Production method of milk protein hydrolyzate

Abstract

To provide a technology to produce a milk protein hydrolyzate with reduced contents of tyrosyl residues.SOLUTION: A production method of a milk protein hydrolyzate, whose content of tyrosyl residues is 35 mg / g or less, includes following production processes, i.e. a process for producing a hydrolyzate, whose ratio of free form of tyrosine in proportion to all tyrosyl residues is 50 wt.% or more, by treating milk protein with both more than one enzyme having an exopeptidase activity and more than one enzyme having an endopeptidase activity, a process for crystallizing the free form of tyrosine in the hydrolyzate, and a process for removing the crystallized free form of tyrosine from the hydrolyzate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a milk protein hydrolysate. [Background technology]

[0002] Tyrosine is an aromatic amino acid found in food, which is produced from phenylalanine in the body and used as a precursor of thyroid hormones and the neurotransmitters noradrenaline and dopamine. It is desirable for healthy people to consume appropriate amounts of tyrosine, but it is said that some people with pathological conditions need to limit their intake in order to suppress the progression of the condition.

[0003] As a method for producing a protein hydrolysate with reduced aromatic amino acids including tyrosine, a method is known in which a protein is hydrolyzed to release at least 90% (by weight) of tyrosine and phenylalanine, the hydrolyzate is subjected to reverse osmosis treatment using a reverse osmosis membrane with a salt rejection rate of 10 to 70%, and then the membrane non-permeable fraction obtained in the above step is mixed with a membrane permeable fraction obtained in the above step from which aromatic amino acids have been removed, to recover a peptide mixture with a low aromatic amino acid content (Patent Document 1). In addition, a method is known in which the raw protein is hydrolyzed until the ratio of the content of free phenylalanine to the total amount of phenylalanine contained therein reaches within 85 to 95%, and then phenylalanine is reduced by gel filtration, adsorption resin method, activated carbon adsorption method, etc. (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3418278 specification [Patent Document 2] Patent No. 3682994 specification Summary of the Invention [Problem to be solved by the invention]

[0005] The manufacturing method described in Patent Document 1 has room for improvement in order to simplify the steps, retain hydrophobic amino acids other than tyrosine, such as tryptophan and phenylalanine, and produce protein hydrolysates with excellent nutritional value. In addition, in the production method described in Patent Document 2, since gel filtration, adsorption resin, activated carbon adsorption, etc. are used, the amino acids removed are not limited to tyrosine, but low molecular weight peptides having aromatic amino acids other than tyrosine bound to their termini and hydrophobic amino acids other than tyrosine are also adsorbed and removed at the same time. Therefore, there is room for improvement in efficiently recovering a peptide mixture that maintains nutritional amino acid balance.

[0006] As a method for producing pharmaceuticals or foods with reduced aromatic amino acids including tyrosine, a method of replacing a part or all of protein-derived components with an amino acid mixture not containing tyrosine is considered. However, in order to produce pharmaceuticals or foods with good flavor, to prevent diarrhea caused by high osmotic pressure in the intestinal tract, and to be cost-effective, a production method that does not use an amino acid mixture is preferable.

[0007] An objective of the present invention is to provide a technique for producing a milk protein hydrolysate in which the total content of tyrosine residues in the milk protein hydrolysate is reduced. [Means for solving the problem]

[0008] The present inventors have treated milk proteins with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity to determine the content of free tyrosine in the milk proteins. The present inventors have found that the above-mentioned problems can be solved by producing a hydrolysate in which the free tyrosine content is 50% by weight or more of the total tyrosine residues in the substance, crystallizing the free tyrosine in the hydrolysate, and removing the crystallized free tyrosine from the hydrolysate, thereby completing the present invention.

[0009] The present invention relates to a method for producing a hydrolysate having a free tyrosine content of 50% by weight or more based on the total tyrosine residues in the milk protein, comprising the steps of: treating a milk protein with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity to produce a hydrolysate having a free tyrosine content of 50% by weight or more based on the total tyrosine residues in the milk protein; Crystallizing the free tyrosine in the hydrolysate; and removing the crystallized free tyrosine from the hydrolysate. Including, The present invention provides a method for producing a milk protein hydrolysate, in which the total tyrosine residue content per gram of the milk protein hydrolysate is 35 mg or less. In a preferred embodiment of the method, the milk protein is casein.

