JP2019126328A - Manufacturing method of dry fruits - Google Patents

Abstract

To provide a manufacturing method of dry fruits capable of manufacturing dry fruits more excellent in feeling and taste as well as manufacturing them easily and maintaining their excellent appearance.SOLUTION: The dry fruit manufacturing method includes: a freezing process for freezing fruits 11 at temperature where the free water in the fruits 11 is frozen and at least a part of the bound water is not frozen; and a drying process for evaporating the water by applying electromagnetic waves under the condition for evaporating the water in the frozen fruits 11 without boiling in a reduced pressure environment in which the water boiling temperature is 50-70°C.SELECTED DRAWING: Figure 1

Description

  The present invention is a method for producing dried fruits (dried fruits) in which an object subjected to a freezing treatment is irradiated with electromagnetic waves (for example, microwaves) and dried under reduced pressure.

  Food drying techniques include sun-drying, hot air drying (also called hot air drying), freeze drying (also called freeze drying), candied sugar, and frying.

  Foods that do not use sugar and oil or other additives tend to be favored by health-consciousness in recent years, but soft fruits such as strawberries have large amounts of inside of fruits (including false fruits) due to their unique shape It contains water, and can not be dried sufficiently by heat source irradiation to the surface of the fruit, and "rot, set or crush" occurs during the drying. For this reason, it is common to dry in the shape which ensured abundant surface areas, such as slicing a fruit.

  Among the drying techniques listed above, lyophilization utilizes sublimation of water in a vacuum environment, and it is possible to carry out drying without thinning the fruit. However, since lyophilization requires processing for a long time of several hours to several tens of hours, not only the processing time but also the cost burden of power consumption is increased.

  Furthermore, in the lyophilization, in order to dry up to the target water content, a combination process of providing a heat source such as warm air or microwave as a compensating means has long been carried out. A "microwave drying" is a drying method that compensates for the lyophilization drawbacks that are long and power intensive.

  “Microwave drying” is a drying technique that applies electromagnetic waves to an object and uses frictional heat associated with the movement of water molecules. “Microwave drying” also includes “microwave vacuum drying” that simultaneously removes water vapor generated around an object in a reduced pressure environment. Until now, the main “microwave vacuum drying” has generally used a method of using both warm air drying and microwave drying (for example, Patent Document 1).

Patent No. 5358772 gazette

  By combining “microwave reduced pressure drying” and “warm air drying”, dried dried fruit with a good texture can be produced. However, when combined with "warm air drying", there is a problem that the manufacturing process and the processing apparatus become complicated. Moreover, development of the manufacturing method of the dried fruit which keeps an external appearance favorable and is more excellent in texture and taste is calculated | required from before.

  The present invention has been made in order to solve the above-mentioned problems, and can be easily produced, and further, a dried fruit that can produce a dried fruit having a better texture and taste while maintaining a good appearance. The purpose is to provide a manufacturing method.

  In order to achieve the above object, the method for producing a dried fruit according to claim 1 is characterized in that free water in the fruit is frozen and at least a part of the bound water is not frozen. Water is applied by applying an electromagnetic wave under the condition of evaporating water without boiling it on the frozen fruit under the freezing process of freezing the fruit and the reduced pressure environment where the boiling point of water is 50 ° C. to 70 ° C. And a drying step of evaporation.

  The method for producing a dried fruit described in claim 2 is the one according to claim 1, wherein, in the drying step, an electromagnetic wave is applied under a condition that the temperature of the fruit is 35 ° C or higher and 45 ° C or lower. Features.

  The method for producing a dried fruit according to claim 3 is the one according to claim 1 or 2, wherein in the drying step, the strength of electromagnetic waves is reduced when a liquid appears on the surface of the fruit. It features.

  The method for producing a dried fruit according to claim 4 is the one according to claim 3, and in the drying step, the strength of the electromagnetic wave when dried to a state where a part of the surface of the fruit begins to dry and harden. To further reduce the

  The method for producing a dried fruit described in claim 5 is the one described in claim 4, and in the drying step, the irradiation of electromagnetic waves is finally stopped until the fruit reaches 30 ° C. or lower. It is characterized in that heat is naturally dissipated under the reduced pressure environment described in the above.

