Antibacterial fresh-keeping method of fresh blueberries

Abstract

The invention discloses an antibacterial fresh-keeping method of fresh blueberries. The antibacterial fresh-keeping method is a combination of a low-frequency polarized electric field and nano-antibacterial packaging, and comprises the following steps: pre-cooling fresh blueberries, putting the fresh blueberries into a nano-antibacterial packaging bag, sealing the bag opening, punching air holes in the surface of the nano-antibacterial packaging bag, and putting the nano-antibacterial packaging bag into a refrigeration house with an electric field for preservation. The antibacterial fresh-keeping method of the fresh blueberries is simple and easy to operate, the equipment cost is low, and the nutrient anthocyanin is effectively enriched through post-harvest electric field treatment; the rotting rate of the picked blueberries is effectively inhibited, the shelf life of the picked blueberries is prolonged, and the economic benefits are improved; good quality can be ensured after 10 days of preservation at 0-2 DEG C, while the fresh-keeping period of common shelf refrigeration is only about 7 days; no chemical reagent is used, so that compared with a common preservative, the preservative is safer, has no biotoxicity and is suitable for large-scale popularization.

Description

Technical Field

[0001] The invention relates to an antibacterial fresh-keeping method, in particular to an antibacterial fresh-keeping method for fresh blueberries. Background Art

[0002] Blueberries are rich in nutrients, including sugar, acid, vitamin C, vitamin E, vitamin A, vitamin B, superoxide dismutase (SOD), arbutin, protein, anthocyanin, dietary fiber, and rich mineral elements such as potassium, iron, zinc, and calcium. Among them, the content of anthocyanin pigments is particularly prominent, which has antioxidant and vision-protecting effects and is beneficial to human health. Antioxidant properties help neutralize free radicals and reduce cellular oxidative damage, thereby preventing a variety of chronic diseases, such as cardiovascular disease and cancer. The protective effect of blueberries on vision is mainly that the ingredients in them help regenerate rhodopsin on the retina, prevent retinopathy, relieve eye fatigue, and improve vision. The best storage and transportation conditions for blueberries are in a low temperature and high humidity environment.

[0003] Low temperature preservation is currently a commonly used method, but in actual operation, temperature fluctuations are difficult to avoid. For example, at the junction of the cold chain transportation link, such as the transfer from the warehouse to the refrigerated truck, and from the refrigerated truck to the sales terminal, there may be a short-term temperature rise, which will affect the quality of blueberries. Moreover, the effect of simple low temperature preservation on extending the shelf life of blueberries still needs to be improved. As the storage time increases, the flavor and nutrients of blueberries will gradually lose. At present, some preservation technologies, such as controlled atmosphere preservation, can inhibit the respiration of blueberries by adjusting the gas composition in the package (reducing the oxygen content and increasing the carbon dioxide content), but the equipment and operation costs are high. For small blueberry growers and distributors, it is difficult to bear the cost of large-scale application of these technologies, which limits their widespread use. Some chemical preservatives will remain on the surface of blueberries during use, posing a potential risk to consumer health. Moreover, the amount of preservatives used and the residual standards are difficult to accurately control in actual operations, and it is easy to exceed the standard.

[0004] Existing blueberry storage and transportation technology During the storage and transportation process, anthocyanins in blueberries are affected by various factors, and the anthocyanin content decreases significantly. The main factors are: 1. The activity of polyphenol oxidase (PPO), peroxidase (POD) and β-glucosidase increases during storage and transportation, catalyzing the hydrolysis of anthocyanins into colorless phenolic acid; 2. During the storage and transportation process, microorganisms grow and produce enzymes that degrade anthocyanins, destroying the nutrients in blueberries, and new preservation methods are urgently needed. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an antibacterial preservation method for fresh blueberry fruit which is non-biotoxic, nutrient-rich and has a prolonged shelf life.

