Microalga extract-containing composite starter culture, and preparation method and application thereof

Abstract

The present application belongs to the field of food microbial fermentation technology, and discloses a compound fermentation agent containing microalgae extract and a preparation method and application thereof.The compound fermentation agent containing microalgae extract comprises the following raw materials in parts by weight: 82-93 parts of compound lactic acid bacteria powder, 3-8 parts of microalgae extract, 3-6 parts of protective agent, and 1-4 parts of dispersion carrier; wherein the microalgae extract is obtained by compounding Chlorella vulgaris water extract and Spirulina alcohol extract at a mass ratio of 1-3:1.The present application adds microalgae extract to the traditional lactic acid bacteria fermentation agent, which can not only effectively inhibit the growth of miscellaneous bacteria in the early fermentation stage and ensure the rapid reproduction of lactic acid bacteria, but also form a protective layer on the surface of lactic acid bacteria, reduce the damage to lactic acid bacteria caused by low pH or high salt environment, osmotic stress, etc., so that lactic acid bacteria can maintain high activity in the fermentation process, and the stability is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of food microbial fermentation technology, specifically to a composite fermentation agent containing microalgae extract, its preparation method, and its application. Background Technology

[0002] Fermented vegetables (such as pickled vegetables, sauerkraut, pickled radishes, and cowpeas) are an important part of my country's traditional fermented foods, with an annual output exceeding ten million tons. They are a significant source of plant protein and dietary fiber in the diet of Chinese residents. The production of fermented vegetables mainly relies on the natural fermentation by microorganisms such as lactic acid bacteria, which gives the vegetables their unique flavor and long shelf life. However, traditional natural fermentation methods suffer from problems such as long fermentation cycles, unstable quality, and susceptibility to contamination by other microorganisms. Furthermore, vegetable raw materials generally contain nitrates, which, under the high pH and aerobic conditions of the early stages of fermentation, are easily reduced to nitrites by the large-scale proliferation of microorganisms such as Escherichia coli and Staphylococcus aureus. Nitrites further react with amines to form nitrosamines, which have carcinogenic risks. Therefore, effectively controlling the nitrite content in fermented vegetables is a key technical challenge to ensure their food safety and improve product quality.

[0003] Currently, the industry mainly employs two technical approaches to address these issues: one is to screen lactic acid bacteria strains with highly efficient nitrite-degrading capabilities; the other is to use compound microbial agents to accelerate the fermentation process and inhibit the growth of nitrate-reducing bacteria such as *Escherichia coli* and *Staphylococcus aureus*, while relying on nitrite reductase produced by the strains to degrade nitrite, thereby reducing the nitrite content in fermented vegetable products. However, in fermentation environments with high salt stress, low pH, and nutrient competition, the survival rate and metabolic activity of the strains are easily inhibited, resulting in limited and unstable nitrite degradation effects. While existing technologies attempt to assist in antibacterial and nitrite degradation by adding natural extracts such as hawthorn, green tea, ginger, and garlic, the antibacterial spectrum of these extracts is generally narrow, and their nitrite degradation effect is weak.

[0004] In view of this, this invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to solve any of the above-mentioned technical problems and provide a compound fermentation agent containing microalgae extract, its preparation method, and its application. This compound fermentation agent can effectively improve the survival rate and metabolic activity of bacterial strains. When used in the preparation of fermented vegetables, it can significantly reduce the nitrite content of the product and improve the product quality.

[0006] To achieve the above objectives, the first technical solution adopted by the present invention is as follows: A compound fermentation agent containing microalgae extract, comprising the following raw materials by weight: 82-93 parts of compound lactic acid bacteria powder, 3-8 parts of microalgae extract, 3-6 parts of protectant, and 1-4 parts of dispersion carrier; The microalgae extract is obtained by compounding Chlorella water extract and Spirulina alcohol extract in a mass ratio of 1-3:1.

[0007] Preferably, the method for preparing the Chlorella water extract is as follows: add water to Chlorella powder, extract in a water bath at 50-60℃ for 1-2 h, and then concentrate the filtrate.

[0008] Preferably, the preparation method of the spirulina ethanol extract is as follows: ethanol is added to spirulina powder, and the extract is extracted at 45-55 °C for 1-1.5 h, followed by vacuum treatment.

[0009] Preferably, the viable count of the compound lactic acid bacteria powder is ≥10. 11 CFU / g.

