Abstract
A rapid, uniform and high-quality thawing method is awaited which is free from a burn and boiling and which is indispensable for a freezing technology that is frequently used in the fishery industry and the fishery processing industry. For rapid thawing, electromagnetic waves of 130 to 300 MHz in which a B zone passage required time serving as a rate limiting step is decreased are utilized, for uniform thawing, electromagnetic waves of 110 to 170 MHz are utilized and in order to prevent boiling and a burn in the application and after the thawing, electromagnetic waves of 110 to 160 MHz in which a temperature increase after the thawing is decreased are utilized, with the result that the corresponding problems can be solved.
Claims
1. A method of thawing a frozen food, wherein electromagnetic waves of 110 to 300 MHz are applied to the frozen food.
2. A method of thawing a frozen food, wherein electromagnetic waves of 130 to 170 MHz are applied to the frozen food.
3. A method of thawing a frozen food, wherein electromagnetic waves of 130 to 150 MHz are applied to the frozen food.
4. A method of thawing a frozen food, wherein in the thawing of the frozen food, thawing in a B zone (in which a temperature of a center of the frozen food ranges from 5 C. to 2 C.) is performed by application of electromagnetic waves of 130 to 150 MHz.
5. A method of thawing a frozen food, wherein in the thawing of the frozen food, thawing in a B zone (in which a temperature of a center of the frozen food ranges from 5 C. to 2 C.) and thawing in a C zone (in which the temperature of the center of the frozen food ranges from 2 C. to room temperature) are performed by application of electromagnetic waves of 1.30 to 150 MHz.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is an illustrative diagram of terms used in the present application document, and is a diagram illustrating temperature changes of frozen products when they are thawed with electromagnetic waves and the temperature variation zones of an A zone (frozen storage temperature to 5 C.), a B zone (5 C. to 2 C.) and a C zone (2 C. to room temperature);
[0017] FIG. 2 is a diagram showing temperature changes (thawing curves) in the center portion when a tuna block (5 cm5 cm4 cm, about 90 g) stored at 50 C. was thawed with electromagnetic waves of 60 MH, 100 MHz, 140 MHz, 170 MHz and 300 MHz;
[0018] FIG. 3 is a diagram showing times necessary for thawing (until 2 C. was reached) when the frozen tuna block was thawed with the electromagnetic waves of 100 to 170 MHz;
[0019] FIG. 4 is a diagram showing an A zone (50 C. to 5 C.) passage required time in the thawing required time of FIG. 3;
[0020] FIG. 5 is a diagram showing a B zone (5 C. to 2 C.) passage required time in the thawing required time of FIG. 3;
[0021] FIG. 6 is a diagram showing thawing curves in the 13 zone (5 C. to 2 C.) when the frozen tuna block was thawed with the electromagnetic waves of 100 to 170 MHz;
[0022] FIG. 7 is a diagram showing thawing temperatures measured with an optical fiber thermometer which was inserted to a depth of 2.5 cm in the center portion (2.5 cm from the surface) and the surface (0.5 cm from the surface) of the frozen tuna block when the froze tuna block was thawed with the electromagnetic waves of 100 to 170 MHz; and
[0023] FIG. 8 is a diagram showing a C zone (2 C. to 20 C.) passage required time when the frozen tuna block was thawed with the electromagnetic waves of 60 to 300 MHz and then the electromagnetic waves were continuously applied.
DESCRIPTION OF EMBODIMENTS
[0024] An embodiment of the present invention will be described below with reference to drawings.
[0025] FIG. 1 shows temperature changes (thawing curve) when frozen products are thawed. All the frozen products are thawed in accordance with such a thawing curve. The temperature changes are formed with three parts that are a part (A zone) whose temperature is increased from a storage freezing temperature so as to reach about 5 C., a part (B zone) which shows a gradual temperature change from 5 C. to 2 C. and a part (C zone) whose temperature is increased from about 2 C. to room temperature or a heating temperature. It is found that it takes a long time to pass the B zone (5 C. to 2 C.) and that the product temperature is slowly increased while the temperature is being repeatedly varied as shown in FIG. 6. Here, the tissue destruction of the frozen product is assumed to occur, and thus it is preferable to provide a thawing method in which the B zone is rapidly passed.
