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

Abstract

The present invention provides a method for producing an oil-in-water emulsion that can foam when an acidic material is added and has excellent shape retention after foaming. [Solution] A first oil-in-water emulsion containing oil and water, with a protein content of 0.8% by mass or less, is homogenized to obtain a homogenized first oil-in-water emulsion; A method for producing an oil-in-water emulsion, comprising the steps of: mixing the homogenized first oil-in-water emulsion with a milk protein-containing raw material to obtain a second oil-in-water emulsion, wherein, prior to the step of obtaining the second oil-in-water emulsion, the first oil-in-water emulsion and / or the milk protein-containing raw material are sterilized.

Description

【Technical Field】 【0001】 The present invention relates to a method for producing an oil-in-water emulsion, a method for producing a bubble-containing oil-in-water emulsion, a method for producing a frozen bubble-containing oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion, a method for producing a bubble-containing acidic oil-in-water emulsion, and an oil-in-water emulsion. 【Background Art】 【0002】 Cream is used for various purposes. For example, whipped cream obtained by foaming edible cream such as fresh cream and compound cream is used for decorating confectionery such as cakes and fruits, or floating on beverages such as Vienna coffee. As cream, for example, an oil-in-water emulsion containing fats and oils, water, and proteins is used. Such an oil-in-water emulsion is generally produced by mixing an aqueous phase portion containing water and proteins 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 skim concentrated 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 refreshing taste with a sour 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, and when the pH decreases, the proteins in the oil-in-water emulsion aggregate, 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. Also, even if an acidic material is mixed after foaming the oil-in-water emulsion, the aggregation of proteins deteriorates the texture of the whipped cream. For this reason, there has been a need for a technique for imparting acid resistance to an oil-in-water emulsion, particularly a technique for imparting a property (acid resistance) that allows foaming operation without an increase in viscosity even when the pH becomes low. Methods for imparting acid resistance to oil-in-water emulsions include modifying the emulsifier formulation (Patent Document 2), modifying the type of protein used (Patent Document 3), and adding an acid-resistant agent such as fermented cellulose (Patent Document 4). [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Patent No. 6612491 [Patent Document 2] Japanese Patent Application Publication No. 8-126470 [Patent Document 3] Japanese Patent Publication No. 2014-79234 [Patent Document 4] Japanese Patent Publication No. 2015-57948 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 However, the methods described in Patent Documents 2 and 3 employ specific emulsifiers and proteins to impart acid resistance, thus restricting the types of emulsifiers and proteins that can be incorporated. This limits the room for innovation in the formulation of emulsifiers and proteins during product design, resulting in a lack of freedom in product design. The method described in Patent Document 4 had the problem that, in order to impart acid resistance, an unnecessary acid-resistance imparting agent was added, resulting in a flavor that differed from the original flavor of the oil-in-water emulsion and increasing the cost of the product. Furthermore, this method also had the problem of limiting the degree of freedom in product design. Furthermore, even if conventional techniques could foam oil-in-water emulsions with added acidic materials, the resulting whipped cream often lacked sufficient shape retention, and its hardness tended to decrease over time. Therefore, there is a need for a technology that can produce oil-in-water emulsions that are not restricted by specific raw materials, do not contain unnecessary components, can be foamed when acidic materials are added, allow for free product design, and have excellent shape retention after foaming. 【0006】 One aspect of the present invention aims to provide a method for producing an oil-in-water emulsion that can foam when an acidic material is added and has excellent shape retention after foaming, a method for producing an oil-in-water emulsion containing bubbles using this method, a method for producing an oil-in-water emulsion containing frozen bubbles, a method for producing an acidic oil-in-water emulsion, a method for producing an acidic oil-in-water emulsion containing bubbles, and an oil-in-water emulsion that can foam when an acidic material is added and has excellent shape retention after foaming. [Means for solving the problem] 【0007】 [1] A step of homogenizing a first oil-in-water emulsion containing oil and water and having a protein content of less than 1.4% by mass to obtain a homogenized first oil-in-water emulsion, A method for producing an oil-in-water emulsion, comprising the step of mixing the homogenized first oil-in-water emulsion with 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 the second oil-in-water emulsion is not homogenized after the step of obtaining the second oil-in-water emulsion. [3] A method for producing the oil-in-water emulsion according to [1] or [2], wherein the 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 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 of [1] to [4], wherein the pH of the oil-in-water emulsion produced by the above 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 around 4.5 is less than 5810 mPa·s. [6] A method for producing an oil-in-water emulsion containing bubbles, comprising foaming an oil-in-water emulsion produced by any of the methods described in [1] to [5] above to form an oil-in-water emulsion containing bubbles. [7] A method for producing a frozen bubble-containing oil-in-water emulsion, comprising freezing a bubble-containing oil-in-water emulsion produced by the method described in [6] above to obtain a frozen bubble-containing oil-in-water emulsion. [8] A method for producing an acidic oil-in-water emulsion, comprising adding an acidic material to an oil-in-water emulsion produced by any of the methods described in [1] to [5] above, and adjusting the pH to a range of 3.0 to 6.5 to produce an acidic oil-in-water emulsion. [9] A method for producing a bubble-containing acidic oil-in-water emulsion, comprising foaming an acidic oil-in-water emulsion produced by the method described in [8] above to form a bubble-containing acidic oil-in-water emulsion.

[10] Oil-in-water emulsion containing oils and fats, 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 is around 4.5 is less than 5810 mPa·s. An oil-in-water emulsion in which the amount of protein precipitate measured by the following measurement method exceeds 0 volume%. Method for measuring the amount of protein precipitate: 50 mL of the oil-in-water emulsion is placed in a graduated centrifuge tube, and centrifugation is performed using a centrifuge at a relative centrifugal acceleration of 1630 × g for 5 minutes. The volume (mL) of protein precipitated in the centrifuge tube is then visually measured, and the ratio (volume %) of the volume of protein to the total volume of the oil-in-water emulsion is defined as the amount of protein precipitate. Furthermore, the present invention may also take the following forms. [1A] A step of homogenizing a first oil-in-water emulsion containing oil and water and having a protein content of 0.8% by mass or less to obtain a homogenized first oil-in-water emulsion, A method for producing an oil-in-water emulsion, comprising the step of mixing the homogenized first oil-in-water emulsion with a milk protein-containing raw material to obtain a second oil-in-water emulsion. [2A] The method for producing an oil-in-water emulsion according to [1A], wherein in the first oil-in-water emulsion, the ratio of the protein to the oil and fat is 1.6% by mass or less. [12A] A step of subjecting a first oil-in-water emulsion containing oil and fat 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 milk protein-containing raw material to obtain a second oil-in-water emulsion. An oil-in-water emulsion is produced by the method for producing an 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 and adjusting the pH to a range of 3.0 to 5.5 to form an acidic oil-in-water emulsion. 【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 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 oil-in-water emulsion that can be foamed when acidified and has excellent shape retention after foaming. 【Brief Description of the Drawings】 【0009】 [Figure 1] It is a flowchart showing a method for producing an oil-in-water emulsion according to an embodiment. [Figure 2] It is a flowchart showing a method for producing an oil-in-water emulsion according to another embodiment. [Figure 3] It is a flowchart showing a method for producing an oil-in-water emulsion according to another embodiment. [Figure 4] It is a flowchart showing a method for producing an oil-in-water emulsion according to another embodiment. [Figure 5] It is a flowchart showing a method for producing an oil-in-water emulsion according to another embodiment. [Figure 6] It is a graph showing the acid resistance test results of Test Example 1. [Figure 7] It is a graph showing the acid resistance test results of Test Example 1. [Figure 8] It is a scatter diagram and a regression equation showing the relationship between the protein content of the first oil-in-water emulsion and the viscosity near pH 4.5 of the cream (oil-in-water emulsion). [Figure 9] It is a graph showing the acid resistance test results of Test Example 2. [Figure 10] It is a graph showing the acid resistance test results of Test Example 3. 