Streptococcus thermophilus compound leavening agent strain composition screening method and compound leavening agent preparation method and application

Abstract

The invention relates to a streptococcus thermophilus compound leavening agent strain composition screening method and a compound leavening agent preparation method and application, and belongs to the technical field of microbial fermentation. The invention provides a streptococcus thermophilus compound leavening agent strain composition screening method. According to the screening method of the compound strain composition, the excellent performance of a single strain in the compound strain can be reserved, and a stable compound strain micro-ecological system is formed, so that the compound strain micro-ecological system has the excellent characteristics of various strains; the possibility is provided for realizing rapid acid production and high exopolysaccharide production in the dairy product fermentation process. In addition, the invention further provides a preparation method of the streptococcus thermophilus compound leavening agent, the preparation process of the compound leavening agent can be simplified, and the production efficiency of the compound leavening agent can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of microbial fermentation, and specifically relates to a method for screening the strain composition of a thermophilic streptococcus composite fermentation agent, and a method for preparing the composite fermentation agent and application thereof. Background Art

[0002] Streptococcus thermophilus can rapidly convert lactose into lactic acid through homotypic fermentation. This process reduces the pH value of milk, promotes protein coagulation and the formation of yogurt texture. The characteristics of different Streptococcus thermophilus determine the differences in yogurt production time and the differences in texture of the produced yogurt. For example, some Streptococcus thermophilus have the characteristics of rapid acid production, which can quickly produce acid and shorten the preparation time of fermented milk; for example, some Streptococcus thermophilus have the characteristics of producing extracellular polysaccharides, which can accumulate extracellular polysaccharides to improve the texture of yogurt and make stirred yogurt have a thick and delicate texture. Therefore, dairy starters are generally compounded with different Streptococcus thermophilus to ensure their acid and viscosity production stability and resistance to bacteriophages. However, conventional yogurt starters are prepared by culturing different single strains for separate fermentation and freeze-drying, and then compounding them in different proportions to prepare composite yogurt starters. This operation is relatively complicated and time-consuming, which limits yogurt preparation to a certain extent. However, how to optimize the preparation process of compound starters to improve the production efficiency of compound starters has not been reported. Summary of the invention

[0003] The purpose of the present invention is to provide a method for screening the strain composition of a thermophilic Streptococcus compound fermentation agent and a method for preparing the compound fermentation agent and application thereof. The method for preparing the thermophilic Streptococcus compound fermentation agent of the present invention can simplify the preparation process of the compound fermentation agent and improve the production efficiency of the compound fermentation agent.

[0004] The present invention provides a method for screening the strain composition of a thermophilic streptococcus composite fermentation agent, comprising the following steps:

[0005] Mixing the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested in a mass ratio of 1:1, and inoculating the mixture into the fermented milk for fermentation to obtain mixed fermented milk;

[0006] The fermentation speed and curd viscosity of the obtained mixed fermented milk are tested. If the fermentation speed and curd viscosity are not lower than 85% of those when the tested thermophilic streptococcus A and the tested thermophilic streptococcus B are fermented alone, the tested thermophilic streptococcus A and the tested thermophilic streptococcus B are used as the strain composition of the composite starter obtained by screening.

[0007] Preferably, when the number of bacterial species in the compound starter is greater than two, the test bacterial species need to be mixed and screened separately in pairs according to the screening method described in the above technical scheme, so that the fermentation speed and curd viscosity of each test bacterial species and any other test bacterial species meet the requirements of not less than 85% of the single fermentation.

[0008] The present invention also provides a method for preparing a thermophilic streptococcus composite fermentation agent, comprising the following steps:

[0009] The bacterial species obtained by the bacterial species screening method described in the above technical solution are inoculated into the same culture medium for fermentation and culture to obtain a mixed culture of thermophilic Streptococcus;

[0010] The obtained composite thermophilic streptococcus mixed culture is centrifuged to obtain thermophilic streptococcus cells;

[0011] The obtained thermophilic streptococcus cells are freeze-dried to obtain the composite starter.

[0012] Preferably, in the strain composition obtained by screening, the mixing mass ratio between the two strains is (1-100):1.

[0013] Preferably, the pH of the culture medium is 5.5-6.5.

[0014] Preferably, a protective agent is added to the composite cultured thermophilic Streptococcus during the freeze-drying process.

[0015] The present invention also provides the application of the preparation method of the compound leavening agent described in the above technical scheme in improving the production efficiency of the compound leavening agent.

