Anthocyanin film with antioxidant activity for strawberry preservation

Abstract

The invention discloses an anthocyanin film with antioxidant activity for strawberry preservation, and a preparation method of the anthocyanin film comprises the following steps: fully dissolving a proper amount of anthocyanin freeze-dried powder in methanol to obtain an anthocyanin solution, then slowly dropwise adding the anthocyanin solution into a chitosan acetic acid solution, and uniformly stirring to obtain a mixture; dropwise adding a sodium polyphosphate solution into the mixture, uniformly stirring, and dialyzing; defoaming, casting, coating and drying to obtain the anthocyanin film. According to the invention, the anthocyanin is added into the traditional chitosan film, so that the prepared anthocyanin film has better mechanical property and good uniformity, and still has good antioxidant activity under the illumination condition; the appearance quality of the strawberries can be effectively maintained, and the refreshing time is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging, and in particular to an anthocyanin film with antioxidant activity for preserving strawberries. Background Art

[0002] Food packaging is an important aspect of food processing, which can protect food from environmental, physical and microbial influences and extend the shelf life of food. Plastics have been widely developed and applied in the field of food packaging due to their excellent barrier properties and low cost. However, plastic packaging is difficult to degrade and causes serious environmental pollution. With the increasing attention paid to environmental protection, more and more scientists are committed to developing environmentally friendly packaging, most of which are based on natural polymers. Among natural polysaccharides, chitosan is widely used in the production of film matrices due to its excellent film-forming properties, environmental friendliness and antibacterial ability. However, the lack of antioxidant properties of pure chitosan packaging film limits its potential as food packaging. Therefore, more and more researchers are trying to solve this problem.

[0003] Anthocyanins are the most important water-soluble pigments in nature. Aronia nigra is widely distributed and grows in my country. Due to its sour taste, it cannot be eaten fresh and is often discarded, which not only causes a waste of resources, but also has a negative impact on the environment. Using anthocyanins extracted from Aronia nigra in the preparation of food packaging films can improve resource utilization, develop high value-added products, reduce environmental pollution, and improve the overall economic benefits of the agricultural products industry.

[0004] For example, the invention application with application number 201911015832.X discloses a modified anthocyanin intelligent active food preservative film. 10-20 parts of anthocyanin modified with amidated phenylalanine, 15-30 parts of low methoxy pectin (methylation degree is 20-30%), 15-30 parts of chitosan, 5-15 parts of glycerol, and 3-5 parts of acetic acid. Among them, the anthocyanin modified with amidated phenylalanine is prepared from the following raw materials in parts by weight: 8-16 parts of natural anthocyanin, 8-16 parts of phenylalanine, 10-20 parts of acetic anhydride, 10-20 parts of thionyl chloride, and 1-2 parts of pyridine.

[0005] For example, the invention patent with application number 201910342468.1 discloses an anthocyanin nanocomposite gelatin edible film that can delay oil oxidation. The preparation method includes the following steps: (1) adding anthocyanin to a chitosan hydrochloride solution and stirring evenly to obtain a mixed solution of anthocyanin and chitosan hydrochloride; (2) slowly adding a carboxymethyl chitosan solution to the mixed solution of anthocyanin and chitosan hydrochloride to cross-link the positively charged chitosan hydrochloride and the negatively charged carboxymethyl chitosan to obtain an anthocyanin nanocomposite suspension; (3) gradually adding a gelatin solution to the anthocyanin nanocomposite suspension to form a film-forming liquid, then adding glycerol to the film-forming liquid, stirring evenly, and then standing for treatment, and finally forming and drying to obtain the edible film.

[0006] The preparation method of the above-mentioned cling film solves the technical problem that the biofilm prepared with chitosan alone has poor mechanical properties. The anthocyanin film in the present invention significantly improves the antioxidant properties of a single film. In addition, the anthocyanin film of the present invention can significantly extend the appearance quality of strawberries, can be used as a packaging material to extend the shelf life of strawberries, and is suitable for preserving strawberries. Summary of the invention

[0007] In view of the deficiencies of the prior art, the object of the present invention is to provide an anthocyanin film with antioxidant activity for preserving strawberries.

[0008] The technical solution adopted by the present invention to solve the technical problem is: an anthocyanin film with antioxidant activity for preserving strawberries, and the preparation method of the anthocyanin film is as follows: taking an appropriate amount of anthocyanin freeze-dried powder and fully dissolving it in methanol to obtain an anthocyanin solution, then slowly dripping the anthocyanin solution into a chitosan acetic acid solution, stirring evenly, to obtain a desired solution; then dripping a sodium polyphosphate solution into the mixed solution, stirring evenly and then dialyzing; obtaining a film-forming liquid for vacuum degassing, and then using a casting method to evenly spread it in a horizontal glass film-making mold, and obtaining an anthocyanin film after vacuum drying.