[0010] Preferably, the compound lactic acid bacteria powder is obtained by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder and Lactobacillus pentosaccharide powder in a mass ratio of 2:0.6-1.2:1-1.5.

[0011] Preferably, the protective agent comprises skim milk powder and trehalose in a mass ratio of 2-4:1.

[0012] Preferably, the dispersion carrier is selected from one or more of maltodextrin and soluble starch.

[0013] The second technical solution adopted in this invention is: The preparation method of the compound fermentation agent containing microalgae extract as described above includes: A bacterial suspension was prepared by dispersing compound lactic acid bacteria powder in sterile water. Microalgae extract, protectant and dispersant were added to the bacterial suspension, mixed evenly and then freeze-dried under vacuum.

[0014] The third technical solution adopted in this invention is: As described above, the application of the compound fermentation agent containing microalgae extract in the preparation of fermented vegetables involves placing the vegetable raw materials in brine and adding the compound fermentation agent for fermentation.

[0015] Preferably, the amount of the compound fermentation agent is 0.1-0.5% of the total mass of the vegetable raw materials and brine.

[0016] The beneficial effects of this invention are as follows: This invention combines Chlorella water extract and Spirulina alcohol extract in a specific mass ratio and adds them to a traditional lactic acid bacteria starter. This not only effectively inhibits the growth of other bacteria in the early stages of fermentation, ensuring the rapid reproduction of lactic acid bacteria, but also forms a protective layer on the surface of the lactic acid bacteria cells, reducing the damage caused to lactic acid bacteria by low pH or high salt environments, osmotic pressure stress, etc., so that the lactic acid bacteria maintain high activity during the fermentation process.

[0017] The compound fermentation agent of this invention, when used in the preparation of fermented vegetables, can effectively inhibit the growth of miscellaneous bacteria in the early stage of vegetable fermentation, allowing compound lactic acid bacteria to quickly become the dominant flora and continuously metabolize and ferment. By rapidly producing acid and lowering the environmental pH, it directly inhibits the growth and reproduction of nitrate-reducing bacteria. At the same time, the active ingredients in the microalgae extract, together with the nitrite reductase produced by bacterial metabolism, can also degrade the nitrite that has already been generated, thereby significantly reducing the nitrite content in fermented vegetables and improving the edible quality of the product. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description of the invention is provided in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are merely exemplary and not intended to limit the scope of the invention. Furthermore, in the following description, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0019] The first embodiment of the present invention provides a compound fermentation agent containing microalgae extract, which, by weight, comprises the following raw materials: 82-93 parts of compound lactic acid bacteria powder, 3-8 parts of microalgae extract, 3-6 parts of protective agent, and 1-4 parts of dispersion carrier; The microalgae extract is obtained by compounding Chlorella water extract and Spirulina alcohol extract in a mass ratio of 1-3:1.

[0020] In the compound fermentation agent of this embodiment, microalgae extract is a key component. Microalgae such as Chlorella and Spirulina are rich in active ingredients such as polysaccharides, polypeptides, polyphenols, and flavonoids. Some of these microalgae have been approved as raw materials for ordinary or new foods and can be used in food production. The applicant discovered in its research that Chlorella water extract is rich in polysaccharides and polypeptides, which can promote the proliferation of lactic acid bacteria, act as a protectant to enhance the stability of lactic acid bacteria, and also have a certain ability to scavenge nitrite. Spirulina alcohol extract is rich in active ingredients such as polyphenols and flavonoids, possessing broad-spectrum antibacterial activity and strong antioxidant properties. It can help inhibit the growth of miscellaneous bacteria, directly remove free nitrite, and block the synthesis of nitrosamines. Mixing these two extracts at a specific mass ratio and then compounding them with lactic acid bacteria can effectively inhibit the growth of miscellaneous bacteria in the early stages of lactic acid bacteria fermentation. Simultaneously, a protective layer is formed on the surface of the lactic acid bacteria cells, reducing damage caused by low pH or high salt environments, osmotic pressure stress, etc., allowing the lactic acid bacteria to maintain high activity during fermentation.

