Method for producing frozen dessert, method for improving survival of bifidobacteria, and frozen dessert

Abstract

This method for producing a frozen dessert has a freezing step in which a raw material liquid containing live bifidobacteria is frozen to obtain a partially frozen product. In order to suppress death of bifidobacteria, the freezing temperature in the freezing step is set to be lower than or equal to the freezing point of the raw material liquid, and the absolute value of the difference between the freezing point of the raw material liquid and the freezing temperature is set to be less than or equal to 2.0°C.

Description

Method for producing frozen dessert, method for improving survival of bifidobacteria, and frozen dessert

[0001] The present invention relates to a method for producing frozen desserts, a method for improving the survival rate of bifidobacteria, and frozen desserts. This application claims priority based on Japanese Patent Application No. 2024-029510, filed on February 29, 2024, the contents of which are incorporated herein by reference.

[0002] Bifidobacteria are representative of useful intestinal bacteria (also known as "probiotics") known to have many physiological functions, such as protection against pathogenic bacteria, and there is increasing demand for foods containing live bifidobacteria. Patent Document 1 aims to produce ice cream containing live bifidobacteria. Specifically, it proposes a method in which bifidobacteria are pre-encapsulated in water-insoluble microcapsules, based on the assumption that anaerobic bifidobacteria will die in the presence of oxygen during the process of passing a raw material mix through a freezer to incorporate a large amount of air.

[0003] Japanese Patent Application Laid-Open No. 2002-171914

[0004] However, the method described in Patent Document 1 requires the preparation of microcapsules encapsulating bifidobacteria, which increases the number of manufacturing steps and the manufacturing cost. Furthermore, microcapsules have the problem of impairing the smooth texture of ice cream. The present invention provides a method for manufacturing frozen desserts that can prevent the death of bifidobacteria during the manufacturing process without protecting the bifidobacteria with microcapsules.

[0005] The present invention has the following aspects. [1] A method for producing a frozen dessert, comprising a freezing step of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product, wherein the freezing temperature in the freezing step is set to -5.5 to -3.0°C. [2] The method for producing a frozen dessert according to [1], wherein the freezing point of the raw material liquid is -5.0 to -1.5°C. [3] The method for producing a frozen dessert according to [1] or [2], wherein the average diameter of ice crystals in the frozen dessert is 45 to 100 μm. [4] A method for improving the viability of bifidobacteria in the steps of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product and hardening the partially frozen product to obtain a frozen dessert, wherein the freezing temperature is adjusted so that the survival rate, expressed as a percentage, of the number of live bifidobacteria in the frozen dessert relative to the number of live bifidobacteria in the raw material liquid is 25% or more. [5] A frozen dessert containing live bifidobacteria, wherein the average diameter of the ice crystals of the frozen dessert is 45 to 100 μm.

[0006] According to the present invention, even without protecting the bifidobacteria with microcapsules, the death of bifidobacteria during the production process can be suppressed, and the survival rate can be improved.

[0007] 1 is a graph showing the survival rates of Examples 1 to 4. 2 is a graph showing the survival rates of Examples 5 to 8. 3 is a graph showing the survival rates of Examples 21 to 24.

[0008] The following definitions apply herein. Frozen desserts in the present invention include those generally classified as "frozen desserts" and frozen yogurt. Specific examples of "frozen desserts" include ice creams (ice cream, ice milk, lacto ice cream) and frozen desserts. Ice creams refer to processed or frozen products made from milk or milk-based foods, containing 3.0% or more milk solids (excluding fermented milk). Ice creams are classified into three categories: ice cream, ice milk, and lacto ice cream, depending on the amount of milk solids and milk fat they contain. On the other hand, those with a milk solids content of less than 3.0% are not classified as ice creams, but are defined as frozen desserts in the Ministry of Health, Labor and Welfare's "Standards and Criteria for Foods, Food Additives, etc." based on the Food Sanitation Act. Frozen yogurt is classified as "fermented milk" by type in the Ministerial Ordinance on the Ingredient Standards for Milk and Dairy Products. Fermented milk is defined as "a product made by fermenting milk or milk containing an equivalent or higher non-fat milk solids with lactic acid bacteria or yeast into a paste or liquid state, or a product obtained by freezing these," and its ingredient standards are stipulated as "a non-fat milk solids content of 8.0% or more, and a lactic acid bacteria or yeast count of 10 million / mL or more." Frozen yogurt corresponds to frozen fermented milk. The frozen dessert in the present invention may be any of ice cream, ice milk, lacto ice cream, and frozen yogurt.

[0009] The "freezing point" is the temperature at which a liquefied sample is cooled at an ambient temperature of -25°C and the product temperature is measured over time, at which point (freezing point) the temperature no longer drops due to the exothermic reaction that occurs when the liquid solidifies. "Freezing" refers to the process of increasing ice crystals while stirring the raw material liquid at a low temperature. In the freezing process in which the raw material liquid is frozen in a freezer to obtain a partially frozen product, the temperature of the partially frozen product immediately after it is discharged from the freezer is called the "freezing temperature." A "partially frozen product" refers to a product that contains ice crystals and has fluidity. "Hardening" refers to a state in which the water freezes and loses fluidity. "Overrun (hereinafter also referred to as "OR")" refers to the percentage of the air volume contained relative to the volume before air is incorporated. For example, an overrun of 100% means that the product contains the same volume of air as before air is incorporated. Unless otherwise specified, a numerical range expressed as "to" refers to a numerical range with the numbers before and after "to" as the lower and upper limits.

[0010] In this specification, the following measurement method is used. The diameter of ice crystals is the circle-equivalent diameter of ice crystals in an image observed with an optical microscope. The number of ice crystals that can be confirmed within the field of view of the optical microscope and the area of ​​all ice crystals are measured, and the diameter (circle-equivalent diameter) of each ice crystal is calculated using the formula: diameter = 2 × √(measured area / π). The arithmetic mean of the diameters of each ice crystal is taken as the average diameter. If the number of ice crystals confirmed within one field of view is less than 100, the number of fields of view is increased until the total number of ice crystals exceeds 100.

