Method of producing frozen vegetable

Abstract

To provide a method of producing frozen vegetable.SOLUTION: A method of producing frozen vegetable comprises the step of: (i) a) performing heating treatment on a vegetable in the presence of additives selected from salt, fat, alcohol, amino acid, saccharide, or a group comprising combination thereof, or b) performing heating treatment on the vegetable and then adding additives selected from salt, fat, alcohol, amino acid, saccharide, or the group comprising combination thereof to the heat-treated vegetable; (ii) cooling the heat-treated vegetable (i) by leaving the vegetable to stand for under the condition of temperature between -9°C and -15°C, and as a result, the vegetable (i) goes in a supercooled state, then the supercooled state is released; and (iii) freezing the vegetable (ii). Herein, the heating treatment (i) is performed in such s degree that cellular tissue of the vegetable is not broken after the freezing treatment (iii).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing frozen vegetables and the produced frozen vegetables.

Background Art

[0002] Freezing treatment of wild vegetables Food freezing technology enables long-term preservation of food and subsequent convenient cooking, greatly contributing to the improvement of eating habits. However, this food freezing technology is still a technology under research and leaves room for consideration. The freezing technology for fresh agricultural products such as vegetables is one of them.

[0003] Conventionally, in freezing vegetables, in order to suppress enzymatic changes during storage, a combination of pretreatment such as blanching (heat treatment) and rapid freezing methods has been used. Blanching is a heat treatment such as boiling or steaming when making frozen vegetables. By performing such preliminary heat treatment, the enzymes in the vegetables are inactivated, thereby suppressing changes in nutritional components and color tone. The processing conditions of blanching are often based on the inactivation of heat-resistant enzymes peroxidase and catalase for that purpose. On the other hand, if heat treatment is applied, the vegetables become soft and softened.

[0004] Also, rapid freezing technology is a technology that suppresses texture deterioration of food by passing through the maximum ice crystal formation zone (-1 to -5 °C) where the ice crystal growth temperature in the food is slow in a short time. It is widely used for general foods, and for blanched vegetables, rapid freezing is widely used commercially because tissue damage can be reduced by rapid freezing. However, among plant-based materials, for fresh vegetables, their texture cannot be maintained even by rapid freezing.

[0005] Supercooling Supercooling refers to a state in which, during the phase transition of a substance, its state does not change even below the temperature at which it should change. For example, it is a phenomenon in which a liquid is cooled below its freezing point (transition point) but does not freeze and remains in a liquid state. In the case of water, it refers to a state where it does not freeze even below 0°C.

[0006] Regarding food as well, after generating this supercooled state, a method has recently been proposed in which the supercooled state is released at a temperature lower than the original freezing temperature and then frozen all at once (supercooling freezing) to uniformly generate fine ice crystals and suppress the destruction of food tissue by ice crystals during freezing. However, in food supercooling technology, the cooling rate when achieving the supercooled state is slow, and there is a possibility that the quality of the food may deteriorate due to oxidation, bacterial growth, etc. Also, since the supercooled state is unstable, supercooling is likely to be released before the lowest achievable temperature in the supercooled state reaches deep enough, and when the lowest achievable temperature is shallow, there are few ice nuclei that can be formed when it is released, resulting in problems such as inability to achieve high-quality freezing.

[0007] In food freezing, the form of ice crystals greatly affects the final quality of the food. The paper by Kobayashi et al. (Transactions of the Japan Society of Refrigeration and Air Conditioning Engineers, Vol. 31, No. 3 (2014), p. 297 - 303) (Non-Patent Document 1) details the influence of the supercooling phenomenon during food freezing on the form of ice crystals and drip using tofu. In this paper, it is summarized that "in practical application of the supercooling freezing method, in addition to more detailed examination of conditions such as the supercooling release temperature and the cooling rate after release, it is also necessary to establish a highly reproducible method for maintaining the supercooled state, that is, to study the control method of supercooling." It has been difficult to produce a stable supercooled freezing state for foods, especially vegetables with a high water content.

[0008] The longer the supercooled state is maintained and the larger the supercooling gap (the temperature difference between the supercooling release point and the freezing point), the more the amount of ice nuclei generated after supercooling release increases, and finer ice crystals can be formed, making it easier to retain cells. Conventionally, a technique of "heating before supercooling" has been proposed as a method for maintaining the supercooled state, but depending on the type of vegetables, fruits, environment, etc., sufficient effects that can be industrially produced have not been obtained.

[0009] WO2019 / 235515 (Patent Document 1) describes a method for freezing vegetables or fruits. The freezing method in this document is based on the discovery that a supercooled state can be generated by moderately heating the vegetables and then cooling the heated vegetables, that the supercooling is automatically released and the vegetables are frozen, and that vegetables that have been subjected to a heating process and then a supercooled state and then frozen tend to maintain their pre-freezing texture even after thawing.

[0010] [Claim 1 of Patent Document 1] A method for freezing vegetables or fruits, comprising the steps of: (i) heat-treating the vegetables or fruits; (ii) cooling the vegetables or fruits of (i), thereby placing the vegetables or fruits in a supercooled state, and then removing the supercooled state; and (iii) freezing the vegetables or fruits of (ii); Including, Here, the heat treatment in (i) is a heat treatment to such an extent that the cellular tissue of the vegetable or fruit is not destroyed even after the freezing treatment in (iii). The freezing method.

[0011] Patent Document 1 particularly describes that the texture is improved by setting the supercooling temperature at -9°C or lower. Frozen wild vegetables using fats, seasonings JP 2018-201502 (Patent Document 2) describes a method for producing frozen foods, which includes immersing fried vegetables in water or a seasoning liquid and then immersing them in liquid nitrogen.

[0012] JP-A-2018-170975 (Patent Document 3) describes a method for improving the texture of frozen vegetables. The method described in the document includes a step of boiling and heating the vegetables, a step of immersing them in a seasoning liquid, and a step of freezing. The step of boiling and heating is a step of heating for 30 to 60 seconds, the step of immersing in the seasoning liquid is a step of applying the seasoning liquid and soaking for 60 to 180 seconds, a step of cooling with ice water and squeezing is provided after the step of boiling and heating, a step of immersing in the seasoning liquid is provided after the step of cooling with ice water and squeezing, and finally a step of freezing is provided. Specifically described as a seasoning is soy sauce.

[0013] JP-A-2021-103963 (Patent Document 4) describes a method for producing frozen strawberries. The method is to coat the once-frozen strawberries with a jelly liquid and then perform secondary freezing.

