Lactobacillus rhamnosus FN518 leavening agent, preparation method thereof and application of lactobacillus rhamnosus FN518 leavening agent in fermented soybean milk

Abstract

The invention discloses a lactobacillus rhamnosus FN518 leavening agent, a preparation method thereof and application of the lactobacillus rhamnosus FN518 leavening agent in fermented soybean milk, and belongs to the technical field of microbial fermentation application. The invention discloses an application of a lactobacillus rhamnosus FN518 leavening agent in fermented soybean milk. The lactobacillus rhamnosus FN518 leavening agent prepared by spray drying is used for fermenting the soybean milk. Compared with the existing leavening agent, the soybean milk obtained by fermenting the lactobacillus rhamnosus FN518 leavening agent disclosed by the invention has lower hardness and better elasticity.

Description

Technical Field

[0001] The invention relates to the technical field of microbial fermentation application, and more particularly to a Lactobacillus rhamnosus FN518 starter, a preparation method thereof and application thereof in fermented soybean milk. Background Art

[0002] Previous studies have shown that higher plant protein intake is associated with a lower risk of cardiovascular disease mortality. Plant protein replaces animal protein in the diet, especially processed red meat protein, which can reduce cardiovascular disease mortality. Plant active ingredients also have good physiological activity in regulating the immune system and lipid metabolism. In addition, plant milk does not contain lactose and cholesterol, and is also a good source of protein for patients with lactose intolerance and people with cardiovascular and cerebrovascular diseases. These health advantages have caused the plant-based wave to sweep the world. Lactic acid bacteria fermentation, as an ancient food production method, has become a new idea in the production of high-quality plant milk products. Lactic acid bacteria fermentation can help improve the sensory characteristics and nutritional properties of plant milk, add a special fermented flavor, and thus avoid the use of food additives.

[0003] Soy milk is rich in high-quality plant protein. Fermenting soy milk with lactic acid bacteria can reduce the beany smell, reduce anti-nutritional factors in soy milk such as soy oligosaccharides and phytic acid, etc., and can also bring a special flavor of fermentation and improve biological activity. According to the national standard GB / T 30885-2014, fermented soy milk is divided into fermented puree soy milk, which is a product fermented with soybean as the main raw material, sugar can be added, and no other food auxiliary materials and food additives are added; fermented and modulated soy milk is a product fermented with soybean as the main raw material, nutritional enhancers, food additives, and other food auxiliary materials. At present, the commonly used fermentation agents for fermented soy milk on the market are Lactobacillus delbrueckii subspecies Bulgaria and Streptococcus thermophilus, which are the traditional fermentation agents for producing yogurt. There is no fermentation agent specifically for fermented soy milk. At present, the lactic acid bacteria preparation prepared by freeze drying is the main form of industrial use of lactic acid bacteria.

[0004] Since soy milk lacks lactose, the Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus thermophilus used in traditional yogurt fermentation agents do not grow well when fermenting soy milk, produce low acid, and lack the sweet and sour flavor of traditional yogurt. Some studies have found that it is not easy to screen out fermentation strains with good acid production ability in soy milk. At the same time, the texture of fermented soy milk generally has problems such as rough taste and high hardness. Researchers have conducted more research on other strains that can ferment soy milk (such as Lactobacillus plantarum, Lactobacillus rhamnosus, Lactobacillus paracasei, etc.), hoping to obtain strains suitable for soy milk fermentation that can efficiently utilize carbohydrates in soy milk, ferment quickly in the absence of lactose, and improve texture.

[0005] At present, lactic acid bacteria preparations are the main form of industrial use of lactic acid bacteria, which are mainly prepared by freeze-drying technology. They have a high survival rate, but they also have disadvantages such as inability to produce continuously, high equipment cost, high energy consumption and long production cycle. These have become an important factor restricting the development of lactic acid bacteria dry preparations in the expanding market. Spray drying technology has the advantages of low cost, high efficiency and continuity, but the contact between bacteria and hot air during spray drying can cause cell damage, resulting in a large number of lactic acid bacteria dying and a significant decrease in vitality after drying.