【Mode 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. Generally, however, the protein content can also be measured by the semi-micro Kjeldahl method (Explanation of the Fourteenth Revised Japanese Pharmacopoeia, General Rules, General Rules for Manufacture, General Test Methods 2001 B-370 to B374). The specific measurement method is shown below. About 1 g of the sample (the mass of the sample is measured to the unit of 0.1 mg) is taken, and the nitrogen amount in the sample is quantified by the semi-micro Kjeldahl method. Specifically, the sample is put into a decomposition flask, 1 g of a decomposition accelerator with a formulation of potassium sulfate: copper sulfate = 10:1 (mass ratio) is added, and further 7 mL of concentrated sulfuric acid is added, followed by heat decomposition. After heat decomposition, the sample is subjected to steam distillation, and the distilled product is received in 20 mL of a 20 mM sulfuric acid aqueous solution. When the distillation is completed, the 20 mM sulfuric acid aqueous solution that has received distilled water is titrated with 40 mM sodium hydroxide. Let the titration amount at that time be b (mL). A blank test is carried out using a control sample containing no protein instead of the sample, and let the titration amount 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 amount of the sample with respect to 1 mL of 40 mM sodium hydroxide, and 6.38 is the coefficient for converting the nitrogen amount to the protein of dairy products. In this invention, the oil and fat content of the oil-in-water emulsion can also be calculated from the raw material composition. However, generally speaking, the fat content can also be measured using the Reese-Gottlieb method (Food Hygiene Inspection Guidelines, Physical and Chemical Section, 2005, pp. 48-49: supervised by the Ministry of Health, Labour and Welfare). The specific measurement method is shown below. First, 1 g of the sample is placed in a beaker, and while rinsing the beaker with approximately 10 mL of warm water, it is transferred to an extraction tube. 2 mL of ammonia water and 1 drop of phenolphthalein reagent are added to the extraction tube, the tube is stoppered, and it is mixed well. Then, 10 mL of ethanol is used to rinse the beaker containing the sample, and this is added to the extraction tube, the tube is stoppered, and it is mixed well. Next, 25 mL of ether is added, the tube is stoppered, and it is shaken vigorously for 30 seconds. Finally, 25 mL of petroleum ether is added, the tube is stoppered, and it is shaken vigorously for 30 seconds. After standing until the upper layer becomes clear, the ether layer is decanted carefully into a pre-weighted dish to recover the organic solvent. This 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 weighing this dish. The oil content is calculated from these measurements using the following formula. Oil and fat content (mass %) = (amount of extracted fat / amount of sample used) × 100 Viscosity is measured using a Type B viscometer. pH values ​​are given at 10°C unless otherwise specified. Relative centrifugal acceleration is calculated using the following formula. RCF = 1118 × r × N 2 ×10 -8 Here, RCF represents the relative centrifugal acceleration (×g), r represents the maximum turning radius (cm), and N represents the rotations per minute (rpm). In this specification, "excellent acid resistance" means that foam can be generated when an acidic material is added, and that the material has excellent shape retention after foaming. 【0011】 [Method for producing oil-in-water emulsions] A method for producing an oil-in-water emulsion according to one aspect of the present invention (hereinafter also referred to as "this production method") comprises the steps of: homogenizing a first oil-in-water emulsion containing oil and water and having 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 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 explained in detail later. 【0012】 In this manufacturing method, it is preferable not to homogenize the second oil-in-water emulsion after the mixing step. "Not homogenizing the second oil-in-water emulsion" means that no mechanical operation is intentionally performed to break down the fat globules in the second oil-in-water emulsion. Note that if the fat globules are naturally broken down by impact or other means during handling of the second oil-in-water emulsion, this is not considered "homogenization of the second oil-in-water emulsion" as defined herein. 【0013】 This manufacturing method may include a step (hereinafter also referred to as the "pre-emulsification step") in which, before the homogenization step, an oil phase containing oil and fat is mixed (pre-mixed) with an aqueous phase containing water, and then emulsified (pre-emulsified) using a mixing device such as a homomixer to prepare a first oil-in-water emulsion. The process may include a step prior to the preliminary emulsification step in which the oil is heated and melted, and other oil-soluble components (such as the first emulsifier described later) are dissolved in the oil as needed to prepare the oil phase. Prior to the preliminary emulsification step, the process may include a step in which water is used directly as the aqueous phase, or in which other water-soluble components (such as a second emulsifier, protein-containing raw material, or chelating agent, as described later) are added to the water to prepare the aqueous phase. The process may include a step of heating (preheating) the first oil-in-water emulsion before the homogenization step. The process may include a step of sterilizing the first oil-in-water emulsion before or after the homogenization step. The process may include a step of aging the first oil-in-water emulsion after the homogenization step. The process may include a step to sterilize the protein-containing raw materials before the mixing process. The process may include a step to homogenize the protein-containing raw materials before the mixing step. However, if the protein-containing raw materials typically do not contain oils or fats, then it is not necessary to homogenize the protein-containing raw materials themselves. The process may include a step of sterilizing the second oil-in-water emulsion after the mixing step. The process may include a step of aging the second oil-in-water emulsion after the mixing step. The oil-in-water emulsion produced by this manufacturing method is typically a second oil-in-water emulsion, an aged second oil-in-water emulsion, or a sterilized and aged second oil-in-water emulsion. Hereinafter, the oil-in-water emulsion produced by this manufacturing method will also be referred to as "the oil-in-water emulsion of the present invention." 【0014】 The following description of this manufacturing method will be given with reference to the attached drawings and examples. Figure 1 is a flowchart showing one embodiment of the manufacturing method. In this embodiment, first, the oil and fat from the raw materials are heated and melted, and other oil-soluble components are dissolved in the oil and fat as needed to prepare the oil phase. Separately, the water from the raw materials is used as the aqueous phase, or other water-soluble components are dissolved in the water to prepare the aqueous phase. These preparations are carried out by heating the oil and fat or water to an appropriate temperature. Next, the oil phase and the aqueous phase are placed in a tank equipped with a stirrer, for example, and pre-mixed. Then, the stirrer is operated, for example, to thoroughly mix the oil phase and the aqueous phase to pre-emulsify them. This prepares the first oil-in-water emulsion. In this first oil-in-water emulsion, it is necessary to keep the protein content low, and the protein content of the first oil-in-water emulsion is less than 1.4% by mass. 【0015】 Next, the first oil-in-water emulsion is passed through a UHT sterilization apparatus with an integrated homogenizer. A UHT sterilization apparatus with an integrated homogenizer typically includes a heat exchanger and a homogenizer. The first oil-in-water emulsion is first preheated by the heat exchanger, preferably to 65-75°C. Then, it is homogenized by the homogenizer. The set pressure (homo-pressure) for homogenizing the first oil-in-water emulsion is preferably 1.0-15.0 MPa, more preferably 3.0-15.0 MPa, and even more preferably 5.0-12.0 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 sterilize it. The sterilization conditions are not particularly limited and can be those of known type. For example, heating at 90°C for 15 seconds, or heating conditions that yield an equivalent sterilization effect, are used. Afterward, the homogenized first oil-in-water emulsion is cooled. Furthermore, some UHT sterilization systems with integrated homogenizers perform homogenization after sterilization but before cooling, and such systems may also be adopted. The cooled first oil-in-water emulsion is stored in a tank equipped with a cooling function. 【0016】 The protein-containing raw material is sterilized and cooled separately. The sterilization conditions are not particularly limited and can be carried out using 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 the second oil-in-water emulsion. The amount of protein-containing raw material mixed is set according to the target 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 then the protein-containing raw material is added and mixed in later to finally adjust it to the desired protein content. Subsequently, the oil-in-water emulsion of the present invention can be obtained by aging the second oil-in-water emulsion. Aging is a process that promotes the crystallization of fats and can be carried out according to conventional methods. The aging conditions are not particularly limited and can be carried out under known aging conditions. For example, conditions of 8 to 10 hours at 3.0 to 6.0°C can be used. After mixing the homogenized first oil-in-water emulsion with the protein-containing raw material, a second oil-in-water emulsion can be stirred, for example, during aging, to ensure uniform mixing. This stirring can be performed using a known stirrer. In this case, it is preferable to stir as slowly as possible to suppress a decrease in the acid resistance of the second oil-in-water emulsion. 