Disclosure of Invention
Aiming at the problem of low effect of ultrasonic waves in the freeze drying technology in the prior art, the invention aims to provide an ultrasonic-assisted freeze drying method.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
an ultrasound-assisted freeze-drying method comprising the steps of:
freezing:
s1, placing a flaky material to be frozen on a temperature control plate in a vacuum tank;
s2, cooling the temperature control plate through a refrigerating system, and applying first ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrators in the cooling process;
s3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, stopping the step S2 and entering the step S4, otherwise, continuing the step S2;
primary drying:
s4, vacuumizing the vacuum tank through a vacuum system, and reducing the pressure of the vacuum tank to a preset pressure;
s5, applying second ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator;
s6, after a first preset time, closing the vacuum tank, detecting whether the pressure rising rate of the vacuum tank is lower than a first pressure rising rate, if so, stopping primary drying and entering S7, otherwise, continuing S5;
and (3) secondary drying:
s7, heating the temperature control plate through a heating system, and preserving heat after the temperature of the temperature control plate reaches a second preset temperature;
s8, applying third ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator in the heating and heat preservation process;
and S9, after the second preset time, closing the vacuum tank, detecting whether the pressure rising rate of the vacuum tank is lower than the second pressure rising rate, if so, stopping secondary drying, otherwise, continuing to S8.
Preferably, in S3, the temperature of the sheet-shaped material to be frozen is detected by an infrared thermometer, and the temperature at the center of the sheet-shaped material to be frozen is used as a judgment basis.
Preferably, in S3, the eutectic point temperature of the sheet-like material to be frozen is obtained by:
putting the flaky material to be frozen into a differential scanning calorimeter, cooling at a cooling rate of 10 ℃/min, cooling from 25 ℃ to-70 ℃, and measuring to obtain the eutectic point temperature;
on the basis of the measured eutectic point temperature, 5 ℃ is reduced as the first preset temperature in S3.
Preferably, in S4, the preset pressure is 5-20Pa; in S7, the second preset temperature is 40 ℃.
Preferably, in S1, the thickness of the sheet-shaped material to be frozen is 5mm-10mm.
Preferably, in S2, the first ultrasonic wave is released in an intermittent manner of 5 minutes per 1S of operation.
Preferably, in S5, the second ultrasonic wave is released in an intermittent manner of 3 minutes per 5 seconds of operation.
Preferably, in S8, the third ultrasonic wave is released in an intermittent manner of 1min per 5S of operation.
Preferably, in S6, the first preset time is 1 to 4 hours, and the pressure rising rate of the vacuum tank is closed and detected every 1min, and the first pressure rising rate is 5Pa/min.
Preferably, in S9, the second preset time is 2 to 5 hours, and the pressure rising rate of the vacuum tank is closed and detected every 10 minutes, and the second pressure rising rate is 10Pa/min.
Preferably, in S9, when it is detected that the pressure rising rate of the vacuum tank is lower than the second rising rate, the secondary drying is continued for 1 hour.
Preferably, the method further comprises: s10, closing the vacuum system and the heating system, taking the dried flaky material to be frozen out of the vacuum tank, and carrying out vacuum sealing packaging.
By adopting the technical scheme, the invention has the beneficial effects that: the materials are processed by using ultrasonic waves in the freezing, primary drying and secondary drying stages, so that: in the freezing stage, ultrasonic waves can effectively promote formation of ice crystals among cells, and meanwhile, the heat conductivity coefficient is improved and the heat transfer effect is improved under the action of the ultrasonic waves; in the primary drying stage, the ultrasonic power used is enhanced, the main effect is to improve the heat transfer effect, and meanwhile, energy is provided, so that water molecules acquire the sublimated kinetic energy, and the primary drying speed is increased; in the secondary drying stage, ultrasonic waves are used for improving the heat transfer effect and providing energy at the same time, so that the crystal water can overflow. Thereby greatly saving the freeze drying time and improving the quality and structural integrity of the product.
