Method for producing oil-in-water emulsion, method for producing bubble-containing oil-in-water emulsion, method for producing frozen bubble-containing oil-in-water emulsion, method for producing acidic oil-in-water emulsion, method for producing bubble-containing acidic oil-in-water emulsion and oil-in-water emulsion

Abstract

To provide a method for producing oil-in-water emulsion that can be foamed when an acidic material is added thereto, and retains its shape well after foaming.SOLUTION: A method for producing oil-in-water emulsion includes the steps of: preparing a homogenized, first oil-in-water emulsion containing oil and fat and water with protein content of less than 1.4 mass%; and mixing the homogenized, first oil-in-water emulsion with protein-containing raw material to prepare a second oil-in-water emulsion.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing an oil-in-water emulsion, a method for producing a foam-containing oil-in-water emulsion, a method for producing a frozen foam-containing oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion, a method for producing a foam-containing acidic oil-in-water emulsion, and an oil-in-water emulsion.

Background Art

[0002] Cream is used for various applications. For example, whipped cream obtained by foaming edible creams such as fresh cream and compound cream is used for decorating confectionery such as cakes and fruits, or floating on beverages such as Wiener coffee. As cream, for example, an oil-in-water emulsion containing fats and oils, water, and protein is used. Such an oil-in-water emulsion is generally produced by mixing a water phase portion containing water and protein and an oil phase portion containing oil-soluble components such as fats and oils for preliminary emulsification, homogenizing, sterilizing, cooling, and more preferably aging thereafter. In order to impart flavors such as a milky taste and a rich taste to cream, it has been proposed to add, mix, and sterilize skimmed condensed milk after aging (Patent Document 1).

[0003] On the other hand, in the market of whipped cream, there is a need to obtain a whipped cream with a sour and refreshing taste by adding acidic foods with a low pH such as fruit juice or acidic materials such as acidic compounds. However, oil-in-water emulsions generally have low acid resistance. When the pH decreases, the protein in the oil-in-water emulsion aggregates, and the oil-in-water emulsion thickens or solidifies. Therefore, it is difficult to add an acidic material to the oil-in-water emulsion and foam it. Further, even if an acidic material is mixed after foaming the oil-in-water emulsion, the protein aggregates, resulting in a poor texture of the whipped cream. For this reason, there has been a demand for a technology for imparting acid resistance to oil-in-water emulsions, particularly a technology for imparting a property (acid resistance) that allows foaming operation without an increase in viscosity even when the pH is lowered. As methods for imparting acid resistance to oil-in-water emulsions, a method of devising the formulation of emulsifiers (Patent Document 2), a method of devising the type of protein (Patent Document 3), and a method of adding an acid resistance-imparting agent such as fermented cellulose (Patent Document 4) have been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the methods of Patent Documents 2 and 3 employ specific emulsifiers or specific proteins to impart acid resistance, so the types of emulsifiers and proteins that can be formulated are restricted. For this reason, there is little room for devising the formulation of emulsifiers and proteins in product design, and there is a problem that the degree of freedom in product design is poor. The method of Patent Document 4 has a problem that, in order to impart acid resistance, a basically unnecessary acid resistance-imparting agent is formulated, so that the flavor of the oil-in-water emulsion becomes different from the original flavor, and the cost of the product increases. Also, this method has a problem that the degree of freedom in product design is low. Furthermore, in the conventional technology, even if an oil-in-water emulsion to which an acidic material has been added can be foamed, the shape retention of the resulting whipped cream is not sufficient, and the hardness of the whipped cream may easily decrease over time. Therefore, there is a need for a technology that can produce an oil-in-water emulsion that can be foamed when an acidic material is added, allows for free product design without being restricted to specific raw materials or adding inherently unnecessary components, and has excellent shape retention after foaming.

[0006] One aspect of the present invention is a method for producing an oil-in-water emulsion that can be foamed when an acidic material is added and can produce an oil-in-water emulsion with excellent shape retention after foaming, a method for producing a bubble-containing oil-in-water emulsion using this production method, a method for producing a frozen bubble-containing oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion, and a method for producing a bubble-containing acidic oil-in-water emulsion, and an object thereof is to provide an oil-in-water emulsion that can be foamed when an acidic material is added and has excellent shape retention after foaming. [Means for Solving the Problems]

[0007] [1] A step of subjecting a first oil-in-water emulsion containing fats and oils and water and having a protein content of less than 1.4% by mass to homogenization to obtain a homogenized first oil-in-water emulsion, A method for producing an oil-in-water emulsion, comprising a step of mixing the homogenized first oil-in-water emulsion and a protein-containing raw material to obtain a second oil-in-water emulsion. [2] A method for producing an oil-in-water emulsion according to [1], wherein after the step of obtaining the second oil-in-water emulsion, the second oil-in-water emulsion is not homogenized. [3] A method for producing an oil-in-water emulsion according to [1] or [2], wherein the fat and oil content of the first oil-in-water emulsion is 1 to 60% by mass. [4] A method for producing an oil-in-water emulsion according to any one of [1] to [3], wherein the protein content of the second oil-in-water emulsion is 0.4% by mass or more and less than 5% by mass. [5] A method for producing an oil-in-water emulsion according to any one of [1] to [4], wherein the pH of the oil-in-water emulsion produced by the production method is 6.5 to 7.5, the viscosity at 10°C is 1 to 1000 mPa·s, and the viscosity at 10°C when the pH of the oil-in-water emulsion is adjusted to around 4.5 is less than 5810 mPa·s. [6]A method for producing an oil-in-water emulsion containing bubbles, which comprises foaming an oil-in-water emulsion produced by any one of the production methods [1] to [5] above to obtain an oil-in-water emulsion containing bubbles. [7]A method for producing a frozen oil-in-water emulsion containing bubbles, which comprises freezing the oil-in-water emulsion containing bubbles produced by the production method [6] above to obtain a frozen oil-in-water emulsion containing bubbles. [8]A method for producing an acidic oil-in-water emulsion, which comprises adding an acidic material to an oil-in-water emulsion produced by any one of the production methods [1] to [5] above and adjusting the pH to a range of 3.0 to 6.5 to obtain an acidic oil-in-water emulsion. [9]A method for producing an oil-in-water emulsion containing bubbles, which comprises foaming the acidic oil-in-water emulsion produced by the production method [8] above to obtain an oil-in-water emulsion containing bubbles.

[10] An oil-in-water emulsion containing oil, water and protein, having a pH of 6.5 to 7.5, having a viscosity at 10°C of 1 to 1000 mPa·s, having a viscosity at 10°C of less than 5810 mPa·s when the pH of the oil-in-water emulsion is around 4.5, and having a protein precipitation amount measured by the following measurement method exceeding 0% by volume. An oil-in-water emulsion. Measurement method of protein precipitation amount: 50 mL of the oil-in-water emulsion is placed in a graduated centrifuge tube, and after centrifugation is carried out for 5 minutes under the condition of a relative centrifugal acceleration of 1630×g using a centrifuge, the volume (mL) of the protein precipitated in the centrifuge tube is visually measured, and the ratio (volume %) of the volume of the protein to the total volume of the oil-in-water emulsion is taken as the protein precipitation amount.

Advantages of the Invention

[0008] According to the present invention, there are provided a method for producing an oil-in-water emulsion that can be foamed when acidified and has excellent shape retention after foaming, a method for producing a gas-containing oil-in-water emulsion using this production method, a method for producing a frozen gas-containing oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion, and a method for producing a gas-containing acidic oil-in-water emulsion, and an oil-in-water emulsion that can be foamed when acidified and has excellent shape retention after foaming.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] In the present invention, the protein content of the oil-in-water emulsion can be calculated by calculation from the protein content of the raw materials and their formulation. However, generally, the protein content can also be measured by the semi-micro Kjeldahl method (General Test Methods, Manufacturing General Rules, Fourteenth Revised Japanese Pharmacopoeia Explanation Book 2001 B-370~B374). The specific measurement method is shown below. Take about 1 g of the sample (the mass of the sample is measured to the unit of 0.1 mg), and quantify the nitrogen content in the sample by the semi-micro Kjeldahl method. Specifically, put the sample into a decomposition flask, add 1 g of a decomposition accelerator with a composition of potassium sulfate: copper sulfate = 10:1 (mass ratio), and further add 7 mL of concentrated sulfuric acid, and perform thermal decomposition. After thermal decomposition, subject the sample to steam distillation, and receive the distilled product in 20 mL of a 20 mM sulfuric acid aqueous solution. When the distillation is completed, titrate the 20 mM sulfuric acid aqueous solution that has received distilled water with 40 mM sodium hydroxide. Let the titration volume at that time be b (mL). Perform a blank test using a control sample containing no protein instead of the sample, and let the titration volume at that time be a (mL). Then, the protein content of the sample is calculated by the following formula. Protein content (mass%) = (0.56×(b - a)×6.38) / weight of sample (g) / 1000×100 Incidentally, 0.56 in the formula is the nitrogen content of the sample per 1 mL of 40 mM sodium hydroxide, and 6.38 is the coefficient for converting the nitrogen content to the protein of dairy products. In the present invention, the oil and fat content of the oil-in-water emulsion can also be calculated by calculation from the formulation of the raw materials. However, generally, the oil and fat content can also be measured by the Rose Gottlieb method (Food Hygiene Inspection Guidelines, Physical and Chemical Edition 2005 p.48-49: supervised by the Ministry of Health, Labour and Welfare). The specific measurement method is shown below. First, collect 1 g of the sample in a beaker, and while washing the inside of the beaker with about 10 mL of warm water, transfer it to an extraction tube. Add 2 mL of ammonia water and 1 drop of phenolphthalein reagent to the extraction tube, stopper it, and mix well. Then, while washing the beaker from which the sample was taken with 10 mL of ethanol, add it to the extraction tube, stopper it, and mix thoroughly. Next, add 25 mL of ether, stopper it, and shake vigorously for 30 seconds. Finally, add 25 mL of petroleum ether, stopper it, and shake vigorously for 30 seconds. After allowing it to stand until the upper layer becomes clear, decant the ether layer into a pre-weighed dish without spilling it to recover the organic solvent. Place this dish in a steam dryer at 100°C to 105°C for 1 hour to evaporate the organic solvent. By measuring the mass of this dish, the amount of extracted fat (g) can be measured. The oil and fat content is calculated from these measured values using the following formula. Oil and fat content (mass %) = (amount of extracted fat / amount of sample used) × 100 Viscosity is measured using a B-type viscometer. Unless otherwise specified, pH is the value at 10°C. Relative centrifugal acceleration is calculated using the following formula. RCF = 1118 × r × N 2 ×10 -8 Here, RCF indicates relative centrifugal acceleration (×g), r indicates the maximum rotation radius (cm), and N indicates the number of rotations per minute (rpm). In this specification, "excellent acid resistance" means that it can foam when an acidic material is added and has excellent shape retention after foaming.

