Method for producing frozen vegetables

Abstract

To provide a method for producing frozen vegetables, by which the frozen vegetables having the same level of high quality as that of conventional frozen vegetables obtained by processing vegetables just after harvesting can be produced while suppressing the deterioration of the vegetables even when the vegetables are stored for a fixed period.SOLUTION: The method for producing frozen vegetables includes a storage step of storing harvested vegetables at low temperature and high humidity for a predetermined period, and a processing step of blanching and freezing the stored vegetables.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing frozen vegetables. [Background technology]

[0002] Demand for frozen vegetables is increasing in Japan. Conventionally, to produce high-quality frozen vegetables, the raw vegetables are blanched (heated) and frozen immediately after harvest, without being stored. Summary of the Invention [Problem to be solved by the invention]

[0003] Because the raw vegetables are processed (blanched and frozen) immediately after harvest, it is difficult to produce high-quality frozen vegetables unless there is a processing plant nearby.

[0004] Furthermore, if the harvest volume of raw vegetables is increased to meet the demand for frozen vegetables, the harvest volume of raw vegetables will exceed the frozen vegetable production capacity, resulting in an increase in the amount of raw vegetable waste.To solve this problem, a method of storing raw vegetables in a cool place as a buffer can be considered.

[0005] Here, as a method for storing raw vegetables in a cooled state, for example, storing raw vegetables in a publicly known ordinary refrigerator is not suitable for long-term storage because dry rot occurs inside the refrigerator.

[0006] The present invention has been invented to solve the above-mentioned problems, and aims to provide a method for producing frozen vegetables that suppresses deterioration of vegetables even when stored for a certain period of time and that can produce frozen vegetables of the same high quality as those processed immediately after harvest. [Means for solving the problem]

[0007] The method for producing frozen vegetables according to the present invention, which achieves the above-mentioned object, comprises a storage step of storing harvested vegetables at low temperature and high humidity for a predetermined period of time, and a processing step of blanching and freezing the stored vegetables. [Effects of the Invention]

[0008] According to the above-described method for producing frozen vegetables, deterioration of vegetables can be suppressed even when stored for a certain period of time, and frozen vegetables of the same high quality as those processed immediately after harvest can be produced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing a low-temperature, high-humidity cooling device used in the storage step of a method for producing frozen vegetables according to an embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a heat exchanger of a low-temperature, high-humidity cooling device. [Figure 3] 10 is a graph showing temperature and humidity changes in a low-temperature, high-humidity cooling device. [Figure 4] 10 is a graph showing temperature and humidity changes in a standard refrigerator according to a comparative example. [Figure 5] 1 is a graph showing the surface hardness of broccoli when stored for a predetermined period of time in a low-temperature, high-humidity cooling device and a normal refrigerator. [Figure 6] 1 is a graph showing the hardness of the inside of broccoli stems after being stored for a predetermined period of time in a low-temperature, high-humidity cooling device and a normal refrigerator and then subjected to a processing step. [Figure 7] 7 is a graph showing the ratio of the surface hardness of the broccoli shown in FIG. 5 to the hardness of the inside of the stem shown in FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] A low-temperature, high-humidity cooling device 1 used in a method for producing frozen vegetables according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Note that identical elements in the drawings are given the same reference numerals, and redundant explanations will be omitted. Dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions.

[0011] Fig. 1 is a schematic diagram showing a low-temperature, high-humidity cooling device 1 used in the storage step of a method for producing frozen vegetables according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing the configuration of a heat exchanger 130 of the low-temperature, high-humidity cooling device 1.

[0012] 1, the low-temperature high-humidity cooling device 1 has a generating section 110 and a housing 80. Each component will be described below.

[0013] The generating unit 110 generates cooled water vapor while maintaining high humidity by bringing moisture adhering to the heat exchange unit 130, which is an evaporator, into contact with the air flowing into the generating unit 110. As shown in FIG. 1, the generating unit 110 has a fan 20, a pre-filter 70, a heat exchange unit 130, a condensing unit 140, an adjustment unit 50, and a casing 60. The fan 20, the pre-filter 70, and the heat exchange unit 130 are configured to be covered by a housing 80. The housing 80 is configured with a heat-insulating wall.

