JP7679184B2 - 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 - Google Patents

Description

The present invention relates to a method for producing an oil-in-water emulsion, a method for producing an oil-in-water emulsion containing gas bubbles, a method for producing an oil-in-water emulsion containing frozen gas bubbles, a method for producing an acidic oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion containing gas bubbles, and an oil-in-water emulsion.

Cream is used for a variety of purposes. For example, whipped cream, which is made by whipping edible cream such as fresh cream or compound cream, is used to decorate cakes and other confectioneries and fruit pulp, and is floated on drinks such as Vienna sausages and coffee.
As the cream, for example, an oil-in-water emulsion containing fats and oils, water, and proteins is used. Such oil-in-water emulsions are generally produced by mixing an aqueous phase containing water and proteins with an oil phase containing oil-soluble components such as fats and oils, pre-emulsifying the mixture, homogenizing it, sterilizing it, cooling it, and preferably aging it thereafter.
In order to impart a milky or rich flavor to the cream, it has been proposed to add and mix skim concentrated milk after aging, followed by sterilization (Patent Document 1).

On the other hand, in the whipped cream market, there is a need to obtain whipped cream with a sour and refreshing taste by adding acidic foods with low pH such as fruit juice or acidic materials such as acidic compounds.
However, oil-in-water emulsions generally have low acid resistance, and when the pH is lowered, proteins in the oil-in-water emulsion aggregate, causing the oil-in-water emulsion to thicken or solidify. Therefore, it is difficult to add an acidic material to the oil-in-water emulsion to foam it. In addition, 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 to impart acid resistance to oil-in-water emulsions, particularly a technology to impart a property (acid resistance) that allows foaming without increasing viscosity even when the pH is lowered.
As methods for imparting acid resistance to an oil-in-water emulsion, a method of adjusting the blending of emulsifiers (Patent Document 2), a method of adjusting 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.

Patent No. 6612491 Japanese Patent Application Publication No. 8-126470 JP 2014-79234 A JP 2015-57948 A

However, the methods of Patent Documents 2 and 3 use specific emulsifiers and specific proteins to impart acid resistance, and therefore restrict the types of emulsifiers and proteins that can be blended in. This reduces the room for devising the blending of emulsifiers and proteins in product design, resulting in a problem of reduced freedom in product design.
The method of Patent Document 4 has the problem that the flavor of the oil-in-water emulsion becomes different from the original flavor by blending an acid resistance imparting agent that is not actually necessary in order to impart acid resistance, and the cost of the product increases. This method also has the problem of reducing the degree of freedom in product design.
Furthermore, even if conventional techniques can whip an oil-in-water emulsion containing an acidic material, the shape retention of the resulting whipped cream is insufficient, and the hardness of the whipped cream tends to decrease over time.
Therefore, there is a demand for a technology that can produce an oil-in-water emulsion that is not restricted to specific raw materials and does not require the incorporation of unnecessary ingredients, that allows for freedom in product design and that has excellent shape retention after foaming when an acidic material is added.

One aspect of the present invention aims to provide a method for producing an oil-in-water emulsion that can be foamed when an acidic material is added and has excellent shape retention after foaming, a method for producing a bubble-containing oil-in-water emulsion using this 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, as well as an oil-in-water emulsion that can be foamed when an acidic material is added and has excellent shape retention after foaming.

[1] A step of 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;
and mixing the homogenized first oil-in-water emulsion with a protein-containing raw material to obtain a second oil-in-water emulsion.
[2] The method for producing an oil-in-water emulsion according to [1], wherein the second oil-in-water emulsion is not homogenized after the step of obtaining the second oil-in-water emulsion.
[3] The method for producing an oil-in-water emulsion according to [1] or [2], wherein the first oil-in-water emulsion has an oil content of 1 to 60 mass%.
[4] The method for producing an oil-in-water emulsion according to any one of [1] to [3], wherein the second oil-in-water emulsion has a protein content of 0.4% by mass or more and less than 5% by mass.
[5] The method for producing an oil-in-water emulsion according to any one of [1] to [4], wherein the oil-in-water emulsion produced by the method has a pH of 6.5 to 7.5, a viscosity of 1 to 1000 mPa s at 10° C., and a viscosity of less than 5810 mPa s at 10° C. when the pH of the oil-in-water emulsion is around 4.5.
[6] A method for producing an air-bubble-containing oil-in-water emulsion, comprising foaming an oil-in-water emulsion produced by any one of the production methods described above in [1] to [5] to obtain an air-bubble-containing oil-in-water emulsion.
[7] 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 for producing the gas bubble-containing oil-in-water emulsion according to [6] above to obtain a frozen gas bubble-containing oil-in-water emulsion.
[8] A method for producing an acidic oil-in-water emulsion, comprising adding an acidic material to the oil-in-water emulsion produced by any one of the production methods described above in [1] to [5], 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 a bubble-containing acidic oil-in-water emulsion, comprising foaming the acidic oil-in-water emulsion produced by the production method of [8] above to obtain a bubble-containing acidic oil-in-water emulsion.
[10] An oil-in-water emulsion comprising fats and oils, water and proteins,
The pH is 6.5 to 7.5,
The viscosity at 10°C is 1 to 1000 mPa·s,
The viscosity of the oil-in-water emulsion at 10° C. when the pH of the emulsion is around 4.5 is less than 5,810 mPa s;
An oil-in-water emulsion having an amount of protein precipitation exceeding 0% by volume as measured by the following measurement method.
Method for measuring the amount of protein precipitation: 50 mL of the oil-in-water emulsion was placed in a graduated centrifuge tube, and centrifuged using a centrifuge at a relative centrifugal acceleration of 1630 × g for 5 minutes. The volume (mL) of the protein precipitated in the centrifuge tube was then measured visually, and the ratio (volume %) of the volume of the protein to the total volume of the oil-in-water emulsion was defined as the amount of protein precipitation.

According to the present invention, it is possible to provide 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 an oil-in-water emulsion containing gas bubbles using this method, a method for producing an oil-in-water emulsion containing frozen gas bubbles, a method for producing an acidic oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion containing gas bubbles, and an oil-in-water emulsion that can be foamed when acidified and has excellent shape retention after foaming.

1 is a flow diagram illustrating a method for producing an oil-in-water emulsion according to one embodiment. 1 is a flow diagram showing a method for producing an oil-in-water emulsion according to another embodiment. 1 is a flow diagram showing a method for producing an oil-in-water emulsion according to another embodiment. 1 is a flow diagram showing a method for producing an oil-in-water emulsion according to another embodiment. 1 is a flow diagram showing a method for producing an oil-in-water emulsion according to another embodiment. 1 is a graph showing the results of an acid resistance test in Test Example 1. 1 is a graph showing the results of an acid resistance test in Test Example 1. 1 is a scatter diagram and a regression equation showing the relationship between the protein content of a first oil-in-water emulsion and the viscosity of a cream (oil-in-water emulsion) at around pH 4.5. 1 is a graph showing the results of an acid resistance test in Test Example 2. 1 is a graph showing the results of an acid resistance test in Test Example 3.

