A method for drying berries

Abstract

The present invention discloses a method for drying berries, which first uses a combined treatment of pulsed electric field and plasma on the berries, and then dries the berries after the combined treatment. This method can change the microstructure inside the berries, including increasing the surface roughness, increasing hydrophilicity, forming surface electroporation holes and internal membrane perforations, thereby promoting water migration, improving the drying efficiency and quality of the berries. This method also has the advantages of no residue and simple operation. By using a combined treatment of pulsed electric field and plasma to treat the berries, it can inactivate the microorganisms on the berries, degrade the biotoxins produced by the microorganisms, reduce the loss of nutrients caused by drying, and at the same time can inactivate oxidase and reduce the oxidation of antioxidant substances during the drying process.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural product processing, and particularly relates to a method for drying berries. Background Art

[0002] Berry fruits have thin skins and are juicy, rich in nutrients, and contain bioactive substances such as anthocyanins, antioxidants, and functional polysaccharides, and have antioxidant activity, anti-tumor, cancer prevention, anti-aging, and immunomodulatory effects. Goji berries and blueberries are typical berry fruits in the north and south of China. However, due to the high water content, thin skin of berries, they are easily eroded by spoilage bacteria, not resistant to storage, and not conducive to transportation. Drying is an important means to prevent berry spoilage, extend the shelf life, and reduce transportation and preservation costs. Traditional natural sun drying does not meet the requirements for high-quality dried berries due to incomplete drying, high moisture content in dried fruits, long drying time, dark color of dried fruits, being easily restricted by meteorological conditions and contaminated by microorganisms such as dust and insects during the process, and difficult to control sanitation conditions. Therefore, modern drying technologies mainly based on hot air drying have emerged. However, since the epidermal wax layer of berries hinders the migration of moisture during the drying process, when using modern drying technologies to dry berries, more energy will be consumed, which will conflict with the green development trend of energy conservation and consumption reduction. On the other hand, excessive dehydration during the drying process will also cause the fruit to crack and the quality to decrease. Therefore, the demand for new drying treatment technologies to shorten the drying time, improve the quality of dried berries, and reduce drying energy consumption is more urgent.

[0003] Pulsed electric field treatment technology is a treatment technology that involves generating a potential difference on the material between two electrodes using short pulses of μs high voltage (<50 kV). Plasma is considered the fourth state of matter in addition to liquids, solids, and gases. Plasma generated by excited air discharge consists of O 3 、O 2 、O, NO, NO 2 、N 2 O and other active substances. When plasma contacts food, complex physical and chemical reactions often occur, which may cause various effects, including but not limited to sterilization, enzyme inactivation, affecting cell physiology, and material modification. A dielectric barrier discharge device is a non-equilibrium gas discharge that inserts an insulating dielectric material between metal electrodes. In a dielectric barrier discharge device, the electrodes are blocked by the dielectric layer, so spark or arc discharge can be avoided, thus generating uniform and stable discharge and plasma. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for drying berries, aiming to solve the problems of high energy consumption and loss of nutrients in dried fruits caused by using existing drying technologies. This method can not only improve the drying efficiency of berries, reduce the drying time, and lower the drying energy consumption, but also improve the drying quality of berries. At the same time, this method and device have the advantages of simple structure, low energy consumption, low usage threshold, and no residue in processing.

[0005] One of the objectives of the present invention is to provide a method for drying berries, the method comprising first treating the berries with a combined treatment of pulsed electric field and plasma, and then drying the berries.

[0006] In one embodiment of the present invention, when treating the berries with the combined treatment, the berries are first treated with a pulsed electric field and then treated with plasma.

[0007] In one embodiment of the present invention, when treating the berries with the combined treatment, the berries are first treated with plasma and then treated with a pulsed electric field.

[0008] In one embodiment of the present invention, the pulsed electric field includes a pulsed electric field generated by a dielectric barrier discharge device.

[0009] In one embodiment of the present invention, the plasma includes plasma generated by a dielectric barrier discharge device. The structural schematic diagram of the dielectric barrier discharge device is as Figure 1 shown.