[0009] Furthermore, in the anthocyanin solution, the dosage of anthocyanin is 0 to 3 mg / mL.

[0010] Further, chitosan is dissolved in 1% acetic acid solution by volume, and fully stirred until dissolved to prepare a chitosan acetic acid solution with a concentration of 1.5-3.5 mg / mL; and a sodium polyphosphate solution with distilled water is prepared with a concentration of 0.5-1.5 mg / mL.

[0011] Furthermore, the mass ratio of chitosan to sodium polyphosphate is 2.5:1, and sodium polyphosphate plays a role in cross-linking chitosan and anthocyanin, making the system more stable. The mass ratio of anthocyanin to chitosan is 2.5:1-3.

[0012] Furthermore, the anthocyanin freeze-dried powder is fully dissolved in methanol after being continuously stirred at 7000-7500 rpm for 8-10 minutes at room temperature.

[0013] Furthermore, the anthocyanin solution is slowly dripped into the chitosan acetic acid solution with magnetic stirring, and stirred at 7000-7500 rpm for 8-10 minutes.

[0014] Furthermore, the dialysis uses a dialysis bag with a molecular weight cutoff of 8000Da, and the dialysis time is 2 to 4 hours.

[0015] Furthermore, the drying temperature is 55-65° C., and the drying time is 7-10 hours.

[0016] The beneficial effects of the present invention are as follows: compared with the prior art, the anthocyanin film with antioxidant activity for preserving strawberries provided by the present invention is prepared by adding anthocyanin to a traditional chitosan film, and the anthocyanin film has better mechanical properties (the tensile strength of anthocyanin film IV is 44.1 Mpa, which is 76.4% higher than that of a single chitosan film) and good uniformity; the anthocyanin antioxidant film still has good antioxidant activity under light conditions; the anthocyanin film can effectively maintain the appearance quality of strawberries and extend their shelf life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a comparison chart of the tensile strength and elongation at break of the chitosan film and films of different anthocyanin concentrations provided by the present invention.

[0018] Figure 2 This is a comparison of the antioxidant activities of free anthocyanins, anthocyanin films and chitosan films under light irradiation.

[0019] Figure 3 This is an observation picture of the appearance of anthocyanin film used to preserve strawberries.

[0020] Figure 4 The effect of anthocyanin membrane on the sensory evaluation of strawberry. DETAILED DESCRIPTION

[0021] The present invention is further described below by specific examples, but these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0022] Example

[0023] 1. Preparation method of anthocyanin film:

[0024] Take an appropriate amount of anthocyanin freeze-dried powder and dissolve it in methanol. After continuous stirring (7200rpm) for 8min at room temperature (25℃) until it is fully dissolved, slowly drip it into the chitosan acetic acid solution, magnetically stir (7200rpm) for 10min, then add the sodium polyphosphate solution dropwise into the mixture, stir evenly, dialyze the mixed solution in distilled water for 3h with a dialysis bag (molecular weight cutoff = 8000Da), remove bubbles with an ultrasonic water bath oscillator, cast it on a horizontal glass plate, dry it in an oven at 60℃ for 8h and set it aside to obtain chitosan film (0mg / mL anthocyanin), anthocyanin film I (1mg / mL anthocyanin), anthocyanin film II (2mg / mL anthocyanin), and anthocyanin film III (3mg / mL anthocyanin).

[0025] 2. Determination of mechanical properties of anthocyanin films

[0026] 2.1 Tensile strength determination

[0027] Turn on the power of the tensile testing machine, press the "monitor" button to select tensile strength and elongation, set the parameters, set the initial clamp distance to 40mm, the measurement speed to 100mm / min, cut the film sample into a 6cm×1cm rectangular strip, press the test button to enter the functional interface standby state, because the film surface is smooth, you can wrap the two ends of the film with facial tissue, fix it on the intelligent electronic tensile testing machine, and then press the test button to start the experiment, and record the maximum force Fmax before the film breaks. Repeat the test 6 times for each group of films.

[0028] Calculate according to the following formula:

[0029] Where:

[0030] Fmax is the maximum force before the film breaks; A is the area of ​​the film.