  A method for producing a dried fruit described in claim 6 is the one according to any one of claims 1 to 5, wherein the fruit is a granular strawberry.

  According to the method for producing dried fruits of the present invention, warm air drying is unnecessary, so even soft fruits rich in water, for example, can be dried conveniently and conveniently. Furthermore, in the drying step, the sugars are crystallized on the surface of the fruit while being dried while being allowed to ooze out bound water containing saccharides such as sucrose on the surface of the fruit. "It becomes the texture of the finish, and can produce more excellent dried fruit of taste. In addition to maintaining good shape, color, flavor, and fragrance, the fruit can be produced, and a dried fruit can be produced that has a sugar crystal appearing on the surface and sparkling.

  When an electromagnetic wave is applied under the condition that the temperature of the fruit is 35 ° C. or more and 45 ° C. or less in the drying step, the boiling of water can be reliably prevented while promoting the evaporation of water.

  When the intensity of electromagnetic waves is reduced when liquid appears on the fruit surface in the drying step, it is possible to prevent a rapid increase in the temperature of the fruit.

  In the case where the strength of electromagnetic waves is further reduced when drying to a state where a part of the surface of the fruit starts to dry and harden in the drying step, the fruit surface can be prevented from being scorched or denatured by heat.

  In the drying process, the irradiation of electromagnetic waves is stopped at the end, and the water is sufficiently dried without scorching or altering the fruit surface with heat by naturally releasing heat in a reduced pressure environment until the fruit reaches 30 ° C. or lower. be able to.

It is a block diagram which shows typically the structure of the microwave decompression drying apparatus used at a drying process. Example: It is a photograph of the manufactured dried strawberry. Example: It is a photograph (photographed from the heta cut surface side) of the manufactured dried strawberry.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, the scope of the present invention is not limited to these forms.

  The method for producing a dried fruit of the present invention includes a freezing step in which free water in the fruit is frozen and the fruit is frozen at a temperature at which at least a part of the combined water does not freeze, and the boiling point of water is 50 ° C. or higher and 70 ° C. or lower. A drying step of applying moisture to the frozen fruit under a reduced pressure environment so as to evaporate water without applying boiling to evaporate water is provided.

  The purpose of performing the freezing step will be described. Take strawberries as an example of fruit.

[Purpose 1 to freeze]
It is not uncommon for strawberry fruits to have a Brix sugar content that exceeds 13%, and they are rich in sugars. This results in a lot of “bound water” in the fruit. The combined water is water combined with sugar or the like. In addition to bound water, “free water”, which is normal water, exists in the fruit.

  When dried in warm air without slicing the strawberries, the finished product has a moisture content of about 18% due to the effect of bound water associated with sugars, and has a brownish stickiness. It is just gummy and caramel-like and does not dry out. If it is further dried with warm air, it burns or hardens.

  When aiming at the production of whole dried strawberries instead of the many slices of dried (dried) strawberries, the problem of bound water stands up and drying of bound water is the most to be solved.

  The bound water is not only difficult to dry but also hard to freeze and freeze. Free water freezes below 0 ° C. On the other hand, the bound water is frozen at a low temperature of about -20 ° C to -40 ° C although it varies depending on the substance to be bound etc. Using this, free water that is easy to dry is solidified as ice, and bound water that is difficult to dry is frozen in a liquid, in a state where the liquid and the solid coexist, or in a state where water molecules are loosely bound even if it is a solid. Process.

  Liquid water is said to be easily heated by microwaves (an example of electromagnetic waves) about 8000 times that of solid ice. In other words, ice is less affected by microwaves by about 1/8000 of water.

  In the present invention, by utilizing “defrosting unevenness” due to microwaves, the combined water is preferentially affected by the microwaves to be thawed, leading to evaporation.

  In other words, by performing a freezing process in which fruit is frozen at a temperature at which free water in the fruit freezes and at least part of the combined water does not freeze, the difference in freezing temperature between “bound water” and “free water” is utilized. Then, in the next drying step, heating (giving energy) is preferentially (first) by applying microwaves from the combined water which is difficult to dry, and dried.

