JP2008187986A - Sterilizing method for fermented milk material, producing method for fermented milk, and fermented milk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the flavor of fermented milk without ruining its favorable qualities. <P>SOLUTION: This method for sterilizing a fermented milk material comprises: a first heating process in which a fermented milk material is heated up to a first process temperature from 85°C to 95°C and then retained for 5 to 15 minutes; a second heating process in which after the first heating process, the fermented milk material is heated up to a second process temperature from 100°C to 150°C and then retained for 2 to 5.5 seconds; and a cooling process in which after the second heating process, the fermented milk material is boiled under reduced pressure and cooled down to a third process temperature below the second process temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for sterilizing fermented milk raw materials, a method for producing fermented milk using the sterilization method, and fermented milk obtained by the method.

Fermented milk is generally a product obtained by fermenting mammalian milk as a main raw material and fermenting it with lactic acid bacteria, bifidobacteria, yeast, etc. (hereinafter sometimes referred to as lactic acid bacteria etc.), and depending on the composition of the product, (1) Plain fermented milk fermented using only milk components as raw materials, (2) Flavored fermented milk seasoned with sweeteners, fragrances, chocolate, coffee, etc. (3) Fermented milk containing fruits with added fruits, etc. are categorized. Moreover, according to the property of a product, it classify | categorizes into (1) solid fermented milk, (2) pasty fermented milk, (3) liquid fermented milk, etc. By such a combination of classifications, fermented milk products suitable for each taste are manufactured for a wide range of consumer ages ranging from infants to the elderly.
Fermented milk is manufactured in the order of sterilization (may include homogenization) consisting of heating and cooling of the fermented milk raw material, addition of starter (lactic acid bacteria, etc.), fermentation, and cooling after preparing the fermented milk raw material. .
The purpose of the sterilization process of fermented milk raw materials is to kill harmful bacteria such as pathogenic bacteria, improve the properties of lactic acid bacteria as a culture medium, prevent water separation of fermented milk and harden the card. Conventionally, in sterilization of fermented milk raw materials, the temperature is raised to a temperature of 85 ° C. or higher and 95 ° C. or lower and heated for 5 to 15 minutes (hereinafter referred to as “conventional sterilization method”). (See Non-Patent Document 1).
Moreover, in order to perform suitable protein denaturation in order to obtain a suitable hardness or viscosity of fermented milk and to perform microbial sterilization, the heat treatment under two different conditions is combined in the sterilization process. A featured method for sterilizing fermented milk raw materials has also been reported (see Patent Document 1).

Conventionally, as a method for sterilizing milk raw materials, drinking milk, and the like, an ultra-high temperature heat treatment method (hereinafter referred to as UHT method) has been mainstream. There are two types of UHT methods, an indirect heat sterilization method and a direct heat sterilization method.
The indirect heat sterilization method is characterized by using a heat exchanger for heating, for example, in an operation of heating drinking milk to a sterilization temperature. The drinking milk is brought into contact with a heat medium through a heat transfer wall, and this heat transfer is performed. Heat through the wall. On the other hand, in the direct heat sterilization method, for example, drinking milk and pressurized steam are brought into direct contact and heated. As this direct heat sterilization method, there are a method in which pressurized steam is blown into drinking milk (injection method) and a method in which drinking milk is discharged into a steam-filled container (infusion method). (See Non-Patent Document 2 or Non-Patent Document 3 above.)

Patent Document 2 below relates to drinking milk that does not go through a fermentation process, and it is described that heat sterilization inevitably causes damage due to heat and changes in flavor due to generation of a heated odor. It is described that the amount of sulfides and ketones that are not contained in raw milk but contained in the heat-sterilized milk can be reduced by performing the infusion type direct heating method under specific conditions.
Japanese Patent No. 3746982 JP 2005-46140 A Edited by Kunio Yamauchi et al., “Encyclopedia of Milk”, Asakura Shoten Co., Ltd., 1998, p. 238 Edited by Kunio Yamauchi et al., “Encyclopedia of Milk”, Asakura Shoten Co., Ltd., 1998, pages 153-155 Shinji Iwatsuki, 1 outside, “New Sterilization Technology”, Dairy Technology, Japan Dairy Industry Association, October 20, 2000, Volume 50, 161-185

As mentioned above, for drinking milk that has not undergone the fermentation process, proposals have been made regarding the suppression of heated odor by heat sterilization, but for fermented milk produced through the fermentation process, heat sterilization of raw materials and product flavors have been proposed. There is no report on the relationship. In fermented milk, unlike drinking milk, the heat treatment conditions affect not only the bactericidal effect but also the properties such as the viscosity and hardness of fermented milk obtained after fermentation. Whether it can be applied to fermented milk is unpredictable.
This invention is made | formed in view of the said situation, Comprising: It aims at improving a flavor, without impairing the preferable property of fermented milk.