[0031] 2.2 Elongation at break

[0032] The prepared film samples were cut into standard specimens of 6cm×2cm and fixed at both ends of the tensile clamp of the intelligent electronic tensile testing machine (the clamped part was wrapped with toilet paper to increase friction), the initial clamp distance was set to 40mm, and the tensile rate was set to 50mm / min. Each film sample was measured six times and the average value was taken, and the elongation at break of the film sample was calculated according to the formula:

[0033]

[0034] In the formula: E represents the elongation at break of the sample, in %; L is the length stretched when the film breaks, in mm; L0 is the original length of the film, in mm (L0 = 40 mm).

[0035] 3. Determination of particle size, potential and dispersion

[0036] After the sample was diluted to an appropriate concentration, the particle size, Zeta potential and polydispersity index were measured by dynamic light scattering technology using a Zetasizer Nano ZS 90 instrument at a fixed scattering angle of 90° at 25±1°C. The experiment was repeated three times to obtain the average value.

[0037] 4. Antioxidant capacity determination

[0038] 4.1 Free radical scavenging ability (DPPH): Mix 3 mg of sample with 2 mL of DPPH solution (0.1 mm), shake vigorously, and let stand in the dark for 30 min (25°C). Use ethanol as blank and measure the absorbance of the solution at 517 nm. The free radical scavenging ability is calculated according to the following formula:

[0039] Free radical scavenging ability (%) = (A c -A s ) / A c ×100

[0040] Wherein, Ac is the absorbance of the blank group, and As is the absorbance of the test group.

[0041] 4.2 Ferric ion reducing antioxidant power (FRAP): 1 mL of sample was mixed with 2.5 mL of phosphate buffer (0.2 M, pH 6.6), added to potassium ferricyanide solution (1%, w / v), incubated at 50°C for 20 min, cooled, added with 2.0 mL of trichloroacetic acid (10%, w / v), centrifuged for 10 min (3000 r / min), and the supernatant was treated with ferric chloride solution (0.1%, w / v) and its absorbance was measured at 700 nm.

[0042] 4.3 Lighting Processing

[0043] The samples were placed in a light incubator and irradiated with fluorescent lamps at a light intensity of 5000±500lx at 25°C for 5 days. During this period, the positions were randomly changed to reduce experimental errors. Samples were taken at 1d, 2d, 3d, 4d and 5d to measure the retention rate and antioxidant activity.

[0044] 5. Effect of anthocyanin antioxidant film on strawberry preservation

[0045] Use an electronic balance to weigh two strawberry samples, each weighing 200g. The samples were placed in marked fresh-keeping boxes, covered with chitosan film and anthocyanin film with the strongest antioxidant activity, respectively, and refrigerated at 0-4℃. The appearance was observed and sensory evaluation was carried out on the 5th and 10th days respectively.

[0046] 6. Statistical Analysis

[0047] All experiments were repeated three times, and the results were expressed as mean ± standard deviation. Excel 2010 was used to process the data. SPSS 19.0 was used for LSD and Duncan comparisons. Lowercase letters were used to represent differences between groups. The same letters indicated no significant differences (p>0.05), and different letters indicated significant differences (p<0.05). Origin 2017 was used to draw the graphs.

[0048] Research findings:

[0049] Mechanical properties of anthocyanin antioxidant films

[0050] Chitosan, as a natural high molecular edible material, has good antibacterial activity and biocompatibility. The application of chitosan film can effectively slow down the respiration rate of fruits and maintain the quality of fruits. In addition, water-soluble chitosan can also reduce the damage of membrane solution to fruits and vegetables, thereby better protecting the storage quality of fruits and vegetables. However, the single chitosan film has the problem of poor mechanical properties. Through experimental research, we found that with the increase of anthocyanin content, the tensile strength of anthocyanin film increased significantly. The tensile strength of anthocyanin film IV was 44.1Mpa, which increased by 76.4% compared with the single chitosan film. In addition, with the increase of anthocyanin content, the tensile strength of anthocyanin film can continue to increase, with good dispersibility and compatibility, and the film as a whole has good flexibility, so we chose anthocyanin film IV for subsequent experimental research.

