the matrix concentration, the tensile strength gradually increases, and the elongation at break decreases significantly. When the matrix concentration is 4g/100mL, the composite film has a certain tensile strength. The best elongation at break, the tensile strength at this time is 5.43MPa, the elongation at break is 134.95%, the matrix concentration is selected as 4g/100mL, and the next step is to optimize the mass ratio of oat protein and pullulan.

Example 2: Optimization of the mass ratio of oat protein and pullulan in the preparation of oat protein/pullulan composite film

(1) Prepare avenin solution and pullulan polysaccharide solution with a mass concentration of 4g/100mL respectively (wherein the pH of the avenin solution is adjusted to 8), respectively, according to the volume ratio of the two solutions (4:0, 3:1, 2 : 2, 1: 3, 0: 4), and then the mixture of oat protein and pullulan in mass ratios of 4: 0, 3: 1, 2: 2, 1: 3 and 0: 4 can be obtained.

(2) after adding the glycerin plasticizer that accounts for 25% of the mass percentage of the solute, it is placed in a water bath constant temperature magnetic stirrer for sealing and stirring for 30 minutes, and the water bath temperature is 70 ° C to obtain a uniform oat protein/pullulan film-forming liquid .

(3) Draw 15mL of the film-forming solution and cast it on a disposable plastic plate to form a film, let it stand for 10 minutes, and then dry it by blasting at 60°C for 4 hours. with saturated _K2CO3 solution ₎ .

The optimization of the mass ratio of oat protein and pullulan is shown in Figure 3. With the increase of the ratio of pullulan, the tensile strength of the film slightly decreased at first and then increased significantly. The best polysaccharide mass ratio of 2:2 is 99.39%, and the film has good tensile strength at this time. The mass ratio of oat protein and pullulan polysaccharide is selected to be 2:2, and the next step is to optimize the amount of glycerin added. .

Example 3: Optimization of glycerol addition in the preparation of oat protein/pullulan composite film

(1) Avenin solution and pullulan polysaccharide solution with a mass concentration of 4g/100mL were respectively prepared (wherein the pH of the avenin solution was adjusted to 8), and the avenin solution and the pullulan polysaccharide solution were mixed in equal volumes.

(2) After adding the glycerol plasticizer whose mass percentage of the solute is (10%, 15%, 20%, 25%, 30%), place it in a water bath constant temperature magnetic stirrer and seal and stir for 30 minutes, and the water bath temperature is 70°C , to obtain a uniform oat protein/pullulan film-forming solution.

The amount of glycerol added was optimized based on tensile strength and elongation at break. The results are shown in Figure 4. When the amount of glycerol added (accounting for the solute mass ratio) was 10%, it was difficult to form a complete film, and the film was brittle and easy to break. With the increase of glycerol addition, the tensile strength of the film gradually decreased, and the elongation at break gradually increased. When the glycerol addition (accounting for the solute mass ratio) was 25%, the film had a certain tensile strength. Good elongation at break, the tensile strength at this time is 5.59MPa, and the elongation at break is 120.96%. Therefore, the amount of glycerol added (accounting for the mass ratio of solute) is selected to be 25%, and the heat treatment time in the next composite membrane preparation is carried out. optimization.

Example 4: Optimization of heat treatment time in the preparation of oat protein/pullulan composite film

(2) after adding the glycerin plasticizer that accounts for 25% of the mass percentage of the solute, place it in a water bath constant temperature magnetic stirrer and seal and stir (0, 10, 20, 30, 40) min respectively, and the water bath temperature is 70 ° C to obtain Homogeneous oat protein/pullulan film-forming solution.

The optimization of heat treatment time is shown in Figure 5. With the increase of heat treatment time, the tensile strength of the composite film gradually increased and then decreased, and the elongation at break gradually increased and then remained unchanged and then decreased. When the heat treatment time was 30 min, the Both the tensile strength and elongation at break reached the maximum value, of which the tensile strength was 3.81MPa and the elongation at break was 234.52%. The heat treatment time was selected as 30min, and the optimization of the next heat treatment temperature was carried out.