[0011] 〔Method for producing water-in-oil emulsion〕 The method for producing a water-in-oil emulsion according to one aspect of the present invention (hereinafter, also referred to as "this production method") includes a step of homogenizing a first water-in-oil emulsion containing oil and fat and water and having a protein content of less than 1.4 mass% to obtain a homogenized first water-in-oil emulsion (hereinafter, also referred to as the "homogenization step"), and a step of mixing the homogenized first water-in-oil emulsion and a protein-containing raw material to obtain a second water-in-oil emulsion (hereinafter, also referred to as the "mixing step"). The first oil-in-water emulsion, the protein-containing raw material, and the second oil-in-water emulsion will be described in detail later.

[0012] In this production method, it is preferable not to perform homogenization of the second oil-in-water emulsion after the mixing step. The phrase "not performing homogenization of the second oil-in-water emulsion" as used herein means that no mechanical operation is intentionally performed to make the fat globules in the second oil-in-water emulsion finer. In the case where the fat globules are naturally crushed by impact or the like during the handling of the second oil-in-water emulsion, it is not included in the "homogenization of the second oil-in-water emulsion" as used herein.

[0013] This production method may have a step (hereinafter also referred to as the "pre-emulsification step") of mixing an oil phase part containing fats and oils and an aqueous phase part containing water (pre-mixing) before the homogenization step and emulsifying (pre-emulsifying) with a mixing device such as a homomixer to prepare a first oil-in-water emulsion. Before the pre-emulsification step, there may be a step of heating and melting the fats and oils and dissolving other oil-soluble components (such as the first emulsifier described later) in the fats and oils as necessary to prepare the oil phase part. Before the pre-emulsification step, there may be a step of using water as the aqueous phase part as it is, or adding other water-soluble components (such as the second emulsifier, the protein-containing raw material, the chelating agent, etc.) to the water to prepare the aqueous phase part. Before the homogenization step, there may be a step of heating (pre-heating) the first oil-in-water emulsion. Before or after the homogenization step, there may be a step of sterilizing the first oil-in-water emulsion. After the homogenization step, there may be a step of aging the first oil-in-water emulsion. Before the mixing step, there may be a step of sterilizing the protein-containing raw material. Before the mixing step, there may be a step of homogenizing the protein-containing raw material. However, the protein-containing raw material typically does not contain fats and oils, and in this case, it may not be necessary to homogenize the protein-containing raw material itself. After the mixing step, there may be a step of sterilizing the second oil-in-water emulsion. After the mixing step, it may have a step of aging the second water-in-oil emulsion. The water-in-oil emulsion produced by this production method is typically a second water-in-oil emulsion, an aged second water-in-oil emulsion, or a second water-in-oil emulsion that has been sterilized and aged. Hereinafter, the water-in-oil emulsion produced by this production method is also referred to as "the water-in-oil emulsion of the present invention".

[0014] Hereinafter, this production method will be described with reference to the accompanying drawings and shown in embodiments. FIG. 1 is a flowchart showing an embodiment of this production method. In this embodiment, first, the fats and oils among the raw materials are heated and melted, and if necessary, other oil-soluble components are dissolved in the fats and oils to prepare an oil phase portion. Separately, among the raw materials, the water is used as the water phase portion as it is, or other water-soluble components are dissolved in the water to prepare the water phase portion. These preparations are carried out by heating the fats and oils or water to an appropriate temperature. Next, the oil phase portion and the water phase portion are put into, for example, a tank equipped with a stirrer and preliminarily mixed. Then, for example, the stirrer is operated, and the oil phase portion and the water phase portion are sufficiently stirred and pre-emulsified. Thereby, a first water-in-oil emulsion is prepared. In this first water-in-oil emulsion, it is necessary to keep the protein content low, and the protein content of the first water-in-oil emulsion is less than 1.4% by mass.

[0015] Next, the first water-in-oil emulsion is passed through a UHT sterilizer integrated with a homogenizer. A UHT sterilizer integrated with a homogenizer usually comprises a heat exchanger and a homogenizer. The first water-in-oil emulsion is first preheated by the heat exchanger and preferably heated to a temperature of 65 to 75°C. Next, it is homogenized by the homogenizer. The set pressure (homo pressure) for homogenization of the first water-in-oil emulsion is preferably 1.0 to 15.0 MPa, more preferably 3.0 to 15.0 MPa, and even more preferably 5.0 to 12.0 MPa. The above homo pressure is a gauge pressure. The homogenized first water-in-oil emulsion is heated to a predetermined sterilization temperature and held for a predetermined time for sterilization. The sterilization conditions are not particularly limited and can be carried out under known sterilization conditions. For example, heating at 90°C for 15 seconds, or heating conditions that can obtain a sterilization effect equivalent thereto can be mentioned. Thereafter, the homogenized first water-in-oil emulsion is cooled. Note that there are also models of UHT sterilizers integrated with a homogenizer that perform homogenization at a stage after sterilization and before cooling, and such models may be adopted. The cooled first water-in-oil emulsion is stored in a tank equipped with a cold insulation function.

[0016] Separately, a protein-containing raw material is sterilized and cooled. The sterilization conditions are not particularly limited and can be carried out under known sterilization conditions. For example, heating at 90°C for 15 seconds, or heating conditions that can obtain a sterilization effect equivalent thereto can be mentioned. Then, the protein-containing raw material is mixed with the stored first water-in-oil emulsion. Thereby, a second water-in-oil emulsion is prepared. The mixing amount of the protein-containing raw material is set according to the target value of the protein content of the second water-in-oil emulsion. That is, the protein content of the first water-in-oil emulsion is kept low, and finally, by additionally mixing the protein-containing raw material, it is adjusted to the desired protein content. Thereafter, by aging the second oil-in-water emulsion, the oil-in-water emulsion of the present invention can be obtained. Aging is a process that promotes the crystallization of fat and can be carried out according to a conventional method. The aging conditions are not particularly limited and can be carried out under known aging conditions. For example, conditions of 3.0 to 6.0 °C for 8 to 10 hours can be mentioned. After mixing the homogenized first oil-in-water emulsion and the protein-containing raw material, for example, during aging, the second oil-in-water emulsion can be stirred to mix them uniformly. Stirring can be carried out using a known stirrer. At this time, in order to suppress the decrease in acid resistance of the second oil-in-water emulsion, it is preferably stirred as slowly as possible. In this regard, it is desirable to store the cooled first oil-in-water emulsion in a tank equipped with a cooling function such as a double jacket with a slowly rotating stirring blade and stir it with the stirring blade in the tank.

[0017] <The first oil-in-water emulsion> The first oil-in-water emulsion contains fats and oils and water. The first oil-in-water emulsion may contain protein as long as the protein content is less than 1.4% by mass. The first oil-in-water emulsion may further contain at least one selected from the group consisting of emulsifiers, stabilizers, and salts. The first oil-in-water emulsion may further contain other components other than those described above.

[0018] Examples of the fats and oils include vegetable fats and oils and animal fats and oils. Examples of the vegetable fats and oils include plant-based ones such as palm oil, palm kernel oil, coconut oil, rapeseed oil, soybean oil, sunflower oil, cottonseed oil, peanut oil, rice oil, rice bran oil, corn oil, safflower oil, olive oil, kapok oil, sesame oil, and evening primrose oil; oleic acid of that plant-based; hydrogenated oils (partially hydrogenated oils, extremely hydrogenated oils) of that plant-based, transesterified oils, fractionated oils, and mixed oils. Examples of the animal fats and oils include milk fat, beef tallow, lard, fish oil, whale oil, their hydrogenated oils (partially hydrogenated oils, extremely hydrogenated oils), transesterified oils, fractionated oils, and mixed oils. These fats and oils may be used alone or in combination of two or more. From the viewpoints of cost and physical properties after whipping, at least a part of the oil and fat is preferably vegetable oil and fat. Animal oil and fat such as milk fat may be used in combination with the vegetable oil and fat. As the vegetable oil and fat, those having a solid fat content of about 50 to 70% by mass at refrigeration temperature (5°C) and a melting point of around 35 to 40°C so that mouth melting can be obtained in the body temperature range when an oil-in-water type emulsion is foamed are preferable. Examples of such vegetable oil and fat include rapeseed oil, soybean oil, palm oil, palm kernel oil, corn oil, cottonseed oil, rice oil, coconut oil, their oleic acid, hydrogenated oils, and the like. Among these, a mixed oil of palm olein and hydrogenated rapeseed oil, palm hydrogenated oil, and palm kernel hydrogenated oil are preferable. These may be used alone or in combination of two or more.

