Method for producing cooked frozen vegetables

Abstract

To provide a technique for producing cooked frozen vegetables reduced in syneresis during thawing.SOLUTION: The method for producing cooked frozen vegetables includes a cooking step of cooking vegetables to obtain cooked vegetables, and a freezing step of freezing the cooked vegetables. The method includes a preheating step of heating the vegetable before the cooking step, and the preheating step includes the following treatment A or B. Treatment A: The vegetable is brought into contact with oil at a temperature of 40 to 80 °C for 5 minutes or more. Treatment B: The vegetables are allowed to stand for 5 minutes or more in an environment with an atmospheric temperature of 40 to 80 °C and a relative humidity of 30 to 80%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing cooked frozen vegetables by freezing cooked vegetables. [Background technology]

[0002] Frozen foods are broadly divided into uncooked frozen foods and cooked frozen foods that have been cooked by heating, etc. The latter, cooked frozen foods, are highly convenient as they can be made edible by simply heating them using a heating cooker such as a microwave oven, and have been popular with many consumers in recent years.

[0003] Some cooked frozen foods include cooked frozen vegetables, which are cooked vegetables that have been frozen. One example of such a food product is a product in which cooked frozen vegetables are placed on top of a frozen staple food such as noodles or rice. When such cooked frozen foods containing cooked frozen vegetables are thawed in a microwave oven, syneresis (drip), in which water leaks from the cooked frozen vegetables, can occur. When syneresis occurs in cooked frozen vegetables, not only does it degrade the appearance and other qualities of the cooked vegetables that have been thawed, but other cooked foods around the cooked vegetables, such as the cooked noodles or cooked rice in the above example, become watery, thereby degrading the quality of the cooked food as a whole. Therefore, frozen foods that are less likely to syneresis when thawed are required to be less susceptible to syneresis.

[0004] Patent Document 1 describes a method for producing frozen vegetables that do not drip after thawing and do not lose their texture when used in cooking, which involves a step of exposing vegetables such as bell peppers and zucchini to air at or below 30°C without heating them, removing a specific amount of moisture, and then freezing them.

[0005] Patent Document 2 describes a method for producing frozen matsutake mushrooms, which includes a step of placing the matsutake mushrooms in an environment with an ambient temperature of 1 to 5°C and a relative humidity of 30 to 50% for 3 to 12 hours to reduce the moisture content of the matsutake mushrooms, and then rapidly freezing the matsutake mushrooms.The technology described in Patent Document 2 is said to produce frozen matsutake mushrooms that can withstand long-term storage and maintain quality that is in no way inferior to fresh matsutake mushrooms even after thawing. Patent Document 3 describes a method for producing containerized frozen warm vegetables that can be eaten as warm vegetables by cooking them using a heating cooking appliance such as a microwave oven, which includes a step of blanching cut vegetables with steam and then flash-freezing the vegetables. Patent Documents 2 and 3 do not describe syneresis, and therefore do not describe any technology for preventing syneresis when cooked frozen vegetables are thawed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-271934 [Patent Document 2] Japanese Patent Application Publication No. 1-39935 [Patent Document 3] International Publication No. 2016 / 152820 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a technique for producing cooked frozen vegetables with reduced water syneresis upon thawing. [Means for solving the problem]

[0008] The present invention provides a method for producing cooked frozen vegetables, which includes a cooking step of cooking vegetables to obtain cooked vegetables, and a freezing step of freezing the cooked vegetables, The method for producing cooked frozen vegetables includes a preheating step of heating the vegetables before the cooking step, and the preheating step includes the following treatment A or B. Process A: Vegetables are placed in oil at a temperature of 40-80°C for at least 5 minutes. Treatment B: Leave the vegetables in an environment with an ambient temperature of 40 to 80°C and a relative humidity of 30 to 80% for at least 5 minutes. [Effects of the Invention]

[0009] According to the present invention, cooked frozen vegetables are provided which are less likely to undergo water separation when thawed by heating in a microwave oven, are prevented from losing their shape due to heating and thawing, and can be cooked vegetables with a good appearance. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for producing cooked frozen vegetables of the present invention (hereinafter also referred to simply as "the production method of the present invention") comprises a cooking step of cooking vegetables to obtain cooked vegetables, a freezing step of freezing the cooked vegetables, and a preheating step of heating the vegetables before the cooking step. That is, the production method of the present invention comprises a preheating step, a cooking step, and a freezing step, and these steps are carried out in this order.