[0016] The present invention also provides a compound leavening agent prepared by the method for preparing the compound leavening agent described in the above technical solution.

[0017] The present invention also provides a compound leavening agent prepared by the method for preparing the compound leavening agent described in the above technical solution or the use of the compound leavening agent described in the above technical solution in preparing a fermentation product.

[0018] Preferably, the fermented product includes fermented milk; and the fermented milk includes yogurt.

[0019] The present invention provides a method for screening the composition of thermophilic streptococcus composite fermentation agent. The screening method of the composite bacterial species composition of the present invention can retain the excellent performance of the single strain itself in the composite bacterial species, form a stable microecological system, so that the composite bacterial strain microecological system has the excellent characteristics of multiple strains, and provides the possibility of high production of extracellular polysaccharides while realizing rapid acid production in the dairy fermentation process, so that the composite fermentation agent finally prepared has the excellent characteristics of fast acid production and high production of extracellular polysaccharides, and the thermophilic streptococcus is applied to the preparation of fermented milk products, which can give the product a fast fermentation speed and good viscosity, improve product texture, improve product stability, and reduce the additional addition of food additives. In addition, it is verified by experiments that the composite fermentation agent prepared by the screening method of the composite bacterial species composition of the present invention and the preparation method of the composite fermentation agent can be further fermented with Lactobacillus bulgaricus and / or Bifidobacterium lactis and / or Lactobacillus paracasei, and the excellent characteristics of each strain are not changed.

[0020] The present invention also provides a method for preparing a thermophilic Streptococcus compound starter, which can simplify the preparation process of the compound starter and improve the production efficiency of the compound starter. Specifically, the preparation method of the compound starter of the present invention only requires one fermentation production and freeze-drying to prepare a composite starter with stable product performance, excellent flavor and texture, thereby simplifying the preparation process of the compound starter and improving the acid production and viscosity production stability of the yogurt starter. The preparation method of the present invention not only simplifies the disadvantage of culturing each strain of bacteria separately and then mixing them when applying a multi-strain compound of a traditional starter, but also can meet the application requirements of complementary advantages of different strains, greatly improving the production efficiency of the compound starter and the production efficiency of the corresponding fermented products.

[0021] Biological deposit information

[0022] Streptococcus thermophilus GA8 is deposited in the General Microbiology Center of China Microorganism Culture Collection Administration, referred to as CGMCC, and the deposit date is October 11, 2024. The address is No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, and the deposit number is CGMCC No. 23562.

[0023] Streptococcus thermophilus ST65 is deposited in the General Microbiology Center of China Microorganism Culture Collection Administration, referred to as CGMCC, and the deposit date is October 11, 2024. The address is No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, and the deposit number is CGMCC No.32180. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A graph showing the results of measuring the acidity and viscosity of two-by-two compoundings of different thermophilic streptococci provided by the present invention;

[0026] Figure 2 The pH change curve diagram of the fermentation process of different leavening agents provided by the present invention;

[0027] Figure 3 A state diagram of different fermented milks provided by the present invention;

[0028] Figure 4 The graph is a test result of rheological properties of different fermented milks provided by the present invention; wherein, □ represents the test result of rheological properties of Example 1; ○ represents the test result of rheological properties of Example 2; △ represents the test result of rheological properties of Example 3; ◇ represents the test result of rheological properties of single strain ST1. DETAILED DESCRIPTION

[0029] The invention provides a method for screening the bacterial strain composition of a thermophilic streptococcus composite starter, comprising the following steps: mixing a thermophilic streptococcus A to be tested and a thermophilic streptococcus B to be tested according to a mass ratio of 1:1, and inoculating the mixture into fermented milk for fermentation to obtain mixed fermented milk; detecting the fermentation speed and curd viscosity of the obtained mixed fermented milk, and if the fermentation speed and curd viscosity are not lower than 85% of those when the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested are fermented separately, the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested are used as the bacterial strain composition of the composite starter obtained by screening.

[0030] The present invention mixes the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested according to a mass ratio of 1:1, and inoculates them in the fermented milk to obtain mixed fermented milk. In a specific embodiment, the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested can be thermophilic streptococcus A and thermophilic streptococcus B with an OD value of 2. In a specific embodiment, the thermophilic streptococcus A and thermophilic streptococcus B with an OD value of 2 can be obtained by adjusting the OD value of thermophilic streptococcus A and thermophilic streptococcus B after activation treatment and centrifugation purification, and using physiological saline to adjust the OD value. In a specific embodiment, the activation treatment can be culturing thermophilic streptococcus using an activation medium. In a specific embodiment, the activation medium can be an MRS medium. In a specific embodiment, the fermented milk can be fresh milk. In a specific embodiment, the fresh milk can be fresh milk sterilized at 95°C for 10 minutes. In a specific embodiment, the inoculation amount of the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested can be 2%.