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 and fitted with slowly rotating impellers, and to stir it within the tank using the impellers. 【0017】 <First oil-in-water emulsion> The first oil-in-water emulsion contains oil and water. The first oil-in-water emulsion may contain protein if its 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 not mentioned above. 【0018】 Examples of fats and oils include vegetable oils and animal oils. Examples of vegetable 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, and other plant-based oils; oleic acid derived from these plant-based oils; hydrogenated oils (partially hydrogenated oils, fully hydrogenated oils), transesterified oils, fractionated oils, and mixed oils derived from these plant-based oils. Examples of animal oils include milk fat, beef tallow, lard, fish oil, whale oil, hydrogenated oils (partially hydrogenated oils, fully hydrogenated oils) derived from these oils, transesterified oils, fractionated oils, and mixed oils. These fats and oils may be used individually or in combination of two or more types. From the standpoint of cost and physical properties after whipping, it is preferable that at least a portion of the oils and fats be vegetable oils. Vegetable oils and animal fats such as milk fats may be used in combination. Preferably, the vegetable oil has a solid fat content of about 50-70% by mass when refrigerated (5°C) and a melting point of around 35-40°C so that it melts in the mouth at body temperature when the oil-in-water emulsion is foamed. Examples of such vegetable oils include rapeseed oil, soybean oil, palm oil, palm kernel oil, corn oil, cottonseed oil, rice oil, coconut oil, and their oleic acid and hydrogenated oils. Of these, a mixture of palm olein and hydrogenated rapeseed oil, or hydrogenated palm oil and hydrogenated palm kernel oil are preferred. These may be used individually or in combination of two or more. 【0019】 Proteins are generally thought to contribute to improving the stability of oil-in-water emulsions, and to improving the stability of foam-containing oil-in-water emulsions obtained by foaming oil-in-water emulsions. However, in this invention, the protein content of the first oil-in-water emulsion is limited to less than 1.4% by mass. This idea of ​​reducing the protein content of the first oil-in-water emulsion is an extremely rare idea in the technical field of this invention. Examples of proteins include milk protein and soy protein, but milk protein is preferred in terms of flavor. In this invention, the protein is typically incorporated into the first oil-in-water emulsion in the form of a protein-containing raw material. Examples of protein-containing raw materials include those similar to those used in the mixing process. 【0020】 Emulsifiers, stabilizers, and salts contribute to improving the stability (emulsification stability) of oil-in-water emulsions. Examples of emulsifiers include lecithin, polyglycerol fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters, polysorbates, organic acid monoglycerides, and fatty acid monoglycerides. These emulsifiers may be used individually or in combination of multiple types. 【0021】 The emulsifier preferably contains a polyglycerol fatty acid ester due to its excellent solubility in water. The polyglycerin fatty acid ester content is preferably 30 to 100% by mass, and more preferably 50 to 100% by mass, relative to the total mass of the emulsifier. Polyglycerin fatty acid esters may be used in combination with other emulsifiers. As for the other emulsifiers, at least one selected from the group consisting of lecithin and sucrose fatty acid esters is preferred in terms of emulsification stability during the manufacturing process, flavor of the foaming oil-in-water emulsion, and foaming properties. 【0022】 The emulsifier preferably comprises a first emulsifier with an HLB (hydrophilic-lipophilic balance) value of 6 or less, and a second emulsifier with 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 aqueous phase. By using the first and second emulsifiers together, the emulsification stability and foaming properties of the oil-in-water emulsion are improved. 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 the value obtained by the Griffin method. 【0023】 As the first emulsifier, for example, one with an HLB value of 6 or less can be appropriately selected from among the emulsifiers listed above. The first emulsifier preferably contains at least one selected from the group consisting of lecithin and sucrose fatty acid esters with an HLB value of 6 or less, as it is easily demulsified when foaming oil-in-water emulsions. An example of a sucrose fatty acid ester with an HLB value of 6 or less 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 with an HLB value of 6 or less is preferably 20 to 100% by mass, and more preferably 50 to 100% by mass, relative to the total mass of the first emulsifier. 【0024】 At least one selected from the group consisting of lecithin and sucrose fatty acid esters with an HLB value of 6 or less may be used in combination with another emulsifier with an HLB value of 6 or less. Other emulsifiers with an HLB value of 6 or less include polyglycerol fatty acid esters with an HLB value of 6 or less. The HLB value of polyglycerol fatty acid esters can be widely adjusted depending on the constituent fatty acids, degree of polymerization, etc. 【0025】 As a second emulsifier, for example, one with an HLB value of 10 to 16 can be appropriately selected from among the emulsifiers mentioned above. The second emulsifier preferably contains a polyglycerol fatty acid ester with an HLB value of 10 to 16, as it exhibits superior solubility in water. The content of polyglycerin fatty acid esters with an HLB value of 10 to 16 is preferably 50 to 100% by mass, and more preferably 80 to 100% by mass, relative to the total mass of the second emulsifier. 【0026】 Polyglycerol fatty acid esters with an HLB value of 10-16 may be used in combination with other emulsifiers with an HLB value of 10-16. Among other emulsifiers with an HLB value of 10-16, sucrose fatty acid esters with an HLB value of 10-16 are preferred because they readily demulsify when foaming oil-in-water emulsions. 【0027】 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. Examples of salts include phosphates such as monophosphates and condensed phosphates. 【0028】 Other ingredients include, for example, chelating agents (such as trisodium citrate), pH adjusters, milk components, egg components, carbohydrates (such as lactose, fructose, glucose, and sugar), dietary fiber, cellulose, flavorings, and colorings. 【0029】 The present invention can also be further combined with the aforementioned prior art. For example, in the present invention, an acid-resistant agent is not necessarily required, but the inclusion of an acid-resistant agent is not excluded. In this case, known acid-resistant agents can be used, such as fermented cellulose (Patent Document 4: Japanese Patent Application Publication No. 2015-57948). Even if an acid-resistant agent is added, in terms of flavor, it is preferable that the content of the acid-resistant agent be 3% by mass or less of the total mass of the second oil-in-water emulsion that is ultimately obtained. It is particularly preferable that the content of the acid-resistant agent be 0% by mass of the total mass of the second oil-in-water emulsion. Furthermore, regarding other prior arts, such as methods for modifying the formulation of emulsifiers (Patent Document 2) and methods for modifying the type of protein (Patent Document 3), while the present invention does not require being constrained to a specific emulsifier to obtain acid resistance, nor does it require adding milk protein hydrolysates for the purpose of acid resistance, this does not preclude combining these prior arts with the present invention. As described above, even if we assume that the present invention is combined with prior art, there is an advantage in that the extent to which prior art is used can be kept to a minimum compared to when such prior art is used alone. 【0030】 In the first oil-in-water emulsion, the oil and fat content is preferably 20 to 70% by mass, and more preferably 40 to 60% by mass, relative to the total mass of the first oil-in-water emulsion. If the oil and fat content is above the lower limit of the above range, it is easier to bring the oil and fat content of the final second oil-in-water emulsion within the preferred range described later. 【0031】 The water content is preferably 20 to 70% by mass, and more preferably 30 to 50% by mass, relative to the total mass of the first oil-in-water emulsion. If the water content is above the lower limit of the above range, the emulsifying properties are better, and if it is below the upper limit of the above range, the foaming properties of the second oil-in-water emulsion are better. 【0032】 The protein content is less than 1.4% by mass of the total mass of the first oil-in-water emulsion, preferably 0.8% by mass or less, more preferably 0.4% by mass or less, and particularly preferably 0% by mass. In other words, it is particularly preferable that the first oil-in-water emulsion does not contain protein. When the protein content is below the above upper limit, the oil-in-water emulsion of the present invention exhibits excellent acid resistance, the acidic oil-in-water emulsion obtained by acidifying the oil-in-water emulsion of the present invention exhibits excellent foaming properties, and the foam-containing acidic oil-in-water emulsion obtained by foaming the acidic oil-in-water emulsion exhibits excellent shape retention. 