JPH0354547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a simple method for freezing foods that can efficiently suppress cell destruction and freeze them.

[Conventional technology]

There are various ways to preserve food, such as drying and salting, but the frozen preservation method, which keeps food below the freezing temperature and freezes it, has become widely used because it allows fresh food to be preserved in its raw state. ,
It has become deeply ingrained in our daily lives through distribution using cold chains and freezing preservation in home freezers.

By freezing food, self-digestion caused by degrading enzymes contained in the food and spoilage caused by bacteria are suppressed, and it becomes possible to preserve the food for a long period of time.

However, fresh foods such as fish, meat, and vegetables usually contain 65 to 95 wt% water, and this water turns into ice crystals when frozen, expanding their volume by about 10%.
Furthermore, the cells are destroyed by the sharp edges of the ice crystals,
When thawing, some of the useful ingredients leak out in the form of drips, resulting in lower quality compared to products that are not frozen.

As a method for suppressing the cell destruction caused by ice crystals, there is a rapid freezing method (special method) in which food is brought into contact with liquid nitrogen, etc. to quickly freeze it, and the ice crystals are made finer to suppress the growth of the ice crystals and cell destruction. Kosho 58−
26950, etc.), a method of freezing by removing part of the moisture before freezing to reduce the volumetric expansion of ice (Japanese Patent Application Laid-open No. 60-130332, JP-A No. 61-166350, etc.),
A method of pre-chilling the entire food to near the freezing point and then cooling it to generate fine ice crystals (Japanese Patent Publications No. 57-35950, No. 59-22509, No. 59)
-41391, etc.).

In particular, the rapid freezing method is widely used as a method for freezing foods distributed in cold chains and the like because frozen foods can be efficiently produced using industrial equipment. However, since it uses liquid nitrogen, it has the disadvantage of high manufacturing costs.

[Problem that the invention seeks to solve]

However, in the quick freezing method, the outer surface is brought into contact with ultra-low temperature to generate microscopic ice crystals, but if an excessive temperature difference is applied between the outer surface and the inside of a thick food, the food may expand and break. However, there are limits to the cooling rate, making it difficult to uniformly generate fine ice crystals throughout the interior. In this method, cell destruction caused by ice crystals can be suppressed to a considerable extent due to dehydration, but it is not perfect. Another method is to cool the food in advance to near the freezing point, reduce the temperature difference between the inside and outside, and control the freezing rate to prevent destruction due to volume expansion during freezing, and to generate fine ice crystals to freeze the food. However, cell destruction cannot be completely prevented, and the freezing cycle is complicated and freezing takes a long time.

The present inventors found that although the above conventional methods cannot completely prevent cell destruction because they cool and freeze the food from the outside surface, they cool the food from the inside to generate fine ice crystals, and then completely freeze the food. I thought that this would prevent cell destruction.

In order to cool food from the inside and generate fine ice crystals, it is sufficient to first bring it into a supercooled state and then release it.

The present invention was developed based on the above considerations, and an object of the present invention is to provide a method for cooling foods that causes almost no deterioration in quality.

[Means for solving problems]

The present invention has been made to achieve the above object, and its gist is to perform a dehydration process to uniformly dehydrate food, supercool it to below the freezing temperature of the food in a stationary state, and then release the supercooled state. There is a method of freezing food in which the entire food is frozen by continuing cooling.

[Effect]

Since the method of the present invention dehydrates the food more uniformly, the concentration of water-soluble components in the food rises, supercooling easily occurs, and once the supercooling state is released, the food is instantly dehydrated. microcrystals of ice are formed. Since this state is followed by cooling and freezing, cell destruction due to ice crystal growth does not occur.

Foods targeted in the method of the present invention include those that can be used as frozen foods, such as fresh seafood, raw meat, fresh vegetables, fruits, heat-treated vegetables, starch foods, and processed foods.

In general, it is difficult to achieve a supercooled state by simply cooling the food mentioned above, but surprisingly, it is possible to uniformly dehydrate the food and remove impurities such as sugars, salts, proteins, and amino acids in the food. By increasing the concentration of the frozen component and leaving it to cool, a supercooled state can be easily achieved.

