Deamidated casein and method for producing same

Abstract

The purpose of the present invention is to provide a modified milk protein that has high solubility in an acidic region, excellent foaming properties and high safety, and a method for producing the milk protein while minimizing the risk of exposure to hydrolysis. This purpose can be solved by, for example, a method for producing deamidated casein that comprises a step for subjecting a casein-containing suspension to a deamidation reaction using a weakly acidic cation exchange resin, which has an alkali metal salt-type ion exchange group, for 4-50 hours at 40-90°C to thereby give deamidated casein having a deamidation ratio of 14% or more and less than 32%.

Description

[Technical Field]

[0001] The present invention relates to deamidated casein having excellent solubility and foamability in an acidic range, and a method for producing the same. [Background technology]

[0002] Casein accounts for approximately 80% of the proteins in milk (milk proteins), and is widely used as a nutritional supplement because it contains a balanced amount of essential amino acids. The remaining milk proteins are whey proteins such as lactalbumin and lactoglobulin.

[0003] Casein is poorly soluble in water, making it difficult to incorporate into foaming compositions used to prepare foamy foods such as foamed milk and whipped cream. Therefore, sodium caseinate (Na caseinate) is known as a modified casein whose functionality has been improved to enhance its water solubility. Na caseinate can be obtained by reacting casein with a basic solution such as an aqueous sodium hydroxide solution. Na caseinate is commonly used as a food additive because it has high solubility in solvents with a neutral to alkaline pH and excellent physicochemical properties such as foaming and emulsifying properties.

[0004] On the other hand, protein deamidation is known as a technique for improving the function of proteins such as casein. Protein deamidation is a reaction that converts the amide groups (-CONH2) in the side chains of glutamine and asparagine residues in proteins into carboxyl groups (-COOH), converting them into other amino acid residues such as glutamic acid and aspartic acid (see Figure 1). The carboxyl groups generated by deamidation are in a state where the hydrogen is ionized (-COO) compared to the amide groups. -), which may lower the isoelectric point of the protein and contribute to improving the solubility and water dispersibility of the protein in the acidic range. Protein deamidation techniques include chemical treatment using acid or alkali, enzymatic treatment using an enzyme (protein glutaminase), and resin treatment using an ion exchange resin.

[0005] Deamidated casein obtained by an enzymatic treatment method with a deamidation rate of more than 35% has been known (see, for example, Patent Documents 1 and 2). On the other hand, deamidated products of soybean proteins obtained by a resin treatment method have been known (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2017-516469 [Patent Document 2] Special Publication No. 2015-524276 [Patent Document 3] Patent No. 4512716 Summary of the Invention [Problem to be solved by the invention]

[0007] Although sodium caseinate has improved water solubility compared to casein, like casein, its solubility decreases significantly under acidic conditions near its isoelectric point, making it unsuitable for use in acidic foods.

[0008] On the other hand, the deamidated casein described in Patent Documents 1 and 2 is obtained by a deamidation reaction in a casein solution using an enzyme called protein glutaminase, which specifically deamidates glutamine residues in proteins to glutamic acid residues.

[0009] The deamidation reaction using protein glutaminase requires a step of inactivating the enzyme remaining after the reaction, specifically, a step of further heating the deamidation reaction at 50°C to 90°C to inactivate the enzyme. Although this step inactivates the enzyme, it also carries the risk of exposing the product, deamidated casein, to hydrolysis.

[0010] In addition, the protein glutaminase currently in use is derived from Chryseobacterium proteolyticum ( Chryseobacterium proteolyticum ) and has not been approved by the Food Safety Commission and cannot be used in Japan.

[0011] Patent Document 3 describes that soybean protein was deamidated by a resin treatment method using a deamidation reaction at pH 7.4, 4°C, and 6 hours. However, the method described in Patent Document 3 targets soybean protein, a vegetable protein, which has a structure completely different from that of milk protein such as casein, an animal protein.

[0012] Furthermore, little is known so far about modified milk proteins that are highly soluble in an acidic range and have excellent foaming properties, and about methods for producing the same.

[0013] Therefore, the problem that the present invention aims to solve is to provide a modified milk protein that has high solubility in the acidic range, excellent foaming properties, and high safety, and to provide a method for producing the milk protein with reduced risk of exposure to hydrolysis. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above problems, and have conducted trial and error to find a method for modifying milk proteins. Among milk proteins, they first focused on whey proteins, which are relatively water-soluble. When whey proteins were deamidated as described in the Examples below, the resulting deamidated whey proteins had a low deamidation rate, and showed almost no improvement in foaming ability compared to whey proteins, and their emulsifying ability was actually reduced. Therefore, it cannot be said that the deamidated whey proteins improve the functionality of whey proteins.

[0015] Next, the present inventors investigated the deamidation of casein sodium and casein. In an attempt to achieve deamidation of casein sodium and casein by a resin treatment method, they found that the deamidation reaction under the conditions described in Patent Document 3 was almost unable to deamidate them. Furthermore, the present inventors found that when the deamidation rate does not fall within a predetermined range, problems such as hydrolysis occur and foamability cannot be stably maintained arise. Furthermore, they found that deamidation of casein sodium by a resin treatment method tends to result in a low recovery rate and a low deamidation rate.

[0016] Under these circumstances, the present inventors further conducted trial and error on the deamidation of casein, and succeeded in obtaining deamidated casein with a deamidation rate within a predetermined range by performing a deamidation reaction using a specific weakly acidic cation exchange resin at a temperature and time set within a specific range. Surprisingly, they found that such deamidated casein not only has excellent solubility and foamability in the acidic range, but also has good emulsifying properties. Furthermore, the method utilizing the above-mentioned deamidation reaction can increase the recovery rate of deamidated casein by avoiding hydrolysis. Moreover, this method does not require the use of enzymes, and the resin used is one that is widely used in the food industry, such as for refining amino acids and sucrose, making it a highly safe method.

[0017] Based on the above findings and successful examples, the present inventors have finally succeeded in creating deamidated casein having a deamidation rate of 14% or more and less than 32%, and a method for producing the same, which can solve the problems of the present invention. The present invention has been completed based on the findings and successful examples first discovered by the present inventors.