[0014] As shown in FIG. 1, the fan 20 is provided on the left side (air inlet side) of the heat exchange unit 130. The fan 20 draws in air after high-humidity cooling of the vegetables and sends it toward the pre-filter 70 and the heat exchange unit 130. That is, the fan 20 takes in the air after high-humidity cooling of the vegetables from the left side shown in FIG. 1 and sends it toward the right side (see arrow V1 in FIG. 1). Here, high-humidity cooling means, for example, cooling at a humidity of 80% or higher. By arranging the fan 20 so that the air is sent horizontally in this way, water can be suitably stored in the heat exchange unit 130.

[0015] The condensing unit 140 includes a compressor and a condenser (not shown). The low-temperature, high-humidity cooling device 1 is called a "direct expansion cooling system" and is connected via refrigerant piping, where the refrigerant expands near the space to be cooled to perform heat exchange and directly cool the air.

[0016] The pre-filter 70 is disposed between the fan 20 and the heat exchanger 130. The pre-filter 70 collects dust and straightens the air taken into the casing 60. The pre-filter 70 may be, for example, a nonwoven fabric filter.

[0017] The heat exchanger 130 exchanges heat between the refrigerant cooled by the condensing unit 140 and the air circulating inside the refrigerator, thereby cooling the air flowing through the heat exchanger 130. The heat exchanger 130 is a microchannel heat exchanger. The configuration of the heat exchanger 130 will be described below with reference to Fig. 2. Fig. 2 is a view of the heat exchanger 130 as viewed from the pre-filter 70 side.

[0018] As shown in FIG. 2, the heat exchange section 130 has two refrigerant headers 131, 132, a plurality of heat transfer tubes 133 that connect the refrigerant headers 131, 132 and are arranged in the vertical direction, and fins 134 that are arranged between the heat transfer tubes 133 so as to be in contact with the heat transfer tubes 133.

[0019] Air is blown by fan 20 from the rear side (left side in FIG. 1) of heat exchanger 130 to the front side (right side in FIG. 1) and flows between fins 134. Meanwhile, refrigerant supplied from condensing unit 140 flows in from refrigerant header 131, which is the refrigerant inlet side, flows through the refrigerant flow path formed inside heat transfer tube 133, and flows to refrigerant header 132, which is the refrigerant outlet side.

[0020] The refrigerant in the refrigerant flow path exchanges heat with the air via the heat transfer tubes 133 and the fins 134 .

[0021] The surfaces of the fins 134 are configured as heat transfer sections that transfer the cold heat of the refrigerant to the air. The adjustment section 50 keeps the moisture contained in the air and vegetables attached to the surfaces of the fins 134. The fins 134 are arranged horizontally.

[0022] In the heat exchange unit 130 configured in this manner, condensation water adheres to the horizontally arranged fins 134 due to the difference in dew point temperature between the temperature of the fins 134 when heat is transferred from the refrigerant and the temperature of the air in contact with them. Here, the pitch of the fins 134 is narrow, which generates surface tension, and the condensation water adheres and is held on the fins 134. As a result, the air blown out from the heat exchange unit 130 is maintained at a high humidity. Note that if the air speed when passing through the heat exchange unit 130 is too high, the condensation water will scatter, so it is preferable to appropriately control the rotation speed of the fan 20.

[0023] The adjusting section 50 maintains a state in which moisture contained in the air and vegetables adheres to the heat exchange section 130.

[0024] As shown in FIG. 1, the generation unit 110 has a first path 210 through which the refrigerant flows from the condenser toward the heat exchange unit 130, a second path 220 through which the refrigerant flows from the heat exchange unit 130 toward the compressor, and a third path 230 that connects the compressor (discharge side) and the second path 220 and supplies the heat generated by the compressor to the second path 220.

[0025] An expansion valve 240 is provided in the first path 210. The expansion valve 240 expands the refrigerant that has been compressed by the compressor, liquefied by the condenser, and flowed into the expansion valve 240, thereby lowering the temperature of the refrigerant.

[0026] A first adjustment valve 250 is provided in the second path 220. The first adjustment valve 250 adjusts the pressure inside the heat exchanger 130 so that the evaporation pressure of the refrigerant inside the heat exchanger 130 does not fall below a specified value, and adjusts the evaporation temperature of the refrigerant inside the heat exchanger 130.