[0014] All of Patent Documents 2 to 4 are premised on rapid freezing and do not mention supercooling at all.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0016]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0017] Even after freezing and thawing, a technique that results in less drip and maintains the texture in vegetables and the like has been desired. It has been known that by using supercooling technology, the frequency of ice nucleus generation during freezing increases and the growth of ice crystals can be suppressed, thus improving the texture. However, stable supercooling has not been achievable. Patent Document 1 proposes a technique of heating the object before supercooling, but depending on the type of vegetable, environment, etc., sufficient effects for industrial production have not been obtained.

Means for Solving the Problems

[0018] As a result of intensive research to solve the above problems, the inventors of the present invention have found that when performing heat treatment before supercooling, by further adding salts, fats and oils, alcohols, amino acids, saccharides, etc., supercooling can be performed more stably, and thus the present invention has been conceived.

[0019] Although not limited thereto, the present invention includes the following aspects. [1] A method for producing frozen vegetables, comprising: (i) a) Heat-treating the vegetables in the presence of an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides or combinations thereof; or b) Heat-treating the vegetables and then adding an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides or combinations thereof; (ii) Allowing the vegetables of (i) to stand and cool under conditions of -9°C to -15°C, whereby the vegetables are in a supercooled state and then the supercooled state is released; and (iii) Freezing the vegetables of (ii), including wherein the heat treatment of (i) is a heat treatment to such an extent that the cell tissue of the vegetables is not destroyed even after the freezing treatment of (iii). The above method.

[0020] [2] The method according to [1], wherein in step (ii), the difference between the temperature at which the vegetables processed in step (i) are released from the supercooled state and the freezing point of the vegetables processed in step (i) is 5°C or more.

[0021] [3] The method according to [1], wherein the additive is salts and is added as a saline solution of 0.5% by weight to 20% by weight.

[0022] [4] The method according to [1], wherein the addition amount of the additive is 0.5% by weight or more of the weight of the vegetables. [5] The method according to [1], wherein the heat treatment step in (i) is carried out under the conditions of 60°C to 300°C.

[0023] [6] The method according to [1], wherein the heat treatment step in (i) is carried out for 5 seconds to 600 seconds. [7] The method according to [1], wherein the heat treatment in (i) is carried out by superheated steam heating, steaming, stir-frying, blanching heating, or deep-frying.

[0024] [8] The method according to [1], wherein the vegetables are selected from the group consisting of root vegetables, leafy vegetables, fruit vegetables, and spice vegetables.

[0025] [9] The method according to [1], wherein the vegetables are selected from the group consisting of bean sprouts, Chinese cabbage, green peppers, carrots, cabbages, onions, bell peppers, daikon radishes, spinach, lettuce, broccoli, cauliflower, asparagus, potatoes, leeks, and ginger.

[0026]

[10] Frozen vegetables produced by any of the methods of [1] - [9].

Advantages of the Invention

[0027] According to the present invention, by adding salts or the like to an object such as a vegetable to penetrate from the surface to the inside of the vegetable, or by coating the vegetable with fats and oils or the like, it is possible to reach a deeper temperature in the supercooled state. Then, when the supercooling is released, a large number of ice nuclei are generated, so that freezing can be performed while suppressing the growth of ice crystals and maintaining the texture.

Mode for Carrying Out the Invention

[0028] The present invention non - limitatively includes the following aspects. Unless otherwise specified in this specification, the technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art. The substances, materials, and examples disclosed in this specification are merely illustrative and are not intended to be limiting. When referring to "in one aspect" in this specification, it means not being limited to that aspect, that is, being non - limiting.

[0029] 1. Method for manufacturing frozen vegetables In one aspect, the present invention relates to a method for manufacturing frozen vegetables. Non - limitatively, the manufacturing method of the present invention is (i) a) Heat - treating the vegetable in the presence of an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides, or combinations thereof, or b) Heat - treating the vegetable and then adding an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides, or combinations thereof; (ii) Allowing the vegetable of (i) to stand and cool under the condition of - 9°C to - 15°C, whereby the vegetable becomes in a supercooled state, and then the supercooled state is released; and (iii) Freezing the vegetable of (ii), including.

[0030] Here, the heat - treatment of (i) is a heat - treatment to such an extent that the cell tissue of the vegetable is not destroyed even after the freezing treatment of (iii). In the production method of the present invention, fresh foods such as vegetables are frozen by cooling after heat treatment, but before reaching freezing, they go through a supercooled state and then the release of the supercooled state. The present invention is characterized by adding an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides or combinations thereof before, during or after the heat treatment of the vegetables.

[0031] (i) "Heat treatment in the presence of an additive" in a) means both adding the additive before the start of heat treatment and adding it during heat treatment. Additives The timing of adding the additive is not particularly limited. It may be any of before, during or after the heat treatment of the vegetables.

[0032] Non - limitatively, the additive is selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides or combinations thereof. The additive is safe even if taken into the living body for consumption.

[0033] Among the examples of additives, fats and oils are a type of lipid and represent an ester compound of a naturally - derived fatty acid and glycerin. Fats and oils are considered to coat the surface of vegetables. The type of fats and oils is not particularly limited as long as it is edible oil. Edible oils non - limitatively include the following.

[0034] Vegetable fat oil (liquid at room temperature) As raw materials, there are sesame oil, soybean oil, corn oil, rapeseed oil (canola oil), torreya oil, rice bran oil, camellia oil, safflower oil (safflower oil), palm kernel oil, cottonseed oil, sunflower oil, perilla oil, linseed oil, olive oil, peanut oil, almond oil, avocado oil, hazelnut oil, walnut oil, grape seed oil, mustard oil, lettuce oil, akebia oil, etc. Classified from the degree of refinement, there are salad oil, refined oil, tempura oil, etc.

[0035] Vegetable fat (solid at room temperature) Hardened oils (margarine, shortening, etc.), cocoa butter, peanut butter, palm oil, coconut oil Animal fat oil (liquid at room temperature) Fish oil, whale oil, shark oil, liver oil, pupa oil (extracted from silkworm pupae) Animal fat (solid at room temperature) Lard (pork fat), tallow (beef fat), chicken fat, rabbit fat, mutton fat, horse fat, schmalz, milk fat (butter, ghee, etc.) In one aspect, the oil or fat has, as a raw material, sesame oil or soybean oil, and as a degree of refinement, refined oil or salad oil.