[0011] The content of components, etc. is measured using the following method. (1) Moisture: Measured by normal pressure heating and drying method (drying aid addition method). Specifically, a sample is dried in an incubator at 99°C for 4 hours, the weight loss is measured, and the moisture content is calculated using the following formula: Moisture (unit: mass %) = (mass of sample before drying (unit: g) - mass of sample after drying (unit: g)) / mass of sample before drying (unit: g) x 100 (2) Solid content: Calculated as solid content (mass %) = 100 - moisture (mass %).

[0012] (3) Fat and Milk Fat Content: This is measured using a method conforming to the method for quantifying milk fat in ice cream, as described in the "Ministry Ordinance on the Compositional Standards of Milk and Dairy Products." Specifically, 4 g of sample is placed in a small beaker, 3 mL of water is added, and the mixture is mixed thoroughly. The sample is then transferred to a Roerich tube. The beaker is thoroughly washed with 3 mL of water, and the washings are added to the Roerich tube and shaken. Next, 2 mL of ammonia water (a 25-30% aqueous solution of ammonia, colorless and transparent) is added and gently mixed. The Roerich tube is then placed in a 60°C water bath and heated for 20 minutes with occasional shaking. 10 mL of ethanol (a 95-96% aqueous solution) is then added and mixed thoroughly. Next, 25 mL of ether is added to the Roerich tube and gently rotated. When a uniform color is achieved, the ether gas is removed, and the tube is horizontally shaken vigorously for 30 seconds. Next, 25 mL of petroleum ether (boiling point below 60°C) is added, shaken for 30 seconds in the same manner, the stopper is loosened, and the tube is left standing upright for at least 2 hours until the supernatant becomes clear. The supernatant is placed in a beaker whose constant weight has been determined in advance. 25 mL of ether and 25 mL of petroleum ether are added to the Roerich tube using the same procedure as above, and mixed, and the supernatant is placed in the beaker. The tip of the side tube is washed with an equal mixture of ether and petroleum ether and added to the beaker. The beaker is heated to approximately 75°C to evaporate the solvent, dried in a dryer at an ambient temperature of 100-105°C for 1 hour, and then weighed. The increase in the beaker's constant weight is taken as the fat content. If the sample does not contain any fats other than milk fat, the fat content determined above is taken as the milk fat content. If the sample contains fats other than milk fat, the milk fat content is determined by subtracting the other fats from the fat content determined above.

[0013] (4) Non-fat milk solids: This is measured using a method conforming to the quantitative method for non-fat milk solids in fermented milk and lactic acid bacteria beverages described in the "Ministry Ordinance on the Compositional Standards, etc. of Milk and Dairy Products." Specifically, approximately 50 g of sample (if frozen, completely melted as quickly as possible at a temperature below 40°C) is accurately weighed and several drops of phenolphthalein solution are added. While stirring, 10% sodium hydroxide solution is gradually added to make the mixture slightly alkaline, and the mixture is then transferred to a volumetric flask. Water is added to make the total volume 100 mL, and 5 mL of this solution is transferred to a 150 mL Kjeldahl digestion flask. 0.2 g of a powder mixture of 9 g of potassium sulfate and 1 g of copper sulfate is added, followed by 10 mL of sulfuric acid, which is then added by allowing it to flow down the inside wall of the flask. The flask is then gradually heated, and the heating is increased slightly when white fumes of sulfur dioxide gas are emitted. After most of the foam has disappeared, the mixture is heated to a high temperature until the liquid turns a clear, pale blue color and no carbonized material is visible on the inside wall of the flask. The heating is then stopped when the liquid turns a clear, pale blue color and no carbonized material is visible on the inside wall of the flask. After cooling, carefully add 30 mL of water, cool again, and connect the flask to the distillation apparatus. In this case, 30 mL of 0.05 mol / L sulfuric acid and a few drops of methyl red solution are placed in a 200 mL absorption flask, with the bottom of the condenser submerged in the liquid. Next, 40 mL of 30% sodium hydroxide solution is placed through the funnel of the Kjeldahl distillation apparatus, rinsed in with 10 mL of water, the pinchcock is closed, and distillation is immediately initiated. When the distillate reaches 80 mL to 100 mL, the bottom of the condenser is removed from the liquid surface and a few mL of distillate is taken. After distillation is complete, the submerged portion of the condenser is washed with a small amount of water, and the washings are combined with the liquid in the absorption flask and titrated with 0.1 mol / L sodium hydroxide solution. The nonfat milk solids (unit: mass%) are calculated using the following formula: Non-fat milk solids = {0.0014 x (A - B)} / sample amount (unit: g) x 6.38 x 2.82 x 100 A: Amount of 0.1 mol / L sodium hydroxide solution required to neutralize 30 mL of 0.05 mol / L sulfuric acid (unit: mL) B: Amount of 0.1 mol / L sodium hydroxide solution required for titration (unit: mL) Indicator: Methyl red solution: Dissolve 1 g of methyl red in 50 mL of ethanol, add water to make 100 mL, and filter if necessary.(5) Milk solids The milk solids are calculated as the sum of the milk fat content determined by the method in (3) above and the non-fat milk solids determined by the method in (4) above.

[0014] <Method for manufacturing frozen dessert> The method for manufacturing frozen dessert of this embodiment includes a freezing step in which a raw material liquid containing live bifidobacteria is frozen to obtain a partially frozen product. The partially frozen product may be used as the frozen dessert as is, or a hardening step may be added to harden the partially frozen product, resulting in a frozen dessert. The hardened partially frozen product may be coated to provide a covering layer. The raw material liquid, the partially frozen product, and the hardened partially frozen product have the same composition by mass. The partially frozen product and the hardened partially frozen product have the same overrun value.

[0015] [Step of Preparing Raw Material Liquid] The raw material liquid is obtained by adding live bifidobacteria to an ice cream ingredient mix. The ice cream ingredient mix is ​​a composition containing water and a sweetener. It is preferable that it further contains a dairy ingredient. It may also contain other ingredients.