  The freezing temperature of the strawberry is preferably set to a temperature at which free water in the strawberry freezes and at least a portion of the bound water does not freeze, for example, −10 ° C. or less −29 ° C. or more. If it is −30 ° C. or lower, most of the bound water may freeze, so the strawberry freezing temperature is more preferably −15 ° C. or lower and −25 ° C. or higher, more preferably around −20 ° C. .

  Freezing may be performed by rapid freezing. Rapid freezing is a freezing method in which the ice crystal maximum production temperature zone (-1 ° C to -5 ° C) is passed within 30 minutes. In the case of rapid freezing, the ice crystals do not grow large, so that the cells of the fruit are not easily damaged, and the generation of unnecessary drips at the time of thawing is reduced.

  In the production method of the present invention, saccharides such as sucrose are crystallized on the fruit surface and dried while allowing bound water containing saccharides to ooze out on the fruit surface. That is, the drip is generated by dare at the time of thawing, and the drip is evaporated and dried on the fruit surface. In normal thawing, it is required to reduce the occurrence of drip, but the present invention is characterized by positively utilizing the occurrence of drip.

  For this reason, it may be quickly frozen in the freezing process, but the maximum ice crystal formation temperature is not used for quick-freezing in order to increase the amount of drip generated depending on the intended quality of the dried fruit. It may be frozen by the usual freezing method in which the zone is passed for a time (period) of more than 30 minutes. The amount of sucrose produced on the fruit surface may be adjusted based on the length of time for passing through the ice crystal maximum production temperature zone.

[Purpose 2 of freezing]
As described above, ice is less affected by microwaves than about 1/8000 of water. For example, when the output is strong by irradiation of 100 W in the experiment, the output fine adjustment of every 10 W or several W is required, but the microwave irradiator is not always a constant output but millisecond unit based on the set output value Thus, the irradiation process is performed within a fluctuation width of several W. For this reason, even if the output value setting change of several W is performed, since there is actually a shake width output exceeding the set value, it can be said that fine adjustment of the output of about several W to 10 W is difficult. From this, if the target is frozen as pretreatment, it becomes less susceptible to microwaves, and even if the target is a small amount of around 100 g or a soft fruit with a water content of around 90%, 50 W to 100 W units You can change the output value in.

  Furthermore, when it is desired to finely adjust the output of microwave drying, by lowering the freezing temperature to −20 ° C. or lower, the crystallization of ice crystals becomes stronger and the electric dipole cannot rotate due to strong hydrogen bonding. It becomes difficult to be heated by the wave. On the other hand, if the freezing temperature is around -5 ° C, the thawing progresses due to factors other than microwaves such as room temperature during microwave application, and it is necessary to complete the microwave drying process in a short period of time. It is effective for

  In other words, in the microwave drying method, the fruit is frozen in advance when it is applied to an object that is more susceptible to heating by microwaves, such as an extremely large amount of moisture in the object or a small mass of the object. Thus, the influence of the microwave output can be reduced. The drying method of the present invention also has such additional effects.

[Pre-cooling]
It is preferable to perform the precooling process which cools a fruit to the temperature of 1 degreeC or more and 10 degrees C or less, before performing a freezing process. By performing the preliminary cooling step in advance, the time for the freezing step can be shortened. In particular, in the case of rapid freezing in the freezing step, it is easy to pass the ice crystal maximum generation temperature zone in a short time.

  Next, the drying step will be described.

[Device by decompression]
As the object shrinks when the vegetables are heated in the microwave, during the microwave drying, the object may be shrunk or crushed depending on the condition before being dried. In addition, soft fruits such as strawberries were also destroyed in the experiment due to the generation of bubbles during boiling. Moreover, when it boils, the fall of the color of a fruit may arise.

  In order to prevent the object itself from being scalded by water that has melted from ice when thawing, it is important to remove the water out of the object quickly and to adjust to a temperature zone that does not lead to boiling. is there. Furthermore, the fruit can be made to have a good color and taste by processing at low temperature. Therefore, it is necessary to thaw and dry the ice without boiling the fruit at a temperature below 50 ° C.