[0036] Among the examples of additives, salts, alcohols, amino acids, and saccharides are substances that penetrate from the surface to the inside of vegetables. These additives may be in the form of an aqueous solution or in powder form. "Salts" may be any salts obtained by reacting an acid and a base. In terms of use in food, it is a general term for substances mainly composed of so-called sodium chloride and produced by drying seawater or mining rock salt. It is desirable that the salts mainly contain table salt used as a seasoning for adding saltiness and also used in food for purposes such as preservation (salting, salting down). In Japan, table salt, kosher salt, refined salt, etc. are collectively referred to as "salts". According to the quality standards of the Salt Industry Center and the Japan Salt Industry Association, etc., "table salt" has a sodium chloride content of 99% or more, "kosher salt" has a content of 95% or more, and "refined salt" refers to those with a sodium chloride content of 99.5% or more according to the quality standards of the Salt Industry Center. "Salts" in this specification may include any of these types of salts. In one aspect, the additive is "salts". In one aspect, the additive is "table salt". In one aspect, the additive is "salt water" (an aqueous solution of salts).

[0037] Alcohols that can be used as additives include ethanol that can be inoculated for edible use, sake, wines such as wine, cooking wine, mirin, etc. "Amino acid" generally refers to a general term for organic compounds having both functional groups of an amino group and a carboxyl group. The amino acids that can be used as additives are not particularly limited as long as they are safe even when taken into the living body for food use. The amino acids may be natural amino acids or non-natural amino acids. The amino acids include, for example, sodium glutamate, glycine, alanine, proline, and the like. The amino acids may be a combination of two or more kinds of amino acids.

[0038] "Sugar" refers to so-called carbohydrates and consists of "sugars" and "dietary fibers". In this specification, "sugars" generally means free sugars, that is, monosaccharides such as sucrose, glucose, and fructose, and disaccharides. However, in the present invention, oligosaccharides, sugar alcohols, etc. are also included as long as they dissolve and exhibit the same behavior as free sugars. Sugars are abundantly contained in plant tissues, honey, and fruits. In particular, glucose is important as an energy source for organisms. "Glucose" or "grape sugar" is a simple sugar having the molecular formula C6H 12 O6.

[0039] "Fructose" or "fruit sugar" is an isomer of glucose. The molecular formula is the same as that of glucose, C6H 12 O6, but the structure is different. Fructose is a water-soluble white crystal and is the most soluble in water among all sugars. Fructose is abundantly contained in honey, fruits on trees, berries, melons, and certain root vegetables.

[0040] "Sucrose" or "cane sugar" is a type of sugar and is the main component of granulated sugar. It is obtained from sugar beets, sugarcane, etc. Sucrose is a substance classified as a disaccharide (two monosaccharides are bonded). Glucose (grape sugar) and fructose (fruit sugar) are α-1,2-glycosidically bonded, and the molecular formula is C 12 H 22 O 11 It has the common properties of disaccharides such as being a colorless crystal, having a sweet taste, and being soluble in water.

[0041] "Maltose" or "malt sugar" generally gets its name because it is abundant in malt (Malt) produced by the decomposition of starch contained in barley, etc. by β-amylase contained in malt. Maltose is a reducing disaccharide in which two glucose molecules are linked by an α-1,4-glycosidic bond, and its molecular formula is C 12 H 22 O 11 . Maltose is the main component of malt syrup.

[0042] "Oligosaccharides" are substances in carbohydrates where about 2 to 10 units are linked together as the smallest units, and are also called oligosaccharides. Non-limiting examples include maltooligosaccharides, fructooligosaccharides, etc. Carbohydrates also include, among others, non-limiting examples such as mannose, galactose, xylulose, lactose, trehalose, cellobiose, sorbitol, maltitol, etc.

[0043] The said carbohydrates also include liquid sugar. "Liquid sugar" is mainly corn syrup (maize) composed of glucose that has been decomposed by an enzyme, and is generally referred to as malt syrup. Also, by using enzymes with different substrate specificities, malt syrup containing carbohydrates (such as maltooligosaccharides) with a specific degree of polymerization can be produced. Tetrap (registered trademark) (Hayashibara Co., Ltd.) used in the examples of this specification is a malt syrup containing maltooligosaccharides.

[0044] Non-limitingly, the said carbohydrates are selected from sucrose, glucose, maltose, and liquid sugar. The said carbohydrates may be a combination of two or more types of carbohydrates. In one aspect, the said additive includes, for example, seasonings, processed products, etc. such as mayonnaise, mayonnaise-type seasonings, dressings, etc., which contain salts, oils and fats, alcohol, amino acids, carbohydrates, or combinations thereof. The said additive may be a compound seasoning such as glass soup, twice-cooked pork-flavored seasoning, marinated tofu-flavored seasoning, eight-treasure pickled vegetable-flavored seasoning, etc. The forms of seasonings and processed products are not limited, and can be any of solid, liquid, semi-solid (such as jelly-like).

[0045] The additive may be a combination of salts, oils and fats, alcohols, amino acids, or saccharides. In one aspect, the additive is a combination of salts and oils and fats. In one aspect, the seasoning is a combination of sesame oil and brine. In one aspect, the additive is a combination of oils and fats and compound seasonings. In one aspect, the additive is a combination of sesame oil and a seasoning with the flavor of twice-cooked pork.

[0046] In one aspect, the additive is salts and is added as brine. The concentration of the brine is not particularly limited and can be appropriately selected according to the type of vegetables used, the conditions of heat treatment, etc. Without limitation, the additive is preferably brine with a concentration of 0.05 wt% or more, 0.1 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, 0.6 wt% or more, 0.7 wt% or more, 0.8 wt% or more, 0.9 wt% or more, 1.0 wt% or more. Without limitation, the additive is preferably brine with a concentration of 40 wt% or less, 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less. Without limitation, the additive is preferably brine with a concentration of from 0.05 wt% to 40 wt%, from 0.05 wt% to 30 wt%, from 0.1 wt% to 30 wt%, from 0.2 wt% to 30 wt%, from 0.3 wt% to 30 wt%, from 0.3 wt% to 25 wt%, from 0.3 wt% to 20 wt%, from 0.4 wt% to 30 wt%, from 0.4 wt% to 20 wt%, from 0.4 wt% to 20 wt%, from 0.5 wt% to 30 wt%, from 0.5 wt% to 25 wt%, from 0.5 wt% to 20 wt%, from 0.5 wt% to 15 wt%, from 0.5 wt% to 10 wt%, from 0.7 wt% to 25 wt%, from 0.7 wt% to 20 wt%, from 0.7 wt% to 15 wt%, from 0.7 wt% to 10 wt%, from 1.0 wt% to 25 wt%, from 1.0 wt% to 20 wt%, from 1.0 wt% to 15 wt%, from 1.0 wt% to 10 wt%. In one aspect, the additive is salts and is added as brine with a concentration of from 0.5 wt% to 20 wt%.