[0019] Protein is generally considered to contribute to the improvement of the stability of the oil-in-water type emulsion and the stability of the oil-in-water type emulsion containing bubbles obtained by foaming the oil-in-water type emulsion. However, in the present invention, the protein content of the first oil-in-water type emulsion is limited to less than 1.4% by mass. The idea of reducing the protein content of the first oil-in-water type emulsion in this way is an extremely rare idea in the technical field of the present invention. Examples of the protein include milk protein, soybean protein, etc., and milk protein is preferable from the viewpoint of flavor. And in the present invention, the protein is typically incorporated into the first oil-in-water type emulsion in the form of a protein-containing raw material. Examples of the protein-containing raw material include the same ones as the protein-containing raw material used in the mixing step.

[0020] Emulsifiers, stabilizers, and salts contribute to the improvement of the stability (emulsion stability) of the oil-in-water type emulsion. Examples of the emulsifier include lecithin, polyglycerol fatty acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, polysorbate, organic acid monoglyceride, fatty acid monoglyceride, and the like. These emulsifiers may be used alone or in combination of a plurality of types.

[0021] The emulsifier preferably contains polyglycerol fatty acid ester because of its excellent solubility in water. The content of polyglycerol fatty acid ester is preferably 30 to 100% by mass, more preferably 50 to 100% by mass, based on the total mass of the emulsifier. Polyglycerol fatty acid ester may be used in combination with other emulsifiers. As other emulsifiers, at least one selected from the group consisting of lecithin and sucrose fatty acid ester is preferable in terms of emulsion stability during the production process, foaming property, flavor of the oil-in-water emulsion, and foaming property.

[0022] The emulsifier preferably contains a first emulsifier having an HLB (hydrophile-lipophile balance) value of 6 or less and a second emulsifier having an HLB value of 10 to 16. The first emulsifier is mainly contained in the oil phase. The second emulsifier is mainly contained in the water phase. By using the first emulsifier and the second emulsifier in combination, the emulsion stability of the oil-in-water emulsion and the physical properties during foaming are more excellent. The HLB value of the first emulsifier is preferably 1 to 6. The HLB value of the second emulsifier is preferably 10 to 16. In this specification, the HLB value is a value determined by the Griffin method.

[0023] As the first emulsifier, for example, among the emulsifiers mentioned above, those having an HLB value of 6 or less can be appropriately selected. The first emulsifier preferably contains at least one selected from the group consisting of lecithin and sucrose fatty acid ester having an HLB value of 6 or less because it is easily demulsified when foaming the oil-in-water emulsion. Examples of sucrose fatty acid ester having an HLB value of 6 or less include Ryoto Sugar Ester P-170 (Mitsubishi Chemical Foods). The content of at least one emulsifier selected from the group consisting of lecithin and sucrose fatty acid ester having an HLB value of 6 or less is preferably 20 to 100% by mass, more preferably 50 to 100% by mass, based on the total mass of the first emulsifier.

[0024] At least one selected from the group consisting of lecithin and sucrose fatty acid esters having an HLB value of 6 or less may be used in combination with another emulsifier having an HLB value of 6 or less. As the other emulsifier having an HLB value of 6 or less, polyglycerol fatty acid esters having an HLB value of 6 or less are preferable. The HLB value of polyglycerol fatty acid esters can be adjusted widely depending on the constituent fatty acids, degree of polymerization, etc.

[0025] As the second emulsifier, for example, those having an HLB value of 10 to 16 can be appropriately selected from the emulsifiers mentioned above. The second emulsifier preferably contains polyglycerol fatty acid esters having an HLB value of 10 to 16 because of their better solubility in water. The content of polyglycerol fatty acid esters having an HLB value of 10 to 16 is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, based on the total mass of the second emulsifier.

[0026] Polyglycerol fatty acid esters having an HLB value of 10 to 16 may be used in combination with other emulsifiers having an HLB value of 10 to 16. As the other emulsifier having an HLB value of 10 to 16, sucrose fatty acid esters having an HLB value of 10 to 16 are preferable because they are easily demulsified when foaming an oil-in-water emulsion.

[0027] Examples of the stabilizer include gums such as xanthan gum and carrageenan; proteins such as casein, soy protein, and gelatin; and polysaccharides such as starch, modified starch, sodium alginate, and carboxymethyl cellulose. Examples of the salts include phosphates such as monophosphate and condensed phosphate.

[0028] Examples of the other components include chelating agents (such as trisodium citrate), pH adjusters, milk components, egg components, saccharides (such as lactose, fructose, glucose, and sucrose), dietary fiber, cellulose, flavors, and coloring agents.

[0029] It is also possible to further combine the present invention with the above-mentioned prior art. For example, in the present invention, an acid resistance-imparting agent is not necessarily required, but it is not excluded that an acid resistance-imparting agent is further included. As the acid resistance-imparting agent in this case, known ones can be used, for example, fermented cellulose (Patent Document 4: JP-A-2015-57948) can be mentioned. Even if an acid resistance-imparting agent is blended, in terms of flavor, the content of the acid resistance-imparting agent is preferably 3% by mass or less with respect to the total mass of the finally obtained second oil-in-water emulsion. The content of the acid resistance-imparting agent is particularly preferably 0% by mass with respect to the total mass of the second oil-in-water emulsion. Also, regarding other conventional techniques, for example, a method of devising the blending of an emulsifier (Patent Document 2), a method of devising the type of protein (Patent Document 3), in the present invention, it is not necessary to be restricted to a specific emulsifier in order to obtain acid resistance, and it is not necessary to add a milk protein hydrolyzate for the purpose of acid resistance, but it is not excluded to combine these conventional techniques with the present invention. As described above, even if it is assumed that a conventional technique is combined with the present invention, there is an advantage that the degree of performing the conventional technique can be suppressed to be small compared to the case of performing such a conventional technique alone.

[0030] In the first oil-in-water emulsion, the oil and fat content is preferably 20 to 70% by mass, more preferably 40 to 60% by mass with respect to the total mass of the first oil-in-water emulsion. When the oil and fat content is at least the lower limit value of the above range, it is easy to make the oil and fat content of the finally obtained second oil-in-water emulsion within the preferable range described later.

[0031] The water content is preferably 20 to 70% by mass, more preferably 30 to 50% by mass with respect to the total mass of the first oil-in-water emulsion. When the water content is at least the lower limit value of the above range, the emulsifying property is more excellent, and when it is at most the upper limit value of the above range, the foaming property of the second oil-in-water emulsion is more excellent.

[0032] The protein content is less than 1.4% by mass, preferably 0.8% by mass or less, more preferably 0.4% by mass or less, and particularly preferably 0% by mass, based on the total mass of the first oil-in-water emulsion. That is, it is particularly preferable that the first oil-in-water emulsion does not contain protein. When the protein content is at or below the above upper limit value, the oil-in-water emulsion of the present invention is excellent in acid resistance, and the foamability of the acidified oil-in-water emulsion obtained by acidifying the oil-in-water emulsion of the present invention and the shape retention of the foam-containing acidified oil-in-water emulsion are excellent.

[0033] In the first oil-in-water emulsion, the ratio of protein to oil and fat (100% by mass) is preferably less than 2.82% by mass, more preferably 2.0% by mass or less, still more preferably 1.6% by mass or less, even more preferably 1.0% by mass or less, particularly preferably 0.8% by mass or less, and most preferably 0% by mass. When the ratio of protein to oil and fat is at or below the above upper limit value, the acid resistance of the oil-in-water emulsion of the present invention is more excellent, and the foamability of the acidified oil-in-water emulsion and the shape retention of the foam-containing acidified oil-in-water emulsion are more excellent.

[0034] The content of the emulsifier is preferably 0.3 to 1.5% by mass, more preferably 0.5 to 1.0% by mass, based on the total mass of the first oil-in-water emulsion. When the content of the emulsifier is at or above the lower limit value of the above range, the smoothness and shape retention of the foam-containing acidified oil-in-water emulsion are more excellent, and when it is at or below the upper limit value of the above range, the shape retention and flavor of the foam-containing acidified oil-in-water emulsion are more excellent.

[0035] When the emulsifier contains a first emulsifier and a second emulsifier, the content of the first emulsifier is preferably 30 to 70% by mass and the content of the second emulsifier is preferably 30 to 70% by mass, based on the total mass of the first emulsifier and the second emulsifier. More preferably, the content of the first emulsifier is 40 to 60% by mass and the content of the second emulsifier is 40 to 60% by mass.

[0036] The pH of the first oil-in-water emulsion is preferably from 6.0 to 8.0, more preferably from 6.5 to 7.5. When the pH is at least the lower limit of the above range, the stability of the liquid state is more excellent, and when it is at most the upper limit of the range, the flavor and foaming property are more excellent.

[0037] The viscosity of the first oil-in-water emulsion at 10 °C is preferably from 20 to 1000 mPa·s, more preferably from 30 to 500 mPa·s. When the viscosity of the first oil-in-water emulsion is within the above range, it is easy to make the viscosity of the second oil-in-water emulsion at 10 °C within the preferred range described below.

