Compound lactic acid bacteria bread leavening agent, preparation method thereof and application of compound lactic acid bacteria bread leavening agent in bread making

Abstract

The invention provides a compound lactic acid bacteria bread leavening agent as well as a preparation method and application thereof in bread making, and belongs to the technical field of food processing and manufacturing. The preparation method of the compound lactic acid bacteria bread leavening agent comprises the following steps: mixing the tartary buckwheat powder with the purified water, inoculating the compound lactic acid bacteria fermentation liquor, stirring, fermenting and refrigerating to obtain the compound lactic acid bacteria bread leavening agent. Wherein the compound lactobacillus fermentation liquor is prepared from lactobacillus plantarum, Weissella fusiformis and pediococcus pentosaceus. The compound lactic acid bacteria bread leavening agent and natural yeast are used for making multi-grain bread together, the quality of the multi-grain bread can be effectively improved, the flavor of the multi-grain bread is increased, and the texture of the bread is improved under the condition that the nutritional value of the multi-grain bread is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing and manufacturing, and in particular relates to a composite lactic acid bacteria bread leavening agent, a preparation method thereof and application thereof in bread making. Background Art

[0002] As people's health awareness continues to improve, consumers' eating experience and understanding of healthy food are also constantly improving. Compared with bread made from refined white flour, bread made from grains (such as buckwheat, whole wheat and oats, etc.) contains rich crude fiber, vitamin E and B vitamins, as well as zinc, potassium and other substances, and has higher nutritional value, and has begun to become a major popular trend. However, bread made from grains generally has poor flavor, a rough and hard taste, and uneven texture, making it difficult for more consumers to accept it.

[0003] Lactic acid bacteria play an important role in fermentation technology. They can adjust the pH value of dough by producing lactic acid and other metabolites, thereby improving the flavor and shelf life of bread. By combining the fermentation of natural yeast and lactic acid bacteria, more complex flavors and better dough properties can be obtained. Therefore, this application hopes to further study how to improve the taste, appearance and nutritional value of multi-grain liquid bread fermented with composite lactic acid bacteria from this perspective. Summary of the invention

[0004] The purpose of the present invention is to provide a composite lactic acid bacteria bread fermentation agent, which can effectively improve the quality of bread, increase the flavor of bread, improve the texture of bread, and solve the problems of rough taste and unbalanced nutrition of cereal bread on the market.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a method for preparing a composite lactic acid bacteria bread starter: tartary buckwheat flour is mixed with purified water, added with composite lactic acid bacteria fermentation liquid, stirred, fermented, and refrigerated to obtain the composite lactic acid bacteria bread starter;

[0007] The composite lactic acid bacteria fermentation liquid consists of Lactobacillus plantarum, Weissella fusion and Pediococcus pentosaceus.

[0008] Preferably, the weight ratio of the tartary buckwheat flour to the purified water is 1-1.5:1-1.5;

[0009] The inoculation amount of the composite lactic acid bacteria fermentation liquid is 2% to 3% of the total mass of tartary buckwheat flour and purified water;

[0010] The fermentation conditions are: 28-32°C, 16-20h;

[0011] The refrigeration conditions are: 3-4°C, 10-12h.

[0012] The preparation method of the composite lactic acid bacteria fermentation liquid is as follows: the plant lactobacillus, fusion Weissella and Pediococcus pentosaceus are activated respectively until the bacterial concentration reaches 10 8 ~10 9 CFU / mL, the mixture is mixed according to the number of bacterial strains of 1:1-1.5:1-1.5 to obtain a mixed bacterial solution, and then the mixed bacterial solution is inoculated into a liquid culture medium at an inoculum size of 2-3% and expanded and cultured at 27-30°C for 16-20h, and the solid-liquid is separated to obtain the clear liquid, which is the composite lactic acid bacteria fermentation liquid.

[0013] Preferably, the Lactobacillus plantarum is Lactobacillus plantarum CICC 21794; the Weissella fusion is Weissella fusion CICC 24453; the Pediococcus pentosaceus is Pediococcus pentosaceus CICC 22231;

[0014] The number of times the strain is activated is 1 to 3 times;

[0015] The conditions for the solid-liquid separation are: centrifugation at 800-2000 rpm for 5-10 min.

[0016] The invention provides a composite lactic acid bacteria bread leavening agent.

[0017] The invention provides application of the composite lactic acid bacteria bread starter in making bread.