In the present invention, the protein content of the oil-in-water emulsion can be calculated from the protein contents of the raw materials and the ratio thereof.
However, in general, the protein content can also be measured by the semi-micro Kjeldahl method (Japanese Pharmacopoeia Commentary, 14th Edition, General Provisions, General Provisions for Manufacturing, General Testing Methods, 2001, B-370 to B-374). The specific measurement method is shown below.
Approximately 1 g of sample (the mass of the sample is measured to the nearest 0.1 mg) is taken, and the amount of nitrogen in the sample is quantified by the semi-micro Kjeldahl method. In detail, the sample is placed in a decomposition bottle, and 1 g of a decomposition promoter with a mixture of potassium sulfate:copper sulfate = 10:1 (mass ratio) and 7 mL of concentrated sulfuric acid are added, followed by thermal decomposition. After thermal decomposition, the sample is subjected to steam distillation, and the distilled product is placed in 20 mL of 20 mM aqueous sulfuric acid. After the distillation is completed, the 20 mM aqueous sulfuric acid solution containing the distilled water is titrated with 40 mM sodium hydroxide. The titration amount at this time is designated b (mL). A blank test is performed using a control sample that does not contain protein instead of the sample, and the titration amount at this time is designated a (mL), and the protein content of the sample is calculated by the following formula.
Protein content (mass%)=(0.56×(b−a)×6.38)/sample weight (g)/1000×100
Incidentally, 0.56 in the formula is the amount of nitrogen in the sample per mL of 40 mM sodium hydroxide, and 6.38 is the coefficient for converting the amount of nitrogen into the protein content of dairy products.
In the present invention, the oil/fat content of the oil-in-water emulsion can also be calculated from the blend of raw materials.
Generally, however, the fat and oil content can also be measured by the Roese-Gottlieb method (Food Hygiene Inspection Guideline, 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, 1 g of sample is collected in a beaker, and transferred to an extraction tube while washing the inside of the beaker with about 10 mL of warm water. 2 mL of ammonia water and one drop of phenolphthalein reagent are added to the extraction tube, plugged, and mixed well. Then, 10 mL of ethanol is used to wash the beaker in which the sample was collected, and the beaker is added to the extraction tube, plugged, and mixed well. Next, 25 mL of ether is added, plugged, and shaken vigorously for 30 seconds. Finally, 25 mL of petroleum ether is added, plugged, and shaken vigorously for 30 seconds. After leaving the mixture to stand until the upper layer becomes transparent, the ether layer is decanted into a dish that has been weighed in advance without spilling, and the organic solvent is recovered. The dish is placed in a steam dryer at 100°C to 105°C for 1 hour to evaporate the organic solvent. The amount of extracted fat (g) can be measured by measuring the mass of the dish. The fat content is calculated from these measurements using the following formula.
Content of fats and oils (mass%)=(amount of fat extracted/amount of sample used)×100
The viscosity is measured by a Brookfield viscometer.
Unless otherwise specified, pH is measured at 10°C.
The relative centrifugal acceleration is calculated using the following formula.
RCF=1118×r× ^N2 × ^10-8
Here, RCF indicates the relative centrifugal acceleration (×g), r indicates the maximum rotation radius (cm), and N indicates the number of rotations per minute (rpm).
In this specification, "having excellent acid resistance" means that the composition can be foamed when an acidic material is added, and has excellent shape retention after foaming.

[Method for producing oil-in-water emulsion]
A method for producing an oil-in-water emulsion according to one embodiment of the present invention (hereinafter also referred to as "this production method") includes a step of homogenizing a first oil-in-water emulsion that contains fats and water and has a protein content of less than 1.4% by mass to obtain a homogenized first oil-in-water emulsion (hereinafter also referred to as "homogenization step"), and a step of mixing the homogenized first oil-in-water emulsion with a protein-containing raw material to obtain a second oil-in-water emulsion (hereinafter also referred to as "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.

In the present production method, it is preferred not to homogenize the second oil-in-water emulsion after the mixing step.
The phrase "not homogenizing the second oil-in-water emulsion" as used herein means that no mechanical operation for breaking down fat globules in the second oil-in-water emulsion is intentionally performed. Note that the case where fat globules are naturally broken down by impact or the like during handling of the second oil-in-water emulsion is not included in the "homogenization of the second oil-in-water emulsion" as used herein.

The present production method may include a step of mixing (premixing) an oil phase containing oils and fats with an aqueous phase containing water, and emulsifying (preemulsifying) the mixture in a mixing device such as a homogenizer to prepare a first oil-in-water emulsion (hereinafter also referred to as a "preemulsification step"), prior to the homogenization step.
Prior to the preliminary emulsification step, a step of raising the temperature and melting the fat or oil and, if necessary, dissolving other oil-soluble components (such as the first emulsifier described below) in the fat or oil to prepare an oil phase may be included.
Prior to the preliminary emulsification step, the water may be used as the aqueous phase as is, or a step of preparing the aqueous phase by adding other water-soluble components (such as a second emulsifier, a protein-containing raw material, a chelating agent, etc., which will be described later) to the water may be included.
The homogenization step may be preceded by a step of heating (preheating) the first oil-in-water emulsion.
The method may include a step of sterilizing the first oil-in-water emulsion before or after the homogenization step.
The homogenization step may be followed by a step of aging the first oil-in-water emulsion.
Before the mixing step, a step of sterilizing the protein-containing raw material may be included.
The mixing step may be preceded by a step of homogenizing the protein-containing raw material, although the protein-containing raw material typically does not contain fats or oils, and in this case, the protein-containing raw material itself does not need to be homogenized.
After the mixing step, a step of sterilizing the second oil-in-water emulsion may be included.
After the mixing step, a step of aging the second oil-in-water emulsion may be included.
The oil-in-water emulsion produced by the present production method is typically the second oil-in-water emulsion, an aged second oil-in-water emulsion, or a pasteurized and aged second oil-in-water emulsion.
Hereinafter, the oil-in-water emulsion produced by this production method will also be referred to as the "oil-in-water emulsion of the present invention."

Hereinafter, the present manufacturing method will be described by way of an embodiment with reference to the accompanying drawings.
FIG. 1 is a flow diagram illustrating one embodiment of the present manufacturing method.
In this embodiment, first, the fats and oils among the raw materials are heated and melted, and other oil-soluble components are dissolved in the fats and oils as necessary to prepare an oil phase. Separately, the water among the raw materials is used as the aqueous phase as it is, or other water-soluble components are dissolved in the water to prepare an aqueous phase. These preparations are performed by heating the fats and oils or water to an appropriate temperature.
Next, the oil phase and the aqueous phase are placed in, for example, a tank equipped with an agitator, and the two are premixed. After that, for example, the agitator is operated to sufficiently agitate the oil phase and the aqueous phase, thereby preemulsifying the mixture. This prepares a first oil-in-water emulsion. It is necessary to keep the protein content of this first oil-in-water emulsion low, and the protein content of the first oil-in-water emulsion is less than 1.4% by mass.

Next, the first oil-in-water emulsion is passed through a homogenizer-integrated UHT sterilizer. The homogenizer-integrated UHT sterilizer is usually equipped with a heat exchanger and a homogenizer. The first oil-in-water emulsion is first preheated by the heat exchanger, and is preferably heated to 65 to 75°C. Then, it is homogenized by the homogenizer. The set pressure (homo pressure) for homogenizing the first oil-in-water 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 homo pressure is a gauge pressure. The homogenized first oil-in-water emulsion is heated to a predetermined sterilization temperature and held for a predetermined time to be sterilized. The sterilization conditions are not particularly limited, and can be performed under known sterilization conditions. For example, heating at 90°C for 15 seconds, or heating conditions that provide an equivalent sterilization effect, can be mentioned. The homogenized first oil-in-water emulsion is then cooled. In addition, as a UHT sterilizer with an integrated homogenizer, there is a model that performs homogenization at a stage after sterilization and before cooling, and such a model may be adopted.
The cooled first oil-in-water emulsion is stored in a tank equipped with a cooling function.