[0010] The present invention can also provide a milk protein hydrolysate having a total tyrosine residue content of 35 mg or less per gram of the milk protein hydrolysate. In a preferred embodiment of the hydrolysate, the milk protein is casein.

[0011] The present invention can also provide a food or drink composition comprising the hydrolysate. Effect of the Invention

[0012] According to the present invention, it is possible to produce a milk protein hydrolysate in which the total content of tyrosine residues in the milk protein hydrolysate is reduced, and the hydrolysate can be suitably used as a pharmaceutical ingredient or a material for patients with pathological conditions. The hydrolysate has excellent nutritional value since hydrophobic amino acid residues other than tyrosine residues are retained. In addition, the hydrolysate does not remove low molecular weight peptides having aromatic amino acid residues other than tyrosine residues attached to the terminals, so that it is possible to recover a peptide mixture with nutritional amino acid balance at a high recovery rate. Furthermore, it is not necessary to supplement the essential amino acids that are lacking, it has a good flavor, does not cause diarrhea, and is cost-effective. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following preferred embodiments, and can be freely modified within the scope of the present invention. In this specification, percentages are expressed by weight (mass) unless otherwise specified.

[0014] One aspect of the present invention is a method for producing a milk protein hydrolysate having a total tyrosine residue content of 35 mg or less per gram of milk protein hydrolysate, the method comprising the steps of treating a milk protein with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity to produce a hydrolysate having a free tyrosine content of 50% by weight or more relative to the total tyrosine residues in the milk protein, crystallizing the free tyrosine in the hydrolysate, and removing the crystallized free tyrosine from the hydrolysate.

[0015] First, the step of producing the hydrolysate will be described. The milk protein that can be used in this step is a protein contained in milk collected from a mammal (excluding humans), and is a hydrolyzed product in which free tyrosine is generated by treating the milk protein with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity, and the content of the free tyrosine is 50% by weight or more of the total tyrosine residues in the milk protein. There are no particular limitations as long as a decomposition product can be produced. Examples of the mammals include cows, goats, sheep, and horses. The milk is preferably milk that is commonly used for food. Specific examples of the milk protein include casein and whey protein. The whey protein is a protein contained in whey (milk serum). Examples of the casein include α-casein, β-casein, and κ-casein. The casein may be edible casein. The casein may be in the form of calcium caseinate, sodium caseinate, or the like.

[0016] The milk protein may also be in the form of a raw material containing the milk protein (e.g., containing carbohydrates, proteins, minerals, etc.). The raw material may be prepared by a conventional method or may be a commercially available product. The concentration of the milk protein in the raw material is preferably 50% or more, since the finally obtained milk protein hydrolysate contains abundant amino acids and peptides derived from the protein.

[0017] The milk protein may be an isolate separated from the raw material, a purified product, or a concentrate, or may be a mixture of two or more selected from the group consisting of such isolates, purified products, and concentrates. All of these may be prepared by a conventional method or may be commercially available products.

[0018] Furthermore, the content of total tyrosine residues per 1 g of the milk protein is not particularly limited, as long as free tyrosine is generated by treating the milk protein with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity, and a hydrolysate is produced in which the content of the free tyrosine is 50% by weight or more relative to the total tyrosine residues in the milk protein; for example, the content is 25 to 60 mg.

[0019] The milk protein can be dissolved in a solvent such as water (e.g., deionized water) and subjected to the enzyme treatment in this step. The concentration of the milk protein in the solution subjected to the enzyme treatment is not particularly limited as long as free tyrosine is generated from the milk protein and a hydrolysate is generated in which the content of the free tyrosine is 50% by weight or more based on the total tyrosine residues in the milk protein, but is preferably 2.5 to 20%. The pH of the solution to be subjected to the enzyme treatment can be adjusted according to the optimum pH of the enzyme used, and is, for example, 6.0 to 10.0. The pH can be adjusted according to a conventional method using a pH adjuster such as an acidifier or an alkali agent, and examples of the alkali agent include sodium hydroxide, potassium hydroxide, and potassium carbonate. The temperature of the solution to be subjected to the enzyme treatment can be set according to the optimum temperature of the enzyme used, etc. If there is a concern about the proliferation of microorganisms during the enzyme treatment, the temperature may be set to a higher or lower temperature range than the optimum temperature of the enzyme used, as necessary, but it is preferably set to 40 to 65° C. in order to maintain the efficiency of the enzyme treatment.