Detailed Description
The following describes the embodiments of the present invention further with reference to the drawings. The description of these embodiments is provided to assist understanding of the present invention, but is not intended to limit the present invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
It should be noted that, in the description of the present invention, the positional or positional relation indicated by the terms such as "upper", "lower", "left", "right", "front", "rear", etc. are merely for convenience of describing the present invention based on the description of the structure of the present invention shown in the drawings, and are not intended to indicate or imply that the apparatus or element to be referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
The terms "first" and "second" in this technical solution are merely references to the same or similar structures, or corresponding structures that perform similar functions, and are not an arrangement of the importance of these structures, nor are they ordered, or are they of a comparative size, or other meaning.
In addition, unless explicitly stated and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., the connection may be a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two structures. It will be apparent to those skilled in the art that the specific meaning of the terms described above in this application may be understood in the light of the general inventive concept in connection with the present application.
Example 1
An ultrasonic assisted freeze drying method comprises three stages of freezing, primary drying and secondary drying, as shown in figure 1, and comprises the following steps:
freezing:
s1, placing the flaky material to be frozen on a temperature control plate in a vacuum tank.
In this embodiment, freeze drying of radix Cynanchi auriculati is taken as an example, radix Cynanchi auriculati is cut into slices with a thickness of 5mm-10mm, preferably 8mm, and uniformly distributed in the middle of the surface of the temperature control plate, so that the slices of radix Cynanchi auriculati (i.e. the slice-shaped material to be frozen) are in good contact with the surface of the temperature control plate. Of course, in other embodiments, other types of Chinese medicinal materials, or foods, such as ginseng, notoginseng, lentinus edodes, strawberry, matsutake, truffle, and medicaments requiring lyophilization, are also possible.
S2, cooling the temperature control plate through the refrigerating system, and applying first ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrators in the cooling process.
In this embodiment, the refrigeration system is configured as a semiconductor refrigeration module, with its cold end applying cold to the temperature control plate and its hot end facing the outside of the vacuum tank. The ultrasonic vibrators are configured in plural, for example, four, and the four ultrasonic vibrators are uniformly installed around the center circumference of the temperature control plate so as to uniformly apply ultrasonic waves to the slice of radix cynanchi bungei, the four ultrasonic vibrators are generally operated simultaneously under the control of the ultrasonic generator, and the generated first ultrasonic waves are released in the form of intermittent 5min per 1s of operation.
S3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, stopping the step S2 and entering the step S4, otherwise, continuing the step S2.
In this embodiment, the temperature of the radix cynanchi bungei slice (slice material to be frozen) is detected by an infrared thermometer installed in a vacuum tank, and the temperature at the center of the radix cynanchi bungei slice (slice material to be frozen) is taken as the actual temperature, and the judgment of S3 is sequentially performed.
And, the first preset temperature of the radix cynanchi bungei slice (slice-shaped material to be frozen) is obtained by the following steps:
putting the flaky material to be frozen into a differential scanning calorimeter, cooling at a cooling rate of 10 ℃/min, cooling from 25 ℃ to-70 ℃, and measuring to obtain the eutectic point temperature; on the basis of the measured eutectic point temperature, 5 ℃ is reduced as the first preset temperature in S3. For example, the measured eutectic point temperature of the bunge auriculate root is-13.5 ℃, then in the embodiment, the temperature is reduced by 5 ℃ on the basis of the measured eutectic point temperature, the actual eutectic point temperature (namely, the first preset temperature) is-18.5 ℃, and the temperature at the center of the bunge auriculate root slice (the slice material to be frozen) is compared with the measured eutectic point temperature.
The ultrasonic wave in the stage can effectively promote the formation of intercellular ice crystals in the slice of the bunge auriculate root, so that more water is frozen into ice crystals in the stage, and the ice crystals are removed in the subsequent primary drying; meanwhile, the intervention of ultrasonic waves can also improve the heat conductivity coefficient, namely, the contact effect between tissues is improved in a vibration mode, so that the heat conductivity effect is improved, and the cold quantity is transferred between the tissues faster and better.