Separately, the protein-containing raw material is sterilized and cooled. The sterilization conditions are not particularly limited, and can be performed under known sterilization conditions. For example, heating at 90° C. for 15 seconds or heating conditions that provide an equivalent sterilization effect can be used.
Then, the protein-containing raw material is mixed with the stored first oil-in-water emulsion. This prepares a second oil-in-water emulsion. The amount of the protein-containing raw material mixed is set according to the target value of the protein content of the second oil-in-water emulsion. That is, the protein content of the first oil-in-water emulsion is kept low, and the protein-containing raw material is subsequently added and mixed to finally adjust the protein content to a desired level.
Thereafter, the second oil-in-water emulsion is aged to obtain the oil-in-water emulsion of the present invention. Aging is a treatment for promoting the crystallization of fat, and can be carried out according to a conventional method. The aging conditions are not particularly limited, and the aging 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 with 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 performed using a known stirrer. At this time, it is preferable to stir as slowly as possible in order to suppress the decrease in the acid resistance of the second oil-in-water emulsion. In this respect, it is preferable to store the cooled first oil-in-water emulsion in a tank equipped with a slowly rotating stirring blade and a cooling function such as a double jacket, and stir it in the tank with the stirring blade.

<First oil-in-water emulsion>
The first oil-in-water emulsion comprises oil and water.
The first oil-in-water emulsion may contain protein, so 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 an emulsifier, a stabilizer, and a salt.
The first oil-in-water emulsion may further contain other components in addition to those described above.

Examples of the fats and oils include vegetable fats and oils, animal fats and oils, etc. Examples of the vegetable fats and oils include 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, evening primrose oil, etc.; oleic acid of the vegetable fats; hardened oils (partially hardened oil, extremely hardened oil), transesterified oil, fractionated oil, and mixed oil of the vegetable fats and oils, etc. Examples of the animal fats and oils include milk fat, beef tallow, lard, fish oil, whale oil, hardened oils (partially hardened oil, extremely hardened oil), transesterified oil, fractionated oil, and mixed oil of the vegetable fats and oils, etc. These fats and oils may be used alone or in combination of two or more kinds.
From the viewpoints of cost and physical properties after whipping, it is preferable that at least a part of the fat is vegetable fat. Vegetable fat may be used in combination with animal fat such as milk fat.
The vegetable oil preferably has a solid fat content of about 50 to 70% by mass when refrigerated (5°C) and a melting point of about 35 to 40°C so that the oil-in-water emulsion can be foamed and melted in the mouth at body temperature. Examples of such vegetable oil include rapeseed oil, soybean oil, palm oil, palm kernel oil, corn oil, cottonseed oil, rice oil, coconut oil, oleic acid and hardened oils thereof, etc. Among these, a mixture of palm olein and hardened rapeseed oil, hardened palm oil, and hardened palm kernel oil are preferred. These may be used alone or in combination of two or more.

Protein is generally considered to contribute to improving the stability of oil-in-water emulsions and foam-containing oil-in-water emulsions produced by foaming oil-in-water emulsions. However, in the present invention, the protein content of the first oil-in-water emulsion is limited to less than 1.4% by mass. The idea of reducing the protein content of the first oil-in-water emulsion in this way is a very rare idea in the technical field of the present invention.
Examples of proteins include milk proteins, soybean proteins, etc., with milk proteins being preferred in terms of flavor.
In the present invention, the protein is typically blended into the first oil-in-water emulsion in the form of a protein-containing raw material. Examples of the protein-containing raw material include the same protein-containing raw material as that used in the mixing step.

The emulsifier, stabilizer and salt contribute to improving the stability of the oil-in-water emulsion (emulsion stability).
Examples of the emulsifier include lecithin, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, polysorbate, organic acid monoglyceride, fatty acid monoglyceride, etc. These emulsifiers may be used alone or in combination.

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

The emulsifier preferably comprises a first emulsifier having an HLB (hydrophilic lipophilic balance) value of 6 or less and a second emulsifier having an HLB value of 10-16.
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 improved.
The HLB value of the first emulsifier is preferably 1-6.
The HLB value of the second emulsifier is preferably 10-16.
In this specification, the HLB value is a value determined by the Griffin method.

As the first emulsifier, for example, one having an HLB value of 6 or less can be appropriately selected from the emulsifiers listed above.
From the viewpoint of easiness of demulsification when foaming an oil-in-water emulsion, the first emulsifier preferably contains at least one selected from the group consisting of lecithin and sucrose fatty acid esters having an HLB value of not more than 6. An example of a sucrose fatty acid ester having an HLB value of not more than 6 is 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 esters 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.

At least one member 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 another emulsifier having an HLB value of 6 or less, a polyglycerol fatty acid ester having an HLB value of 6 or less is preferred. The HLB value of the polyglycerol fatty acid ester can be adjusted over a wide range depending on the constituent fatty acid, the degree of polymerization, and the like.

As the second emulsifier, for example, one having an HLB value of 10 to 16 can be appropriately selected from the emulsifiers listed above.
The second emulsifier preferably contains a polyglycerol fatty acid ester having an HLB value of 10 to 16, since this has better solubility in water.
The content of the polyglycerol fatty acid ester 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.

A polyglycerol fatty acid ester having an HLB value of 10 to 16 may be used in combination with another emulsifier having an HLB value of 10 to 16.
As another emulsifier having an HLB value of 10 to 16, a sucrose fatty acid ester having an HLB value of 10 to 16 is preferred because it is easily demulsified when foaming an oil-in-water emulsion.

Examples of stabilizers 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 carboxymethylcellulose.
The salts include phosphates such as monophosphates and condensed phosphates.

Other ingredients include, for example, chelating agents (such as trisodium citrate), pH adjusters, milk components, egg components, carbohydrates (lactose, fructose, glucose, sugar, etc.), dietary fiber, cellulose, flavorings, coloring agents, etc.

The present invention can also be combined with the above-mentioned conventional techniques.
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 may be further contained. In this case, known acid resistance imparting agents can be used, for example, fermented cellulose (Patent Document 4: JP 2015-57948 A).
Even if an acid-resistant agent is added, the content of the acid-resistant agent is preferably 3% by mass or less, based on the total mass of the second oil-in-water emulsion finally obtained, from the viewpoint of flavor, and the content of the acid-resistant agent is particularly preferably 0% by mass, based on the total mass of the second oil-in-water emulsion.
In addition, with regard to other conventional techniques, such as a method of devising the emulsifier blend (Patent Document 2) or a method of devising the type of protein (Patent Document 3), the present invention does not require that the present invention be restricted to a specific emulsifier in order to achieve acid resistance, nor does it require that milk protein hydrolysates be added for the purpose of acid resistance, but this does not exclude the combination of these conventional techniques with the present invention.
As described above, even if it is assumed that the present invention is combined with a conventional technique, there is an advantage in that the extent to which the conventional technique is used can be kept small compared to the case in which such a conventional technique is used alone.

In the first oil-in-water emulsion, the fat content is preferably 20 to 70% by mass, more preferably 40 to 60% by mass, based on the total mass of the first oil-in-water emulsion. When the fat content is equal to or greater than the lower limit of the range, the fat content of the final second oil-in-water emulsion is easily adjusted to fall within the preferred range described below.

The water content is preferably 20 to 70% by mass, and more preferably 30 to 50% by mass, based on the total mass of the first oil-in-water emulsion. When the water content is equal to or greater than the lower limit of the range, the emulsifiability is superior, and when the water content is equal to or less than the upper limit of the range, the foamability of the second oil-in-water emulsion is superior.

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, relative to the total mass of the first oil-in-water emulsion. In other words, it is particularly preferable that the first oil-in-water emulsion does not contain protein. When the protein content is equal to or less than the upper limit, the oil-in-water emulsion of the present invention has excellent acid resistance, and the foamability of the acidic oil-in-water emulsion obtained by acidifying the oil-in-water emulsion of the present invention and the shape retention of the bubble-containing acidic oil-in-water emulsion obtained by foaming the acidic oil-in-water emulsion are excellent.

In the first oil-in-water emulsion, the ratio of protein to fat (100% by mass) is preferably less than 2.82% by mass, more preferably 2.0% by mass or less, even 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 fat is equal to or less than the upper limit, the acid resistance of the oil-in-water emulsion of the present invention is superior, and the foamability of the acidic oil-in-water emulsion and the shape retention of the bubble-containing acidic oil-in-water emulsion are superior.