【0033】 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 below the above upper limit, the acid resistance of the oil-in-water emulsion of the present invention is better, the foaming properties of the acidic oil-in-water emulsion and the shape retention properties of the bubble-containing acidic oil-in-water emulsion are better. 【0034】 The emulsifier content is preferably 0.3 to 1.5% by mass, and more preferably 0.5 to 1.0% by mass, relative to the total mass of the first oil-in-water emulsion. When the emulsifier content is above the lower limit of the above range, the smoothness and shape retention of the bubble-containing acidic oil-in-water emulsion are better, and when it is below the upper limit of the above range, the shape retention and flavor of the bubble-containing acidic oil-in-water emulsion are better. 【0035】 When the emulsifier contains a first emulsifier and a second emulsifier, it is preferable that the content of the first emulsifier is 30-70% by mass and the content of the second emulsifier is 30-70% by mass, and more preferably that the content of the first emulsifier is 40-60% by mass and the content of the second emulsifier is 40-60% by mass, relative to the total mass of the first and second emulsifiers. 【0036】 The pH of the first oil-in-water emulsion is preferably 6.0 to 8.0, and more preferably 6.5 to 7.5. When the pH is above the lower limit of the above range, the stability of the liquid state is better, and when it is below the upper limit of the above range, the flavor and foaming properties are better. 【0037】 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. When 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 later. 【0038】 <Protein-containing ingredients> Protein-containing ingredients contain protein. The protein-containing raw material may also contain components other than protein. Examples of components other than protein include the other components mentioned above and water. The other components used in the mixing process are preferably water-soluble. The protein-containing raw material may be liquid or solid (particulate, powder, etc.), but it is preferable that it be liquid because it is easily mixed with the homogenized first oil-in-water emulsion. Examples of liquid protein-containing raw materials include skimmed condensed milk, whole condensed milk, skimmed milk powder solution, and whole milk powder solution. Other components may be blended into these liquid protein-containing raw materials. Furthermore, since it is preferable not to homogenize the protein-containing raw materials after the mixing process, a lower oil and fat content is preferable. The oil and fat content in the protein-containing raw materials is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably approximately 0% by mass, and particularly preferably 0% by mass, based on the total mass of the protein-containing raw materials. Note that "approximately 0% by mass" means a trace amount such that fat separation does not occur during storage of the final oil-in-water emulsion of the present invention even without homogenization of the protein-containing raw materials 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 with a protein-containing raw material, and contains at least oil, 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. The respective content of oils and fats, water, proteins, emulsifiers, and other components relative to the total mass of the second oil-in-water emulsion should preferably be equal to the respective content of oils and fats, water, proteins, emulsifiers, and other components relative to the total mass of the first oil-in-water emulsion and the protein-containing raw material. However, this does not preclude the mixing of other components when mixing the first oil-in-water emulsion and the protein-containing raw material. 【0040】 The fat and oil content is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass, relative to the total mass of the second oil-in-water emulsion. If the fat and oil content is above the lower limit of the above range, a good texture and flavor are easily obtained when foaming is performed, and if it is below the upper limit of the above range, the flavor when foaming is performed is even better. 【0041】 The water content is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, relative to the total mass of the second oil-in-water emulsion. When the water content is above the lower limit of the above range, the flavor and smoothness when foamed are superior, and when it is below the upper limit of the above range, the flavor when foamed is superior. 【0042】 The protein content is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 3.0% by mass, relative to the total mass of the second oil-in-water emulsion. If the protein content is above the lower limit, the emulsion stability before foaming is better, and if it is below the upper limit, the acid resistance of the second oil-in-water emulsion is better. 【0043】 The emulsifier content is preferably 0.1 to 2.0% by mass, and more preferably 0.3 to 1.5% by mass, relative to the total mass of the second oil-in-water emulsion. If the emulsifier content is above the lower limit of the above range, the emulsification stability before foaming is better, and if it is below the upper limit of the above range, the flavor after foaming is better. 【0044】 When the emulsifier contains a first emulsifier and a second emulsifier, it is preferable that the content of the first emulsifier is 30-70% by mass and the content of the second emulsifier is 30-70% by mass, and more preferably that the content of the first emulsifier is 40-60% by mass and the content of the second emulsifier is 40-60% by mass, relative to the total mass of the first and second emulsifiers. 【0045】 <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 oils and fats, water, and proteins. The second oil-in-water emulsion may further contain an emulsifier. The second oil-in-water emulsion may further contain other components. The respective content of oils and fats, water, proteins, emulsifiers, and other components relative to the total mass of the oil-in-water emulsion of the present invention is preferably equal to the respective content of oils and fats, water, proteins, emulsifiers, and other components relative to the total mass of the second oil-in-water emulsion. 【0046】 The oil-in-water emulsion of the present invention typically exhibits foaming properties. For example, when the oil-in-water emulsion of the present invention is foamed at 6-10°C, a foamed product with an overrun of 80-180% can be obtained. The overrun is preferably 100-160%, and more preferably 120-150%. The overrun can be 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" refers to cream that is not foamed, or in other words, cream that has not undergone any artificial foaming process. "Cream" refers to an emulsion prepared using fat-containing ingredients, and includes both cream as defined in the Ministerial Ordinance on Milk and Dairy Products (Ministerial Ordinance on Standards for Ingredients of Milk and Dairy Products) (hereinafter also referred to as "fresh cream"), and cream classified as "food made primarily from milk or dairy products" as defined in the Ministerial Ordinance on Milk and Dairy Products (hereinafter also referred to as "milk-based cream"). Fresh cream is "made by removing components other than milk fat from raw milk, milk, or special milk." Milk-based cream contains components other than milk fat (vegetable oils, proteins, various additives (emulsifiers, stabilizers, flavorings, etc.)), and is classified into pure milk fat type (pure milk fat cream) which contains only milk fat as its fat component, mixed type (so-called compound cream) which contains both milk fat and vegetable oil as its fat component, and pure vegetable oil type (so-called non-dairy cream) which contains only vegetable oil as its fat component. The oil-in-water emulsion of the present invention can be applied to various oil-in-water emulsions, but to fully enjoy the effects of the present invention, an unfermented oil-in-water emulsion is more preferable. Furthermore, as an oil-in-water emulsion with foaming properties, one that does not contain components for solidifying air bubbles, such as gelatin or egg white, is preferable. From this viewpoint, whipped cream is particularly preferable to sour cream, mousse cream, or bavarian cream. 【0048】 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 above the lower limit of the above range, the emulsion stability before foaming is better, and when it is below the upper limit of the above range, the flavor after foaming is better. 【0049】 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. If the viscosity of the oil-in-water emulsion of the present invention is above the lower limit of the above range, the texture and flavor after foaming are better, and if it is below the upper limit of the above range, the foaming ability and flavor are better. 【0050】 Furthermore, the oil-in-water emulsion of the present invention preferably has a viscosity of less than 5810 mPa·s, more preferably less than 5394 mPa·s, more preferably less than 5000 mPa·s, more preferably 4660 mPa·s or less, more preferably less than 4498 mPa·s, more preferably less than 4049 mPa·s, more preferably 4000 mPa·s or less, more preferably 3390 mPa·s or less, more preferably less than 3153 mPa·s, more preferably 2000 mPa·s or less, and more preferably 1400 mPa·s or less when the pH is set to around 4.5. The area 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 approximately 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. Furthermore, if the viscosity at pH 4.5 is below the aforementioned upper limit, sufficient foaming can be achieved. In particular, if the viscosity is 4000 mPa·s or less, overrun will be good, and if it is 2000 mPa·s or less, it will be even better. When the pH of the oil-in-water emulsion of the present invention is set to around 4.5, the viscosity is preferably 50 mPa·s or higher, and more preferably 100 mPa·s or higher, in terms of flavor when foamed. 