[0021] In this embodiment, the novel food ingredient *Chlorella proteoglycans* is selected. The water extract is prepared by adding water to *Chlorella* powder and extracting it in a water bath at 50-60°C for 1-2 hours. The filtrate is then concentrated. The preferred solid-liquid ratio during extraction is 1:8-10. After extraction, the extract is concentrated under low-temperature vacuum at 50-60°C and a vacuum degree of -0.09 to -0.07 MPa until the soluble solids content reaches 20-25%. This gentle water extraction process enriches water-soluble polysaccharides, small-molecule amino acids, and polypeptides in *Chlorella*, effectively improving the strain's stress resistance and metabolic activity, and indirectly enhancing the nitrite degradation capacity of the fermentation agent.

[0022] Spirulina selected is *Spirulina maxima*, an approved food ingredient. The preparation method for its ethanol extract is as follows: ethanol is added to spirulina powder, and extraction is carried out at 45-55 °C for 1-1.5 h, followed by vacuum treatment. The preferred solid-liquid ratio during extraction is 1:8-12, and the preferred ethanol concentration is 40-60% food-grade ethanol. After extraction, vacuum treatment is carried out at a vacuum degree of -0.09 to -0.075 MPa and a temperature of 40-50 °C until the ethanol is completely removed. This extraction process effectively ensures the full extraction of fat-soluble active ingredients such as polyphenols and flavonoids from spirulina.

[0023] In this embodiment of the compound fermentation agent, the viable count of the compound lactic acid bacteria powder is ≥10. 11 The CFU / g live bacteria count ensures rapid fermentation initiation. The compound lactic acid bacteria powder is prepared by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder, and Lactobacillus pentosaccharide powder in a mass ratio of 2:0.6-1.2:1-1.5.

[0024] The role of the protectant is to further improve the survival rate of the bacterial strain, effectively inhibit the attenuation of live bacteria during room temperature storage and transportation of the fermentation agent, and ensure the long-term stable effect of the fermentation agent. The protectant includes skim milk powder and trehalose in a mass ratio of 2-4:1.

[0025] The dispersing carrier is used to improve the physical properties of the starter culture powder, prevent the microalgae extract and lactic acid bacteria powder from agglomerating, and ensure that the functional components are uniformly dispersed in the fermentation material. The dispersing carrier can be selected from commonly used food carriers such as polysaccharide carriers and protein carriers; this embodiment is not particularly limited. In some preferred embodiments, the dispersing carrier is selected from one or more of maltodextrin and soluble starch. Soluble starch can also slowly degrade during fermentation, providing a supplementary carbon source for the lactic acid bacteria and assisting in strain proliferation.

[0026] The second embodiment of the present invention provides a method for preparing a composite fermentation agent containing microalgae extract as described above, comprising: A bacterial suspension was prepared by dispersing compound lactic acid bacteria powder in sterile water. Microalgae extract, protectant and dispersant were added to the bacterial suspension, mixed evenly and then freeze-dried under vacuum.

[0027] In this embodiment, the solid-liquid ratio of the compound lactic acid bacteria powder and sterile water is preferably 1:5-8. After adding microalgae extract and other components to the bacterial suspension, the mixture is first stirred at 20-30℃ and 100-200 r / min for 30-60 min to ensure uniform mixing of all components, and then vacuum freeze-dried until the moisture content is ≤5%. The vacuum freeze-drying process can be conventionally adjusted according to the specific composition of the components. For example, pre-freezing at -60~-40℃ for 4-6 h, and then drying at -30℃~-20℃ until the moisture content of the fermentation agent is ≤5%.

[0028] The third embodiment of the present invention provides the application of the compound fermentation agent containing microalgae extract as described above in the preparation of fermented vegetables, wherein the vegetable raw materials are placed in brine and the compound fermentation agent is added for fermentation.

[0029] The compound fermentation agent of this embodiment is used in the preparation of fermented vegetables. The broad-spectrum antibacterial properties of the microalgae extract can effectively inhibit the growth of miscellaneous bacteria in the early stage of fermentation, allowing the compound lactic acid bacteria to quickly become the dominant flora and continuously metabolize and ferment. By rapidly producing acid and lowering the environmental pH, it directly inhibits the growth and reproduction of nitrate-reducing bacteria. At the same time, the active ingredients in the microalgae extract, together with the nitrite reductase produced by the bacterial metabolism, degrade the nitrite that has already been generated, thereby significantly reducing the nitrite content in fermented vegetables.

