Method for manufacturing fermented milk

Abstract

To provide a method for manufacturing fermented milk with superior functionality and texture.SOLUTION: A method for manufacturing co-fermented milk comprises any one of the following steps of: (a) co-fermenting raw milk in the presence of protein phosphatase with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and with Bifidobacterium bacteria; and (b) co-fermenting treated milk, obtained by enzymatically treating raw milk with protein phosphatase, with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and with Bifidobacterium bacteria.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Fermented milk is produced by fermenting raw milk with microorganisms such as lactic acid bacteria. In recent years, the physiological functions of exopolysaccharides (EPS), which are produced extracellularly by lactic acid bacteria during fermentation, have been attracting attention. The main protein in milk is casein, and when the pH drops during fermentation, casein micelles aggregate and form a gel. Casein is mainly α- S1 , α S2 Caseins are classified into four types: β, β, and κ, which have 8, 11, 5, and 1 phosphate bonded to serine residues, respectively. The phosphate modification in casein is known to affect the hydrophobicity of the casein micelle surface and hydrophobic core. The texture (physical properties) of fermented milk changes over time, and syneresis (separation of whey) during storage is one of the factors that reduces its commercial value. To prevent syneresis, stabilizers such as pectin and functional milk ingredients such as milk protein concentrates have been used. The use of enzymes has also been investigated, and methods using enzymes with milk-clotting activity, such as transglutaminase, glucose oxidase, and protein phosphatase, have been reported (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 041194 [Patent Document 2] International Publication No. 2021 / 210539 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a method for producing fermented milk having better functionality and texture. [Means for solving the problem]

[0005] The present inventors further studied the method for producing fermented milk using the protein phosphatase and found that co-fermenting raw milk in the presence of protein phosphatase, or raw milk enzymatically treated with protein phosphatase, with lactic acid bacteria (sometimes referred to as lactic acid bacteria) selected from the genera Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus and Bifidobacterium (sometimes referred to as bifidobacteria) results in fermented milk with an increased viable count of Bifidobacterium bacteria and good taste and texture, leading to the completion of the present invention. Furthermore, the inventors also found that lactic acid fermentation of non-fat raw milk in the presence of protein phosphatase significantly increased the breaking strength and produced fermented milk with good texture.

[0006] That is, the present invention provides the following [1] to [5]. [1] A method for producing co-fermented milk, comprising any one of the following steps: (a) co-fermenting raw milk with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium in the presence of protein phosphatase; (b) a step of co-fermenting the treated milk obtained by enzymatically treating raw milk with protein phosphatase with lactic acid bacteria selected from Lactobacillus bacteria, Lactococcus bacteria, Streptococcus bacteria, Leuconostoc bacteria, and Enterococcus bacteria, and Bifidobacterium bacteria; [2] The method for producing co-fermented milk according to [1], wherein the amount of fat contained in the raw material milk is within the range of 0% by mass to 5% by mass. [3] Fermented milk that is co-fermented with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium, in which the number of viable Bifidobacterium bacteria is increased. [4] The fermented milk according to [3], which is obtained by the manufacturing method according to [1]. [5] A method for producing non-fat fermented milk, comprising any one of the following steps: (a) fermenting non-fat raw milk with bacteria selected from the group consisting of bacteria of the genus Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Enterococcus, and Bifidobacterium in the presence of protein phosphatase; (b) fermenting the non-fat raw milk enzymatically treated with protein phosphatase with bacteria selected from the group consisting of Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Enterococcus, and Bifidobacterium; [Effects of the Invention]

[0007] The co-fermented milk obtained by the present invention is enriched with Bifidobacterium bacteria, which have excellent intestinal regulating effects, and is useful as fermented milk with added new functions. Furthermore, the fermented milk obtained by the present invention using non-fat or low-fat raw material milk is non-fat or low-fat fermented milk and is useful as fermented milk with a good texture. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows the transition of viable cell count of bifidobacteria during fermentation (A) and the transition of viable cell count of bifidobacteria during refrigerated storage (B). [Figure 2] FIG. 1 shows the transition of viable cell counts of bifidobacteria in fermented milk without enzyme addition (A) and in fermented milk with enzyme addition (B). [Figure 3] FIG. 1 shows the results of breaking strength analysis of non-fat yogurt (A) and full-fat yogurt (B). DETAILED DESCRIPTION OF THE INVENTION

[0009] Terms used in this specification are used in the sense commonly used in the art unless otherwise specified.