[0020] In addition, this embodiment may include a sterilization step before the enzyme treatment after preparing the solution to be subjected to the enzyme treatment as described above. As a sterilization method, for example, a heat sterilization method is mentioned. As a specific example, sterilization by heating at 65 to 140°C for 2 seconds to 30 minutes is mentioned. Furthermore, this embodiment may include a pH adjustment step of adjusting the pH of the solution after the sterilization and before the enzyme treatment, for example, to 6.0 to 10.0. The pH adjustment may be performed according to a conventional method using a pH adjuster such as an acidifier or an alkaline agent, and examples of the alkaline agent include sodium hydroxide, potassium hydroxide, and potassium carbonate.

[0021] The milk protein is treated with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity. Each enzyme produces free tyrosine from the milk protein, and the content of the free tyrosine is 50% or more of the total tyrosine residues in the milk protein. There are no particular limitations as long as a hydrolysate having a molecular weight of 100 or more by weight is produced, but it is preferable that the hydrolysate is harmless from the viewpoint of food hygiene.

[0022] The enzyme having exopeptidase activity may be an enzyme having only exopeptidase activity, or an enzyme having exopeptidase activity and endopeptidase activity. Incidentally, the enzyme having endopeptidase activity is usually an enzyme having only endopeptidase activity.

[0023] Examples of enzymes having exopeptidase activity and endopeptidase activity include pancreatin (e.g., Pancreatin x 4.0 sterilized product (manufactured by Amano Enzyme Co., Ltd.)), Protease A Amano (manufactured by Amano Enzyme Co., Ltd.), Proteax (manufactured by Amano Enzyme Co., Ltd.), Protease M Amano (manufactured by Amano Enzyme Co., Ltd.), Flavorzyme (manufactured by Novozymes), Sumiteam LP-50 (manufactured by Shinnihon Kagaku Co., Ltd.), and Sumiteam AP (manufactured by Shinnihon Kagaku Co., Ltd.).

[0024] Examples of enzymes that have only exopeptidase activity include Sumiteam FLAP (manufactured by Shinnihon Kagaku Co., Ltd.) and FD-H (manufactured by Morinaga Milk Industry Co., Ltd.). FD-H is an enzyme derived from Lactobacillus helveticus LHE-511 (J. Dairy Sci., Vol. 75, No. 1, 1992).

[0025] Examples of enzymes having endopeptidase activity (enzymes having only endopeptidase activity) include Protease N Amano (Amano Enzyme), Papain W-40 (Amano Enzyme), Neutrase (Novozymes), PTN6.0S (Novozymes), and Bioprase SP-20 (Nagase ChemteX).

[0026] The final concentration of each enzyme added to the solution to be subjected to the enzyme treatment is not particularly limited as long as free tyrosine is generated from the milk protein and a hydrolysate is generated in which the content of the free tyrosine is 50% by weight or more relative to the total tyrosine residues in the milk protein.For example, based on the activity of each enzyme (for example, activity expressed as a unit), the enzyme treatment can be performed preliminarily under various conditions, taking into account the pH, temperature, and treatment time during the enzyme treatment, and the final concentration can be appropriately set so that free tyrosine is generated from the milk protein and a hydrolysate in which the content of the free tyrosine is 50% by weight or more relative to the total tyrosine residues in the milk protein is generated.At this time, for example, even if the final concentration of the enzyme is set to a low level, the desired hydrolysate can be obtained by setting the treatment time to a long level.

