Manufacturing methods for vegetable food products

Abstract

The present invention aims to provide a method for easily producing vegetable food products from frozen vegetables in which the growth of spoilage bacteria is suppressed. [Solution] The method for producing a vegetable food product according to the present invention is characterized by including a step of thawing frozen vegetables by immersing them in a hypertonic solution.

Description

Technical Field

[0001] The present invention relates to a method for simply producing a vegetable food product with suppressed growth of spoilage bacteria from frozen vegetables.

Background Art

[0002] The distribution volume of frozen vegetables is showing an increasing trend in Japan due to their easy storage and convenient cooking, exceeding 1 million tons in 2012 and still increasing. Along with this, improvement in storage technology and processing technology for frozen vegetables is demanded.

[0003] However, different from fresh vegetables, frozen vegetables have a problem that ice crystals are formed during freezing, which destroys cells, and thus a cell sap component called drip comes out after thawing. Since the drip contains abundant nutritional components such as proteins, the growth of spoilage bacteria using the drip as nutrients may significantly deteriorate the quality of vegetable food products using frozen vegetables as raw materials. Therefore, various techniques for solving problems associated with thawing of frozen vegetables have been studied.

[0004] For example, Patent Document 1 discloses a method of heating a vegetable in the presence of an aqueous solution of glycerin and inorganic salts and then freezing it in order to suppress deterioration of texture and drip caused by thawing of frozen vegetables.

[0005] Patent Document 2 discloses a method of immersing a vegetable in a solution containing urea and then freezing it in order to provide frozen vegetables with less tissue denaturation and water separation due to freezing and thawing and excellent texture.

[0006] Further, Patent Document 3 discloses a method of immersing peeled fresh carrots in a hypotonic solution, pulverizing and compressing them for squeezing, and further cooling the squeezed residues such as squeezed pulp in order to produce carrot juice with less unique odor and harshness and carrot squeezed residues having a soft and moist texture.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2024-77475 [Patent Document 2] Japanese Patent Publication No. 2001-224304 [Patent Document 3] Japanese Patent Publication No. 2023-108755 [Overview of the project] [Problems that the invention aims to solve]

[0008] As mentioned above, methods of treating vegetables with salt or urea solutions before freezing are known to suppress drip loss during thawing and improve the texture of thawed vegetables. However, it is unclear whether these methods suppress the deterioration of quality due to the growth of spoilage bacteria after thawing. Therefore, the present invention aims to provide a method for easily producing vegetable food products from frozen vegetables in which the growth of spoilage bacteria is suppressed. [Means for solving the problem]

[0009] The inventors diligently conducted research to solve the above problems. As a result, they discovered that thawing frozen vegetables using a hypertonic solution can reduce drip loss and suppress the growth of spoilage bacteria, thus completing the present invention. The present invention is described below.

[0010] [1] A method for producing vegetable food products, A method characterized by including a step of thawing frozen vegetables by immersing them in a hypertonic solution. [2] The method according to [1], further comprising the step of immersing thawed frozen vegetables in a seasoning liquid. [3] The method according to [1] or [2], wherein the salt concentration of the hypertonic solution is 5% by mass or more and 20% by mass or less. [4] The method according to any one of the above [1] to [3], wherein the hypertonic solution is an aqueous solution of one or more food additives selected from sodium chloride, potassium chloride, amino acids, organic acids, and sugars. [Effects of the Invention]

[0011] According to the method of the present invention, drip resulting from cell damage caused by freezing and thawing can be easily removed. Furthermore, the growth of spoilage bacteria after thawing frozen vegetables can be suppressed. In addition, it is possible that solutes, possibly derived from the hypertonic solution, penetrate the thawed vegetables, thereby suppressing enzyme activity in the vegetables and inhibiting spoilage. Therefore, the present invention is industrially excellent as a technology that can produce high-quality products from frozen vegetables, whose distribution volume is continuously increasing. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a graph comparing the number of spoilage bacteria in vegetable foods thawed with the hypertonic solution according to the present invention and in vegetable foods thawed with water. [Modes for carrying out the invention]

[0013] The present invention will be described below step by step, but the present invention is not limited to the following specific examples.

