JPS62201540A - Vacuum expansion drying of vegetable - Google Patents

Abstract

PURPOSE:To obtain dried vegetables having improved reconstituting property without weight loss in drying, by previously wetting the surface of a vegetable with water, vacuum expanding the wetted vegetable under specific condition, drying the expanded vegetable while heating and returning the pressure to ordinary pressure. CONSTITUTION:The surface of a vegetable, e.g. potato, broad bean, etc., is wetted by a method for dipping in water, etc. The resultant wetted vegetable is then placed under reduced pressure condition at a speed sufficient to expand the vegetable at a relatively high speed and vacuum degree sufficient to freeze water in the vegetable, specifically <=600 Pa and kept under the condition until the water in the above-mentioned vegetable is frozen. The resultant frozen vegetable is then dried while heating by a method, e.g. infrared heating, microwave heating, etc., and the pressure is returned to ordinary pressure to afford the aimed vegetable capable of reconstituting to give the sense of eating after reconstitution in a short time by pouring hot water, etc., almost the same as that before drying.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a vacuum swelling drying method for vegetables. This invention relates to a vacuum swelling drying method for vegetables that can obtain dried vegetables that can be restored in a short period of time without changing.

<Prior Art> Many instant foods that can be easily reconstituted by adding hot water or the like have been developed in the past, and along with this, a wide variety of research and development have been conducted on drying techniques.

Typical examples include hot air drying, microwave drying, freeze drying, deep-frying, and vacuum drying. Furthermore, there is a swelling drying method in which the material to be dried is exposed to a flow of superheated steam under pressure for a short time, heated and dehydrated, and then rapidly released into the atmosphere to obtain a swollen product.

<Problems to be Solved by the Invention> The dried foods prepared by such conventional drying methods have a disadvantage in that satisfactory restorability, especially texture after restoring, cannot be obtained.

The present applicant has developed a previously filed vacuum swelling drying method for foods as a method for obtaining dried foods that overcome these drawbacks (Japanese Patent Application No. 135469/1982).

The gist of this is that the food is placed under a rapid depressurization condition that causes the moisture in the food to freeze at a rate sufficient to cause the food to swell, and after the moisture in the food freezes, the food is heated and dried. This is a vacuum swelling drying method for foods that is characterized by returning the food to pressure.

However, in the case of vegetables such as potatoes, sweet potatoes, green peas, carrots, and asparagus, the above-mentioned methods have not always produced satisfactory vegetables in terms of drying-thinning and restorability.

<Means for Solving the Problem> In order to solve these problems, the inventors of the present invention have conducted various studies and found that, before the vegetables are subjected to vacuum swelling and drying treatment, the surfaces of the vegetables are wetted with water in advance. The present invention was completed based on the knowledge that the above-mentioned problems could be solved by applying the following methods.

The gist of the present invention, which has been completed in this way, is that after the surface of the vegetables is moistened, the vegetables are treated relatively quickly at a rate sufficient to cause the vegetables to swell, and the moisture in the vegetables is removed. This is a vacuum swelling drying method for vegetables, which is characterized by placing the vegetables under a rapid reduced pressure to the extent that they freeze, heating and drying the vegetables after the moisture in the vegetables freezes, and then returning the pressure to normal pressure.

Hereinafter, the content of the present invention will be explained in detail.

Vegetables that can be dried according to the present invention include tubers such as potatoes and sweet potatoes, legumes such as green peas and fava beans, root vegetables such as carrots and daikon radish, stem and scale vegetables such as asparagus, lily, and bamboo shoots, kapocha, Fruit vegetables such as cucurbits.

In the present invention, the surface of such vegetables is first subjected to a wet treatment, but before that, the vegetables may be processed by cutting, slicing, shaping, etc. into appropriate sizes. It is preferable to make the width 20 mm or less from the viewpoint of achieving the object of the present invention. Furthermore, boiling treatment may be performed. By pre-boiling the vegetables, the tissue of the vegetable becomes easier to loosen, and tissue gaps are more likely to be formed during vacuum swelling.

Examples of methods for moistening the surface of vegetables include water immersion and water spraying. This treatment slightly increases the moisture content on the surface of vegetables, specifically 2
An increase of about 10% by weight is preferred. This can prevent the surface of the vegetables from drying and thinning during the subsequent step of vacuum swelling drying. As a result, the restorability of the obtained dried product can be improved.

Furthermore, it is also possible to improve drying efficiency.

Vegetables whose surfaces have been moistened will be more easily invaded.
Preferably, the vacuum swelling treatment is carried out within 1 minute. As the time until the vacuum swelling treatment becomes longer, the moisture on the surface of the vegetables gradually dries out or drips, making it impossible to maintain a desirable moisture adhesion, and as a result, the objective of the present invention cannot be achieved. It's getting difficult.

Next, in the vacuum expansion treatment, the following two conditions must be satisfied.

The first condition is to subject the vegetables to a certain reduced pressure quickly enough for puffing to occur. Here, the speed sufficient to cause the vegetables to swell refers to the speed sufficient to cause the moisture in the vegetables to evaporate rapidly in a short period of time. In general, the swelling phenomenon caused by water evaporation of various vegetables differs depending on the type of vegetable, and the speed sufficient for the swelling of vegetables to occur also varies depending on the type of vegetable, but it is preferably within 1 second. .

Next, the condition M2 is to make the specific degree of reduced pressure mentioned in the first condition above a degree of reduced pressure sufficient to cause the moisture in the vegetables to freeze. Specifically, it is about 600 Pascal or less, preferably about 106 Pascal or less.