[0006] Therefore, providing a Lactobacillus rhamnosus FN518 starter and a preparation method thereof and application in fermented soy milk are problems that those skilled in the art need to solve urgently. Summary of the invention

[0007] In view of this, the present invention provides a Lactobacillus rhamnosus FN518 starter and a preparation method thereof and an application in fermenting soy milk, and specifically provides a lactic acid bacteria starter containing Lactobacillus rhamnosus FN518, which is mainly used for fermenting soy milk, can coagulate the soy milk, and improve the quality of the soy milk such as hardness.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: The preservation number of a strain of Lactobacillus rhamnosus FN518 is CCTCC NO: M2020830. It has been deposited in the China Center for Type Culture Collection, abbreviated as CCTCC, address: Wuhan University, Wuhan, China. The preservation date is December 2, 2020, and the classification name is Lactobacillus rhamnosus FN518, Lactobacillus rhamnosusFN518.

[0009] Further, a method for preparing a Lactobacillus rhamnosus FN518 starter comprises the following steps: (1) Activation of strains: Take out the glycerol tube of Lactobacillus rhamnosus FN518 from the -80℃ strain collection, inoculate it into MRS medium at a 2% (v / v) inoculation volume, and culture at 37℃ with shaking for 24 h; (2) Expanded culture: The activated Lactobacillus rhamnosus FN518 was inoculated into MRS medium. After culturing for 24 hours, the number of viable bacteria reached 10 9 CFU / mL; (3) Centrifugation to obtain bacterial sludge: Centrifuge at 4°C, 6000 r / min for 10 min to collect the bacteria; wash the bacteria twice with saline, and then centrifuge at 4°C, 6000 r / min for 10 min to collect the bacteria to obtain bacterial sludge; (4) Mixing protective agent: Mix the bacterial sludge, protective agent and water in a mass ratio of 1:2:7; the protective agent is composed of the following ingredients in parts by weight: 100 parts of skim milk, 10 parts of trehalose, 10 parts of sucrose, 50 parts of milk alkaline protein, 2 parts of glutamic acid, 50 parts of maltodextrin and 5 parts of glycerol; (5) Spray drying: Spray drying conditions are: air volume: 380m 3 / h, air inlet / outlet temperature: 120 / 70℃, atomization pressure 0.9m 3 / h, adjust the feed rate so that the inlet and outlet air temperatures meet the preset values; after all materials are dried, collect the bacterial powder to obtain the starter.

[0010] Furthermore, the method for preparing a Lactobacillus rhamnosus FN518 starter agent is used to prepare a Lactobacillus rhamnosus FN518 starter agent.

[0011] Further, the application of the Lactobacillus rhamnosus FN518 starter in fermenting soy milk comprises the following steps: (1) Soaking: Select soybeans with good maturity, remove impurities and moldy particles, and soak the soybeans in water at room temperature for 8 hours; (2) Grinding: After draining and washing the soybeans and peeling them, the soaked and swollen soybeans were ground into pulp using a soybean milk machine at a soybean-water ratio of 1:8 (w / v); the blade speed of the soybean milk machine was 11,000 r / min; (3) Filtration: After grinding, filter the soy milk with a 120-mesh filter cloth to remove large particles of dregs; (4) Sterilization: sterilize the filtered soy milk at 115°C for 15 min and store the sterilized soy milk in a refrigerator at 4°C until use; (5) Inoculation: adding 1 g of the starter culture per liter of sterilized soy milk; (6) Fermentation: Ferment at 37°C for 6 h. After fermentation, the soy milk will solidify.

[0012] It can be seen from the above technical scheme that, compared with the prior art, the present invention discloses a Lactobacillus rhamnosus FN518 starter and a preparation method thereof and an application thereof in fermented soy milk, which solves the problem of thermal death of lactic acid bacteria during spray drying, and the number of effective live bacteria is greater than 10 9 CFU / g; compared with the existing starter, the soymilk obtained by fermenting with the starter of the present invention has lower hardness and better elasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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 or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0014] Figure 1 The present invention provides a technical roadmap for fermenting soy milk using the Lactobacillus rhamnosus FN518 starter.