[0027] The solution to be subjected to the enzyme treatment may contain one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity at the start of the enzyme treatment, but the enzyme treatment may also be performed in a stepwise manner in which the solution contains only one or more enzymes having endopeptidase activity at the start of the enzyme treatment and an enzyme having exopeptidase activity is added after a certain period of enzyme treatment.

[0028] The time of the enzyme treatment is not particularly limited as long as free tyrosine is produced from the milk protein and a hydrolysate is produced in which the content of the free tyrosine is 50% by weight or more relative to the total tyrosine residues in the milk protein, but is preferably 4 hours or more, more preferably 8 hours or more, and preferably 20 hours or less from the start of the enzyme treatment. As mentioned above, when there is a concern about the growth of microorganisms during the enzyme treatment, the time is preferably 8 hours or more and 20 hours or less.

[0029] The enzyme treatment results in a content of free tyrosine relative to the total tyrosine residues in the milk protein. A hydrolysate having a free tyrosine content of 50% or more, preferably 85% or more, more preferably 94% or more is produced. The concentration of free tyrosine can be measured over time, for example, by high performance liquid chromatography (HPLC). Therefore, the content of free tyrosine relative to the total tyrosine residues in the milk protein can be calculated. As the HPLC, for example, an HPLC (manufactured by Shimadzu Corporation) equipped with an Inertosil PREP-ODS column (manufactured by GL Science, 6.5 x 250 mm) can be mentioned.

[0030] Next, the step of crystallizing free tyrosine in the hydrolysate will be described. In this step, the method is not particularly limited as long as it can crystallize the free tyrosine in the hydrolysate. However, since the solubility of free tyrosine in the hydrolysate is low, a preferred method includes cooling the hydrolysate to crystallize the free tyrosine in the hydrolysate. The cooling method may be a conventional method, for example, placing the hydrolyzate in a plate cooler, a refrigerator, a low-temperature room, etc. Stirring may be performed as necessary. The temperature during the cooling is preferably 20° C. or lower, more preferably 10° C. or lower, in order to crystallize a larger amount of free tyrosine, while it is, for example, 0° C. or higher in order to prevent freezing. The cooling time is preferably 30 minutes or more, more preferably 2 hours or more, since a larger amount of free tyrosine is crystallized, while the upper limit is not particularly limited, and is, for example, 24 hours or less.

[0031] This aspect may include a step of stopping the enzymatic treatment by deactivating and / or removing enzymes after the step of forming the hydrolysate and before the step of crystallization. The inactivation method may be, for example, a heat treatment method. Conditions for sufficient inactivation may be appropriately set in consideration of the thermal stability of the enzyme used, and a specific example may be a heat treatment at 80 to 130° C. for 2 seconds to 30 minutes. The removal method may be, for example, a method using an ultrafiltration membrane, etc. Either method may be performed according to a conventional method.

[0032] In addition, since the free tyrosine in the hydrolysate can be efficiently crystallized, the present embodiment may include a step of concentrating the hydrolysate after the step of generating the hydrolysate and before the step of crystallization. If the present embodiment includes a step of stopping the enzyme treatment, the concentration step may be included after the step. The method for concentrating the hydrolysate includes, for example, a concentrating method using a concentrator or a reverse osmosis membrane. Either method can be performed according to a conventional method. For example, the hydrolysate can be concentrated until the solid content is 10% or more and 60% or less.

[0033] Next, the step of removing the crystallized free tyrosine from the hydrolysate will be described. Methods for removing the crystallized free tyrosine from the hydrolysate include, for example, diatomaceous earth filtration, microfiltration, ultrafiltration, and centrifugation. All of these methods can be performed according to conventional methods. In addition, examples of methods for removing free tyrosine from the hydrolysate to a greater extent include gel filtration chromatography, as well as adsorption methods using activated carbon or an adsorption resin, either alone or in combination. Either method can be performed according to a conventional method.