[0031] After obtaining the mixed fermented milk, the present invention detects the fermentation speed and curd viscosity of the obtained mixed fermented milk. If the fermentation speed and curd viscosity are not lower than 85% of the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested when fermented separately, the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested are used as the composite starter strain composition obtained by screening. In a specific embodiment, the fermentation speed can be compared by detecting the titrated acidity of the fermented milk within a specific time. In a specific embodiment, the titrated acidity is determined according to the national standard GB 5413.34. In a specific embodiment, the titrated acidity of the fermented milk within the specific time can be the titrated acidity of the fermented milk after fermentation for 6 hours. In a specific embodiment, the curd viscosity can be the viscosity of the fermented milk after fermentation for 12 hours. In a specific embodiment, the viscosity can be determined using a proRheo viscometer. In a specific embodiment, the proRheo viscometer can be used to measure the viscosity of the fermented milk using a No. 2 rotor at an interval of 10s and a rotation speed of 64r / min. In a specific embodiment, when the number of bacterial species in the compound starter is greater than two, the test bacterial species need to be mixed and screened separately in pairs according to the screening method described in the above technical scheme, so that the fermentation speed and curd viscosity of each test bacterial species and any other test bacterial species meet the requirements of not less than 85% of the single fermentation.

[0032] The present invention also provides a method for preparing a thermophilic streptococcus composite fermentation agent, comprising the following steps: inoculating the bacterial species obtained by the bacterial species composition screening method described in the above technical scheme into the same culture medium for fermentation and culturing to obtain a composite thermophilic streptococcus mixed culture; centrifuging the obtained composite thermophilic streptococcus mixed culture to obtain thermophilic streptococcus cells; and freeze-drying the obtained thermophilic streptococcus cells to obtain the composite fermentation agent.

[0033] In the present invention, the bacterial species obtained by the bacterial species screening method described in the above technical solution are inoculated into the same culture medium for fermentation and culture to obtain a composite thermophilic streptococcus mixed culture.

[0034] In a specific embodiment, the total inoculation amount of the bacterial composition can be 2% to 5% of the mass of the fermented milk. In a specific embodiment, in the bacterial composition obtained by screening, the mixing mass ratio between the two bacterial species is (1 to 100): 1. In a specific embodiment, the culture medium can be an MRS culture medium, and can also be a culture medium that has been improved to a certain extent on the basis of the MRS culture medium. In a specific embodiment, the pH of the culture medium is 5.5 to 6.5. In a specific embodiment, the pH of the culture medium can be controlled by adding sodium hydroxide. In a specific embodiment, the fermentation is terminated when there is no need to add sodium hydroxide.

[0035] After obtaining the composite thermophilic streptococcus mixed culture, the present invention centrifuges the composite thermophilic streptococcus mixed culture to obtain thermophilic streptococcus cells.

[0036] After obtaining the thermophilic streptococcus cells, the present invention performs freeze-drying treatment on the obtained thermophilic streptococcus cells to obtain the composite starter.

[0037] In a specific embodiment, when the freeze-drying treatment is performed, a protective agent is added to the composite cultured thermophilic streptococcus. In a specific embodiment, the mixing ratio of the thermophilic streptococcus and the protective agent can be 1:1 by mass.

[0038] The present invention also provides the application of the preparation method of the compound leavening agent described in the above technical scheme in improving the production efficiency of the compound leavening agent.

[0039] The present invention also provides the composite ferment prepared by the preparation method of the composite ferment described in the technical scheme. In a specific embodiment, the composite ferment can also continue to be composited with other bacterial strains. In a specific embodiment, the other bacterial strains include one or more of Lactobacillus bulgaricus, Bifidobacterium lactis and Lactobacillus paracasei.

[0040] The present invention also provides a composite starter prepared by the method for preparing the composite starter described in the above technical solution or the use of the composite starter described in the above technical solution in preparing a fermented product. In a specific embodiment, the fermented product includes fermented milk; the fermented milk includes yogurt.