[0006] Technical solution: The present invention discloses an antibacterial preservation method for fresh blueberries, which is a combination of a low-frequency polarized electric field and nano antibacterial packaging, and includes the following steps:

[0007] (1) Pre-cool fresh blueberries for 10-12 hours;

[0008] (2) putting the pre-cooled blueberry fruits into a nano antibacterial packaging bag, sealing the bag opening, and punching air holes on the surface of the nano antibacterial packaging bag;

[0009] (3) The packaged blueberry fruits are placed in a cold storage equipped with an electric field for storage, wherein the electric field has a field strength of 2000V-3000V and a current of 1-2mA.

[0010] Wherein, in step (1), the precooling temperature is 0-2°C, and the precooling time is preferably 12h.

[0011] Wherein, in step (2), the nano antibacterial packaging bag is made of a mixture of nano composite powder, LDPE, LLDPE, dispersant, lubricant and coupling agent, and is formed by granulation and blowing; the nano composite powder is composed of nano Ag, nano TiO2, nano attapulgite and nano SiO2; specifically: 15.55% nano composite powder (30% 3% Ag content nano Ag, 35% nano TiO2, 25% nano attapulgite, 10% nano SiO2) and 49.01% LDPE, 23.44% LLDPE, 9% dispersant, 1% lubricant, 2% coupling agent are mixed and formed by granulation and blowing.

[0012] Wherein, in step (2), the number of the air holes is 2-3, and the diameter is 3-5 mm; preferably, the diameter is 5 mm.

[0013] Wherein, in step (2), the thickness of the nano antibacterial packaging bag is 0.15-0.2 mm, preferably 0.2 mm.

[0014] Wherein, in step (3), the horizontal distance between the pre-cooled fresh blueberry fruit and the electric field is less than 50 cm.

[0015] Wherein, in step (3), the temperature of the cold storage is 0-2°C.

[0016] Wherein, in step (3), the electric field is energized for 3-4 hours every day to treat the blueberries.

[0017] Principle of the invention: The antibacterial preservation method for fresh blueberries of the present invention uses a low-frequency polarized electric field in combination with nano-antibacterial packaging. Among them, electric field preservation technology is a pollution-free physical preservation method. Through electric field stimulation, the metabolic level in fruits and vegetables is changed to further enrich the internal nutrients. It has the advantages of simple equipment operation, low energy consumption, and safety. Nano-antibacterial packaging materials have excellent antibacterial properties, low cost, acid and alkali corrosion resistance, and long-term action without loss. The combination of the two can not only inhibit the activity of related enzymes that degrade anthocyanins in the body, but also inhibit the interference of in vitro microorganisms, thereby realizing the preservation of fresh blueberries and reasonably solving the current technical problems. The low-frequency polarized electric field can effectively reduce the enzyme activity in blueberries, and the nano-antibacterial packaging inhibits the growth of microorganisms. The combination of the two just solves the problem of anthocyanin loss.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The antibacterial preservation method of fresh blueberries of the present invention effectively enriches the nutrient anthocyanin through post-harvest electric field treatment; (2) The decay rate of post-harvest blueberries is effectively inhibited, the shelf life of post-harvest blueberries is extended, and the economic benefits are improved; good quality can be guaranteed when stored at 0-2°C for 10 days, while the shelf life of ordinary shelves is only about 7 days; (3) The present invention does not use chemical reagents, which is safer than ordinary preservatives and has no biological toxicity; (4) The present invention is simple and easy to operate and has low equipment cost, and will not significantly increase the storage and transportation costs of blueberries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a picture showing the effect of storing fresh blueberry fruits for ten days in Example 1 and Comparative Examples 1 to 3;

[0020] Figure 2 The H2O2 content of fresh blueberry fruit after storage in Example 1 and Comparative Examples 1 to 3;

[0021] Figure 3 The weight loss rate of fresh blueberry fruits after storage in Example 1 and Comparative Examples 1 to 3;

[0022] Figure 4 The peel hardness of fresh blueberry fruits after storage in Example 1 and Comparative Examples 1 to 3;

[0023] Figure 5 The anthocyanin content of fresh blueberry fruits after storage in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention is further described below in conjunction with the examples. The test materials used in the examples can all be purchased through conventional channels.