[0034] Examples of the gel filtration agent in the gel filtration chromatography include those having an exclusion limit molecular weight of 5000 or less, preferably 2000 or less. Examples of the hydrophobic side chain having the property of adsorbing tyrosine include those having a carboxyl group, a butyl group, a phenyl group, and a hydrophobic site. Examples of the gel filtration agent include Sephadex. G-10 (Pharmacia), and Cellulofine GCL-25 (Seikagaku Corporation). An example of the activated carbon is Hokuetsu ZN (manufactured by Ajinomoto Fine-Techno Co., Ltd.). The adsorption resin may be, for example, a porous synthetic adsorbent, such as KS-35 (manufactured by Hokuetsu Carbon Industries Co., Ltd.), Diaion HP (manufactured by Mitsubishi Chemical Corporation), or Amberlite XAD (manufactured by Rohm and Haas Co., Ltd.).

[0035] The crystallized free tyrosine removed from the hydrolysate by this step has a high purity, preferably 90% or more, and can be used for many purposes as high-purity tyrosine.

[0036] By the above steps, a milk protein hydrolysate can be obtained having a total tyrosine residue content of 35 mg or less, preferably 19 mg or less, more preferably 11 mg or less per gram of the milk protein hydrolysate.

[0037] The molecular weight of the hydrolysate of the milk protein is not particularly limited as long as free tyrosine is produced from the milk protein and a hydrolysate is produced in which the content of the free tyrosine is 50% by weight or more relative to the total tyrosine residues in the milk protein, but since it is necessary to lower the molecular weight of the protein to some extent from the viewpoint of efficiently releasing tyrosine, the average molecular weight is preferably 200 to 2000, and more preferably 200 to 400. The average molecular weight can be calculated, for example, as follows. The molecular weight distribution is measured by high performance liquid chromatography (Nobuo Ui et al., eds., "High Performance Liquid Chromatography of Proteins and Peptides," Chemical Special Issue No. 102, p. 241, Kagaku Dojin Co., Ltd., 1984). Specifically, a polyhydroxyethyl aspartamide column (PolyLC, diameter 4.6 mm, length 220 mm) was used, and elution was performed with 20 mM sodium chloride and 50 mM formic acid at a rate of 0.5 mL / min. Detection was performed with a UV detector (Shimadzu Corporation), and data analysis was performed with a GPC analysis system (Shimadzu Corporation). [Percentage of each molecular weight range (%)] = [area of ​​each molecular weight range in the molecular weight distribution / total area of ​​hydrolyzates in the molecular weight distribution (total area)] The average molecular weight (Da: Dalton) is calculated based on the concept of number average molecular weight as follows. The number average molecular weight (Number Average of Molecular Weight) indicates the average value of the molecular weight of a polymer compound based on different indices as follows, as described in the literature ("Basics of Polymer Science" edited by the Society of Polymer Science, pp. 116-119, Tokyo Kagaku Dojin Co., Ltd., 1978). That is, since polymer compounds such as protein hydrolysates are heterogeneous substances and have a distribution in molecular weight, the molecular weight of a protein hydrolysate must be indicated by an average molecular weight in order to handle it physicochemically, and the number average molecular weight (hereinafter sometimes abbreviated as Mn) is the average of the number of molecules, and is defined by the following formula, where the molecular weight of peptide chain i is Mi and the number of molecules is Ni.

number

[0038] This embodiment may include a step of drying and powdering the hydrolysate after the step of removing the crystallized free tyrosine from the hydrolysate. Examples of the method of drying and powdering include spray drying.

[0039] Another embodiment of the present invention is a milk protein hydrolysate having a total tyrosine residue content of 35 mg or less per gram of the milk protein hydrolysate. For details, the description of the above embodiment is incorporated herein by reference.

[0040] The milk protein hydrolysate produced as described above can be used as an ingredient for a food or beverage composition. That is, another aspect of the present invention is a food or beverage composition containing a milk protein hydrolysate, in which the total tyrosine residue content per gram of the milk protein hydrolysate is 35 mg or less.