[0030] In this embodiment, the fermented vegetable raw materials include common vegetables such as cabbage, radish, cowpea, and mustard greens. The fermentation process parameters and the amount of compound fermenting agent can be routinely adjusted according to the type of vegetable raw materials and product requirements. For example, the preparation method of fermented vegetables is as follows: wash and cut the vegetable raw materials, add brine with a mass concentration of 4-6%, the brine amount should be enough to submerge the vegetable raw materials, then add 0.1-0.5% of the total mass of vegetable raw materials and brine to the compound fermenting agent, and ferment at 20-25 ℃ for 7-10 days to obtain the finished fermented vegetable product.

[0031] It should be noted that because the compound fermentation agent in this embodiment contains Chlorella proteinensis, it is not suitable for infants and young children. Therefore, the vegetable products obtained by fermentation are not suitable for infants and young children to consume.

[0032] The following will disclose specific embodiments of the present invention, as well as corresponding comparative examples to demonstrate the relevant technical effects of the composite fermentation agent containing microalgae extract of the present invention.

[0033] The *Lactobacillus plantarum* powder (ATCC14917), *Lactobacillus brevis* powder (ATCC14869), and *Lactobacillus pentosaccharide* powder (ATCC8041) used in the following examples are all standard deposited strains publicly available from the American Type Culture Collection (ATCC) and obtained through authorized agents; the viable count of the compound lactic acid bacteria powder is ≥10. 11 CFU / g; Chlorella powder and Spirulina powder are essentially Chlorella pyrenoidosa powder and Spirulina macrophylla powder; the remaining raw materials are all available from the market.

[0034] Example 1: Preparation of a compound fermentation agent containing microalgae extract Raw material preparation: A compound lactic acid bacteria powder is obtained by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder, and Lactobacillus pentosaccharide powder in a mass ratio of 2:0.6:1. Water was added to Chlorella powder at a solid-liquid ratio of 1:10, and the mixture was extracted in a water bath at 50 °C for 1 h. The filtrate was then collected and concentrated under low temperature vacuum at 50 °C and a vacuum degree of -0.09 MPa until the soluble solids content was 25%, thus obtaining Chlorella water extract. Add 60% edible ethanol to spirulina powder at a solid-liquid ratio of 1:12, extract at 45 ℃ for 1 h, and then treat under reduced pressure at a vacuum of -0.09 MPa and a temperature of 40 ℃ until the ethanol is completely removed to obtain spirulina ethanol extract. Microalgae extract was obtained by combining Chlorella water extract and Spirulina alcohol extract at a mass ratio of 1:1. A protective agent is obtained by mixing skim milk powder and trehalose at a mass ratio of 2:1.

[0035] Preparation of compound fermentation agent: Take 93 portions of compound lactic acid bacteria powder and disperse them in sterile water at a solid-liquid ratio of 1:8 to prepare a bacterial suspension. Take 3 parts of microalgae extract, 3 parts of protectant, and 1 part of maltodextrin, add them to the above bacterial suspension, stir for 30 min at 30 ℃ and 100 r / min, and then freeze-dry under vacuum until the moisture content is ≤5% to obtain a compound fermentation agent containing microalgae extract.

[0036] Example 2: Preparation of a compound fermentation agent containing microalgae extract Raw material preparation: A compound lactic acid bacteria powder was obtained by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder, and Lactobacillus pentosaccharide powder in a mass ratio of 2:0.9:1.2. Water was added to Chlorella powder at a solid-liquid ratio of 1:9, and the mixture was extracted in a water bath at 55 °C for 1.5 h. The filtrate was then collected and concentrated under low temperature vacuum at 55 °C and a vacuum degree of -0.08 MPa until the soluble solids content was 22%, thus obtaining Chlorella water extract. Add 50% edible ethanol to spirulina powder at a solid-liquid ratio of 1:10, extract at 50 ℃ for 1.2 h, and then treat under reduced pressure at a vacuum of -0.08 MPa and a temperature of 45 ℃ until the ethanol is completely removed to obtain spirulina ethanol extract. Microalgae extract was obtained by combining Chlorella water extract and Spirulina alcohol extract at a mass ratio of 2:1. A protective agent is obtained by mixing skim milk powder and trehalose at a mass ratio of 3:1.