[0018] Therefore, according to the present invention, there are provided the following methods, compositions, and deamidated casein in each aspect. [1] A step of subjecting a suspension containing casein to a deamidation reaction using a weakly acidic cation exchange resin whose ion exchange groups are in the alkali metal salt form at 40°C to 90°C for 4 hours to 50 hours to obtain deamidated casein having a deamidation rate of 14% or more but less than 32%. A method for producing deamidated casein, comprising: [2] The method according to [1], further comprising a step of subjecting the resin residue recovered after the deamidation reaction to an elution treatment using an acidic aqueous solution to obtain deamidated casein. [3] The method according to [2], wherein the recovery rate of the deamidated casein is 70% or more relative to the casein. [4] The method according to any one of [1] to [3], wherein the alkali metal salt type is at least one alkali metal salt type selected from the group consisting of a sodium type and a potassium type. [5] A foamable composition comprising deamidated casein having a deamidation rate of 14% or more but less than 32% and water. [6] The foaming composition is a compound containing Chryseobacterium proteolyticum ( Chryseobacterium proteolyticum The composition according to [5], which is substantially free of protein glutaminase derived from Bacillus subtilis. [7] Deamidated casein having a deamidation rate of 14% or more but less than 32%. [8] A step of improving foamability by using deamidated casein having a deamidation rate of 14% or more but less than 32% and water, compared to the case where casein or sodium caseinate is used instead of the deamidated casein. A method for improving foamability, comprising: [Effects of the Invention]

[0019] According to a method of one aspect of the present invention, deamidated casein that has high solubility in the acidic range, excellent foaming ability, and high safety can be produced with reduced risk of exposure to hydrolysis. The deamidated casein of one aspect of the present invention has good emulsifying ability in addition to solubility and foaming ability in the acidic range, and is therefore expected to be used as a food additive such as a foaming agent, emulsifier, or stabilizer, or as a food ingredient as a milk protein, over a wide pH range.

[0020] According to one embodiment of the foamable composition of the present invention, since it has good foaming and emulsifying properties and is easy to work with, it is possible to easily produce and use foamed foods such as foamed milk and whipped cream with stable foam quality in a short time. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of protein deamidation. [Figure 2] FIG. 2 is a graph showing the measurement results of the solubility of casein, sodium caseinate, and deamidated casein in the acidic range, as described in the Examples below. [Figure 3] 3 shows the measurement results of the foaming properties of casein, sodium caseinate, and deamidated casein in the acidic range, as described in the Examples below. The upper left figure shows the measurement results immediately after foaming (0 minutes), the upper right figure shows the measurement results 30 minutes after foaming, and the lower left figure shows the measurement results 60 minutes after foaming. [Figure 4] 4 shows the results of measuring the emulsifying properties of casein, sodium caseinate, and deamidated casein in the acidic range, as described in the Examples below. The left graph shows the results measured immediately after emulsification (0 minutes), and the right graph shows the results measured 10 minutes after emulsification. [Figure 5]FIG. 5 shows the results of two-dimensional electrophoresis of casein and deamidated casein, showing the change in the isoelectric point of casein due to deamidation, as described in the Examples below. [Figure 6] FIG. 6 shows the results of SDS-PAGE of casein, sodium caseinate, and deamidated casein, indicating the degree of hydrolysis of casein due to deamidation, as described in the Examples below. [Figure 7] FIG. 7 shows the results of SDS-PAGE of casein and sodium caseinate, as well as deamidated casein obtained at deamidation reaction temperatures of 55°C to 80°C, indicating the degree of casein hydrolysis depending on the reaction temperature, as described in the Examples below. [Figure 8] FIG. 8 is a diagram showing the measurement results of the solubility of casein, sodium caseinate, and deamidated casein in the acidic range, as described in the Examples below. [Figure 9] FIG. 9 is a diagram showing the results of measuring the emulsifying properties of casein, sodium caseinate, and deamidated casein, as described in the Examples below. [Figure 10] FIG. 10 is a graph showing the measurement results of the foaming properties of casein, sodium caseinate, and deamidated casein, as described in the Examples below. [Figure 11] FIG. 11 shows the results of SDS-PAGE of casein, sodium caseinate, and deamidated casein, showing the degree of casein hydrolysis due to deamidation, as described in the Examples below. DETAILED DESCRIPTION OF THE INVENTION

[0022] Each aspect of the present invention will be described in detail below, but the present invention can take various forms as long as it achieves its object.

[0023] Unless otherwise specified, the terms used in this specification are used in the sense commonly used by those skilled in the food industry and should not be construed as having an unduly restrictive meaning. Furthermore, the speculations and theories made in this specification are based on the inventors' knowledge and experience to date, and therefore the present invention is not limited solely to such speculations and theories.

[0024] Among the meanings of terms used in this specification, those that are set forth in the "Ministerial Ordinance on Milk and Dairy Products Compositional Standards, etc." (hereinafter referred to as the "Milk, etc. Ministerial Ordinance"; the entire contents of said document are incorporated herein by reference) shall be interpreted as having the meanings set forth in the Milk, etc. Ministerial Ordinance.

[0025] The term "composition" is not particularly limited to the meaning normally used, but may refer to, for example, a substance formed by combining two or more components. "Content" is synonymous with concentration and amount used (amount added), and refers to the amount of a component relative to the total amount of the composition, provided that the total amount of the components does not exceed 100%. The unit "vol%" is synonymous with "%(v / v)" and "volume %". The unit "wt%" is synonymous with "%(w / w)" and "mass %". The unit "%(w / v)" is synonymous with "mass volume %". The term "and / or" means any one or any or all combinations of two or more of the associated listed items. The "to" in a numerical range includes the preceding and following numerical values; for example, "0% to 100%" means a range greater than or equal to 0% and less than or equal to 100%. "More than" and "less than" mean the lower and upper limits, respectively, excluding the preceding numerical value; for example, "more than 1" means a numerical value greater than 1, and "less than 100" means a numerical value less than 100. "Comprising" means that elements other than those explicitly stated as being included can be added (same meaning as "comprising at least"), but also encompasses "consisting of" and "consisting essentially of." That is, "comprising" can mean including the explicitly stated elements and any one or more elements, consisting of the explicitly stated elements, or consisting essentially of the explicitly stated elements. Elements include limitations such as ingredients, steps, conditions, and parameters. "Substantially free of" a specific component means that it is not intentionally included, except in cases where it is unavoidably mixed in due to the raw materials or manufacturing process of components other than the specific component. Therefore, "substantially free of" means that it is not included at all, or if it is included, it is in an extremely small amount.

[0026] The number of digits in an integer value matches the number of significant digits. For example, 1 has one significant digit, and 10 has two significant digits. Also, the number of digits after the decimal point in a decimal value matches the number of significant digits. For example, 0.1 has one significant digit, and 0.10 has two significant digits.

[0027] [1. Method for producing deamidated casein] A method according to one aspect of the present invention is a method for producing deamidated casein having a deamidation rate within a predetermined range, characterized in that the method comprises subjecting raw material casein to a deamidation reaction under predetermined conditions using a weakly acidic cation exchange resin in which the ion exchange groups are in the alkali metal salt form, thereby obtaining deamidated casein.

[0028] In one aspect of the method of the present invention, a suspension containing casein is subjected to a deamidation reaction.