[0016] In the preparation process of the raw material liquid, the ingredients of the ice cream ingredient mix are dissolved or dispersed in water to obtain the ice cream ingredient mix. For example, the ingredients are added to water (or warm water) and mixed. The ingredients may be heated within a range where the ingredients do not deteriorate (for example, below 80°C). The ice cream ingredient mix is ​​preferably heat sterilized by a conventional method. If necessary, the ice cream ingredient mix may be filtered and homogenized. Next, live bifidobacteria are added to the ice cream ingredient mix and mixed uniformly to obtain the raw material liquid. The composition of the raw material liquid is the same as that of the ice cream ingredient mix, except for the bifidobacteria. The physical properties of the raw material liquid and the ice cream ingredient mix are almost the same.

[0017] [Bifidobacteria] Bifidobacteria are bacteria belonging to the genus Bifidobacterium. Known bifidobacteria can be used in fermented foods. For example, Bifidobacterium longum subsp. longum, Bifidobacterium breve, Bifidobacterium longum subsp. infantis, Bifidobacterium bifidum, Bifidobacterium lactis, Bifidobacterium animalis, animalis), and Bifidobacterium adolescentis. Bifidobacterium longum subsp. longum may be abbreviated simply as Bifidobacterium longum. Bifidobacterium longum subsp. infantis may be abbreviated simply as Bifidobacterium infantis. In the present invention, Bifidobacterium longum subsp. longum and Bifidobacterium breve are preferred. Among these, Bifidobacterium longum subsp. longum BB536 (NITE BP-02621) and Bifidobacterium breve MCC1274 (FERM BP-11175) are preferred. One type of bifidobacterium may be used, or two or more types may be used in combination.

[0018] The bacterium assigned the accession number NITE BP-02621 was internationally deposited under the Budapest Treaty on January 26, 2018, at the Patent Microorganisms Depositary Center of the National Institute of Technology and Evaluation (Room 122, 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, 292-0818) under the accession number NITE BP-02621. This bacterium is the same bacterium as Bifidobacterium longum subsp. longum BB536. The bacterium, assigned the accession number FERM BP-11175, was internationally deposited under the Budapest Treaty with the Patent Organism Depositary of the National Institute of Advanced Industrial Science and Technology (currently the Patent Organism Depositary of the National Institute of Technology and Evaluation, Room 120, 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, 292-0818) on August 25, 2009. This bacterium is identical to Bifidobacterium breve MCC1274.

[0019] The content of live Bifidobacterium cells in the raw material liquid is preferably 100 million (unit: Colony Forming Unit (CFU)) or more, 200 million or more, 300 million or more, 400 million or more, 500 million or more, 600 million or more, 700 million or more, 800 million or more, 900 million or more, 1 billion or more, 1.5 billion or more, 2 billion or more, 4 billion or more, 6 billion or more, 8 billion or more, 10 billion or more, 20 billion or more, 30 billion or more, 40 billion or more, or 50 billion or more per 100 g of raw material liquid, and preferably 100 billion or less, 90 billion or less, or 80 billion or less per 100 g of raw material liquid.

[0020] [Ice cream ingredient mix] Examples of sweeteners include sugars (white sugar, granulated sugar, brown sugar, brown sugar), starch syrup, powdered sugar, mixed sugar isomerized sugar, isomerized sugar, lactose, glucose, maltose, fructose, invert sugar, reduced malt syrup, honey, trehalose, palatinose, D-xylose, and other saccharides; sugar alcohols such as xylitol, sorbitol, maltitol, and erythritol; and high-intensity sweeteners such as saccharin sodium, cyclamate and its salts, acesulfame potassium, thaumatin, aspartame, sucralose, alitame, neotame, and stevioside contained in stevia extract. One type of sweetener may be used alone, or two or more types may be used in combination.

[0021] Examples of dairy ingredients include dairy products such as raw milk, cow's milk, cream, butter, skim milk powder, concentrated skim milk, condensed milk, cheese, whey, whey protein concentrate, etc. One type of dairy component may be used alone, or two or more types may be used in combination.

[0022] Examples of other ingredients include egg components, vegetable oils and fats, dietary fiber, emulsifiers, stabilizers, acidulants, flavorings, colorants, flavoring materials, and other food additives. Examples of stabilizers include locust bean gum, guar gum, and carrageenan. Examples of emulsifiers include glycerin fatty acid esters. Flavoring materials are food ingredients that can be uniformly dissolved or dispersed in the ice cream ingredient mix, and examples of such ingredients include salt, fruit juice, matcha (green tea), coffee, black tea, and alcohol. The ice cream ingredient mix may also contain solid materials that are uniformly dispersed in the ice cream ingredient mix, such as fruits and nuts and seeds, to the extent that they do not interfere with the production of frozen desserts.

[0023] The freezing point of the ice cream ingredient mix may be, as a lower limit, −5.0°C or higher, −4.9°C or higher, −4.8°C or higher, −4.7°C or higher, −4.6°C or higher, −4.5°C or higher, −4.4°C or higher, −4.3°C or higher, −4.2°C or higher, −4.1°C or higher, −4.0°C or higher, −3.9°C or higher, −3.8°C or higher, −3.7°C or higher, −3.6°C or higher, or −3.5°C or higher; The upper limit is preferably −1.5°C or less, −1.6°C or less, −1.7°C or less, −1.8°C or less, −1.9°C or less, −2.0°C or less, −2.1°C or less, −2.2°C or less, −2.3°C or less, −2.4°C or less, −2.5°C or less, −2.6°C or less, −2.7°C or less, −2.8°C or less, −2.9°C or less, −3.0°C or less, −3.1°C or less, or −3.2°C or less. Furthermore, the preferred freezing point range of the ice cream ingredient mix is ​​−5.0°C to −1.5°C, more preferably −4.5°C to −2.5°C, and even more preferably −4.0°C to −3.2°C. The above ranges facilitate increased survival of bifidobacteria. The freezing point of the ice cream ingredient mix can be adjusted by the solid content, etc. The freezing point of the raw material liquid can be considered to be the same as the freezing point of the ice cream ingredient mix.

[0024] The pH of the ice cream ingredient mix at 5°C is preferably 4 to 7, more preferably 5 to 7, and even more preferably 6 to 7. The pH of the ice cream ingredient mix can be adjusted by the component composition of the ice cream ingredient mix. The pH of the raw material liquid can be considered to be the same as the pH of the ice cream ingredient mix.