[0037] Preparation of compound fermentation agent: Take 87.5 parts of compound lactic acid bacteria powder and disperse it in sterile water at a solid-liquid ratio of 1:6 to prepare a bacterial suspension; Take 5.5 parts of microalgae extract, 4.5 parts of protectant, and 2.5 parts of soluble starch, add them to the above bacterial suspension, stir for 45 min at 25℃ and 150 r / min, and then freeze-dry under vacuum until the moisture content is ≤5% to obtain a compound fermentation agent containing microalgae extract.

[0038] Example 3: Preparation of a compound fermentation agent containing microalgae extract Raw material preparation: A compound lactic acid bacteria powder is obtained by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder, and Lactobacillus pentosaccharide powder in a mass ratio of 2:1.2:1.5. Water was added to Chlorella powder at a solid-liquid ratio of 1:8, and the mixture was extracted in a water bath at 60 °C for 2 h. The filtrate was then collected and concentrated under low temperature vacuum at 60 °C and a vacuum degree of -0.07 MPa until the soluble solids content was 20%, thus obtaining Chlorella water extract. Add 40% edible ethanol to spirulina powder at a solid-liquid ratio of 1:8, extract at 55 ℃ for 1.5 h, and then treat under reduced pressure at a vacuum of -0.075 MPa and a temperature of 50 ℃ until the ethanol is completely removed to obtain spirulina ethanol extract. Microalgae extract was obtained by combining Chlorella water extract and Spirulina alcohol extract at a mass ratio of 3:1. A protective agent is obtained by mixing skim milk powder and trehalose at a mass ratio of 4:1. A dispersion carrier is obtained by mixing maltodextrin and soluble starch at a mass ratio of 1:1.

[0039] Preparation of compound fermentation agent: Take 82 parts of compound lactic acid bacteria powder and disperse them in sterile water at a solid-liquid ratio of 1:5 to prepare a bacterial suspension. Take 8 parts of microalgae extract, 6 parts of protectant, and 4 parts of dispersion carrier, add them to the above bacterial suspension, stir for 60 min at 20 ℃ and 200 r / min, and then freeze-dry under vacuum until the moisture content is ≤5% to obtain a compound fermentation agent containing microalgae extract.

[0040] Comparative Example 1 The preparation method is the same as in Example 1, except that no microalgae extract is added.

[0041] Comparative Example 2 The preparation method is the same as in Example 1, except that the microalgae extract is replaced with an equal amount of Chlorella water extract.

[0042] Comparative Example 3 The preparation method is the same as in Example 1, except that the microalgae extract is replaced with an equal amount of spirulina alcohol extract.

[0043] Comparative Example 4 The preparation method is the same as in Example 1, except that the mass ratio of Chlorella water extract to Spirulina alcohol extract in the microalgae extract is 0.5:1.

[0044] Comparative Example 5 The preparation method is the same as in Example 1, except that the mass ratio of Chlorella water extract to Spirulina alcohol extract in the microalgae extract is 3.5:1.

[0045] Comparative Example 6 The preparation method is the same as in Example 1, except that no protective agent is added.

[0046] Comparative Example 7 The preparation method is the same as in Example 1, except that maltodextrin is not added.

[0047] Experimental Example 1 The compound fermenting agent of the above examples and comparative examples was used to prepare Chinese cabbage kimchi. The preparation method is as follows: Fresh cabbage was washed, chopped, and submerged in 60% (5% by weight) brine. Then, 0.3% of the total cabbage and brine mass of the compound fermenting agent from the example or comparative example was added. After mixing thoroughly, the mixture was sealed and fermented at 25°C for 8 days to obtain kimchi. Kimchi prepared using traditional natural fermentation was used as a control group. Quality indicators of each group of kimchi products were measured, including nitrite, pH value, lactic acid bacteria count, and sensory evaluation. The measurement methods are as follows, and the results are shown in Table 1.

[0048] Nitrite: GB 5009.33-2025 Determination of Nitrite and Nitrate in Food - Spectrophotometric Method.

[0049] pH value: GB / T 10468-1989 "Determination of pH value of fruit and vegetable products".

[0050] Lactic acid bacteria count: GB 4789.35-2023 "Food Microbiology Examination - Lactic Acid Bacteria Examination", operated according to 6.3.4, anaerobic culture, the result is the total number of Lactobacillus spp.