The above-mentioned dehydration requires uniform dehydration of food, and contact dehydration sheets using osmotic pressure, which have been developed rapidly in recent years (Japanese Patent Publication No. 59-58124, Japanese Patent Application Laid-open No. 61
-249341, etc.), or contact with a high osmotic solution through a water-permeable semipermeable membrane (Japanese Patent Application No. 60-217202, etc.), either of which can be used.

The above-mentioned supercooled state is caused by sound waves being applied to the supercooled food.
It can be easily released by applying a shock such as mechanical vibration or thermal shock.

At this time, the temperature of the food instantly rises to the freezing temperature of the food, and ice crystals are formed, but because the speed is extremely fast, many fine crystals are formed, and the subsequent growth of ice crystals freezes the cells. Prevent destruction.

The operating procedure of the freezing method of the present invention is shown in FIG. 1. That is, (a) Dehydration treatment is performed to uniformly remove water in food.

(b) Cool in a freezer with minimal vibration and temperature fluctuations.

(c) Bringing food to a supercooled state below freezing temperature.

(d) Apply shock to release the supercooled state. This returns the food to freezing temperature and at the same time creates fine ice crystals within the food.

(e) Continue cooling in the freezer to complete freezing.

(f) Foods are kept at -18℃ or below for frozen storage or distribution.

Next, the method of the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 Raw saury was wrapped in a dehydrating sheet (manufactured by Showa Denko K.K., trade name: Pichitsuto Sheet), and its weight was
2wt% was dehydrated and used as a specimen. A thermometer was inserted into the center of this sample, and the sample was left standing in a freezer at -10 to -12°C, and the change in temperature at the center of the sample over time was measured.
The results are shown in Figure 2.

Part A in the figure shows a supercooled state. Part B shows the heat generated when the supercooled state is released and the sample freezes. Also C
indicates the freezing temperature of the specimen.

In this sample, there was almost no freezing destruction of the cells, and a good frozen food was obtained.

Comparative Example 1 A specimen was frozen in the same manner as in Example 1, except that no dehydration treatment was performed. The results are shown in Figure 3.

As is clear from the comparison between Figures 2 and 3, Figure 3 shows a normal freezing curve, with no supercooling, and the resulting frozen food had many drips due to freezing breakdown. . Furthermore, the freezing temperature C showed a slightly higher value than in Example 1.

Example 2 Raw red sardine was dehydrated using a sheet (manufactured by Showa Denko Co., Ltd.,
Wrap it in Pichitsuto Sheet (product name) and
27wt% was dehydrated and used as a sample. A thermometer was inserted into the center of the specimen, and it was placed in a freezer at -23°C.
Temperature over time was measured. The results are shown in Figure 4.

Part A shows a supercooled state, part B shows heat generated by instantaneous freezing after the supercooled state has been released, and part C shows the freezing point of the specimen.

No cryolysis destruction of cells during freezing was observed in this specimen.

Comparative Example 2 A specimen was frozen in the same manner as in Example 2, except that no dehydration treatment was performed. The results are shown in Figure 5.

As is clear from the comparison between Figures 4 and 5, Figure 5 shows a normal freezing curve, there was no supercooling state, and the obtained frozen food had many drips due to freezing breakage. . Furthermore, the freezing temperature C showed a considerably higher value than in Example 2.

〔Effect of the invention〕

As described above, the food freezing method according to the present invention uniformly dehydrates the food to bring it into a supercooled state, and by releasing the supercooled state, micro ice crystals are instantly generated in the food, and then Cell destruction is prevented by the simple operation of whole freezing, which greatly contributes to the frozen preservation of fresh foods.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the operating procedure of the method of the present invention,
FIG. 2, FIG. 3, FIG. 4, and FIG. 5 are diagrams showing the temperature over time of Example 1, Comparative Example 1, Example 2, and Comparative Example 2, respectively.

Claims (1)

[Claims] 1. After applying dehydration treatment to uniformly dehydrate the food, supercooling the food to below the freezing temperature of the food in a stationary state, canceling the supercooling state, and continuing cooling to freeze the whole food. A food freezing method characterized by: 2. The method for freezing food according to claim 1, wherein the dehydration treatment for uniformly dehydrating the food is a method of bringing the food into contact with a substance whose osmotic pressure is higher than the osmotic pressure of the food through a water-permeable semipermeable membrane. . 3. The method of freezing food according to claim 1 or 2, wherein the method for releasing the supercooled state is a method of applying shock to the supercooled food.