[0041] The food and drink composition is not particularly limited as long as it contains the milk protein hydrolysate produced as described above. The food and drink composition may be in the form of liquid, paste, gel-like solid, powder, etc., and may be a food or drink, and may include, in addition to tablet confectionery, liquid food, etc., wheat flour products such as bread, macaroni, spaghetti, noodles, cake mix, fried chicken flour, bread crumbs, etc.; instant noodles, cup noodles, retort / cooked foods, cooked canned foods, microwave foods, instant soup / stew, instant miso soup / cleansing soup, canned soup, freeze-dried foods, other instant foods, etc.; canned agricultural products, canned fruits, jasmine, etc. processed agricultural products such as marmalades, pickles, boiled beans, dried agricultural goods, cereals (processed grain products); processed marine products such as canned seafood, fish ham and sausages, fish paste products, marine delicacies, tsukudani (fried fish paste) and other seafood products; processed livestock products such as canned livestock pastes, livestock ham and sausages and other livestock products; processed milk, milk drinks, fermented milk, infant milk, yogurt, lactic acid bacteria drinks, cheese, ice cream, modified milk powder, cream, other dairy products and other dairy products; fats and oils such as butter, margarines, vegetable oils and other fats; soy sauce, Basic seasonings such as miso, sauces, processed tomato seasonings, mirin, vinegar, etc.; complex seasonings and foods such as cooking mixes, curry bases, sauces, dressings, noodle soups, spices, and other complex seasonings; frozen foods such as ingredient frozen foods, semi-cooked frozen foods, and cooked frozen foods; caramel, candy, gummies, chewing gum, chocolate, cookies, biscuits, cakes, pies, snacks, crackers, Japanese sweets, rice snacks, bean snacks, dessert snacks, jellies, and other sweets, etc. These include all kinds of sweets; carbonated drinks, natural fruit juice, fruit juice drinks, soft drinks with fruit juice, fruit pulp drinks, fruit drinks with fruit particles, vegetable drinks, soy milk, soy milk drinks, coffee drinks, tea drinks, powdered drinks, concentrated drinks, sports drinks, nutritional drinks, alcoholic drinks, and other beverages; other commercially available foods such as baby food, furikake, and ochazuke nori; infant formula; enteral nutritional foods; special purpose foods, health functional foods (foods for specified health uses, foods with nutritional functions, foods with functional claims); nutritional supplements, etc.

[0042] The food and drink composition of the present invention can be produced by adding the milk protein hydrolysate produced as described above to the raw material of a normal food and drink, and can be produced in the same manner as normal food and drink, except for adding the milk protein hydrolysate produced as described above. The milk protein hydrolysate produced as described above may be added at any stage of the production process of the food and drink composition. In addition, it can be added to breast milk or formula milk, and it is also assumed that the milk after addition is ingested by infants. EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0044] [Test Example 1] This test was carried out to investigate conditions that can reduce the content of total tyrosine residues in milk protein hydrolysates.

[0045] Edible casein [Alacid 720. Manufactured by Fonterra. Edible casein content: 88%, total tyrosine The milk protein used was edible casein (content of casein residue: 51 mg / g). 10 kg of edible casein was dispersed in deionized water at a concentration of 10%, and dissolved by adjusting the pH to 7.0 with 10% sodium hydroxide solution. The resulting solution was sterilized by heating at 80°C for 10 minutes, kept at 50°C, and adjusted to pH 9.0 with 10% sodium hydroxide solution, and 300 g of sterilized pancreatin x 4.0 (manufactured by Amano Enzyme Co., Ltd.) and 150 g of FD-H (manufactured by Morinaga Milk Industry Co., Ltd.) were added. The hydrolysis reaction was carried out while measuring the free tyrosine concentration in the hydrolysate of the edible casein over time using an HPLC (Shimadzu Corporation) equipped with an Inertosil PREP-ODS column (GL Science, 6.5 x 250 mm), and when the content of free tyrosine reached a certain percentage relative to the total tyrosine residues in the edible casein, the enzyme was inactivated by heat treatment at 90°C for 10 minutes. The resulting hydrolysate was concentrated to a solid content of 12% and kept at 10°C for 4 hours. The resulting concentrate was treated with diatomaceous earth silica 300SA (Chuo Silica) to remove precipitates, and spray-dried to obtain a powdered hydrolysate of the edible casein.