[0025] The viscosity of the ice cream ingredient mix at 5°C is preferably 90 mPa·s or more, 95 mPa·s or more, or 100 mPa·s or more as a lower limit, and 130 mPa·s or less, 125 mPa·s or less, or 120 mPa·s or less as an upper limit. A preferred range is 90 to 130 mPa·s, more preferably 95 to 130 mPa·s, and even more preferably 100 to 130 mPa·s. In this specification, the viscosity of the ice cream ingredient mix at 5°C is measured using a Brookfield viscometer with a No. 2 rotor at a rotation speed of 60 rpm. The viscosity of the raw material liquid can be considered to be the same as the viscosity of the ice cream ingredient mix.

[0026] Preferred embodiments of the composition of the ice cream ingredient mix are described below, but are not limited to these. The lower limit of the solids content, relative to the total mass of the ice cream ingredient mix, is preferably 30% by mass or more, 31% by mass or more, or 32% by mass or more, and the upper limit is preferably 50% by mass or less, 49% by mass or less, 48% by mass or less, 47% by mass or less, 46% by mass or less, or 45% by mass or less. For example, a range of 30 to 50% by mass is preferred, 32 to 48% by mass is more preferred, and 35 to 45% by mass is even more preferred. Within the above ranges, the freezing point range of the ice cream ingredient mix is ​​likely to be favorable. In addition, the flavor of the frozen dessert is likely to be favorable.

[0027] The sweetener content, relative to the total mass of the ice cream ingredient mix, is preferably 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, 10% by mass or more, 11% by mass or more, or 12% by mass or more as a lower limit, and preferably 20% by mass or less, 19% by mass or less, or 18% by mass or less as an upper limit. For example, a range of 5 to 20% by mass is preferred, 8 to 18% by mass is more preferred, 10 to 18% by mass is even more preferred, and 12 to 18% by mass is particularly preferred. Within the above ranges, the freezing point range of the ice cream ingredient mix is ​​likely to be favorable. In addition, the flavor of the frozen dessert is likely to be favorable.

[0028] The ice cream ingredient mix preferably contains fat, more preferably milk fat. The lower limit of the fat content, relative to the total mass of the ice cream ingredient mix, is preferably 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and the upper limit is preferably 20% by mass or less, 19% by mass or less, 18% by mass or less, 17% by mass or less, 16% by mass or less, 15% by mass or less, 14% by mass or less, or 13% by mass or less. For example, a range of 1 to 20% by mass is preferred, 2 to 18% by mass is more preferred, 3 to 15% by mass is even more preferred, and 4 to 13% by mass is particularly preferred. Within the above range, the freezing point range of the ice cream ingredient mix is ​​likely to be favorable. Additionally, the flavor of the frozen dessert is likely to be favorable.

[0029] The lower limit of the milk fat content, relative to the total mass of the ice cream ingredient mix, is preferably 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and the upper limit is preferably 20% by mass or less, 19% by mass or less, 18% by mass or less, 17% by mass or less, 16% by mass or less, 15% by mass or less, 14% by mass or less, or 13% by mass or less. For example, a range of 1 to 20% by mass is preferred, 2 to 18% by mass is more preferred, 3 to 15% by mass is even more preferred, and 4 to 13% by mass is particularly preferred. Within the above ranges, the freezing point range of the ice cream ingredient mix is ​​likely to be favorable. In addition, the flavor of the frozen dessert is likely to be favorable.

[0030] The lower limit of the non-fat milk solids content relative to the total mass of the ice cream ingredient mix is ​​preferably 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more, and the upper limit is preferably 15% by mass or less, 14% by mass or less, 13% by mass or less, or 12% by mass or less. For example, a range of 1 to 15% by mass is preferred, 3 to 12% by mass is more preferred, 4 to 12% by mass is even more preferred, and 5 to 12% by mass is particularly preferred. When the content is at or above the lower limit of the above range, the fat emulsion stability of the ice cream ingredient mix tends to be good. When the content is below the upper limit, the manufacturing suitability tends to be good.

[0031] Preferred compositions of the ice cream ingredient mix include, for example, the following compositions (i) and (ii): Composition (i): An ice cream ingredient mix having, relative to the total mass of the ice cream ingredient mix, 35 to 45% by mass of solids, 12 to 18% by mass of sweetener, 4 to 13% by mass of fat, and 4 to 12% by mass of non-fat milk solids. Composition (ii): An ice cream ingredient mix having, relative to the total mass of the ice cream ingredient mix, 36 to 40% by mass of solids, 15 to 18% by mass of sweetener, 9 to 13% by mass of fat, and 7 to 12% by mass of non-fat milk solids.

[0032] [Freezing Step] Next, the raw material liquid is frozen. In the freezing step, the raw material liquid is frozen at a temperature lower than the freezing point while flowing, to obtain a partially frozen product with fluidity. At this time, freezing may be performed while incorporating air. Freezing can be performed by a known method. For example, it can be performed using a known continuous freezer or a known batch freezer. A typical continuous freezer comprises a roughly cylindrical cylinder and a dasher having a rotating shaft coaxial with the cylinder. The cylinder freezes the water in the raw material liquid flowing inside from one end to the other end. The dasher rotates while scraping off any deposits on the inner wall of the cylinder, stirring the inside of the cylinder. Below, the freezing step using a continuous freezer will be described as an example, but a batch freezer can also be used.