[0029] Casein refers to a phosphorus-containing milk protein contained in mammalian milk, and may include α-casein, β-casein, and κ-casein. Casein may be casein micelles. Although casein is less soluble in water than sodium caseinate, by subjecting it to the method of one aspect of the present invention, it can exhibit solubility and / or foaming properties in the acidic range that are equivalent to or superior to those of sodium caseinate.

[0030] The mammalian milk from which casein is derived is not particularly limited, and examples thereof include milk from cows, goats, sheep, etc., but cow's milk is preferred from the viewpoints of palatability and availability. The form of casein is not particularly limited, and examples thereof include powder, granules, paste, etc., and any of these forms can be used.

[0031] The casein may be either one separated and processed from mammalian milk and its skim milk by a known method, or a commercially available product. The casein is preferably a purified product, but casein with an increased amount of casein to a certain extent may also be used. The protein content of the casein is preferably 50% (w / w) to 100% (w / w). The casein may be one of the above-mentioned types alone, or a combination of two or more types.

[0032] A casein-containing suspension can be obtained by dispersing casein in water. The water is not particularly limited as long as it is water used in food production, and examples include tap water, purified water, and ultrapure water. The degree of dispersion of casein in the suspension is not particularly limited, but preferably, for example, to the extent that no obvious casein clumps are visible to the naked eye. The casein content in the suspension is not particularly limited, but, for example, to maintain good casein dispersibility, it is preferably 0.1% (w / v) to 10% (w / v), and more preferably 0.5% (w / v) to 5% (w / v).

[0033] The deamidation reaction is carried out by contacting a suspension containing casein with a weakly acidic cation exchange resin whose ion exchange groups are in the alkali metal salt form under specified conditions. Through the deamidation reaction, the asparagine and glutamine residues constituting casein are converted to aspartic acid and glutamic acid residues via the substitution of hydroxyl groups (-OH) for the amino groups (-NH2) in the amide groups (-CO-NH2) to form carboxyl groups (-COOH).

[0034] The weakly acidic cation exchange resin is not particularly limited as long as it is a cation exchange resin having a weakly acidic ion exchange group, and examples thereof include cation exchange resins having -COOH and -N(CH2COOH)2 as weakly acidic ion exchange groups. The ion exchange capacity of the weakly acidic cation exchange resin is not particularly limited, and is preferably, for example, 0.5 g equivalents / L wet resin to 5 g equivalents / L wet resin.

[0035] The weakly acidic cation exchange resin may be either one produced by a known method or a commercially available one, such as "Amberlite IRC76," "Amberlite FPC3500," or "Amberlite IRC718" (Organo Corporation).

[0036] Before contacting the resin with a suspension containing casein, the ion exchange groups of the weakly acidic cation exchange resin are converted to the alkali metal salt form. If the ion exchange groups are already in the alkali metal salt form, they can be used in that state. However, if the ion exchange groups are in the H form, they are converted to the alkali metal salt form. The method for converting the ion exchange groups to the alkali metal salt form is not particularly limited, but examples include converting the weakly acidic cation exchange resin to the H form with an acid, and then immersing or passing it through a solution containing an alkali metal salt to convert it to the alkali metal salt form.

[0037] The type of alkali metal salt form is not particularly limited, and examples include sodium (Na) form, potassium (K) form, and lithium (Li) form. However, the Na and K forms are preferred because the alkali metal salt form can be obtained easily and economically. To obtain a weakly acidic cation exchange resin whose alkali metal salt form is the Na or K form, sodium chloride or potassium chloride may be used as the neutral salt; or sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, or the like may be used as the hydroxide. However, when the resulting deamidated casein is to be used as a food product, the alkali metal salt form is preferably the Na form. For general and economic reasons, it is preferred to use an aqueous solution of table salt, sodium hydroxide, or a mixture thereof for conversion to the Na form.

[0038] For example, conversion of a weakly acidic cation exchange resin to the Na form can be achieved by first adding a 0.5N to 2N aqueous hydrochloric acid solution to a container containing the weakly acidic cation exchange resin to convert it to the H form, and then adding a 0.5N to 2N aqueous sodium hydroxide solution to convert it to the Na form.

[0039] The method for contacting the casein-containing suspension with the weakly acidic cation exchange resin is not particularly limited, and either a batch method in which the weakly acidic cation exchange resin is immersed in the casein-containing suspension or a column method in which the casein-containing suspension is passed through a column packed with the weakly acidic cation exchange resin can be used. In either method, stirring is preferred to increase the number of times the casein comes into contact with the weakly acidic cation exchange resin.

[0040] The amount of weakly acidic cation exchange resin used is not particularly limited, but for example, from the viewpoint of ensuring good contact between the casein in the suspension and the weakly acidic cation exchange resin, when the suspension contains 0.1% (w / v) to 10% (w / v) casein, the amount is preferably 1 g to 200 g, more preferably 10 g to 100 g, and even more preferably 30 g to 70 g per 100 mL of suspension.

[0041] Generally, the deamidation reaction of a protein by the resin treatment method is carried out at a low temperature such as 4°C or at room temperature (20°C to 30°C) to avoid decomposition or inactivation of the protein. For the same reason, the deamidation reaction of a protein is carried out for several hours.

[0042] However, according to the investigations of the present inventors, even if the deamidation reaction of casein is carried out for several hours at a low temperature or at room temperature, the deamidation rate of the resulting deamidated casein is very small. Therefore, when the deamidation reaction of casein is carried out at a temperature higher than room temperature for several hours to several tens of hours according to the temperature, deamidated casein with a high deamidation rate is obtained. On the other hand, as the reaction temperature increases, although the deamidation rate increases, deamidated casein that stably maintains foamability also progresses, and it becomes impossible to obtain deamidated casein.

[0043] In view of the above circumstances, in a method of one embodiment of the present invention, the deamidation reaction is carried out at a temperature of 40°C to 90°C, preferably 50°C to 85°C, and more preferably 50°C to 80°C, for 4 hours to 50 hours, preferably 5 hours to 40 hours, and more preferably 6 hours to 35 hours. Furthermore, the deamidation reaction is preferably carried out at 80°C to 90°C for 4 hours to 10 hours, preferably at 60°C to 70°C for 10 hours to 15 hours, or preferably at 40°C to 50°C for 25 hours to 35 hours. The deamidation reaction may be carried out under conditions within the above-mentioned temperature and time ranges that result in deamidated casein having the desired deamidation rate.

[0044] The pH of the deamidation reaction is not particularly limited, but is preferably near neutral, more preferably 6 to 10, from the viewpoint of suppressing decomposition of deamidated casein, for example.