[0047] The amount of the additive is not particularly limited. In one embodiment, the amount of the additive is 0.1% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, 0.7% by weight or more, 1.0% by weight or more, 1.5% by weight or more, 2.0% by weight or more, 3.0% by weight or more, 5.0% by weight or more, 7.0% by weight or more of the vegetable weight. Without limitation, the amount of the additive is preferably 0.5% by weight or more of the vegetable weight. In one embodiment, the amount of the additive is 30.0% by weight or less, 15.0% by weight or less, 12.0% by weight or less, 10.0% by weight or less, 9.0% by weight or less, 8.0% by weight or less, 7.5% by weight or less, 7.0% by weight or less of the vegetable weight. Non-limiting examples of the amount of additive added include 0.1% to 30.0%, 0.3% to 15.0%, 0.3% to 12.0%, 0.4% to 10.0%, and 0.5% to 7.0% by weight of the vegetable.

[0048] Heat treatment The heat treatment in (i) is not too strong to destroy the cellular tissue of the vegetable even after the freezing treatment in (iii). If the vegetable is heated to such an extent that the cellular tissue is destroyed and cannot be maintained, the texture, such as chewiness, crispness, and crunchiness, and the taste will be deteriorated, which is not preferable.

[0049] On the other hand, if the heat treatment step (i) is not performed appropriately, the supercooled state and subsequent release of the supercooled state will not occur in the cooling step (ii). In one aspect, this refers to a state in which moderate damage is given to the cells of the vegetable, and the supercooled state occurs inside the cells, but the cells are not completely destroyed, or a state in which the cells are damaged, and the supercooled state occurs inside the cells, but the destruction of the cell tissue is not caused.

[0050] The method of performing the heat treatment is not particularly limited and can be carried out by any known method. In one aspect, the heat treatment is carried out by superheated steam heating, steaming, stir-frying, blanching heating, or deep-frying cooking including frying. Preferably, it is superheated steam heating or steaming. Boiling heating (blanching) can also be used. However, boiling heating (blanching) requires more careful setting of heating conditions because moisture easily penetrates into the interior of the vegetables during heating and the moisture content tends to increase more easily compared to superheated steam heating, steaming, stir-frying, and deep-frying cooking. Most preferably, it is superheated steam heating.

[0051] The temperature and time for performing the heat treatment step vary depending on factors such as the type of vegetables to be frozen, moisture content, size, shape, component amount, state at the time of freezing, during supercooling, subsequent supercooling release conditions, and further freezing state, storage state, etc.

[0052] In one aspect, the heat treatment in (i) is preferably carried out at 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 120°C or higher. More preferably, it is 100°C or higher. In one aspect, the heat treatment in (i) is preferably carried out at 350°C or lower, 300°C or lower, 280°C or lower, 250°C or lower, 200°C or lower, 180°C or lower. In one aspect, the step of the heat treatment in (i) is carried out under the conditions of 60°C to 300°C. In one aspect, the step of the heat treatment in (i) is carried out under the conditions of 100°C to 250°C.

[0053] In one aspect, the step of the heat treatment in (ii) is carried out for 3 seconds or more, 5 seconds or more, 10 seconds or more, 20 seconds or more, 30 seconds or more, 45 seconds or more, 60 seconds or more, 90 seconds or more, 100 seconds or more, 120 seconds or more, 180 seconds or more, 300 seconds or more, 400 seconds or more, 500 seconds or more, 550 seconds or more. In one aspect, the step of the heat treatment in (ii) is carried out within 900 seconds, within 800 seconds, within 700 seconds, within 600 seconds, within 300 seconds, within 200 seconds, within 180 seconds.

[0054] In one aspect, the heat treatment step in (ii) is carried out for 3 seconds to 900 seconds, 5 seconds to 800 seconds, 5 seconds to 700 seconds, 5 seconds to 600 seconds, 10 seconds to 700 seconds, 10 seconds to 600 seconds, 10 seconds to 500 seconds, 20 seconds to 800 seconds, 20 seconds to 700 seconds, 20 seconds to 600 seconds, 30 seconds to 700 seconds, 30 seconds to 600 seconds, 30 seconds to 500 seconds, 60 seconds to 600 seconds, 60 seconds to 500 seconds, 60 seconds to 400 seconds. Non-limitingly, in one aspect, the heat treatment step in (ii) is carried out for 5 seconds to 600 seconds. Non-limitingly, in one aspect, the heat treatment step in (ii) is carried out for 30 seconds to 300 seconds.

[0055] In one aspect, the heat treatment step in (i) is carried out for 5 seconds to 600 seconds under the conditions of 60°C to 300°C. In one aspect, the heat treatment step in (i) is carried out for 30 seconds to 600 seconds under the conditions of 60°C to 300°C. In one aspect, the heat treatment step in (i) is carried out for 10 seconds to 600 seconds under the conditions of 100°C to 250°C. In one aspect, the heat treatment step in (i) is carried out for 30 seconds to 600 seconds under the conditions of 60°C to 250°C. In one aspect, the heat treatment step in (i) is carried out for 30 seconds to 600 seconds under the conditions of 100°C to 250°C.

[0056] In the examples of this specification, various vegetables were subjected to heat treatment under various conditions to obtain frozen vegetables. In one aspect, in these examples, the heating conditions when supercooling and supercooling release occurred and frozen vegetables were obtained can be applied.

[0057] The heating conditions vary depending on factors such as the type of vegetables to be frozen, the moisture content, size, shape, component amount, state at the time of freezing, during supercooling, subsequent supercooling release conditions, and further the frozen state, storage state, etc. For example, in the case of larger-sized vegetables, stronger heating conditions (e.g., longer heat treatment time, etc.) may be required, and the opposite is true for smaller-sized vegetables. Also, when the vegetables are cut, the conditions also vary depending on the size and shape after cutting. When cut into smaller pieces, weaker heating conditions (e.g., shorter heat treatment time, etc.) may be required, and the opposite is true for larger cut sizes. Or, for example, when the moisture content is high or when the vegetables are ripe and soft, weaker heating conditions (e.g., shorter heat treatment time, etc.) may be required. Also, the conditions such as time may change depending on the device used for the heat treatment, etc. Also, in the case of stir-frying, the heat treatment time varies depending on the heat intensity. Those skilled in the art can appropriately apply suitable heating conditions according to the situation of the vegetables to be frozen, the device used, etc.

[0058] (ii) The vegetables subjected to the cooling step are preferably those without moisture adhering to the surface because it is easier to obtain the effects that the supercooling release temperature becomes lower and / or high-sensory-evaluation frozen vegetables can be obtained. Therefore, in one aspect, (i) after the heat treatment step, the moisture on the surface of the vegetables is removed. In particular, since steaming is processed in a state filled with saturated water vapor, there is an excessive amount of moisture on the tissue surface after the heat treatment. In such a case, it is preferable to remove the moisture present on the surface of the vegetables. The method for removing moisture is not particularly limited. It can be done by means such as pressing a hygroscopic cloth or paper such as kitchen paper against the surface.

