Method for refrigerating and preserving blueberries with assistance of magnetic field

Abstract

The invention relates to the technical field of biology and electromagnetism, in particular to a method for refrigerating and preserving blueberries with the assistance of a magnetic field. The method comprises the following steps: S1, screening raw materials: screening freshly picked blueberries, removing softened and seriously dehydrated bad fruits, and reserving fresh blueberry fruits which are hard, complete in appearance and free of mildew and softening; according to the method, magnetic field combined low-temperature refrigeration is used as a treatment means, fresh blueberries (highbush blueberries, lowbush blueberries and rabbiteye blueberries) are used as treatment objects, stable low-temperature refrigeration is performed while a static magnetic field or an alternating magnetic field in the X-axis direction or the X-Y-axis direction is applied, the quality or nutritional ingredients of the blueberries can be effectively reserved, the shelf life is prolonged to 20-27 days, and the quality of the blueberries is improved. And the method has the advantages of mild treatment process, no addition of allogenic substances, safety, greenness, high efficiency, controllable process parameters, no adverse effect on sample substances, and good industrial production potential.

Description

Technical Field

[0001] The present invention relates to the fields of biology and electromagnetic technology, and in particular to a method for refrigerating and preserving blueberries with the assistance of a magnetic field. Background Art

[0002] Blueberries are deciduous shrubs belonging to the genus Vaccinium in the Ericaceae family. Their twigs are green, angular or cylindrical in structure, and often covered with regularly arranged soft hairs. Blueberries have a unique flavor, combining sour and sweet notes. They are rich in anthocyanins, phenolic compounds, vitamin C, and other bioactive ingredients. They have demonstrated significant biological benefits in preventing neurodegenerative diseases, improving vision, enhancing heart function, fighting tumors, protecting blood vessels, and boosting immunity. They possess significant economic value and broad prospects for industrial development.

[0003] However, due to the biological characteristics of the fruit, the development of blueberry storage and preservation technology has lagged behind. Because the berry tissue is soft and contains as much as 85%-90% water, the shelf life of half-ripe fruit is only 7-10 days under room temperature storage conditions, and fully ripe fruit is shortened to 2-3 days, severely limiting the blueberry industry's cross-regional distribution and market expansion. While traditional cold chain logistics systems can delay fruit aging, they still face problems during storage and transportation, such as high preservation costs, rapid quality deterioration, and a loss rate of up to 20%-30%, resulting in significant economic losses for the blueberry industry. Therefore, there is an urgent need to develop new preservation technologies and storage processes to break through existing technological bottlenecks and maintain the quality of blueberries after harvest and extend their shelf life.

[0004] Chemical methods for preserving blueberries include natural antibacterial agents such as natamycin and tea polyphenols, which are expensive and difficult to control costs. The coating method uses polyvinyl alcohol or edible wax to cover the surface of blueberries, but it is inconvenient to eat. Therefore, the development of physical preservation technology can provide a method for safe and effective blueberry preservation. Among them, magnetic field-assisted refrigeration is a method that controls the storage environment (magnetic field strength, magnetic field frequency) under suitable temperature conditions. According to the different stress responses of different types of blueberries to the magnetic field, the corresponding magnetic field mode, magnetic field strength and magnetic field frequency are selected. At the same time, factors such as temperature and humidity are comprehensively considered. Through the effect of the magnetic field on respiratory enzymes, cell growth hormones, microorganisms, etc. in the berries, metabolism is slowed down, thereby extending the storage period of blueberries and maintaining good quality. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preserving blueberries with magnetic field assistance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preserving blueberries by magnetic field-assisted refrigeration comprises the following steps:

[0008] S1. Raw material screening: Freshly picked blueberries are screened to remove any softened or severely dehydrated blueberries. Only those that are firm, intact, and free of mold or softening are retained. The blueberries should be 80% to 90% mature.

[0009] S2. Pretreatment: The screened blueberry fruits are washed with a running solution of 1%-3% (m / v) alkaline solution for 3-5 minutes, followed by rinsing with water 2-3 times to remove residual solution on the surface, and then air-drying the residual water;

[0010] S3. Packaging: Pack the blueberries without water on the surface into PE, PVC or other polymer material packaging bags and seal them;

[0011] S4. Pre-cooling blueberries: Place the packaged blueberries evenly on an iron plate and place them in a refrigerator for pre-cooling for 16-23 hours to reduce the temperature to around 0-10°C.