[0045] By subjecting a suspension containing casein to a deamidation reaction under the above conditions, deamidated casein can be obtained in the reaction solution. However, some of the deamidated casein may be adsorbed to the resin. Therefore, in order to increase the recovery rate of deamidated casein, it is preferable to separate the reaction solution from the resin residue after the deamidation reaction, and then subject the recovered resin residue to an elution treatment using an acidic aqueous solution to obtain deamidated casein as an eluate.

[0046] The acidic aqueous solution used for the elution treatment is not particularly limited in type, concentration, or amount used, as long as it can elute deamidated casein from the weakly acidic cation exchange resin, i.e., can adjust the pH around the weakly acidic cation exchange resin to a pH that is equal to or lower than the isoelectric point of deamidated casein, specifically 3.7 or lower, and may be appropriately selected depending on the type and amount of the weakly acidic cation exchange resin, the type and volume of the container such as a tank or column that contains or is filled with the weakly acidic cation exchange resin, the amount of deamidated casein adsorbed, etc.

[0047] Specific examples of acidic aqueous solutions include aqueous solutions containing inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, with an aqueous solution containing hydrochloric acid being preferred from the viewpoint of safety, more preferably an aqueous solution containing 0.1 N to 5 N hydrochloric acid, and even more preferably an aqueous solution containing 0.5 N to 1.5 N hydrochloric acid. The elution treatment may be carried out by contacting the resin with an aqueous solution containing hydrochloric acid, or by contacting the resin with water and then adding an inorganic acid.

[0048] By carrying out the elution treatment with stirring, workability is improved even when a large amount of resin is used, and the pH around the weakly acidic cation exchange resin can be lowered uniformly and quickly, allowing deamidated casein to be eluted more efficiently. The elution treatment may be carried out once or multiple times, but is preferably carried out once to avoid decomposition of the deamidated casein.

[0049] Deamidated casein can be obtained from the reaction solution after the deamidation reaction and the eluate after the elution treatment. For use as a food ingredient, deamidated casein is preferably in the form of solid deamidated casein. For example, the reaction solution after the deamidation reaction and the eluate after the elution treatment can be subjected, individually or in combination, to a solid-liquid separation treatment such as filtration, a desalting treatment (dialysis) using water and a dialysis membrane, or a drying treatment such as freeze-drying, thereby obtaining powdery deamidated casein. The conditions, procedures, and other methods for each treatment are not particularly limited, and known methods can be used, as long as they do not significantly decompose or lose deamidated casein.

[0050] As described above, deamidated casein having a deamidation rate within a predetermined range is obtained. The deamidation rate of deamidated casein is a rate at which the deamidated casein has solubility and / or foamability in the acidic range equivalent to or greater than that of sodium caseinate, specifically, 14% or more and less than 32%. However, from the viewpoint of, for example, good foamability and emulsifying properties, it is more preferably 15% or more and less than 32%, even more preferably 15% to 31%, and even more preferably 16% to 27%. The recovery rate of deamidated casein is not particularly limited, but is preferably, for example, 70% or more, and more preferably 75% or more. Deamidated casein obtained with a recovery rate of less than 70% may have undergone hydrolysis and may have poor solubility and / or foamability in the acidic range. The recovery rate is calculated as the ratio of the amount of deamidated casein obtained to the amount of casein used as raw material (=[amount of deamidated casein] / [amount of casein]×100).

[0051] The method of one aspect of the present invention can include various steps and / or operations before, after, or between the steps described above, as long as the object of the present invention can be achieved. Specific embodiments of the method of one aspect of the present invention will be described below, but the method of the present invention is not limited to the following.

[0052] Casein separated from milk by a commercially available or known method is suspended in water to prepare a 0.5% (w / v) to 5% (w / v) casein suspension. Next, a sodium-type weakly acidic cation exchange resin is added to 100 mL of the suspension to a concentration of 30 g to 70 g, and the deamidation reaction is carried out by stirring at pH 6 to 8, 50 to 60°C, and 25 to 35 hours. The reaction solution is then separated from the resin, and the reaction solution is recovered. Water and a 0.5N to 1.5N aqueous hydrochloric acid solution are added to the remaining resin, and the mixture is stirred at room temperature for several tens of minutes to carry out an elution treatment. The eluate is then separated from the resin, and the eluate is recovered. The mixture of the reaction solution and eluate is dialyzed against water at low temperature for several days, followed by drying to obtain powdered deamidated casein with a deamidation rate of 20% or more but less than 32%.

[0053] [2. Deamidated casein] Another aspect of the present invention is deamidated casein having a deamidation rate of 14% or more and less than 32%. The deamidation rate of the deamidated casein may be 14% or more and less than 32%, but from the viewpoint of good foaming and emulsifying properties, the deamidation rate is preferably 15% to 31%, and more preferably 16% to 27%.

[0054] The deamidated casein of one embodiment of the present invention has excellent solubility and foamability in the acidic range. The solubility and foamability of the deamidated casein of one embodiment of the present invention in the acidic range are not particularly limited, but it is preferable that, for example, the solubility measured in a pH range of 4.5 to 6.0 is approximately higher than that of sodium caseinate; and / or the foamability measured in a pH range of 3.0 to 6.0 30 minutes after foaming is approximately higher than that of sodium caseinate.

[0055] The deamidated casein of one embodiment of the present invention also has good emulsifying properties. The emulsifying properties of the deamidated casein of one embodiment of the present invention are not particularly limited, but it is preferable that the emulsifying properties be higher than those of casein, for example, when measured at a pH range of 4.5 to 5.5 10 minutes after preparation.

[0056] The deamidation rate, solubility in an acidic range, foaming ability and emulsifying ability are measured by the methods described in the Examples below.

[0057] The method of using the deamidated casein of one embodiment of the present invention is not particularly limited. For example, because the deamidated casein has excellent emulsifying properties in addition to solubility and foamability in the acidic range, it can be used as a foaming agent, emulsifier, and / or stabilizer in foamable compositions for producing foamed foods such as foamed milk and whipped cream.

[0058] [3. Foaming composition] Another aspect of the present invention is a foaming composition comprising the deamidated casein of one aspect of the present invention and water.

[0059] The content of deamidated casein in the foamable composition is not particularly limited as long as the desired foamed food is formed when the foamable composition is foamed, but from the viewpoint of the foaming properties and palatability of the foamed food, it is preferably 0.01% (w / v) to 50% (w / v), more preferably 0.1% (w / v) to 50% (w / v), and even more preferably 0.1% (w / v) to 10% (w / v).

[0060] The water is not particularly limited as long as it is water used in food production, and examples thereof include tap water, purified water, ultrapure water, etc. The water content is not particularly limited as long as it is an amount normally used in foamable compositions, and is preferably 10% (w / v) to 99.9% (w / v), for example, from the viewpoint of palatability and foaming properties of the foamy food produced.