In order to achieve the above-mentioned object, the present invention is a method for sterilizing fermented milk raw material, raising the temperature of the fermented milk raw material to a first treatment temperature of 85 ° C. or higher and 95 ° C. or lower and holding it for 5 minutes or longer and 15 minutes or shorter Performing the first heat treatment step, and after the first heat treatment, raising the temperature to a second treatment temperature of 100 ° C. or higher and 150 ° C. or lower and holding for 2 seconds or more and 5.5 seconds or less Disinfection of fermented milk raw material characterized by comprising a step of performing a heat treatment and a step of cooling to a third treatment temperature lower than the second treatment temperature by boiling under reduced pressure after the second heat treatment Provide a method.
The present invention also comprises a step of preparing a fermented milk raw material, a step of sterilizing the fermented milk raw material by the sterilization method of the present invention, and a step of fermenting the fermented milk raw material after sterilization. A manufacturing method is provided.
Moreover, this invention provides fermented milk whose content of 2-pentanone is 31 ppb or less.

  ADVANTAGE OF THE INVENTION According to this invention, a heating odor can be reduced and flavor can be improved, without impairing the preferable property of fermented milk.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following preferred embodiments, and can be freely changed within the scope of the present invention. In the present specification, percentages are expressed by mass unless otherwise specified.

<Fermented milk ingredients>
The fermented milk raw material in this invention mixes milk and the other raw material added as needed with water.
The milk is not particularly limited as long as it is commonly used in the production of fermented milk. For example, raw milk such as cow's milk, horse milk, goat milk, and sheep milk, skim milk, skim milk powder, and reduced milk in which skim milk powder is dissolved. , Milk protein, whey protein isolate (WPI) and the like. Moreover, the raw material containing fats, such as a butter and cream, can also be used as needed. In terms of improving the flavor, the milk fat in the fermented milk raw material is preferably 1.5% or more, particularly preferably 2.0% or more.
As other raw materials, various saccharides, emulsifiers, thickeners, sweeteners, acidulants, fruit juices, fragrances, vegetable fats and other food materials can be appropriately blended. Specifically, sugars such as sucrose, fructose, glucose, dextrin, reduced maltose; sugar alcohols such as sorbitol, xylitol, erythritol, lactitol, reduced starch syrup, reduced maltose starch syrup; orange juice, lemon juice, apple juice, strawberry juice Juices such as sucrose fatty acid ester, glycerin fatty acid ester, lecithin; thickeners such as pectin, agar, gelatin, carrageenan, guar gum, xanthan gum, locust bean gum; coconut oil, olive oil And vegetable fats such as soybean oil.

<Method of sterilizing fermented milk ingredients>
In the sterilization method of the present invention, the heat treatment is performed at least under two different conditions of the first heat treatment and the second heat treatment.
[First heat treatment]
In the first heat treatment, the temperature is raised to a first treatment temperature of 85 ° C. or more and 95 ° C. or less, and the heat treatment is performed while maintaining the first treatment temperature for 5 minutes or more and 15 minutes or less. This heating condition is equivalent to the conventional sterilization method, and a sufficient sterilization effect can be obtained by this treatment. Moreover, the fermented milk raw material can be heat-denatured by the first heat treatment, so that the viscosity of the fermented milk obtained after the fermentation step can be within a preferable range.
If the first treatment temperature is lower than the above range, or if the holding time to be kept at the first treatment temperature is shorter than the above range, the heat history is insufficient, and the sterilization effect and / or the heat denaturation of the fermented milk raw material is not possible. May be sufficient. On the other hand, if the first treatment temperature is higher than the above range, or if the holding time is longer than the above range, the structure of the fermented milk may become soft. In particular, it is desirable to perform heat treatment at 90 to 95 ° C. for 5 to 10 minutes.
In order to perform the heat treatment based on the above conditions, the first heat treatment is desirably performed by an indirect heating method using a plate sterilizer, a tubular sterilizer, or the like.

[Second heat treatment and first cooling treatment]
In the second heat treatment, the temperature is raised to a second treatment temperature of 100 ° C. or more and 150 ° C. or less, and the heat treatment is performed while maintaining the second treatment temperature for 2 seconds or more and 5.5 seconds or less.
If the second treatment temperature is lower than the above range, or if the holding time for maintaining the second treatment temperature is shorter than the above range, the effects of reducing the heating odor and improving the flavor may not be sufficiently obtained.
On the other hand, if the second treatment temperature is higher than the above range, or if the holding time is longer than the above range, excessive heat treatment may occur, and a good structure of fermented milk may not be obtained.
The second treatment temperature is more preferably 110 ° C. or higher and 150 ° C. or lower. By heat-treating at 110 ° C. or higher, heat-resistant live bacteria such as spore bacteria can be sterilized.

