JP7526573B2 - Method for producing frozen food containing vegetables - Google Patents

Description

The present invention relates to a method for producing vegetable-containing frozen foods.

With the recent development of freezing technology, various types of frozen foods are distributed and sold commercially. However, conventional frozen foods have a problem in that their quality deteriorates due to damage caused by the freezing process. For example, frozen foods that contain vegetables may lose their texture or drip when thawed, which reduces the commercial value of the frozen foods.

A technique for improving the texture and appearance of frozen vegetables is disclosed. Patent Document 1 describes frozen vegetables that have been dry-heat treated before freezing, and that have a drip rate of 7.20% or less when naturally thawed, and a bulk density variation of 1.90 or less when compared with fresh vegetables. Patent Document 2 describes a method for producing frozen foods, which includes immersing deep-fried vegetables in water or a seasoning liquid, and then immersing them in liquid nitrogen. Patent Document 3 describes a method for producing frozen vegetables, which includes a first step of heating the vegetables until the hottest part is 95°C or more, a second step of dehydrating the vegetables obtained by the first step within 5 minutes until the yield is within the range of 70 to 90%, and a step of freezing the vegetables obtained by the second step. Patent Document 4 describes a method for producing frozen foods, which is characterized by suppressing drips that occur during thawing by subjecting cut vegetables to a superheated steam treatment, reducing the moisture content at the same time as the heating treatment, and then performing a freezing treatment. Patent Document 5 describes a method for improving the texture of frozen vegetables such as leafy vegetables and bean sprouts, which involves boiling the vegetables, cooling them in ice water, squeezing them, then immersing them in a seasoning liquid and freezing them.

International Publication No. 2018/159585 JP 2018-201502 A JP 2015-198587 A JP 2006-271352 A JP 2018-170975 A

The present invention provides a vegetable-containing frozen food product that has an improved texture of the vegetables after thawing.

The inventors have discovered that by subjecting vegetables to heat treatment, dehydration, and then immersing the resulting heat-treated vegetables in a seasoning liquid and then freezing them, it is possible to produce frozen vegetables that maintain a good texture even after thawing.

Therefore, the present invention is a method for producing a vegetable-containing frozen food, comprising the steps of:
(a) heating the vegetables by steaming and/or boiling;
(b) dehydrating the heated vegetables obtained in (a) so that the mass of the heated vegetables is 90 to 70% of the mass of the vegetables before heating;
(c) immersing the dehydrated vegetables obtained in (b) in a seasoning liquid;
(d) freezing the vegetables obtained in (c);
The present invention provides a method comprising:

According to the present invention, it is possible to produce high-quality vegetable-containing frozen foods in which the vegetables have a good texture after thawing, without a spongy or stringy texture.

The present invention provides a method for producing vegetable-containing frozen foods. Types of vegetables that can be contained in frozen foods produced by the present invention include, for example, root vegetables such as carrots, lotus root, burdock, and radish; fruit vegetables such as green peppers, paprika, and eggplant; flower vegetables such as broccoli; leafy vegetables such as spinach; stem vegetables such as bamboo shoots and onions; potatoes; fruit vegetables; beans; mushrooms, and the like, with root vegetables and fruit vegetables being preferred. Among these, root vegetables are preferred as vegetables to be contained in frozen foods produced by the method of the present invention, since they tend to have a spongy or stringy texture after thawing. In addition, preferred examples of vegetable-containing frozen foods produced by the present invention include stew-like (for example, Chikuzen-ni-like, etc.) frozen foods.

In the method for producing a vegetable-containing frozen food of the present invention (hereinafter also referred to as the method of the present invention), the vegetables are (a) heated, (b) dehydrated, (c) immersed in a seasoning liquid, and then (d) frozen.

In the method of the present invention, the vegetables to be subjected to the heating step (a) may be cut to an appropriate size as necessary. The size of the vegetables can be appropriately set according to the type and recipe. For example, it is preferable that each piece of the vegetables before heating is 30 g or less.