After the above two conditions are satisfied and the vegetables are placed under reduced pressure, they are held until the moisture in the vegetables freezes, preferably until the moisture in the vegetables freezes and the product temperature no longer decreases. By this treatment, the shape of the swollen vegetables is maintained as it is, and the dried vegetables that are finally 19 are brought into a swollen state, thereby making it possible to speed up restoration using hot water or the like. Above 2
The following two methods of decompression can be used to satisfy the following two conditions:
There is one.

The first method involves puffing the vegetables and freezing the water in the vegetables in one step. In other words, the vegetables are placed under reduced pressure to the extent that the water in the vegetables freezes. It's a way to keep it fast enough for it to happen. According to this method, the swelling of the vegetables and the freezing of the vegetables occur almost instantly.

The second method involves puffing the vegetables and freezing the water in the vegetables in two stages. The vegetables are swollen under a reduced pressure that does not reach a degree of reduced pressure sufficient for
- This is a method of lowering the pressure to a degree of vacuum. According to this method, the swelling of vegetables and the freezing of water in the vegetables occur separately over time.

The drying process is performed after the moisture in vegetables is frozen by the method described above, but the purpose of the present invention can be achieved by heating and drying at any time after the vegetables have frozen. Although there is no problem from above, it is preferable to heat and dry the frozen vegetables when the temperature of the frozen vegetables becomes constant. The above-mentioned heat drying is carried out using conventional heating means such as infrared heating and microwave heating, but it is most preferable to use an auxiliary heating method such as infrared rays, and the heating temperature should be such that the product temperature is 60°C or less. preferable.

Dried vegetables, which are the object of the present invention, are obtained by the method described above.

<Examples> Example 1 Four potatoes (approximately 300 g) were washed with water, peeled, and cut into a size of 10 mm x 10 mm x 10 mm. Approximately 2 diced potatoes obtained in this way
00g was boiled for 6 minutes.

Thereafter, the hot water was drained and the product was placed on a mesh tray, and after water was poured onto it, it was immediately placed in a vacuum drying device, and the degree of vacuum in the vacuum drying device was reduced to about 3000 Pascal within 1 second. After that, the pressure inside the vacuum drying device was increased to 50
Pascal, and heat drying using a heater was started 5 minutes after the start of pressure reduction. For heating drying, the heater temperature is 100℃.
for 30 minutes, and then at a heater temperature of 50° C. for 4 hours and 30 minutes. Thereafter, the pressure inside the vacuum drying device was gradually returned to normal pressure to obtain diced dried potatoes. The dried potatoes thus obtained had a good appearance without dryness and were good in terms of restorability.

Example 2 Two sweet potatoes (approximately 350 g) were treated in the same manner as in Example 1 to obtain dice-shaped dried sweet potatoes.The dried sweet potatoes thus obtained had a good appearance without dryness. I am.

It was also good in terms of restorability.

Example 3 Two Western carrots (approximately 300 g) 8 mm x 8 m
It was cut into shoestring shapes measuring m x 40 mm.

This was boiled in 0.3% saline for 5 minutes. after that,
Dried carrots were obtained in the same manner as in Example 1 except that the initial temperature of the heater was 80° C. for 30 minutes. The dried carrots obtained were of good quality.

Comparative Examples Example 1 for potatoes, Example 2 for sweet potatoes, and Example 3 for carrots, except that all potatoes, sweet potatoes, and carrots were not treated with water before the vacuum swelling and drying treatment. Dried potatoes, dried sweet potatoes, and dried carrots were obtained by processing in the same manner. The obtained dried potatoes, dried sweet potatoes, and dried carrots were slightly dry and thin, and their appearance was not necessarily satisfactory.

The restorability of dried potatoes, dried sweet potatoes, and dried carrots obtained according to the present invention and comparative examples was immersed in hot water and confirmed from changes in water absorption over time. The results are shown in Tables 1-3 and Figures 1-3. Note that the water absorption amount is calculated by converting the weight after immersion into the weight when the sample before immersion is 1 g. In addition, in the figure, the vertical axis represents the weight of the sample,
The horizontal axis represents immersion time. In each table, 1 represents the amount of water absorbed by the example amount of the present invention, and 2 represents the change over time in the amount of water absorbed by each amount of the comparative example.

(Margins below) Table 1 (Potatoes) Table 3 (Carrots) As is clear from Tables 1 to 3 and Figures 1 to 3, dried potatoes, dried sweet potatoes, and dried carrots obtained by the method of the present invention are The hot water absorption rate is better than those obtained by the comparative method. This does not indicate that the product obtained by the method of the present invention has better restorability with hot water or the like.

According to the present invention, even for vegetables for which conventional drying methods did not always give satisfactory results in terms of drying, shading, and restoring properties, the present invention can produce dried vegetables that do not suffer from dryness and are full of restoring properties. can be obtained.

[Brief explanation of drawings]

Figures 1 to 3 are drawings showing changes over time in water absorption m in hot water of dried vegetables obtained in Examples 1 to 3 and Comparative Example (thus obtained).

Claims (1)

[Claims] After the surface of the vegetables is moistened with water, the vegetables are relatively quickly subjected to a rapid decompression state at a rate sufficient to cause the vegetables to swell and to the extent that the water in the vegetables freezes; A vacuum swelling drying method for vegetables, which comprises heating and drying after the moisture in the vegetables has frozen, and then returning the pressure to normal pressure.