[0059] Non-limitingly, the heat treatment is preferably carried out uniformly up to the inside of the vegetables (heating uniformity). Cooling treatment (i) The vegetables are then cooled. As a result, the vegetables are in a supercooled state, and then the supercooled state is released.

[0060] The conditions such as the temperature, time, and means of cooling are not particularly limited. It can be carried out by leaving the vegetables at a temperature of 0°C or lower. Since it is necessary to place the vegetables at a temperature lower than the supercooling release temperature, in one aspect, the cooling temperature is -1°C or lower, -3°C or lower, -5°C or lower, -7°C or lower, -9°C or lower, -10°C or lower. In one aspect, the cooling temperature is -30°C or higher, -25°C or higher, -20°C or higher, -18°C or higher, -15°C or higher, -12°C or higher.

[0061] In one aspect, in the step (ii), the vegetables are placed under the conditions of -9°C to -25°C for cooling. In one aspect, in the step (ii), the vegetables are placed under the conditions of -9°C to -15°C for cooling. In one aspect, in the step (ii), the vegetables are placed under the conditions of -9°C to -12°C for cooling. In one aspect, in the step (ii), the vegetables are placed under the conditions of -5°C to -30°C for cooling. In one aspect, in the step (ii), the vegetables are placed under the conditions of -5°C to -25°C for cooling.

[0062] The cooling time is not particularly limited. It may be the time required for supercooling, the release of the supercooled state, and freezing to occur. In one aspect, it is 5 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 30 minutes or more. By placing the vegetables at a temperature lower than the supercooling release temperature, it is possible to proceed to the freezing step (iii). Alternatively, the vegetables in which the supercooled state has been released and freezing has occurred may be transferred to a lower temperature freezing condition. The cooling step in (ii) can be carried out by means of devices such as a refrigerator, a deep freezer, a cryostat, etc. Preferably, a device capable of temperature control is used non-limitingly.

[0063] Generally, when any stimulus such as vibration is applied to a liquid in a supercooled state, it rapidly crystallizes and the supercooled state is released. However, in one aspect of the present invention, the release of the supercooled state in (ii) occurs naturally over time without external stimulus during the cooling step.

[0064] The temperature at which the supercooled state is released is not particularly limited. In one aspect, the supercooling release temperature is -1°C or lower, -3°C or lower, -5°C or lower, -7°C or lower, -9°C or lower, -10°C or lower. Preferably, it is -9°C or lower or -10°C or lower.

[0065] In this specification, the "difference between the temperature at which the vegetables treated in step (i) are released from the supercooled state in step (ii) and the freezing point of the vegetables treated in step (i)" may be referred to as the "supercooling gap". The "freezing point of the vegetables treated in step (i)" refers to the temperature at which the vegetables treated in step (i) solidify and freeze when they are normally frozen. When no supercooled state occurs, they freeze at that temperature.

[0066] In one aspect, it is preferable that the difference between the temperature at which the vegetables treated in step (i) are released from the supercooled state in step (ii) and the freezing point of the vegetables treated in step (i) is larger. In one aspect, the difference between the temperature at which the vegetables treated in step (i) are released from the supercooled state in step (ii) and the freezing point of the vegetables treated in step (i) is 5°C or higher, 6°C or higher, 7°C or higher, 8°C or higher. Without limitation, the difference between the temperature at which the vegetables treated in step (i) are released from the supercooled state in step (ii) and the freezing point of the vegetables treated in step (i) is 5°C or higher.

[0067] In the examples described later, it was clarified that there is a correlation between the supercooling gap and the sensory texture evaluation of frozen vegetables. Preferably, the frozen vegetables produced using the above manufacturing method have a better texture (appropriate hardness, crispness, chewiness, etc.) than the evaluation during rapid freezing or when supercooled without adding additives. In the examples described later, the sensory evaluation of the frozen vegetables obtained by the above manufacturing method was higher than the evaluation during rapid freezing or when supercooled without adding additives.

[0068] Non - limitatively, the heating conditions, freezing conditions, and additive conditions (such as the type and amount of additives) in the manufacturing method are conditions that, for example, exceed 9 points, are 9 points or more, 10 points or more, 11 points or more, or 12 points or more in the sensory evaluation in the examples described later. In one aspect, preferably, in the examples, the condition is such that the sensory ≧ 9 rate is 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more.

[0069] Non - limitatively, the heating conditions, freezing conditions, and additive conditions (such as the type and amount of additives)) in the manufacturing method are conditions where the difference between the temperature at which the vegetables processed in step (i) are released from the supercooled state and the freezing point of the vegetables processed in step (i) in step (ii) is 5°C or more, 6°C or more, 7°C or more, 8°C or more.

[0070] Wild vegetables The type of vegetables targeted by the method is not particularly limited. In one aspect, the vegetables are selected from the group consisting of root vegetables, leaf - stem vegetables, fruit vegetables, and spice vegetables.

[0071] Examples of root vegetables: daikon radish, carrot, potato, taro, turnip, burdock, lotus root, yam; Examples of leaf - stem vegetables: Chinese cabbage, cabbage, spinach, lettuce, spring onion, onion, komatsuna, chingensai, butterbur, Mitsuba, shungiku, mizuna, celery, asparagus, cauliflower, broccoli, chives, garlic; Examples of fruit vegetables: cucumber, eggplant, tomato, green pepper, pumpkin, sweet corn, green bean, green pea, green pea, broad bean, edamame; Examples of spice vegetables: ginger The vegetables include bean sprouts. "Bean sprouts" are mainly the seeds of cereals, beans such as mung beans and soybeans, which are soaked in water and germinated without exposure to sunlight. In a broad sense, it is a general term that includes sprout vegetables and soft - white cultivated vegetables. Sprout vegetables (new sprout vegetables) are collectively called sprouts, and bean sprouts are a type of sprout, but unlike other sprouts, they are not eaten raw but are heated and eaten.

[0072] In one aspect, the vegetable is selected from the group consisting of mung bean sprouts, Chinese cabbage, green pepper, carrot, cabbage, onion, bell pepper, daikon radish, spinach, lettuce, broccoli, cauliflower, asparagus, potato, leek, and ginger, according to the method of claim 1 In one aspect, the vegetable is mung bean sprouts, Chinese cabbage, green pepper, carrot, or cabbage.

[0073] In one aspect, the vegetable is not chicory. 2. Frozen vegetables In one aspect, the present invention relates to a vegetable produced by the above method.