In the heating step (a), the vegetables are heated substantially without using fats and oils. Here, "heating substantially without fats and oils" means that fats and oils are not used as a heating medium. For example, deep-frying, stir-frying, and grilling using a large amount of oil are not included in "heating substantially without fats and oils". In addition, the heating in the heating step (a) is preferably performed by a method that can maintain the yield of the vegetables, taking into consideration the subsequent dehydration step (b). Preferably, the heating in the heating step (a) is performed by steaming and/or boiling, and more preferably by boiling. The heating by steaming or boiling not only contributes to improving the texture of the frozen vegetables obtained by the method of the present invention, but also improves the flavor by suppressing the grassy odor of the vegetables. Examples of the steaming or boiling method include boiling in hot water and steaming with water vapor. The heating time in the heating step may vary depending on the type and size of the vegetables, but is preferably 1 minute or more, and more preferably 2 to 30 minutes. Short-term heating such as blanching is not included in the heating in the heating step (a). It is not necessary to season the vegetables when heating in the heating step (a), but the use of seasonings (e.g., salt) for other purposes such as preventing discoloration of the vegetables during steaming or boiling is permitted in the heating step (a).
In addition, from the viewpoint of improving the texture of the frozen vegetables after thawing, it is preferable to quickly lower the temperature of the heated vegetables after the heating step (a) and before the step (b) described below. The product temperature of the heated vegetables subjected to the step (b) is preferably 50° C. or less, more preferably 30° C. or less. More preferably, the product temperature of the heated vegetables obtained in the step (a) is preferably lowered to the above temperature within 10 minutes. Examples of means for lowering the temperature of the heated vegetables include running water cooling, air cooling, and cooling in a thermostatic chamber.

In the method of the present invention, the heated vegetables obtained in the heating step (a) are then subjected to the dehydration step (b). In the step (b), the heated vegetables are dehydrated so that the mass of the heated vegetables is 90 to 70%, preferably 90 to 73%, more preferably 90 to 75% of the mass of the vegetables before heating. The dehydration method includes, but is not limited to, microwave heating, oven heating, superheated steam heating, air drying, drying under reduced pressure (e.g., vacuum cooling drying), and any combination thereof. Following the dehydration by the above means, drying and cooling under reduced pressure using cooling equipment such as a vacuum cooler or a differential pressure cooling chamber may be performed. From the viewpoint of maintaining the texture of the vegetables, dehydration by heating or drying at a lower temperature is preferable than dehydration by heating in an environment of 150°C or higher, such as normal oven heating. For example, air drying, superheated steam heating, microwave heating, drying under reduced pressure, or a combination thereof is preferable, and drying under reduced pressure and air drying at room temperature are more preferable. When drying under reduced pressure or air drying, the heated vegetables are preferably dried in an environment of 0 to 100°C, more preferably 0 to 85°C, and even more preferably 0 to 50°C. Before drying under reduced pressure or air drying, the product temperature of the heated vegetables may be increased to promote evaporation of water. For example, the heated vegetables may be heated at a temperature of 100°C or less, and then dried under reduced pressure or air dried.

In the soaking step (c), the dehydrated vegetables obtained in the step (b) are soaked in a seasoning liquid. If necessary, the dehydrated vegetables may be allowed to cool before the soaking. The seasoning liquid is preferably a liquid containing sugar or salt, and more preferably a liquid containing sugar and salt. Examples of the seasoning liquid include water containing seasonings (e.g., salts, sugars, mirin, sake, soy sauce, miso, etc., and mixed seasonings obtained by mixing any of them), liquid seasonings (noodle soup, liquid sauce, etc.) or dilutions thereof, and mixtures thereof. Examples of the sugars include sucrose, trehalose, fructose, glucose, etc., and any one or a combination of two or more of these can be used. Preferably, the sugars include trehalose. Examples of salts include table salt. The concentrations of sugar and salt in the seasoning liquid may be appropriately changed according to preference. For example, in the seasoning liquid, the sugar concentration is preferably 2 to 25% by mass, more preferably 4 to 22% by mass, and the salt concentration is preferably 0.3 to 8.0% by mass, more preferably 0.5 to 5.0% by mass.