【0051】 <Effects and Effects> In the embodiments described above, the protein content of the homogenized oil-in-water emulsion (first oil-in-water emulsion) is set to less than 1.4% by mass, and the protein-containing raw material is mixed after homogenization. Since the resulting second oil-in-water emulsion is not homogenized as much as possible, an oil-in-water emulsion with excellent acid resistance despite containing protein (the oil-in-water emulsion of the present invention) 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 foam well, and an acidic oil-in-water emulsion containing bubbles obtained by foaming the acidic oil-in-water emulsion has excellent shape retention. The reason for its excellent acid resistance is not entirely clear, but the following hypotheses can be considered. In other words, conventionally, when manufacturing oil-in-water emulsions containing protein, the homogenized emulsion generally contained 1.4% by mass or more of protein. When such an oil-in-water emulsion is homogenized, a large amount of protein adheres to the surface of the emulsion film of the pulverized oil droplets. Therefore, it is thought that when the pH decreases, the oil droplets tend to aggregate due to protein aggregation, leading to increased viscosity. In contrast, in this manufacturing method, the first oil-in-water emulsion to be homogenized contains little to no 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. Furthermore, after mixing the protein-containing raw material with this first oil-in-water emulsion to form a second oil-in-water emulsion, homogenization is avoided as much as possible. For this reason, the state of the oil droplets of the first oil-in-water emulsion is maintained in the oil-in-water emulsion of the present invention. As a result, the oil-in-water emulsion of the present invention is less prone to protein aggregation and thickening even when the pH decreases, resulting in good foaming properties, less decrease in hardness after foaming, and excellent shape retention. It should be noted that the above is merely a hypothesis added for the purpose of clearly explaining the technical content of the present invention. 【0052】 As described above, the oil-in-water emulsion of the present invention has excellent acid resistance, and can therefore foam even when acidic substances such as fruit juice or fruit are added to make it acidic. Furthermore, since it can foam in both neutral and acidic ranges, it can be used in a variety of applications. Furthermore, conventional methods involved adding unnecessary ingredients to impart acid resistance, resulting in problems such as altered taste and flavor, and limited freedom in product design. In contrast, this manufacturing method does not require the addition of unnecessary ingredients, thus preserving the taste and flavor and providing greater freedom in product design. 【0053】 It should be noted that this manufacturing method is not limited to the embodiments described above. The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications to the configurations are possible without departing from the spirit of the present invention. For example, an existing oil-in-water emulsion may be used as the first emulsion. In this case, the preliminary emulsification step may not be necessary. An example of homogenization, sterilization, and cooling of a first oil-in-water emulsion using a UHT sterilization apparatus with an integrated homogenizer has been shown. However, there are also models of UHT sterilization apparatus with integrated homogenizers that perform homogenization after sterilization and before cooling, and such models may be used. Homogenization and sterilization may also be performed using separate devices, without using a UHT sterilization apparatus with an integrated homogenizer. Homogenization can be performed using a known homogenizer. Sterilization can be performed using a known sterilization device. When performing sterilization or aging, the timing of these processes, as well as the timing of mixing the first oil-in-water emulsion with the protein-containing raw material, are not limited to the embodiments described above. 【0054】 Figures 2-5 are flowcharts illustrating another embodiment of this manufacturing method. In the embodiment shown in Figure 1, a second oil-in-water emulsion is obtained by mixing a protein-containing raw material with a homogenized first oil-in-water emulsion and then aging is performed. However, in the embodiment shown in Figure 2, the protein-containing raw material is mixed into the homogenized first oil-in-water emulsion while it is aging, and then aging is continued. Specifically, the protein-containing raw material is added and mixed in the aging tank while the homogenized first oil-in-water emulsion is stored in an aging tank and maintained at a low temperature. Generally, aging tanks are equipped with stirring blades that stir at a low speed, and the mixing process is carried out using these stirring blades. Then, the aging of the obtained second oil-in-water emulsion is continued. In the embodiment shown in Figure 3, the first homogenized oil-in-water emulsion is aged, and then the protein-containing raw material is mixed in. In the embodiment shown in Figure 4, sterilization is performed after the mixing step. That is, a protein-containing raw material is mixed with the homogenized first oil-in-water emulsion to obtain a second oil-in-water emulsion, which is then sterilized. In this case, the protein-containing raw material does not need to be sterilized in advance. The second oil-in-water emulsion is then aged after sterilization and cooling. Even in this case, homogenization of the second oil-in-water emulsion is not performed after the mixing step. In the embodiment shown in Figure 5, the homogenized first oil-in-water emulsion is heat-sterilized and then pre-cooled to lower its temperature, 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 subjected to full cooling and aging. As described above, there are various ways in which a protein-containing raw material can be mixed with the homogenized first oil-in-water emulsion. As mentioned above, the protein content of the first oil-in-water emulsion is reduced to less than 1.4% by mass. However, by mixing a protein-containing raw material with the first oil-in-water emulsion, the protein content of the second oil-in-water emulsion ultimately becomes higher than that of the first oil-in-water emulsion. 【0055】 [Oil-in-water emulsion] An oil-in-water emulsion according to one aspect of the present invention (hereinafter also referred to as "the emulsion") contains oils and fats, water, and proteins. This emulsion may further contain emulsifiers. This emulsion may further contain other components not listed above. 【0056】 Examples of oils and fats, proteins, emulsifiers, and other components are the same as those described above, and the preferred embodiments are also the same. 【0057】 The fat and oil content is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass, relative to the total mass of the emulsion. If the fat and oil content is above the lower limit of the above range, a good texture and flavor are easily obtained when foaming is performed, and if it is below the upper limit of the above range, the flavor when foaming is performed is even better. 【0058】 The water content is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, relative to the total mass of the emulsion. When the water content is above the lower limit of the above range, the flavor and smoothness when foamed are superior, and when it is below the upper limit of the above range, the flavor when foamed is superior. 【0059】 The protein content is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 3.0% by mass, relative to the total mass of the emulsion. When the protein content is above the lower limit, the emulsion stability before foaming is better, and when it is below the upper limit, the acid resistance of the emulsion is better. 【0060】 The emulsifier content is preferably 0.1 to 2.0% by mass, and more preferably 0.3 to 1.5% by mass, relative to the total mass of the emulsion. If the emulsifier content is above the lower limit of the above range, the emulsification stability before foaming is better, and if it is below the upper limit of the above range, the flavor after foaming is better. 【0061】 When the emulsifier contains a first emulsifier and a second emulsifier, it is preferable that the content of the first emulsifier is 30-70% by mass and the content of the second emulsifier is 30-70% by mass, and more preferably that the content of the first emulsifier is 40-60% by mass and the content of the second emulsifier is 40-60% by mass. 【0062】 This emulsion typically exhibits foaming properties. For example, when this emulsion is foamed at 6-10°C, a foamed product with an overrun of 80-180% can be obtained. The overrun is preferably 100-160%, and more preferably 120-150%. The overrun can be determined by the method described in the examples below. 【0063】 This emulsion may be a liquid cream. While the present invention can be applied to various emulsions, unfermented emulsions are more preferable to fully enjoy the effects of the present invention. Furthermore, as for foaming emulsions, those that do not contain components for solidifying air bubbles, such as gelatin or egg whites, are preferable. From this viewpoint, whipped cream is particularly preferable to sour cream, mousse cream, and bavarian cream. 【0064】 The pH of this emulsion is 6.0 to 8.0, preferably 6.5 to 7.5. If the pH is above the lower limit of the above range, the emulsion stability before foaming is excellent, and if it is below the upper limit of the above range, the flavor after foaming is excellent. 【0065】 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. When the viscosity of this emulsion is above the lower limit of the above range, it has excellent texture and flavor when foamed, and when it is below the upper limit of the above range, it has excellent foaming properties and flavor. 