[0038] <Protein-containing raw material> The protein-containing raw material contains protein. The protein-containing raw material may contain components other than protein. Examples of the components other than protein include the other components described above and water. The other components used in the mixing step are preferably water-soluble components. The protein-containing raw material may be liquid or solid (particulate, powdery, etc.), but is preferably liquid from the viewpoint of being easily mixed with the homogenized first oil-in-water emulsion. Examples of the liquid protein-containing raw material include skim concentrated milk, whole milk concentrated milk, skim milk powder solution, whole milk powder solution, etc. These liquid protein-containing raw materials may be blended with other components. In addition, since it is preferable that the protein-containing raw material is not homogenized after the mixing step, the lower the oil content, the more preferable. The oil content in the protein-containing raw material is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, still more preferably substantially 0% by mass, and particularly preferably 0% by mass with respect to the total mass of the protein-containing raw material. Note that "substantially 0% by mass" means a trace amount such that fat floating does not occur during storage of the finally obtained oil-in-water emulsion of the present invention even without homogenizing the protein-containing raw material or the second oil-in-water emulsion.

[0039] <Second oil-in-water emulsion> The second oil-in-water emulsion is obtained by mixing the first oil-in-water emulsion and a protein-containing raw material, and contains at least oil and fat, water, and protein. The second oil-in-water emulsion may further contain an emulsifier. The second oil-in-water emulsion may further contain other components. It is desirable that the content of each of the oil and fat, water, protein, emulsifier, and other components with respect to the total mass of the second oil-in-water emulsion is equal to the content of each of the oil and fat, water, protein, emulsifier, and other components with respect to the total mass of the first oil-in-water emulsion and the protein-containing raw material. However, it does not exclude mixing other components together when mixing the first oil-in-water emulsion and the protein-containing raw material.

[0040] The content of the oil and fat is preferably 20 to 60% by mass, more preferably 30 to 50% by mass, with respect to the total mass of the second oil-in-water emulsion. When the content of the oil and fat is at least the lower limit value of the above range, a good texture and flavor are easily obtained when foamed, and when it is at most the upper limit value of the above range, the flavor when foamed is more excellent.

[0041] The content of water is preferably 30 to 70% by mass, more preferably 40 to 60% by mass, with respect to the total mass of the second oil-in-water emulsion. When the content of water is at least the lower limit value of the above range, the flavor and smoothness when foamed are more excellent, and when it is at most the upper limit value of the above range, the flavor when foamed is more excellent.

[0042] The content of protein is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 3.0% by mass, with respect to the total mass of the second oil-in-water emulsion. When the content of protein is at least the lower limit value, the emulsification stability before foaming is more excellent, and when it is at most the upper limit value, the acid resistance of the second oil-in-water emulsion is more excellent.

[0043] The content of the emulsifier is preferably 0.1 to 2.0% by mass, more preferably 0.3 to 1.5% by mass, based on the total mass of the second oil-in-water emulsion. When the content of the emulsifier is equal to or higher than the lower limit of the above range, the emulsification stability before foaming is more excellent, and when it is equal to or lower than the upper limit of the above range, the flavor when foamed is more excellent.

[0044] When the emulsifier contains the first emulsifier and the second emulsifier, the content of the first emulsifier is preferably 30 to 70% by mass, and the content of the second emulsifier is preferably 30 to 70% by mass, based on the total mass of the first emulsifier and the second emulsifier. More preferably, the content of the first emulsifier is 40 to 60% by mass, and the content of the second emulsifier is 40 to 60% by mass.

[0045] <Oil-in-water emulsion of the present invention> The oil-in-water emulsion of the present invention contains at least oil, water, and protein, similar to the second oil-in-water emulsion. The second oil-in-water emulsion may further contain an emulsifier. The second oil-in-water emulsion may further contain other components. It is desirable that the content of each of oil, water, protein, emulsifier, and other components with respect to the total mass of the oil-in-water emulsion of the present invention is equal to the content of each of oil, water, protein, emulsifier, and other components with respect to the total mass of the second oil-in-water emulsion.

[0046] The oil-in-water emulsion of the present invention typically has foamability. For example, when the oil-in-water emulsion of the present invention is foamed at 6 to 10°C, a foamed product with an overrun of 80 to 180% can be obtained. The overrun is preferably 100 to 160%, more preferably 120 to 150%. The overrun is determined by the method described in the examples below.

[0047] The oil-in-water emulsion of the present invention may be a liquid cream. "Liquid cream" means a cream that is not substantially foamed, in other words, a cream that has not undergone an artificial foaming operation. "Cream" is an emulsion prepared using raw materials containing fat, and includes both cream defined by the Milk Products Ordinance (Ordinance Concerning Standards for Components of Milk and Milk Products, hereinafter also referred to as "raw cream"), and cream classified as a "food product mainly made from milk or milk products" as defined by the Milk Products Ordinance (hereinafter also referred to as "milk-based raw cream"). Raw cream is "raw milk, cow's milk, or that from which components other than milk fat have been removed". Milk-based raw cream contains components other than milk fat (such as vegetable oils, proteins, various additives (emulsifiers, stabilizers, flavors, etc.)), and is classified into a pure milk fat type (pure milk fat cream) containing only milk fat as the fat component, a mixed type (so-called compound cream) containing milk fat and vegetable oil as the fat component, and a pure vegetable oil type (so-called non-dairy cream) containing only vegetable oil as the fat component. The oil-in-water emulsion of the present invention can be applied to various oil-in-water emulsions, but in order to maximize the effects of the present invention, it can be said that an unfermented oil-in-water emulsion is more suitable. Also, among oil-in-water emulsions having foamability, those that do not contain components for solidifying bubbles such as gelatin or egg white are preferred. From such a perspective, it can be said that whipped cream is particularly preferred over sour cream, mousse cream, and baba au rhum cream.

[0048] The pH of the oil-in-water emulsion of the present invention is preferably 6.0 to 8.0, more preferably 6.5 to 7.5. When the pH of the oil-in-water emulsion of the present invention is at or above the lower limit value of the above range, the emulsification stability before foaming is more excellent, and when it is at or below the upper limit value of the above range, the flavor when foamed is more excellent.

[0049] The viscosity of the oil-in-water emulsion of the present invention at 10°C varies depending on the pH. For example, when the pH is 6.5 to 7.5, it is preferably 1 to 1000 mPa·s, more preferably 50 to 700 mPa·s, and even more preferably 100 to 500 mPa·s. When the viscosity of the oil-in-water emulsion of the present invention is at or above the lower limit value of the above range, the texture and flavor after foaming are more excellent, and when it is at or below the upper limit value of the above range, the foamability and flavor are more excellent.

[0050] Moreover, for the oil-in-water emulsion of the present invention, when the pH is adjusted from 6.5 - 7.5 to around 4.5, the viscosity is less than 5810 mPa·s, further less than 5394 mPa·s, further less than 5000 mPa·s, further 4660 mPa·s or less, further less than 4498 mPa·s, further less than 4049 mPa·s, further 4000 mPa·s or less, further 3390 mPa·s or less, further less than 3153 mPa·s, further 2000 mPa·s or less, and further 1400 mPa·s or less. Around pH 4.5 is typically from pH 4.45 to 4.60. For the oil-in-water emulsion of the present invention, the viscosity within this range is approximately the same. Since the isoelectric point of casein is around pH 4.5, the viscosity of the oil-in-water emulsion of the present invention tends to be highest around pH 4.5. The lower the viscosity at pH 4.5, the better the acid resistance. Also, if the viscosity at pH 4.5 is below the above upper limit value, sufficient foaming can be achieved. In particular, if the viscosity is 4000 mPa·s or less, the overrun is also good, and if it is 2000 mPa·s or less, it is even better. When the pH of the oil-in-water emulsion of the present invention is adjusted from 6.5 - 7.5 to around 4.5, the viscosity is preferably 50 mPa·s or more, and more preferably 100 mPa·s or more in terms of the flavor when foamed.

[0051] <Advantages and effects> In the embodiment described above, the protein content of the oil-in-water emulsion (the first oil-in-water emulsion) to be homogenized is less than 1.4% by mass, and after homogenization, a protein-containing raw material is mixed, and the obtained second oil-in-water emulsion is not homogenized as much as possible. Thus, an oil-in-water emulsion (the oil-in-water emulsion of the present invention) that contains protein and has excellent acid resistance can be obtained. The acidified oil-in-water emulsion obtained by adding an acidic material to the oil-in-water emulsion of the present invention can be foamed well, and the foam-containing acidified oil-in-water emulsion obtained by foaming the acidified oil-in-water emulsion has excellent shape retention. The reason for the excellent acid resistance is not clear, but the following can be considered as a hypothesis. That is, conventionally, when producing an oil-in-water emulsion containing a protein, generally, the oil-in-water emulsion to be homogenized contained 1.4% by mass or more of the protein. When such an oil-in-water emulsion was homogenized, many proteins adhered to the surface of the emulsified film of the pulverized oil droplets. For this reason, when the pH decreased, it was considered that the oil droplets aggregated due to the aggregation of the proteins and easily thickened. In contrast, in this production method, since the first oil-in-water emulsion to be homogenized does not contain a protein or contains only a trace amount of it, when this is homogenized, no protein adheres to the surface of the emulsified film of the oil droplets, or only a trace amount adheres. Then, after mixing a protein-containing raw material with such a first oil-in-water emulsion to form a second oil-in-water emulsion, homogenization is not performed as much as possible. For this reason, also in the oil-in-water emulsion of the present invention, the state of the oil droplets of the first oil-in-water emulsion is maintained as it is. As a result of the above, the oil-in-water emulsion of the present invention is less likely to cause protein aggregation and less likely to thicken even when the pH decreases, so it is considered that good foaming properties can be obtained, the hardness after foaming is less likely to decrease, and the shape retention property is excellent. Note that the above is only a hypothesis added for the sake of explanation for the purpose of easily understanding the technical content of the present invention.