Primary drying:
and S4, vacuumizing the vacuum tank through a vacuum system, and reducing the pressure of the vacuum tank to a preset pressure.
In this embodiment, the vacuum system is configured as a system including a vacuum pump, a vacuum valve, a pressure detecting device, and necessary piping. The vacuum pump is used for vacuumizing the vacuum tank, so that the vacuum degree inside the vacuum tank is maintained, the vacuum valve is used for conveniently and flexibly controlling vacuumizing, and the pressure detection device is used for accurately observing the vacuum degree inside the vacuum tank. And specifically configuring the preset pressure to be 5-20Pa, the pressure of the vacuum tank is maintained at a level of 10Pa in general.
S5, applying second ultrasonic waves to the sheet-shaped material to be frozen through the ultrasonic vibrator.
After the pressure of the vacuum tank reaches the above-mentioned preset pressure, the ultrasonic vibrators disposed in the vacuum tank are generally operated simultaneously under the control of the ultrasonic generator, and the generated second ultrasonic waves are released in the form of intermittent 3 minutes every 5 seconds of operation, and typically, the ultrasonic power is maintained at a level of 100W.
So set up, through the ultrasonic wave that uses higher power in the primary drying process to can effectively promote the heat transfer effect between the tissue, the ultrasonic wave can also provide the sonic energy simultaneously, make the hydrone acquire the kinetic energy of sublimation, thereby accelerate the speed of primary drying.
And S6, after the first preset time, closing the vacuum tank, detecting whether the pressure rising rate of the vacuum tank is lower than the first pressure rising rate, if so, stopping primary drying and entering S7, otherwise, continuing S5.
The first preset time is generally configured to be 1-4 hours, and the specific time is determined according to the thickness of the sliced radix cynanchi bungei (slice-shaped material to be frozen), and the larger the thickness is, the longer the first preset time is, that is, the vacuum maintaining time and the time of the second ultrasonic intervention are longer, for example, in this embodiment, the first preset time is configured to be 1 hour. In addition, in this embodiment, the vacuum tank was closed by closing the vacuum valve, and the pressure rise rate of the vacuum tank was closed and detected every 1 minute, and the first pressure rise rate was set to 5Pa/min.
And (3) secondary drying:
and S7, heating the temperature control plate through a heating system, and preserving heat after the temperature of the temperature control plate reaches a second preset temperature.
In this embodiment, the temperature control board is heated by changing the current direction or changing the direction of the semiconductor refrigeration module, and the second preset temperature is set to 40 ℃, and the temperature detection is still obtained through the detection of the infrared thermometer.
And S8, applying third ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator in the heating and heat preservation process.
In this embodiment, under the control of the ultrasonic generator, the ultrasonic vibrators disposed in the vacuum tank are normally operated simultaneously, the generated third ultrasonic wave is released in the form of intermittent 1min every 5s of operation, and the ultrasonic power is maintained at a level of 100W.
By means of the arrangement, the heat transfer effect between tissues can be effectively improved by using the ultrasonic waves with higher power in the secondary drying process, and meanwhile, the ultrasonic waves are also used for providing sound wave energy, so that the crystal water can be overflowed more efficiently.
And S9, after the second preset time, closing the vacuum tank, detecting whether the pressure rising rate of the vacuum tank is lower than the second pressure rising rate, if so, stopping secondary drying, otherwise, continuing to S8.
The second preset time is generally configured to be 2-5 hours, and the specific time is determined according to the thickness of the sliced radix cynanchi bungei (slice-shaped material to be frozen), and the larger the thickness is, the longer the second preset time is, that is, the heating time and the time of the third ultrasonic intervention are longer, for example, in this embodiment, the second preset time is configured to be 2 hours. In addition, in this embodiment, the vacuum tank was closed by turning off the vacuum pump, and the pressure rise rate of the vacuum tank was closed and detected every 10 minutes, and the second pressure rise rate was set to 10Pa/min.