[0061] The foamable composition may contain oils and fats such as vegetable oils (vegetable fats) and milk fats derived from mammalian milk, because the foamable composition has good emulsifying properties due to the presence of deamidated casein. That is, another aspect of the present invention is a foamable oil-in-water emulsion composition containing deamidated casein having a deamidation rate of 14% or more and less than 32%, water, and oils and fats.

[0062] Specific examples of vegetable oils include coconut oil, palm oil, soybean oil, rapeseed oil, cottonseed oil, corn oil, sunflower oil, olive oil, safflower oil, kapok oil, palm kernel oil, margarine, shortening, and the like, as well as fractionated oils, hardened oils, and interesterified oils, but are not limited to these.

[0063] The milk fat content is not particularly limited as long as it is derived from mammalian milk, but for example, milk fat content derived from cow's milk is preferred because of its good flavor and palatability, and fresh cream is more preferred in order to obtain good emulsion stability. Fresh cream is as described as "cream" in the Ministerial Ordinance on Milk, etc., that is, cream obtained by removing components other than milk fat from raw milk, cow's milk, or special milk, and has a milk fat content of 18.0% by mass or more.

[0064] The content of the oil or fat is not particularly limited as long as it is the amount normally contained in a foamable oil-in-water emulsion composition, but is preferably 0.5% (w / w) to 50.0% (w / w) from the viewpoint of the palatability and foaming properties of the resulting foamy food product.

[0065] The fats and oils may be any one of the above-mentioned types used alone or a combination of two or more of them. The method for obtaining the fats and oils is not particularly limited, and they may be either those produced according to a conventional method or commercially available products.

[0066] The foamable composition preferably contains non-fat milk solids, as this is expected to provide better flavor and emulsion stability. The non-fat milk solids are not particularly limited as long as they are solids obtained by removing water and milk fat from mammalian milk, and typically contain proteins, carbohydrates, minerals, vitamins, etc., which are contained in milk.

[0067] The content of non-fat milk solids is not particularly limited, but from the viewpoint of the palatability and foaming properties of the foamy food product to be produced, it is preferably 1% (w / w) or more, more preferably 1% (w / w) to 30% (w / w), and even more preferably 1% (w / w) to 10% (w / w).

[0068] The method for obtaining non-fat milk solids is not particularly limited, and non-fat milk solids may be either those produced according to conventional methods or commercially available products. Non-fat milk solids are contained in various dairy products such as skim milk powder, non-fat milk, low-fat milk, processed milk, skim milk, concentrated skim milk, and cream, and these dairy products may be used as non-fat milk solids. The non-fat milk solids may be used alone or in combination of two or more of the above-mentioned products.

[0069] If necessary, the foamable composition may contain other ingredients such as food additives, such as sweeteners, emulsifiers, thickening and stabilizing agents, flavorings, preservatives, antioxidants, vitamins, minerals, etc. Specific examples of food additives are listed below, but the food additives are not limited to these.

[0070] Examples of sweeteners include sugars, sugar alcohols such as maltitol, erythritol, sorbitol, palatinit, xylitol, lactitol, and isomaltitol, aspartame, acesulfame potassium, sucralose, alitame, neotame, licorice extract (glycyrrhizin), saccharin, saccharin sodium, stevia extract, and stevia powder. Among these, examples of sugars include sucrose, granulated sugar, glucose, fructose, isomerized sugar, invert sugar, isomaltooligosaccharides, oligosaccharides such as reduced xylooligosaccharides, reduced gentiooligosaccharides, xylooligosaccharides, gentiooligosaccharides, nigerooligosaccharides, theandeooligosaccharides, and soybean oligosaccharides, trehalose, starch syrup, reduced starch syrup, and honey.

[0071] Examples of emulsifiers include monoglycerin fatty acid esters, polyglycerin fatty acid esters, diglycerin fatty acid esters, sorbitan fatty acid esters, and lecithin.

[0072] Examples of thickening stabilizers include methylcellulose, hydroxypropylcellulose, agar, gelatin, carrageenan, xanthan gum, locust bean gum, gellan gum, and pectin.

[0073] Flavorings include vanilla flavor, milk flavor, cream flavor, and the like.

[0074] Preservatives include sodium metaphosphate, alkali metal citrate, and alkali metal phosphate.

[0075] Antioxidants include tocopherol and tea extract.

[0076] Vitamins include vitamin B1, ascorbic acid, and pantothenic acid.

[0077] Minerals include potassium, sodium, calcium, and the like.

[0078] The foaming composition may contain food ingredients as other components as needed. Examples of food ingredients include, but are not limited to, dairy products and egg yolk. Examples of dairy products include milk, formula-adjusted milk, skim milk powder, condensed milk, yogurt, cheese, fermented milk, lactic acid bacteria drinks, and dairy drinks.

[0079] The content of other components in the foamable composition is not particularly limited as long as it does not interfere with the solution of the problems of the present invention, and from the viewpoint of the stability and palatability of the resulting foamy food product, it is preferably 0.0% (w / w) to 30.0% (w / w), and more preferably 1.0% (w / w) to 20.0% (w / w).

[0080] The other components may be any one of the above-mentioned components alone or a combination of two or more of them. The method for obtaining the other components is not particularly limited, and for example, commercially available components can be used.

[0081] The deamidated casein of one embodiment of the present invention is obtained by a resin treatment method, not an enzymatic treatment method. Therefore, the foaming composition of one embodiment of the present invention is prepared by using Chryseobacterium proteolyticum ( Chryseobacterium proteolyticum ) is preferably substantially free of, and more preferably completely free of, protein glutaminase derived from the fungus.

[0082] The foamable composition can be produced by a process of mixing the deamidated casein of one embodiment of the present invention and water, and, if necessary, other ingredients such as fats and oils, non-fat milk solids, and sweeteners to obtain the foamable composition.

[0083] The method for mixing the components in the foamable composition is not particularly limited, but examples thereof include mixing using a mixer under conditions that do not cause foaming, since vigorous stirring will cause foaming. The fats and oils, non-fat milk solids, and any other components may be premixed and commercially available creams, compounds, etc.

[0084] The foaming composition can be packed in a container and sealed to form a packaged foaming composition. The container is not particularly limited, but examples include packaging containers made of paper, plastics such as PET and PTP, glass, and metals such as aluminum. The packaged foaming composition can be sold independently and commercially available in distribution. The foaming composition can be subjected to a sterilization treatment before or after being packed in a container.