Example 5: Optimization of heat treatment temperature in the preparation of oat protein/pullulan composite film

(2) after adding the glycerin plasticizer that accounts for 25% of the mass percentage of the solute, it is placed in a water bath constant temperature magnetic stirrer and sealed and stirred for 30min respectively, and the water bath temperature is respectively (50, 60, 70, 80, 90) ℃, and obtains Homogeneous oat protein/pullulan film-forming solution.

The optimization of the heat treatment temperature is shown in Figure 6. With the increase of the heat treatment temperature, the tensile strength of the composite film first increased slightly and then decreased, and the elongation at break first increased and then remained unchanged. When the heat treatment temperature was 70 °C, the composite film had Therefore, the heat treatment temperature was selected to be 70 °C, and the optimization of the composite film prepared by ultrasonic was carried out in the next step.

Example 6: Optimization of ultrasonic time in the preparation of oat protein/pullulan composite film

(3) Take an appropriate amount of film-forming liquid into a plastic bag, and carry out ultrasonic treatment at room temperature. The ultrasonic frequency is 60 kHz, the ultrasonic power is 40 W/L, and the ultrasonic time is (0, 5, 10, 15, 20, 30 )min.

(4) Draw 15mL of the film-forming solution and cast it on a disposable plastic plate to form a film, let it stand for 10min, and then dry it by blasting at 60°C for 4h, and then place it in a drying dish with a relative humidity of 43% for later use (place in a drying dish). with saturated _K2CO3 solution ₎ .

Taking the mechanical properties of the composite film as an index, the optimization results of ultrasonic time are shown in Figure 7. With the increase of ultrasonic time, the tensile strength of the composite film has no significant change, and the elongation at break first decreases slightly and then increases significantly. There was no significant change in the length of the film, indicating that the composite membrane had better mechanical properties when the ultrasonic time was 10 min. Therefore, the ultrasonic time of 10 min was selected to optimize the ultrasonic frequency in the next step.

Example 7: Optimization of ultrasonic frequency in the preparation of oat protein/pullulan composite film

(3) Take an appropriate amount of film-forming liquid into a plastic bag, and carry out ultrasonic treatment at room temperature. The ultrasonic time is 10min, the ultrasonic power is 40W/L, and the ultrasonic frequency is (20, 40, 60, 20/40, 20 /60, 40/60, 20/40/60) kHz.

Taking the mechanical properties of the composite film as an index, the optimization results of ultrasonic frequency are shown in Figure 8. When single-frequency ultrasonic, the tensile strength of the composite film has no significant change, and the elongation at break remains unchanged after a significant increase; dual-frequency ultrasonic at 20/ At 60kHz, the elongation at break of the composite film is significantly better than that of single-frequency ultrasound and triple-frequency ultrasound. At this time, the composite film has good ductility on the basis of certain tensile strength, and the elongation at break reaches 290.71. %. Therefore, the ultrasonic frequency of 20/60 kHz was selected to optimize the ultrasonic power in the next step.

Example 8: Optimization of ultrasonic power in the preparation of oat protein/pullulan composite film

(3) Take an appropriate amount of film-forming liquid into a plastic bag, and carry out ultrasonic treatment at room temperature. The ultrasonic time is 10min, the ultrasonic frequency is 20/60kHz, and the ultrasonic power is (40, 50, 60, 70, 80) W respectively. /L.

Taking the mechanical properties of the composite film as an index, the optimization results of ultrasonic power are shown in Figure 9. With the increase of ultrasonic power, the tensile strength of the composite film decreased significantly and then remained unchanged, and the elongation at break first increased significantly and then decreased significantly. When the power is 50W/L, the elongation at break of the composite film is the highest, reaching 309.77%. Therefore, the ultrasonic power of 50W/L is selected to optimize the preparation of the composite film in the next step.