[0010] In one embodiment of the present invention, when treating the berries with a pulsed electric field, the distance between the berries and the high-voltage electrode plate is 1 - 20 mm, and the treatment time is 5 - 20 s.

[0011] In one embodiment of the present invention, when treating the berries with a pulsed electric field, the pulse frequency is 0.01 - 0.5 kHz, the pulse width is 5 - 15 μs, and the treatment voltage is 10 - 20 kV.

[0012] In one embodiment of the present invention, when treating the berries with plasma, the distance between the berries and the high-voltage electrode plate is 1 - 5 mm, and the treatment time is 20 - 120 s.

[0013] In one embodiment of the present invention, when treating the berries with plasma, the pulse frequency is 2 - 10 kHz, the pulse width is 5 - 20 μs, and the treatment voltage is 15 - 40 kV.

[0014] In one embodiment of the present invention, when drying the berries, the drying method includes hot air drying, the drying temperature is 40 - 70 °C, and the wind speed is 5 - 10 m / s.

[0015] In one embodiment of the present invention, when the berries are subjected to hot air drying, the drying temperature is 45 - 65°C.

[0016] In one embodiment of the present invention, the specific steps for drying the berries are as follows:

[0017] (1) Place the berries between the high - voltage electrode plate and the grounded electrode plate of a dielectric barrier discharge device driven by a high - voltage pulse power supply;

[0018] (2) Adjust the distance between the upper dielectric layer and the berries to be 1 - 5 mm, and adjust the pulse frequency to be 0.01 - 0.5 kHz, the pulse width to be 5 - 15 μs, and the treatment voltage to be 10 - 20 kV, so that a pulsed electric field is generated in the dielectric barrier discharge device, and the berries are treated under the pulsed electric field for 0.1 - 30 s to obtain berries treated by the pulsed electric field;

[0019] (3) Adjust the distance between the upper dielectric layer and the berries to be 1 - 5 mm, adjust the pulse frequency to be 2 - 10 kHz, the pulse width to be 5 - 15 μs, and the treatment voltage to be 15 - 40 kV, so that a plasma is generated in the dielectric barrier discharge device, and the berries treated by the pulsed electric field are further treated in the plasma for 20 - 120 s to obtain berries treated by the plasma;

[0020] (4) Perform hot air drying on the berries treated by the plasma in step (3), with a drying temperature of 40 - 70°C and a wind speed of 5 - 10 m / s.

[0021] In one embodiment of the present invention, the specific steps for drying the berries are as follows:

[0022] (1) Place the berries between the high - voltage electrode plate and the grounded electrode plate of a dielectric barrier discharge device driven by a high - voltage pulse power supply;

[0023] (2) Adjust the distance between the upper dielectric layer and the berries to be 1 - 5 mm, adjust the pulse frequency to be 2 - 10 kHz, the pulse width to be 5 - 20 μs, and the treatment voltage to be 15 - 40 kV, so that a plasma is generated in the dielectric barrier discharge device, and the berries are further treated in the plasma for 20 - 120 s to obtain berries treated by the plasma;

[0024] (3) Adjust the distance between the upper dielectric layer and the berries to be 1 - 5 mm, and adjust the pulse frequency to be 0.01 - 0.5 kHz, the pulse width to be 5 - 15 μs, and the treatment voltage to be 10 - 20 kV, so that a pulsed electric field is generated in the dielectric barrier discharge device, and the berries treated by the plasma are treated under the pulsed electric field for 5 - 20 s to obtain berries treated by the pulsed electric field;

[0025] (4) The berries treated by pulsed electric field in step (3) are subjected to hot air drying, with the drying temperature being 40 - 70 °C and the wind speed being 5 - 10 m / s.

[0026] The second object of the present invention is to provide a dried fruit prepared by using the above method.

[0027] Advantages of the present invention:

[0028] (1) Treating berries with pulsed electric field can change the internal microstructure of the berries, causing a membrane perforation effect in the berries and promoting water migration; treating berries with plasma, the plasma can not only etch the surface of the berries, increasing their surface roughness and hydrophilicity, but also electro-perforation holes will be generated on the surface of the berries, effectively promoting water migration; treating berries with the combination of pulsed electric field and plasma can increase the water diffusion efficiency of the berries during the drying process, thereby shortening the drying time and reducing the drying energy consumption.