[0012] S5. Magnetic Field Refrigeration Treatment: The pre-cooled blueberries are removed and placed in a magnetic field and refrigerated conditions for combined treatment. The treatment intensity is 3-10 mT, and the direction can be X-axis or XY-axis (i.e., horizontal direction or horizontal and vertical direction). The magnetic field uniformity is greater than 90%. During the refrigeration period, the internal temperature is -1-6°C, with a stable temperature fluctuation of no more than 0.5°C. The humidity in the space is controlled at 85%-95%.

[0013] Preferably, the blueberries are highbush blueberries, lowbush blueberries, rabbiteye blueberries and their respective varieties, with a maturity of 80% to 90%, but are not limited thereto.

[0014] Preferably, the alkaline cleaning solution includes sodium carbonate solution (Na2CO3, i.e. soda ash), sodium bicarbonate solution (Na2HCO3, baking soda), sodium phosphate solution (Na3PO4, trisodium phosphate), disodium hydrogen phosphate solution (Na2HPO4) and alkaline potassium permanganate cleaning solution, etc., but is not limited thereto.

[0015] Preferably, the packaging material includes polymer materials such as polyethylene (PE), polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC), but is not limited thereto.

[0016] Preferably, the magnetic field may be a static magnetic field or an alternating magnetic field. If it is an alternating magnetic field, the magnetic field frequency is 0-50 Hz, but is not limited thereto.

[0017] The present invention has the following beneficial effects:

[0018] The present invention utilizes a magnetic field combined with low-temperature refrigeration as a treatment method, with fresh blueberries (highbush blueberries, lowbush blueberries, and rabbiteye blueberries) as the treatment objects. By applying a static magnetic field or an alternating magnetic field in the X-axis or XY-axis directions while performing stable low-temperature refrigeration, the quality or nutritional components of the blueberries can be effectively preserved, and the shelf life can be extended to 20-27 days. In addition, the treatment process is gentle, no exogenous substances are added, and it is safe, green, and efficient. The process parameters are controllable, and there is no adverse effect on sample substances. Therefore, the method has good industrial production potential. DETAILED DESCRIPTION

[0019] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Example 1

[0021] A method for preserving blueberries using a magnetic field and low-temperature refrigeration comprises the following steps:

[0022] S1. Raw material screening: Freshly picked BlueFeng blueberries are screened, and the softened and severely dehydrated blueberries are removed. Only the firm, intact blueberries without mold or softening are retained. The maturity level should be 90%.

[0023] S2. Pretreatment: Wash the selected blueberries with a running solution of 1% (m / v) baking soda for 4 minutes. Rinse with clean water three times to remove any residual surface solution and air dry in a cool place for 30 minutes to remove any residual surface moisture.

[0024] S3. Repackaging: Place the dried-out Bluefeng blueberries in PE fresh-keeping boxes (size: 20cm x 15cm x 8cm). Each box contains about 80 blueberries, weighing about 250g. Seal each box with plastic wrap.

[0025] S4. Pre-cooling blueberries: Place the packaged blueberries evenly on an iron plate and pre-cool them in a 0°C refrigerator for 20 hours to reduce the temperature to about 3°C.

[0026] S5. Magnetic Field Refrigeration Treatment: The pre-cooled blueberries were removed and placed in a combined magnetic field and refrigeration treatment with a treatment intensity of 9 mT, an XY-axis static magnetic field (i.e., horizontal and vertical directions), a magnetic field uniformity of 95%, an internal temperature of 4°C during refrigeration, a stable temperature fluctuation of no more than 0.5°C, and a humidity of 95%. The blueberries were stored for up to 25 days.

[0027] Comparative Example 1

[0028] A method for preserving blueberries using a magnetic field and low-temperature refrigeration comprises the following steps:

[0029] S1. Raw material screening: Freshly picked BlueFeng blueberries are screened, and the softened and severely dehydrated blueberries are removed. Only the firm, intact blueberries without mold or softening are retained. The maturity level should be 90%.

[0030] S2. Pretreatment: Wash the selected blueberries with a running solution of 1% (m / v) baking soda for 4 minutes. Rinse with clean water three times to remove any residual surface solution and air dry in a cool place for 30 minutes to remove any residual surface moisture.

