Probiotic fermented milk and preparation method thereof

Abstract

The invention relates to the technical field of dairy product processing, in particular to probiotic fermented milk and a preparation method thereof, and the preparation method of the probiotic fermented milk comprises the following steps: 1) preheating raw milk to 40-50 DEG C, mixing the raw milk with sugar, and performing pasteurization; 2) cooling, inoculating the raw milk with the lactobacillus paracasei Bd-II according to 0.3%-0.5% of the mass of the raw milk, and fermenting; and 3) after fermentation is completed, refrigerating for after-ripening to obtain the probiotic fermented milk. The lactobacillus paracasei Bd-II is used for independent fermentation, the production cost can be greatly reduced, the lactobacillus paracasei Bd-II has excellent fermentation performance and probiotic function as a probiotic, the fragrance of the fermented milk can be improved, and additives such as a thickening agent and a stabilizing agent are not needed, so that the ingredient surface is clean; the fermented milk obtained by fermentation has high quality, long-time storage stability and excellent flavor.

Description

Technical Field

[0001] The invention relates to the technical field of dairy product processing, in particular to a probiotic fermented milk and a preparation method thereof. Background Art

[0002] Fermented milk is popular among consumers for its unique flavor and rich nutrition. However, during the production and storage process, fermented milk is prone to stratification, whey precipitation and unstable texture, which directly affects the sensory quality and market competitiveness of the product. Traditionally, in order to solve the stability problem of fermented milk, a series of thickeners and stabilizers such as pectin, starch and other chemical substances are usually added, but the addition of these additives makes the ingredient list more complicated, which is inconsistent with the current health concept of consumers. Therefore, it is particularly important to explore a green, safe and economical method to improve the storage stability of fermented milk. Summary of the invention

[0003] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a probiotic fermented milk and a preparation method thereof, so as to solve the problems in the prior art.

[0004] To achieve the above object and other related objects, the present invention provides a method for preparing probiotic fermented milk, the preparation method comprising the following steps:

[0005] 1) preheating the raw milk to 40-50° C., mixing with sugar and then pasteurizing the mixture, wherein the sugar is selected from white sugar and / or sucrose;

[0006] 2) cooling, inoculating Lactobacillus paracasei Bd-II at 0.3%-0.5% of the mass of the raw milk for fermentation;

[0007] 3) After fermentation is completed, the milk is refrigerated for post-ripening to obtain the probiotic fermented milk.

[0008] Preferably, in step 1), the raw milk is selected from raw cow's milk, reconstituted milk, low-fat milk or skimmed milk.

[0009] Preferably, the mass of the sugar is 5-9% of the mass of the raw milk.

[0010] Preferably, in step 2), the mixture is cooled to 37-40° C. before inoculation with Lactobacillus paracasei Bd-II.

[0011] Preferably, the Lactobacillus paracasei Bd-II is Lactobacillus casei Bd-IICMGCC.0849 in the invention patent with application number CN03128995.9.

[0012] Preferably, in step 2), the fermentation temperature is 36-38° C., preferably 37° C., and / or the fermentation is performed until the pH value of the system is 4.0-4.2.

[0013] The present invention also provides probiotic fermented milk obtained by the preparation method.

[0014] As described above, a probiotic fermented milk and a preparation method thereof of the present invention have the following beneficial effects: no Lactobacillus bulgaricus and Streptococcus thermophilus are required, and no additives such as thickeners and stabilizers are required, so the ingredient list is clean; Lactobacillus paracasei Bd-II can be used alone in fermented milk, thereby greatly reducing the production cost, and as a probiotic, it has excellent fermentation performance and prebiotic function, and can also improve the aroma of fermented milk. The fermented milk obtained by fermentation has high quality, long-term storage stability and excellent flavor, and can be positioned as high-end fermented milk for production and sales. DETAILED DESCRIPTION

[0015] The present invention provides a method for preparing probiotic fermented milk, the preparation method comprising the following steps:

[0016] 1) preheating the raw milk to 40-50° C., mixing with sugar and then pasteurizing the mixture, wherein the sugar is selected from white sugar and / or sucrose;

[0017] 2) cooling, inoculating Lactobacillus paracasei Bd-II at 0.3%-0.5% of the mass of the raw milk for fermentation;

[0018] 3) After fermentation is completed, the milk is refrigerated for post-ripening to obtain the probiotic fermented milk.

[0019] In the present invention, the probiotic fermented milk refers to a product with a reduced pH value that is made from raw milk, sterilized, and fermented with probiotics.

[0020] In certain embodiments of the present invention, in step 1), the raw milk is selected from raw cow's milk, raw goat's milk, reconstituted milk, low-fat milk or skimmed milk.

[0021] The low-fat milk is raw milk with a fat content lower than that of full-fat milk, for example, its fat content is half of that of full-fat milk, and the fat content is between 1.0% and 1.5%.