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 equal to or greater than the lower limit of the above range, the smoothness and shape retention of the bubble-containing acidic oil-in-water emulsion are superior, and when the content is equal to or less than the upper limit of the above range, the shape retention and flavor of the bubble-containing acidic oil-in-water emulsion are superior.

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, 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, relative to the total mass of the first emulsifier and the second emulsifier.

The pH of the first oil-in-water emulsion is preferably 6.0 to 8.0, and more preferably 6.5 to 7.5. If the pH is equal to or higher than the lower limit of the range, the stability of the liquid state is superior, and if the pH is equal to or lower than the upper limit of the range, the flavor and foaming properties are superior.

The viscosity of the first oil-in-water emulsion at 10°C is preferably 20 to 1000 mPa·s, and more preferably 30 to 500 mPa·s. If the viscosity of the first oil-in-water emulsion is within the above range, it is easier to set the viscosity of the second oil-in-water emulsion at 10°C within the preferred range described below.

<Protein-containing ingredients>
The protein-containing raw material comprises protein.
The protein-containing raw material may contain components other than proteins. Examples of the components other than proteins 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, powder, etc.), but is preferably liquid because it is easily mixed with the homogenized first oil-in-water emulsion. Examples of liquid protein-containing raw materials include skim concentrated milk, full fat concentrated milk, skim milk powder solution, full fat powder solution, etc. Other components may be blended with these liquid protein-containing raw materials.
In addition, since it is preferable that the protein-containing raw material is not homogenized after the mixing step, the lower the fat content, the better. The fat content in the protein-containing raw material is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably about 0% by mass, and particularly preferably 0% by mass, based on the total mass of the protein-containing raw material. Note that "about 0% by mass" means a small amount that does not cause fat floating during storage of the finally obtained oil-in-water emulsion of the present invention, even if the protein-containing raw material or the second oil-in-water emulsion is not homogenized.

<Second oil-in-water emulsion>
The second oil-in-water emulsion is obtained by mixing the first oil-in-water emulsion with a protein-containing raw material, and contains at least fats and oils, water, and proteins.
The second oil-in-water emulsion may further comprise an emulsifier.
The second oil-in-water emulsion may further comprise other ingredients.
The respective contents of fats and oils, water, protein, emulsifier, and other components relative to the total mass of the second oil-in-water emulsion are desirably equal to the respective contents of fats and oils, water, protein, emulsifier, and other components relative to the total mass of the first oil-in-water emulsion and the protein-containing raw material, although this does not exclude mixing other components together when mixing the first oil-in-water emulsion with the protein-containing raw material.

The fat/oil content is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass, based on the total mass of the second oil-in-water emulsion. When the fat/oil content is equal to or greater than the lower limit of the range, good texture and flavor are easily obtained when the emulsion is whipped, and when the fat/oil content is equal to or less than the upper limit of the range, the flavor when the emulsion is whipped is superior.

The water content is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, based on the total mass of the second oil-in-water emulsion. When the water content is equal to or greater than the lower limit of the range, the flavor and smoothness when foamed are superior, and when the water content is equal to or less than the upper limit of the range, the flavor when foamed is superior.

The protein content is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 3.0% by mass, based on the total mass of the second oil-in-water emulsion. When the protein content is equal to or greater than the lower limit, the emulsion stability before foaming is superior, and when the protein content is equal to or less than the upper limit, the acid resistance of the second oil-in-water emulsion is superior.

The content of the emulsifier is preferably 0.1 to 2.0% by mass, and 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 greater than the lower limit of the above range, the emulsion stability before foaming is superior, and when the content is equal to or less than the upper limit of the above range, the flavor after foaming is superior.

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, 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, relative to the total mass of the first emulsifier and the second emulsifier.

<Oil-in-water emulsion of the present invention>
The oil-in-water emulsion of the present invention, like the second oil-in-water emulsion, contains at least fats and oils, water, and proteins.
The second oil-in-water emulsion may further comprise an emulsifier.
The second oil-in-water emulsion may further comprise other ingredients.
It is desirable that the respective contents of fats and oils, water, protein, emulsifier, and other components relative to the total mass of the oil-in-water emulsion of the present invention are equal to the respective contents of fats and oils, water, protein, emulsifier, and other components relative to the total mass of the second oil-in-water emulsion.

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

The oil-in-water emulsion of the present invention may be a liquid cream.
The term "liquid cream" refers to cream that has not been substantially whipped, in other words, cream that has not been subjected to an artificial whipping operation.
"Cream" is an emulsion prepared using ingredients containing fat, and includes both cream (hereinafter also referred to as "fresh cream") as specified in the Ministerial Ordinance on Milk, etc. (Ministerial Ordinance on the Ingredient Standards, etc. of Milk and Dairy Products) and cream classified as "foods whose main ingredient is milk or dairy products" as specified in the Ministerial Ordinance on Milk, etc. (hereinafter also referred to as "dairy-based cream"). Fresh cream is "a product obtained by removing ingredients other than milk fat from raw milk, cow's milk, or special cow's milk." Dairy-based cream contains ingredients other than milk fat (vegetable fats and oils, proteins, various additives (emulsifiers, stabilizers, flavors, etc.), etc.), and is classified into pure milk fat type (pure milk fat cream) that contains only milk fat as fat, mixed type (so-called compound cream) that contains milk fat and vegetable fat as fat, and pure vegetable fat type (so-called non-dairy cream) that contains only vegetable fat as fat.
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 is more preferable to use an unfermented oil-in-water emulsion. In addition, it is preferable for the oil-in-water emulsion to have foaming properties and not contain a component for solidifying bubbles, such as gelatin or egg white. From this perspective, whipping cream is particularly preferable compared to sour cream, mousse cream, and Bavarian cream.

The pH of the oil-in-water emulsion of the present invention is preferably 6.0 to 8.0, and more preferably 6.5 to 7.5. When the pH of the oil-in-water emulsion of the present invention is equal to or higher than the lower limit of the above range, the emulsion stability before aeration is superior, and when the pH is equal to or lower than the upper limit of the above range, the flavor after aeration is superior.

The viscosity of the oil-in-water emulsion of the present invention at 10°C varies depending on the pH, but 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 equal to or higher than the lower limit of the above range, the texture and flavor after foaming are superior, and when it is equal to or lower than the upper limit of the above range, the foamability and flavor are superior.

In addition, the oil-in-water emulsion of the present invention preferably has a viscosity of less than 5810 mPa·s, even less than 5394 mPa·s, even less than 5000 mPa·s, even 4660 mPa·s or less, even less than 4498 mPa·s, even less than 4049 mPa·s, even 4000 mPa·s or less, even 3390 mPa·s or less, even less than 3153 mPa·s, even 2000 mPa·s or less, or even 1400 mPa·s or less when the pH is changed from 6.5 to 7.5 to around 4.5. Around pH 4.5 is typically pH 4.45 to 4.60. The viscosity of the oil-in-water emulsion of the present invention is almost the same within this range. 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 equal to or lower than the upper limit, sufficient foaming is possible. In particular, if the viscosity is 4000 mPa·s or less, the overrun is 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, from the viewpoint of flavor when foamed.