Example 1
[0026] FIG. 2 is a diagram showing temperature changes (thawing curves) in the center portion when a frozen tuna block (5 cm5 cm4 cm, about 90 g) was thawed with electromagnetic waves of 60 MH, 100 MHz, 140 MHz, 170 MHz and 300 MHz. The thawing using the electromagnetic waves was performed by prototyping the thawing device disclosed in Patent Literature 4. The output of the electromagnetic waves was set to 25 W, and the electromagnetic waves were applied without the frequency and the output of the electromagnetic waves being changed until the completion of the thawing. The temperature was measured with an optical fiber thermometer (made by ASTECH Corporation) which was inserted to a depth of 2.5 cm in the center portion (2.5 cm from the surface) of the frozen tuna block. In the thawing at 100 MHz disclosed in Patent Literature 4, it takes 20 minutes or more to pass the B zone. It is clear from this information that as compared with the thawing at 60 MHz, the thawing at 100 MH is excellent but this needs to be improved as compared with 140 MHz, 170 MHz and 300 MHz. On the other hand, it is also clear that when electromagnetic waves of 140 MHz or more are adopted, the degree of a rapid temperature increase in the C zone is increased, and thus the risk for boiling is high as compared with 100 MHz. Hence, it is found that it is important to perform thawing at appropriate electromagnetic waves.
Example 2
[0027] FIG. 3 is a diagram showing times necessary for thawing (until 2 C. was reached) when the frozen tuna block was thawed with the electromagnetic waves whose frequencies were changed from 100 to 170 MHz at intervals of 10 MHz. The conditions other than the frequencies used were the same as in Example 1. As shown in FIG. 3, it was found that the thawing time was minimized at 130 MHz and that almost no difference was produced in the thawing time up to 170 MHz. Hence, it was found that in the present example, the application frequencies were preferably ranged from 130 to 170 MHz.
Example 3
[0028] FIG. 4 is a diagram showing times necessary for the center portion of the tuna block to pass the A zone (50 C. to 5 C.) when the frozen tuna block was thawed with the electromagnetic waves whose frequencies were changed from 100 to 170 MHz at intervals of 10 MHz. The performance conditions were the same as in Example 2. As shown in FIG. 4, it was found that almost no difference was produced in an A zone passage required time in a range from 100 to 170 MHz, and it was suggested that the total thawing time significantly depended on a B zone passage required time. This result means that the storage of frozen products in a freezer is not necessarily stable and safe storage, and suggests a possibility that an automatic defrosting operation repeated in the freezer causes a considerable instability factor.
Example 4
[0029] FIG. 5 is a diagram showing times necessary for the center portion of the tuna block to pass the B zone when the frozen tuna block was thawed with the electromagnetic waves whose frequencies were changed from 100 to 170 MHz at intervals of 10 MHz. The performance conditions were the same as in Examples 2 and 3. As shown in FIG. 5, it was found that the thawing time was maximized at 100 MHz used in Patent Literature 4, that the thawing time was minimized at 130 MHz and that almost no difference was produced in the thawing time up to 170 MHz. Since the tendencies of variations in the thawing time for the individual frequencies shown in FIGS. 3 and 5 coincided with each other, it was confirmed again in the present example that the contribution of the B zone passage required time to the total thawing time suggested in Example 3 was significant. It was also made clear from a close examination of data in Example 2 and the present example that at 170 MHz, 27% of the total thawing time was occupied by the B zone and that at 100 MHz, 58% thereof was occupied. Hence, in the present example, as in the result of Example 2, it was confirmed that the application frequencies ranging from 130 to 170 MHz were appropriate for the thawing.