[0022] The reconstituted milk refers to liquid milk reconstituted by mixing skimmed milk powder and water in proportion.

[0023] In certain embodiments of the present invention, the white sugar or sucrose can be used together or alone, and the ratio of the two when used together is not specifically limited.

[0024] In certain embodiments of the present invention, the mass of the sugar is 5-9% of the mass of the raw milk. For example, the mass of the sugar is 5-6%, 6-7%, 7-8%, 8-9% of the mass of the raw milk.

[0025] In certain embodiments of the present invention, step 1) further comprises purifying the raw milk to remove impurities. Purification includes filtering and separation to ensure the quality and purity of the raw milk.

[0026] In certain embodiments of the present invention, in step 2), the Lactobacillus paracasei Bd-II is inoculated after cooling to 37-40°C.

[0027] In certain embodiments of the present invention, the deposit number of the lactobacillus paracasei Bd-II is CGMCC No.0849, which is deposited in the General Microbiological Center of China Microbiological Culture Collection Committee CGMCC on December 6, 2002, and the deposit address is Institute of Microbiology, Chinese Academy of Sciences, Beijing, China. The lactobacillus paracasei Bd-II has high viscosity, high hardness, low whey precipitation rate and significant storage stability.

[0028] In certain embodiments of the present invention, the Lactobacillus paracasei Bd-II in step 2) is a seed solution of Lactobacillus paracasei Bd-II. The seed solution of Lactobacillus paracasei Bd-II is obtained by the following method: after activating Lactobacillus paracasei Bd-II for two generations using an MRS plate, a single colony is picked and inoculated into MRS broth, and the seed solution is obtained by culturing for 10 to 14 hours, for example, 12 hours.

[0029] In certain embodiments of the present invention, the fermentation temperature in step 2) is 36-38°C, preferably 37°C, and / or the fermentation is carried out until the pH value of the system is 4.0-4.2. The fermentation time is not specifically limited, and the specific fermentation time is determined according to the pH value of the system. For example, in certain embodiments of the present invention, the fermentation time is 14-18 hours.

[0030] In certain embodiments of the present invention, the refrigeration temperature in step 3) is 3.5-4.5°C, and / or the refrigeration time is 10-20 hours. The refrigeration time is, for example, 10-12 hours, 12-14 hours, 14-16 hours, 16-18 hours, or 18-20 hours.

[0031] The purposes of post-ripening include the following aspects:

[0032] a. Control acidity: During the ripening period, the growth rate of Lactobacillus paracasei Bd-II will slow down, but it will continue to ferment, increasing the acidity of the fermented milk.

[0033] b. Produce aromatic substances: During the ripening process, fermentation produces some other beneficial substances, such as pyruvic acid, acetic acid, lactic acid and carbon dioxide, which give fermented milk a unique flavor and aroma.

[0034] c. Improve texture: During the ripening period, milk protein begins to coagulate and form a soft gel-like substance, making the fermented milk more delicate.

[0035] d. Changes in protein structure: Changes in the structure of protein make it easier to digest and absorb, thereby improving the nutritional value and digestibility of fermented milk.

[0036] e. Impact on shelf life and stability: The ripening period has a certain impact on the shelf life and stability of fermented milk. As the ripening period proceeds, the number of bacteria in the fermented milk will gradually decrease, slowing down the fermentation rate and making the shelf life of the fermented milk longer.

[0037] f. Improved taste: The longer the ripening period, the more delicate and smooth the taste of the fermented milk, and the more balanced the acidity. This is because the growth of bacteria produces more organic acids, which combine with milk protein to form a synergistic effect, giving the fermented milk a better flavor and texture.

[0038] g. Stable product structure: Post-ripening is a stable storage period, which is the basis for the stability of the whey protein and casein structure.

[0039] The fermented milk obtained by the preparation method of the present invention has the following characteristics:

[0040] a) The initial viscosity is relatively high, at 56.8 Pa·S, and the texture stability is remarkable;

[0041] b) The initial particle size D(50) is 554.67±8.97μm, and the particles are uniform and fine.

[0042] c) The instability index is low, only 0.063±0.004

[0043] d) The whey precipitation rate on the first day of storage was 24.62±3.65; and the whey precipitation rate on the seventh day of storage was 28.73±1.06. Therefore, the storage stability of the fermented milk was higher than that of the traditional probiotic fermented milk.

[0044] e) During the storage period (1-7 days), it can maintain high hardness, consistency and cohesion, and has excellent sensory quality.

[0045] The present invention also provides probiotic fermented milk obtained by the preparation method.

[0046] The probiotic fermented milk is additive-free fermented milk.