[0015] Figure 2 The present invention relates to fermented soybean milk curd.

[0016] Figure 3 is the hardness of soymilk gel fermented by different lactic acid bacteria starters of the present invention; wherein, S1-7 are Lactobacillus delbrueckii subsp. lactis 6-12 (B), Limosilactobacillus fermentumMN-56, Limosilactobacillus fermentum MZZX M27, Limosilactobacillus fermentumMN-67, Limosilactobacillus fermentum MN-61, Enterococcus faecium YZX-8, Enterococcus faecium YZX-39, respectively; and FN518 is the FN518 starter prepared by spray drying.

[0017] Figure 4 The elasticity of soymilk gel fermented with different lactic acid bacteria starters of the present invention; wherein, S1-7 are Lactobacillus delbrueckii subsp. lactis 6-12 (B), Limosilactobacillus fermentumMN-56, Limosilactobacillus fermentum MZZX M27, Limosilactobacillus fermentumMN-67, Limosilactobacillus fermentum MN-61, Enterococcus faecium YZX-8, Enterococcus faecium YZX-39, respectively; and FN518 is the FN518 starter prepared by spray drying. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1 Application of Lactobacillus rhamnosus FN518 starter in fermented soy milk (technical route see Figure 1 ), the steps are as follows: 1) Preparation of Lactobacillus rhamnosus FN518 starter culture (1) Activation of strains: Take out the glycerol tube of Lactobacillus rhamnosus FN518 from the -80℃ strain collection, inoculate it into 1 mL of MRS medium at a 2% (v / v) inoculum, and culture at 37℃ with shaking for 24 h.

[0020] (2) Expanded culture: The activated Lactobacillus rhamnosus FN518 was inoculated into 100 mL MRS. After culturing for 24 h, the number of viable bacteria reached 10 9 CFU / mL.

[0021] (3) Centrifugation to obtain bacterial sludge: Collect the bacteria by centrifugation at 4°C, 6000 r / min for 10 min; wash the bacteria twice with saline, and then centrifuge again at 4°C, 6000 r / min for 10 min to collect the bacteria to obtain 2 g of bacterial sludge.

[0022] (4) Mixed protective agent: Mix 1g of bacterial sludge with 2g of protective agent and 7g of water. The protective agent consists of the following ingredients: 100g of skim milk, 10g of trehalose, 10g of sucrose, 50g of milk alkaline protein, 2g of glutamic acid, 50g of maltodextrin, and 5g of glycerol.

[0023] (5) Spray drying: Spray drying conditions are: air volume: 380m 3 / h, air inlet / outlet temperature: 120 / 70℃, atomization pressure 0.9m 3 / h, and the feed rate was adjusted to make the inlet and outlet air temperatures meet the preset values. After all materials were dried, the bacterial powder was collected to obtain the starter. The number of live bacteria, survival rate and moisture content of the starter were measured, and the results are shown in Table 1.

[0024] Table 1 Analysis of characteristics of Lactobacillus rhamnosus FN518 spray-dried starter culture

[0025] (6) Preparation of fermented soy milk ① Soaking: Select soybeans with good maturity (the soybean variety used in this experiment is Dongnong 252, whose protein content accounts for about 40% of the dry weight of soybeans), remove impurities and moldy particles, and soak the soybeans in water at room temperature for 8 hours.

[0026] ② Grinding: After draining and washing the soybeans and peeling them, use a soybean milk machine to grind the soaked and swollen soybeans at a soybean-water ratio of 1:8 (w / v). The blade speed of the soybean milk machine is 11000 r / min.

[0027] ③Filtration: After grinding, filter the soy milk with a 120-mesh filter cloth to remove large particles of dregs.

[0028] ④Sterilization: Sterilize the filtered soy milk at 115°C for 15 minutes. Store the sterilized soy milk in a refrigerator at 4°C for later use.

[0029] ⑤ Inoculation: Add 0.01 g of the above-mentioned FN518 starter culture to 10 mL of sterilized soy milk (the control group is composed of 7 existing fermented lactic acid bacteria with the same inoculation amount).