The temperature of the seasoning liquid during the immersion is not particularly limited. For example, the seasoning liquid may be chilled (e.g., about 4°C), room temperature (e.g., about 20°C), or heated to 80°C or higher. From the viewpoint of the infiltration of the seasoning liquid into the vegetables, the temperature of the seasoning liquid is preferably 20°C or higher, more preferably 35°C or higher, and even more preferably 50°C or higher. The amount of the seasoning liquid used for the immersion may be an amount that allows the entire dehydrated vegetables to be immersed in the seasoning liquid. The time for immersing the dehydrated vegetables in the seasoning liquid can be changed depending on the size of the vegetables, the temperature of the seasoning liquid, etc., but is preferably 5 minutes or more, more preferably 10 to 60 minutes, and even more preferably 15 to 40 minutes. The vegetables are preferably immersed in a seasoning liquid of 35°C or higher for 5 minutes or more, preferably 10 to 60 minutes, and more preferably 15 to 40 minutes. At this time, the higher the temperature of the seasoning liquid used, the shorter the immersion time that can be adopted. For example, if the seasoning liquid is 20 to 50°C, the soaking time may be preferably 15 to 60 minutes, more preferably 30 to 40 minutes. Alternatively, if the seasoning liquid is 50 to 80°C, the soaking time may be preferably 10 to 40 minutes, more preferably 15 to 40 minutes.

In the method of the present invention, the vegetables soaked in the seasoning liquid obtained in step (c) are then frozen in the freezing step (d). If necessary, before step (d), the surface moisture of the vegetables soaked in the seasoning liquid may be lightly removed by draining them. Alternatively, the vegetables may be frozen together with the seasoning liquid. The means of freezing in step (d) is not particularly limited, but quick freezing by air blast or the like is preferred.

The vegetables frozen in step (d) may be stored under normal freezing conditions (e.g., -18°C or lower). The vegetable-containing frozen food provided by the present invention contains the frozen vegetables obtained by the above procedure. The frozen food provided by the present invention may contain only the frozen vegetables, but may also contain other ingredients. There is no particular limitation on the type of the other ingredients.

The method of thawing the vegetable-containing frozen food produced by the present invention is not particularly limited, and includes slow thawing such as room temperature thawing, low temperature thawing, and thawing in running water, and rapid thawing such as thawing with microwave heating. The frozen food produced by the method of the present invention prevents deterioration in texture of frozen vegetables due to the freezing and thawing processes, and the vegetables are less likely to have a spongy or stringy texture even after thawing.

Examples are provided to specifically explain the present invention, but the present invention is not limited to the following examples.

Test Example 1
1. Ingredients (1-1) Vegetables Peel the vegetables and prepare the following cut vegetables.
Carrots: 7 g each, chopped into random pieces Burdock: 7 g each, chopped into random pieces Radish: cut into 1 cm thick pieces and cut into 6 ginkgo pieces The mass of each cut vegetable piece was measured.

(1-2) Seasoning Liquid A seasoning liquid (sugar content 19.2%, salt content 1.6%) was prepared by thoroughly mixing 70% water, 10% soy sauce, and 20% trehalose.

2. Production of frozen vegetables: Boiling → Dehydration → Soaking (2-1) Boiling and heating The cut vegetables from (1-1) were placed in boiling water, brought to a boil again, and boiled for the following times.
Carrot: 5 minutes Burdock: 10 minutes Radish: 5 minutes The boiled vegetables were cooled under running water for 1 minute, then drained and left to cool at room temperature (about 25° C.) for 15 minutes.

(2-2) Dehydration The heated vegetables obtained in (2-1) were dehydrated under the following conditions. The mass of the vegetables after the dehydration was measured.
(i) Microwave: The vegetables were heated in a microwave oven (200 W) for 2 minutes 30 seconds to 6 minutes. After that, the vegetables were cooled to about 10°C at -0.1 MPa in a vacuum cooler (MIURA CMJ-20).
(ii) Vacuum cooling: The vegetables were reheated in a steam convection oven (Fujimak SelfCooking Center XS) in steam mode (100°C, 100%) for 8 minutes. After that, the vegetables were cooled to about 10°C at -0.1 MPa in a vacuum cooler (MIURA CMJ-20).
(iii) Vacuum cooling: The vegetables were left in a thermostatic chamber (80°C, humidity 20%) for 25 minutes, and then cooled to about 10°C at -0.1 MPa in a vacuum cooler (MIURA CMJ-20).