[0025] Example 1

[0026] The antibacterial preservation method for fresh blueberries of the present invention uses a low-frequency polarized electric field in combination with nano antibacterial packaging, and the operating steps are as follows:

[0027] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0028] (2) Put the pre-cooled blueberry fruits into the nano antibacterial packaging bag, seal the bag, and use a hole puncher with a diameter of 5 mm to evenly punch 2-3 holes on the nano packaging bag;

[0029] (3) The packaged blueberry fruits were placed in a cold storage equipped with an electric field at 2°C for storage. The electric field strength was 2500V, the current was 1 mA, the treatment time was 3 hours, and the treatment was performed once a day; this was recorded as the composite group.

[0030] Example 2

[0031] The antibacterial preservation method for fresh blueberries of the present invention uses a low-frequency polarized electric field in combination with nano antibacterial packaging. Compared with Example 1, the electric field strength is changed. The operation steps are as follows:

[0032] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0033] (2) Put the pre-cooled blueberry fruits into the nano antibacterial packaging bag, seal the bag, and use a hole puncher with a diameter of 5 mm to evenly punch 2-3 holes on the nano packaging bag;

[0034] (3) The packaged blueberry fruits are placed in a cold storage equipped with an electric field and stored at 2° C. The electric field strength is 2000 V, the current is 1 mA, the treatment time is 3 hours, and the treatment is performed once a day.

[0035] Example 3

[0036] The antibacterial preservation method for fresh blueberries of the present invention uses a low-frequency polarized electric field in combination with nano antibacterial packaging. Compared with Example 1, the electric field strength is changed. The operation steps are as follows:

[0037] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0038] (2) Put the pre-cooled blueberry fruits into the nano antibacterial packaging bag, seal the bag, and use a hole puncher with a diameter of 5 mm to evenly punch 2-3 holes on the nano packaging bag;

[0039] (3) The packaged blueberry fruits are placed in a cold storage equipped with an electric field and stored at 2° C. The electric field strength is 3000 V, the current is 1 mA, the treatment time is 3 hours, and the treatment is performed once a day.

[0040] Comparative Example 1

[0041] A method for preserving blueberries, compared with Example 1, the nano packaging bag is replaced with a commercially available ordinary packaging bag, the material of which is low-density polyethylene (LDPE) and the operating steps are as follows:

[0042] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0043] (2) Put the pre-cooled blueberry fruits into a commercially available ordinary packaging bag, seal the bag mouth, and use a hole puncher with a diameter of 5 mm to evenly punch 2-3 holes on the nano packaging bag;

[0044] (3) The packaged blueberry fruits were placed in a cold storage equipped with an electric field at 2° C., where the field strength of the electric field was 2500 V, the current was 1 mA, the treatment time was 3 h, and the treatment was performed once a day; this was recorded as the ordinary packaging bag group.

[0045] Comparative Example 2

[0046] A method for preserving blueberries, compared with Example 1, without electric field treatment, the operating steps are as follows:

[0047] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0048] (2) Put the pre-cooled blueberry fruits into the nano antibacterial packaging bag, seal the bag, and use a hole puncher with a diameter of 5 mm to evenly punch 2-3 holes on the nano packaging bag;

[0049] (3) The packaged blueberries were placed in a cold storage at 2°C; this was recorded as the nanomaterial group.