[0041] To further illustrate the present invention, a method for screening the strain composition of a thermophilic Streptococcus composite fermentation agent and a method for preparing a composite fermentation agent and an application thereof provided by the present invention are described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Screening of bacterial composition of thermophilic Streptococcus compound fermentation agent.

[0043] Four different thermophilic streptococci were randomly selected and numbered ST1 to 4. The specific thermophilic streptococci ST1 to 4 are as follows:

[0044] ST1 Streptococcus thermophilus, CGMCC No. 23562 (the name in the deposit certificate is: Streptococcus thermophilus GA8);

[0045] ST2 Streptococcus thermophilus, CGMCC No.15752 (the name in the deposit certificate is: Streptococcusthermophilus ST81, see patent CN113913352B, a strain of Streptococcus thermophilus producing elastic extracellular polysaccharide and its culture method and application);

[0046] ST3 Streptococcus thermophilus, CGMCC No.32180 (the name in the deposit certificate is: Streptococcus thermophilus ST65);

[0047] ST4 Streptococcus thermophilus, Body-3 strain commercially available from Hansen.

[0048] Thermophilic Streptococcus ST1-4 were activated with MRS medium, centrifuged, and adjusted to OD value of 2 with appropriate amount of physiological saline. They were inoculated into fresh milk (sterilized at 95℃ for 10min) at an inoculum of 2% and fermented for 6h. The titrated acidity of the fermented milk was measured at 6h. The fermentation was continued until 12h. At this time, the viscosity of the fermented milk was measured after the 4 portions of fermented milk had fully coagulated. Among them, the titrated acidity was determined in accordance with the national standard GB5413.34; the viscosity was determined using a proRheo viscometer (rotor No. 2, interval 10s, speed 64r / min). The results of the acidity and viscosity determination of different thermophilic Streptococcus fermented alone for 6h and 12h are shown in Table 1.

[0049] Table 1 Results of 6h acidity and 12h viscosity determination of different thermophilic streptococci fermented separately

[0050]

[0051] Thermophilic Streptococcus ST1-4 were combined in pairs, and the two thermophilic Streptococci were mixed in a 1:1 ratio. They were inoculated with a 2% inoculum into fresh milk sterilized at 95°C for 10 minutes for fermentation, and the titrated acidity of the fermented milk after 6 hours of fermentation and the viscosity after full coagulation after 12 hours of fermentation were measured. Among them, the titrated acidity was determined in accordance with the national standard GB5413.34; the viscosity was determined using a proRheo viscometer (rotor No. 2, interval 10s, speed 64r / min). The acidity and viscosity measurement results of different thermophilic Streptococci in pairs were obtained as shown in the following figure. Figure 1 shown.

[0052] Depend on Figure 1 It can be seen that after the combination of ST1+ST2, ST1+ST3, ST1+ST4, ST2+ST3 and ST2+ST4 was mixed and fermented in a mass ratio of 1:1, the titrated acidity results after 6h of fermentation and the viscosity results after 12h of fermentation were not less than 85% of the fermentation acidity and viscosity of each single strain, and the composite fermentation was feasible. However, for the combination of ST3+ST4, it can be seen from the fermentation test data of the strains that ST3 and ST4 have an inhibitory effect. When the two are combined for fermentation, the acidity after 6h of fermentation is 45°T, which is lower than the fermentation acidity of ST3. ST4 has an inhibitory effect on ST3, and it is mostly not feasible for composite fermentation.

[0053] Example 1

[0054] Preparation of composite fermentation culture of Streptococcus thermophilus ST1 and ST2

[0055] (1) ST1 and ST2 were inoculated into MRS medium at a ratio of 1:1, with a total inoculation amount of 2%. Sodium hydroxide was used to control the pH of the fermentation process to be maintained at about 6.0. The fermentation was continued until no more sodium hydroxide was added and the OD value of the fermentation liquid was 10.5. The cells were collected by centrifugation, mixed with a lyophilization protective agent at a ratio of 1:1, and freeze-dried to obtain a thermophilic Streptococcus composite lyophilized powder, which was stored at -20°C for use. This process took a total of 4 days.

[0056] (2) The freeze-dried powder obtained in step (1) is used for the preparation of fermented milk. The powder is inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L and fermented until the titrated acidity reaches 70°T. The fermentation is terminated to obtain fermented milk. The fermentation time is 4.6 h and the viscosity of the fermented milk is 1.02 Pa.s, which meets the industrialization requirements of fermented milk.