The ultrasonic-assisted freeze drying process is finished, and the bunge auriculate root slices with low water content and high quality are obtained.
As shown in fig. 2, a time-consuming schematic of vacuum freeze-drying and ultrasound-assisted freeze-drying of this example at each stage is shown. It can be seen that: the freezing stage, the time spent in this example is 68min, while vacuum freeze drying requires 143.3min; in the primary drying stage, 273min is used in the embodiment, and 623min is used for vacuum freeze drying; in the secondary drying stage, the time for the embodiment is 116min, and the time for vacuum freeze drying is 253min; for the bulk drying process, the present example used 458min and the vacuum freeze drying time 1020min, and the present example used only 44.9% of the vacuum freeze drying.
As shown in fig. 3, there is shown a schematic diagram showing the differences in dry matter content and porosity in the three modes of ultrasonic-assisted freeze-drying, vacuum freeze-drying and hot air drying, respectively, of the present example. It can be seen that the three drying modes can be fully dried without significant difference in dry matter content in the present embodiment, and the three drying modes have significant difference in porosity, which is due to the fact that the hot air drying has the conditions of expanding pores, cracking materials and the like in the drying process, and the quality is reduced.
As shown in fig. 4, there is shown a schematic diagram of the differences in the core weight and the outer skin weight of the radix cynanchi bungei slice in the three modes of ultrasonic-assisted freeze-drying, vacuum freeze-drying and hot air drying of the present example, respectively. It can be seen that the drying mode of this example is significantly better than the other two drying modes, both in terms of core weight and outer skin weight of the radix cynanchi bungei slice.
In addition, puncture hardness of the core and the outer cortex of the radix cynanchi bungei slice obtained by three drying methods was measured by a texture analyzer, respectively, and found that: the result of hot air drying can cause the slice of the bunge auriculate root to be hardened, which is caused by fiber coking in the dehydration process, and the hardness of tissues is reduced by vacuum freeze drying and ultrasonic assisted drying in the embodiment, so that the structure is better protected, the drug effect leaching of Chinese herbal medicines is facilitated, and the ultrasonic assisted freeze drying in the embodiment can obtain the slice of the bunge auriculate root with better toughness.
As shown in fig. 5, the brightness of three different drying modes of ultrasonic-assisted freeze drying, vacuum freeze drying and hot air drying of the present embodiment, which are measured by a full-automatic color difference meter, are shown. The slice brightness of the radix cynanchi bungei after hot air drying is 72.28; the slice brightness of the radix cynanchi bungei after vacuum freeze drying is 91.67; the brightness of the slice of radix cynanchi bungei after ultrasonic-assisted freeze drying in this embodiment is 93.10; the above luminance data are all the average values from three different processes. The results show that hot air drying causes a decrease in the brightness of the radix cynanchi bungei slices, while both vacuum freeze drying and ultrasound-assisted freeze drying of this example increase the brightness of the radix cynanchi bungei slices. The method is characterized in that adverse reactions such as oxidation and the like are generated by hot air drying, and the influence of vacuum freeze drying is small, and the quality of the ultrasonic-assisted freeze drying is superior to that of the two methods due to short time.
Example two
It differs from embodiment one in that: in S9, when it is detected that the pressure rising rate of the vacuum tank is lower than the second rising rate, the secondary drying is continued for 1 hour, that is, the steps of S7 and S8 are continued for 1 hour.
Example III
It differs from the first or second embodiment in that: as shown in fig. 6, the method further includes S10.
S10, closing the vacuum system and the heating system, taking the dried flaky material to be frozen out of the vacuum tank, and carrying out vacuum sealing packaging.