[0085] By whipping the foaming composition according to a conventional method, foamed foods such as foamed milk and whipped cream can be obtained. For example, whipped cream that maintains a foamed state can be produced by stirring the foaming composition using a tool such as a whisk or a dedicated mixer to incorporate air. Note that sugars such as granulated sugar, sugar, and liquid sugar, flavorings, liqueurs, etc. may be added during whipping.

[0086] A foamed food product obtained using the foaming composition can stably maintain a foamed state. The degree of stability of the foamed food product is not particularly limited, but for example, the foam volume is larger 30 minutes after foaming, preferably 60 minutes after foaming, than when sodium caseinate is used instead of the deamidated casein of one embodiment of the present invention.

[0087] 4. Other Aspects of the Present Invention In view of the properties of the foamy food obtained using the foamable composition described above, another aspect of the present invention provides a method for improving foamability, which includes a step of using the deamidated casein of one aspect of the present invention and water to improve foamability compared to when casein or sodium caseinate is used instead of the deamidated casein.

[0088] In addition, as another aspect of the present invention, there are provided a composition for stabilizing foamy foods, which comprises the deamidated casein of one embodiment of the present invention and water, and a method for stabilizing foamy foods, which comprises using the composition.

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples, and the present invention can take various forms as long as the object of the present invention can be achieved. [Example]

[0090] [1. Method for preparing deamidated casein] (1-1) Example 1 A schematic diagram of protein amidation is shown in Figure 1. As shown in Figure 1, deamidated proteins are obtained by converting the amide groups (-C=O-NH2) of asparagine and glutamine, which are amino acids that make up proteins, to carboxyl groups (-C=O-OH).

[0091] Casein (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was suspended in ultrapure water to prepare a 1% (w / v) casein suspension. Next, a carboxylate-type cation exchange resin ("Amberlite IRC76"; manufactured by Organo Corporation) converted to the Na form at 0.5 g / mL was added to the suspension, and the deamidation reaction was carried out by stirring at pH 8-10, 55°C, and 30 hours. The reaction solution after the deamidation reaction was subjected to suction filtration to recover filtrate (1). Next, 200 mL of ultrapure water and an equal amount of 1N hydrochloric acid were added to the remaining resin, and the mixture was stirred at room temperature (20°C to 30°C) for 30 minutes, followed by suction filtration to recover filtrate (2). The filtrate (1) and filtrate (2) were mixed to obtain filtrate (1+2). The filtrate (1+2) was dialyzed against ultrapure water at 4°C for 2 days, and then freeze-dried to obtain deamidated casein powder.

[0092] (1-2) Example 2 A deamidated casein powder was obtained in the same manner as in Example 1, except that an H-type carboxylate-type cation exchange resin and a 1N aqueous sodium hydroxide solution were used instead of the Na-type carboxylate-type cation exchange resin and 1N hydrochloric acid.

[0093] [2. Evaluation method for deamidated casein] (2-1) Deamidation rate The nitrogen and carbon amounts in casein and deamidated casein were measured using a total nitrogen / total carbon analyzer ("Sumigraph NC-220F"; manufactured by Sumika Chemical Analysis Center Co., Ltd.), and the deamidation rate was calculated from the ratio of the nitrogen amount in deamidated casein to the nitrogen amount in casein.

[0094] (2-2) Solubility in acidic regions Deamidated casein, casein, and sodium caseinate (Fujifilm Wako Pure Chemical Industries, Ltd.) were suspended in 3 mL of citrate-phosphate buffer (pH 3.0-6.0) to prepare 1% (w / v) suspensions. The resulting suspensions were then stirred at room temperature for 60 minutes and centrifuged (10,000 g, 20°C, 15 minutes). The nitrogen content of the resulting supernatant was then measured using a total nitrogen / total carbon analyzer. Solubility was evaluated based on the soluble nitrogen content calculated from the ratio of the nitrogen content in the supernatant to the nitrogen content in each protein.

[0095] (2-3) Foaming in the acidic range Deamidated casein, casein, and sodium caseinate were suspended in 5.0 mL of citrate phosphate buffer (pH 3.0-6.0) to prepare 0.5% (w / v) suspensions. The resulting suspensions were then whipped for 1 minute using an electric milk frother ("CQT-45"; manufactured by HARIO). The foam volume was measured at 0, 30, and 60 minutes after whipping to evaluate foamability (measured at 0 minutes) and foam stability (measured at 30 to 60 minutes).

[0096] (2-4) Emulsifying properties in the acidic range Deamidated casein and sodium caseinate were suspended in 2.4 mL of citrate-phosphate buffer (pH 3.0–6.0) to prepare 1% (w / v) suspensions. Next, 0.8 mL of corn oil (Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the resulting suspension, and the mixture was emulsified using a homogenizer (NS-52K; Microtech Nichion Co., Ltd.) at room temperature, 25,000 rpm, for 1 minute. 50 μL of the resulting emulsion was then suspended in 5 mL of 0.1% SDS aqueous solution to stabilize the emulsion. The absorbance at 500 nm was measured immediately after preparation (0 min) and after 10 minutes of standing (10 min) to evaluate emulsifying ability (0 min measurement) and emulsion stability (10 min measurement).

[0097] (2-5) Isoelectric point Isoelectric points were measured by two-dimensional electrophoresis (10 μg of casein and deamidated casein) using isoelectric focusing (pH 3-10) as the first dimension and SDS-PAGE as the second dimension. Ten μg of casein and deamidated casein were dissolved in 155 μL of 60 mM Tris-HCl buffer (pH 8.8) containing 0.5% (v / v) ZOOM Carrier Ampholytes pH 3-10 (Thermo Fisher Scientific) and 0.02% (w / v) bromphenol blue. The solution was loaded onto a first-dimension gel (ZOOM strip pH 3-10NL; Thermo Fisher Scientific) and subjected to isoelectric focusing at 175 V for 20 min, 175 V–2,000 V for 45 min, and 2,000 V for 60 min. After isoelectric focusing, the gel was reduced to SDS and placed on a second-dimensional gel (NuPAGE 4-12% Bis-Tris ZOOM Gels; Thermo Fisher Scientific) for SDS-PAGE at 200 V for 45 minutes. After SDS-PAGE, the gel was stained with CBB, and the isoelectric point was measured based on the detected bands.

[0098] (2-6) Presence or absence of hydrolysis The presence or absence of hydrolysis of deamidated casein was evaluated by SDS-PAGE using a 14% acrylamide gel. Deamidated casein, casein, and sodium caseinate were each dissolved in SDS sample buffer and applied to a 14% acrylamide gel at 5 μg / well. After application, the gel was subjected to electrophoresis at 100 mA and a constant voltage of 50 V for 30 minutes, followed by electrophoresis at 100 mA and a constant voltage of 150 V for approximately 60 minutes. After electrophoresis, the gel was stained with CBB, and the presence or absence of hydrolysis was evaluated by confirming that the band where deamidated casein had been applied was not smeared.