[0010] In this specification, fermented milk refers to fermented milk and lactic acid bacteria beverages as defined in the Ministerial Ordinance on Milk, etc. (Ministerial Ordinance on the Compositional Standards of Milk and Dairy Products, Ministry of Health and Welfare Ordinance No. 52 of 1951). Fermented milk is defined as "a product made by fermenting milk or milk, etc. containing an equivalent or higher amount of non-fat milk solids with lactic acid bacteria or yeast into a paste or liquid form, or a product that has been frozen," and lactic acid bacteria beverage is defined as "a beverage (excluding fermented milk) that is processed or uses as a main ingredient milk, etc. that has been fermented with lactic acid bacteria or yeast." Examples of fermented milk classified as "paste-formed" include hard yogurt and soft yogurt, fermented milk classified as "liquid" such as drinkable yogurt (drinkable yogurt), and fermented milk classified as "frozen" such as frozen yogurt. The fermented milk of the present invention is preferably hard yogurt or soft yogurt, as it is easier to enjoy the effects of the present invention.

[0011] In this specification, the co-fermented milk is the fermented milk that has been fermented simultaneously with two or more types of bacteria, and may also be fermented simultaneously with three or more types of bacteria.

[0012] One aspect of the present invention is a method for producing co-fermented milk, comprising any one of the following steps: (a) co-fermenting raw milk with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium in the presence of protein phosphatase; (b) a step of co-fermenting the treated milk obtained by enzymatically treating raw milk with protein phosphatase with lactic acid bacteria selected from Lactobacillus bacteria, Lactococcus bacteria, Streptococcus bacteria, Leuconostoc bacteria, and Enterococcus bacteria, and Bifidobacterium bacteria;

[0013] The raw milk may contain casein, and may be any common milk-derived raw material, such as raw milk, cow's milk, special cow's milk, raw goat's milk, pasteurized goat's milk, raw sheep's milk, adjusted milk, low-fat milk, non-fat milk, processed milk, cream, butter, butter oil, cheese, concentrated whey, ice cream, concentrated milk, concentrated skim milk, unsweetened evaporated milk, unsweetened evaporated skim milk, sweetened condensed milk, sweetened evaporated skim milk, whole milk powder, skim milk powder, cream powder, whey powder, protein-enriched whey powder, buttermilk powder, etc. Of these raw milks, it is preferable to use non-fat or low-fat raw milk in order to obtain low-fat fermented milk, and more specifically, it is more preferable to use raw milk with a fat content of 0% to 5% by mass. The upper limit of the fat content in the raw milk may be 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.2% by mass or less. These upper limits may be combined with lower limits. The amount of casein contained in the raw milk is not particularly limited, but is preferably 0.01 to 10 g / 100 g, more preferably 0.1 to 8 g / 100 g, and even more preferably 1 to 5 g / 100 g. The pH of the raw material milk is preferably 4.0 to 8.0, more preferably 4.7 to 7.5, and even more preferably 5.3 to 6.8. The same applies to the pH of raw material milk to which components other than the raw material milk described below have been added. The raw milk may contain other ingredients that can be added before fermentation or after fermentation, as needed, within the scope of not impairing the effects of the present invention. Examples of such ingredients include sweeteners (monosaccharides, oligosaccharides, sugar alcohols, synthetic sweeteners, etc.), stabilizers (gelatin, pectin, carrageenan, xanthan gum, etc.), fruit juice, fruit pulp, flavorings, etc.