[0029] (2) Using the combination of plasma and pulsed electric field technology to treat berries can improve the structure of the berries from two aspects: the internal microstructure of the berries and the surface structure characteristics of the berries, effectively enhancing the drying efficiency of the berries during the subsequent drying process, and there is no residue and no pollution during the treatment process.

[0030] (3) Using the combination of pulsed electric field and plasma to treat berries can inactivate the microorganisms on the berries and degrade the biotoxins produced by the microorganisms.

[0031] (4) The technical solution of the present invention can not only shorten the drying time, but also reduce the loss of nutrients caused by drying. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the dielectric barrier discharge device used in the present invention.

[0033] Figure 2 It is a comparison chart of the drying time of the comparative example and the examples

[0034] Figure 3 It is a comparison chart of the drying energy consumption of the comparative example and the examples

[0035] Figure 4 It is a comparison chart of the flavonoid content of the comparative example and the examples

[0036] Figure 5 It is a comparison chart of the number of molds and yeasts of the comparative example and the examples

[0037] Figure 6 It is a comparison chart of the microstructures of Chinese wolfberries in Comparative Example 1 and Example 1 Detailed Embodiments

[0038] The present invention will be further described below in combination with comparative examples and specific embodiments. The following are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto.

[0039] Calculation of drying energy consumption:

[0040]

[0041] W represents the power when the oven temperature is 65°C and the wind speed is 7.0 m / s, t represents the drying time, G represents the drying weight, and the unit of drying energy consumption is (kW·h·kg -1 ).

[0042] Determination of microbial content: The microbial content on the dried berries was determined with reference to "GB 4789.15-2016 National Food Safety Standard - Microbiological Examination of Foods - Enumeration of Molds and Yeasts".

[0043] Determination of flavonoid content: The total flavonoid content in the dried berries was determined with reference to "NY / T 3903-2021 Determination of Flavonoid Compounds in Lycium barbarum".

[0044] Example 1: Drying Lycium barbarum

[0045] The freshly picked Lycium barbarum was placed between the dielectric layers of the dielectric barrier discharge device, and the distance between the upper dielectric layer and the berries was 2 mm. The parameters of the high-voltage pulse power supply were adjusted so that the pulse frequency was 500 Hz, the pulse width was 10 μs, and the processing voltage was 19 kV, so as to generate a pulsed electric field between the upper and lower dielectric layers, and the Lycium barbarum was processed between the pulsed electric fields for 10 s. The parameters of the high-voltage pulse power supply were adjusted so that the pulse frequency was 7000 Hz, the pulse width was 10 μs, and the processing voltage was 19 kV, so as to generate a plasma between the upper and lower dielectric layers, and the Lycium barbarum processed by the pulsed electric field was further processed in the plasma for 50 s. Finally, the Lycium barbarum processed by the pulsed electric field and the plasma was dried in a hot air drying device at a drying temperature of 65°C and a wind speed of 7.0 m / s. The water content of the Lycium barbarum was measured every 60 min, and the drying was stopped when the water content of the Lycium barbarum was lower than 13%, and dried Lycium barbarum was obtained, and the drying time was recorded.

[0046] After being processed by the present invention, the water content of the Lycium barbarum can be reduced to less than 13% after drying for 9 ± 0.34 h. The total flavonoid content in the dried Lycium barbarum is 4.11 ± 0.28 g / kg, the number of molds and yeasts is 0.68 ± 0.12 Lg CFU / g, and the drying energy consumption is 1.8 ± 0.07 kW·h·kg -1 .

[0047] Example 2: Drying blueberries

[0048] Place the freshly picked blueberries between the dielectric layers of the dielectric barrier discharge device. The distance between the upper dielectric layer and the blueberries is 1 mm. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 500 Hz, the pulse width is 20 μs, and the processing voltage is 19 kV, so as to generate a pulsed electric field between the upper and lower dielectric layers, and process the blueberries between the pulsed electric fields for 10 s. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 8000 Hz, the pulse width is 10 μs, and the processing voltage is 19 kV, so as to generate plasma between the upper and lower dielectric layers, and continue to process the goji berries treated by the pulsed electric field in the plasma for 60 s. Finally, dry the blueberries treated by the pulsed electric field and plasma in a hot air dryer at a temperature of 55 °C and a wind speed of 7.0 m / s. Measure the water content of the blueberries every 60 min. Stop drying when the water content of the blueberries is lower than 18%, obtain dried blueberries, and record the drying time.