[0033] First, the ice cream ingredient mix and a raw material liquid containing bifidobacteria are stirred and mixed and supplied to a continuous freezer. The raw material liquid supplied to the continuous freezer is mixed with air and introduced into a cylinder, where it is frozen while containing air bubbles within the cylinder, becoming a partially frozen product that is then discharged. The temperature (freezing temperature) of the partially frozen product discharged from the continuous freezer may be, as a lower limit, −5.5°C or higher, −5.4°C or higher, −5.3°C or higher, −5.2°C or higher, −5.1°C or higher, −5.0°C or higher, −4.9°C or higher, −4.8°C or higher, −4.7°C or higher, −4.6°C or higher, −4.5°C or higher, −4.4°C or higher, −4.3°C or higher, −4.2°C or higher, −4.1°C or higher, or −4.0°C or higher, and may, as an upper limit, be −3.0°C or lower, −3.1°C or lower, −3.2°C or lower, −3.3°C or lower, −3.4°C or lower, or −3.5°C or lower. When the freezing temperature is equal to or higher than the lower limit, the survival rate of bifidobacteria is likely to be increased. When the freezing temperature is equal to or lower than the upper limit, the shape retention of the partially frozen product is likely to be increased. A particularly suitable range is -5.5 to -3.0°C, preferably -5.0 to -3.0°C, more preferably -4.5 to -3.0°C, and particularly preferably -4.0 to -3.5°C. When the freezing temperature is equal to or higher than the lower limit of the above range, the survival rate of bifidobacteria is excellent. When the freezing temperature is equal to or lower than the upper limit of the above range, the shape retention of the partially frozen product is likely to be excellent.

[0034] The temperature of the partially frozen product (freezing temperature) is equal to or lower than the freezing point of the raw material liquid, and the absolute value of the difference between the freezing temperature and the freezing point of the raw material liquid is 2.0°C or less. The temperature (freezing temperature) of the partially frozen product is preferably (T-2.0) ° C. to T ° C., (T-1.9) ° C. to T ° C., (T-1.8) ° C. to T ° C., (T-1.7) ° C. to T ° C., (T-1.6) ° C. to T ° C., (T-1.5) ° C. to T ° C., (T-1.4) ° C. to T ° C., (T-1.3) ° C. to T ° C., (T-1.2) ° C. to T ° C., (T-1.1) ° C. to T ° C., (T-1.0) ° C. to T ° C., (T-0.9) ° C. to T ° C., (T-0.8) ° C. to T ° C., (T-0.7) ° C. to T ° C., (T-0.6) ° C. to T ° C., (T-0.5) ° C. to T ° C., (T-0.4) ° C. to T ° C., or (T-0.3) ° C. to T ° C.

[0035] The overrun value (volume basis) when air is mixed into the raw material liquid in the freezer (freezing step) may be 20% or more, 25% or more, or 30% or more as a lower limit, and 150% or less, 140% or less, 130% or less, 120% or less, or 110% or less as an upper limit. A suitable range is preferably about 20 to 140%, more preferably 25 to 130%, and even more preferably 30 to 120%. The rotation speed of the dasher in the continuous freezer is preferably, for example, 200 to 400 rpm.

[0036] [Shaping Step / Hardening Step] The method for producing a frozen dessert using the partially frozen product obtained in the freezing step is not particularly limited. For example, the partially frozen product may be shaped into a desired product form to form a molded product, and the molded product may be cooled and hardened to produce a frozen dessert consisting of a hardened product. The shaping step can be carried out using a known method. For example, a method of filling the partially frozen product into a cup or mold, etc., and shaping it, or a method of extrusion molding the partially frozen product, etc., can be used. In the hardening step, the molded product is frozen and hardened, for example, in a freezer with an ambient temperature of −30° C. or below. A composite frozen dessert consisting of a hardened partially frozen product (frozen dessert) and the filling may be produced by adding ingredients to the partially frozen product and shaping and hardening it. The hardened partially frozen product (frozen dessert) preferably consists of a homogeneous continuous phase formed by hardening a uniform oil-in-water emulsion.

[0037] In the present invention, "good survival rate of bifidobacteria" means that in a frozen dessert produced through a freezing step in which a raw material liquid containing live bifidobacteria is frozen to obtain a partially frozen product, and a hardening step in which the partially frozen product is hardened, few bifidobacteria in the raw material liquid die during the production process, and many bifidobacteria remain viable in the frozen dessert. According to the production method of this embodiment, as shown in the examples described below, by adjusting the freezing temperature in the freezing step, the survival rate of bifidobacteria can be improved without protecting the bifidobacteria with microcapsules. For example, by setting the freezing temperature in the freezing step to -5.5 to -3.0°C, the survival rate, expressed as a percentage of the number of live bifidobacteria in the frozen dessert relative to the number of live bifidobacteria in the raw material liquid, can be improved to 25% or more, preferably 30% or more, more preferably 35% or more, and even more preferably more than 55%.

[0038] According to the manufacturing method of this embodiment, a frozen dessert containing viable bifidobacteria can be obtained. For example, a frozen dessert can be obtained in which the viable cell count of bifidobacteria per 100 g of the frozen dessert made from a partially frozen and hardened product is 40 billion CFU or more, preferably 50 billion CFU or more, and more preferably 60 billion CFU or more. The upper limit is not particularly limited, but may be, for example, 90 billion CFU or less, or 80 billion CFU or less. Furthermore, the viable cell count of bifidobacteria per 100 g of the frozen dessert may range from 40 billion to 90 billion CFU, 50 billion to 90 billion CFU, or 60 billion to 80 billion CFU. For example, the average diameter of ice crystals in a frozen dessert made from a hardened partially frozen material may be, as a lower limit, 45 μm or more, 46 μm or more, 47 μm or more, 48 μm or more, 56 μm or more, 57 μm or more, 58 μm or more, 59 μm or more, 60 μm or more, 63 μm or more, 65 μm or more, 67 μm or more, 70 μm or more, 71 μm or more, 72 μm or more, 73 μm or more, 74 μm or more, 75 μm or more, 76 μm or more, 77 μm or more, or 78 μm or more, and may be, as an upper limit, 100 μm or less, 99 μm or less, 98 μm or less, 97 μm or less, 96 μm or less, 95 μm or less, 94 μm or less, 93 μm or less, 92 μm or less, 91 μm or less, 90 μm or less, or 85 μm or less. A particularly preferred range is 45 to 100 μm, more preferably 56 to 100 μm, and even more preferably 60 to 100 μm. If the average diameter of the ice crystals is at least the lower limit of the above range, the survival rate of bifidobacteria can be increased, and if it is at or below the upper limit, excessive ice crystal texture can be suppressed. The average diameter of the ice crystals in frozen desserts can be adjusted by the freezing temperature, etc. For example, increasing the freezing temperature tends to increase the diameter of the ice crystals.