[0051] 1. Particle size, potential and dispersion of anthocyanin oxide film

[0052] Table 1 Particle size, potential and dispersion of anthocyanin antioxidant film

[0053] sample Particle size (nm) Polydispersity Zeta-potential(mV) Chitosan film 103.5 0.048 +42.6 Anthocyanin membrane Ⅳ 192.7 0.033 +43.3

[0054] In this experiment, the particle size, polydispersity and Zeta potential of chitosan film and anthocyanin film IV were measured, and the results are shown in Table 1. The Zeta potential value of chitosan film is 42.6mV, and the Zeta potential value of anthocyanin film IV is 43.3mV. The absolute values ​​of the potentials of both are large, indicating that both have good stability. In addition, the particle size of chitosan film is 103.5nm, and the particle size of anthocyanin antioxidant film is 192.7nm. The particle size of anthocyanin film IV has increased significantly, which is due to the change of ion gel structure caused by the addition of anthocyanin, which has caused the increase of particle size, but its particle size is still in the nanometer level, and the dispersion is 0.033, indicating that anthocyanin film IV has good uniformity.

[0055] 2. Antioxidant Capacity

[0056] like Figure 2 As shown in the figure, each lowercase letter represents the difference between the groups, the same letters represent no significant difference (p>0.05), and different letters represent significant difference (p<0.05).

[0057] In the presence of white fluorescence, the DPPH value and FRAP value of free anthocyanin and anthocyanin antioxidant film showed a downward trend. However, the antioxidant activity of anthocyanin film decreased more slowly, and after 5 days of light treatment, anthocyanin antioxidant film had higher DPPH scavenging activity than free anthocyanin, which was 64.83% and 46.17%, respectively, and the difference was significant (p < 0.05). In addition, the FRAP value of anthocyanin active film was also significantly higher than that of free anthocyanin, which was 0.42 and 0.33 (p < 0.05), respectively. It can be seen that anthocyanin antioxidant film still has good antioxidant activity under light conditions, among which the DPPH scavenging activity and FRAP value of chitosan film are very low. It is inferred that the oxidative stability of anthocyanin antioxidant film is derived from the loading and protection of anthocyanin.

[0058] like Figure 3 and 4 As shown, anthocyanin active film can extend the shelf life of strawberries

[0059] Anthocyanin, as a new food raw material, has good antioxidant activity, antibacterial properties, anti-inflammatory properties and other properties. It was initially found that anthocyanin film has a certain preservation effect on strawberries. With the extension of storage time, the sensory evaluation score of strawberries gradually decreased. On the 6th day of storage, the sensory evaluation score of strawberries with a single chitosan film dropped to 5.6, which was lower than the sales limit of strawberries. At this time, the sensory evaluation score of strawberries in the anthocyanin film IV group was 8.1, which was significantly higher than that of the control group (p<0.05), and still had good marketability. On the 10th day of storage, the sensory evaluation scores of strawberries with a single chitosan film and anthocyanin film IV were 2.4 and 6.1, respectively, and it was not until the 10th day that the sensory evaluation of strawberries in the anthocyanin film IV group began to be lower than the sales limit of strawberries. Therefore, anthocyanin film IV can effectively maintain the appearance quality of strawberries and extend their shelf life.

[0060] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. An anthocyanin film with antioxidant activity for strawberry preservation, characterized in that: The preparation method of the anthocyanin film is as follows: taking an appropriate amount of anthocyanin freeze-dried powder and fully dissolving it in methanol to obtain an anthocyanin solution, then slowly dripping the anthocyanin solution into a chitosan acetic acid solution, stirring evenly, to obtain a desired solution; then dripping a sodium polyphosphate solution into the mixed solution, stirring evenly and then dialyzing; vacuum degassing the obtained film-forming liquid, then evenly spreading it on a horizontal glass film-making mold by a casting method, and obtaining an anthocyanin film after vacuum drying.

2. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: In the anthocyanin solution, the dosage of anthocyanin is 0-3 mg / mL.

3. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: Dissolve chitosan in 1% acetic acid solution by volume, stir thoroughly until dissolved, and prepare chitosan acetic acid solution with a concentration of 1.5-3.5 mg / mL; use distilled water to prepare sodium polyphosphate solution with a concentration of 0.5-1.5 mg / mL.

4. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: The mass ratio of chitosan to sodium polyphosphate is 2.5:1; the mass ratio of anthocyanin to chitosan is 2.5:1-3.

5. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: The anthocyanin freeze-dried powder is fully dissolved in methanol after being continuously stirred at 7000-7500 rpm for 8-10 minutes at room temperature.

6. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: The anthocyanin solution is slowly dripped into the chitosan acetic acid solution with magnetic stirring, and stirred at 7000-7500 rpm for 8-10 minutes.

7. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: The dialysis uses a dialysis bag with a molecular weight cutoff of 8000Da, and the dialysis time is 2 to 4 hours.

8. The anthocyanin film with antioxidant activity for strawberry preservation according to claim 1, characterized in that: The drying temperature is 55-65° C., and the drying time is 7-10 hours.

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