[0074] The type of the vegetable is as described in "1. Method for producing frozen vegetables". The vegetables include not only those in a frozen state but also those thawed after freezing. The vegetable has the characteristic that the cell tissue of the vegetable is not destroyed even after the freezing treatment. Non-limitingly, in one aspect, the vegetable is moderately damaged and in a state where supercooling can occur.

[0075] In one aspect, the vegetable has an excellent texture compared to a vegetable frozen (e.g., rapidly frozen) without going through a supercooled state. In one aspect, the vegetable also has an excellent texture compared to a vegetable frozen through a supercooled state without adding an additive.

[0076] An excellent texture means, for example, being excellent (having a high evaluation) in one or all of chewiness, crispness, and a crunchy feeling. In one aspect, the vegetable has an undestroyed tissue, less drip occurs, and as a result, there is no dilution and the taste is strongly felt. Also, since the tissue remains, the texture is maintained.

[0077] In one aspect, the vegetables can have the above excellent texture not only by natural thawing but also by thawing in a microwave oven, thawing in a pan, etc. The vegetables can be used, for example, in ramen with vegetables or fried rice with vegetables. Also, even if stir-frying treatment is directly performed and cooking such as stir-fried vegetables is carried out, stir-fried vegetables having a texture and texture similar to those of fresh vegetables can be produced.

Example

[0078] Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to these examples. Those skilled in the art can easily modify and change the present invention based on the description of this specification, and they are included in the technical scope of the present invention.

[0079] Example 1: About the effect of the pretreatment process WO2019 / 235515 (Patent Document 1) describes that heat treatment as a pretreatment of vegetables increases the subsequent supercooling stability. In this example, when heat treatment was performed on vegetables as a pretreatment of vegetables, further addition of each additive to the vegetables was carried out to examine the effects on supercooling stability and texture.

[0080] (Test method) (1) Sample For the bean sprouts, fresh green bean sprouts (manufactured by Narita Foods) were used.

[0081] (2) Regarding heat treatment The following method was used for heating. Superheated steam heating: For superheated steam heating, a superheated steam oven (manufactured by Naomoto Kogyo Co., Ltd.) was used, and 13 g (15 pieces) of bean sprouts were arranged side by side without overlapping and heated.

[0082] Stir-frying heating: An IH rotary stir-fryer (manufactured by Nichiba Electric Co., Ltd.) was used. After the apparatus was sufficiently preheated, 26 g (30 pieces) of bean sprouts were put in and heated while stirring. Details of each heating condition of superheated steam heating and stir-frying heating are described in Table 1.

[0083] (3) Additives The following additives were used. Table salt: Table salt (manufactured by the Salt Business Center) was used. The mung beans were immersed in 10 wt% saline solution for 10 seconds, or 2% by weight of table salt relative to the mung beans was directly sprinkled.

[0084] Sesame oil: Sesame oil (manufactured by Kadoya Oil Mill) was used, and 5% by weight relative to the mung beans was directly added. The additives were added before the start of the heat treatment in the case of superheated steam heating, and were added simultaneously with the start of heating in the case of stir-frying heating.

[0085] (4) Freezing conditions After the heat treatment, the mung beans were frozen under the following conditions. Supercooling (invention): The mung beans treated by a predetermined pretreatment method were precooled (for 5 minutes in a 5°C space) before freezing, and then 15 mung beans were placed on a 300 mm × 300 mm stainless steel plate. Further, the stainless steel plate was placed still in a freezer (manufactured by Maekawa Seisakusho) with the ambient temperature set to -12°C, and the supercooled state was observed. The cooling rate was 0.01°C / second.

[0086] Rapid freezing (comparative example): Using an air blast type rapid freezing chamber (manufactured by Panasonic), the mung beans pretreated by a predetermined method were placed still in the same manner as in supercooling and frozen at an ambient temperature of -40°C.

[0087] Temperature measurement: The surface temperature of the standard sample was measured with an infrared thermograph Testo885 (manufactured by Testo). (5) Measurement of supercooling gap temperature From the temperature change records of each obtained mung bean, the difference between the temperature immediately before the release of supercooling (supercooling release point) and the temperature immediately after the release (freezing point) was calculated, and the difference temperature was recorded as the supercooling gap temperature. The supercooling gap temperature was divided into five levels: 4.9°C or less, 5 - 5.9°C, 6 - 6.9°C, 7 - 7.9°C, and 8°C or more. Each condition was tested with at least 15 or more mung beans. The mung beans were sorted into five levels based on the obtained supercooling gap temperatures, and the number and ratio of each level were calculated.

[0088] (6) Sensory evaluation The sensory evaluation was carried out on the whole amount of mung beans after freezing, each placed in a bag and left standing at room temperature for 1 hour. For the tooth feel (stress, the force felt when biting down), the tooth cutting ability (the force required to break), and the crispy feeling (the feeling of a preferable crispy texture felt when biting down on fruits and vegetables), each was scored on a scale of 0 to 5 points according to the following criteria and evaluated. On the other hand, the respective scores, totaling 15 points in all, were added up, and those with a total value of 9 points or more were judged as "good" as being at a level where a clear difference could be seen compared with the conventional ones.

[0089] 1: Poor tooth feel and tooth cutting ability, no crispy feeling 2: Fair tooth feel and tooth cutting ability, little crispy feeling 3: Some degree of tooth feel, tooth cutting ability, and crispy feeling 4: Tooth feel, tooth cutting ability, and crispy feeling 5: Very preferable tooth feel, tooth cutting ability, and crispy feeling (7) Measurement of the salt concentration of the sample The salt concentration of the sample was measured using a salt meter (Atago) on the squeezed juice obtained when the sample was crushed.

[0090] (8) Results The results are shown in Table 1.

[0091]

Table 1-1

[0092]

Table 1-2

[0093] First, verification was carried out on raw soybeans without a heating process as a control. For those without an additive, those immersed in 10 wt% saline solution for 10 seconds, and those with sesame oil added, in all cases, freezing started without the supercooling gap reaching 5°C, and the supercooled state was not maintained to a low temperature. The results of the sensory evaluation were also all low evaluations of 3.0 to 4.0 points, and the proportion of 9 points or more was 0%.

[0094] On the other hand, for those subjected only to heat treatment, some were able to maintain the supercooled state up to a supercooling gap of 5°C or more. Along with this, the proportion of the sensory evaluation results of 9 points or more increased from 0% for raw soybeans to 37% for superheated steam heating and 51% for stir-frying heating, and the texture as a whole improved. As described in Patent Document 1, by performing heat treatment, the supercooled state was maintained to a lower temperature, and thereby the texture of the object improved.