[0014] Protein phosphatase is an enzyme that dephosphorylates phosphorylated proteins, and in the present specification, any protein phosphatase can be used as long as it can remove phosphate from phosphorylated serine of casein in raw milk. Preferably, the protein phosphatase removes phosphate from phosphorylated serine of casein in raw milk during fermentation. The optimum (optimum) pH of the protein phosphatase is preferably in the range of 4.0 to 7.5, more preferably 4.5 to 7.0, and even more preferably 5.0 to 6.0. Protein phosphatase is gradually inactivated during the production of fermented milk, and is preferably inactivated in the fermented milk. Specifically, it is active even in a weakly acidic pH range of 5.0 to 6.0, and is preferably inactivated at a pH of less than 4.5. During the fermentation process of raw milk, phosphate is gradually released from casein. The increased free phosphate in the milk acts as a pH buffer, and the pH range period in which lactic acid bacteria metabolize nutrients is extended, which is thought to facilitate the production of EPS. Inactivation of protein phosphatase after the end of fermentation is preferable, as it makes it easier to maintain the quality of fermented milk stably. The optimum temperature for protein phosphatase is preferably in the range of 1°C to 60°C, more preferably in the range of 10°C to 55°C. The protein phosphatase used in the present invention preferably has the above-mentioned optimum pH and optimum temperature. While the type and origin of the protein phosphatase are not critical, protein phosphatases derived from microorganisms belonging to the genera Trichoderma, Aspergillus, Saccharomyces, Bacillus, and Streptomyces are preferred, protein phosphatases derived from Trichoderma virens are more preferred, and the hypothetical protein (XP_013951069.1 hypothetical protein TRIVIDRAFT_87714) derived from Trichoderma virens Gv29-8 described in Patent Document 2 is even more preferred. The disclosure of Patent Document 2 is incorporated herein by reference.

[0015] The bacteria used for fermentation in the present invention are a combination of one or more lactic acid bacteria selected from the group consisting of Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium. Examples of bacteria of the genus Lactobacillus include Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus delbrueckii, and Lactobacillus delbrueckii subsp. bulgaricus. Examples of bacteria of the genus Lactococcus include Lactococcus lactis. Examples of bacteria of the genus Streptococcus include Streptococcus thermophilus. Examples of bacteria of the genus Leuconostoc include Leuconostoc mesenteroides. Examples of bacteria of the genus Enterococcus include Enterococcus faecalis. Examples of the Bifidobacterium bacteria include Bifidobacterium bifidum, Bifidobacterium breve, and Bifidobacterium animalis subsp. lactis. These two types of bacteria (Lactobacillus and Bifidobacterium) are usually used as starters. The number of live bacteria of these two types of bacteria contained in a starter is, for example, 10 5 ~10 14 cfu / g, preferably 10 6 ~10 13 cfu / g, more preferably 10 7 ~10 12 cfu / g, more preferably 10 8 ~10 11 The number of bacteria is the same when two or more types of lactic acid bacteria are used. The amount of starter used is not particularly limited and can be set appropriately depending on the type, but is, for example, 0.01 to 10 mass% of the raw milk and / or enzyme-treated milk, preferably 0.1 to 10 mass%, and more preferably 0.5 to 10 mass%.

[0016] Step (a) is a step in which raw milk is co-fermented with the two types of bacteria (lactic acid bacteria and Bifidobacterium bacteria) in the presence of protein phosphatase. In step (a), the protein phosphatase may be present during the fermentation of the raw material milk, and there are no particular limitations on the timing of its addition. The amount of protein phosphatase used in step (a) may be any concentration capable of releasing phosphate from phosphorylated serine of casein in the raw milk. For example, 0.1 to 25 U per 1 mL of raw milk is preferred, 0.5 to 15 U is more preferred, and 1 to 10 U is even more preferred. Herein, 1 U refers to the amount of enzyme that liberates 1 μmol of phosphate per minute when a substrate solution containing 20 mg of bovine milk casein is added to 1 mL of 20 mM MES-NaOH buffer (pH 6.0) containing 10 mM Tris-HCl at 1 / 10 the volume of enzyme solution, reacted at 37°C, and an equal volume of reaction stop solution is added. The fermentation method in step (a) is based on a general method. For example, the raw milk and other raw materials are mixed and dissolved to prepare a fermentation mix, which is then homogenized, heat-sterilized, and cooled. The two starters (lactic acid bacteria and Bifidobacterium) and protein phosphatase are then added, and the mixture is fermented. After cooling, the mixture may be crushed and homogenized as necessary. The fermentation temperature may be set appropriately depending on the type of starter, as long as it allows the two starters to grow and does not inactivate the enzymes. A temperature of 20°C to 45°C is preferred, and a temperature of 30°C to 43°C is more preferred. The fermentation time is, for example, 1 to 48 hours, preferably 2 to 24 hours, more preferably 3 to 10 hours, even more preferably 3 to 6 hours, and particularly preferably 3 to 5 hours. The pH of the fermented milk is preferably 4.0 to 5.0.