[0039] When a frozen dessert contains milk fat, for example, the average fat particle size in a frozen dessert made from a hardened partially frozen product is preferably 1.0 μm or more, 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm or more, 1.5 μm or more, or 1.6 μm or more as a lower limit, and preferably 25 μm or less, 24 μm or less, 23 μm or less, 22 μm or less, 21 μm or less, 20 μm or less, 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, 10 μm or less, 9 μm or less, 8 μm or less, or 7 μm or less as an upper limit. A preferred range is 1.0 to 25 μm, more preferably 1.0 to 20 μm, and even more preferably 1.0 to 15 μm. The average fat particle size of frozen desserts can be adjusted by the pressure used in freezing and homogenization. For example, lowering the pressure tends to increase the average fat particle size, while increasing the pressure tends to decrease the average fat particle size.

[0040] <Method for Improving Survival of Bifidobacteria> The method for improving the survival of bifidobacteria of the present invention is a method for improving the survival of bifidobacteria in the steps of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product and hardening the partially frozen product to obtain a frozen dessert, in which the freezing temperature is adjusted so that the survival rate, expressed as a percentage, of the number of live bifidobacteria in the frozen dessert relative to the number of live bifidobacteria in the raw material liquid is 25% or more. The survival rate is determined by the method described in the Examples below.

[0041] As shown in the Examples below, in the freezing step, changes in overrun or dasher rotation speed do not affect the survival rate of bifidobacteria, and adjusting the freezing temperature can improve the survival rate of bifidobacteria. For example, when the composition of the raw material liquid and the freezing conditions other than the freezing temperature are the same, increasing the freezing temperature toward the freezing point tends to increase the survival rate of bifidobacteria. Therefore, in the freezing step, it is preferable to adjust the freezing temperature so that the survival rate is 25% or more, preferably 30% or more, more preferably 35% or more, and even more preferably more than 55%.

[0042] The present invention has the following aspects. <1> A method for producing a frozen dessert, comprising a freezing step of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product, wherein the bifidobacteria are one or more species selected from Bifidobacterium longum subsp. longum and Bifidobacterium breve, and the freezing temperature in the freezing step is -5.5 to -3.0°C. <2> The method for producing a frozen dessert according to <1>, wherein the bifidobacteria are one or both of NITE BP-02621 and FERM BP-11175. <3> The method for producing a frozen dessert according to <1> or <2>, wherein the freezing point of the raw material liquid is -5.0 to -1.5°C, the freezing temperature is below the freezing point of the raw material liquid, and the absolute value of the difference between the freezing temperature and the freezing point of the raw material liquid is 2.2°C or less. <4> The method for producing a frozen dessert according to <1> or <2>, wherein the freezing point of the liquid ingredient is -5.0 to -1.5°C, the freezing temperature is below the freezing point of the liquid ingredient, and the absolute value of the difference between the freezing temperature and the freezing point of the liquid ingredient is 2.0°C or less. <5> The method for producing a frozen dessert according to <3>, wherein the freezing point of the liquid ingredient is -5.0 to -1.5°C, the freezing temperature is -5.0 to -3.0°C, and when the freezing point of the liquid ingredient is T°C, the freezing temperature is (T-1.8)°C to T°C. <6> The method for producing a frozen dessert according to <3>, wherein the freezing point of the liquid ingredient is -4.5°C to -2.5°C, the freezing temperature is -4.5 to -3.0°C, and when the freezing point of the liquid ingredient is T°C, the freezing temperature is (T-1.3)°C to T°C. <7> The method for producing a frozen dessert according to the above <3>, wherein the freezing point of the liquid ingredient is −4.0° C. to −3.2° C., the freezing temperature is −4.0° C. to −3.5° C., and when the freezing point of the liquid ingredient is T° C., the freezing temperature is (T−0.8)° C. to T° C. <8> The method for producing a frozen dessert according to any one of the above <1> to <7>, wherein the viscosity of the liquid ingredient at 5° C. is 90 to 130 mPa s.<9> The method for producing a frozen dessert according to any one of <1> to <8>, wherein the pH of the liquid ingredient at 5°C is 4 to 7. <10> The method for producing a frozen dessert according to any one of <1> to <8>, wherein the pH of the liquid ingredient at 5°C is 5 to 7. <11> The method for producing a frozen dessert according to any one of <1> to <8>, wherein the pH of the liquid ingredient at 5°C is 6 to 7. <12> The method for producing a frozen dessert according to any one of <1> to <11>, wherein the liquid ingredient is a mixture of live bifidobacteria and an ice cream ingredient mix, and the ice cream ingredient mix contains water, a sweetener, and a milk ingredient. <13> The method for producing a frozen dessert according to the above <12>, wherein the ice cream ingredient mix has a solid content of 35 to 45% by mass, a sweetener content of 12 to 18% by mass, a fat content of 4 to 13% by mass, and a non-fat milk solids content of 4 to 12% by mass. <14> The method for producing a frozen dessert according to the above <12>, wherein the ice cream ingredient mix has a solid content of 36 to 40% by mass, a sweetener content of 15 to 18% by mass, a fat content of 9 to 13% by mass, and a non-fat milk solids content of 7 to 12% by mass. <15> The method for producing a frozen dessert according to any one of the above <1> to <14>, wherein the content of live bifidobacteria per 100 g of the ingredient liquid is 2 billion to 100 billion CFU. <16> The method for producing a frozen dessert according to any one of <1> to <14>, wherein the content of live Bifidobacterium is 10 billion to 100 billion CFU per 100 g of the liquid material. <17> The method for producing a frozen dessert according to any one of <1> to <14>, wherein the content of live Bifidobacterium is 50 billion to 100 billion CFU per 100 g of the liquid material. <18> The method for producing a frozen dessert according to any one of <1> to <17>, wherein an overrun in the freezing step is 20 to 140%. <19> The method for producing a frozen dessert according to any one of <1> to <17>, wherein an overrun in the freezing step is 25 to 130%.<20> The method for producing a frozen dessert according to any one of <1> to <17>, wherein an overrun in the freezing step is 30 to 120%. <21> The method for producing a frozen dessert according to any one of <1> to <20>, wherein the freezing step is carried out using a continuous freezer. <22> The method for producing a frozen dessert according to <21>, wherein the rotation speed of a dasher of the continuous freezer in the freezing step is 200 to 400 rpm.