  For these reasons, in the drying process, in a reduced pressure environment in which the boiling point of water is 50 ° C. or more and 70 ° C. or less, the frozen fruit is applied with electromagnetic waves under the condition of evaporating without boiling the water. Evaporate. Since the atmospheric pressure when the boiling point of water is 50 ° C. is 0.012 MPa and the atmospheric pressure when the boiling point of water is 70 ° C. is 0.031 MPa, the pressure is expressed as 0.012 MPa or more and 0.031 MPa or less. The pressure at which the boiling point of water is 60 ° C. is 0.020 MPa. Since a reduced pressure environment of this degree can be realized by a relatively inexpensive vacuum pump, the present invention can be implemented simply and inexpensively.

  Here, the electromagnetic wave under the condition of evaporating water without boiling is the wavelength, intensity and irradiation time of the electromagnetic wave applied to the fruit. As an example of the electromagnetic wave, a microwave (frequency: 300 MHz to 3 THz) is taken as an example. A microwave similar to the microwave oven (for example, 915 MHz and 2450 MHz) may be used using the same principle as that of the microwave oven. For example, a high frequency of 13.56 MHz may be used. If the intensity of the electromagnetic wave is strong, the water will boil, so the intensity is adjusted appropriately. The electromagnetic wave may be applied continuously or intermittently. The intensity may be changed according to the passage of time or temperature.

  In the drying step, it is preferable to apply electromagnetic waves under the above-mentioned reduced pressure environment under the condition that the temperature of the fruit is 35 ° C. or higher and 45 ° C. or lower. By setting this temperature range, the boiling of water can be reliably prevented while promoting the evaporation of water. If the temperature is lower than this, the time of the drying step will be long. If the temperature is higher than this, the water tends to boil.

  In the present invention, in a reduced pressure environment in which the boiling point of water is 50 ° C. or higher and 70 ° C. or lower, the moisture generated in the object by the thawing step is moved onto the surface using the reduced pressure, thereby effect of applying the microwave. Is increasing. Even if there is a void inside due to the reduced pressure environment, the original shape can be maintained without crushing the object at atmospheric pressure. Furthermore, in the present invention, since there is a reduced pressure environment rather than a high vacuum environment, there is a slight amount of water or water vapor generated with the drying in the processing container, and by continuously sucking with a vacuum pump, It is possible to collect the water vapor generated in the trap with a weak air flow.

[Microwave decompression device]
In the drying process, for example, a microwave vacuum drying apparatus 1 schematically shown in FIG. 1 is used. The microwave decompression drying device 1 includes a microwave irradiation device 2, a container 5, a vacuum pump 9, and a trap 8. The microwave irradiation apparatus 2 includes a microwave generator 3 such as a magnetron, and applies (irradiates) microwaves to the fruit 11 accommodated in the internal space. The fruit 11 is accommodated in the container 5 and accommodated in the internal space of the microwave irradiation device 2. The container 5 is made of, for example, glass or ceramic that does not contain moisture and transmits microwaves. The container 5 is formed to be separable up and down, for example, so as to accommodate the fruit 11. The container 5 has sufficient strength to withstand even if the inside is depressurized. The container 5 has a mouth part to which a pipe line 6 for decompressing the inside can be connected. A conduit 6 connected to the mouth of the container 5 is connected to a vacuum pump 9 via a trap 8 for cooling and collecting water.

  A pressure gauge 7 is provided in the conduit 6. The vacuum pump 9 is operated manually or automatically so that the pressure gauge 7 indicates the desired pressure. The microwave irradiation device 2 is configured such that the intensity can be adjusted manually or automatically so that the microwave generator 3 outputs a microwave having a desired intensity. Although not shown, the temperature of the strawberry is measured by a known infrared temperature sensor that can measure the temperature in a non-contact manner, or a known contact-type temperature sensor such as a thermocouple that is attached to the surface or inside of the strawberry to detect the temperature. do it.

"Stepwise change of microwave output intensity"
In the drying step, it is preferable to reduce the intensity of electromagnetic waves when a liquid appears on the fruit surface. Furthermore, in the drying step, it is preferable to further reduce the intensity of the electromagnetic wave when the portion of the surface of the fruit is dried to a state where drying and hardening start.