The second heat treatment can be performed by a direct heating method or an indirect heating method. Examples of the direct heating method include an infusion method and an injection method. Examples of the indirect heating method include a method using a plate sterilizer and a method using a tubular sterilizer. When the second heat treatment is performed by an indirect heating method, the fermented milk raw material is concentrated by performing a cooling treatment by boiling under reduced pressure (hereinafter, also referred to as a first cooling treatment). When the second heat treatment is performed by an infusion-type or injection-type direct heating method, steam is mixed into the fermented milk raw material, so that the mixed steam can be removed by boiling under reduced pressure. Therefore, the direct heating method is preferable in that the second heat treatment and the cooling treatment by boiling under reduced pressure can be performed without concentrating the fermentation raw material milk. The direct heating method is also preferable in that overheating is unlikely to occur because the temperature can be raised and lowered in a shorter time.
Moreover, it is preferable to perform 2nd heat processing and the cooling process (1st cooling process) by reduced pressure boiling continuously.

  For example, the procedure of the infusion type direct heating method is as follows. That is, first, the fermented milk raw material is preheated to an intermediate temperature, and then the fermented milk raw material is released into the heating container filled with pressurized steam. At this time, since the fermented milk raw material comes into contact with the steam and the steam flows into the fermented milk raw material, the fermented milk raw material is heated to a predetermined temperature (second processing temperature). The heated fermented milk raw material is held for a predetermined time by passing through a holding tube having a predetermined length. Thereafter, the heated fermented milk raw material is sent to the suction chamber. The suction chamber is sucked so as to have a predetermined negative pressure. For this reason, the fed fermented milk raw material is boiled under reduced pressure, and steam that flows in at the time of heating is removed and the temperature is lowered (first cooling process). And cooled to the third processing temperature.

  For example, the procedure of the direct heating method of the injection method is as follows. That is, first, the fermented milk raw material is preheated to an intermediate temperature, and pressurized steam is blown into the fermented milk raw material. As a result, the fermented milk raw material comes into contact with the steam and is heated to a predetermined temperature (second processing temperature). The heated fermented milk raw material is held for a predetermined time by passing through a holding tube having a predetermined length. Thereafter, the heated fermented milk raw material is sent to the suction chamber. The suction chamber is sucked so as to have a predetermined negative pressure. For this reason, the fed fermented milk raw material is boiled under reduced pressure, the steam blown during heating is removed and the temperature is lowered (first cooling treatment) ), And cooled to the third processing temperature.

  In addition, it is possible to add a step of cooling the fermented milk raw material between the first heat treatment and the second heat treatment. However, the cooling step is not performed, and the second heat treatment is followed by the second heat treatment. It is preferable to perform the heat treatment. In that case, the step of preheating the fermented milk raw material can be omitted.

The third processing temperature in the first cooling process is set to a temperature lower than the second processing temperature. When the second heat treatment is performed by the direct heating method, if the first treatment temperature is the same as the third treatment temperature, in the fermented milk raw material before the second heat treatment and after the first cooling treatment. The moisture content of the water does not change. That is, it is not concentrated. On the other hand, when the third processing temperature is lower than the first processing temperature, the fermented milk raw material is concentrated. Moreover, fermented milk raw material can be diluted when 3rd process temperature is made higher than 1st process temperature.
The difference between the third processing temperature and the second processing temperature can be set as appropriate according to the scale of the apparatus. The difference between the third treatment temperature and the second treatment temperature is preferably in the range of 1 to 100 ° C., from the point of reducing the heating odor in fermented milk, and maintaining the original flavor and richness of milk. 5 to 55 ° C is more preferable.

[Second cooling process and homogenization process]
After cooling to the 3rd processing temperature by the 1st cooling process, the 2nd cooling process is further performed, and temperature is finally lowered to fermentation temperature vicinity. The fermentation temperature is about 25 to 45 ° C. The second cooling process can be performed using, for example, a plate heat exchanger.
In the second cooling treatment, for example, it is once cooled to 55 to 95 ° C., preferably 60 to 85 ° C., homogenized at a homogeneous pressure of 5 to 25 MPa, preferably 10 to 20 MPa, and further cooled. The fermentation temperature is preferred.
In addition, although a homogenization process is not essential, in order to obtain a favorable structure | tissue, it is preferable to perform the homogenization process which satisfy | fills said conditions. The timing of performing the homogenization process may be in the middle of the second cooling process, but may be performed in the heating stage leading to the first heating process or in the middle of the first heating process, or the first cooling process. It can also be done after.
In addition, before and after the sterilization process of the fermented milk raw material, it is possible to appropriately add a heat treatment for another purpose that does not significantly affect the heat history.