[0014] 1. Pre-treatment process In this process, the raw vegetables are processed as needed before freezing. However, this process is optional; for example, if frozen vegetables are available or if vegetables similar to those obtained in this process can be obtained by other means, this process is not necessary.

[0015] The vegetable raw materials of the vegetable food products according to the present invention are not particularly limited as long as they can be frozen. For example, solanaceous fruits such as okra; leguminous fruits such as edamame; cucurbitaceous fruits such as cucumber, bitter melon, zucchini, wax gourd; solanaceous fruits such as pepper, tomato, eggplant, green pepper; liliaceous stem vegetables such as garlic, scallion, Chinese onion; convolvulaceous stem vegetables such as sweet potato, water spinach; zingiberaceous stem vegetables such as ginger; gramineous stem vegetables such as corn, bamboo shoot; brassicaceous root vegetables such as broccoli, cauliflower, turnip, chrysanthemum greens, daikon radish; umbelliferous root vegetables such as carrot; zingiberaceous flower vegetables such as myoga; brassicaceous leaf vegetables such as green vegetable, cabbage, komatsuna, Chinese kale, chrysanthemum greens, takana, chingensai, wild vegetable, Chinese cabbage, spinach, mizuna, ninasai; liliaceous leaf vegetables such as leek; asteraceous leaf vegetables such as lettuce; grains such as rice, beans, wheat, barley; fruits such as grape; rice bran; mushrooms such as shimeji, maitake, eryngii, nameko, shiitake, etc. can be mentioned.

[0016] The pretreatment performed in this step is not particularly limited as long as it is a treatment for making the raw vegetables suitable for freezing, consumption, etc. For example, washing, peeling, cutting, sterilization, heating, etc. can be mentioned.

[0017] Since mud, soil, microorganisms, etc. adhere to the vegetables immediately after harvesting, it is preferable to wash them. For example, they may be washed with water such as tap water. At that time, aeration washing may also be used industrially. Aeration washing is a washing method in which gas is introduced while the raw vegetables are immersed in a water tank, and the water and vegetables are made to flow for washing. Ozone may be blended into the gas introduced for the purpose of sterilization, etc. Also, an aqueous solution of sodium hypochlorite may be used for sterilization.

[0018] Depending on the type of vegetable, pretreatment such as peeling or removing the fibrous roots may be performed as necessary. Also, the vegetables may be cut into an appropriate size according to the form of the final product, etc. When cutting, it is preferable to unify the size and cutting method in order to unify the penetration degree of food additive components such as salts.

[0019] Heating can be carried out for purposes such as sterilization, prevention of destruction of the vegetable tissue by freezing, and inactivation of enzymes contained in the vegetables. The heating conditions can be adjusted as appropriate. For example, the raw vegetables that have been washed, etc. may be heated to 60°C or higher and 100°C or lower. By heating at 60°C or higher, it is possible to more reliably sterilize particularly spoilage-causing bacteria. Also, if the heating temperature is 100°C or lower, it is possible to more reliably suppress the discoloration of the vegetables. The heating time can also be adjusted as appropriate, and for example, it can be set to 30 seconds or longer and 2 minutes or shorter. As the heating method, for example, warm water heating, steam heating, etc. may be used.

[0020] 2. Freezing step In this step, the vegetables are frozen. The vegetables to be frozen are preferably those heated in the above step 1. By freezing the vegetables, the storage period can be extended and transportation becomes possible. The implementation of this step is optional. For example, when frozen vegetables are available, there is no need to implement this step.

[0021] The freezing conditions can be adjusted as appropriate. For example, the raw vegetables that have been heat-treated, etc. may be cooled to -30°C or higher and -15°C or lower. By freezing within this temperature range, more reliable stable storage of the vegetables becomes possible. The cooling time can also be adjusted as appropriate, and for example, it can be set to 24 hours or longer. The upper limit of the cooling time is not particularly limited according to the frozen storage period, and for example, it can be set to within 3 years.