[0011] The production method of the present invention is characterized in that the preheating step includes the following treatment A or B. Due to this feature, the production method of the present invention can produce cooked frozen vegetables with reduced syneresis upon thawing. Treatment A: Leave the vegetables in oil at a temperature of 40-80°C for at least 5 minutes. Treatment B: Leave the vegetables in an environment with an ambient temperature of 40 to 80°C and a relative humidity of 30 to 80% for at least 5 minutes.

[0012] The vegetables subjected to the treatment A or B are typically uncooked vegetables (raw vegetables). The vegetables subjected to the treatment A or B may also be subjected to treatment other than heat treatment, provided that the desired effects of the present invention are not impaired. Specific examples of such treatments include cutting, peeling, skewering, seasoning, flouring, and soaking in water, and these treatments may be used alone or in combination of two or more.

[0013] The process A will be described below. The process A uses oil as a heat medium and heats the vegetables to be treated by bringing them into contact with the oil. The oil used in the process A can be any oil that can be used for food, and may be either vegetable oil or animal oil. Specific examples include vegetable oils such as canola oil, salad oil, corn oil, soybean oil, safflower oil, rapeseed oil, palm oil, cottonseed oil, sunflower oil, rice bran oil, sesame oil, and olive oil; animal oils such as beef tallow, lard, and fish oil; hydrogenated oils and fats; and mixed oils containing two or more of these. These can be used alone or in combination. Typically, oils and fats that are liquid at room temperature and normal pressure (ambient temperature 25°C, 1 atmosphere) are used.

[0014] In the process A, the temperature of the oil brought into contact with the vegetables is 40 to 80° C., preferably 45 to 75° C., and more preferably 50 to 70° C. If the oil temperature is below 40° C., the effect of preventing syneresis when the cooked frozen vegetables are thawed is poor, and if the oil temperature exceeds 80° C., the cooked vegetables produced through the preheating step in the process A and the subsequent cooking step may be overheated, which may adversely affect the quality of the vegetables, such as their appearance, taste, and texture.

[0015] In the process A, the contact time (heating time) between the vegetables and oil is 5 minutes or more, preferably 10 minutes or more, and more preferably 20 minutes or more. If the heating time is less than 5 minutes, the effect of preventing syneresis when the cooked frozen vegetables are thawed is poor. There is no particular upper limit to the heating time, but from the viewpoint of preventing overheating of the cooked vegetables produced through the preheating step in the process A and the subsequent cooking step, it is preferably 240 minutes or less, more preferably 180 minutes or less.

[0016] In the above-mentioned treatment A, the method of contacting vegetables with oil is not particularly limited as long as it satisfies the above-mentioned treatment conditions (oil temperature, heating time). Examples of methods for contacting vegetables with oil include a method of immersing vegetables in oil adjusted to a specific temperature, a method of continuously applying oil adjusted to a specific temperature to vegetables, and a method of immersing vegetables in oil and adjusting the temperature to a specific temperature. In the above-mentioned "method of continuously applying oil to vegetables," the method of applying oil is not particularly limited, and examples include a method of pouring oil from above the vegetables and a method of spraying oil. In order to more reliably achieve the desired effects of the present invention, it is preferable that the entire vegetables are contacted with the oil, regardless of the method. A preferred example of a method for contacting vegetables with oil is a method of placing vegetables and oil adjusted to a specific temperature in a sealable container, sealing the contents, and heating the container.