<Action and effect>
In the embodiment described above, the protein content of the oil-in-water emulsion to be homogenized (first oil-in-water emulsion) is set to less than 1.4% by mass, and the protein-containing raw material is mixed after homogenization, and homogenization of the obtained second oil-in-water emulsion is avoided as much as possible, so that an oil-in-water emulsion (oil-in-water emulsion of the present invention) that contains protein but has excellent acid resistance can be obtained. An acidic 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 a bubble-containing acidic oil-in-water emulsion obtained by foaming the acidic oil-in-water emulsion has excellent shape retention.
The reason for its excellent acid resistance is unclear, but the following hypothesis is considered.
That is, in the past, when producing an oil-in-water emulsion containing protein, the oil-in-water emulsion to be homogenized generally contained 1.4% by mass or more of protein. When such an oil-in-water emulsion is homogenized, a large amount of protein is attached to the surface of the emulsion film of the crushed oil droplets. Therefore, when the pH is lowered, the oil droplets are likely to aggregate with each other due to the aggregation of the protein, and the viscosity is likely to increase.
In contrast, in the present production method, the first oil-in-water emulsion to be homogenized does not contain protein or contains only a small amount of protein, so when it is homogenized, no protein adheres to the surface of the emulsion film of the oil droplets, or only a small amount of protein adheres. And, after mixing the 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. Therefore, even 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, the oil-in-water emulsion of the present invention is unlikely to cause protein aggregation and thicken even when the pH is lowered, so that it has good foaming properties, is unlikely to decrease in hardness after foaming, and is excellent in shape retention. Note that the above is merely a hypothesis added for the purpose of explaining the technical content of the present invention in an easy-to-understand manner.

As described above, the oil-in-water emulsion of the present invention has excellent acid resistance, and can be foamed even when acidic by adding acidic substances such as fruit juice, fruit, etc. In addition, since it can be foamed in both neutral and acidic ranges, it can be used for various purposes.
In addition, in the past, unnecessary ingredients were added to impart acid resistance, which resulted in problems such as changes in taste and flavor, low freedom in product design, etc. In contrast, the present manufacturing method does not require the addition of unnecessary ingredients, so there is no change in taste and flavor and there is a high degree of freedom in product design.

It should be noted that the present manufacturing method is not limited to the above-described embodiment. Each configuration and combination thereof in the above-described embodiment is merely an example, and addition, omission, substitution, and other modifications of the configuration are possible without departing from the spirit of the present invention.
For example, the first oil-in-water emulsion may be an existing one, in which case the preliminary emulsification step does not need to be carried out.
Although an example of homogenizing, sterilizing and cooling the first oil-in-water emulsion using a homogenizer-integrated UHT sterilizer has been shown, there are also models of homogenizing at a stage after sterilization and before cooling as homogenizer-integrated UHT sterilizers, and such models may be adopted. Homogenization and sterilization may be performed in different devices without using a homogenizer-integrated UHT sterilizer. Homogenization can be performed using a known homogenizer. Sterilization can be performed using a known sterilizer.
When sterilization or aging is performed, the timing thereof and the timing of mixing the first oil-in-water emulsion with the protein-containing raw material are not limited to those in the above embodiment.

2 to 5 are each a flow chart showing another embodiment of the present manufacturing method.
In the embodiment shown in Fig. 1, the homogenized first oil-in-water emulsion is mixed with a protein-containing raw material to obtain a second oil-in-water emulsion, and then aging is performed, but in the embodiment shown in Fig. 2, the protein-containing raw material is mixed during aging of the homogenized first oil-in-water emulsion, and aging is continued. Specifically, while the homogenized first oil-in-water 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 a stirring blade that stirs at a low speed, and the mixing step is performed using this stirring blade. Then, aging of the obtained second oil-in-water emulsion is continued as it is.
In the embodiment shown in FIG. 3, the homogenized first oil-in-water emulsion is aged prior to mixing with the protein-containing ingredient.
In the embodiment shown in Fig. 4, sterilization is performed after the mixing step. That is, the homogenized first oil-in-water emulsion is mixed with a protein-containing raw material to obtain a second oil-in-water emulsion, which is then sterilized. In this case, it is not necessary to sterilize the protein-containing raw material in advance. Then, the second oil-in-water emulsion after sterilization and cooling is aged. Even in this case, the second oil-in-water emulsion is not homogenized after the mixing step.
In the embodiment shown in Fig. 5, the homogenized first oil-in-water emulsion is pre-cooled to lower its temperature after heat sterilization, and then mixed with a protein-containing raw material that has also been sterilized and cooled. The second oil-in-water emulsion obtained by mixing is then fully cooled and aged.
As described above, the protein-containing raw material can be mixed with the homogenized first oil-in-water emulsion in various ways.
As described above, the protein content in the first oil-in-water emulsion is reduced to less than 1.4% by mass, but by mixing a protein-containing raw material with the first oil-in-water emulsion, the protein content of the second oil-in-water emulsion will ultimately be greater than that of the first oil-in-water emulsion.

[Oil-in-water emulsion]
An oil-in-water emulsion according to one embodiment of the present invention (hereinafter also referred to as "the emulsion") contains fats and oils, water, and proteins.
The emulsion may further comprise an emulsifier.
The emulsion may further contain other ingredients in addition to those mentioned above.

The oils and fats, proteins, emulsifiers, and other ingredients are the same as those described above, and the preferred embodiments are also the same.

The content of fats and oils is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass, based on the total mass of the emulsion. When the content of fats and oils is equal to or greater than the lower limit of the range, good texture and flavor are easily obtained when whipped, and when the content is equal to or less than the upper limit of the range, the flavor is better when whipped.

The water content is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, based on the total mass of the emulsion. If the water content is equal to or greater than the lower limit of the range, the flavor and smoothness when foamed will be superior, and if the water content is equal to or less than the upper limit of the range, the flavor when foamed will be superior.

The protein content is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 3.0% by mass, based on the total mass of the emulsion. When the protein content is equal to or greater than the lower limit, the emulsion stability before foaming is superior, and when the protein content is equal to or less than the upper limit, the acid resistance of the emulsion is superior.

The content of the emulsifier is preferably 0.1 to 2.0% by mass, and more preferably 0.3 to 1.5% by mass, based on the total mass of the emulsion. When the content of the emulsifier is equal to or greater than the lower limit of the above range, the emulsion stability before foaming is superior, and when the content is equal to or less than the upper limit of the above range, the flavor after foaming is superior.

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, 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, relative to the total mass of the first emulsifier and the second emulsifier.

The emulsion typically has foaming properties. For example, when the emulsion is foamed at 6 to 10°C, a foam with an overrun of 80 to 180% can be obtained. The overrun is preferably 100 to 160%, and more preferably 120 to 150%. The overrun can be determined by the method described in the Examples below.

The emulsion may be a liquid cream.
The present invention can be applied to various emulsions, but in order to maximize the effects of the present invention, it is more preferable to use a non-fermented emulsion. In addition, it is preferable for the foaming emulsion to not contain a component that solidifies bubbles, such as gelatin or egg white. From this perspective, it is particularly preferable to use whipped cream rather than sour cream, mousse cream, or Bavarian cream.

The pH of this emulsion is 6.0 to 8.0, preferably 6.5 to 7.5. If the pH is equal to or higher than the lower limit of the range, the emulsion stability before foaming is excellent, and if the pH is equal to or lower than the upper limit of the range, the flavor after foaming is excellent.

The viscosity of this emulsion at 10°C is 1 to 1000 mPa·s, preferably 50 to 700 mPa·s, and more preferably 100 to 500 mPa·s. If the viscosity of this emulsion is equal to or higher than the lower limit of the above range, the texture and flavor when foamed are excellent, and if the viscosity is equal to or lower than the upper limit of the above range, the foamability and flavor are excellent.

In addition, the viscosity of the present emulsion is preferably less than 5810 mPa·s, further less than 5394 mPa·s, further less than 5000 mPa·s, further less than 4660 mPa·s, further less than 4498 mPa·s, further less than 4049 mPa·s, further less than 4000 mPa·s, further less than 3390 mPa·s, further less than 3153 mPa·s, further less than 2000 mPa·s, further less than 1400 mPa·s when the pH is changed from 6.5 to 7.5 to around 4.5. Around pH 4.5, typically, pH is 4.45 to 4.60. The viscosity of the present emulsion is almost 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 highest around pH 4.5. The lower the viscosity at pH 4.5, the better the acid resistance. Also, if the viscosity at around pH 4.5 is equal to or lower than the upper limit, sufficient foaming is possible. In particular, if the viscosity is 4000 mPa·s or less, the overrun is good, and if it is 2000 mPa·s or less, it is 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, and more preferably 100 mPa·s or more, from the viewpoint of flavor when foamed.