[0022] [[ID=!13]] The vegetables may be rapidly frozen. Rapid freezing means cooling at a cooling rate of -30°C / min or higher. With rapid freezing, uniform freezing is possible while suppressing freezing unevenness, and since cell destruction can be suppressed, deterioration and shape collapse can be suppressed.

[0023] 3. Thawing step In this process, frozen vegetables are thawed by immersing them in a hypertonic solution. When vegetables are frozen, ice crystals form in the cytoplasm, damaging the cells, and thawing can cause cytoplasmic fluid to leak from the damaged cells. This cytoplasmic fluid, called drip, contains proteins and other substances, which can cause spoilage bacteria to proliferate. However, thawing in a hypertonic solution allows the drip to be released into the solution, thus suppressing spoilage of the vegetables. In addition, the components of the hypertonic solution penetrate into the vegetables, creating a hypertonic state inside the vegetables, which may suppress enzyme activity and prevent deterioration due to enzymatic reactions after harvesting. Furthermore, the hypertonic solution dehydrates the cells of the raw vegetables, making the tissue more flexible, which allows seasoning liquids to penetrate the vegetables more easily. Depending on the components of the hypertonic solution, it may also impart flavors such as umami and saltiness to the vegetables.

[0024] A hypertonic solution is an aqueous solution with a higher osmotic pressure than intracellular fluid. Components of a hypertonic solution include, for example, salts such as sodium chloride and potassium chloride; amino acids and their salts, such as glycine, glutamic acid, and monosodium glutamate; nucleic acids such as inosinic acid and guanylic acid; other organic acids and their salts, such as acetic acid, citric acid, and ascorbic acid; and sugars such as glucose, sucrose, sorbitol, xylitol, and sucrose. A single component may be used in the hypertonic solution, or two or more components may be used in combination.

[0025] The concentration of the solute in the hypertonic solution can be, for example, 1% by mass or more and 40% by mass or less, depending on the type of solute and the osmotic pressure of the hypertonic solution being greater than 2 MPa. Preferably, the concentration is 2% by mass or more, more preferably 5% by mass or more or 10% by mass or more, even more preferably 15% by mass or more or 20% by mass or more, and preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0026] The salt concentration in the hypertonic solution can be adjusted, for example, to 5% by mass or more and 20% by mass or less.

[0027] Thawing conditions can be adjusted as appropriate within a range that allows for good thawing of vegetables. For example, frozen vegetables can be immersed in a hypertonic solution at a temperature of 0°C or higher for at least 1 hour and no more than 120 hours. At temperatures above 0°C, vegetables can be thawed efficiently. There is no particular upper limit to the thawing temperature, but it can be, for example, 40°C or lower. Thawing at a temperature of 40°C or lower can more reliably suppress spoilage of vegetables. Thawing can also be done at room temperature or at a temperature of 15°C or lower. Thawing at a temperature of 15°C or lower can more reliably suppress the growth of spoilage bacteria and the deterioration of vegetables. The thawing temperature may also be 10°C or lower. The thawing time can be determined by confirming that the vegetables have thawed, or by conducting small-scale preliminary experiments.

[0028] After thawing, the usual post-processing steps should be followed. For example, the thawed vegetables and the hypertonic liquid can be separated by decantation, filtration, or centrifugation.

[0029] 4. Seasoning process In this step, the thawed frozen vegetables are flavored by immersing them in a seasoning liquid. Performing this step is optional; for example, if the vegetables have been sufficiently flavored with the hypertonic solution during the thawing process, this step is not necessary.