  Objects containing abundant sugar such as fruits are easily affected by scorching by a drying method mainly using a heat source such as microwave drying. For this reason, in the drying step, it is preferable to proceed with drying with stepwise or continuous output change.

First, in the "thawing" stage, heating of "bound water" (in order to promote liquefaction of frozen bound water) in a short time so as to minimize the effects other than microwaves such as room temperature etc. In addition, it is necessary to process in a short time with a relatively high output intensity. Processing is performed until water droplets are visible on the surface of the object.
(In the experiment, 200W was irradiated to a total of 70g for 15 minutes)

Next, in the “initial drying” stage, if the water appearing on the surface is not quickly steamed and removed, the surface hardens and does not lead to the drying inside, or it becomes its own weight due to the softening due to thawing. There is a risk of losing. On the other hand, since the thawing progresses and the moisture is shifted to a stage where it is easily affected by the microwave, the output intensity of the microwave is reduced (for example, the intensity is reduced by one stage). With this output intensity, microwave application is performed until solidification on the surface of the object starts.
(In the experiment, a total of 70 g of the object was irradiated with 100 W for 25 minutes)

The last is the stage of "final drying". Processing is carried out until drying reaches about 90%, and the fruit is dried and solidified in the form of a hole. In this process, the bound water is evaporated and sugars such as sucrose left on the surface are crystallized and it is very easy to burn, so after further lowering the output intensity, cool down under reduced pressure until the temperature drops below 30 ° C. I do.
(In the experiment, a total of 70 g of the object was irradiated with 50 W for 10 minutes, and then the output was turned off and 15 minutes of cool down)

  Thus, by adjusting so that the output intensity of a microwave may be reduced in steps, it is possible to reliably prevent the fruit from collapsing and scorching.

  Note that the intensity of the microwave may be appropriately changed from the above-mentioned conditions from “thawing” to “final drying”. For example, microwaves of weak constant intensity may be applied continuously from the beginning to the end so that the liquid does not boil and the surface of the fruit does not deteriorate due to heat.

"Deliverables"
From the viewpoint of dried fruit in which the shape of the strawberry remains granular (hole type), the conventional freeze-drying method and the drying method according to the present invention are the same. However, when the fruit is dried according to the production method of the present invention, the bound water containing the sugar exudes by thawing on the surface of the fruit and then evaporates, thereby sugars such as sucrose being crystallized on the surface of the fruit. The fruits are drying. For this reason, compared with the "puff-like" finish of the dried fruit manufactured by the conventional freeze-drying method, the dried fruit by the production method of the present invention becomes a "snack-like / crispy" finish with a crisp texture It is possible to produce dried fruits with completely different textures. The dried fruit according to the present invention has a good taste. According to the present invention, even a granular fruit is not crushed, and a dried fruit having a good shape, color, flavor and aroma can be produced. Furthermore, according to the present invention, it is possible to produce an aesthetically pleasing dried fruit in which sugar crystals appear as if on the surface like a diamond and have a sparkling appearance. According to the present invention, even soft fruits containing a large amount of sugar, such as strawberries, can be dried in the form of particles. According to the present invention, the sliced or divided fruit may be dried.

  The fruits to be dried (including false fruits) of the present invention are not limited to strawberries. Fruits include, for example, strawberries, grapes, melons, blueberries, prune, apples, persimmons, citrus, avocado, figs, apples, pears, kiwis, pineapples, mangos, watermelons, jujubes, pumpkins. In general, foods such as carrots and sweet potatoes processed as dried fruits (dried fruits, dried fruits) are included in the fruits of the present invention even if they are foods corresponding to vegetables and grains.

  It should be noted that the present invention is different from the conventional drying method in which microwave irradiation is used in combination with freeze-drying. The lyophilization method is a method of subliming the water of frozen fruits in a high vacuum. The combination of microwave irradiation promotes the sublimation of water from solid to gas. That is, in the drying method using microwave irradiation in combination with conventional lyophilization, there is no water in the liquid state. Therefore, sugar crystals such as sucrose are not generated so as to be visible on the fruit surface. On the other hand, in the drying method of the present invention, frozen fruit ice is melted into a liquid by microwave irradiation and then the liquid is evaporated (or the bound water in a liquid state is evaporated). In the present invention, this liquid exudes to the surface of the fruit and then evaporates, whereby crystals of sugar such as sucrose are generated on the surface.