This emulsion has an amount of protein precipitation exceeding 0% by volume as measured by the following measurement method.
Method for measuring the amount of protein precipitation: 50 mL of a sample (oil-in-water emulsion) was placed in a graduated centrifuge tube, and centrifuged using a centrifuge at a relative centrifugal acceleration of 1630 × g for 5 minutes. The volume (mL) of the protein precipitated in the centrifuge tube was then measured visually, and the ratio (volume %) of the volume of the protein to the total volume of the oil-in-water emulsion was defined as the amount of protein precipitation.
The amount of protein precipitation is an index of the amount of protein present in a free state in the continuous phase (aqueous phase) of the emulsion. When the amount of protein precipitation is more than 0% by volume, the emulsion has excellent acid resistance.
The amount of protein precipitation in the emulsion is preferably 0.1% by volume or more. The upper limit of the amount of protein precipitation is not particularly limited, but is, for example, 2.0% by volume.

The present emulsion can be produced, for example, by the present production method described above.
Conventionally, in the production of oil-in-water emulsions containing proteins, the aqueous phase containing proteins and the oil phase are usually mixed and then homogenized. It is presumed that the oil-in-water emulsions thus obtained have oil droplets scattered as a dispersed phase in the aqueous phase, which is the continuous phase, and that the proteins in the aqueous phase cover and firmly adhere to the surfaces of the oil droplets through homogenization. For this reason, it is considered that the amount of protein present in the continuous phase of the oil-in-water emulsions produced by the conventional method is small.
On the other hand, in the above-mentioned production method of the present invention, since the protein content of the first oil-in-water emulsion is lower than that of the conventional method, the amount of protein adhering to the surface of the oil droplets is small even after the first oil-in-water emulsion is homogenized. Then, the protein-containing raw material is mixed thereafter, and homogenization is not performed as much as possible thereafter, so that it is considered that a large amount of protein exists in the continuous phase.
However, the method for producing the present emulsion is not limited to this.

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

The oil-in-water emulsion produced by the present production method or the present emulsion can be used for whipping, cooking, and the like.
The oil-in-water emulsion produced by the present production method or the present emulsion is particularly useful for whipping.

For whipping purposes, the oil-in-water emulsion obtained by the present production method or the present emulsion is whipped to form an air bubble-containing oil-in-water emulsion (such as whipped cream).
Here, the term "foaming" is not particularly limited, but refers to incorporating air bubbles into an oil-in-water emulsion by subjecting it to physical stress such as stirring or contacting it with air. In this case, it is preferable to whip the emulsion until it is 60% to 90% whipped.
Before foaming, a carbohydrate may be blended with the oil-in-water emulsion obtained by the present production method or with the present emulsion.
The amount of carbohydrate is preferably 0 to 10% by mass based on the total mass of the oil-in-water emulsion obtained by the present production method or the present emulsion. When the amount of carbohydrate is equal to or less than the upper limit, the flavor of the obtained bubble-containing oil-in-water emulsion is good.

The resulting bubble-containing oil-in-water emulsion may be frozen as is to form a frozen bubble-containing oil-in-water emulsion.
The resulting bubble-containing oil-in-water emulsion may be made into a package of frozen bubble-containing oil-in-water emulsion. For example, the bubble-containing oil-in-water emulsion may be filled directly into a container and preferably sealed to obtain a package of the bubble-containing oil-in-water emulsion.
Before freezing, the gas bubble-containing oil-in-water emulsion may be filled and sealed in a packaging container for storage or distribution, and after freezing, the frozen gas bubble-containing oil-in-water emulsion may be filled and sealed in a packaging container for storage or distribution.

The oil-in-water emulsion obtained by the present production method or the present emulsion has excellent acid resistance, so even if the oil-in-water emulsion becomes acidic, it can be foamed to form a bubble-containing oil-in-water emulsion. Therefore, an acidic material can be added to the oil-in-water emulsion obtained by the present production method or the present emulsion to adjust the pH to acidic to form an acidic oil-in-water emulsion. In addition, this acidic oil-in-water emulsion can be foamed to form a bubble-containing acidic oil-in-water emulsion.
The pH of the acidic oil-in-water emulsion is preferably 2.0 to 6.5, more preferably 3.0 to 5.5, from the viewpoint of the texture when foamed.

In addition, the oil-in-water emulsion obtained by the present production method or the bubble-containing oil-in-water emulsion obtained by foaming the present emulsion has excellent acid resistance, so that an acidic material can be added to the bubble-containing oil-in-water emulsion to adjust the pH to acidic to produce an acidic bubble-containing oil-in-water emulsion.
The pH of the acidic bubble-containing oil-in-water emulsion is preferably 2.0 to 6.5, more preferably 3.0 to 5.5, from the viewpoint of texture.

Acidic materials include edible acidic compounds, crushed, ground or fragmented pieces, juices, and the like of acidic foods.
Examples of the acidic compound include organic acids such as citric acid, lactic acid, acetic acid, oxalic acid, glucuronic acid, and carbonic acid; and inorganic acids such as phosphoric acid.

Examples of acidic foods include processed products of sour fruits and/or vegetables. Examples of processed acidic foods include sour fruit juice and fruit pulp; sour vegetable juice and vegetable pieces. Examples of processed acidic foods include purees, pastes, sauces, jams, juices, etc., which may be used alone or in appropriate combination.
Generally, "puree" refers to crushed and strained fruits and/or vegetables, and can be used raw or cooked. "Paste" generally refers to something thicker than puree. "Fruit sauce" includes fruit puree thickened with starch or jam.
Examples of fruit juice and pieces of fruit include citrus fruits such as lemon, orange, sudachi, and bitter orange, strawberry, raspberry, grape, pineapple, blueberry, kiwi fruit, apple, etc. Examples of vegetable juice and pieces of vegetable include tomato, etc.

As the acidic food, processed products of acidic fruits and/or vegetables are suitable.
The processed product of acidic fruits and/or vegetables is preferably one or more selected from crushed products, pressed products, juices, purees, and sauces.
The amount of the acidic food added is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 10 to 100 parts by mass, per 100 parts by mass of the oil-in-water emulsion or bubble-containing oil-in-water emulsion.
The oil-in-water emulsion obtained by the present production method or the present emulsion can be used not only for acidic compounds or acidic foods but also for a wide range of foods and the like.

Conventionally, when producing an acidic food-containing, air-containing oil-in-water emulsion, a production method called "separate mixing" or "co-mixing" is generally used. When producing an air-containing oil-in-water emulsion, other ingredients such as gelatin may be added.
"Combined whipping" is a method for producing an air-bubble-containing oil-in-water emulsion containing an acidic food, which includes a step of mixing and whipping an acidic food and an oil-in-water emulsion to obtain an air-bubble-containing oil-in-water emulsion containing an acidic food. "Separate whipping" is a method for producing an air-bubble-containing oil-in-water emulsion containing an acidic food, which includes a step of whipping the oil-in-water emulsion to obtain an air-bubble-containing oil-in-water emulsion containing an acidic food, and a step of mixing the obtained air-bubble-containing oil-in-water emulsion with an acidic food to obtain an air-bubble-containing oil-in-water emulsion containing an acidic food.
Conventionally, when a general oil-in-water emulsion (e.g., fresh cream) is mixed with an acidic food and whipped, the texture of the resulting bubble-containing oil-in-water emulsion becomes lumpy due to the influence of the acidic food. For this reason, the bubble-containing oil-in-water emulsion obtained by "mixing together" has poor texture and flavor. Therefore, in order to improve the texture and flavor, "separate mixing" is usually used for small-scale production in stores, etc. However, this "separate mixing" requires at least two steps, and the work efficiency is poor. Therefore, in the case of mass production, a method of producing an air-containing oil-in-water emulsion containing an acidic food by "mixing together" with the addition of conventional stabilizers, etc. has been adopted, but the bubble-containing oil-in-water emulsion obtained by this "mixing together" tends to have difficulty in improving the texture and flavor due to the influence of conventional stabilizers, etc.
The oil-in-water emulsion obtained by the present production method or the present emulsion has excellent acid resistance, so that a bubble-containing oil-in-water emulsion containing acidic food with good texture and flavor can be produced by "co-mixing" without the addition of conventional stabilizers, etc.