[0050] Comparative Example 3

[0051] A method for preserving blueberries, compared with Example 1, is to place the fresh blueberries directly into an electric field without packaging, and the operation steps are as follows:

[0052] (1) Take fresh blueberries that are free of mechanical damage, pests and diseases, and have not been processed, and pre-cool them in a 2°C cold storage for 12 hours;

[0053] (2) The pre-cooled blueberry fruits were placed in a cold storage equipped with an electric field and stored at 2°C. The electric field strength was 2500V, the current was 1 mA, the treatment time was 3 hours, and the treatment was performed once a day; this was recorded as the electric field treatment group.

[0054] Figure 1 The decay rate of Example 1 was significantly lower than that of the comparative example. After the treatment of the example, the oxidative metabolism level in the blueberries and the microbial level in vitro were reduced, so that the decay rate of the blueberries was reduced.

[0055] Figure 2 The H2O2 level in Example 1 was significantly lower than that in the control example, which proved that the oxidative stress level in the blueberries after treatment was low and the metabolic level in the blueberries was effectively inhibited.

[0056] Figure 3 The weight loss rate of Example 1 is significantly lower than that of the comparative example, which also shows that the metabolic level of blueberries is significantly reduced after being treated by the example.

[0057] Figure 4 The fruit skin hardness of Example 1 is significantly higher than that of the comparative example, and the shrinkage and softening of blueberries during storage are relatively lower. This is because the fruit skin hardness is maintained by inhibiting cell wall degrading enzymes, reducing oxidative damage and regulating the ripening process.

[0058] Figure 5 The anthocyanin content of Example 1 is significantly higher than that of the comparative example. The low-frequency polarized electric field can effectively reduce the enzyme activity in blueberries, effectively inhibiting the enzymes related to anthocyanin metabolism. At the same time, combined with nano-antibacterial packaging, it inhibits the growth of microorganisms and reduces exogenous degradation pathways.

[0059] Therefore, the antibacterial preservation method of fresh blueberries of the present invention effectively enriches the nutrient anthocyanin through post-harvest electric field treatment; effectively inhibits the decay rate of post-harvest blueberries, and can ensure good quality when stored at 0-2°C for 10 days, thereby extending the shelf life of post-harvest blueberries and improving economic benefits; and does not use chemical reagents, is safer than ordinary preservatives, has no biological toxicity, and is suitable for large-scale promotion.

Claims

1. A method for antibacterial preservation of fresh blueberry fruit, characterized in that: The antibacterial and fresh-keeping method is a combination of a low-frequency polarized electric field and nano antibacterial packaging, comprising the following steps: (1) Pre-cool fresh blueberries for 10-12 hours; (2) putting the pre-cooled blueberry fruits into a nano antibacterial packaging bag, sealing the bag opening, and punching air holes on the surface of the nano antibacterial packaging bag; (3) The packaged blueberry fruits are placed in a cold storage equipped with an electric field for storage, wherein the electric field has a field strength of 2000V-3000V and a current of 1-2mA.

2. The antibacterial preservation method according to claim 1, characterized in that: In step (1), the precooling temperature is 0-2°C.

3. The antibacterial preservation method according to claim 1, characterized in that: In step (2), the nano antibacterial packaging bag is made of a mixture of nano composite powder, LDPE, LLDPE, dispersant, lubricant and coupling agent, and granulated and blown; the nano composite powder is composed of nano Ag, nano TiO2, nano attapulgite and nano SiO2.

4. The antibacterial preservation method according to claim 1, characterized in that: In step (2), the number of the air holes is 2-3 and the diameter is 3-5 mm.

5. The antibacterial preservation method according to claim 1, characterized in that: In step (2), the thickness of the nano antibacterial packaging bag is 0.15-0.2 mm.

6. The antibacterial preservation method according to claim 1, characterized in that: In step (3), the horizontal distance between the pre-cooled fresh blueberry fruit and the electric field is less than 50 cm.

7. The antibacterial preservation method according to claim 1, characterized in that: In step (3), the temperature of the cold storage is 0-2°C.

8. The antibacterial preservation method according to claim 1, characterized in that: In step (3), the electric field is energized for 3-4 hours every day to treat the blueberries.

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