[0051] Sensory evaluation: A sensory evaluation team of 10 trained food industry professionals (5 men and 5 women) evaluated the cabbage kimchi products based on four aspects: color, flavor, taste, and overall acceptability. The maximum score was 100 points, and the average score was taken.

[0052] Table 1. Results of Quality Indicators Measurement for Chinese Cabbage Kimchi .

[0053] Experimental Example 2 The compound fermenting agent of the above examples and comparative examples was used to prepare radish kimchi. The preparation method is as follows: Fresh radishes were washed, cut, and submerged in 62.5% (4% by mass) brine. Then, the compound fermentation agent from the example or comparative example was added at 0.1% of the total radish and brine mass. After mixing thoroughly, the mixture was sealed and fermented at 22°C for 7 days to obtain radish pickles. Radish pickles prepared using traditional natural fermentation techniques were used as a control group. Quality indicators of each group of radish pickle products were measured, including nitrite, pH value, lactic acid bacteria count, and sensory evaluation. The measurement methods were the same as in Experiment 1, and the results are shown in Table 2.

[0054] Table 2. Results of Quality Indicators Measurement for Radish Pickles .

[0055] Experimental Example 3 The compound fermentation agent of the above examples and comparative examples was used to prepare cowpea kimchi. The preparation method is as follows: Fresh cowpeas were washed, cut, and submerged in 65% (5% by weight) brine. Then, the compound fermentation agent from the example or comparative example was added at 0.5% of the total mass of cowpeas and brine. After mixing thoroughly, the mixture was sealed and fermented at 23 °C for 10 days to obtain cowpea pickles. Cowpea pickles prepared using traditional natural fermentation techniques were used as a control group. Quality indicators of each group of cowpea pickle products were measured, including nitrite, pH value, lactic acid bacteria count, and sensory evaluation. The measurement methods were the same as in Experiment 1, and the results are shown in Table 3.

[0056] Table 3. Results of Quality Indicators Measurement for Cowpea Pickles .

[0057] As can be seen from the test results in Tables 1-3, the kimchi products fermented using the compound fermentation agent of the embodiments have significantly lower nitrite content than the control group and each comparative example, and significantly higher lactic acid bacteria count and sensory scores than the control group and each comparative example. This indicates that the compound fermentation agent provided by the present invention can significantly reduce the nitrite content in fermented vegetables and improve the overall edible quality of the product.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A compound fermentation agent containing microalgae extract, characterized in that, By weight, it contains the following ingredients: 82-93 parts of compound lactic acid bacteria powder, 3-8 parts of microalgae extract, 3-6 parts of protectant, and 1-4 parts of dispersion carrier; The microalgae extract is obtained by compounding Chlorella water extract and Spirulina alcohol extract in a mass ratio of 1-3:

1.

2. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The method for preparing the Chlorella water extract is as follows: add water to Chlorella powder, extract in a water bath at 50-60℃ for 1-2 h, and then concentrate the filtrate.

3. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The preparation method of the spirulina ethanol extract is as follows: add ethanol to spirulina powder, extract at 45-55 ℃ for 1-1.5 h, and then treat under reduced pressure.

4. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The viable count of the compound lactic acid bacteria powder is ≥10. 11 CFU / g.

5. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The compound lactic acid bacteria powder is obtained by mixing Lactobacillus plantarum powder, Lactobacillus brevis powder and Lactobacillus pentosaccharide powder in a mass ratio of 2:0.6-1.2:1-1.

5.

6. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The protective agent comprises skim milk powder and trehalose in a mass ratio of 2-4:

1.

7. The compound fermentation agent containing microalgae extract as described in claim 1, characterized in that, The dispersion carrier is selected from one or more of maltodextrin and soluble starch.

8. The method for preparing the composite fermentation agent containing microalgae extract as described in any one of claims 1-7, characterized in that, include: The compound lactic acid bacteria powder was dispersed in sterile water to obtain a bacterial suspension; Microalgae extract, protectant and dispersant were added to the bacterial suspension, mixed evenly and then freeze-dried under vacuum.

9. The application of the composite fermentation agent containing microalgae extract as described in any one of claims 1-7 in the preparation of fermented vegetables, characterized in that, The vegetable raw materials are placed in salt water, and the compound fermentation agent is added for fermentation.

10. The application as described in claim 9, characterized in that, The amount of the compound fermentation agent is 0.1-0.5% of the total mass of the vegetable raw materials and brine.