[0052] Thus, since the oil-in-water emulsion of the present invention is excellent in acid resistance, it can be foamed even when an acidic substance such as fruit juice or fruit is added to make it acidic. In addition, since it can be foamed in both the neutral range and the acidic range, it can be used for various applications. Further, conventionally, since components that are not originally necessary were blended to impart acid resistance, there were problems such as changes in taste and flavor and low degrees of freedom in product design. In contrast, in this production method, it is not necessary to blend components that are not originally necessary, so the taste and flavor do not change, and the degree of freedom in product design is also high.

[0053] Note that this production method is not limited to the above-described embodiments. Each configuration and their combinations in the above-described embodiments are examples, and additions, omissions, substitutions, and other changes of the configuration are possible without departing from the gist of the present invention. For example, an existing first water-in-oil emulsion may be used. In this case, the pre-emulsification step may not be performed. An example was shown in which homogenization, sterilization, and cooling of the first water-in-oil emulsion were performed using a homogenizer-integrated UHT sterilizer. However, as a homogenizer-integrated UHT sterilizer, there are also models that perform homogenization at a stage after sterilization and before cooling, and such models may be adopted. Homogenization and sterilization may be performed using different apparatuses without using a homogenizer-integrated UHT sterilizer. Homogenization can be performed using a known homogenizer. Sterilization can be performed using a known sterilization apparatus. When performing sterilization or aging, the timing thereof and the timing of mixing the first water-in-oil emulsion and the protein-containing raw material are not limited to the above-described embodiments.

[0054] Figures 2 to 5 are respectively flowcharts showing other embodiments of the present manufacturing method. In the embodiment shown in FIG. 1, aging is performed after mixing a protein-containing raw material with the homogenized first water-in-oil emulsion to obtain a second water-in-oil emulsion. However, in the embodiment shown in FIG. 2, the protein-containing raw material is mixed while the homogenized first water-in-oil emulsion is being aged, and aging is further continued. Specifically, while the homogenized first water-in-oil emulsion is stored in an aging tank and maintained at a low temperature, the protein-containing raw material is added and mixed in the aging tank. Generally, the aging tank is provided with stirring blades that stir at a low speed, and the mixing step is performed using these stirring blades. Then, the aging of the obtained second water-in-oil emulsion is continued as it is. In the embodiment shown in FIG. 3, after aging the homogenized first water-in-oil emulsion, a protein-containing raw material is mixed. In the embodiment shown in FIG. 4, sterilization is performed after the mixing step. That is, a protein-containing raw material is mixed with the homogenized first water-in-oil emulsion to obtain a second water-in-oil emulsion, and then sterilized. In this case, it is not necessary to sterilize the protein-containing raw material in advance. Then, the second water-in-oil emulsion after sterilization and cooling is aged. Even in this case, after the mixing step, the second water-in-oil emulsion is not homogenized. In the embodiment shown in FIG. 5, the homogenized first water-in-oil emulsion is pre-cooled after heat sterilization to lower the temperature, and then mixed with the protein-containing raw material whose temperature has also been lowered after sterilization. The second water-in-oil emulsion obtained by mixing is then subjected to full cooling and aging. As described above, the mode of mixing the protein-containing raw material with the homogenized first water-in-oil emulsion can take various modes. In addition, as described above, in the first water-in-oil emulsion, the protein content is reduced to less than 1.4% by mass. However, a protein-containing raw material is mixed with the first water-in-oil emulsion, and as a result, the protein content of the final second water-in-oil emulsion becomes higher than that of the first water-in-oil emulsion.

[0055] 〔Water-in-oil emulsion〕 The water-in-oil emulsion according to one aspect of the present invention (hereinafter, also referred to as "this emulsion") contains oil and fat, water, and protein. This emulsion may further contain an emulsifier. This emulsion may further contain other components other than the above.

[0056] The oil and fat, protein, emulsifier, and other components are the same as those described above, and the preferred embodiments are also the same.

[0057] The content of the oil and fat is preferably 20 to 60% by mass, more preferably 30 to 50% by mass, based on the total mass of this emulsion. When the content of the oil and fat is equal to or higher than the lower limit value of the above range, a good texture and flavor are easily obtained when foamed, and when it is equal to or lower than the upper limit value of the above range, the flavor when foamed is more excellent.

[0058] The water content is preferably 30 to 70% by mass, more preferably 40 to 60% by mass, based on the total mass of the present emulsion. When the water content is at least the lower limit of the above range, the flavor and smoothness when foamed are more excellent, and when it is at most the upper limit of the range, the flavor when foamed is more excellent.

[0059] The protein content is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 3.0% by mass, based on the total mass of the present emulsion. When the protein content is at least the lower limit, the emulsification stability before foaming is more excellent, and when it is at most the upper limit, the acid resistance of the present emulsion is more excellent.

[0060] The emulsifier content is preferably 0.1 to 2.0% by mass, more preferably 0.3 to 1.5% by mass, based on the total mass of the present emulsion. When the emulsifier content is at least the lower limit of the above range, the emulsification stability before foaming is more excellent, and when it is at most the upper limit of the range, the flavor when foamed is more excellent.

[0061] When the emulsifier contains a first emulsifier and a second emulsifier, the content of the first emulsifier is preferably 30 to 70% by mass and the content of the second emulsifier is preferably 30 to 70% by mass, based on the total mass of the first emulsifier and the second emulsifier, and more preferably the content of the first emulsifier is 40 to 60% by mass and the content of the second emulsifier is 40 to 60% by mass.

[0062] The present emulsion typically has foamability. For example, when the present emulsion is foamed at 6 to 10°C, a foamed product with an overrun of 80 to 180% can be obtained. The overrun is preferably 100 to 160%, more preferably 120 to 150%. The overrun is determined by the method described in the examples below.

[0063] The present emulsion may be a liquid cream. The present invention can be applied to various emulsions. However, in order to maximize the effects of the present invention, it can be said that unfermented emulsions are more suitable. Further, as the foaming emulsion, those that do not contain components for solidifying bubbles, such as gelatin and egg white, are preferred. From this perspective, whipped cream is particularly preferred over sour cream, mousse cream, and babaroa cream.

[0064] The pH of the present emulsion is 6.0 to 8.0, preferably 6.5 to 7.5. When the pH is equal to or higher than the lower limit value of the above range, the emulsion stability before foaming is excellent, and when it is equal to or lower than the upper limit value of the range, the flavor when foamed is excellent.

[0065] The viscosity of the present emulsion at 10 °C is 1 to 1000 mPa·s, preferably 50 to 700 mPa·s, and more preferably 100 to 500 mPa·s. When the viscosity of the present emulsion is equal to or higher than the lower limit value of the above range, the texture and flavor when foamed are excellent, and when it is equal to or lower than the upper limit value of the range, the foaming property and flavor are excellent.

[0066] Further, when the pH of the present emulsion is changed from 6.5 to 7.5 to around 4.5, the viscosity is less than 5810 mPa·s, further less than 5394 mPa·s, further less than 5000 mPa·s, further 4660 mPa·s or less, further less than 4498 mPa·s, further less than 4049 mPa·s, further 4000 mPa·s or less, further 3390 mPa·s or less, further less than 3153 mPa·s, further 2000 mPa·s or less, and further 1400 mPa·s or less. Around pH 4.5 is typically from pH 4.45 to 4.60. The viscosity of the present emulsion is substantially the same within this range. Since the isoelectric point of casein is around pH 4.5, the viscosity of the present emulsion tends to be the highest around pH 4.5. The lower the viscosity at pH 4.5, the better the acid resistance. Also, if the viscosity around pH 4.5 is equal to or lower than the above upper limit value, sufficient foaming can be achieved. In particular, when the viscosity is 4000 mPa·s or less, the overrun is also good, and when it is 2000 mPa·s or less, it becomes even better. When the pH of the present emulsion is adjusted from 6.5 - 7.5 to around 4.5, the viscosity is preferably 50 mPa·s or more, more preferably 100 mPa·s or more, in terms of the flavor when foamed.

[0067] The present emulsion has a protein precipitation amount measured by the following measurement method exceeding 0% by volume. Measurement method of protein precipitation amount: 50 mL of a sample (oil-in-water emulsion) is placed in a graduated centrifuge tube, and after centrifugation using a centrifuge under the conditions of a relative centrifugal acceleration of 1630×g for 5 minutes, the volume (mL) of the protein precipitated in the centrifuge tube is visually measured, and the ratio (volume %) of the volume of the protein to the total volume of the oil-in-water emulsion is defined as the protein precipitation amount. The protein precipitation amount is an index of the amount of protein present in a free state in the continuous phase (aqueous phase) of the present emulsion. The fact that the protein precipitation amount exceeds 0% by volume indicates excellent acid resistance. The protein precipitation amount of the present emulsion is preferably 0.1% by volume or more. The upper limit of the protein precipitation amount is not particularly limited, but is, for example, 2.0% by volume.