[0047] Compared with the fermented milk fermented by traditional thermophilic streptococcus or bulgaricus lactobacillus, the fermented milk obtained by fermenting with the probiotic Lactobacillus paracasei Bd-II of the present invention not only has the beneficial effects of general probiotics, such as the health functions of regulating intestinal flora, inhibiting intestinal pathogens and delaying aging, but also has the effect of assisting in regulating blood lipids and reducing serum cholesterol concentration.

[0048] The probiotic fermented milk complies with the provisions of GB 19302 national food safety standard fermented milk.

[0049] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0050] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0051] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0052] Example 1: Preparation of fermented milk samples based on Lactobacillus paracasei Bd-II

[0053] (1) raw milk is used as raw milk, preheated to 45° C., 7% white sugar by weight of the raw milk is added, and the mixture is pasteurized and then cooled;

[0054] (2) Inoculate the seed liquid of Bd-II strain at 0.3% of the mass of raw milk and ferment it at 37°C for 14 hours; the preparation method of the seed liquid is as follows: use MRS plates to activate Lactobacillus paracasei Bd-II with a preservation number of CMGCC.0849 for two generations, pick out a single colony and inoculate it in MRS broth, and obtain the seed liquid after culturing for 12 hours.

[0055] (3) Post-ripening: After the yogurt fermentation is completed, place it in a 4°C refrigerator for post-ripening for 12 hours.

[0056] Example 2 Detection of Viscosity of Lactobacillus paracasei Bd-II Fermented Milk

[0057] The dynamic viscoelasticity of fermented milk samples was measured by dynamic rheometer MCR302 at 25°C. Test parameters: CC27-SN27450 rotor and CC27-SS23848 mold were used. The test found that the initial viscosity of Bd-II fermented milk during storage was as high as 56.8 Pa·S.

[0058] Example 3 Detection of particle size of Lactobacillus paracasei Bd-II fermented milk

[0059] The particle size was detected using Malvern MS 3000 laser particle size analyzer, with the following parameters: 25°C, 1000r / min, fermented milk refractive index 1.52, absorptivity 0.01, water refractive index 1.33, measurement time 10s, shading 0.1% to 20%. The experiment found that the particle size distribution of Bd-II fermented milk is shown in Table 1, where D(10) is the corresponding particle size when the cumulative distribution accounts for 10% of the system, D(50) is the corresponding particle size when the cumulative distribution accounts for 50% of the system, and D(90) is the corresponding particle size when the cumulative distribution accounts for 90% of the system. Since the whey precipitation rate is correlated with the particle size of fermented milk, the larger the particle size of the fermented milk, the lower the whey precipitation rate and the higher the product stability.

[0060] Table 1 Particle size distribution of different fermented milks of Lactobacillus paracasei Bd-II

[0061]

[0062] Example 4 Analysis of the instability index of Lactobacillus paracasei Bd-II fermented milk

[0063] Lumisizer 6121-31 was used to analyze the stability of fermented milk. The parameters were set as follows: 180 lines were tested at 10s / line at 25℃ and 1800r / min. The larger the instability index, the more unstable the system is, and the easier it is to separate the gel and whey. Conversely, the more stable it is. The instability index of milk fermented by Lactobacillus paracasei Bd-II was low, only 0.063±0.004

[0064] Example 5 Detection of whey precipitation rate of Lactobacillus paracasei Bd-II fermented milk during storage

[0065] Take a fermented milk sample, centrifuge it at 10000r / min for 10min, aspirate the supernatant and weigh it, and calculate the whey precipitation rate according to the following formula:

[0066] Whey precipitation rate (%) = m2 / m1×100.

[0067] Where: m1 represents the weight of fermented milk; m2 represents the weight of whey.

[0068] The experiment found that the whey precipitation rate of Bd-II fermented milk on the first day of storage was 24.62±3.65, and the whey precipitation rate on the seventh day of storage was 28.73±1.06 (Table 2).

[0069] Table 2 Detection of whey precipitation rate of Lactobacillus paracasei Bd-II

[0070]

[0071] Example 6 Detection of the texture characteristics of Lactobacillus paracasei Bd-II fermented milk during storage

[0072] The texture characteristics were tested using a texture analyzer, and the A / BE-d35 pressure plate was selected. The parameters were set as follows: the trigger force was 5 g, the probe travel speed was 2 mm / s before the test, the probe travel speed was 2 mm / s during the test, the probe return travel speed was 6 mm / s, and the downward pressure distance was 10 mm. The texture characteristics of fermented milk were fed back through hardness, consistency, and cohesiveness indicators. Table 3 shows that the hardness, consistency, and cohesiveness of the fermented milk of Lactobacillus paracasei Bd-II increased during storage.