【0066】 Furthermore, it is preferable that the viscosity of this emulsion is less than 5810 mPa·s, more preferably less than 5394 mPa·s, more preferably less than 5000 mPa·s, more preferably 4660 mPa·s or less, more preferably less than 4498 mPa·s, more preferably less than 4049 mPa·s, more preferably 4000 mPa·s or less, more preferably 3390 mPa·s or less, more preferably less than 3153 mPa·s, more preferably 2000 mPa·s or less, and more preferably 1400 mPa·s or less when the pH is set to around 4.5. The area around pH 4.5 is typically pH 4.45 to 4.60. The viscosity of this emulsion is almost the same within this range. Since the isoelectric point of casein is around pH 4.5, the viscosity of this emulsion tends to be highest around pH 4.5. The lower the viscosity at pH 4.5, the better the acid resistance. Furthermore, if the viscosity at around pH 4.5 is below the aforementioned upper limit, sufficient foaming can be achieved. In particular, if the viscosity is 4000 mPa·s or less, overrun will be good, and if it is 2000 mPa·s or less, it will be even better. When the pH of this emulsion is adjusted from 6.5 to 7.5 to around 4.5, the viscosity is preferably 50 mPa·s or higher, and more preferably 100 mPa·s or higher, in terms of flavor when foamed. 【0067】 This emulsion contains more than 0% by volume of protein precipitate, as measured by the following method. Method for measuring protein precipitate amount: 50 mL of the sample (oil-in-water emulsion) is placed in a graduated centrifuge tube, and centrifugation is performed using a centrifuge at a relative centrifugal acceleration of 1630 × g for 5 minutes. The volume (mL) of protein precipitated in the centrifuge tube is then visually measured, and the ratio (volume %) of the volume of protein to the total volume of the oil-in-water emulsion is defined as the protein precipitate amount. The amount of protein precipitate is an indicator of the amount of free protein present in the continuous phase (aqueous phase) of this emulsion. A protein precipitate amount greater than 0% by volume indicates excellent acid resistance. The amount of protein precipitate in this emulsion is preferably 0.1% by volume or more. The upper limit of the protein precipitate is not particularly limited, but is, for example, 2.0% by volume. 【0068】 This emulsion can be produced, for example, by the manufacturing method described above. Conventionally, in the production of oil-in-water emulsions containing proteins, the aqueous phase containing the protein and the oil phase are usually mixed and then homogenized. It is presumed that in the oil-in-water emulsion obtained in this way, oil droplets are dispersed as a dispersed phase within the continuous aqueous phase, and due to homogenization, the proteins in the aqueous phase cover the surface of the oil droplets and adhere firmly. Therefore, it is thought that oil-in-water emulsions produced by conventional methods have a small amount of protein present in the continuous phase. On the other hand, in the aforementioned manufacturing method, the protein content of the first oil-in-water emulsion is lower than in conventional methods. Therefore, even after homogenizing the first oil-in-water emulsion, the amount of protein adhering to the surface of the oil droplets is small. Furthermore, since the protein-containing raw material is mixed in thereafter and homogenization is avoided as much as possible, it is thought that a large amount of protein remains in the continuous phase. However, the method of producing this emulsion is not limited to this. 【0069】 The oil-in-water emulsion or emulsion produced by this manufacturing method may be filled into a packaging container, sealed, and stored or distributed in that form. The packaging container is not particularly limited as long as it does not leak, and examples include paper containers, plastic containers, and retort containers. Oil-in-water emulsions, packaged in containers, should be opened and used at the time of use (e.g., when foaming). 【0070】 The oil-in-water emulsion or emulsion produced by this manufacturing method can be used for whipping, cooking, and other purposes. The oil-in-water emulsion or emulsion produced by this manufacturing method is particularly useful for whipping. 【0071】 For whipping applications, the oil-in-water emulsion obtained by this manufacturing method, or this emulsion, is foamed to produce an oil-in-water emulsion containing bubbles (such as whipped cream). Here, "foaming" is not particularly limited, but it refers to the process of incorporating bubbles into an oil-in-water emulsion by applying physical stress such as stirring or by bringing it into contact with air. It is desirable to perform this process at a soft peak (60-90%). Before foaming, sugars may be added to the oil-in-water emulsion or emulsion obtained by this manufacturing method. The amount of carbohydrates added is preferably 0 to 10% by mass of the total mass of the oil-in-water emulsion or emulsion obtained by this manufacturing method. When the amount of carbohydrates is below the upper limit, the resulting bubble-containing oil-in-water emulsion has a good flavor. 【0072】 The resulting bubble-containing oil-in-water emulsion may be frozen as is to obtain a frozen bubble-containing oil-in-water emulsion. The resulting bubble-containing oil-in-water emulsion may be used as packaging for the frozen bubble-containing oil-in-water emulsion. For example, packaging for the bubble-containing oil-in-water emulsion can be obtained by filling the resulting bubble-containing oil-in-water emulsion directly into a container and preferably sealing it. Furthermore, before freezing, the bubble-containing oil-in-water emulsion may be filled and sealed in packaging containers for storage or distribution, or after freezing, the frozen bubble-containing oil-in-water emulsion may be filled and sealed in packaging containers for storage or distribution. 【0073】 The oil-in-water emulsion or emulsion obtained by this manufacturing method is endowed with excellent acid resistance, so even if the oil-in-water emulsion becomes acidic, it can foam and become a foam-containing oil-in-water emulsion. Therefore, by adding an acidic material to the oil-in-water emulsion or emulsion obtained by this manufacturing method and adjusting the pH to acidic, an acidic oil-in-water emulsion can be obtained. Furthermore, this acidic oil-in-water emulsion can be foamed to become a foam-containing acidic oil-in-water emulsion. The pH of the acidic oil-in-water emulsion is preferably 2.0 to 6.5, and more preferably 3.0 to 5.5, in terms of the texture when foaming. 【0074】 Furthermore, the oil-in-water emulsion obtained by this manufacturing method, or the bubble-containing oil-in-water emulsion obtained by foaming this emulsion, has excellent acid resistance. Therefore, by adding an acidic material to the bubble-containing oil-in-water emulsion and adjusting the pH to acidic, a bubble-containing acidic oil-in-water emulsion can be obtained. The pH of the acidic foam-containing oil-in-water emulsion is preferably 2.0 to 6.5, and more preferably 3.0 to 5.5, in terms of texture. 【0075】 Examples of acidic materials include acidic compounds that can be used in food, as well as crushed, ground, or fragmented materials and juices of acidic foods. Examples of acidic compounds 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. 【0076】 Examples of acidic foods include processed products of sour fruits and / or vegetables. Examples of processed acidic foods include sour fruit juices and pulp; sour vegetable juices and vegetable pieces. Examples of processed acidic foods include purees, pastes, sauces, jams, and juices, which may be used alone or in appropriate combinations. Generally, "puree" refers to crushed and strained fruit and / or vegetables, used in their raw or cooked state. "Paste," on the other hand, is generally thicker than puree. "Fruit sauce" can include fruit puree thickened with starch or jam. Examples of fruit juices and pulp include citrus fruits such as lemons, oranges, sudachi, and bitter oranges; and fruits such as strawberries, raspberries, grapes, pineapples, blueberries, kiwifruit, and apples. Examples of vegetable juices and vegetable pieces include tomatoes. 【0077】 Suitable acidic foods include processed products of acidic fruits and / or vegetables. Suitable processed products of acidic fruits and / or vegetables include one or more selected from crushed products, pressed products, juices, purees, and sauces. The amount of 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. Furthermore, the oil-in-water emulsion or emulsion obtained by this manufacturing method can be used in a wide range of foods, not limited to acidic compounds or acidic foods. 【0078】 Conventionally, when manufacturing oil-in-water emulsions containing bubbles in acidic foods, the "separate-egg" and "co-egg" manufacturing methods are generally used. Furthermore, other components such as gelatin may be added when manufacturing oil-in-water emulsions containing bubbles. "Could preparation" refers to a method for producing an oil-in-water emulsion containing bubbles, which includes the 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 an acidic food. "Separate preparation" refers to a method for producing an oil-in-water emulsion containing bubbles with an acidic food, which includes the step of foaming an oil-in-water emulsion to make an oil-in-water emulsion containing bubbles, and the 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 an acidic food. Traditionally, when a common oil-in-water emulsion (such as fresh cream) is mixed with an acidic food and whipped, the resulting foamy oil-in-water emulsion has a crumbly texture due to the acidic food. As a result, foamy oil-in-water emulsions obtained by the "all-in-one" method have poor texture and flavor. Therefore, to improve texture and flavor, the "separate-egg" method was typically used for small-scale production in stores, etc. However, this "separate-egg" method requires at least two steps, making it inefficient. For mass production, the conventional method of adding stabilizers and producing foamy oil-in-water emulsions containing acidic foods using the "all-in-one" method was adopted. However, foamy oil-in-water emulsions obtained by this "all-in-one" method tended to have poor texture and flavor due to the influence of conventional stabilizers. The oil-in-water emulsion or emulsion obtained by this manufacturing method has excellent acid resistance, so it is possible to produce an oil-in-water emulsion containing bubbles with good texture and flavor for acidic foods using the "co-preparation" method without adding conventional stabilizers. 