[Whey protein denaturation rate]
The whey protein denaturation rate of the fermented milk raw material that has undergone such a sterilization method is an indicator of the property (hardness or viscosity) in the fermented milk after the fermentation process. The value of the whey protein denaturation rate in the present specification is “influence of bactericidal conditions on sensory characteristics of milk”, Journal of Japanese Society for Food Science and Technology, No. 46, No. 8, August 1999, pp. 535-542. It is a value calculated by the following mathematical formula (1), measured according to the method of Iwatsuki et al. There exists a tendency for the hardness or viscosity in fermented milk after a fermentation process to become high, so that this value is large.
Denaturation rate (%) = [(absorbance at 420 nm of fermented milk raw material before sterilization) − (absorbance at 420 nm of fermented milk raw material after sterilization)] / (absorbance at 420 nm of fermented milk raw material before sterilization) × 100 ( 1)
The fermented milk raw material has a whey protein denaturation rate of preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The upper limit is not particularly limited and may be 100%. When the whey protein denaturation rate is 80% or more, the viscosity and altitude of fermented milk are increased, and the tissue can be improved.

<Method for producing fermented milk ingredients>
After adding a starter such as lactic acid bacteria to the fermented milk raw material that has been heat sterilized by the sterilization method of the present invention and cooled to around the fermentation temperature, fermentation is performed while maintaining a predetermined fermentation temperature. After fermentation, fermented milk is obtained by cooling according to a conventional method in order to terminate the fermentation.
Bacteria used as a starter are not particularly limited, and industrially usable strains can be used. Specifically, Streptococcus thermophilus and Streptococcus cremoris are available. It is preferable to employ bacterial species with low acid production, such as Lactobacillus bulgaricus (Lactobacillus delbrueckii subsp. Bulgaricus).
Fermentation is preferably performed at 37 ° C. until the lactic acid acidity reaches 0.70%. The value of lactic acid acidity is a value determined according to “Method for Measuring Acidity of Milk and Dairy Products” in “Ministerial Ordinance on Component Standards of Milk and Dairy Products”.
It is also possible to continue the fermentation as appropriate after the acidity reaches 0.70% and adjust the acidity to a desired value.

<Fermented milk>
According to the production method of the present invention, fermented milk having a viscosity at 10 ° C. of 1500 mPa · s or more, preferably 2000 mPa · s or more can be obtained. The value of the viscosity in this specification is a value measured using a B-type viscometer (for example, manufactured by Tokyo Keiki Co., Ltd.) under the conditions of No. 4 rotor, 60 revolutions / minute, and sample temperature of 10 ° C.
The texture of fermented milk will become favorable as the value of this viscosity is 1500 mPa * s or more. The upper limit of the viscosity is not particularly limited, but a practically achievable range is 10,000 mPa · s or less.

The present invention is suitable for producing solid fermented milk or pasty fermented milk.
Solid fermented milk means fermented milk having a non-flowable tissue. Specific examples of such solid fermented milk include stationary plain yogurt and hard yogurt, which are filled with sterilized fermented milk raw material in advance and then fermented by adding a starter, or paste-like fermentation described later Examples thereof include fermented milk obtained by adding a gelling agent such as gelatin or agar to milk.
Paste-like fermented milk means fermented milk that has a high fluidity in tissue and is eaten using a spoon or the like. For example, paste-like fermented milk can be obtained by adding a starter to a sterilized fermented milk raw material in a tank for fermentation, and crushing the resulting curd. The pulverization step is preferably performed at a homogeneous pressure of 1.0 MPa or less. It is also possible to produce flavored fermented milk, fermented milk containing fruit, and the like by mixing the pasty fermented milk thus obtained with, for example, chocolate, fruit sauce, or pulp.

The fermented milk obtained by the production method of the present invention is reduced in the sulfur compounds and ketones that are the cause of the heated odor generated in the sterilization stage of the fermented milk raw material and has a good flavor.
Specifically, sulfur compounds such as dimethylsulfide (DMS) and ketones such as pentanone are reduced, and 2-pentanone is reduced to 31 ppb or less as shown in a test example described later. Fermented milk having a good sensory evaluation of flavor is obtained.
On the other hand, as shown in the evaluation results for samples 31 to 34, which will be described later, the sensory evaluation of the flavor is not always better when the 2-pentanone content in the fermented milk is smaller. This is because milk raw materials originally contain very small amounts of sulfur compounds and ketones, and these are part of the components that make up the scent of milk, etc., which contributes to the original flavor of fermented milk. It is thought that there is. Therefore, it is desirable to remove the causative substance of the heated odor as long as the original flavor and richness of milk are not impaired.
In addition, the measuring method of aromatic components, such as the said sulfur compound and ketones in this specification, is explained in full detail in the following test example.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide fermented milk with favorable flavor by which the heating odors, such as a sulfur compound and ketones, were reduced. In addition, as shown in the test examples described later, the fermentation time is shortened as compared with the case of sterilization using only the conventional sterilization method. The sterilization method of the present invention can be easily applied on an industrial scale, and fermented milk can be produced at low cost using this method.