[0031] S3. Repackaging: Place the dried-out Bluefeng blueberries in PE fresh-keeping boxes (size: 20cm x 15cm x 8cm). Each box contains about 80 blueberries, weighing about 250g. Seal each box with plastic wrap.

[0032] S4. Pre-cooling blueberries: Place the packaged blueberries evenly on an iron plate and pre-cool them in a 0°C refrigerator for 20 hours to reduce the temperature to about 3°C.

[0033] S5. Refrigeration treatment: During the refrigeration period, the internal temperature is 4°C, the temperature fluctuation is stable and no more than 0.5°C, and the humidity of the space is controlled at 95%. The storage period is up to 25 days.

[0034] During storage, the blueberries in Example 1 and Comparative Example 1 were regularly inspected daily for changes in their condition. The temperature of the refrigerated test chamber was also checked at least three times, and the chamber was ventilated. At the end of the 25-day storage period, the blueberries' appearance, weight loss, VC retention, and sensory scores were compared as shown in the following table:

[0035] Appearance Weight loss rate VC retention rate Sensory score Example 1 hard and brittle 2.6±0.23％ 63±0.6％ 15 points Comparative Example 1 Soften 9.2±0.31％ 40±0.2％ 9 points

[0036] As shown in the table above, the blueberries taken out in Example 1 have a firm and crisp texture, retaining the original flavor of the blueberries. The color is not significantly different from that of the blueberries at the beginning of storage. In addition, no disease or browning occurs during storage, and the preservation effect is good.

[0037] The appearance of the blueberries in Comparative Example 1 became softer, which was significantly lower than that in the group treated with magnetic field combined with low-temperature refrigeration.

[0038] Among them, the total sensory evaluation score of blueberries on the 25th day was 14 points. The evaluation method was based on the sensory evaluation method in a paper titled "Quality and Physiological Changes of Blueberries in Low-Temperature Controlled Atmosphere Storage" published in 2018, which is prior art. The sensory evaluation of blueberries is divided into color, color, taste, smell, and texture, with each item having 4 levels (4.0, 3.0, 2.0, 1.0). The total score of the five items is 20 points. A score below 8 indicates that the fruit is spoiled and rotten and is inedible.

[0039] The VC content was determined by referring to the 2,6-dichloroindophenol method, which is an existing technology.

[0040] Weight loss rate ω (%) = (M0-M1) / M0×100.

[0041] Where ω is the weight loss rate, %; M0 is the mass of fresh blueberries, g; M1 is the mass of blueberries during measurement, g.

[0042] Example 2

[0043] A method for preserving blueberries using a magnetic field and low-temperature refrigeration comprises the following steps:

[0044] S1. Raw material screening: Freshly picked O'Neill blueberries are screened to remove any softened or severely dehydrated blueberries. Only fresh blueberries that are firm, intact, and free of mold or softening are retained. The maturity level should be 80%.

[0045] S2. Pretreatment: Wash the selected blueberries with a running solution of 1.5% (m / v) sodium carbonate solution for 3 minutes. Rinse with clean water three times to remove any residual surface solution and air-dry in a cool place for 25 minutes to remove any residual surface moisture.

[0046] S3. Repackaging: Place the blueberries without water on the surface in a PVC fresh-keeping box (specifications: length × width × height: 20cm × 12cm × 6cm). Each box contains about 60 blueberries, weighing about 200g. Seal each box with plastic wrap.

[0047] S4. Pre-cooling blueberries: Place the packaged blueberries evenly on an iron plate and pre-cool them in a 0°C refrigerator for 16 hours to reduce the temperature to around 4°C.

[0048] S5. Magnetic Field Refrigeration Treatment: The pre-cooled blueberries are removed and placed in a combined magnetic field and refrigeration treatment with a treatment intensity of 9 mT, an XY-axis alternating magnetic field (i.e., horizontal and vertical directions), a magnetic field frequency of 50 Hz, and a magnetic field uniformity of 95%. During the refrigeration period, the internal temperature is maintained at 2°C, with a stable temperature fluctuation of no more than 0.5°C. The humidity of the space is controlled at 90%, and the storage period is up to 27 days.