[0017] In the treatment A, the amount of oil used is not particularly limited and may be adjusted appropriately depending on the method of contacting the vegetables with the oil, etc. For example, when the method of contacting the vegetables with the oil involves immersing the vegetables in oil adjusted to a specific temperature, the amount of oil used (mass of oil in which the vegetables are immersed) is preferably 1.5 to 20 kg, more preferably 3 to 20 kg, per 1 kg of vegetables, from the viewpoint of more reliably achieving the desired effects of the present invention.

[0018] The process B will now be described. The process B is a process in which the vegetables to be treated are left for a certain period of time in an environment in which the ambient temperature and relative humidity are adjusted to specific ranges. The process B is preferably carried out using equipment capable of controlling such temperature and humidity, and an example of such equipment is a commercially available constant temperature and humidity cabinet.

[0019] In the process B, the ambient temperature of the environment in which the vegetables are left is 40 to 80° C., preferably 45 to 75° C., and more preferably 50 to 70° C. If the ambient temperature is below 40° C., the effect of preventing syneresis when the cooked frozen vegetables are thawed is poor, and if the ambient temperature exceeds 80° C., the cooked vegetables produced through the preheating step in the process B and the subsequent cooking step may be overheated, which may adversely affect the quality of the vegetables, such as their appearance, taste, and texture.

[0020] In the process B, the relative humidity of the environment in which the vegetables are left is 30 to 80%, preferably 40 to 70%, and more preferably 45 to 65%. If the relative humidity is less than 30%, the vegetables may be excessively dried, which may adversely affect the quality of the vegetables, such as their appearance, taste, and texture. If the relative humidity is more than 80%, the effect of preventing syneresis when the cooked frozen vegetables are thawed may be poor.

[0021] In the process B, the time (heating time) for leaving the vegetables in an environment where the ambient temperature and relative humidity are within the specific ranges is 5 minutes or more, preferably 10 minutes or more, and more preferably 20 minutes or more. If the heating time is less than 5 minutes, the effect of preventing syneresis when thawing cooked frozen vegetables is poor. There is no particular upper limit to the heating time, but from the viewpoint of preventing overheating of cooked vegetables produced through the preheating step in process B and the subsequent cooking step, it is preferably 240 minutes or less, more preferably 180 minutes or less.

[0022] In the production method of the present invention, vegetables are subjected to a preheating step using the treatment A or B, followed by a cooking step in which the vegetables are cooked to obtain cooked vegetables. The cooking method for the vegetables in the cooking step can be any method applicable to vegetables, without particular limitation, and examples include deep-frying, boiling, baking, steaming, hot air cooking, steam cooking, and infrared cooking. Depending on the type of vegetable, one of these methods can be used alone, or two or more can be used in combination. The steam used in steam cooking may be saturated steam evaporated at 100°C, or superheated steam obtained by heating saturated steam.

[0023] The cooking method in the cooking step is preferably one or more selected from deep-frying, boiling, hot air cooking, and steam cooking. By carrying out a cooking step using one or more of these four cooking methods after the preheating step using the treatments A or B, cooked vegetables can be obtained with further reduced water syneresis during thawing. Hot air cooking and steam cooking can each be carried out in a conventional manner using an oven, which is a known cooking appliance. For example, a cooking step using a combination of hot air cooking and steam cooking (hot air / steam cooking) can be carried out using a commercially available steam convection oven.

[0024] In the production method of the present invention, cooked vegetables are obtained by subjecting the vegetables to a preheating step using the treatment A or B and a cooking step in this order, and then the cooked vegetables are frozen (freezing step). In the freezing step, the method for freezing the cooked vegetables is not particularly limited, and may be, for example, slow freezing, which involves freezing relatively slowly, or quick freezing, which involves freezing in a shorter time than slow freezing.