[0027] A second adjustment valve 260 is provided in the third path 230. The second adjustment valve 260 adjusts the amount of hot heat supplied to the second path 220. This allows a desired amount of hot heat from the refrigerant compressed by the compressor through the third path to be supplied to the refrigerant gas in the second path 220, thereby controlling the degree of superheat of the refrigerant gas flowing through the second path 220 and improving cooling performance.

[0028] Next, a cooling method of the low-temperature, high-humidity cooling device 1 will be described as an example with reference to Fig. 1. It should be noted that the present invention is not limited to the following example.

[0029] The adjustment unit 50 adjusts the rotation speed of the fan 20 so that the front wind speed of the air entering the pre-filter 70 is 1.5 to 2.5 m / s. At this time, the amount of air circulating inside the housing 80 is 20 to 40 m / s. 3 / min.

[0030] The adjustment unit 50 adjusts the opening of the expansion valve 240 within a range of 5 to 95%. Furthermore, when the temperature inside the refrigerator is 0°C and the humidity is 90% or higher, the adjustment unit 50 adjusts the evaporation temperature of the refrigerant to -1.0 to -0.2°C. For example, when R410A is used as the refrigerant, the adjustment pressure of the first adjustment valve 250 is adjusted within a range of 6.7 to 6.9 bar. Furthermore, the adjustment unit 50 adjusts the opening of the second adjustment valve 260 to adjust the amount of heat supplied to the second path 220.

[0031] In this state, air is circulated within the housing 80, and the air taken into the casing 60 first passes through the pre-filter 70, where dust is collected and the air is rectified. Then, for example, air taken into the casing 60 at a temperature of 1°C is cooled in the heat exchanger 130 while maintaining a high humidity, and is blown out of the casing 60 as water vapor with a temperature of 0°C and a humidity of 90% or more. This then cools vegetables and other items placed inside the housing 80 at a high humidity.

[0032] The configuration and cooling method of the low-temperature, high-humidity cooling device 1 used in the method for producing frozen vegetables according to this embodiment have been described above. Next, the method for producing frozen vegetables will be described.

[0033] The method for producing frozen vegetables includes a storage step S01 in which harvested raw vegetables are stored for a predetermined period in a low-temperature, high-humidity cooling device 1, and a processing step S02 in which the raw vegetables stored in the low-temperature, high-humidity cooling device 1 are blanched and frozen.

[0034] The storage step S01 will be described below. In the storage step S01, although not particularly limited, it is preferable to store the raw vegetables at a humidity of, for example, 90% to 100%, more preferably 95% to 100%. By increasing the humidity in this way, it is possible to prevent the raw vegetables from drying out in the storage step S01.

[0035] Furthermore, in the storage step S01, although not particularly limited, it is preferable to store the raw vegetables at a temperature of, for example, 0° C. or higher and 5° C. or lower, more preferably 0° C. or higher and 2° C. or lower. By storing the raw vegetables at such low temperatures, the respiration rate of the raw vegetables can be suppressed, and the freshness of the raw vegetables can be maintained.

[0036] The storage period of the raw vegetable material in the storage step S01 varies depending on the type of raw vegetable material to be stored, but is, for example, within four weeks, and more preferably within two weeks.

[0037] Next, the processing step S02 will be described. In the processing step S02, as described above, the raw vegetables stored in the low-temperature, high-humidity cooling device 1 are blanched (heated) and then frozen.

[0038] The method for blanching the raw vegetables is not particularly limited, but may be, for example, boiling the raw vegetables in boiling water for 2 minutes. The method for freezing the raw vegetables is not particularly limited, but may be, for example, freezing the raw vegetables in a known freezer.

[0039] Hereinafter, examples and comparative examples of the present invention will be described using broccoli as a raw vegetable.

[0040] <Example> As an example, harvested broccoli was stored for two or four weeks in a Super Fresh ZERO (manufactured by Maekawa Manufacturing Co., Ltd., equivalent to low-temperature, high-humidity cooling device 1). The surface hardness of the broccoli stems was measured at 10 locations before and after storage, and the average value was calculated. The broccoli stems and florets were then cut 5 cm from the apex of the florets before and after storage to ensure uniform floret sizes. The broccoli was then boiled in boiling water for two minutes (blanching) and cooled in ice water. The broccoli cooled in ice water was then flash-frozen for 10 minutes in a Thermojack Freezer (manufactured by Maekawa Manufacturing Co., Ltd.). The flash-frozen broccoli was then allowed to thaw naturally at room temperature for two hours. The center of the cross-section of the broccoli stem was then hollowed out with a cork borer, and a 5 mm section of the hollowed tissue was sampled from the cross-section of the stem to measure the internal hardness of the stem.