[0017] In step (b), raw milk is enzymatically treated with protein phosphatase, and the treated milk is then co-fermented with the two bacteria (lactic acid bacteria and Bifidobacterium). By preliminarily treating the raw milk with protein phosphatase, more casein can be dephosphorylated, and the degree of casein dephosphorylation can be easily controlled. The amount of protein phosphatase used in step (b) may be any concentration that can remove phosphate from phosphorylated serine in casein in the raw milk, for example, preferably 0.1 to 25 U, more preferably 0.5 to 15 U, and even more preferably 1 to 10 U per part by mass of raw milk. The enzyme treatment of raw milk is preferably carried out for 0.1 to 24 hours at a reaction temperature of 1 to 60° C. The reaction temperature is preferably 10 to 60° C., more preferably 30 to 55° C., and even more preferably 40 to 50° C. The reaction time is preferably 0.3 to 12 hours, more preferably 0.5 to 5 hours, and particularly preferably 1 to 4 hours. Before the raw material milk is subjected to the enzymatic treatment with protein phosphatase, the pH of the raw material milk may be adjusted. After the enzyme treatment, the raw milk may be fermented without inactivating the enzyme, or may be fermented after being treated to inactivate the enzyme by heating or the like. It is preferable to ferment the raw milk without inactivating the enzyme. Dephosphorylation of casein also progresses gradually during fermentation. The heating conditions for the treatment to inactivate the enzyme are preferably high temperature for a short period of time, for example, heating for 1 to 30 minutes at 60 to 100° C. The enzyme treatment may be carried out before the sterilization step of the raw material milk, and then the enzyme may be inactivated during the sterilization step of the raw material milk. The fermentation method in step (b) is similar to that in step (a) and is based on a general method, for example, a fermentation mix containing raw milk enzymatically treated with protein phosphatase and other raw materials is homogenized, heat sterilized, and cooled, and then the two starters (lactic acid bacteria and Bifidobacterium bacteria) are added and fermented. After cooling, the mixture may be crushed and homogenized as necessary. The fermentation temperature can be set appropriately as in step (a), but is preferably 20°C to 45°C, more preferably 30°C to 43°C. The fermentation time is, for example, 1 to 48 hours, preferably 2 to 24 hours, more preferably 3 to 10 hours, even more preferably 3 to 6 hours, and particularly preferably 3 to 5 hours. The pH of the fermented milk is preferably 4.0 to 5.0.

[0018] In the present invention, it is preferable to produce co-fermented milk by step (a) from the viewpoints of facilitating the formation of a uniform curd and being excellent in terms of handling properties and cost.

[0019] The fermented milk obtained by the present invention may contain other ingredients that can be added before or after fermentation, as needed, within the scope of not impairing the effects of the present invention. Examples of such ingredients include sweeteners (monosaccharides, oligosaccharides, sugar alcohols, synthetic sweeteners, etc.), stabilizers (gelatin, pectin, carrageenan, xanthan gum, etc.), fruit juice, fruit pulp, flavorings, etc.

[0020] As shown in the Examples below, the co-fermented milk obtained by the method of the present invention has an increased viable cell count of Bifidobacterium bacteria, and is fermented milk that has the physiological functions of Bifidobacterium bacteria in addition to the physiological functions of ordinary fermented milk. Furthermore, the viable cell count of Bifidobacterium bacteria is maintained even during refrigerated storage. Therefore, another aspect of the present invention is fermented milk co-fermented with lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium, in which the viable count of Bifidobacterium is increased. Here, the increase rate of Bifidobacterium bacteria is preferably 200% or more.

[0021] According to the co-fermentation method of the present invention, the viable cell count of Bifidobacterium bacteria increases, so when ordinary fermented milk is to be produced, the amount of Bifidobacterium bacteria used as a starter can be reduced.