  As an example, the method for producing dried fruits of the present invention was applied to produce dried strawberries. Strawberries were cultivated at AIP Corporation's own farm and harvested in a fully ripe state. The strawberry variety is red poppy.

[Precooling process]
Strawberries were pre-cooled in a 6 ° C cool box.

[Freezing process]
The pre-chilled strawberries were scraped off and immediately placed in a shock freezer (rapid freezer) and flash frozen until the core temperature of the strawberries reached -20 ° C.

[Drying process]
Three rapidly frozen strawberries (total 70 g) are placed in a glass container 5 as shown in FIG. 1 and housed in the microwave irradiation device 2 of the microwave decompression drying device 1 to a pressure of 0.02 MPa (0.2 MPa). The pressure was reduced to (under a reduced pressure environment with a water boiling temperature of 60 ° C.) and irradiation with microwaves was performed. As the microwave irradiation apparatus 2, model name μ Reactor EX manufactured by Shikoku Keiki Kogyo Co., Ltd. was used. The frequency of the microwave was 2450 MHz.

  When continuous irradiation was performed at a microwave intensity of 200 W for 15 minutes, a liquid (moisture) appeared on the surface. Therefore, the microwave intensity was reduced to 100 W and irradiation was continued for 25 minutes. The liquid did not boil and was in a state of evaporation (the generation of steam). By this irradiation, it dried to the state to which the drying hardening of a part of surface of strawberry started. In addition, the conditions of this microwave irradiation are conditions determined experimentally beforehand so that the temperature (internal temperature) of a strawberry may be 35 to 45 degreeC. Subsequently, the intensity of the microwave was lowered to 50 W and the irradiation was continued for 10 minutes to stop the microwave irradiation. Thereafter, cool down was performed for 15 minutes under reduced pressure until the temperature dropped below 30 ° C.

  The photograph of the dried strawberry manufactured in the Example is shown in FIG. 2, FIG. Dried strawberries with good shape, color, flavor and aroma were produced. Crystals of saccharides such as sucrose were formed on the surface of dried strawberries. The transparent substance present on the surface of the dried strawberry shown in FIGS. 2 and 3 is a sugar crystal. Component data and the like of dried strawberries are shown in Table 1.

  As a comparative example, component data and the like of dried strawberries produced by hot air drying are shown in Table 1.

  1 is a microwave vacuum drying apparatus, 2 is a microwave irradiation apparatus, 3 is a microwave generator, 5 is a container, 6 is a conduit, 7 is a pressure gauge, 8 is a trap, 9 is a vacuum pump, and 11 is a fruit. .

Claims (6)

Freezing the fruit at a temperature at which free water in the fruit freezes and at least a portion of the bound water does not freeze;
A drying step of evaporating water by applying an electromagnetic wave under the condition of evaporating water without boiling it under the reduced pressure environment where the boiling point of water is 50 ° C. or more and 70 ° C. or less; Of producing dried fruits characterized by   In the said drying process, electromagnetic waves are applied on the conditions which become the temperature of 35 degreeC or more and 45 degrees C or less of the said fruit, The manufacturing method of the dried fruit of Claim 1 characterized by the above-mentioned.   The method for producing dried fruits according to claim 1 or 2, wherein in the drying step, the intensity of the electromagnetic wave is reduced when a liquid appears on the surface of the fruits.   The method for producing a dried fruit according to claim 3, wherein, in the drying step, the intensity of the electromagnetic wave is further reduced when the portion of the surface of the fruit is dried to a state where drying and hardening start.   In the said drying process, irradiation of electromagnetic waves is stopped at the end, and it carries out natural heat dissipation in the pressure-reduced environment of Claim 1 until the said fruit becomes 30 degrees C or less, The dried fruit of Claim 4 characterized by the above-mentioned. Production method. The method for producing dried fruit according to any one of claims 1 to 5, wherein the fruit is granular strawberry.