[0049] After the treatment of the present invention, the water content of the blueberries can be reduced to below 13% after drying for 21 ± 1.73 h. The total flavonoid content in the dried blueberries is 40.80 ± 1.39 g / kg, the number of molds and yeasts is 0.95 ± 0.07 Lg CFU / g, and the drying energy consumption is 4.2 ± 0.35 kW·h / kg. -1 。

[0050] Example 3 Drying Goji Berries

[0051] Place the freshly picked goji berries between the dielectric layers of the dielectric barrier discharge device. The distance between the upper dielectric layer and the berries is 3 mm. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 100 Hz, the pulse width is 8 μs, and the processing voltage is 10 kV, so as to generate a pulsed electric field between the upper and lower dielectric layers, and process the goji berries between the pulsed electric fields for 15 s. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 5 kHz, the pulse width is 10 μs, and the processing voltage is 14 kV, so as to generate plasma between the upper and lower dielectric layers, and continue to process the goji berries treated by the pulsed electric field in the plasma for 90 s. Finally, dry the goji berries treated by the pulsed electric field and plasma in a hot air drying device at a drying temperature of 65 °C and a wind speed of 7.0 m / s. Measure the water content of the goji berries every 60 min. Stop drying when the water content of the goji berries is lower than 13%, obtain dried goji berries, and record the drying time.

[0052] After the treatment of the present invention, the water content of the goji berries can be reduced to below 13% after drying for 10 ± 1.73 h. The total flavonoid content in the dried goji berries is 2.49 ± 0.34 g / kg, the number of molds and yeasts is 0.89 ± 0.10 Lg CFU / g, and the drying energy consumption is 2.00 ± 0.35 kW·h / kg. -1 。

[0053] Example 4: First, treat goji berries with plasma and then with pulsed electric field

[0054] Place the freshly picked goji berries between the dielectric layers of a dielectric barrier discharge device. The distance between the upper dielectric layer and the berries is 3 mm. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 5 kHz, the pulse width is 10 μs, and the treatment voltage is 14 kV, so as to generate plasma between the upper and lower dielectric layers, and let the goji berries treated with pulsed electric field continue to be treated in the plasma for 90 s. Then adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 100 Hz, the pulse width is 8 μs, and the treatment voltage is 10 kV, so as to generate pulsed electric field between the upper and lower dielectric layers, and let the goji berries be treated between the pulsed electric fields for 15 s. Finally, dry the goji berries treated with pulsed electric field and plasma in a hot air drying device. The drying temperature is 65 °C, the wind speed is 7.0 m / s, measure the water content of the goji berries every 60 min, and stop drying when the water content of the goji berries is lower than 13%, obtain dried goji berries, and record the drying time.

[0055] After the treatment of the present invention, the water content of goji berries can be reduced to less than 13% after drying for 9 ± 0.56 h. The total flavonoid content in the dried goji berries is 2.66 ± 0.28 g / kg, the number of molds and yeasts is 0.79 ± 0.07 Lg CFU / g, and the drying energy consumption is 1.8 ± 0.11 kW·h / kg -1 。

[0056] Comparative Example 1

[0057] Place the freshly picked goji berries in a hot air drying device for drying. The temperature is 65 °C, the wind speed is 7.0 m / s, measure the water content of the goji berries every 60 min, and stop drying when the water content of the goji berries is lower than 13%, obtain dried goji berries, and record the drying time.

[0058] Comparative Example 2

[0059] Place the freshly picked blueberries in a hot air drying device for drying. The temperature is 55 °C, the wind speed is 7.0 m / s, measure the water content of the blueberries every 60 min, and stop drying when the water content of the blueberries is lower than 18%, obtain dried blueberries, and record the drying time of the blueberries.