Example IV
An ultrasonic-assisted freeze drying apparatus for carrying out the method of any of the above embodiments, as shown in fig. 7 to 10, comprises a vacuum tank 1, a cover 2, a temperature control plate 3, a vacuum pump 4, a vacuum valve 5, a pressure detecting device 6, an ultrasonic vibrator 7, a semiconductor refrigeration module 8, an infrared thermometer 9, and an insulating layer 10.
The vacuum tank 1 is integrally in a cylindrical structure, and the vacuum tank 1 specifically comprises a tank body and a cover 2 which is detachably and fixedly connected to the top of the tank body, namely, the top of the tank body is opened, and the tank body is closed through the cover 2. Correspondingly, the outer side walls of the tank body and the cover 2 are respectively provided with an insulating layer made of insulating materials. Wherein, the inside of the vacuum tank 1 is fixedly provided with a temperature control plate 3 for bearing materials. In this embodiment, an opening adapted to the temperature control plate 3 is specifically formed at the bottom of the tank, and the temperature control plate 3 is fixedly installed in the opening. The temperature control plate 3 is preferably a rigid plate structure made of a heat conductive material, such as a stainless steel plate, and is preferably circular.
The vacuum pump 4 is arranged outside the vacuum tank 1, the suction end of which is connected to the tank side wall of the vacuum tank 1 via a pipe 11, and on which pipe 11 a vacuum valve 5 and a pressure detection device 6 are also mounted, wherein the pressure detection device 6 is preferably configured as a pressure gauge or in other embodiments also as a digital display pressure gauge. The vacuum pump 4 is used for vacuumizing the vacuum tank 1, so that the vacuum degree inside the vacuum tank 1 is maintained, the vacuum valve 5 is used for conveniently and flexibly controlling vacuumizing, and the pressure detection device 6 is used for accurately observing the vacuum degree inside the vacuum tank 1.
The ultrasonic transducers 7 are arranged in plural, for example, four, and all the ultrasonic transducers 7 are fixedly attached to the inside of the vacuum tank 1, or may be attached to the outside of the vacuum tank. In addition, the plurality of timeout wave vibrators are uniformly arranged around the center circumference of the temperature control plate 3. In this embodiment, each ultrasonic vibrator 7 is fixedly installed at the peripheral edge of the temperature control plate 3, so as to better apply ultrasonic waves to the material carried on the temperature control plate 3.
An ultrasonic generator (not shown) is disposed outside the vacuum tank 1, and the ultrasonic generator is electrically connected to each ultrasonic vibrator 7 through a wire, so as to control the ultrasonic vibrator 7 to emit ultrasonic waves with a suitable frequency.
The semiconductor refrigeration module 8 is fixedly arranged at the bottom of the vacuum tank 1, and the semiconductor refrigeration module 8 is connected with the temperature control plate 3, so that cold and heat are released to the temperature control plate 3, and the purpose of controlling the temperature of the temperature control plate 3 is achieved. In this embodiment, the semiconductor refrigeration module 8 is fixedly installed on the bottom surface side of the temperature control plate 3, and an insulation layer 10, such as an insulation layer 10 made of polyurethane foam material, is additionally applied on the bottom surface side of the temperature control plate 3. The semiconductor refrigeration module 8 operates by receiving a current and switches a refrigeration mode and a heating mode according to a change in a current direction.
The infrared thermometer 9 is fixedly installed in the vacuum tank 1, and the infrared thermometer 9 is used for detecting the temperature of the temperature control plate 3 and the materials carried by the temperature control plate. In this embodiment, the infrared thermometer 9 is disposed at a position right above the center of the temperature control plate 3, for example, the infrared thermometer 9 is fixedly connected with the side wall of the vacuum tank 1 through the support pipe 12, and the support pipe 12 penetrates the side wall of the vacuum tank 1, while the support pipe 12 is penetrated with a cable for connecting with the infrared thermometer 9.
The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, and yet fall within the scope of the invention.