[0043] <23> The method for producing a frozen dessert according to any one of <1> to <22>, comprising a step of hardening the partially frozen material to obtain a frozen dessert, wherein a survival rate, expressed as a percentage, of the number of viable bifidobacteria in the frozen dessert relative to the number of viable bifidobacteria in the raw material liquid is 25% or more. <24> The method for producing a frozen dessert according to <23>, wherein the survival rate is 25% or more. <25> The method for producing a frozen dessert according to <23>, wherein the survival rate is 30% or more. <26> The method for producing a frozen dessert according to <23>, wherein the survival rate is 35% or more. <27> The method for producing a frozen dessert according to <23>, wherein the survival rate is more than 55%. <28> The method for producing a frozen dessert according to any one of <23> to <27>, wherein the average diameter of ice crystals in the frozen dessert is 45 to 100 μm. <29> The method for producing a frozen dessert according to any one of the above <23> to <27>, wherein the average diameter of ice crystals in the frozen dessert is 56 to 100 μm. <30> The method for producing a frozen dessert according to any one of the above <23> to <27>, wherein the average diameter of ice crystals in the frozen dessert is 60 to 100 μm. <31> The method for producing a frozen dessert according to any one of the above <23> to <30>, wherein the frozen dessert contains milk fat and the average fat particle diameter in the frozen dessert is 1.0 to 25 μm. <32> The method for producing a frozen dessert according to any one of the above <23> to <30>, wherein the frozen dessert contains milk fat and the average fat particle diameter in the frozen dessert is 1.0 to 20 μm. <33> The method for producing a frozen dessert according to any one of <23> to <30>, wherein the frozen dessert contains milk fat, and the average fat particle size in the frozen dessert is 1.0 to 15 μm.

[0044] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0045] <Measurement Method> [pH of Ice Cream Ingredient Mix] An ice cream ingredient mix was prepared and stored overnight in a refrigerator at 5°C, and then the pH was measured using a pH meter (Horiba Ltd., product name "LAQUA F-72").

[0046] [Viscosity of Ice Cream Ingredient Mix] An ice cream ingredient mix was prepared and stored overnight in a refrigerator at 5°C, after which the viscosity was measured. Specifically, approximately 100 ml of the ice cream ingredient mix was poured into a 200 ml beaker, and the mixture was cooled to 5°C on ice. The viscosity was then measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd. under the product name "PB-80L") with a No. 2 rotor at a rotation speed of 60 rpm, and the value was taken as the viscosity of the ice cream ingredient mix at 5°C.

[0047] [Viability of Bifidobacteria] The viable cell count C1 of bifidobacteria in the raw material liquid immediately before being fed to the continuous freezer, and the viable cell count C2 of bifidobacteria in a frozen dessert sample obtained by filling a 90 mL paper cup with the partially frozen product discharged from the continuous freezer and freezing it overnight in an atmosphere of -35°C, were measured using the following method. The viability (unit: %) was calculated using the following formula (1): Viability = C2 / C1 × 100 (1) (Method for Measuring Viable Cell Count) 5.0 g of the sample to be measured (raw material liquid or frozen dessert sample) was collected aseptically. The collected sample (5.0 g) was suspended in 95.0 g of sterilized physiological saline to prepare 100 g of sample suspension. The sample suspension was then serially diluted to the desired concentration using sterilized physiological saline to prepare a sample dilution. The obtained sample dilutions were spread in aliquots of 0.1 to 1.0 ml onto petri dishes, mixed with agar medium (TOS propionic acid agar medium), and allowed to stand and solidify. The volume V (unit: ml) of the sample dilutions spread onto the petri dishes was determined so that the number of colonies per dish would be 30 to 300, and three petri dishes were used per sample. After the medium solidified, the samples were cultured at 37°C for 72 hours under anaerobic conditions. After the culture was completed, the number of colonies (unit: CFU) on each of the three petri dishes was counted, and the average value (colony average, unit: CFU) was calculated. The viable cell count (unit: CFU / g) was calculated using the following formula (2): Viable cell count [CFU / g] = colony average [CFU] × (1 [ml] / volume V [ml]) × dilution factor of serial dilution × 100 [g] ÷ 5.0 [g] (2)

[0048] [Average Ice Crystal Diameter] Partially frozen material discharged from a continuous freezer was filled into a 90 mL paper cup and frozen overnight in a -35°C atmosphere. A portion of the frozen dessert sample was taken and observed under an optical microscope. The circle-equivalent diameter of the ice crystals in the observed image was determined as the diameter. The measurement equipment used was an optical microscope (Nikon Co. Ltd., product name: Nikon Eclipse E400) and a slide (Matsunami Glass Ind., Ltd., product name: S1225). The temperature inside a temperature-controllable refrigerated glove box was set to -15°C, and the optical microscope and experimental equipment were placed inside. After the interior of the box had cooled sufficiently, the frozen dessert sample to be measured was transferred into the box and stored for approximately 12 hours to adjust the temperature. A small sample was taken from the center of the frozen dessert sample using a spoon. The sample was placed in the center of a slide, and a few drops of isobutanol were added to remove fat. Another slide was placed on top of this to expel air bubbles. The slide was held away from the sample and slowly moved back and forth and side to side to disperse the ice crystals in the sample so that they did not overlap. In this state, the slide was placed on an observation stage, and the ice crystals in the sample were observed at 350x magnification. The image of the obtained field of view was analyzed using image analysis software (Media Cybernetics, product name Image Pro Plus ver. 7.0) to measure the area of ​​the ice crystals observed two-dimensionally from above. The diameter (R, equivalent diameter of a circle) of the measured area (A) was calculated using the following formula: R = 2 × √(A / π) The number and diameter (R, unit: μm) of all ice crystals observed within the field of view were measured, and the average diameter was calculated.