[0049] Comparative Example 2

[0050] A method for preserving blueberries using a magnetic field and low-temperature refrigeration comprises the following steps:

[0051] S1. Raw material screening: Freshly picked O'Neill blueberries are screened to remove any softened or severely dehydrated blueberries. Only fresh blueberries that are firm, intact, and free of mold or softening are retained. The maturity level should be 80%.

[0052] S2. Pretreatment: Wash the selected blueberries with a running solution of 1.5% (m / v) sodium carbonate solution for 3 minutes. Rinse with clean water three times to remove any residual surface solution and air-dry in a cool place for 25 minutes to remove any residual surface moisture.

[0053] S3. Repackaging: Place the blueberries without water on the surface in a PVC fresh-keeping box (specifications: length × width × height: 20cm × 12cm × 6cm). Each box contains about 60 blueberries, weighing about 200g. Seal each box with plastic wrap.

[0054] S4. Pre-cooling blueberries: Place the packaged blueberries evenly on an iron plate and pre-cool them in a 0°C refrigerator for 16 hours to reduce the temperature to around 4°C.

[0055] S5. Refrigeration treatment: Store the pre-cooled blueberries in a cold storage at 1±0.5℃ for up to 27 days.

[0056] During storage, the blueberries in Example 2 and Comparative Example 2 were regularly inspected daily for changes in their condition. The temperature of the refrigerated test chamber was also checked at least three times, and the chamber was ventilated. At the end of the 27-day storage period, the blueberries' appearance, weight loss, VC retention, and sensory scores were compared as shown in the following table:

[0057] Appearance Weight loss rate VC retention rate Sensory score Example 2 hard and brittle 2.5±0.15％ 70±0.1％ 17 points Comparative Example 2 Soften 5.1±0.24％ 65±0.6％ 9 points

[0058] As shown in the table above, the blueberries taken out in Example 2 had a firm and crisp texture, maintaining the original flavor of the blueberries. The color was not significantly different from that at the beginning of storage. Moreover, no disease or browning occurred during storage, indicating a good preservation effect.

[0059] The appearance of the blueberries in Comparative Example 2 became softer, which was significantly lower than that in the group treated with magnetic field combined with low-temperature refrigeration.

[0060] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preserving blueberries with magnetic field assistance, characterized in that: The method includes the following steps: S1. Raw material screening: freshly picked blueberries are screened to remove the softened and severely dehydrated blueberries, and only those that are firm, intact, and free of mold and softening are retained. S2. Pretreatment: The screened blueberries are washed with a flowing mixed solution of 1%-3% (m / v) alkaline solution for 3-5 minutes, followed by rinsing with water 2-3 times to remove residual solution on the surface, and air-drying the residual moisture; S3. Packaging: Pack the blueberries without water on the surface and seal them; S4. Pre-cooling blueberries: Place the packaged blueberries in a single layer evenly on an iron tray and place them in a refrigerator for pre-cooling to a temperature of about 0-10°C. S5. Magnetic field refrigeration treatment: The pre-cooled blueberries are taken out and placed in a magnetic field and refrigeration condition for combined treatment. The treatment intensity is 3-10mT. The direction can be X-axis or XY-axis. The magnetic field uniformity is greater than 90%. During the refrigeration period, the internal temperature is -1-6°C, with a fluctuation of no more than 0.5°C.

2. The method for preserving blueberries with magnetic field assistance according to claim 1, characterized in that: In step S1, the blueberries are highbush blueberries, lowbush blueberries, rabbiteye blueberries and their respective varieties, and are 80% to 90% mature.

3. The method for preserving blueberries with magnetic field assistance according to claim 1, characterized in that: In step S2, the alkaline cleaning solution is sodium carbonate solution, sodium bicarbonate solution, sodium phosphate solution, disodium hydrogen phosphate solution and alkaline potassium permanganate solution.

4. The method for preserving blueberries with magnetic field assistance according to claim 1, characterized in that: In step S3, the packaging material is a polymer material such as polyethylene, polyvinyl chloride and polyvinylidene chloride.

5. The method for preserving blueberries with magnetic field assistance according to claim 1, characterized in that: In step S5, the magnetic field is one of a static magnetic field and an alternating magnetic field, wherein the magnetic field frequency of the alternating magnetic field is 0-50 Hz.