【0079】 The resulting bubble-containing acidic oil-in-water emulsion may be frozen to obtain a frozen bubble-containing acidic oil-in-water emulsion. Before freezing, the bubble-containing acidic oil-in-water emulsion may be filled into packaging containers, sealed, and stored or distributed. Alternatively, after freezing, the frozen bubble-containing acidic oil-in-water emulsion may be filled into packaging containers, sealed, and stored or distributed. The frozen bubble-containing acidic oil-in-water emulsion is thawed before use and used as a bubble-containing acidic oil-in-water emulsion. 【0080】 The resulting bubble-containing oil-in-water emulsion or bubble-containing acidic oil-in-water emulsion can be used, for example, as whipped cream; whipped cream with acidic foods; whipped cream for decorating cakes, pancakes, confectionery, jelly, pudding, ice cream, frozen dairy products, etc.; and whipped cream for Viennese coffee, juice, and beverages. Examples of whipped cream with acidic foods include whipped cream containing processed products of acidic fruits and / or vegetables. Examples include whipped cream with fruit and / or vegetable puree, and whipped cream with fruit and / or vegetable juice (for example, whipped cream with citrus juice, etc.). 【0081】 Examples of foods using 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 filled with lemon-flavored whipped cream to enhance the fruity taste, shortcakes and decorated cakes using mandarin orange-flavored whipped cream, jellies and puddings topped with strawberry-flavored whipped cream, sandwiches with whipped cream flavored with fruit juice, and cream puffs and bread filled with fruit juice-infused cream or filling. [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, unless otherwise specified, "%" refers to "mass%" except for overrun percentages. "Parts" refers to "parts by mass". The creams of Examples 1 to 8 correspond to the oil-in-water emulsion of the present invention. 【0083】 <Test Example 1> (Cream manufacturing) In this test example, five types of creams were prepared as oil-in-water emulsions according to Table 1. The overall composition of these creams was the same. The overall composition of each cream is shown in Table 2. The procedure for preparing each cream is roughly as follows: First, the aqueous phase and the oil phase are prepared separately and pre-mixed to form the 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 the second oil-in-water emulsion. Then, the second oil-in-water emulsion is aged to obtain the creams of Examples 1-3 and Comparative Examples 1-2. This test was conducted 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). 【0084】 The detailed procedure for manufacturing each example cream is shown below. In Examples 1-3 and Comparative Example 1, first, the aqueous phase was prepared by dissolving the emulsifier and skim milk powder in water while stirring, according to the composition of the aqueous phase shown in Table 1. For the aqueous phase, 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 polyglycerin fatty acid ester. Emulsifier A: Polyglycerin fatty acid ester (manufactured by Sakamoto Pharmaceutical Co., Ltd., HLB approximately 12). Emulsifier B: Polyglycerin fatty acid ester (manufactured by Sakamoto Pharmaceutical Co., Ltd., HLB approximately 12). Furthermore, according to the composition of the oil phase shown in Table 1, the oil phase was prepared by dissolving an emulsifier and soy lecithin in vegetable oil. Polyglycerin fatty acid ester (manufactured by Sakamoto Pharmaceutical Co., Ltd., HLB approximately 5) was used as the emulsifier for the oil phase. Palm kernel oil was used as the vegetable oil. Next, the aqueous phase was heated to 70°C while stirring, and the oil phase, also heated to 70°C, was added and pre-mixed to prepare the synthesis phase. This synthesis phase was pre-emulsified by stirring at 7000 rpm for 3 minutes using a homomixer to obtain the 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 Industry Co., Ltd.), preheated to 70°C, and then homogenized under a pressure of 9.0 MPa. After that, it was heat-sterilized at 80°C, cooled to 5°C, and stored in an aging tank. Next, according to the composition of the protein-containing raw materials shown in Table 1, skim milk powder, modified starch, and trisodium citrate were dissolved in water to prepare the protein-containing raw materials. This protein-containing raw material was batch sterilized to a temperature of 80°C, then cooled to approximately 5°C and added to an aging tank containing 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. This resulted in a cream with an oil content of 35% and a protein content of 2.87%. In Comparative Example 2, all the components blended into the protein-containing raw material were blended into the aqueous phase, and the protein-containing raw material was not added to the homogenized first oil-in-water emulsion. The process was carried out in the same manner as in Example 3, and a cream with an oil content of 35%, a protein content of 2.87%, and a pH of 7.0 was obtained. The fat and protein content were calculated from the formulation. pH was measured using a pH meter (HORIBA). 【0085】 [Table 1] 【0086】 [Table 2] 【0087】 The obtained 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 protein precipitate amount. 【0088】 (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 method for measuring pH is as described above. The method for measuring viscosity is shown below. 【0089】 "viscosity" Viscosity was measured using a Type B viscometer (TOKI Corporation) under the conditions of 30 seconds and 60 rpm. The upper limit 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 viscosity of the cream before the addition of citric acid solution and the viscosity of the cream after adding citric acid solution to bring the pH to around 4.5 (the isoelectric point of casein) (hereinafter also referred to as "acidic cream"). Figure 7 shows the viscosity of the acidic cream at around 4.5 pH. Figure 8 shows a scatter plot and regression equation showing the relationship between the protein content of the first oil-in-water emulsion and the viscosity of the cream (oil-in-water emulsion) at around 4.5 pH in each example. Furthermore, creams that are not acid-resistant will thicken when the pH is around 4.5, making them impossible to whip, or if they can be whipped, the specific gravity of the whipped cream will increase. On the other hand, creams that are acid-resistant will have a lower specific gravity when whipped. 【0091】 [Table 3] 【0092】 The creams of Comparative Examples 1 and 2 had a viscosity of 5810 mPa·s or higher when the pH was lowered to around 4.5, resulting in an acidic solution. In contrast, the creams of Examples 1 to 3 had a viscosity of 5000 mPa·s or less when the pH was lowered to around 4.5. A viscosity of 5000 mPa·s or less is particularly sufficient for whipping. A comparison of Examples 1-3 and Comparative Examples 1-2 shows that even with the same final composition, a lower protein content in the first oil-in-water emulsion resulted in suppressed thickening and better foaming properties when the pH was reduced to around 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. 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, looking at Figure 8, it can be seen that the viscosity of the acidic cream around pH 4.5 is linear for Examples 1-3 and Comparative Example 1. If the protein content of the first oil-in-water emulsion is 1.4%, the viscosity of the acidic cream can be calculated to be 5394 mPa·s from the regression equation in Figure 8 (y = 2240.1x + 2257.4). Therefore, the preferred viscosity range for the acidic cream can also be said to be less than 5394 mPa·s, according to the regression equation. Furthermore, since the protein content of the first oil-in-water emulsion that results in a more preferable viscosity of 5000 mPa·s is 1.2% when calculated inversely from the regression equation, it can be estimated that the more preferable range for 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 value around Example 1 (approximately 0%) is particularly preferable. 【0093】 (foaming test) Sweetened cream was obtained by adding 64g of sugar to 800g of neutral cream. The sweetened cream was whipped using a mixer (Kenmix) at 180 rpm for the whipping time shown in Table 4 to obtain whipped cream. The whipping was stopped when the hardness of the whipped cream reached a penetrating depth (hereinafter also referred to as "penetro value") of 20 ± 1 mm. The overrun and penetro value of the whipped cream were measured using the following measurement method. The overrun values ​​of the obtained whipped cream are 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】 "Penetro value (Penetro penetration degree)" The penetro value is a unitless value obtained by multiplying the penetration distance (mm) of a specific cone-shaped cone dropped into a composition under predetermined conditions by 10. A larger value indicates a softer composition. Specifically, a penetrometer was used to penetrate the sample with a 12g aluminum cone with a base diameter of 24mm, a height of 33.5mm, and a tip angle of 40°. The penetration depth (mm) was measured, and the measured value was multiplied by 10 to obtain the penetrometer value. 【0096】 [Table 4] 【0097】 The creams of Examples 1-3 and Comparative Examples 1-2 all exhibited foaming properties at a neutral pH. 