[0049] [Average fat particle diameter] The partially frozen product discharged from the continuous freezer was filled into a 90 mL paper cup and frozen in an atmosphere of -35°C to prepare a frozen dessert sample for measurement. The frozen dessert sample was stored overnight in a refrigerator at 5°C to thaw, and then distilled water was added to the sample to dilute it 100 to 2000 times to prepare a diluted solution. The particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., product name "Partica LA-950V2"). The particle size distribution of the particles contained in the sample was obtained, and the 50% diameter on a volume basis in the obtained particle size distribution was taken as the average fat particle diameter (median diameter).

[0050] <Ingredients> Dairy ingredient (1): Cream (milk fat 45.0% by mass, non-fat milk solids 5.2% by mass, solids 50.2% by mass). Dairy ingredient (2): Skim milk powder (milk fat 1.0% by mass, non-fat milk solids 95.2% by mass, solids 96.2% by mass). Sweetener: Granulated sugar. Stabilizer: Locust bean gum, guar gum, carrageenan. Emulsifier: Glycerin fatty acid ester. Bifidobacterium (1): Bifidobacterium breve MCC1274 (FERM BP-11175 strain). Bifidobacterium (2): Bifidobacterium lougum BB536 (NITE BP-02621 strain).

[0051] The following Examples 1, 5, and 21 are comparative examples, and Examples 2 to 4, 6 to 20, and 22 to 24 are working examples.

[0052] Example 1: A raw material liquid was prepared by adding bifidobacteria to an ice cream ingredient mix having the composition shown in Table 1. Specifically, the ingredients shown in Table 1 were mixed and dissolved by stirring at 70°C, followed by heat sterilization at 90°C for 30 seconds using a plate sterilizer, homogenization at 15 MPa using a homogenizer, and cooling to 5°C to obtain an ice cream ingredient mix. Live bifidobacteria (1) were added to the cooled ice cream ingredient mix, and the mixture was stirred for 7 minutes to obtain a raw material liquid. The amount of bifidobacteria added was such that the bacterial count per 100 g of the raw material liquid was 50 to 100 billion CFU. The obtained raw material liquid (5°C) was supplied to a continuous freezer (SOREN product name "CS-200-2P") and frozen under the conditions shown in Table 2 to obtain a partially frozen product. The resulting partially frozen product was filled into a 90 mL paper cup and then cooled in a -35°C freezer for 18 hours or more to harden, producing a frozen dessert. The items listed in the table were measured using the methods described above. The results are shown in the table (the same applies hereinafter).

[0053] [Examples 2 to 4] Frozen desserts were produced in the same manner as in Example 1, except that the freezing temperature was changed as shown in Table 2. Figure 1 is a graph showing the survival rates of Examples 1 to 4 when the viable cell count of bifidobacteria in the raw material liquid is taken as 100%. In the figure, "*" indicates that there was a significant difference (p<0.05) in the Tukey HSD test (the same applies hereinafter).

[0054] [Examples 5 to 8] Frozen desserts were produced in the same manner as in Examples 1 to 4, except that Bifidobacterium (1) was replaced with Bifidobacterium (2). Figure 2 is a graph showing the survival rates of Examples 5 to 8, when the viable cell count of Bifidobacterium in the raw material liquid was taken as 100%.

[0055]

[0056]

[0057] As shown in Table 2 and Figures 1 and 2, the survival rate of bifidobacteria was significantly improved by changing the freezing temperature. In particular, high survival rates were obtained when the freezing temperature was in the range of -5.5 to -3.0°C, more preferably in the range of -4.5 to -3.5°C.

[0058] [Examples 9 to 11] Frozen desserts were produced in the same manner as in Example 2, except that the overrun values ​​were changed as shown in Table 3.

[0059] Examples 12 to 14 Frozen desserts were produced in the same manner as in Example 6, except that the overrun values ​​were changed as shown in Table 3.

[0060] [Examples 15 to 17] Frozen desserts were produced in the same manner as in Example 2, except that the dasher rotation speed was changed as shown in Table 4.

[0061] [Examples 18 to 20] Frozen desserts were produced in the same manner as in Example 6, except that the dasher rotation speed was changed as shown in Table 4.

[0062]

[0063]

[0064] As shown in the results in Table 3, there was no significant difference in the survival rate of bifidobacteria due to changes in overrun. As shown in the results in Table 4, there was no significant difference in the survival rate of bifidobacteria due to changes in dasher rotation speed.

[0065] [Examples 21 to 24] In these examples, survival rates were measured by changing the difference between the freezing temperature and the freezing point. The raw material liquid for the ice cream ingredient mix was formulated as shown in Table 5. Frozen desserts were otherwise produced in the same manner as in Example 2. In the formulations of Examples 21 to 24, the solid content was in the range of 30 to 50%. The survival rate of bifidobacteria was measured using the method described above. The results are shown in Table 5 and Figure 3.

[0066]

[0067] As shown in the results in Table 5 and Figure 3, the smaller the difference between the freezing temperature and the freezing point, the more improved the survival rate of bifidobacteria. The survival rate in Example 21 was 23%, and the survival rate in Example 22 was 37%, showing a significant difference between the two.

Claims

1. A method for producing a frozen dessert, comprising a freezing step of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product, wherein the freezing temperature in the freezing step is below the freezing point of the raw material liquid, and the absolute value of the difference between the freezing temperature and the freezing point of the raw material liquid is 2.0°C or less.

2. The method for producing frozen desserts according to claim 1, wherein the freezing point of the liquid material is -5.0 to -1.5°C.

3. The method for producing a frozen dessert according to claim 1, wherein the average diameter of the ice crystals in the frozen dessert is 45 to 100 μm.

4. A method for improving the survival rate of bifidobacteria in a process of freezing a raw material liquid containing live bifidobacteria to obtain a partially frozen product and hardening the partially frozen product to obtain a frozen dessert, the method comprising adjusting the freezing temperature so that the survival rate, expressed as a percentage, of the number of live bifidobacteria in the frozen dessert relative to the number of live bifidobacteria in the raw material liquid is 25% or more.

5. A frozen dessert containing live bifidobacteria, wherein the average diameter of the ice crystals of said frozen dessert is 45 to 100 μm.

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