[0041] The reason for adopting the surface and internal hardness of the stem as an index of quality evaluation is that the hardness of broccoli directly affects the texture, and consumers often prefer a moderate hardness that is neither too hard nor too soft, so the surface and internal hardness of the stem were evaluated.

[0042] <Comparative Example> As a comparative example, the surface hardness and internal hardness of broccoli stems were measured in the same manner as in the example, except that the broccoli was stored in a known ordinary refrigerator instead of the Super Fresh ZERO.

[0043] Here, the temperature and humidity changes in the low-temperature high-humidity cooling device 1 and the ordinary refrigerator will be described with reference to FIGS.

[0044] In the case of the low-temperature, high-humidity cooling device 1, as shown in Figure 3, the average temperature inside the storage compartment was 0.57°C with a temperature fluctuation of 0.7°C, the average humidity inside the storage compartment was 96.8%, and the humidity fluctuation was 8.7%. On the other hand, in the case of the standard refrigerator, as shown in Figure 4, the average temperature inside the storage compartment was 5.14°C with a temperature fluctuation of 4.0°C, the average humidity inside the storage compartment was 84.5%, and the humidity fluctuation was 17.5%. As such, the temperature inside the storage compartment of the standard refrigerator is higher and the humidity is lower than that of the low-temperature, high-humidity cooling device 1. Furthermore, the temperature and humidity fluctuations inside the storage compartment of the standard refrigerator were larger than those of the low-temperature, high-humidity cooling device 1. This is because the standard refrigerator is defrosted at regular intervals.

[0045] The surface hardness of broccoli stems before and after the storage step S01 will be described with reference to Figure 5. In Figure 5, the dark gray graph shows the results of measuring the surface hardness of broccoli stored in the low-temperature, high-humidity cooling device 1 after harvesting, while the light gray graph shows the results of measuring the surface hardness of broccoli stored in a standard refrigerator after harvesting. The open graph shows the results of measuring the surface hardness (initial value) of broccoli immediately after harvesting without conventional storage. In other words, broccoli with less variation from the initial value after storage can be considered to have the same high quality as broccoli processed immediately after harvesting.

[0046] The graph in Figure 5 shows that in low-temperature, high-humidity cooling device 1, the stem surface hardness showed little variation (softening) from the initial value even after storing broccoli for two and four weeks after harvest, whereas in the standard refrigerator, the stem surface hardness showed large variation from the initial value when stored for two and four weeks after harvest. This is thought to be because the relatively low humidity in the standard refrigerator causes dryness, which causes the water inside the broccoli to evaporate and breaks down the tissue on the broccoli surface, causing the broccoli surface to soften during storage.

[0047] On the other hand, when storing broccoli using the low-temperature, high-humidity cooling device 1, the broccoli is stored at a lower temperature than in a regular refrigerator, which reduces the amount of respiration of the broccoli during storage and keeps it fresh. Also, the broccoli is stored at a higher humidity than in a regular refrigerator, which prevents the broccoli from drying out during storage and helps maintain the surface firmness of the stems. In other words, it is possible to produce frozen vegetables of the same high quality as when processed immediately after harvesting.

[0048] Next, the hardness of the inside of broccoli stems after processing step S02 will be described with reference to Figure 6. In Figure 6, the dark gray graph shows the results of measuring the hardness of the inside of the stems after processing step S02 when harvested broccoli was stored in the low-temperature, high-humidity cooling device 1, while the light gray graph shows the results of measuring the hardness of the inside of the stems after processing step S02 when harvested broccoli was stored in a standard refrigerator. The white graph shows the results of measuring the hardness of the inside of broccoli stems (initial values) after processing step S02 when broccoli was not stored in the conventional manner. In other words, broccoli with a smaller numerical deviation from the initial value for the hardness of the inside of the stem can be considered to be of the same high quality as broccoli processed immediately after harvesting.