[0022] The present inventors have found that when non-fat raw milk is fermented with lactic acid bacteria in the presence of protein phosphatase, the breaking strength increases significantly, and fermented milk with a good texture is obtained. Therefore, another aspect of the present invention is a method for producing non-fat fermented milk, comprising any one of the following steps: (a) fermenting non-fat raw milk with bacteria selected from the group consisting of bacteria of the genus Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Enterococcus, and Bifidobacterium in the presence of protein phosphatase; (b) fermenting the non-fat raw milk enzymatically treated with protein phosphatase with bacteria selected from the group consisting of Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Enterococcus, and Bifidobacterium;

[0023] The raw material milk used in the present invention is non-fat raw material milk, which has a fat content of substantially 0% by mass. Specific examples include non-fat cow's milk, concentrated skim milk, and skim milk powder. The upper limit of the fat content in the raw material milk may be 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.2% by mass or less. These upper limits may be combined with lower limits. The starter may be selected from the group consisting of Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Enterococcus, and Bifidobacterium. Specific examples of the starter are the same as those used in the co-fermentation method described above. The process is similar to the steps (a) and (b) except that the raw material milk is non-fat raw material milk and the starter is not limited to the combination of the two types mentioned above.

[0024] The fermented milk obtained by the present invention has a significantly increased breaking strength and a good texture.

[0025] Furthermore, since the co-fermented milk and fermented milk obtained by the present invention have been treated with protein phosphatase, as described in Patent Document 2, they are free from syneresis and contain a large amount of exopolysaccharides (EPS). [Example]

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

[0027] Example 1 (Effect of increasing viable count of bifidobacteria) <Method> 2.8g (2% concentration) of skim milk (Morinaga) was added to 137.2g of LTLT milk (Takanashi pasteurized milk), stirred, and then placed in a boiling water bath for 20 minutes, followed by pre-incubation at 43°C. The fat content of the mixture of LTLT milk and skim milk was 5.38g (3.8% fat). As starters, Christian Hansen's YF-L812 (Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus) was used at a final concentration of 10mg / 100g, and the same company's Bifidobacterium BB-12 TM After adding 5 mg / 100 g of Bifidobacterium animalis subsp. lactis, 70 g of the mixture was dispensed into medium bottles. Protein phosphatase (protein phosphatase from Trichoderma virens Gv29-8 (hereafter referred to as "PPase")) was added to one of the bottles at 1.0 U / g, and the same amount of PPase, which had been inactivated by placing it in a boiling water bath for 10 minutes, was added to the other bottle. 13 mL of the sample was dispensed into 15 mL centrifuge tubes and fermented at 43°C. Sampling was performed every 0, 1.5, 3, and 4 hours, and the bacterial count was measured. The bacterial count was measured using the following method: 100 μL of the sample was diluted with 0.85% sterile saline for 10 min. 4 ~10 6 The diluted solution was poured onto TOS propionic acid agar medium (Eiken Chemical) in an anaerobic jar. The AnaeroPack was placed in an anaerobic jar and incubated at 37°C for two days, after which the bacterial count was counted. For the storage test, yogurt prepared in the same manner was stored in a refrigerator and the bacterial count was measured every two to four days.

[0028] <Results / Discussion> Figure 1(A) shows the change in viable cell count of bifidobacteria during fermentation of fermented milk using YF-L812 (two types of lactic acid bacteria) and BB12 (bifidobacteria), and Figure 1(B) shows the change in viable cell count during refrigerated storage. From three hours after the start of fermentation, the number of viable bifidobacteria tended to increase in the PPase-added sample compared to the unadded sample (Fig. 1(A)). During refrigerated storage, the number of viable bifidobacteria tended to remain unchanged for approximately 20 days in both the PPase-added and unadded groups (Fig. 1(B)). Therefore, the difference in viable bifidobacteria count caused by the addition of PPase tended to be maintained during storage.

[0029] Example 2 (Bifidobacterium starter reduction effect) <Method> 240g of delicious milk (Meiji UHT milk) was placed in a medium bottle and pre-incubated at 43°C for approximately 30 minutes, after which 80g was dispensed into three medium bottles. The fat content of the UHT milk was 9.36g (3.9% fat). YF-L812 (Christian Hansen, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus) was added at a final concentration of 10mg / 100g, and Bifidobacterium BB-12 TM A control sample was prepared by adding 5 mg / 100 g of Bifidobacterium animalis subsp. lactis (Christian Hansen) and stirring. The PPase-added sample contained the same concentration of L812 and 4 or 2.5 mg / 100 g of BB12, with PPase added to a concentration of 1.0 U / g. The sample was dispensed into 15 mL centrifuge tubes in 13 mL portions and fermented at 43°C until the pH reached approximately 4.6. The bacterial count was measured after 0, 2, and 4.5 hours. The bacterial count was measured in the same manner as in Example 1. For comparison, samples were prepared in the same manner except that the BB12 concentration was reduced to 4 or 2.5 mg / 100 g without adding any enzyme, and the bacterial count was measured.