Next, the present invention will be described in detail with reference to test examples. In the following test examples, the following measuring methods were used.
[Lactic acidity]
Lactic acid acidity is measured with a 0.1 mol / l sodium hydroxide solution using phenolphthalein as an indicator according to “Method for measuring acidity of milk and dairy products” in “Ministerial Ordinance on Component Specifications of Milk and Dairy Products”. Measured by titration.

[Whey protein denaturation rate]
Using the fermented milk material after sterilization (sample after sterilization) and the fermented milk material before sterilization (sample before sterilization), the whey protein denaturation rate was measured by the following method. That is, 22 g of each sample was kept at 37 ° C. for 30 minutes, 8 g of sodium chloride was added, followed by filtration, 10 ml of acidic saturated brine (4 ml of glacial acetic acid was added to 1 L of saturated brine), Absorbance (disposel, optical path length 10 mm, room temperature) at 420 nm was measured using a spectrophotometer (manufactured by Hitachi, Ltd., product name: U-2000 type double beam spectrophotometer). Based on the measured value of absorbance, the denaturation rate (%) was calculated by the mathematical formula (1).

[viscosity]
The viscosity of the sample stored for 20 hours at 10 ° C. after the fermented milk was prepared was measured using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), using a No. 4 rotor, at 60 rpm and a sample temperature of 10 ° C. Each was measured 5 times, and the average value was calculated.

[Peak area and quantification of aroma components]
Aroma components (dimethyl sulfide and 2-pentanone) were measured by the following method for samples stored at 10 ° C. for a predetermined period after preparing fermented milk. Dimethyl sulfide (hereinafter sometimes abbreviated as DMS) and 2-pentanone are compounds known as causative substances for the heated odor produced during the heat sterilization of milk.
To 5 g of the sample, 1 g of sodium chloride and 4 g of dissolved water were added and mixed, and allowed to stand at 40 ° C. for 30 minutes. Then, the aroma component was extracted by solid-phase microextraction, and the extracted aroma component was supplied to Agilent Technologies. Measurement was performed by gas chromatography / mass spectrometry (GC / MS) using an analytical instrument (GC-MS5973A, GC6890, etc.), and the peak area of each aroma component was analyzed. The smaller the peak area, the smaller the content. As standard samples, dimethyl sulfide was manufactured by Wako Pure Chemical Industries, and 2-pentanone was manufactured by Wako Pure Chemical Industries. Quantification was performed by the standard addition method.

[Flavored milk flavor]
After preparing the fermented milk, a sample stored at 10 ° C. for a predetermined period was sampled by 10 male and female panelists, and the taste was subjected to sensory evaluation by the following evaluation method.
(Evaluation methods)
“Poor”: 1 point “Slightly good”: 2 points “Good”: 3 points “Very good”: Evaluated in 4 stages of 4 points, and the average value of 10 evaluation points for each sample was calculated, The average value is less than 1.5 points: “Bad”
1.5 or more and less than 2.5: "Slightly good"
2.5 points or more and less than 3.5 points are "good"
A score of 3.5 or more and 4.0 or less was judged as “very good”.

[Test Example 1]
In this test, fermented milk was produced by changing the presence or absence of the first heat treatment or the second heat treatment, and the whey protein modification rate of the fermented milk raw material and the viscosity of the fermented milk after fermentation were evaluated. Table 1 shows the main production conditions and evaluation results.
(1) Preparation of sample 11.
Commercial skim milk powder (manufactured by Morinaga Milk Industry Co., Ltd.) 9.0 kg, 45% cream (manufactured by Morinaga Milk Industry Co., Ltd.) 6.6 kg, WPI (whey protein isolate: manufactured by Mirai Co., Ltd.) 0.7 kg, sugar (manufactured by Mitsui Sugar Co., Ltd.) 6.0 kg and 77.1 kg of water were uniformly mixed and dissolved to prepare a fermented milk raw material (sample before sterilization).
Next, as a first heat treatment, a plate heat exchanger (manufactured by APV) was used to heat the fermented milk raw material to the first treatment temperature and held for a predetermined time in a holding tube (manufactured by APV).
Subsequently, as the second heat treatment, it was heated to the second treatment temperature with a direct heat sterilizer (infusion type, manufactured by APV) and held for a predetermined time.
Next, as a first cooling process, vacuum boiling is performed in a vacuum chamber to cool to a third processing temperature, and as a second cooling process, cooling is performed to 75 ° C. with a plate heat exchanger, and a homogenizer (manufactured by APV) ) Was further homogenized at a pressure of 15 MPa, and further cooled to 37 ° C. (final cooling temperature) with a plate heat exchanger to prepare a sterilized fermented milk raw material (sample after sterilization).
To 4940 g of the obtained fermented milk raw material (sample after sterilization), 30 g of Streptococcus thermophilus and 30 g of Lactobacillus bulgaricus (both manufactured by Hansen) were added and mixed uniformly as a lactic acid bacteria starter. This was maintained at 37 ° C. and fermented, and when the lactic acid acidity reached 0.70%, it was rapidly cooled to 15 ° C. with stirring in ice water to complete the fermentation.
The fermented milk thus obtained was homogenized at a pressure of 1.0 MPa or less using a homogenizer (manufactured by Sanmaru Kikai Co., Ltd.), filled into a paper cup, and sealed with an aluminum lid to prepare a fermented milk sample (sample 11). did.