[0049] Referring to Figure 6, the hardness of the inside of broccoli stems after processing step S02 was performed on broccoli without conventional storage was 52.6 N. In a standard refrigerator, the hardness of the inside of broccoli stems increased to 76.6 N when processing step S02 was performed after storage for two weeks after harvest, and the hardness of the inside of broccoli stems after processing step S02 after storage for four weeks after harvest was 69.2 N, indicating a large variation from the initial value. This is thought to be because in the standard refrigerator, the surface dried during storage, causing moisture inside the broccoli to move to the surface, disrupting the moisture balance and increasing the hardness of the inside of the broccoli stems after processing step S02.

[0050] On the other hand, the hardness of the inside of the broccoli stems after storage in the low-temperature, high-humidity cooling device 1 and then processing step S02 was 56.5 N when stored for 2 weeks, and 55.2 N when stored for 4 weeks, with little variation from the initial value. This is thought to be because, in the case of the low-temperature, high-humidity cooling device 1, there was little surface drying of the broccoli during storage, which suppressed the increase in hardness inside the broccoli stems after processing step S02.

[0051] Next, with reference to FIG. 7, the ratio of the broccoli surface firmness shown in FIG. 5 to the broccoli stem interior firmness shown in FIG. 6 will be described. FIG. 7 shows the ratio obtained by dividing the value of the broccoli stem interior firmness by the value of the broccoli stem surface firmness. The graphs shown in white also show the ratio (initial value) obtained by dividing the value of the broccoli stem interior firmness without conventional storage by the value of the broccoli stem surface firmness. In FIG. 7, of the graphs after two weeks and four weeks, the graphs shown in light gray represent the ratio when the broccoli was stored in a standard refrigerator, and the graphs shown in dark gray represent the ratio when the broccoli was stored in the low-temperature, high-humidity cooling device 1.

[0052] The graph in Figure 7 shows that in the case of a standard refrigerator, the ratio gradually increases compared to the initial value after two weeks and four weeks of storage of harvested broccoli, and the balance between the firmness of the inside and outside of the broccoli is disrupted.

[0053] The reason for this is thought to be that when broccoli is stored in a regular refrigerator, the surface of the broccoli softens as it dries, while the inside of the stem hardens as the moisture content decreases.

[0054] On the other hand, when broccoli is stored in the low-temperature, high-humidity cooling device 1, the balance of hardness between the surface and the inside of the stem of the broccoli is maintained from the initial value, and it was found that the frozen vegetable manufacturing method of this embodiment can produce frozen vegetables of the same high quality as those processed immediately after harvesting in the conventional method.

[0055] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims.

[0056] For example, in the above-described embodiment, broccoli was used as an example of a vegetable. However, other vegetables that can be stored include cauliflower and Romanesco, which are flower vegetables; spinach, which is a leafy vegetable; carrots, potatoes, and radishes, which are root vegetables; pumpkin, which is a fruit vegetable; asparagus, which is a stem vegetable; and edamame, which is a bean. Among these, the method for producing frozen vegetables according to this embodiment can be particularly suitable for storing flower vegetables and leafy vegetables, which have a high respiration rate.

[0057] Furthermore, in the above-described embodiment, a direct expansion type is adopted as the low-temperature, high-humidity cooling device 1, but an indirect expansion type may also be adopted. [Explanation of symbols]

[0058] 1 Low temperature and high humidity cooling equipment, 20 fans, 130 heat exchange section, 50 adjustment section, 110 Generator.

Claims

1. A storage process of storing the harvested vegetables at low temperature and high humidity for a predetermined period of time; A method for producing frozen vegetables, comprising a processing step of blanching and freezing the stored vegetables.

2. The method for producing frozen vegetables according to claim 1 , wherein the humidity during the storage step is 90% or more and 100% or less.

3. The method for producing frozen vegetables according to claim 1 or 2, wherein the temperature in the storage step is 0°C or higher and 5°C or lower.

4. 3. The method for producing frozen vegetables according to claim 1, wherein the humidity during the storage step is 95% or more and 100% or less, and the temperature is 0°C or more and 2°C or less.

5. 3. The method for producing frozen vegetables according to claim 1, wherein the storage period in the storage step is 4 weeks or less.

6. The method for producing frozen vegetables according to claim 1 or 2, wherein the vegetables are flower vegetables or leafy vegetables.

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