[0095] Next, the effects of adding each additive to this heat treatment were verified. First, in superheated steam heating, when further immersed in 10 wt% saline solution for 10 seconds or when 5% sesame oil was added, the supercooled state became more stable, and the proportion reaching a supercooling gap of 5°C or more was further improved compared to the case of only heating. Also, the proportion of the sensory evaluation results of 9 points or more increased from 37% for only superheated steam heating to 91% for immersion in 10% saline solution and 47% for sesame oil addition.

[0096] Next, the effects of adding these additives simultaneously with stir-frying heating were verified. In the case of stir-frying heating as well, when 2% salt was added or 2% sesame oil was added, for each case, the supercooled state became more stable, and the proportion reaching a supercooling gap of 5°C or more was further improved compared to the case of only heating. The proportion of the sensory evaluation results of 9 points or more increased from 51% for only stir-frying to 80% for salt addition and 64% for sesame oil addition.

[0097] As described above, compared with raw mung beans and mung beans that have only been heated, mung beans with added oil or salt have a greater degree of supercooling down to a lower temperature, and the attainment rate of a supercooling gap of 5°C or more has improved. Along with this, an improvement in texture was also observed. The stabilization effect of the supercooled state obtained by heat-treating mung beans was found to be enhanced by adding additives such as salt and fats and oils before and after the heat treatment.

[0098] (9) Discussion In this example, a supercooling stabilization effect was obtained by adding additives such as salt and sesame oil. Without being bound by any theory, for fats and oils, coating the surface may suppress the freezing of surface water, which is likely to trigger the release of supercooling, leading to the stabilization of supercooling. On the other hand, for water-soluble components such as salts, sugars, and amino acids, since they penetrate into the sample, the salt concentration, sugar concentration, etc. on the attached surface change, creating a situation where freezing such as freezing point depression is suppressed, and it is speculated that supercooling release becomes less likely to occur even at lower temperatures.

[0099] Example 2: Examination of the method of adding salt In Example 1, by further adding salts such as salt to the heat treatment, it was shown that there is a possibility of stably supplying mung beans with a high supercooling stabilization effect and better texture. In this example, by changing the concentration and addition method of the salt to be added, it was examined whether it affects the stability of supercooling. Specifically, when immersing in salt water adjusted by dissolution, the relationship between the concentration and the immersion time was verified.

[0100] (Test method) Mung beans were immersed in 10 wt% salt water for 10 seconds before and after heating, and then heated with superheated steam at 180°C for 10 seconds, and cooled and frozen in the same manner as in Example 1. Similarly, they were immersed in 4 wt% salt water at 5°C for 1 hour, heated with superheated steam at 180°C for 30 seconds, and cooled and frozen in the same manner as in Example 1.

[0101] (Results) The results are shown in Table 2.

[0102]

Table 2-1

[0103]

Table 2-2

[0104] When immersed in 10 wt% saline solution before and after heating, the proportion where the supercooling gap becomes 5 °C or more improved in both cases, and the proportion where the sensory evaluation becomes 9 points or more also improved. In particular, immersion before heating is more likely to cause supercooling, and the proportion where the sensory evaluation becomes 9 points or more is also higher. Similarly high evaluations were obtained even when immersed in 4 wt% saline solution for 1 hour.

[0105] From these results, it became clear that as methods of adding saline solution, both the method of immersing for a short time at a high concentration (10 wt% saline solution) so as to form a film on the surface before and after heating and the method of immersing for a long time at a low concentration (4 wt% saline solution) so as to penetrate to the inside of the tissue have the same effect.

[0106] Example 3: Examination of salt concentration In this example, the salt concentration to be added was examined in more detail. First, the influence of the addition concentration when adding salt as a powder was examined. Heating was carried out by placing a frying pan on an IH cooker (manufactured by Nichiba Electric). After sufficiently preheating the frying pan, 13 g (15 pieces) of the sample was put in, and then a predetermined amount of salt was added and stir-fried while heating, that is, so-called stir-frying cooking was performed. The results are shown in Table 3.

[0107]

Table 3-1

[0108]

Table 3-2

[0109] It was confirmed that, at a salt addition concentration of 0.5% by weight to 2% by weight based on the weight of the bean sprouts, an increase in the addition amount resulted in an improvement in the supercooling gap temperature and the texture. Furthermore, the influence of the concentration of the brine when immersed in the brine for 10 seconds was examined. The immersion in the brine was carried out before heating. Heating was performed using superheated steam at 180°C for 10 seconds. The results are shown in Table 4.

[0110]

Table 4-1

[0111]

Table 4-2

[0112] It was confirmed that, at a brine concentration of 0.5% by weight to 20% by weight, increasing the salt concentration resulted in an improvement in the supercooling gap temperature and the texture. Example 4: Examination of heating conditions In this example, by changing the heating temperature and time, effective heating conditions were verified. The heating method was superheated steam heating, and the addition method was immersion in 10% by weight brine for 10 seconds. Also, instead of superheated steam heating, the effect of the combination of blanching heating at 100°C for 1 minute and the additive (immersion in 10% by weight brine for 10 seconds) was examined.

[0113] The results are shown in Table 5, and the summary of the results is shown in Table 6.

[0114]

Table 5-1

[0115]

Table 5-2

[0116]

Table 6

[0117] When the heating temperature was low (120 °C, 140 °C), heating was insufficient for short times (5 seconds, 10 seconds), and even with the use of additives, the supercooling stability was low and the sensory test results were poor. On the other hand, even when the heating temperature was high (300 °C), for short times (5 seconds, 10 seconds), the supercooling stability was lower compared to others and the sensory test results were poor. It is presumed that this is because the superheated steam was too dry, resulting in low heat conduction efficiency of the superheated steam and insufficient heating as a result.

[0118] Also, a combination of blanching heating at 100 °C for 1 minute and an additive (10 wt% saline solution, immersion for 10 seconds) instead of superheated steam heating gave the same effect as the combination of superheated steam heating at 220 °C for 100 seconds and an additive.

[0119] From the above results, it was found from this example that there is a minimum required heating time according to the heating temperature. Also, after that minimum heating time, until the standard product burned, both the supercooling stability and the sensory test results were high.

[0120] Example 5: Examination of heating conditions for various wild vegetables In this example, heating conditions for various vegetables other than mung beans were examined. As vegetables, Chinese cabbage (the same leafy vegetable as mung beans), green pepper (fruit vegetable), and carrot (root vegetable) were used. The heating conditions, results, etc. are shown in Tables 7 - 9.