The resulting bubble-containing acidic oil-in-water emulsion may be frozen to form a frozen bubble-containing acidic oil-in-water emulsion.
Before freezing, the bubble-containing acidic oil-in-water emulsion may be filled and sealed in a packaging container for storage or distribution, and after freezing, the frozen bubble-containing acidic oil-in-water emulsion may be filled and sealed in a packaging container for storage or distribution.
The frozen bubble-containing acidic oil-in-water emulsion is thawed when in use and used as the bubble-containing acidic oil-in-water emulsion.

The obtained bubble-containing oil-in-water emulsion or bubble-containing acidic oil-in-water emulsion can be used, for example, as whipped cream; whipped cream containing acidic foods; whipped cream for decorating cakes, pancakes, confectionery, jellies, puddings, ice creams, frozen dairy products, and the like; whipped cream for Vienna coffee, juice, beverages, and the like. Examples of whipped cream containing acidic foods include whipped cream containing processed fruits and/or vegetables with sour tastes. Examples include whipped cream containing fruit and/or vegetable purees, and whipped cream containing fruit and/or vegetable juices (e.g., whipped cream containing citrus juice, etc.).

Foods that use oil-in-water emulsions or acidic oil-in-water emulsions, or bubble-containing oil-in-water emulsions or bubble-containing acidic oil-in-water emulsions include roll cakes and tarts with lemon-flavored whipped cream that have a stronger fruity feel, shortcakes and decorated cakes that use mandarin whipped cream, jellies and puddings topped with strawberry-flavored whipped cream, sandwiches with whipped cream flavored with fruit juice, cream puffs and breads filled with cream or fillings that contain fruit juice, etc.

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, unless otherwise specified, "%" refers to "% by mass" except for the % of overrun. "Parts" refers to "parts by mass." The creams of Examples 1 to 8 correspond to the oil-in-water emulsions of the present invention.

<Test Example 1>
(Cream production)
In this test example, five types of creams were produced as oil-in-water emulsions according to Table 1. These creams had the same overall composition. The overall composition of each cream is shown in Table 2. The procedure for producing each cream is roughly as follows. That is, first, the aqueous phase and the oil phase are prepared separately, and these are premixed to obtain 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 obtain a second oil-in-water emulsion. The second oil-in-water emulsion is then aged to obtain the creams of Examples 1 to 3 and Comparative Examples 1 and 2.
This test example was carried out to evaluate the effect of the protein concentration of the first oil-in-water emulsion on the acid resistance of the final cream (oil-in-water emulsion).

Detailed procedures for making each example cream are provided below.
In Examples 1 to 3 and Comparative Example 1, first, an aqueous phase was prepared by dissolving an emulsifier and skim milk powder in water with stirring according to the composition of the aqueous phase in Table 1. As the emulsifier for the aqueous phase, the following two types of emulsifiers A and B were used in a mass ratio of emulsifier A:emulsifier B = 2:1. Emulsifiers A and B differ in the fatty acids that constitute the polyglycerol fatty acid ester.
Emulsifier A: Polyglycerol fatty acid ester (manufactured by Sakamoto Pharmaceutical Industry Co., Ltd., HLB approximately 12).
Emulsifier B: Polyglycerol fatty acid ester (manufactured by Sakamoto Pharmaceutical Industry Co., Ltd., HLB approximately 12).
An oil phase was prepared by dissolving an emulsifier and soybean lecithin in vegetable oil according to the composition of the oil phase in Table 1. The emulsifier used in the oil phase was polyglycerol fatty acid ester (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., HLB approximately 5). Palm kernel oil was used as the vegetable oil.
The aqueous phase was then heated to 70°C while stirring, and the oil phase, which had also been heated to 70°C, was added thereto and premixed to prepare a synthesis part. The synthesis part was preemulsified 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 first oil-in-water emulsion was passed through a homogenizer (manufactured by Sanmaru Machinery Co., Ltd.), preheated to 70° C., and homogenized under a pressure of 9.0 MPa. Thereafter, the emulsion was subjected to heat sterilization at a temperature of 80° C., 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, processed starch, and trisodium citrate were dissolved in water to prepare a protein-containing raw material. This protein-containing raw material was batch sterilized until it reached 80°C, then cooled to about 5°C and added to an aging tank storing the homogenized first oil-in-water emulsion. The first oil-in-water emulsion and the protein-containing raw material were mixed with a stirring blade in the aging tank to obtain a second oil-in-water emulsion. This second oil-in-water emulsion was further aged in a refrigerator at 5°C for 24 hours. As a result, a cream with an oil content of 35% and a protein content of 2.87% was obtained.
In Comparative Example 2, a cream with 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 all of the ingredients blended in the protein-containing raw material were blended in the aqueous phase and no protein-containing raw material was added to the homogenized first oil-in-water emulsion.
The fat and oil content and protein content were values calculated from the formulation. The pH was measured using a pH meter (HORIBA).

The resulting cream (hereinafter also referred to as "neutral cream") was subjected to the following acid resistance test 1, foaming test, acid resistance test 2, and measurement of the amount of protein precipitation.

(Acid resistance test 1)
1.0 mL of 10% citric acid solution was added to 200 g of neutral cream, and the pH and viscosity were measured. The pH measurement method was as described above. The viscosity measurement method is as follows.

"viscosity"
The viscosity was measured using a Brookfield viscometer (TOKI Corporation) at 30 seconds and 60 rpm, with the upper limit of the viscosity measurement being 10,000 mPa·s.

The measurement results (horizontal axis: pH, vertical axis: viscosity) are shown in Figure 6. Table 3 shows the measurement results of the viscosity of the cream before the addition of the citric acid solution and the viscosity of the cream (hereinafter also referred to as "acidic cream") to which the citric acid solution was added to adjust the pH to about 4.5 (the isoelectric point of casein). Figure 7 shows the viscosity of the acidic cream adjusted to about pH 4.5. Figure 8 shows a scatter diagram and 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) at about pH 4.5.
In addition, when the pH of a cream that is not acid-resistant is brought to about 4.5, the cream thickens and becomes unable to be whipped, or even if it can be whipped, the specific gravity of the whipped cream becomes high. On the other hand, when the cream is acid-resistant, the specific gravity of the whipped cream becomes low.

The creams of Comparative Examples 1 and 2 had a viscosity of 5810 mPa·s or more when the pH was lowered to about 4.5 to make them acidic. In contrast, the creams of Examples 1 to 3 had a viscosity of 5000 mPa·s or less when the pH was lowered to about 4.5. A viscosity of 5000 mPa·s or less makes the creams particularly whippable.
A comparison of Examples 1 to 3 and Comparative Examples 1 and 2 shows that even if the final composition was the same, the lower the protein content of the first oil-in-water emulsion, the more suppressed the thickening when the pH was lowered to around 4.5 and the better the foaming properties.
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. Therefore, 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, from Fig. 8, it can be understood that the viscosity of the acidic cream at around pH 4.5 is linear for Examples 1 to 3 and Comparative Example 1. Therefore, 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 be said that the preferred viscosity range of the acidic cream is less than 5394 mPa·s based on the regression equation.
In addition, since the protein content of the first oil-in-water emulsion that results in a more preferred viscosity of 5000 mPa·s is 1.2% when calculated backwards from the regression equation, it is estimated that the more preferred range of the protein content of the first oil-in-water emulsion is 1.2% or less. Among these, 1.0% or less is preferable, the value of Example 3 (0.8%) or less is more preferable, the value of Example 2 (0.4%) or less is even more preferable, and the vicinity of Example 1 (near approximately 0%) is particularly preferable.