【0098】 (Acid resistance test 2) 400g of the neutral cream from Example 1, Example 3, or Comparative Example 1 was placed in a mixer (DeLonghi Chef Classic), and a 10% citric acid solution was added to adjust the pH to 4.5 or less. Then, the mixture was whipped at a rotation 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 penetro values. The whipped cream was stored in a 5°C refrigerator for 24 hours, and then the penetro value (penetro value after 1 day) was measured. The difference between this value and 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 "difference in penetro value after 1 day") was calculated. Based on the results, the state after 1 day was evaluated according to the following criteria. The results are shown in Table 5. ×: The difference in Penetro value after 1 day is +100 or more. △: The difference in Penetro value after 1 day is +50 or more but less than +100. ○: The Penetro value difference after 1 day is between -15 and +50. △: The Penetro value difference after 1 day is -25 or more but less than -15. ×: Penetrometry value difference after 1 day is less than -25. The methods for measuring pH, overrun, and penetrometer value are as described above. 【0099】 [Table 5] 【0100】 Compared to the cream of Comparative Example 1, the creams of Examples 1 and 3 showed suppressed changes in their state after the addition of acidic materials and foaming. 【0101】 (Measurement of protein precipitate amount) For three types of creams—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 amount of protein precipitate was determined using the following procedure. 50 mL of the sample (cream) was dispensed into a graduated centrifuge tube and centrifuged using a Hitachi himac CT6E compact centrifuge with a T4SS swing rotor 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 amount of protein precipitated in the centrifuge tube (mL) was visually confirmed. From this precipitated amount (mL), the percentage of the volume of precipitated protein relative to the total volume of the sample (volume %) was calculated and defined as the protein precipitate amount. The results are shown in Table 6. Furthermore, the centrifugation conditions used in this test are harsh and therefore unrelated to the occurrence of precipitation under normal standing conditions. 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. 【0102】 [Table 6] 【0103】 As described above, Comparative Example 1, in which the protein content of the first oil-in-water emulsion was 1.4%, showed a protein precipitate of 0%. In contrast, the creams of Example 1 and Example 3 had a protein precipitate amount greater than 0%. Furthermore, the lower the protein content of the first oil-in-water emulsion, the greater the protein precipitate. 【0104】 <Test Example 2> This test was conducted to verify whether similar results could be obtained by adding modified starch and trisodium citrate, which were added to the protein-containing raw materials in Examples 1-3, to the aqueous phase. 【0105】 The cream of Example 4 was obtained in the same manner as in Example 1, except that the composition of the aqueous phase and the protein-containing raw materials was changed as shown in Table 7. The obtained cream was subjected to the foaming and acid resistance tests described above in a neutral state. The results of the foaming test are shown in Table 8, and the results of the acid resistance test are shown in Figure 9. Figure 9 also includes the results for Example 1. 【0106】 [Table 7] 【0107】 [Table 8] 【0108】 In Example 4, the whipping time was about 1 minute shorter than in Example 1, and the viscosity also decreased. The overrun was about the same. In the acid resistance test, similar to Example 1, no rapid increase in viscosity was observed even when the pH was lowered. From this, it can be concluded that the timing of adding modified starch or trisodium citrate does not matter, whether before or after homogenization. 【0109】 <Test Example 3> This study was conducted to evaluate the effect of the cream's protein concentration on its acid resistance. 【0110】 Creams for Examples 5 to 7 were obtained in the same manner as in Example 1, except that the composition of the aqueous phase and protein-containing raw materials was 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 foaming and acid resistance tests described above. The results of the foaming test are shown in Table 11, and the results of the acid resistance test are shown in Figure 10. Figure 10 also shows the results for Example 1 and Comparative Example 2. 【0111】 [Table 9] 【0112】 [Table 10] 【0113】 [Table 11] 【0114】 As shown in the results above, in the foaming test, the whipping time increased as the protein content of the cream increased. Also, the overrun decreased. In the acid resistance tests, thickening was suppressed when the pH was lowered in all of Examples 5 to 7. The results were particularly good when the cream's protein content was less than 5.00%, especially 3.00% or less. 【0115】 <Example 8> 200g of the cream from Example 1 and 200g of fruit puree (raspberry, 15% added sugar, manufactured by Boiron) were mixed to obtain the cream from Example 8. The resulting cream was whipped using a DeLonghi whisk (Kitchen Machine Chef Classic) at a rotation speed of 180 rpm to obtain whipped cream. Table 12 shows the pH of the cream before whipping (after mixing with fruit puree), the temperature during whipping (from the start of whipping to the end of whipping), the whipping time, the specific gravity of the whipped cream, the overrun, and the penetrometry value (penetrometry). The obtained whipped cream was stored in a refrigerator at 5°C for 24 hours, and then the penetrovalue (penetrovalue after 1 day) was measured. The difference in penetrovalue after 1 day was calculated. The results were evaluated in the same manner as in Acid Resistance Test 2. The results are shown in Table 12. The methods for measuring pH, overrun, and penetrometer value are as described above. 【0116】 [Table 12] 【0117】 The cream of Example 8 showed less change in its 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 0%, or it may be 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 comprising a protein source, oils and fats, water, and other raw materials, comprising the steps of: preparing a first oil-in-water emulsion by mixing all of the oils and fats, part of the water, and part of the other raw materials, homogenizing and sterilizing them; preparing a protein-containing raw material by mixing the remaining water, the remaining raw materials, and all of the protein source, and sterilizing them; and preparing a second oil-in-water emulsion by mixing the protein-containing raw material with the first oil-in-water emulsion. [B] A method for producing an oil-in-water emulsion comprising a protein source, oils and fats, water, and other raw materials, comprising the steps of: mixing all of the oils and fats, a portion of the water, a portion of the other raw materials, and a portion of the protein source, homogenizing and sterilizing them to prepare a first oil-in-water emulsion having a protein content greater 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, 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.

Claims

[Claim 1] A step of homogenizing a first oil-in-water emulsion containing oil and water, having a protein content of 0.8% by mass or less, to obtain a homogenized first oil-in-water emulsion, The process includes a step of mixing the homogenized first oil-in-water emulsion with a milk protein-containing raw material to obtain a second oil-in-water emulsion. A method for producing an oil-in-water emulsion, comprising the steps of sterilizing the first oil-in-water emulsion and / or sterilizing the milk protein-containing raw material, before the step of obtaining the second oil-in-water emulsion. [Claim 2] A method for producing an oil-in-water emulsion according to claim 1, wherein the protein content in the first oil-in-water emulsion is 0% by mass. [Claim 3] A method for producing an oil-in-water emulsion according to claim 1 or 2, wherein the milk protein-containing raw material includes skim milk powder. [Claim 4] A method for producing an oil-in-water emulsion according to any one of claims 1 to 3, wherein, after the step of obtaining the second oil-in-water emulsion, the second oil-in-water emulsion is not homogenized. [Claim 5] A method for producing an oil-in-water emulsion according to any one of claims 1 to 4, wherein the oil and fat content of the first oil-in-water emulsion is 1 to 60% by mass. [Claim 6] A method for producing an oil-in-water emulsion according to any one of claims 1 to 5, wherein the protein content of the second oil-in-water emulsion is 0.4% by mass or more and less than 5% by mass. [Claim 7] A method for producing an oil-in-water emulsion according to any one of claims 1 to 6, wherein the pH of the oil-in-water emulsion produced by the above-mentioned 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 around 4.5 is less than 5810 mPa·s. [Claim 8] A 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. [Claim 9] A method for producing an oil-in-water emulsion containing bubbles, comprising foaming an oil-in-water emulsion produced by the manufacturing method described in any one of claims 1 to 8 to form an oil-in-water emulsion containing bubbles. [Claim 10] A method for producing a frozen bubble-containing oil-in-water emulsion, comprising freezing a bubble-containing oil-in-water emulsion produced by the manufacturing method described in claim 9 to obtain a frozen bubble-containing oil-in-water emulsion. [Claim 11] A method for producing an acidic oil-in-water emulsion, comprising adding an acidic material to an oil-in-water emulsion produced by the manufacturing method described in any one of claims 1 to 8, and adjusting the pH to a range of 3.0 to 5.5 to produce an acidic oil-in-water emulsion. [Claim 12] A method for producing a bubble-containing acidic oil-in-water emulsion, comprising foaming an acidic oil-in-water emulsion produced by the manufacturing method described in claim 11 to form a bubble-containing acidic oil-in-water emulsion.

Images