(2) Preparation of samples 12 and 13.
The first heat treatment was not performed, and the second heat treatment was performed under the conditions shown in Table 1. Otherwise, fermented milk samples (Samples 12 and 13) were prepared in the same manner as Sample 11.
(3) Preparation of control sample 10.
The second heat treatment and the first cooling treatment were not performed. That is, after performing 1st heat processing, it cooled to predetermined temperature (cooling temperature before homogenization: 75 degreeC) with a plate heat exchanger, and used for the homogenization process. Otherwise, a fermented milk sample (Sample 10) was prepared in the same manner as Sample 11.

(4) Evaluation results As shown in the results of Table 1, the control sample 10 and the sample 11 subjected to the first heat treatment are whey in comparison with the sample 12 and the sample 13 subjected to the second heat treatment alone. The protein denaturation rate was high.
Concerning the viscosity, the viscosity of Sample 12 and Sample 13 was too low, whereas in Control Sample 10 and Sample 11, sufficient viscosity was obtained as pasty fermented milk.
Therefore, at least the first heat treatment is necessary to obtain a preferable viscosity after fermentation, and even if the second heat treatment and the first cooling treatment by boiling under reduced pressure are performed in addition to that, the preferable viscosity is obtained. It was recognized that it was not damaged.

[Test Example 2]
In this test, fermented milk is produced by changing the second treatment temperature in the second heat treatment while performing the first heat treatment and the second heat treatment, and the fermentation time is stored at 10 ° C. for 1 day after the production. The aroma component (peak area) and flavor of the fermented milk were evaluated. The fermentation time here is the time from when the starter is added until the lactic acid acidity reaches 0.70%. Table 2 shows the main production conditions and evaluation results.
(1) Preparation of samples 21-26.
Fermented milk samples (Samples 21 to 26) were prepared in the same manner as Sample 11, except that the second treatment temperature was changed as shown in Table 2 in the preparation of Sample 11 of Test Example 1.
(2) Preparation of control sample 20.
A fermented milk sample (sample 20) was prepared in the same manner as sample 21 except that the second treatment temperature in the second heat treatment was set to be the same as the first treatment temperature and no boiling under reduced pressure was performed. That is, the temperature of the 95 ° C. treatment liquid after the first heat treatment was maintained in the holding tube for 5.5 seconds, and then cooled to the homogenization temperature with a plate heat exchanger.

(3) Evaluation results As shown in Table 2, the fermented milk of samples 21 to 26, in which the second treatment temperature was set to 100 ° C. or higher and the first cooling treatment by vacuum boiling was performed, was the second treatment. The peak areas of dimethyl sulfide and 2-pentanone were reduced compared to the control sample 20 where the temperature was 95 ° C. and no boiling under reduced pressure was performed. Moreover, in the sensory evaluation results of flavor, a good evaluation equal to or higher than that of the control sample 20 was obtained.
Regarding the fermentation time, compared to the control sample 20, the samples 21 to 26 were shortened by 2 hours or more.

[Test Example 3]
In this test, fermented milk was produced by performing the first heat treatment and the second heat treatment and changing the second treatment temperature in the second heat treatment, and storing the fermented milk at 10 ° C. for 7 days after the production. Was evaluated for 2-pentanone content and flavor. Table 3 shows the main production conditions and evaluation results.
(1) Preparation of samples 31-34.
In the preparation of Sample 11 of Test Example 1, the sample was changed except that the second treatment temperature and holding time in the second heat treatment and the third treatment temperature in the first cooling treatment were changed as shown in Table 3. In the same manner as in Example 11, fermented milk samples (Samples 31 to 34) were prepared.
(2) Preparation of control sample 30.
A fermented milk sample (sample 30) was prepared in the same manner as sample 31 except that the second treatment temperature in the second heat treatment was set to be the same as the first treatment temperature and no vacuum boiling was performed.

(3) Evaluation results As shown in Table 3, the fermented milk of samples 31 to 34 in which the second treatment temperature was set to 100 ° C. or higher and the first cooling treatment by vacuum boiling was performed was the second treatment. The content of 2-pentanone was reduced to 31 ppb or less as compared with the control sample 30 in which the temperature was 95 ° C. and boiling was not performed under reduced pressure. Also, samples 31 to 34 had a better sensory evaluation of flavor than control sample 30. In particular, the results of sensory evaluation were excellent in samples 33 and 34 in which the second treatment temperature was 130 ° C. or higher.