(Foaming test)
Sweetened cream was obtained by adding 64 g of sugar to 800 g of neutral cream. The obtained sweetened cream was whipped using a mixer (Kenmix) at 180 rpm for the whipping time shown in Table 4 to obtain whipped cream. The end point of whipping was when the hardness of the whipped cream reached 20±1 mm in terms of Penetro penetration (hereinafter also referred to as "Penetro value"). The overrun and Penetro value of the whipped cream were measured by the following measurement method. The overrun values of the obtained whipped cream are shown in Table 4.

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

"Penetro value (Penetro penetration)"
The Penetro value is a value (unitless) calculated by multiplying the penetration distance (mm) of a specific cone dropped into a composition under specified conditions by 10. The larger this value, the softer the composition is.
Specifically, using a penetrometer, an aluminum cone having a base diameter of 24 mm, a height of 33.5 mm, a tip angle of 40°, and weighing 12 g was penetrated into the sample, the penetration depth (mm) was measured, and the measured value was multiplied by 10 to obtain the penetro value.

The creams of Examples 1 to 3 and Comparative Examples 1 and 2 all had foaming properties at neutral pH.

(Acid resistance test 2)
400 g of the neutral cream of Example 1, Example 3, or Comparative Example 1 was placed in a mixer (De'Longhi Chef Classic), and a 10% citric acid solution was added to adjust the pH to 4.5 or less. The mixture was then whipped at a rotation speed of 180 rpm for the whipping time shown in Table 5 to obtain whipped cream.
The pH of the cream before whipping (after pH adjustment), the temperature during whipping (at the start of whipping → at the end of whipping), the specific gravity, overrun and penetro value of the whipped cream are shown in Table 5.
The whipped cream thus obtained was stored in a refrigerator at 5°C for 24 hours, after which the penetro value (penetro value after 1 day) was measured, and the difference from the penetro value at the end of whipping (penetro value after 1 day - penetro value at the end of whipping) (hereinafter also referred to as "penetro value difference after 1 day") was calculated. From the results, the condition after 1 day was evaluated according to the following criteria. The results are shown in Table 5.
×: Penetro value difference after one day is +100 or more.
△: The difference in penetro value after one day is between +50 and +100.
○: The difference in penetro value after one day is between -15 and +50.
△: The difference in penetro value after one day is between -25 and -15.
×: The difference in penetro value after one day is less than -25.
The methods for measuring pH, overrun and penetro value are as described above.

Compared to the cream of Comparative Example 1, the creams of Examples 1 and 3 showed less change in state after the acidic material was added and foamed.

(Measurement of protein precipitation amount)
The amount of protein precipitation was determined for three types of cream: Example 1 (protein content of first oil-in-water emulsion: 0%/protein content of cream: 2.87%), Example 3 (protein content of first oil-in-water emulsion: 0.8%/protein content of cream: 2.87%), and Comparative Example 1 (protein content of first oil-in-water emulsion: 1.4%/protein content of cream: 2.87%), by the following procedure.
50 mL of the sample (cream) was dispensed into a graduated centrifuge tube and centrifuged at 3000 rpm for 5 minutes using a centrifuge (Hitachi mini centrifuge himac CT6E, rotor "T4SS swing type"). 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 amount of precipitated protein (mL) in the centrifuge tube was visually confirmed. From this amount of precipitate (mL), the ratio (volume %) of the volume of precipitated protein to the total volume of the sample was calculated, and this was taken as the amount of precipitated protein. The results are shown in Table 6.
In addition, because the conditions of the centrifugation in this test are severe, it is unrelated to the occurrence of precipitation when the sample is left to stand normally. In other words, the amount of precipitation in this test has no relation whatsoever to the product quality, such as the length of storage period of each sample.

As described above, in Comparative Example 1 in which the protein content of the first oil-in-water emulsion was 1.4%, the amount of protein precipitation was 0%.
In contrast, the amount of protein precipitation was greater than 0% in the creams of Examples 1 and 3. Furthermore, the amount of protein precipitation increased as the protein content of the first oil-in-water emulsion decreased.

<Test Example 2>
This test example was carried out to verify whether similar results could be obtained by adding the modified starch and trisodium citrate added to the protein-containing raw material in Examples 1 to 3 to the aqueous phase.

The 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.
The cream thus obtained was subjected to the above-mentioned foaming test and acid resistance test under neutral conditions. The results of the foaming 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.

In Example 4, the whipping time was about 1 minute shorter than in Example 1, and the viscosity was also reduced. The overrun was about the same. In the acid resistance test, as in Example 1, no sudden increase in viscosity was observed even when the pH was lowered. From this, it is considered that the timing of adding the modified starch and trisodium citrate can be either before or after homogenization.

<Test Example 3>
This test example was carried out to evaluate the effect of the protein concentration of the cream on the acid resistance of the cream.

Creams of Examples 5 to 7 were 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 9. The overall composition of each cream (second oil-in-water emulsion) is 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.
The obtained cream was subjected to the above-mentioned foaming property test and acid resistance test. The results of the foaming property test are shown in Table 11, and the results of the acid resistance test are shown in Figure 10. Figure 10 shows the results of Example 1 and Comparative Example 2.

As shown in the above results, in the whipping test, as the protein content of the cream increased, the whipping time increased and the overrun decreased.
In the acid resistance test, thickening was suppressed when the pH was lowered in all of Examples 5 to 7. In particular, the results were good when the protein content of the cream was less than 5.00%, particularly 3.00% or less.

Example 8
The cream of Example 8 was obtained by mixing 200 g of the cream of Example 1 and 200 g of fruit puree (raspberry, 15% sugar added, manufactured by Boiron).
The obtained cream was whipped at 180 rpm using a DeLonghi whipper (Kitchen Machine Chef Classic) to obtain whipped cream.
The pH of the cream before whipping (after mixing of the fruit puree), the temperature during whipping (at the start of whipping → at the end of whipping), the whipping time, the specific gravity of the whipped cream, the overrun and the penetro value (penetro penetration) are shown in Table 12.
The obtained whipped cream was stored in a refrigerator at 5°C for 24 hours, and then the penetro value (penetro value after 1 day) was measured, and the penetro value difference 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 methods for measuring pH, overrun and penetro value are as described above.

The cream of Example 8 showed less change in state after foaming than the cream of Comparative Example 1.

In the present invention as described above, the protein content of the first oil-in-water emulsion may be either 0% or in the range of 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 consisting of a protein source, fats and oils, water, and other raw materials, comprising the steps of: mixing all of the fats and oils, a portion of the water, and a portion of the other raw materials, and homogenizing and sterilizing them to prepare a first oil-in-water emulsion; mixing the remainder of the water, the remainder of the other raw materials, and the protein source, and sterilizing them 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 consisting of a protein source, fats and oils, water, and other raw materials, comprising the steps of: mixing all of the fats and oils, a portion of the water, a portion of the other raw materials, and a portion of the protein source, homogenizing and sterilizing the mixture 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 sterilizing the mixture 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 (13)

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. 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. 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 claim 1 , wherein the second oil-in-water emulsion is not homogenized after the step of obtaining the second oil-in-water emulsion. 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 claim 1 , 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. 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. 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. 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. 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. 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. A method for producing an acidic oil-in-water emulsion, comprising adding an acidic material to the oil-in-water emulsion produced by the 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. 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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