[0121] (1) Chinese cabbage

[0122]

Table 7 - 1

[0123]

Table 7 - 2

[0124] Chinese cabbage was cut into 20 - 40 mm squares. Regarding the heating time, starting from 10 seconds or more, at the temperature until it burns, a high supercooling generation rate and an improvement in texture were confirmed. In the case of Chinese cabbage, even with only heating, the supercooling stability was quite high. However, by adding soybean white refined oil (manufactured by Nisshin Oillio Group) and an emulsifier (sugar ester S - 1670, manufactured by Mitsubishi Chemical), the supercooling stability was further improved, and it was confirmed that a product with excellent texture could be obtained. Also, when the heating method was changed from superheated steam heating to steam, the same effect was confirmed. It became clear that Chinese cabbage can obtain the effect within the same heating condition range as mung bean sprouts.

[0125] (2) Bell pepper

[0126]

Table 8 - 1

[0127]

Table 8 - 2

[0128] Bell peppers (fruits and vegetables) were cut into 7 - mm widths. When heated at 180°C for 10 minutes, for those with a supercooling gap exceeding 5°C, compared with the case of rapid freezing, the texture was improved. Bell peppers, in particular, showed a remarkable effect when soybean fat was added and when immersed in 10 wt% saline solution for 10 seconds.

[0129] (3) Carrot

[0130]

Table 9 - 1

[0131]

Table 9 - 2

[0132] Carrots (root vegetables) were cut into pieces with a thickness of 5 mm × length of 10 mm × width of 40 mm. When immersed in 5 wt% saline solution for 10 seconds, the supercooling state and the texture of the vegetables were verified when the heating time with superheated steam was changed. As a result, it was revealed that the supercooling stability and the texture of carrots were improved by extending the heating time of the pretreatment.

[0133] From this example, within the range verified this time, it was confirmed that for any vegetable, by combining pretreatment with heating and the addition of salts, fats and oils, etc., the supercooling stability was improved, and as a result, the texture was improved.

[0134] Example 6: Effects of various additives In this example, the effects of various additives were investigated. The heating method was superheated steam heating, and the heating conditions were 180 °C and 10 seconds. Mung beans were used as the vegetable.

[0135] [Additives investigated] 10 wt% saline solution Sesame oil 50 wt% ethanol (ethanol (95), manufactured by FUJIFILM Wako Pure Chemical Corporation) 10 wt% ethanol (ethanol (95), manufactured by FUJIFILM Wako Pure Chemical Corporation) 20 wt% sodium glutamate (GluAce, manufactured by Mitsubishi Corporation Life Sciences) 20 wt% glucose solution (hydrous crystalline glucose, manufactured by San-Ei Shokuhin Kako Co., Ltd.) Maltose syrup (Tetraup (registered trademark), manufactured by Hayashibara) The results are shown in Table 10.

[0136]

Table 10-1

[0137]

Table 10-2

[0138] The effects were shown for all the additives verified this time. Therefore, it became clear that salts, fats and oils, alcohols, amino acids, saccharides, etc. can be used as effective additives. Example 7: Effects of combinations of additives In this example, the effects when using a combination of multiple additives were examined. Specifically, assuming stir-frying cooking, the heating method was stir-frying heating, sesame oil as stir-frying oil was added, and furthermore, salt water or the blended seasoning was added for seasoning. Mung beans were used as the vegetables, and an IH rotary stir-fryer was used as the cooking machine.

[0139] The results are shown in Table 11.

[0140]

Table 11-1

[0141]

Table 11-2

[0142] As shown at the top of Table 11, the proportion of the sensory evaluation results being 9 points or more for stir-frying only was 51%, while for stir-frying with the addition of sesame oil it was 64%, and by further adding 10 wt% salt water it improved to 82%. This suggests that the effect of fats and oils and the combined use of the addition of salts such as salt further enhance the effect.

[0143] Also, when stir-frying using an IH cooker and a frying pan as the heat treatment, the effects when using sesame oil and a twice-cooked pork flavor seasoning in combination were verified. Cabbage was used as the vegetable. The cabbage was cut into 20 - 40 mm squares. The twice-cooked pork flavor seasoning used was a mixture with the composition of sweet noodle sauce 3:soy sauce 1:liquor 1:broad bean paste 1.

[0144] The results are shown in Table 11. Table 11. As shown below, when only stir-fried, the proportion of sensory test results reaching 9 points or more was 67%, while by adding sesame oil in the stir-frying process, it improved to 71%. By further adding twice-cooked pork flavoring in addition to sesame oil, the proportion of sensory test results reaching 9 points or more improved to 92%.

[0145] Thus, it was revealed that when additives such as salts and seasonings are further combined with fats and oils, a higher supercooling stabilization effect can be obtained.

Industrial Applicability

[0146] In the present invention, by adding salts and the like to objects such as vegetables and allowing them to penetrate from the surface to the inside of the vegetables, or by coating them with fats and oils, it becomes possible to manufacture frozen vegetables in which the growth of ice crystals is suppressed and the texture is maintained.

Claims

1. A method for producing frozen vegetables, comprising: (i) (a) subjecting the vegetables to heat treatment in the presence of an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides, or combinations thereof; or (b) subjecting the vegetables to heat treatment and then adding an additive selected from the group consisting of salts, fats and oils, alcohols, amino acids, saccharides, or combinations thereof; (ii) allowing the vegetables treated in (i) to stand and cool under conditions of -9°C to -15°C, whereby the vegetables are in a supercooled state and then the supercooled state is released; and (iii) freezing the vegetables treated in (ii), wherein the heat treatment in (i) is a heat treatment to such an extent that the cell tissue of the vegetables is not destroyed even after the freezing treatment in (iii). The method as described above.

2. The method according to claim 1, wherein the difference between the temperature at which the vegetables treated in step (i) are released from the supercooled state and the freezing point of the vegetables treated in step (i) in step (ii) is 5°C or more.

3. The method according to claim 1, wherein the additive is salts and is added as a saline solution of 0.5% by weight to 20% by weight.

4. The method according to claim 1, wherein the addition amount of the additive is 0.5% by weight or more based on the weight of the vegetables.

5. The method according to claim 1, wherein the heat treatment step in (i) is carried out under conditions of 60°C to 300°C.

6. The method according to claim 1, wherein the heat treatment step in (i) is carried out for 5 seconds to 600 seconds.

7. The method according to claim 1, wherein the heat treatment in (i) is carried out by superheated steam heating, steaming, stir-frying, blanching heating, or deep-frying.

8. The method according to claim 1, wherein the vegetables are selected from the group consisting of root vegetables, leafy vegetables, fruit vegetables, and spice vegetables.

9. The method according to claim 1, wherein the vegetables are selected from the group consisting of bean sprouts, Chinese cabbage, green peppers, carrots, cabbages, onions, paprika, daikon radishes, spinach, lettuce, broccoli, cauliflower, asparagus, potatoes, leeks, and ginger.

10. Frozen vegetables produced by the method according to any one of claims 1 to 9. ​

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