[0068] The present emulsion can be produced, for example, by the above-described production method. Conventionally, in the production of an oil-in-water emulsion containing protein, usually, after mixing an aqueous phase portion containing protein and an oil phase portion, homogenization is carried out. The oil-in-water emulsion thus obtained is presumed to be in a state where oil droplets are dispersed as a dispersed phase in the aqueous phase, which is the continuous phase, and the protein in the aqueous phase portion firmly adheres covering the surface of the oil droplets due to homogenization. For this reason, it is considered that the amount of protein present in the continuous phase in the oil-in-water emulsion produced by the conventional method is small. On the other hand, in the above-described production method of the present invention, since the protein content of the first oil-in-water emulsion is reduced compared to the conventional method, even after homogenizing the first oil-in-water emulsion, the amount of protein adhering to the surface of the oil droplets is small. Then, since a protein-containing raw material is mixed thereafter and homogenization is not carried out as much as possible, it is considered that the amount of protein present in the continuous phase is large. However, the method for producing the present emulsion is not limited thereto.

[0069] The oil-in-water emulsion produced by the present production method or the present emulsion may be filled and sealed in a packaging container to form a package and then stored or distributed. The packaging container is not particularly limited as long as it does not leak liquid, and examples thereof include paper containers, plastic containers, retort containers, and the like. The oil-in-water emulsion filled in the packaging container is opened and used at the time of use (for example, at the time of foaming).

[0070] The oil-in-water emulsion produced by the present production method or the present emulsion can be used for applications such as whipping and cooking. The oil-in-water emulsion produced by the present production method or the present emulsion is particularly useful for whipping.

[0071] In the whipping application, the oil-in-water emulsion or the present emulsion obtained by the present production method is foamed to form a bubble-containing oil-in-water emulsion (such as whipped cream). Here, "foaming" is not particularly limited, but it is to make the oil-in-water emulsion contain bubbles by applying physical stress such as stirring or contacting with air. At this time, it is desirable to carry out at 6 to 9 o'clock standing. Before foaming, a saccharide may be blended into the oil-in-water emulsion or the present emulsion obtained by the present production method. The blending amount of the saccharide is preferably 0 to 10% by mass based on the total mass of the oil-in-water emulsion or the present emulsion obtained by the present production method. When the blending amount of the saccharide is below the above upper limit value, the flavor of the obtained bubble-containing oil-in-water emulsion is good.

[0072] The obtained bubble-containing oil-in-water emulsion may be frozen as it is to form a frozen bubble-containing oil-in-water emulsion. The obtained bubble-containing oil-in-water emulsion may be made into a package of the frozen bubble-containing oil-in-water emulsion. For example, if the obtained bubble-containing oil-in-water emulsion is filled into a container as it is and preferably sealed, a package of the bubble-containing oil-in-water emulsion can be obtained. Before freezing, the oil-in-water emulsion containing bubbles may be filled and sealed in a packaging container for storage or distribution, and after freezing, the frozen oil-in-water emulsion containing bubbles may also be filled and sealed in a packaging container for storage or distribution.

[0073] The oil-in-water emulsion obtained by this production method or this emulsion is imparted with excellent acid resistance. Therefore, even if the oil-in-water emulsion is in an acidic state, it can be foamed to form an oil-in-water emulsion containing bubbles. Therefore, an acidic material can be added to the oil-in-water emulsion obtained by this production method or this emulsion, and the pH can be adjusted to acidic to form an acidic oil-in-water emulsion. Further, this acidic oil-in-water emulsion can be foamed to form an acidic oil-in-water emulsion containing bubbles. The pH of the acidic oil-in-water emulsion is preferably 2.0 to 6.5, more preferably 3.0 to 5.5, in terms of the texture at the time of foaming.

[0074] In addition, the oil-in-water emulsion containing bubbles obtained by foaming the oil-in-water emulsion obtained by this production method or this emulsion has excellent acid resistance. Therefore, an acidic material can be added to the oil-in-water emulsion containing bubbles, and the pH can be adjusted to acidic to form an acidic oil-in-water emulsion containing bubbles. The pH of the acidic oil-in-water emulsion containing bubbles is preferably 2.0 to 6.5, more preferably 3.0 to 5.5, in terms of texture.

[0075] Examples of the acidic material include acidic compounds that can be used in food, crushed products, pulverized products, fragments, juices, etc. of acidic foods. Examples of the acidic compound include organic acids such as citric acid, lactic acid, acetic acid, oxalic acid, glucuronic acid, carbonic acid; inorganic acids such as phosphoric acid.

[0076] Examples of the acidic food include processed products of sour fruits and / or vegetables. Examples of the processed products of acidic foods include sour fruit juices and fruit pulps; sour vegetable juices and vegetable pieces. In addition, examples of the processing of acidic foods include purees, pastes, sauces, jams, juices, etc., and these may be used alone or in appropriate combinations. Generally, "purée" refers to crushed and sieved fruits and / or vegetables, which can be used in their raw state or after heating. Also, "paste" generally refers to a state that is thicker than purée. Examples of "fruit sauce" include those obtained by adding thickeners such as starch to fruit purée or those using jam. Examples of fruit juices and fruit pieces include citrus fruits such as lemon, orange, sudachi, and daidai; strawberries, raspberries, grapes, pineapples, blueberries, kiwifruits, apples, etc. Examples of vegetable juices and vegetable pieces include tomatoes, etc.

[0077] As acidic foods, processed products of acidic fruits and / or vegetables are preferred. As processed products of acidic fruits and / or vegetables, one or more selected from crushed products, squeezed products, juices, purées, and sauces are preferred. The addition amount of the acidic food is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 10 - 100 parts by mass with respect to 100 parts by mass of the oil-in-water emulsion or the oil-in-water emulsion containing bubbles. Note that the oil-in-water emulsion obtained by this production method or this emulsion can be used not only for acidic compounds and acidic foods but also for a wide range of foods and the like.

[0078] Conventionally, when producing an oil-in-water emulsion containing bubbles with acidic foods, generally, production methods called "separate" and "simultaneous" are used. Also, when producing an oil-in-water emulsion containing bubbles, other components such as gelatin may be blended. "Simultaneous" is a production method of an oil-in-water emulsion containing bubbles that includes a step of mixing an acidic food and an oil-in-water emulsion and whipping them to obtain an oil-in-water emulsion containing bubbles with acidic foods. "Separate" is a production method of an oil-in-water emulsion containing bubbles with acidic foods that includes a step of foaming an oil-in-water emulsion to obtain an oil-in-water emulsion containing bubbles and a step of mixing the obtained oil-in-water emulsion containing bubbles with an acidic food to obtain an oil-in-water emulsion containing bubbles with acidic foods. Conventionally, when a general water-in-oil emulsion (e.g., fresh cream) and an acidic food are mixed together and whipped, the texture of the resulting bubble-containing water-in-oil emulsion is loose due to the influence of the acidic food. For this reason, the bubble-containing water-in-oil emulsion obtained by "simultaneous whipping" has poor texture and flavor. Therefore, in small-scale production at stores and the like, "separate whipping" was usually used to improve the texture and flavor. However, this "separate whipping" requires at least two steps and has poor working efficiency. Therefore, in the case of mass production, a method of manufacturing a bubble-containing water-in-oil emulsion containing an acidic food by "simultaneous whipping" by adding conventional stabilizers and the like has been adopted. However, the bubble-containing water-in-oil emulsion obtained by this "simultaneous whipping" tends to be difficult to improve in texture and flavor due to the influence of conventional stabilizers and the like. Since the water-in-oil emulsion or this emulsion obtained by this production method is excellent in acid resistance, a bubble-containing water-in-oil emulsion containing an acidic food with good texture and flavor can be manufactured by "simultaneous whipping" without adding conventional stabilizers and the like.

[0079] The obtained bubble-containing acidic water-in-oil emulsion may be frozen to obtain a frozen bubble-containing acidic water-in-oil emulsion. Before freezing, the bubble-containing acidic water-in-oil emulsion may be filled and sealed in a packaging container for storage or distribution, or after freezing, the frozen bubble-containing acidic water-in-oil emulsion may be filled and sealed in a packaging container for storage or distribution. The frozen bubble-containing acidic water-in-oil emulsion is thawed at the time of use and used as a bubble-containing acidic water-in-oil emulsion.

[0080] The obtained oil-in-water emulsion containing bubbles or oil-in-water emulsion containing bubbles in acidic water can be used, for example, as whipped cream; whipped cream containing acidic foods; whipped cream for decoration such as cakes, pancakes, confectioneries, jellies, puddings, ice confectioneries, frozen dairy products, etc.; whipped cream for wieners, coffee, juices, beverages, etc. Examples of whipped cream containing acidic foods include whipped cream containing processed products of sour fruits and / or vegetables. For example, whipped cream containing fruit and / or vegetable puree, whipped cream containing fruit and / or vegetable juice (e.g., whipped cream containing citrus juice, etc.) can be mentioned.

[0081] Examples of foods using an oil-in-water emulsion or an oil-in-water emulsion in acidic water, or an oil-in-water emulsion containing bubbles or an oil-in-water emulsion containing bubbles in acidic water include roll cakes and tarts with lemon-flavored whipped cream that gives a more fruity feeling, shortcakes and decorated cakes using mandarin-flavored whipped cream, jellies and puddings with strawberry-flavored whipped cream on top, sandwiches with whipped cream flavored with other fruit juices, cream puffs and breads with fillings wrapped with cream or filling containing fruit juice.

Examples

[0082] The present invention will be described in more detail below using examples. However, the present invention is not limited to these examples. In the following description, "%" indicates "mass%" in all cases except for the % of overrun when not otherwise specified. "Parts" indicates "parts by mass". The creams of Examples 1 to 8 correspond to the oil-in-water emulsions of the present invention.