[0057] Example 2

[0058] Preparation of composite starter cultures of Streptococcus thermophilus ST1, ST2 and ST3

[0059] (1) ST1, ST2 and ST3 were inoculated into MRS medium at a ratio of 50:5:1, with a total inoculation amount of 3%. The pH of the fermentation process was controlled with sodium hydroxide to maintain at about 5.5. The fermentation was continued until no more sodium hydroxide was added and the OD value of the fermentation liquid was 12.3. The cells were collected by centrifugation, mixed with a lyophilization protective agent in a ratio of 1:1, and freeze-dried to obtain a thermophilic Streptococcus composite lyophilized powder, which was stored at -20°C for use. This process took a total of 4 days.

[0060] (2) The freeze-dried powder obtained in step (1) is used for the preparation of fermented milk. It is inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L and fermented to a titrated acidity of 70°T. The fermentation is terminated to obtain fermented milk. The fermentation time is 4.7 h and the viscosity of the fermented milk is 1.26 Pa.s, which meets the industrialization requirements of fermented milk.

[0061] Example 3

[0062] Preparation of composite starter cultures of Streptococcus thermophilus ST1, ST2 and ST4

[0063] (1) ST1, ST2 and ST4 were inoculated into MRS medium at a ratio of 0.1:1:10, with a total inoculation amount of 5%. The pH of the fermentation process was controlled with sodium hydroxide to maintain at about 6.5. The fermentation was continued until no more sodium hydroxide was added and the OD value of the fermentation liquid was 12.3. The cells were collected by centrifugation, mixed with a lyophilization protective agent in a ratio of 1:1, and freeze-dried to obtain a thermophilic Streptococcus composite lyophilized powder, which was stored at -20°C for use. This process took a total of 4 days.

[0064] (2) The freeze-dried powder obtained in step (1) is used for the preparation of fermented milk. It is inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L and fermented to a titrated acidity of 70°T. The fermentation is terminated to obtain fermented milk. The fermentation time is 5.1 h and the viscosity of the fermented milk is 1.48 Pa.s, which meets the industrialization requirements of fermented milk.

[0065] Example 4

[0066] The preparation method of this embodiment is different from that of embodiment 1 only in that step (2) is changed to: the bacterial powder obtained in step (1) is mixed with commercially available lactic acid Bifidobacterium BLa80 bacterial powder produced by Suzhou Weikang Probiotics in a ratio of 100:1, and inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L, and fermented to a titrated acidity of 70°T, and the fermentation is terminated to obtain fermented milk, and its fermentation speed and viscosity are consistent with those of embodiment 1, so the addition of Bifidobacterium lactis does not affect the fermentation of the starter.

[0067] Example 5

[0068] The preparation method of this embodiment is different from that of Embodiment 2 only in that step (2) is changed to: the bacterial powder obtained in step (1) is mixed with commercially available Lactobacillus bulgaricus LB42 produced by Suzhou Weikang Probiotics and commercially available Lactobacillus paracasei L.casei 01 produced by Hansen in an amount of 100:1:1, inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L, and fermented to a titrated acidity of 70°T, and fermented milk is obtained. The fermentation rate and viscosity of the fermented milk are consistent with those of Embodiment 2, so the addition of Lactobacillus bulgaricus LB42 and Lactobacillus paracasei L.casei01 does not affect the fermentation of the starter.

[0069] Comparative Example 1

[0070] The preparation of traditional thermophilic Streptococcus ST1, ST2 and ST4 composite fermentation agents is to culture thermophilic Streptococcus separately, use sodium hydroxide to control the pH of the fermentation process to maintain at about 6.0, ferment until it is no longer necessary to add sodium hydroxide, collect the bacteria by centrifugation, mix with a lyophilization protective agent in a ratio of 1:1, freeze-dry to obtain a separate lyophilized powder of each thermophilic Streptococcus, and store at -20°C for standby use. The three bacteria are produced separately, with a total production cycle of 12 days. After the three bacteria are produced, they are mixed in a ratio of 0.1:1:10 to obtain a composite fermentation agent.

[0071] The obtained composite starter was used for the preparation of fermented milk. It was inoculated into fresh milk sterilized at 95°C for 10 min at an inoculum amount of 30 mg / L and fermented to a titrated acidity of 70°T. The fermentation was terminated to obtain fermented milk. The fermentation time was 5.2 h. The viscosity of the fermented milk was 1.12 Pa.s. The fermentation speed was slightly slower than that of Example 3, and the viscosity of the fermented milk was slightly higher than that of Example 3. The overall product texture and flavor were similar.