[0030] FIG. 6 is the detailed plots (thawing curves) of variations in the temperature of the center of the tuna Hock at the time of the B zone passage at the individual frequencies in Example 4. Even when any frequency was selected, there was a time zone where the temperature was varied between 3.5 C. and 3.0 C., and it was shown that in the meantime, the melting and re-freezing of ice progressed. It is considered that as the time zone was shorter, the quality after the thawing was more satisfactorily kept. Even when the thawing curves were evaluated based on this viewpoint, as in the evaluation based on FIG. 5, it was confirmed that the application frequencies ranging from 130 to 170 MHz were appropriate for the thawing.
Example 5
[0031] FIG. 7 shows thawing temperatures measured with the optical fiber thermometer (made by ASTECH Corporation) which was inserted to a depth of 2.5 cm in the center portion (2.5 cm from the surface) and the surface (0.5 cm from the surface) of the tuna block when the frozen tuna block was thawed with the electromagnetic waves whose frequencies ranged from 100 to 170 MHz. The other thawing conditions (the size of the frozen tuna block and the frequencies and the output) were the same as in the examples described above. In the thawing, a temperature difference between the surface and the center portion contributes to boiling after the thawing of frozen products, and thus it is possible to evaluate that conditions in which the temperature difference is smaller are more excellent conditions. As shown in FIG. 7, the thawing in which the temperature difference between the surface and the center portion was minimized was the thawing performed by the application of electromagnetic waves whose frequency was 140 MHz. The tendency that as the frequencies were lower or higher than 140 MHz, the temperature difference between the surface and the center portion increased was observed. It was made clear from the overall evaluation of the results of Example 4 and the present example that the electromagnetic waves in an electromagnetic wave band from 130 to 150 MHz were appropriate for uniform thawing and rapid thawing.
Example 6
[0032] FIG. 8 shows results obtained by measuring times required for the center portion of the tuna block to pass the C zone (from 2 C. to 20 C.) when the frozen tuna block was thawed with the electromagnetic waves whose frequencies were 60 MHz, 100 MHz, 140 MHz, 170 MHz and 300 MHz. The other performance conditions were the same as in Example 1. As shown in FIG. 8, at 170 MHz and 300 MHz where the C zone passage required time was short, a burn and boiling occurred in the margin portion of the tuna. Hence, with consideration given to influences in the C zone, it was suggested that it was not appropriate to select the thawing using the electromagnetic waves of 170 MHz or more as frequencies for the thawing in the A zone and the B zone. With consideration given to the results of the examination in the present example and the results of the examination in Examples 4 and 5, it was confirmed that the frequency band appropriate for the thawing was the range from 130 to 150 MHz.
[0033] Since in Example 3 and FIG. 4, the passage required time in the A zone passage was little affected by the frequency selection, the following aspects of the thawing method are effective for performing appropriate thawing. One aspect is to select an arbitrary frequency in the thawing for the A zone passage and then select a frequency in the range from 130 to 150 MHz in a stage where the A zone is transferred to the B zone. The other aspect is to apply the electromagnetic waves of a frequency in the range from 130 to 150 MHz continuously from the A zone to the B zone in order to maximize the effect in the B zone. In the former aspect, the application in the A zone may be performed within the same application device as that for performing the application in the B zone or another application device may be used to perform the thawing in the A zone.
[0034] Based on the examples of the present invention where the temperature changes of the frozen foods in the C zone were observed, in the C zone, the selection of a frequency equal to or more than 170 MHz is not appropriate for pursuing satisfactory thawing quality. Here, with consideration given to the results of the examination in the B zone, it is preferable to also select a frequency for the C zone from the range from 130 to 150 MHz selected for the B zone. Preferably, when the same frequency is used both for the B zone and the C zone, the thawing from the B zone to the C zone is continuously performed with the same application device.
INDUSTRIAL APPLICABILITY
[0035] The present invention provides, instead of a thawing method using the electromagnetic waves of 10010 MHz proposed as a method of thawing frozen agricultural and marine products/processed foods, a technology which is a more rapid, good-quality thawing method without variations in temperature and which can be utilized not only in a fishery industry dealing with frozen products but also in various industries and homes. Since the present invention focuses on the time passage for thawing frozen products, the present invention can be applied in general to the thawing of other foods such as frozen meat, frozen vegetables, frozen seasoning processed foods and other frozen products.