[0025] The production method of the present invention is applicable to all vegetables, but is particularly effective for vegetables that tend to synerase when thawed after freezing, such as Cucurbitaceae (e.g., zucchini, cucumber, bitter melon, winter melon), Solanaceae (e.g., paprika, bell pepper, eggplant, tomato, cherry tomato), Brassicaceae (e.g., turnip, broccoli), Asparagaceae (e.g., asparagus), Asteraceae (e.g., lettuce, puntarella, radicchio), Apiaceae (e.g., carrot, celery, fennel), Amaryllidaceae (e.g., onion, leek), and Amaranthaceae (e.g., beet). [Example]

[0026] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0027] [Examples A1 to A8, Comparative Examples A1 to A6] Using zucchini as the vegetable, cooked frozen zucchini, a type of cooked frozen vegetable, was produced according to the following procedure. Details of the production conditions are shown in Table 1 below. (Other than Comparative Example A1) Zucchini sliced ​​into 15 mm thick pieces and a heat transfer medium (canola oil or water) at a predetermined temperature were placed in a nylon poly pouch and sealed. The mass of the zucchini in the pouch was 80 to 90 g, and the mass of the heat transfer medium was 300 g. The pouch was kept warm for a predetermined time in a water bath (TM-1A, manufactured by AS ONE Corporation) adjusted to the same temperature as the heat transfer medium, thereby immersing the zucchini in the heat transfer medium adjusted to a specific temperature (preheating step). This warming time corresponds to the heating time in the preheating step. After the warming step was completed, the zucchini was quickly removed from the pouch and fried in canola oil at 150°C using an electric fryer (PRO-5FLT, manufactured by KIPROSTAR (Yasukichi Co., Ltd.)) until the core temperature of the zucchini reached 90°C (cooking step). After deep-frying, the cooked zucchini was left to stand for 5 minutes in an ambient temperature environment to cool, then placed in a sealed pouch and stored in a thermostatic chamber (LU-114, manufactured by Espec Corporation) at an internal temperature of -20°C for 1 week (freezing process). In this way, the desired cooked frozen zucchini was produced. (Comparative Example A1) Cooked frozen zucchini was produced in the same manner as above (except for Comparative Example A1), except that the preheating step was not carried out and the ginkgo-sliced ​​zucchini was fried as is.

[0028] [Examples A9 to A16, Comparative Examples A7 to A11] Using zucchini as the vegetable, cooked frozen zucchini, a type of cooked frozen vegetable, was produced according to the following procedure. Details of the production conditions are shown in Table 2 below. (Other than comparative example A7) Zucchini sliced ​​into 15 mm thick pieces like ginkgo nuts and a heat transfer medium (canola oil or water) at a predetermined temperature were placed in a nylon plastic pouch bag and sealed. The pouch bag was then kept warm for a predetermined period of time in a water bath (TM-1A, manufactured by AS ONE Corporation) adjusted to the same temperature as the heat transfer medium (preheating step). This warming time corresponds to the heating time in the preheating step. After the warming step, the zucchini were promptly removed from the pouch bag and oven cooked, specifically, cooked with hot air and steam, in a steam convection oven (SCOS-10RS, manufactured by Nichiwa Electric Co., Ltd.) at a heating temperature of 250°C in combination mode until the core temperature of the zucchini reached 90°C (cooking step). After oven cooking, the cooked zucchini was left to stand for 5 minutes in an ambient temperature environment to cool, then placed in a pouch bag, sealed, and stored in a thermostatic chamber (Espec Corporation, LU-114) at an internal temperature of -20°C for 1 week (freezing process). In this way, the desired cooked frozen zucchini was produced. (Comparative example A7) Cooked frozen zucchini was produced in the same manner as above (except for Comparative Example A7), except that the preheating step was not carried out and the ginkgo-cut zucchini was directly cooked in the oven (hot air / steam heating cooking).

[0029] [Examples B1 to B10, Comparative Examples B1 to B5] The zucchini was sliced ​​into 15 mm thick pieces, similar to ginkgo nuts, and left to stand for a predetermined period of time in a constant temperature and humidity cabinet (Espec Corporation, LHU-114), where the ambient temperature and humidity were adjusted to a predetermined range (preheating step). The standing time in the constant temperature and humidity cabinet corresponds to the heating time in the preheating step. Except for the above points, cooked frozen zucchini was produced in the same manner as above (except for Comparative Example A1). Details of the production conditions are shown in Table 3 below.