[Test Example 4]
In this test, fermented milk was produced by performing the second heat treatment by the direct heating method or the indirect heating method, and the flavor components (peak area) and flavor of the fermented milk stored at 10 ° C. for 1 day were evaluated. . Table 4 shows the main production conditions and evaluation results.
(1) Preparation of the sample 41 using the direct heating method (infusion type).
A fermented milk sample (Sample 41) was prepared in the same manner as Sample 32.
(2) Preparation of a control sample 40 using an indirect heating method (plate type) and not boiling under reduced pressure.
A fermented milk raw material (sample before sterilization) was prepared in the same manner as Sample 11 of Test Example 1, and the first heat treatment was performed.
Next, as a second heat treatment, it was heated to 110 ° C. (second treatment temperature) with an indirect heating sterilizer (heat exchange plate type, manufactured by APV) and held for 2 seconds.
Next, after cooling to 75 ° C. with a plate heat exchanger and homogenizing in the same manner as Sample 11, it is cooled to 37 ° C. with a plate heat exchanger, and the fermented milk raw material (sample after sterilization) after sterilization is obtained. Prepared. Thereafter, a fermented milk sample (Sample 40) was obtained in the same manner as Sample 11.

(3) Evaluation results As shown in Table 4, the sample 41 that was subjected to the second heat treatment by the direct heating method and was subjected to the cooling treatment by the vacuum boiling was the sample 41 that was not subjected to the vacuum boiling using the indirect heating method. In comparison, although the treatment temperature and holding time were the same, the peak areas of dimethyl sulfide and 2-pentanone were reduced, and the sensory evaluation of flavor was also improved.
Moreover, the peak area of the aroma component in the sample 40 and the sensory evaluation results of the flavor were almost the same as those of the control sample 20.

[Test Example 5]
In this test, the second heat treatment is performed by a direct heating method (injection method), fermented milk is produced by changing the presence or absence of boiling under reduced pressure, and the aroma components of fermented milk stored at 10 ° C. for 1 day after production ( Peak area), fermented milk flavor, and fermented milk viscosity were evaluated. Table 5 shows the main production conditions and evaluation results.
(1) Preparation of sample 51.
A fermented milk raw material (sample before sterilization) was prepared in the same manner as Sample 11 of Test Example 1, and the first heat treatment was performed.
Next, as a second heat treatment, it was heated to 110 ° C. (second treatment temperature) with a direct heat sterilizer (injection type, manufactured by APV) and held for 2 seconds.
Next, as a first cooling treatment, the solution was boiled under reduced pressure in a vacuum chamber and cooled to 80 ° C. (third treatment temperature). Subsequently, as a second cooling treatment, the plate is cooled to 75 ° C. with a plate heat exchanger, homogenized in the same manner as Sample 11, and further cooled to 37 ° C. (final cooling temperature) with a plate heat exchanger. Fermented milk raw material (sample after sterilization) was prepared. Thereafter, a fermented milk sample (Sample 51) was obtained in the same manner as Sample 11.
(2) Preparation of control sample 50.
A fermented milk sample (sample 50) was prepared in the same manner as sample 51 except that the second treatment temperature in the second heat treatment was set to be the same as the first treatment temperature and no boiling under reduced pressure was performed.
The method for preparing the sample 50 corresponds to a method in which the infusion type in the method for preparing the sample 30 is simply changed to the injection type.

(3) Evaluation results As shown in Table 5, the sample 51 that was subjected to the cooling treatment by boiling under reduced pressure using the injection-type direct heating method in the second heat treatment, the second treatment temperature was 110 ° C, Compared with sample 50 in which the treatment temperature of 2 was 95 ° C. and vacuum boiling was not performed, the peak area of 2-pentanone was reduced, and the sensory evaluation of flavor was also improved.
About viscosity, it was substantially equivalent with the control sample 50 and the sample 51, and all had sufficient viscosity as pasty fermented milk.
In addition, the result based on the injection formula obtained in this test is almost the same as the result of the infusion type direct heating method. Therefore, in the present invention, when the second heat treatment is performed by the direct heating method. It can be seen that substantially the same effect can be obtained by using either the infusion type or the injection type.