[0073] Table 3 Texture characteristics of Lactobacillus paracasei Bd-II during storage

[0074]

[0075] Comparative Example 1: Preparation and detection of fermented milk using Lactobacillus paracasei J4

[0076] 1. Process flow: Same as Example 1

[0077] 2. Detection indicators:

[0078] ·Viscosity: 39.4η / Pa·S;

[0079] The whey separation rate on the first day was 43.75±1.24;

[0080] The instability index is 0.142±0.001

[0081] Comparative Example 2: Preparation and detection of fermented milk using Lactobacillus paracasei J8

[0082] 1. Process flow: Same as Example 1

[0083] 2. Detection indicators:

[0084] ·Viscosity: 20.0Pa·S;

[0085] The whey extraction rate on the first day was 43.75±1.24%;

[0086] The instability index is 0.238±0.002

[0087] Comparative Example 3: Preparation and detection of fermented milk using Lactobacillus paracasei J15

[0088] 1. Process flow: Same as Example 1

[0089] 2. Detection indicators:

[0090] ·Viscosity: 40.3Pa·S;

[0091] The whey extraction rate on the first day was 29.57±0.85

[0092] The instability index is 0.101±0.002

[0093] The fermented milk prepared in Example 1 and the fermented milk prepared in the comparative example were subjected to sensory evaluation. The sensory evaluation was carried out according to the Chinese dairy industry standard RHB104-2020 "Detailed Rules for Sensory Evaluation of Fermented Milk", which is briefly described as follows. 18 sensory evaluators were selected to taste the fermented milk samples and conduct sensory evaluations in appearance, texture, taste, and taste. The best value of each score is 10 points. The closer to 0 points, the worse the attribute. The sensory scoring standard is shown in Table 4.

[0094] Table 4 Sensory scoring criteria

[0095]

[0096]

[0097] The results are shown in Table 5: the score of Example 1 is 9.2, the score of Comparative Example 1 is 8.5, the score of Comparative Example 2 is 7.2, and the score of Comparative Example 3 is 8.7.

[0098] Table 5 Sensory evaluation results

[0099] strains Appearance texture Taste Smell Total score Example 1 2 2.6 2.8 1.8 9.2 Comparative Example 1 1.6 2.6 2.6 1.7 8.5 Comparative Example 2 1.5 2 2.2 1.5 7.2 Comparative Example 3 2 2.6 2.6 1.5 8.7

[0100] in conclusion

[0101] The present invention uses Lactobacillus paracasei Bd-II as the core strain, and can improve the texture and stability of traditional probiotic fermented milk through storage monitoring and verification. Experimental verification shows that the fermented milk produced by the present invention has high initial viscosity, low whey precipitation rate, fine texture, low instability index, can maintain high hardness, consistency and cohesion during storage (1-7 days), and has excellent sensory quality and is suitable for promotion and application in the high-end dairy industry.

[0102] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limiting the present invention. In addition, the various modifications listed herein and the variations of the methods in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for preparing probiotic fermented milk, characterized in that: The preparation method comprises the following steps: 1) preheating the raw milk to 40-50° C., mixing with sugar and then pasteurizing the mixture, wherein the sugar is selected from white sugar and / or sucrose; 2) cooling, inoculating Lactobacillus paracasei Bd-II at 0.3%-0.5% of the mass of the raw milk for fermentation; 3) After fermentation is completed, the milk is refrigerated for post-ripening to obtain the probiotic fermented milk.

2. The preparation method according to claim 1, characterized in that: In step 1), the raw milk is selected from raw cow's milk, raw goat's milk, reconstituted milk, low-fat milk or skimmed milk.

3. The preparation method according to claim 1, characterized in that: The mass of the sugar is 5-9% of the mass of the raw milk.

4. The preparation method according to claim 1, characterized in that: In step 2), the mixture is cooled to 37-40° C. and then inoculated with Lactobacillus paracasei Bd-II.

5. The preparation method according to claim 1, characterized in that: The Lactobacillus casei Bd-II is Lactobacillus casei Bd-IICMGCC.0849 in the invention patent with application number CN03128995.

9.

6. The preparation method according to claim 1, characterized in that: The Lactobacillus paracasei Bd-II in step 2) is the seed liquid of Lactobacillus paracasei Bd-II.

7. The preparation method according to claim 6, characterized in that: The seed liquid of Lactobacillus paracasei Bd-II is obtained by the following method: after activating Lactobacillus paracasei Bd-II for two generations using an MRS plate, a single colony is picked and inoculated into MRS broth, and the seed liquid is obtained by culturing for 10 to 14 hours.

8. The preparation method according to claim 1, characterized in that: In step 2), the fermentation temperature is 36-38° C., and / or the fermentation is performed until the pH value of the system is 4.0-4.

2.

9. The preparation method according to claim 1, characterized in that: In step 3), the refrigeration temperature is 3.5-4.5° C., and / or the refrigeration time is 10-20 hours.

10. Probiotic fermented milk obtained by the preparation method according to any one of claims 1 to 9.

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