[0030] [Examples B11 to B16, Comparative Examples B6 to B11] Instead of zucchini, peppers were used as the vegetable. The peppers were sliced ​​into strips 5 to 7 mm wide and allowed to stand for a predetermined period of time in a constant temperature and humidity cabinet (Espec Corporation, LHU-114), where the ambient temperature and humidity were adjusted to a predetermined range (preheating step). The standing time in the constant temperature and humidity cabinet corresponded to the heating time in the preheating step. After standing, the peppers were promptly removed from the cabinet and placed in boiling water at 100°C, where they were boiled until their core temperature reached 85°C (cooking step). After boiling, the cooked peppers were allowed to stand for 5 minutes in an ambient temperature environment to cool, then blast-frozen at -40°C. The frozen cooked peppers were then placed in a pouch, sealed, and stored in a constant temperature cabinet (Espec Corporation, LU-114) at an internal temperature of -20°C for one week (freezing step). Thus, the desired cooked frozen peppers were produced. The details of the production conditions are shown in Table 4 below.

[0031] [Evaluation test] For each cooked frozen vegetable in each Example and Comparative Example, the syneresis rate was measured by the following method, and the appearance was evaluated by the following method. The results are shown in Tables 1 to 4 below.

[0032] (Method for measuring syneresis rate) Four sheets of filter paper (Advantech Co., Ltd., Qualitative Filter Paper No. 2, 150 mm) were placed on a microwave-resistant ceramic plate, 60 g of cooked frozen vegetables to be evaluated were placed on the filter paper, and one sheet of filter paper (Advantech Co., Ltd., Qualitative Filter Paper No. 1, 150 mm) was placed on the cooked frozen vegetables. The entire filter paper and cooked frozen vegetables on the plate were wrapped in food wrap and microwave-defrosted at 600 W for 1 minute and 20 seconds. The water leaked from the cooked frozen vegetables by this defrosting was absorbed and retained by the filter paper. After defrosting, the total weight of the five filter papers on the plate was measured, and the total weight of the five filter papers before the measurement was subtracted from the measured value to calculate the water absorption (g) of the filter paper. The syneresis rate (%) was calculated using the following formula. The lower the syneresis rate, the higher the evaluation. Syneresis rate (%) = (amount of water absorbed by filter paper (g) / weight of cooked frozen vegetables on a plate before thawing (g) (= 60g)) × 100

[0033] (Appearance evaluation method) The cooked frozen vegetables to be evaluated are placed directly on a microwave-resistant ceramic plate, the entire cooked frozen vegetables are wrapped in food wrap, and the plate is then thawed in a microwave oven at 600W for 1 minute 20 seconds to obtain cooked vegetables. The cooked vegetables are visually observed and evaluated according to the following evaluation criteria. Evaluation is performed by a panel of 10 experts, and the average score of the 10 experts is used as the evaluation result for the evaluation subject. <Appearance evaluation criteria> 5 points: The vegetables were perfectly intact and the amount of water that flowed out of the vegetables due to syneresis was extremely small, making the results extremely good. 4 points: The shape of the vegetables is barely broken down and the amount of water that flows out of the vegetables due to syneresis is small, which is good. 3 points: The shape of the vegetables is slightly distorted or a certain amount of water has leaked out of the vegetables due to separation, but this is not a problem. 2 points: The vegetables are noticeably out of shape or a large amount of water has leaked out of the vegetables due to separation, making them unsuitable. 1 point: The vegetables are noticeably deformed or a large amount of water has leaked out of the vegetables due to separation, making the vegetables extremely poor quality.