[0046] The results are shown in Table 1. As is clear from Table 1, when hydrolysis was performed until the content of free tyrosine was 50% or more of the total tyrosine residues in the edible casein, the content of total tyrosine residues per gram of the edible casein hydrolysate after filtration through diatomaceous earth silica 300SA was significantly reduced compared to the content of total tyrosine residues per gram of the edible casein. Furthermore, the contents of each of the other amino acids were not significantly different compared to the contents of each of the amino acids contained in the edible casein.

[0047] [Table 1]

[0048] [Example 1] Calcium caseinate [Tatua 400. Manufactured by Tatua. Protein content: 93%, total tyrosine residues Content: 54 mg / g calcium caseinate] was used as the milk protein. 10 kg calcium caseinate was dissolved in deionized water at a concentration of 12%, heat sterilized at 121°C for 1 minute, held at 55°C, adjusted to pH 8.5 with 10% sodium hydroxide solution, 300 g of sterilized pancreatin x 4.0 (manufactured by Amano Enzyme Co., Ltd.) and 100 g of FD-H (manufactured by Morinaga Milk Industry Co., Ltd.) were added, and hydrolysis was performed for 11 hours. As a result of the hydrolysis, the content of free tyrosine became 81% of the total tyrosine residues in the calcium caseinate. The obtained hydrolyzate was then heat-treated at 90°C for 15 minutes to inactivate the enzyme, concentrated in a concentrator to a solid content of 20%, and held at 5°C for 6 hours. The obtained concentrate was then filtered through a microfiltration membrane, the permeate was collected, and the obtained permeate was spray-dried to obtain 8.3 kg of powdered calcium caseinate hydrolyzate. The total tyrosine residue content per gram of the calcium caseinate hydrolysate obtained was 14 mg.

[0049] [Example 2] Sodium caseinate [Tatua 100. Manufactured by Tatua. Protein content: 93%, total tyrosine residues Content: 54 mg / g sodium caseinate] was used as the milk protein. 10 kg of sodium caseinate was dissolved in deionized water at a concentration of 10%, heat sterilized at 90°C for 6 minutes, kept at 52°C, adjusted to pH 8.0 with 10% potassium hydroxide solution, and diluted with 4.0 x pancreatin. 400 g of sterilized product (manufactured by Amano Enzyme Co., Ltd.), 100 g of Proteax (manufactured by Amano Enzyme Co., Ltd.), and 150 g of FD-H (manufactured by Morinaga Milk Industry Co., Ltd.) were added, and hydrolysis was carried out for 17 hours. As a result of the hydrolysis, the content of free tyrosine became 93% of the total tyrosine residues in the sodium caseinate. The obtained hydrolyzate was then subjected to a heat treatment at 95°C for 10 minutes to inactivate the enzyme, concentrated in a concentrator to a solid content of 20%, and held at 3°C ​​for 10 hours. The obtained concentrate was then filtered through diatomaceous earth, and the permeate was collected, and the obtained permeate was spray-dried to obtain 8.2 kg of powdered hydrolyzate of the sodium caseinate. The content of total tyrosine residues per 1 g of the obtained sodium caseinate hydrolyzate was 5 mg.

[0050] [Production Example 1] The pH was adjusted to 3.6 with citric acid, and 40 g of the powdered caseinate sodium hydrolysate obtained in Example 2 was dissolved at 80°C in 0.8 L of purified water containing 110 g of sugar, 2 g of calcium lactate, 1 g of emulsifier, and 10 g of soybean polysaccharides, and then cooled to obtain an acidic beverage. [Industrial Applicability]

[0051] The present invention can be applied to foods and beverages intended to provide nutritional supplementation to subjects who need to limit their tyrosine intake.

Claims

1. A step of treating a milk protein with one or more enzymes having exopeptidase activity and one or more enzymes having endopeptidase activity to produce a hydrolysate having a free tyrosine content of 50% by weight or more based on the total tyrosine residues in the milk protein; Crystallizing the free tyrosine in the hydrolysate; and removing the crystallized free tyrosine from the hydrolysate. Including, A method for producing a milk protein hydrolysate, in which the total tyrosine residue content per gram of the milk protein hydrolysate is 35 mg or less.

2. The method of claim 1 , wherein the milk protein is casein.

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