Example 9: Optimization of Nisin addition in the preparation of Nisin-loaded oat protein/pullulan composite membrane

(2) Weigh Nisin of different quality and add it to the beaker, dissolve in water and add avenin/pullulan mixed solution, so that the Nisin concentration in the film-forming solution is (0, 0.02, 0.04, 0.06, 0.08, 0.1) g /100mL, add glycerin plasticizer with a mass percentage of 25% of the solute, place it in a water bath constant temperature magnetic stirrer, seal and stir for 30 minutes, and the water bath temperature is 70 ℃ to obtain a uniform Nisin-loaded oat protein/pullulan film-forming film liquid.

Taking the mechanical properties of the composite film as an index, the optimization of the amount of Nisin added in the preparation of the composite film is shown in Figure 10. With the increase of the amount of Nisin added, the tensile strength of the film first increased significantly, then remained unchanged, and then decreased significantly. The elongation at break It increased significantly and then decreased significantly. When the amount of Nisin added was 0.04g/100mL, the elongation at break was the highest, which was 68.12% higher than that of the control group. Therefore, the addition amount of Nisin was chosen to be 0.04g/100mL.

Example 10: Preparation of Nisin-loaded oat protein/pullulan composite membrane

(2) Weigh a certain mass of Nisin and add it to the beaker, dissolve in water and then add avenin/pullulan mixed solution, so that the Nisin concentration in the film-forming solution is 0.04g/100mL, and the mass percentage of the solute is 25%. The glycerol plasticizer was placed in a water bath constant temperature magnetic stirrer, sealed and stirred for 30 minutes, and the water bath temperature was 70° C. to obtain a uniform Nisin-loaded oat protein/pullulan film-forming solution.

(3) Take an appropriate amount of the film-forming liquid into a plastic bag, and carry out ultrasonic treatment at room temperature. The ultrasonic time is 10 min, the ultrasonic frequency is 20/60 kHz, and the ultrasonic power is 50 W/L.

(4) Draw 15mL of the film-forming solution and cast it on a disposable plastic plate to form a film, let it stand for 10min, and then dry it by blasting at 60°C for 4h, and then place it in a drying dish with a relative humidity of 43% for later use (place in a drying dish). A saturated K2CO3 solution).

Experimental Example Performance test of Nisin-loaded oat protein/pullulan composite membrane

The preparation methods of different types of membranes in the experimental examples are as follows:

Preparation of pure oat protein film (op): Reference Example 2, wherein the mass ratio of oat protein and pullulan is 4:0;

Pure pullulan film (pul): Reference Example 2, wherein the mass ratio of oat protein and pullulan is 0:4;

Avenin/pullulan composite film (op-pul): Reference Example 2, wherein the mass ratio of avenin and pullulan is 2:2;

Ultrasonic oat protein/pullulan composite membrane (cs-op-pul): Reference Example 6, wherein the ultrasonic time is 10min;

Nisin-loaded oat protein/pullulan composite membrane (n-op-pul): Reference Example 9, wherein the Nisin concentration is 0.04g/100mL;

Ultrasonic loaded Nisin oat protein/pullulan composite membrane (csn-op-pul): Reference Example 10.