[0083] <Test Example 1> (Manufacture of Cream) In this test example, five creams were produced as oil-in-water emulsions according to Table 1. The overall composition of these creams is the same. The overall composition of each cream is shown in Table 2. The procedure for producing each cream is generally as follows. That is, first, the aqueous phase and the oil phase are prepared separately, and these are preliminarily mixed to form a first oil-in-water emulsion. Separately, a protein-containing raw material is prepared. The first oil-in-water emulsion and the protein-containing raw material are mixed to form a second oil-in-water emulsion. Then, the second oil-in-water emulsion is aged to obtain the creams of Examples 1 to 3 and Comparative Examples 1 to 2. This test example was conducted to evaluate the effect of the protein concentration of the first oil-in-water emulsion on the acid resistance of the finally obtained cream (oil-in-water emulsion).

[0084] The details of the procedure for producing the cream of each example are shown below. In Examples 1 to 3 and Comparative Example 1, first, according to the composition of the aqueous phase in Table 1, an emulsifier and skim milk powder were dissolved in water while stirring to prepare the aqueous phase. The emulsifiers in the aqueous phase were the following two kinds of emulsifiers A and B, which were used at a mass ratio of emulsifier A:emulsifier B = 2:1. Emulsifiers A and B differ in the fatty acids that make up the polyglycerol fatty acid ester. Emulsifier A: Polyglycerol fatty acid ester (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., HLB about 12). Emulsifier B: Polyglycerol fatty acid ester (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., HLB about 12). Also, according to the composition of the oil phase in Table 1, an emulsifier and soy lecithin were dissolved in vegetable oil to prepare the oil phase. The emulsifier in the oil phase used was polyglycerol fatty acid ester (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., HLB about 5). The vegetable oil used was palm kernel oil. Next, the aqueous phase was heated to 70°C while stirring, and the oil phase, which was also heated to 70°C, was added thereto and preliminarily mixed to prepare a synthesis part. This synthesis part was preliminarily emulsified by stirring at 7000 rpm for 3 minutes using a homomixer to obtain a first oil-in-water emulsion. The protein content of the first oil-in-water emulsion is shown in Table 1. Next, the above first water-in-oil emulsion was passed through a homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd.), preheated to 70°C, and then homogenized under a pressure of 9.0 MPa. Thereafter, after subjecting it to heating sterilization at 80°C until the temperature was reached, it was cooled to 5°C and stored in an aging tank. Next, according to the composition of the protein-containing raw material in Table 1, skim milk powder, modified starch, and trisodium citrate were dissolved in water to prepare a protein-containing raw material. This protein-containing raw material was batch sterilized until the temperature reached 80°C, then cooled to about 5°C, and added to an aging tank for storing the homogenized first water-in-oil emulsion. The first water-in-oil emulsion and the protein-containing raw material were mixed with a stirring blade in the aging tank to obtain a second water-in-oil emulsion. This second water-in-oil emulsion was further aged in a refrigerator at 5°C for 24 hours. Thereby, cream having an oil content of 35% and a protein content of 2.87% was obtained. In Comparative Example 2, all the components blended in the protein-containing raw material were blended in the aqueous phase portion, and cream having an oil content of 35%, a protein content of 2.87%, and a pH of 7.0 was obtained in the same manner as in Example 3 except that the protein-containing raw material was not added to the homogenized first water-in-oil emulsion. Note that the oil content and the protein content are values calculated from the formulation. The pH was measured using a pH meter (manufactured by HORIBA).

[0085]

Table 1

[0086]

Table 2

[0087] Regarding the obtained cream (hereinafter, also referred to as "neutral cream"), the following acid resistance test 1, foaming property test, acid resistance test 2, and measurement of the amount of protein precipitation were carried out.

[0088] (Acid resistance test 1) To 200 g of the neutral cream, 1.0 mL of a 10% citric acid solution was added each time, and the pH and viscosity were measured. The method for measuring the pH was as described above. The method for measuring the viscosity is shown below.

[0089] "Viscosity" The viscosity was measured using a B-type viscometer (manufactured by TOKI) under the conditions of 30 seconds and 60 rpm. The upper limit value for viscosity measurement was set at 10,000 mPa·s.

[0090] Figure 6 shows the measurement results (horizontal axis: pH, vertical axis: viscosity). Table 3 shows the measurement results of the viscosity of the cream before adding the citric acid solution and the cream with a pH near 4.5 (the isoelectric point of casein) after adding the citric acid solution (hereinafter also referred to as "acidic cream"). Figure 7 shows the viscosity of the acidic cream with a pH near 4.5. Figure 8 shows a scatter diagram and a regression equation showing the relationship between the protein content of the first oil-in-water emulsion in each example and the viscosity of the cream (oil-in-water emulsion) near pH 4.5. Note that the cream without acid resistance thickens when the pH is near 4.5, and it becomes impossible to whip, or even if it can be whipped, the specific gravity of the whipped cream increases. On the other hand, for the cream with acid resistance, the specific gravity of the whipped cream decreases.

[0091]

Table 3

[0092] For the creams of Comparative Examples 1 to 2, the viscosity at an acidic pH where the pH was lowered to near 4.5 was 5810 mPa·s or more. In contrast, for the creams of Examples 1 to 3, the viscosity when the pH was lowered to near 4.5 was 5000 mPa·s or less. If the viscosity is 5000 mPa·s or less, it is particularly sufficiently whipable. From the comparison between Examples 1 to 3 and Comparative Examples 1 to 2, it can be seen that even when the final compositions are the same, the lower the protein content of the first oil-in-water emulsion, the more the thickening is suppressed and the better the foaming property when the pH is lowered to near 4.5. In particular, in Comparative Example 1, the protein content of the first oil-in-water emulsion was 1.4%, and the viscosity of the final acidic cream was 5810 mPa·s. Then, it can be said that the preferred protein content of the first oil-in-water emulsion is less than 1.4%, and the preferred viscosity range of the final acidic cream is less than 5810 mPa·s. On the other hand, referring to Fig. 8, it is understood that the viscosity of the acidic cream near pH 4.5 is linear for Examples 1 to 3 and Comparative Example 1. Then, when the protein content of the first oil-in-water emulsion is 1.4%, the viscosity of the acidic cream is calculated to be 5394 mPa·s from the regression equation (y = 2240.1x + 2257.4) in Fig. 8. Therefore, it can also be said that the preferred viscosity range of the acidic cream is less than 5394 mPa·s from above the regression equation. Also, since the protein content of the first oil-in-water emulsion that reaches a more preferred viscosity of 5000 mPa·s is 1.2% when calculated backward from the regression equation, it is also estimated that the more preferred range of the protein content of the first oil-in-water emulsion is 1.2% or less. Among them, 1.0% or less is preferred, the value of Example 3 (0.8%) or less is more preferred, the value of Example 2 (0.4%) or less is even more preferred, and near Example 1 (near approximately 0%) is particularly preferred.

[0093] (Foaming property test) 64 g of sugar was added to 800 g of neutral cream to obtain a sweetened cream. The obtained sweetened cream was whipped at 180 rpm for the whipping time shown in Table 4 using a mixer (Kenmix) to obtain whipped cream. The end point of whipping was when the hardness of the whipped cream reached 20 ± 1 mm in penetrometer needle penetration (hereinafter also referred to as "penetrometer value"). The overrun and penetrometer value of the whipped cream were measured by the following measurement methods. The overrun value of the obtained whipped cream is shown in Table 4.

[0094] "Overrun" The specific gravity (ρ0) of the sweetened cream before whipping and the specific gravity (ρw) of the whipped cream were measured, and the overrun (OR) was calculated using the following formula. OR (%) = (ρ0 - ρw) / ρw × 100

[0095] "Penetration value (penetrometer penetration)" The penetration value is a value (unitless) obtained by multiplying by 10 the penetration distance (mm) of a specific conical cone when it is dropped and penetrated into the composition under predetermined conditions. The larger this value, the softer it indicates. Specifically, using a penetrometer, a conical cone made of aluminum with a bottom diameter of 24 mm, a height of 33.5 mm, a tip angle of 40°, and a weight of 12 g was penetrated into the sample, the penetration depth (mm) was measured, and the value obtained by multiplying the measured value by 10 was taken as the penetration value.

[0096]

Table 4

[0097] The creams of Examples 1 to 3 and Comparative Examples 1 to 2 were all foamy when neutral.

[0098] (Acid resistance test 2) 400 g of the neutral cream of Example 1, Example 3, or Comparative Example 1 was placed in a mixer (Chef Classic manufactured by DeLonghi), a 10% citric acid solution was added to adjust the pH to 4.5 or less, and then whipped at a rotational speed of 180 rpm for the whipping time shown in Table 5 to obtain whipped cream. Table 5 shows the pH of the cream before whipping (after pH adjustment), the temperature during whipping (from the start of whipping to the end of whipping), the specific gravity of the whipped cream, the overrun, and the penetration value. The obtained whipped cream was stored in a refrigerator at 5°C for 24 hours, and then the penetrometer value (the penetrometer value after 1 day) was measured. The difference from the penetrometer value at the end of whipping (the penetrometer value after 1 day - the penetrometer value at the end of whipping) (hereinafter, also referred to as the "penetrometer value difference after 1 day") was calculated. Based on the following criteria, the state after 1 day was evaluated from the results. The results are shown in Table 5. ×: The penetrometer value difference after 1 day is +100 or more. △: The penetrometer value difference after 1 day is +50 or more and less than +100. ○: The penetrometer value difference after 1 day is -15 or more and less than +50. △: The penetrometer value difference after 1 day is -25 or more and less than -15. ×: The penetrometer value difference after 1 day is less than -25. The measurement methods of pH, overrun, and penetrometer value are as described above.