EXAMPLES Next, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to a following example.
[Example 1]
Commercial skim milk powder (manufactured by Morinaga Milk Industry Co., Ltd.) 9.0 kg, 45% cream (manufactured by Morinaga Milk Industry Co., Ltd.) 6.6 kg, WPI (whey protein isolate: manufactured by Mirai Co., Ltd.) 0.7 kg, sugar (manufactured by Mitsui Sugar Co., Ltd.) 6.0 kg and 77.1 kg of water were uniformly mixed and dissolved to prepare a raw material for fermented milk.
Next, as a first heat treatment, the fermented milk raw material was heated to 95 ° C. with a plate heat exchanger (manufactured by APV) and held for 6 minutes with a holding tube (manufactured by APV). Subsequently, as a second heat treatment, a direct heat sterilizer (infusion type, manufactured by APV) was held for 2 seconds at a temperature of 110 ° C. Furthermore, as a first cooling treatment, the solution was boiled under reduced pressure in a vacuum chamber and cooled to 95 ° C. Further, as a second cooling treatment, after cooling to 75 ° C. with a plate heat exchanger, homogenization is performed at a pressure of 15 MPa using a homogenizer (manufactured by APV), cooling to 37 ° C. with a plate heat exchanger, A fermented milk ingredient was obtained.
Next, to 4940 g of the obtained fermented milk raw material, 30 g of Streptococcus thermophilus and 30 g of Lactobacillus bulgaricus (both manufactured by Hansen) were added as lactic acid bacteria starters and mixed uniformly, and this was fermented at 37 ° C. When the lactic acid acidity reached 0.70%, the mixture was rapidly cooled to 15 ° C. with stirring in ice water to complete the fermentation.
The fermented milk thus obtained was homogenized at a pressure of 1.0 MPa or less using a homogenizer (manufactured by Sanmaru Kikai Co., Ltd.), filled into a paper cup, and sealed with an aluminum lid to produce pasty fermented milk.
The produced fermented milk had a preferred viscosity with reduced heating odor and a fine and creamy structure.

[Example 2]
Commercially available skim milk powder (Morinaga Milk Industry Co., Ltd.) 9.9 kg, unsalted butter (Morinaga Milk Industry Co., Ltd.) 3.5 kg, sugar (Mitsui Sugar Co., Ltd.) 6 kg, and water 80 kg are uniformly mixed and dissolved to produce fermented milk ingredients Was heated to 70 ° C. and homogenized at a pressure of 15 MPa using a homogenizer (manufactured by Sanmaru Kikai Co., Ltd.).
Next, a first heat treatment was performed in the same manner as in Example 1. Subsequently, the second heat treatment was performed in the same manner as in Example 1 except that the heating temperature in the second heat treatment was changed from 110 ° C. to 130 ° C. Next, the first cooling treatment was performed in the same manner as in Example 1 except that the cooling temperature by boiling under reduced pressure was changed from 95 ° C. to 85 ° C. Thereafter, a fermented milk raw material was obtained in the same manner as in Example 1.
0.6 kg of a yogurt starter (manufactured by Hansen) consisting of Streptococcus thermophilus was added to the fermented milk raw material and mixed uniformly. This was filled in a paper cup and fermented at 37 ° C. for 24 hours, and then cooled in a refrigerator at 5 ° C. to finish the fermentation, thereby producing solid fermented milk. This fermented milk had a smooth texture suitable for eating with reduced odor, and had a preferable hardness.

  The present invention provides a novel fermented milk raw material sterilization method, a fermented milk manufacturing method, and fermented milk that has never been seen, with a focus on reducing heated odors in milk raw materials that increase in the production stage. is there. ADVANTAGE OF THE INVENTION According to this invention, while being able to apply to fermented milk which has various flavors and new characteristics, it can respond also to consumers' preference and needs to fermented milk which is spreading in recent years.

Claims (8)

A method for sterilizing fermented milk raw material, wherein the first heat treatment is performed by heating the fermented milk raw material to a first treatment temperature of 85 ° C. or higher and 95 ° C. or lower and holding it for 5 minutes or longer and 15 minutes or less;
After the first heat treatment, performing a second heat treatment that raises the temperature to a second treatment temperature of 100 ° C. or more and 150 ° C. or less and maintains the temperature for 2 seconds or more and 5.5 seconds or less;
A method for sterilizing fermented milk raw material, comprising: after the second heat treatment, having a step of boiling under reduced pressure and cooling to a third treatment temperature lower than the second treatment temperature.   The fermented milk raw material sterilization method according to claim 1, wherein the second heat treatment is performed by a direct heating method.   The method for sterilizing fermented milk material according to claim 1 or 2, wherein the difference between the third treatment temperature and the second treatment temperature is 5 to 55 ° C.   It has the process of performing a homogenization process after the said cooling process, The sterilization method of the fermented milk raw material as described in any one of Claims 1-3 characterized by the above-mentioned.   The fermented milk raw material sterilization method according to any one of claims 1 to 4, wherein the second heat treatment is performed following the first heat treatment.   Having a step of preparing a fermented milk raw material, a step of sterilizing the fermented milk raw material by the sterilization method according to any one of claims 1 to 5, and a step of fermenting the fermented milk raw material after sterilization. A method for producing fermented milk.   Fermented milk having a 2-pentanone content of 31 ppb or less.   The fermented milk according to claim 7, wherein the fermented milk is solid fermented milk or pasty fermented milk.