[0099] [3. Evaluation results of deamidated casein] In the preparation method of Example 1, the recovery rate calculated from the amount of deamidated casein powder relative to the amount of casein (dry mass) used was 47% when filtrate (1) alone was used, and 83% when filtrate (1+2) was used. That is, the recovery rate was significantly improved by eluting the Na-type resin after the deamidation reaction with hydrochloric acid. On the other hand, in the preparation method of Example 2, when the deamidation reaction was carried out using H-type resin, casein was insolubilized in the deamidation reaction solution, and the recovery rate when filtrate (1+2) was used was low at 62%. These results demonstrate that deamidated casein can be efficiently recovered by using Na-type resin and eluting the resin with hydrochloric acid. Similarly, the recovery rate of deamidated sodium caseinate obtained by deamidating sodium caseinate was lower than that of deamidated casein.

[0100] In the preparation method of Example 1, the deamidation rate of the deamidated casein obtained using the filtrate (1+2) (hereinafter simply referred to as deamidated casein) was measured and found to be 23.3%. The deamidation rate of the above-mentioned deamidated sodium caseinate was 8 to 9%. Therefore, it was found that the preparation method of Example 1 is not suitable for deamidating sodium caseinate.

[0101] The results of measuring the solubility of deamidated casein, casein, and sodium caseinate (n=3, ±SD) are shown in Figure 2. As shown in Figure 2, in the acidic range of pH 4.5 to 6.0, deamidated casein had significantly improved solubility compared to casein and sodium caseinate.

[0102] The results of measuring the foaming properties of deamidated casein, casein, and sodium caseinate (n=3, ±SD) are shown in Figure 3. As Figure 3 shows, regardless of the time after foaming, when deamidated casein was used, the foam volume was stably large and the foaming properties were stably excellent over a wide pH range of 3.0 to 6.0.

[0103] The results of measuring the emulsifying properties of deamidated casein, casein, and sodium caseinate (n=4, ±SD) are shown in Figure 4. As Figure 4 shows, in the acidic range of pH 4.5 to 4.6, deamidated casein had a stably high absorbance and consistently excellent emulsifying properties.

[0104] The results of measuring the isoelectric points of deamidated casein and casein are shown in Figure 5. As shown in Figure 5, the isoelectric point of deamidated casein was found to be shifted to the acidic side compared to casein. This also revealed that the excellent solubility, foamability, and emulsifying properties of deamidated casein in the acidic range may be due to the lower isoelectric point caused by deamidation.

[0105] The results of SDS-PAGE measurement of deamidated casein, casein, and sodium caseinate are shown in Figure 6. As shown in Figure 6, it was found that deamidated casein, like casein and sodium caseinate, was hardly hydrolyzed.

[0106] From the above results, it was found that the deamidated casein obtained by the preparation method of Example 1 was not hydrolyzed, had a high deamidation rate, and had excellent solubility, foaming property, and emulsifying property in the acidic range. Furthermore, although deamidated casein is a protein that does not exist in nature, it is obtained by converting amino acids such as glutamine and asparagine in the protein to other amino acids such as glutamic acid and aspartic acid, respectively, and therefore is safer as a food product than other non-natural proteins.

[0107] Furthermore, unlike the enzymatic method, the preparation method of Example 1 can omit the heat treatment for enzyme inactivation, thereby preventing the problem of the deterioration of the taste of deamidated casein due to heat treatment. Furthermore, the ion exchange resin used is a resin that is widely used in the food manufacturing industry, and is therefore highly safe and easy to operate for deamidation.

[0108] [4. Comparison of deamidated casein and deamidated whey protein] Deamidated whey protein was prepared and its emulsifying and foaming properties were compared with those of deamidated casein.

[0109] (4-1) Method for preparing deamidated whey protein Whey protein isolate (Davisco Foods International) was dissolved in ultrapure water to prepare a 3% (w / v) whey protein solution. The solution was then dialyzed against ultrapure water at 4°C to remove lecithin, which contaminates the whey protein. The dialyzate was then freeze-dried to obtain whey protein powder (hereafter referred to as whey protein).

[0110] Whey protein was dissolved in ultrapure water to prepare a 1% (w / v) whey protein solution. Subsequently, H-form carboxylate cation exchange resin ("Amberlite IRC76"; manufactured by Organo Corporation) was added to the solution to a concentration of 0.5 g / mL, and the mixture was stirred at 4°C for 6 to 30 hours to carry out a deamidation reaction. The reaction solution was then subjected to suction filtration to recover filtrate (1). To the remaining resin, an equal amount of 1N aqueous sodium hydroxide solution as that of ultrapure water was then added, and the mixture was stirred at room temperature for 30 minutes, followed by suction filtration to recover filtrate (2). The filtrate (1) and the filtrate (2) were mixed to obtain filtrate (1+2). The filtrate (1+2) was dialyzed against ultrapure water and then lyophilized to obtain a deamidated whey protein powder.

[0111] The reason for using H-type cation exchange resin in the deamidation reaction is that when Na-type resin was used, the reaction solution gave off a putrid odor and was therefore deemed unsuitable for food use. The temperature for the deamidation reaction was 4°C, as whey proteins are heat-sensitive and would denature at 55°C.

[0112] (4-2) Deamidation rate The deamidation rate of the obtained deamidated whey protein was calculated in the same manner as in (2-1) above.

[0113] (4-3) Emulsifying properties at neutral pH A suspension was prepared in the same manner as in (2-3) above, except that ultrapure water was used instead of the citrate phosphate buffer (pH 3.0 to 6.0), and the absorbance of the suspension immediately after preparation was measured.

[0114] (4-4) Foaming at neutral pH Deamidated whey protein, whey protein, deamidated casein, and sodium caseinate were suspended in 20 mL of ultrapure water to prepare 0.2% (w / v) suspensions. The resulting suspensions were then transferred to a 200 mL graduated cylinder with an air stone (18mm diameter round, King Whetstone) attached to a silicone tube at the bottom. Air was pumped into the tube at 8 kPa using an air pump (SSPP-3S; Suisaku Co., Ltd.) to foam the solution for 1 minute. Foaming ability was evaluated by measuring the volume of the resulting foam.

[0115] (4-5) Evaluation results The deamidation rate of the obtained deamidated whey protein was 2.0% when the reaction time was 6 hours, 3.3% when it was 18 hours, and 9.7% when it was 30 hours.

[0116] The measurement results of the emulsifying properties and foaming properties of whey protein and deamidated whey protein are shown in Table 1, and the measurement results of the emulsifying properties and foaming properties of casein, sodium caseinate, and the deamidated casein obtained in Example 1 are shown in Table 2.