(1) Light transmittance

Reducing the light transmittance of the film can protect food from ultraviolet and visible light irradiation, and can inhibit the influence of food lipid oxidation, color change, loss of nutritional value and other unfavorable factors. The film was cut into a long strip and placed on one side of the cuvette, and the light transmittance of the film was measured using an ultraviolet-visible spectrophotometer. The results are shown in Figure 11. As can be seen from the figure, 6 kinds of films of different types (pure oat protein film op, pure Pullulan membrane pul, oat protein/pullulan composite membrane op-pul, ultrasonic oat protein/pullulan composite membrane cs-op-pul, Nisin loaded oat protein/pullulan composite membrane n-op -pul, ultrasonic-loaded Nisin oat protein/pullulan composite film csn-op-pul), the transmittances were 75.16%, 95.10%, 83.84%, 86.60%, 54.31%, 62.34%, pullulan film The light transmittance is high, and the light transmittance decreases slightly after adding oat protein, because the oat protein itself is light yellow, and the light transmittance of the composite film prepared after adding Nisin decreases significantly. The addition of Nisin improves the opacity of the film, indicating that Nisin is a Active ingredient that prevents light from penetrating into food packaging materials.

(2) Water-soluble

Water solubility is an important indicator reflecting the water resistance of membrane materials. It is related to the hydrophilicity of materials and is an important property of composite membranes, which determines the application range and prospects of composite membranes. The determination of water solubility of membranes is shown in Figure 12. The orchid polysaccharide film is a hydrophilic film, which is easy to dissolve in water and has a narrow application range. There are hydrophobic groups in oat protein, so the water solubility of pure oat protein film is low, which is 52.73%; oat protein/pullulan composite film op The water solubility of -pul was 79.70%. After adding Nisin, the water solubility of the film slightly decreased to 74.79%. After ultrasonic treatment, the water solubility of the film decreased significantly to 66.46%, indicating that adding Nisin and ultrasonic treatment can enhance the water resistance of the film. performance.

(3) Oxygen permeability

The presence of oxygen will seriously affect the storage stability of food under certain conditions. For example, the oxygen of lipids, vitamins and other substances will cause food spoilage. A good composite film can prevent the diffusion of oxygen into the package, which can better delay the oxidative deterioration of food. Add 25mL soybean oil to a 250mL conical flask, seal the bottle mouth with a film material, and fasten it with a rubber band. After 7 days at room temperature, determine the peroxide value content in the oil according to GB/T 5009.227-2016. The oxidation value indirectly reflects the barrier properties of the composite film to oxygen. The oxygen permeability results are shown in Figure 13. The oxygen permeability of the control group (without the film) was high, and the oxygen permeability of the oat protein/pullulan composite film op-pul decreased significantly. The oxidation value decreased from 6.53meq/kg to 6.33meq/kg and 6.26meq/kg, respectively. After adding Nisin to the membrane, the peroxide value in the oil dropped to 5.97meq/kg and the oxygen permeability of the membrane decreased significantly. At this time, the film has better oxygen barrier properties.

(4) Antibacterial properties

Listeria monocytogenes was selected as the test bacteria to investigate the antibacterial effect of different Nisin additions on the composite membrane. The composite films with different Nisin concentrations were cut into discs with a diameter of 1 cm, and then the samples were sterilized under UV light. Prepare 10 ⁵ CFU/mL bacterial suspension and draw 0.1 mL and spread it evenly on PYG solid medium. Distribute film samples with different Nisin concentrations evenly on the plate coated with bacterial liquid, and invert at appropriate temperature. Culture, observe the antibacterial effect of the film on bacteria. The bacteriostatic results are shown in Figure 14. In the figure, 1, 2, 3, 4, and 5 are composite membranes with Nisin additions of 0, 0.04, 0.08, 0.12, and 0.2g/100mL, respectively. It can be seen from the figure that Nisin-loaded composite membranes have better resistance to Listeria The bacteriostatic effect, and the bacteriostatic zone increased with the increase of Nisin concentration.

Application example Test of the effect of composite film coating on strawberry freshness

In the application example, the op-pul film, n-op-pul film, and csn-op-pul film film-forming liquid are the same as those in the experimental example in the preparation of op-pul film, n-op-pul film, and csn-op-pul film. The film-forming solution before drying.