[0072] Test Example 1

[0073] The starter prepared in Examples 1 to 3 was inoculated into fresh milk sterilized at 95°C for 10 min at 30 mg / L for fermentation, and the pH change during the fermentation process was measured using a continuous acidity meter, cinic. The pH change curves of the fermentation process of different starters were obtained as shown in Figure 2 shown.

[0074] from Figure 2 It can be seen that when the starter prepared in Examples 1 to 3 is inoculated into fresh milk for fermentation, the acid production starts 2 hours after inoculation, the pH value can be reduced to below 4.5 within 6 hours, and the fermentation speed can meet the fermentation speed requirement for industrial preparation of fermented milk. The fermented milk prepared in Examples 1 to 3 and the fermented milk prepared by the single strain ST1 are poured onto the table for observation, and the states of the different fermented milks on the table are obtained as follows: Figure 3As shown. It can be seen that since ST1 does not produce extracellular polysaccharides, the fermented milk prepared by using ST1 alone has a rough texture. In Example 1, Example 2 and Example 3, ST1 is compounded with strains (ST2, ST3 and / or ST4) that have the function of producing extracellular polysaccharides, so that the fermented milk produced by the composite starter prepared after compounding is smooth and delicate, and at the same time maintains its fast acid production characteristics, thereby improving the fermentation speed and texture of the composite starter.

[0075] The fermented milk prepared in Examples 1 to 3 and the fermented milk prepared by the single strain ST1 were subjected to rheological tests using a TAHR10 rheometer. The test fixture used a 60 cm flat plate, the sample loading height was 1000 μm, and the shear rate during the test was 100 S -1 Gradually increase to 0.1S -1 , the rheological properties test results of different fermented milks were obtained as follows Figure 4 As shown. Figure 4 It can be seen that the samples of Examples 1 to 3 have improved sample viscosity through composite fermentation, and their viscosity is higher than that of the fermented milk prepared by the single strain ST1.

[0076] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for screening the composition of thermophilic Streptococcus composite fermentation agent, comprising the following steps: Mixing the thermophilic streptococcus A to be tested and the thermophilic streptococcus B to be tested in a mass ratio of 1:1, and inoculating the mixture into the fermented milk for fermentation to obtain mixed fermented milk; The fermentation speed and curd viscosity of the obtained mixed fermented milk are tested. If the fermentation speed and curd viscosity are not lower than 85% of those when the tested thermophilic streptococcus A and the tested thermophilic streptococcus B are fermented alone, the tested thermophilic streptococcus A and the tested thermophilic streptococcus B are used as the strain composition of the composite starter obtained by screening.

2. The method for screening the composite bacterial species composition according to claim 1, characterized in that: When the number of bacterial species in the composite starter is greater than two, the test bacterial species shall be mixed and screened separately in pairs according to the screening method described in claim 1, so that the fermentation speed and curd viscosity of each test bacterial species and any other test bacterial species are not less than 85% of that of the single fermentation.

3. A method for preparing a thermophilic streptococcus composite fermentation agent, comprising the following steps: The bacterial species obtained by the bacterial species screening method according to claim 1 are inoculated into the same culture medium for fermentation and culture to obtain a mixed culture of thermophilic Streptococcus; The obtained composite thermophilic streptococcus mixed culture is centrifuged to obtain thermophilic streptococcus cells; The obtained thermophilic streptococcus cells are freeze-dried to obtain the composite starter.

4. The method for preparing the composite leavening agent according to claim 3, characterized in that: In the strain composition obtained by screening, the mixing mass ratio between the two strains is (1-100):

1.

5. The method for preparing the composite leavening agent according to claim 3, characterized in that: The pH of the culture medium is 5.5-6.

5.

6. The method for preparing the composite leavening agent according to claim 3, characterized in that: When the freeze-drying treatment is carried out, a protective agent is added to the composite cultured thermophilic streptococcus.

7. Use of the preparation method of the composite leavening agent according to any one of claims 3 to 6 in improving the production efficiency of the composite leavening agent.

8. The composite leavening agent prepared by the method for preparing the composite leavening agent according to any one of claims 3 to 6.

9. Use of the compound leavening agent prepared by the method for preparing the compound leavening agent according to any one of claims 3 to 6 or the compound leavening agent according to claim 8 in preparing fermented products.

10. The use according to claim 9, characterized in that: The fermented product includes fermented milk; the fermented milk includes yogurt.

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