[0034] [Table 1]

[0035] [Table 2]

[0036] As shown in Tables 1 and 2, in the examples, oil was used as the heat medium in the preheating step in which the heat medium was brought into contact with the vegetables to be treated (zucchini), and the temperature of the heat medium was set to 40 to 80°C and the heating time (contact time between the vegetables and the heat medium) was set to 5 minutes or more.Therefore, compared to the comparative examples which did not meet these requirements, the water separation rate of the cooked frozen vegetables when thawed in a microwave oven was lower, and the appearance of the cooked vegetables obtained by such heating and thawing was good. In particular, in a comparison of Examples A1 to A5 in Table 1 with Comparative Examples A4 and A5, the former received a higher rating, and in a comparison of Examples A9 to A13 in Table 2 with Comparative Examples A9 and A10, the former received a higher rating, indicating that the temperature of the heat transfer medium (oil) in the preheating step is preferably in the former range of 40 to 80°C. Furthermore, in a comparison of Examples A6 to A8 in Table 1 with Comparative Example A6, the former received a higher rating, and in a comparison of Examples A14 to A16 in Table 2 with Comparative Example A11, the former received a higher rating, indicating that the heating time in the preheating step is preferably in the former range of 5 minutes or more. Furthermore, in a comparison of Examples A2 and A4 in Table 1 with Comparative Examples A2 and A3, the former received a higher rating, and in a comparison of Example A10 in Table 2 with Comparative Example A8, the former received a higher rating, indicating that the oil used in the former is a more effective heat transfer medium in the preheating step than the water used in the latter.

[0037] [Table 3]

[0038] [Table 4]

[0039] As shown in Tables 3 and 4, in the examples, in the preheating step in which the vegetables to be treated (zucchini or peppers) were left standing in a specified environment, the ambient temperature of the environment was set to 40 to 80°C, the relative humidity to 30 to 80%, and the heating time (the time the vegetables were left standing in the specified environment) to 5 minutes or more.Therefore, compared to the comparative examples which did not meet these requirements, the water separation rate of the cooked frozen vegetables when thawed in a microwave oven was lower, and the appearance of the cooked vegetables obtained by such heating and thawing was good. In particular, in a comparison of Examples B1 to B5 in Table 3 with Comparative Examples B1 and B2, the former received higher ratings, and in a comparison of Examples B11 to B13 in Table 4 with Comparative Examples B7 and B8, the former received higher ratings, indicating that the ambient temperature in the preheating step is preferably in the former range of 40 to 80°C. Furthermore, in a comparison of Examples B6 to B9 in Table 3 with Comparative Examples B3 and B4, the former received higher ratings, and in a comparison of Examples B14 and B15 with Comparative Examples B9 and B10 in Table 4, the former received higher ratings, indicating that the relative humidity in the preheating step is preferably in the former range of 30 to 80%. Furthermore, in a comparison of Example B10 in Table 3 with Comparative Example B5, the former received higher ratings, and in a comparison of Example B16 with Comparative Example B11 in Table 4, the former received higher ratings, indicating that the heating time in the preheating step is preferably in the former range of 5 minutes or more.

Claims

1. A method for producing cooked frozen vegetables, comprising a cooking step of cooking vegetables to obtain cooked vegetables, and a freezing step of freezing the cooked vegetables, A method for producing cooked frozen vegetables, comprising a preheating step of heating vegetables before the cooking step, the preheating step comprising the following treatment A or B: Treatment A: Vegetables are brought into contact with oil at a temperature of 40 to 80°C for 5 minutes or more. Treatment B: The vegetables are left to stand in an environment with an atmospheric temperature of 40 to 80°C and a relative humidity of 30 to 80% for 5 minutes or more.

2. The method for producing cooked frozen vegetables according to claim 1 , wherein the cooking step is performed by one or more methods selected from the group consisting of deep-frying, boiling, hot air cooking, and steam cooking.

3. The method for producing cooked frozen vegetables according to claim 1 or 2, wherein the vegetables are one or more selected from the Cucurbitaceae, Solanaceae, and Brassicaceae families.

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