Choose fresh strawberries with no pests and no mechanical damage, immerse the strawberries in op-pul film, n-op-pul film, and csn-op-pul film-forming solution for 2 minutes, take them out, and place them in a fume hood to dry quickly. After being placed at room temperature, strawberries without membrane coating and strawberries coated with PE membrane were selected as controls, and the changes within 14 days were detected.

(1) Rot rate and appearance

Calculation method of decay rate:

Rot rate = (X ₁ /X ₂ )×100%

In the formula: X ₁ - the number of rotten fruits;

X ₂ - Total fruit count.

The rot rate of strawberries is one of the most intuitive indicators for judging the fresh-keeping effect. The rot rate of strawberries is shown in Figure 15. It can be seen from the figure that the rot rate increases gradually with the prolongation of storage time, and the rot rate of strawberries in the composite film coating group is significantly lower than that in the control group, indicating that the composite film has obvious fresh-keeping effect on strawberries treated by coating. Strawberries did not rot in the first 4 days of storage. From the 5th day, the uncoated film group rotted, and the pe film and op-pul film treated strawberries rotted on the 6th day, while the csn The -op-pul membrane group showed decay on the 12th day, and the shelf life was extended by 7 days. This may be because ultrasonic treatment improves the degree of cross-linking between Nisin and the matrix, which can better exert the antibacterial effect of Nisin. At the same time, the csn-op-pul film has better oxygen barrier properties, which regulates the respiration efficiency of strawberries. Extends the shelf life of strawberries.

The strawberries treated by different treatment methods were placed in a glass dish in groups of 10, and photographed and recorded to further observe the changes in the appearance of the strawberries. The results are shown in Figure 16.

(2) Weight loss rate

A group of 3 strawberries is placed in a plastic plate, weighed every 24 hours, and the weight loss rate is measured by the differential method. The calculation formula of the weight loss rate is:

Weight loss rate=[(M ₀ -M _i )/M ₀ ]×100%

In the formula: M ₀ - initial weight, g;

M _i - weight on day i, g.

Weight loss rate is one of the important indicators to judge the freshness of strawberries. Strawberries are easy to lose water during storage, mainly because of a series of physiological activities such as water transpiration and metabolism. The effect of different treatments on the weight loss rate of strawberries is shown in Figure 17. With the prolongation of storage time, the weight loss rate of strawberries also shows an increasing trend. In the same storage time, the weight loss rate of the uncoated control group was the largest, which was 59.26%, and the weight loss rate of the pe film group was the smallest, which was 16.08%, mainly due to the good sealing performance of the pe film and the low water vapor transmission rate. After the coating treatment, the weight loss rate was significantly lower than that of the control group. The weight loss rate of strawberries treated with csn-op-pul film was slightly higher than that of the other two coating methods, because the WVP value of csn-op-pul film was higher. In op-pul film and n-op-pul film, resulting in slightly higher water loss, but significantly lower than the control group. To sum up, the coating treatment of strawberries can reduce the volatilization of water to a certain extent, thereby prolonging the shelf life of strawberries.

(3) Hardness

The hardness of fruits and vegetables is one of the main factors that determine whether the fruits and vegetables are spoiled. The reduction of the hardness of fruits and vegetables will shorten the shelf life of fruits and vegetables, promote the infection of pathogens in fruits and vegetables, and limit the transportation and storage of fruits and vegetables. Due to the degeneration of the middle layer of the cell wall of the parenchyma cells of the cortex, strawberries often soften a lot during the ripening process, so hardness is an important indicator for evaluating the quality and shelf life of strawberries. The hardness of the strawberry surface was tested by a physical property analyzer, with a P/2 probe and a test speed of 1 mm/s. The results are shown in Figure 18. It can be seen from Figure 18 that with the prolongation of storage time, the hardness of strawberries also showed a downward trend. The hardness of the pe film group and the coating treatment group was significantly higher than that of the control group, and the hardness of the pe film group was higher than that of the coating treatment 9 days before storage. group, the reason is that the pe film has a strong gas barrier ability, which limits the evaporation of water in the strawberries and reduces the rate of strawberry texture softening. After the 10th day, the hardness of the pe film group decreases rapidly, because the strawberry rot rate increases and the strawberry texture becomes soft. ; The hardness reduction levels of the three coating treatment groups were not significantly different, which were all higher than those of the control group, and the hardness of the csn-op-pul film group was slightly higher than that of the op-pul film group and the n-op-pul film group, which may be due to Because the csn-op-pul film has better oxygen barrier properties, it adjusts the atmospheric environment and reduces the respiration rate of strawberries, thereby reducing the loss of hardness.