(2-3) Immersion The seasoning liquid (1-2) and the vegetables obtained in (2-2) were added to a pouch, which was then sealed and treated for 15 minutes in a water bath at 80° C. The treated cooked vegetables were quickly cooled in water together with the pouch.

(2-4) Freezing The soaked vegetables obtained in (2-3) were frozen together with the pouch for 2 hours by air blast cooling (with HOSHIZAKI HBC-12B3, at −40° C. and air speed set at 6). The frozen vegetables were stored frozen at −20° C. for 1 week to obtain a stew-like frozen food.

3. Production of frozen vegetables: oven heating → soaking (3-1) Oven heating The cut vegetables of (1-1) were placed in an oven at 100°C or 180°C and heated for 6 to 10 minutes. The heated vegetables were cooled to 10°C at -0.1 MPa in a vacuum cooler (MIURA CMJ-20). The mass of the vegetables after cooling was measured.

(3-2) Soaking The vegetables obtained in (3-1) were soaked in seasoning liquid in the same manner as in (2-3).

(3-3) Freezing The vegetables obtained in (3-2) were frozen in the same manner as in (2-4), and stored frozen for one week to obtain a stew-like frozen food.

4. Production of frozen vegetables: heating with seasoning liquid → freezing The cut vegetables (1-1) were boiled in the seasoning liquid (1-2) for 20 minutes. In some cases, the vegetables were then dehydrated using the procedure in (2-2) (i) and then frozen using the same procedure as in (2-4), and stored frozen for one week.

5. Evaluation Test The frozen foods produced in 2. to 4. above were frozen for one week, then thawed at 10°C for three hours, and the texture of the thawed vegetables was subjected to a sensory evaluation according to the following evaluation criteria. In the evaluation, evaluations were obtained from five trained evaluators, and for the spongy texture, if four or more out of the five people rated it as ○, it was judged as ○, and if less than four people rated it as ×. For hardness, the average score of the five people was calculated. The results are shown in Tables 1 to 3.
(Sponge-like texture)
○: The sponge-like texture is not noticeable.
×: The texture is spongy and poor.
(Hardness)
4 points: Moderate hardness.
3 points: Somewhat stringy.
2 points: Streaky and slightly defective.
1 point: Significant streaking, poor quality;

Test Example 2
Carrots were treated in the same manner as in Production Example 1-1 to obtain a stew-like frozen food. However, in the soaking treatment (Procedure (2-3)), the temperature of the water bath was changed to 25°C, 50°C, or 80°C, and the treatment time was changed to 5 minutes, 15 minutes, or 30 minutes. The frozen foods stored in a freezer for one week were thawed at 10°C for three hours, and the penetration of the seasoning liquid into the thawed vegetables and the texture of the vegetables were subjected to a sensory evaluation. The evaluation was performed by five trained evaluators. The penetration of the seasoning liquid was evaluated according to the following evaluation criteria, and the average score of the five evaluators was calculated. The texture of the vegetables (sponge-like texture and hardness) was evaluated according to the same criteria as in Test Example 1. The results are shown in Table 4.
(Seasoning liquid soaks in)
4 points: The seasoning is absorbed better than the control product, and the vegetables and seasoning are very well integrated (more like a stew).
3 points: The seasoning is absorbed slightly better than the control product, and the vegetables and seasoning are more integrated (it feels a bit more like a stew).
2 points: Same consistency as the control product 1 point: The seasoning is not absorbed as well as the control product, and the consistency between the vegetables and the seasoning is poor (less like a stewed dish)

Claims (4)

A method for producing a vegetable-containing frozen food, comprising the steps of:
(a) heating the vegetables by steaming and/or boiling;
(b) dehydrating the heated vegetables obtained in (a) so that the mass of the heated vegetables is 90 to 75 % of the mass of the vegetables before heating;
(c) immersing the dehydrated vegetables obtained in (b) in a seasoning liquid at 50 to 80°C for 10 to 60 minutes ;
(d) freezing the vegetables obtained in (c);
A method comprising: The method of claim 1, wherein the vegetables include root vegetables. The method according to claim 1 or 2, wherein the seasoning liquid contains sugar or salt. The method according to any one of claims 1 to 3, wherein the vegetables are cut into pieces having a size of 30 g or less.