[0030] ⑥ Fermentation: Ferment at 37℃ for 6 hours. After fermentation, the soy milk solidifies. Figure 2 shown.

[0031] The seven fermenting lactic acid bacteria are Lactobacillus delbrueckii subsp. lactis 6-12(B), Limosilactobacillus fermentum MN-56, Limosilactobacillus fermentum MZZX M27, Limosilactobacillus fermentum MN-67, Limosilactobacillus fermentum MN-61, Enterococcus faecium YZX-8, Enterococcus faecium YZX-39, for details, see Liang Liu, Youtao Huang, Xiaoqian Zhang, Texture analysis and physicochemical characteristics of fermented soymilk gel by different lactic acid bacteria, Food Hydrocolloids 136 (2023) 108252.

[0032] The texture profile of fermented soymilk gel was analyzed by TPA (texture profile analysis) using a 50 mm cylindrical probe of a texture analyzer. The operating parameters of the texture analyzer were as follows: stress 500 N; test speed 30 mm / min; strain degree 30%. Figure 3 and Figure 4 It can be seen that compared with the soy milk fermented by the 7 existing fermented lactic acid bacteria in the laboratory, the soy milk fermented by the Lactobacillus rhamnosus FN518 starter prepared by spray drying has lower hardness and better elasticity.

[0033] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A strain of Lactobacillus rhamnousus FN518, characterized in that: Its deposit number is CCTCC NO: M 2020830.

2. A method for preparing a Lactobacillus rhamnosus FN518 starter, characterized in that: The following steps are involved: (1) Activation of strains: Take out the Lactobacillus rhamnosus FN518 stored in the glycerol tube of claim 1 from the -80°C strain storage bank, inoculate it into MRS medium at a 2% (v / v) inoculation amount, and culture at 37°C with shaking for 24 h; (2) Expanded culture: The activated Lactobacillus rhamnosus FN518 in step (1) was inoculated into MRS medium. After culturing for 24 hours, the number of viable bacteria reached 10 9 CFU / mL; (3) Centrifugal sludge: collect the bacteria by centrifugation at 4°C, 6000 rpm for 10 min; After washing the bacteria twice with saline, centrifuge again at 4°C, 6000 r / min for 10 min to collect the bacteria to obtain bacterial sludge; (4) Mixing protective agent: Mix the bacterial sludge, protective agent and water in a mass ratio of 1:2:7; the protective agent is composed of the following ingredients in parts by weight: 100 parts of skim milk, 10 parts of trehalose, 10 parts of sucrose, 50 parts of milk alkaline protein, 2 parts of glutamic acid, 50 parts of maltodextrin and 5 parts of glycerol; (5) Spray drying: Spray drying conditions are: air volume: 380m 3 / h, air inlet / outlet temperature: 120 / 70℃, atomization pressure 0.9m 3 / h, adjust the feed rate so that the inlet and outlet air temperatures meet the preset values; after all materials are dried, collect the bacterial powder to obtain the starter.

3. The Lactobacillus rhamnosus FN518 starter prepared by the preparation method according to claim 2.

4. Use of the Lactobacillus rhamnosus FN518 starter culture according to claim 3 in fermented soymilk.

5. The use of the Lactobacillus rhamnosus FN518 starter in fermented soymilk according to claim 4, characterized in that: Here are the steps: (1) Soaking: Select soybeans with good maturity, remove impurities and moldy particles, and soak the soybeans in water at room temperature for 8 hours; (2) Grinding: After draining and washing the soybeans and peeling them, the soaked and swollen soybeans were ground into pulp using a soybean milk machine at a soybean-water ratio of 1:8 (w / v); the blade speed of the soybean milk machine was 11,000 r / min; (3) Filtration: After refining, filter the soy milk with a 120-mesh filter cloth; (4) Sterilization: sterilize the filtered soy milk at 115°C for 15 min and store the sterilized soy milk in a refrigerator at 4°C until use; (5) Inoculation: adding 1 g of the Lactobacillus rhamnosus FN518 starter culture per liter of sterilized soy milk; (6) Fermentation: Ferment at 37°C for 6 h.

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