[0030] The seasoning liquid can be selected appropriately according to the type of final product to be made, and is not particularly limited, but examples include salts such as table salt and sodium chloride; amino acids such as glutamic acid, monosodium glutamate, glycine, and alanine and their salts; nucleic acids such as guanylic acid and inosinic acid; sweeteners such as sugar, isomerized sugar, starch syrup, oligosaccharides, stevia, saccharin, sorbitol, erythritol, xylitol, and maltitol; pH adjusters such as citric acid, lactic acid, acetic acid, and sodium acetate; and seasonings such as soy sauce, fish sauce, acid-hydrolyzed amino acid solution, protein hydrolysates, animal and plant extracts, yeast extract, and mirin.

[0031] After thawing the vegetables, they may be immersed in the seasoning liquid and then individually packaged as a product, or the seasoning liquid may be removed from the vegetables before packaging. In either case, the growth of spoilage bacteria is suppressed in this invention, thus preventing deterioration during storage and distribution. [Examples]

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0033] Example 1 After washing the okra with water, it was sterilized by washing it in a 200 ppm sodium hypochlorite solution at room temperature for 5 minutes. Then, the stems were cut off and removed, and it was sterilized again by washing it in a 200 ppm sodium hypochlorite solution at room temperature for 5 minutes. Next, it was heat-sterilized by immersing it in 75-80°C water for 1 minute. After heat sterilization, it was immediately cooled and frozen at -20°C for 10 days. Separately, a first and second immersion solution were prepared with the compositions shown in Table 1 below. In Table 1, "%" represents "mass%".

[0034] [Table 1]

[0035] After freezing, the okra was thawed by immersing it in the first pickling solution at 10°C for 24 hours. After thawing, the okra was separated from the first pickling solution and immersed in the second pickling solution at 10°C to produce lightly pickled okra.

[0036] Comparative Example 1 Lightly pickled okra was prepared in the same manner as in Example 1, except that the frozen okra was thawed by immersing it in water instead of the first pickling liquid.

[0037] Test Example 1: Evaluation of the number of bacteria causing spoilage The pickles prepared in Example 1 and Comparative Example 1 were treated with the spoilage-causing bacterium (Leuconostoc mesenteroides) at a concentration of 10 per gram of pickles. 2 CFU was inoculated and stored in a refrigerator at 10°C for 7 days. Next, the lightly pickled vegetables were placed in a bag and tapped from the outside with a stick to obtain juice. The total number of viable bacteria in the obtained juice was measured according to the official method for measuring bacterial viability in the Food Hygiene Inspection Guidelines 2018 (Microbiology). Specifically, the juice was diluted 10-fold, 100-fold, 1,000-fold, 10,000-fold, 100,000-fold, 1,000,000-fold, or 10,000,000-fold with a 0.9% by mass peptone aqueous solution and spread onto a general viable bacteria detection medium consisting of peptone, yeast extract, glucose, and agar. After incubating the medium at 35°C for 2 days, the number of spoilage-causing bacteria in the lightly pickled vegetables was calculated from the number of colonies that grew. The results are shown in Figure 1 and Table 2.

[0038] [Table 2]

[0039] Generally, a sample is considered to have no commercial value (spoilage) due to cloudiness of the pickling liquid, etc., if it is 10% per gram. 7 This is when a bacterial count exceeding the above is detected (see "Asama Partner News" 2012-1, No. 146). In addition, according to the old Food Hygiene Standards for Bento and Prepared Foods, unheated products such as salads and raw vegetables must have a bacterial count (viable count) of 1,000,000 or less per gram of sample (10 6 The following is required: In Comparative Example 1, which was thawed with water, spoilage bacteria exceeding these criteria were identified, whereas in Example 1, which was thawed with hypertonic solution, both criteria were met.

Claims

1. A method for manufacturing vegetable food products, A method characterized by including a step of thawing frozen vegetables by immersing them in a hypertonic solution.

2. Furthermore, the method according to claim 1, further comprising the step of immersing thawed frozen vegetables in a seasoning liquid.

3. The method according to claim 1, wherein the salt concentration of the hypertonic solution is 5% by mass or more and 20% by mass or less.

4. The method according to claim 1, wherein the hypertonic solution is an aqueous solution of one or more food additives selected from sodium chloride, potassium chloride, amino acids, organic acids, and sugars.

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