[0060] Comparative Example 3

[0061] Place the freshly picked goji berries between the dielectric layers of the dielectric barrier discharge device. The distance between the upper dielectric layer and the berries is 2 mm. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 500 Hz, the pulse width is 10 μs, and the treatment voltage is 19 kV, so as to generate a pulsed electric field between the upper and lower dielectric layers and treat the goji berries in the pulsed electric field for 10 s. Then, dry the goji berries treated by the pulsed electric field in a hot air drying device at a drying temperature of 65 °C and a wind speed of 7.0 m / s. Measure the water content of the goji berries every 60 min. Stop drying when the water content of the goji berries is lower than 13%, obtain dried goji berries, and record the drying time.

[0062] Comparative Example 4

[0063] Place the freshly picked goji berries between the dielectric layers of the dielectric barrier discharge device. The distance between the upper dielectric layer and the berries is 2 mm. Adjust the parameters of the high-voltage pulse power supply so that the pulse frequency is 7000 Hz, the pulse width is 10 μs, and the treatment voltage is 19 kV, so as to generate plasma between the upper and lower dielectric layers and continue to treat the goji berries treated by the pulsed electric field in the plasma for 50 s. Then, dry the goji berries treated by the plasma in a hot air drying device at a drying temperature of 65 °C and a wind speed of 7.0 m / s. Measure the water content of the goji berries every 60 min. Stop drying when the water content of the goji berries is lower than 13%, obtain dried goji berries, and record the drying time.

[0064] Figures 2 to 5 The drying time, energy consumption, and the contents of total flavonoids and microorganisms in the dried berries when drying the berries by using the methods of Examples 1 to 4 and Comparative Examples 1 to 4 are respectively recorded. The results show that drying goji berries and blueberries by using the method of the present invention can greatly reduce the drying energy consumption and shorten the drying time. At the same time, the total content of flavonoids in goji berries and blueberries is relatively high, and the microorganism content is relatively low. Compared with the traditional hot air drying method, although the method of treating goji berries with pulsed electric field or plasma and then hot air drying can also shorten the drying time and reduce the drying energy consumption, the reduction amplitude of time and energy consumption is limited, and the loss of nutrients in the berries is serious, and the microorganism content is relatively high.

[0065] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for drying berries, characterized in that, the method comprises first treating the berries by combining pulsed electric field and plasma, and then subjecting the berries to hot air drying treatment; the pulsed electric field and the plasma are both generated by a dielectric barrier discharge device driven by the same pulsed power supply, the treatment time of the pulsed electric field is 5 - 20 s, and the treatment time of the plasma is 20 - 120 s.

2. The method for drying berries according to claim 1, characterized in that, when combining to treat the berries, first use the dielectric barrier discharge device to only generate a low - frequency pulsed electric field to treat the berries, and then increase the pulsed voltage and frequency of the device to generate plasma to treat the berries.

3. The method for drying berries according to claim 1, characterized in that, when combining to treat the berries, first use the dielectric barrier discharge device to generate plasma by using a high - frequency and high - voltage pulsed electric field to treat the berries, and then reduce the pulsed voltage and frequency of the device to only use a low - frequency pulsed electric field to treat the berries.

4. The method for drying berries according to any one of claims 1 - 3, characterized in that, when using the dielectric barrier discharge device to treat the berries, the distance between the berries and the high - voltage electrode plate is 1 - 5 mm, and there is a dielectric layer between the electrode plates.

5. The method for drying berries according to any one of claims 1 - 3, characterized in that, when only using the pulsed electric field to treat the berries, the pulsed frequency is 0.01 - 0.5 kHz, the pulse width is 5 - 15 μs, and the treatment voltage is 10 - 20 kV; when using the pulsed electric field and the plasma to treat the berries, the distance between the berries and the high - voltage electrode plate is 1 - 5 mm, the pulsed frequency is 2 - 10 kHz, the pulse width is 5 - 20 μs, and the treatment voltage is 15 - 40 kV.

6. The method for drying berries according to any one of claims 1 - 3, characterized in that, when drying the berries, the drying method includes hot air drying, the drying temperature is 40 - 70 °C, and the wind speed is 5 - 10 m / s.

7. Dried fruits prepared by the method for drying berries according to claim 1.

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