[0117] [Table 1]

[0118] [Table 2]

[0119] As shown in Table 1, the emulsifying properties of whey protein were reduced by deamidation. Furthermore, no significant difference was observed in the foaming properties before and after deamidation.

[0120] In contrast, as shown in Table 2, deamidation of casein, which had low emulsifying properties and no foaming properties, significantly improved both emulsifying properties and foaming properties. Furthermore, the foaming properties of deamidated casein were approximately 1.6 times that of sodium caseinate, which was very good.

[0121] These results demonstrate that deamidation does not necessarily improve the emulsifying and foaming properties of all proteins. This suggests that the balance between the surface charge and surface hydrophobicity of the protein before and after deamidation may be related. In other words, with the exception of solubility, which increases in proportion to the surface charge, physical properties such as foaming and emulsifying properties do not necessarily improve in proportion to the deamidation rate.

[0122] Therefore, the preparation method of Example 1 is an excellent method for improving the physical properties of casein, and is an excellent method from the viewpoint of reaction control, since it can omit the heat inactivation step required in the enzymatic method and the reaction can be stopped by removing the ion exchange resin.

[0123] [5. Evaluation of casein deamidation rate and recovery rate at different reaction temperatures (1)] (5-1) Example 3 Deamidated casein powders were obtained in the same manner as in Example 1, except that the deamidation reaction temperatures were 55°C, 60°C, 70°C, and 80°C. The deamidated casein powders obtained were evaluated for deamidation rate and the presence or absence of hydrolysis by the methods described in (2-1) and (2-6) above. The recovery rate was calculated from the amount of deamidated casein powder relative to the amount of casein (dry mass) used.

[0124] (5-2) Deamidation rate, recovery rate, and presence or absence of hydrolysis The evaluation results of the deamidation rate and recovery rate are shown in Table 3. The electrophoresis results for evaluating the presence or absence of hydrolysis are shown in Figure 7.

[0125] [Table 3]

[0126] As shown in Table 3, the deamidation rate of casein increased as the temperature of the deamidation reaction increased. However, the recovery rate decreased as the deamidation rate increased. Furthermore, as shown in Figure 7, the casein band disappeared as the temperature of the deamidation reaction increased, and at temperatures above 70°C, the band was barely detectable. These results indicate that when the deamidation reaction time is long, such as 30 hours, a temperature below 70°C is recommended. It is possible that casein was converted into peptides by hydrolysis, which led to a strong bond with the ion exchange groups of the resin, resulting in a decrease in recovery rate.

[0127] [6. Evaluation of casein deamidation rate and recovery rate at different reaction temperatures (2)] (6-1) Example 4 Deamidated casein powders were obtained in the same manner as in Example 1, except that the deamidation reaction temperatures were set to 55°C, 60°C, 70°C, and 80°C and the time period was set to 6 hours. The obtained deamidated casein powders were evaluated for the deamidation rate, recovery rate, solubility in the acidic range, emulsifying ability, foaming ability, and the presence or absence of hydrolysis, as described above in (2-1) to (2-4), (2-6), and (5-1).

[0128] (6-2) Various evaluation results The deamidation rate and recovery rate of deamidated casein are shown in Table 4. As shown in Table 4, there was a tendency for the deamidation rate to increase as the reaction temperature increased.

[0129] [Table 4]

[0130] The results of evaluating solubility in the acidic range are shown in Figure 8. As shown in Figure 8, it was found that the deamidated casein obtained by carrying out the deamidation reaction at 80°C for 6 hours had high solubility relative to sodium caseinate within the pH range of 5.5 to 6.0.

[0131] The results of the emulsifying property evaluation are shown in Figure 9. In this evaluation, pure water was used instead of the citrate phosphate buffer. As shown in Figure 9, it was found that the deamidated casein obtained by carrying out the deamidation reaction at 80°C for 6 hours exhibited excellent emulsifying property with sodium caseinate.

[0132] The results of the evaluation of foaming properties are shown in Figure 10. In this evaluation, pure water was used instead of the citrate phosphate buffer. As shown in Figure 10, the deamidated casein obtained by carrying out the deamidation reaction at 80°C for 6 hours exhibited foaming properties equal to or greater than those of sodium caseinate.

[0133] Taking the results of Figures 8 to 10 together, it was found that the deamidated casein obtained by carrying out the deamidation reaction at 80°C for 6 hours has improved solubility in the acidic range, and therefore functions as an excellent emulsifier and foaming agent in the pH range where sodium caseinate has poor solubility.

[0134] The results of evaluating the presence or absence of hydrolysis are shown in Figure 11. As shown in Figure 11, almost no hydrolysis of casein was confirmed at any of the reaction temperatures.

[0135] The deamidated casein obtained by carrying out the deamidation reaction at 80°C for 6 hours had excellent solubility, emulsifying properties, and foaming properties in the acidic range (pH 5.5 to 6.0) without hydrolysis, compared to casein and sodium caseinate. [Industrial Applicability]

[0136] By utilizing the method, composition, and deamidated casein of one embodiment of the present invention, stable foamed foods such as foamed milk and whipped cream can be produced and used simply and in a short time, and foamable compositions that can be widely distributed can be produced and used on an industrial scale.

[0137] Furthermore, by focusing on the solubility of deamidated casein in the acidic range, it is possible to develop new protein drinks by combining it with acidic foods such as fruit juice, which have limited use with conventional casein. Furthermore, deamidated casein alone can be used as a protein raw material with improved solubility compared to conventional casein.

[0138] Currently, active protein intake is recommended as a measure for low-carb control, improving immunity, and preventing muscle weakness. Milk protein, in particular, is added to a variety of foods due to its excellent amino acid score and high absorbability. The deamidated casein of one embodiment of the present invention is expected to be used in a wider range of foods than previously possible. Cross-reference to related applications

[0139] This application claims priority from Japanese Patent Application No. 2021-029031, filed February 25, 2021, the entire disclosure of which is incorporated herein by reference.

Claims

1. A method for producing deamidated casein, comprising a step of subjecting a suspension containing casein to a deamidation reaction using a weakly acidic cation exchange resin whose ion exchange groups are in the alkali metal salt form at 40°C to 90°C for 4 hours to 50 hours, thereby obtaining deamidated casein having a deamidation rate of 14% or more but less than 32%.

2. The method according to claim 1, further comprising a step of subjecting the resin residue recovered after the deamidation reaction to an elution treatment using an acidic aqueous solution to obtain deamidated casein.

3. 3. The method according to claim 2, wherein the recovery rate of the deamidated casein is 70% or more based on the casein.

4. The method according to any one of claims 1 to 3, wherein the alkali metal salt type is at least one alkali metal salt type selected from the group consisting of a sodium type and a potassium type.

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