[0099]

Table 5

[0100] For the creams of Example 1 and Example 3, compared with the cream of Comparative Example 1, the addition of an acidic material suppressed the change in the state after whipping.

[0101] (Measurement of protein precipitation amount) For three types of creams, namely Example 1 (protein content of the first oil-in-water emulsion: 0% / protein content of the cream: 2.87%), Example 3 (protein content of the first oil-in-water emulsion: 0.8% / protein content of the cream: 2.87%), and Comparative Example 1 (protein content of the first oil-in-water emulsion: 1.4% / protein content of the cream: 2.87%), the protein precipitation amount was determined by the following procedure. 50 mL of the sample (cream) was dispensed into a graduated centrifuge tube, and centrifugation was performed using a centrifuge (Hitachi small centrifuge himac CT6E, rotor "T4SS swing type") at 3000 rpm for 5 minutes. The maximum rotation radius r was 16.2 cm, the rotation speed N was 3000 rpm, and the relative centrifugal acceleration was 1630×g. After centrifugation, the precipitation volume (mL) of the protein in the centrifuge tube was visually confirmed. From this precipitation volume (mL), the ratio (volume %) of the volume of the precipitated protein to the total volume of the sample was determined and taken as the protein precipitation amount. The results are shown in Table 6. Since the centrifugation conditions in this test are severe, it has nothing to do with the occurrence of precipitation in the state where the sample is normally left standing. That is, the magnitude of the precipitation amount in this test has nothing to do with the product quality such as the length of the storage period of each sample.

[0102]

Table 6

[0103] As described above, in Comparative Example 1 where the protein content of the first oil-in-water emulsion was 1.4%, the protein precipitation amount was 0%. In contrast, the creams of Example 1 and Example 3 had a protein precipitation amount greater than 0%. Also, the lower the protein content of the first oil-in-water emulsion, the greater the protein precipitation amount.

[0104] <Test Example 2> This test example was conducted to verify whether the same results can be obtained by adding the modified starch and trisodium citrate added to the protein-containing raw material to the aqueous phase in Examples 1 to 3.

[0105] A cream of Example 4 was obtained in the same manner as in Example 1, except that the compositions of the aqueous phase and the protein-containing raw material were changed as shown in Table 7. For the obtained cream, the foaming property test and the acid resistance test described above were performed in a neutral state. The results of the foaming property test are shown in Table 8, and the results of the acid resistance test are shown in Figure 9. The results of Example 1 are also shown in Figure 9.

[0106]

Table 7

[0107]

Table 8

[0108] In Example 4, compared with Example 1, the whipping time was shortened by about 1 minute and the viscosity also decreased. The overrun was about the same. In the acid resistance test, even when the pH was lowered as in Example 1, no sharp increase in viscosity was observed. From this, it is considered that the timing of adding the modified starch and trisodium citrate can be either before or after homogenization.

[0109] <Test Example 3> This test example was conducted to evaluate the effect of the protein concentration of the cream on the acid resistance of the cream.

[0110] Creams of Examples 5 to 7 were obtained in the same manner as in Example 1, except that the compositions of the aqueous phase portion and the protein-containing raw material were changed as shown in Table 9. The overall compositions of each cream (second water-in-oil emulsion) are shown in Table 10. In Table 10, the value of Y is 6.70 for Example 5, 8.80 for Example 6, and 14.70 for Example 7. For the obtained creams, the above-described foaming property test and acid resistance test were conducted. The results of the foaming property test are shown in Table 11, and the results of the acid resistance test are shown in FIG. 10. In FIG. 10, the results of Example 1 and Comparative Example 2 are also shown.

[0111]

Table 9

[0112]

Table 10

[0113]

Table 11

[0114] As shown in the above results, in the foaming property test, as the protein content of the cream increased, the whipping time became longer. Also, the overrun decreased. In the acid resistance test, in any of Examples 5 to 7, the thickening when the pH was lowered was suppressed. In particular, good results were obtained when the protein content of the cream was less than 5.00%, especially 3.00% or less.

[0115] <Example 8> 200 g of the cream of Example 1 and 200 g of fruit puree (raspberries, 15% sugar added, manufactured by Bonne Maman) were mixed to obtain the cream of Example 8. The obtained cream was whipped at 180 rpm using a whisk (Kitchen Machine Chef Classic) manufactured by Delonghi, and whipped cream was obtained. Table 12 shows the pH of the cream before whipping (after mixing with the fruit puree), the temperature during whipping (starting time of whipping → ending time of whipping), the whipping time, the specific gravity of the whipped cream, the overrun, and the penetrometer value (penetration needle penetration). The obtained whipped cream was stored in a refrigerator at 5°C for 24 hours, and then the penetrometer value (penetrometer value after 1 day) was measured, and the difference in penetrometer value after 1 day was calculated. The results were evaluated in the same manner as in the acid resistance test 2. The results are shown in Table 12. The measuring methods of pH, overrun, and penetrometer value are as described above.

[0116]

Table 12

[0117] The cream of Example 8 showed less change in the state after foaming compared to the cream of Comparative Example 1.

[0118] In the present invention as described above, the protein content of the first oil-in-water emulsion may be either 0% or more than 0% and less than 1.4% by mass. The present invention can also be expressed as follows. [A] A method for producing an oil-in-water emulsion comprising a protein source, oil and fat, water, and other raw materials, the method comprising the steps of: mixing all of the oil and fat, a part of the water, and a part of the other raw materials, and subjecting the mixture to homogenization and sterilization to prepare a first oil-in-water emulsion; mixing the remainder of the water, the remainder of the other raw materials, and all of the protein source, and subjecting the mixture to sterilization to prepare a protein-containing raw material; and mixing the protein-containing raw material with the first oil-in-water emulsion to prepare a second oil-in-water emulsion. [B] A method for producing an oil-in-water emulsion comprising a protein source, oil and fat, water, and other raw materials, the method comprising the steps of: mixing all of the oil and fat, a part of the water, a part of the other raw materials, and a part of the protein source, and subjecting the mixture to homogenization and sterilization to prepare a first oil-in-water emulsion having a protein content of more than 0% by mass and less than 1.4% by mass; mixing the remainder of the water, the remainder of the other raw materials, and the remainder of the protein source, and subjecting the mixture to sterilization to prepare a protein-containing raw material; and mixing the protein-containing raw material with the first oil-in-water emulsion to prepare a second oil-in-water emulsion.

Claims

1. a step of homogenizing a first oil-in-water emulsion, the first oil-in-water emulsion including fats and water, a protein content of 0.8% by mass or less, and a ratio of the protein to the fats and oils of 1.6% by mass or less, to obtain a homogenized first oil-in-water emulsion; and mixing the homogenized first oil-in-water emulsion with a milk protein-containing raw material to obtain a second oil-in-water emulsion.

2. 2. The method for producing an oil-in-water emulsion according to claim 1, wherein the content of the protein in the first oil-in-water emulsion is 0% by mass.

3. The method for producing an oil-in-water emulsion according to claim 1 or 2, wherein the milk protein-containing raw material comprises skim milk powder.

4. The method for producing an oil-in-water emulsion according to any one of claims 1 to 3, wherein the second oil-in-water emulsion is not homogenized after the step of obtaining the second oil-in-water emulsion.

5. The method for producing an oil-in-water emulsion according to any one of claims 1 to 4, wherein the first oil-in-water emulsion has an oil content of 1 to 60 mass%.

6. The method for producing an oil-in-water emulsion according to any one of claims 1 to 5, wherein the second oil-in-water emulsion has a protein content of 0.4% by mass or more and less than 5% by mass.

7. 7. The method for producing an oil-in-water emulsion according to claim 1, wherein the oil-in-water emulsion produced by the method has a pH of 6.5 to 7.5 and a viscosity at 10°C of 1 to 1000 mPa·s, and when the pH of the oil-in-water emulsion is around 4.5, the viscosity at 10°C is less than 5810 mPa·s.

8. 8. The method for producing an oil-in-water emulsion according to claim 7, wherein the viscosity of the oil-in-water emulsion at 10° C. when the pH of the emulsion is around 4.5 is 4660 mPa·s or less.

9. A method for producing an air bubble-containing oil-in-water emulsion, comprising foaming an oil-in-water emulsion produced by the method according to any one of claims 1 to 8 to obtain an air bubble-containing oil-in-water emulsion.

10. A method for producing a frozen gas bubble-containing oil-in-water emulsion, comprising freezing the gas bubble-containing oil-in-water emulsion produced by the method according to claim 9 to obtain a frozen gas bubble-containing oil-in-water emulsion.

11. homogenizing a first oil-in-water emulsion containing fats and oils and water and having a protein content of less than 1.4% by mass to obtain a homogenized first oil-in-water emulsion; mixing the homogenized first oil-in-water emulsion with a milk protein-containing raw material to obtain a second oil-in-water emulsion; The method for producing an acidic oil-in-water emulsion comprises adding an acidic material to the oil-in-water emulsion to adjust the pH to a range of 3.0 to 5.5 to obtain an acidic oil-in-water emulsion.

12. A method for producing an acidic oil-in-water emulsion, comprising adding an acidic material to the oil-in-water emulsion produced by the production method according to any one of claims 1 to 8, and adjusting the pH to a range of 3.0 to 5.5 to obtain an acidic oil-in-water emulsion.

13. A method for producing a bubble-containing acidic oil-in-water emulsion, comprising foaming the acidic oil-in-water emulsion produced by the method according to claim 11 or 12 to obtain a bubble-containing acidic oil-in-water emulsion.

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