[0030] <Results / Discussion> Figure 2 shows the transition of viable counts of bifidobacteria in each test group. In the sample in which the starter was reduced by 20%, the bacterial count was nearly the same at 5 mg / 100 g at the end of fermentation (Figure 2(A)), but the addition of PPase resulted in the bacterial count exceeding that of the control at the end of fermentation (Figure 2(B)). Furthermore, in the fermented milk sample in which the starter was reduced by 50%, the initial difference in bacterial count tended to be maintained (Figure 2(A)), but the addition of PPase resulted in the bacterial count approaching the control level (Figure 2(B)). These results suggest that PPase promotes the proliferation of bifidobacteria and may enable the amount of bifidobacterial starter used to be reduced by about half.

[0031] Example 3 (Improvement of physical properties of non-fat yogurt) <Method> 490 g of nonfat milk (Koiwai) was weighed into a medium bottle, and 10 g of skim milk was added and stirred. The fat content of the mixture of nonfat milk and skim milk was 0.59 g (0.118% fat). After incubating at 43°C, 500 μL of YF-L812 starter was added (final concentration: 10 mg / 100 g) to sterilized water at 0.1 g / mL. After stirring, 250 g of the mixture was dispensed into sterile medium bottles, and filter-sterilized PPase was added to a concentration of 1.0 U / g. As a control, the original medium bottle was filled with the same volume of filter-sterilized 20 mM phosphate buffer. After stirring, the mixture was dispensed into two jam bottles (55 g each), and the remaining mixture was dispensed into 15 mL centrifuge tubes (13 mL each) for pH monitoring. Fermentation was carried out in a water bath at 43°C, and the pH was measured every 30 minutes to 1 hour, aiming for completion of fermentation at around pH 4.65. The fermented samples were refrigerated overnight and then subjected to breaking strength and texture analysis (RHEONER II CREEP METER RE2-3305C, YAMADEN. No. 3 plunger was used). For comparison, full-fat yogurt was prepared as described above using Oishii Gyunyu (Meiji) instead of non-fat milk.

[0032] (Breaking strength analysis) The equipment used was a creep meter RE2-33005C (manufactured by Yamaden), and the plunger was No. 3. Measurements were performed with a load cell of 0.01, an amplifier magnification of 0.1, a storage pitch of 0.09 seconds, a measurement strain rate of 60%, a measurement speed of 1 mm / second, and automatic measurement of the sample thickness.

[0033] <Results / Discussion> The results of the breaking strength analysis of non-fat milk yogurt are shown in Figure 3(A). PPase showed a tendency for the breaking strength to increase significantly. For comparison, Figure 3(B) shows the results for full-fat yogurt. The maximum load of non-fat yogurt was smaller than that of full-fat yogurt, indicating a tendency for the curd to become softer. However, PPase was thought to have the effect of increasing the curd strength to the same level as or even greater than that of full-fat yogurt.

Claims

1. A method for producing co-fermented milk, comprising any one of the following steps: (a) co-fermenting raw milk with one or more lactic acid bacteria selected from Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Enterococcus, and Bifidobacterium in the presence of protein phosphatase; (b) a step of co-fermenting the treated milk obtained by enzymatically treating raw milk with protein phosphatase with one or more lactic acid bacteria selected from the group consisting of Lactobacillus bacteria, Lactococcus bacteria, Streptococcus bacteria, Leuconostoc bacteria, and Enterococcus bacteria, and Bifidobacterium bacteria;

2. The method for producing co-fermented milk according to claim 1, wherein the amount of fat contained in the raw milk is in the range of 0% by mass to 5% by mass.

3. This co-fermented milk is one or more lactic acid bacteria selected from the group consisting of Lactobacillus bacteria, Lactococcus bacteria, Streptococcus bacteria, Leuconostoc bacteria and Enterococcus bacteria, and Bifidobacterium bacteria, in which the number of viable Bifidobacterium bacteria is increased.

4. The co-fermented milk according to claim 3, which is obtained by the method according to claim 1.

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