Claims

The ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film is characterized in that carrying out according to the following steps:

(1) take oat protein and pullulan polysaccharide by weighing respectively and dissolve in distilled water, stir at room temperature for 1h, prepare oat protein solution and pullulan polysaccharide solution of certain mass concentration, adjust the pH of oat protein solution to 8;

(2) mixing oat protein solution and pullulan solution in a certain proportion, adding above-mentioned mixed solution after dissolving Nisin with a small amount of water, and slowly adding a certain amount of glycerol as plasticizer to obtain mixed solution;

(3) placing the mixed solution of step (2) in a water bath constant temperature magnetic stirrer, sealing and stirring for several hours at a certain temperature to obtain a film-forming solution;

(4) Take the film-forming liquid in a sealed bag, place it in a multi-mode ultrasonic treatment equipment at room temperature and take out after ultrasonic treatment for several times;

(5) Take the film-forming liquid and form a film by the casting method, let it stand for 10 minutes, and dry it by blasting at 60° C. for 4 hours; after the film is formed, take it out and cool it to room temperature to obtain a fresh-keeping film.
According to the ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, it is characterized in that wherein in step (1), the pH of oat protein solution is adjusted to 8 with 5mol/L NaOH.
according to the ultrasonic preparation method of the described oat protein and pullulan polysaccharide compound fruit and vegetable fresh-keeping film of claim 1, it is characterized in that the matrix concentration of oat protein and pullulan polysaccharide in wherein step (2) described mixed solution is 4g/100mL- 12g/100mL, preferably the matrix concentration is 4g/100mL.
The ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, it is characterized in that wherein in the mixed solution described in step (2), the mass ratio of oat protein and pullulan polysaccharide is 3:1-1 :3, preferably 2:2.
The ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, wherein the Nisin mass concentration in the mixed solution of step (2) is 0.02g/100mL-0.1g/100mL, preferably The mass concentration of Nisin is 0.04g/100mL; it is calculated by the mass and volume ratio of Nisin mass to avenin solution, pullulan solution and Nisin aqueous solution.
The ultrasonic preparation method of the oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, wherein the glycerin plasticizer addition amount in the mixed solution of step (2) is 15%-30%, preferably It accounts for 25% of the mass ratio of the solute; it is calculated based on the mass ratio of the glycerol plasticizer to the mass ratio of oat protein and pullulan.
According to the ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, it is characterized in that the heat treatment time of the water bath described in the step (3) is 10min-40min, and the preferred heat treatment time is 30min.
The ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, it is characterized in that wherein the heat treatment temperature of the water bath described in step (3) is 50 ℃-90 ℃, preferably the heat treatment temperature is 70 ℃ .
The ultrasonic preparation method of oat protein and pullulan polysaccharide composite fruit and vegetable fresh-keeping film according to claim 1, it is characterized in that wherein the concrete parameter of the ultrasonic action described in step (4) is ultrasonic time 5min-30min, preferably ultrasonic time is 10min; Ultrasonic frequency 20kHz, 40kHz, 60kHz, 20/40kHz, 20/60kHz, 40/60kHz, 20/40/60kHz, preferably ultrasonic frequency 20/60kHz; ultrasonic power 40W/L-80W/L, preferably ultrasonic power is 50W/L .