[0018] The present invention provides a composite lactic acid bacteria fermented multi-grain liquid seed bread, comprising the following raw materials in percentage by mass: 40% to 55% of multi-grain flour, 13% to 27% of purified water, 1.0% to 2.5% of yeast, 5% to 15% of white sugar, 0.3% to 1.2% of salt, and 15% to 35% of the composite lactic acid bacteria bread starter;

[0019] The multi-grain flour includes one or more of whole wheat flour, oat flour and buckwheat flour.

[0020] Preferably, when the multi-grain flour is whole wheat flour, oat flour and buckwheat flour, the mass ratio of the whole wheat flour, oat flour and buckwheat flour is 15-17:5:3.

[0021] The present invention also provides a method for preparing the composite lactic acid bacteria fermented multi-grain liquid seed bread, comprising the following steps:

[0022] (a) mixing multi-grain flour, purified water, yeast, white sugar, salt and the composite lactic acid bacteria bread starter, beating at 18-23° C. for 6-7 minutes to obtain a composite lactic acid bacteria fermented multi-grain liquid main dough, exhausting the air and cutting and shaping to obtain a composite lactic acid bacteria fermented multi-grain liquid dough, and proofing at low temperature;

[0023] (b) after the low-temperature proofed composite lactic acid bacteria fermented multi-grain liquid seed dough is warmed up, it is baked and cooled to obtain composite lactic acid bacteria fermented multi-grain liquid seed bread.

[0024] Preferably, the temperature of the purified water in step (a) is 4-8°C;

[0025] Preferably, the low-temperature proofing condition is 4-7°C, 30-60min;

[0026] Preferably, the temperature recovery time in step (b) is 10 to 30 minutes, and the temperature is recovered to 24 to 26°C;

[0027] Preferably, the baking conditions are: upper and lower fire 180-200° C., 17-22 minutes.

[0028] Beneficial Effects

[0029] The Lactobacillus plantarum CICC 21794 in the present invention can ferment carbohydrates to produce organic acids such as lactic acid, thereby creating an acidic environment that is not conducive to the growth of harmful bacteria but is conducive to the survival of beneficial bacteria. At the same time, antibacterial substances such as bacteriocins may be produced to further inhibit the growth of harmful microorganisms; the fusion of Weissella CICC 24453 can improve the quality of fermented food and produce some flavor substances, such as diacetyl, etc., giving the fermented food a unique flavor; Pediococcus pentosaceus CICC 22231 can decompose sugars in cereals and produce organic acids such as lactic acid, which can not only extend the shelf life of cereal products, but also improve their texture and flavor. The three strains of bacteria provided by the present invention have a synergistic relationship in the utilization of nutrients during fermentation, wherein Lactobacillus plantarum CICC21794 and Pediococcus pentosaceus CICC 22231 utilize different types of sugars during the fermentation process, and the metabolites produced can provide a more suitable growth environment for the fusion of Weissella CICC 24453, and the metabolites such as short-chain fatty acids produced by the fusion of Weissella CICC 24453 can also be utilized by the other two strains, thereby promoting the growth of each other. In addition, the exopolysaccharides produced by the three strains are complementary in structure. The exopolysaccharides of Lactobacillus plantarum CICC 21794 have good viscosity, the exopolysaccharides of Weissella fusion CICC 24453 are conducive to biofilm formation, and the exopolysaccharides of Pediococcus pentosaceus CICC 22231 have good adsorption. When the three exist together, these characteristics can complement each other to form an exopolysaccharide system with better comprehensive performance, which can better improve the texture in fermented cereal foods and have a positive impact on different aspects of bread such as specific volume, texture and aroma.

[0030] The composite lactic acid bacteria fermented multi-grain liquid seed bread provided by the present invention is rich in nutrition, contains rich protein, fiber, vitamins and minerals, and helps to provide the nutrition and energy required by the body; and it also contains relatively high dietary fiber, which can improve the health of the digestive system and promote intestinal peristalsis; the multi-grain raw materials of the present invention include buckwheat, whole wheat and oats, etc., and compared with bread with a single ingredient, can provide more vitamins, fiber, minerals and antioxidants, high fiber can increase satiety, help control weight, and its low sugar index helps maintain a stable blood sugar level, which is particularly important for diabetic patients; the present invention can obtain a more complex flavor and better dough properties by combining the fermentation of natural yeast and lactic acid bacteria, which not only improves the physical properties of the bread, but also improves its nutritional components; compared with ordinary bread, the multi-grain bread made with the composite lactic acid bacteria bread starter provided by the present invention has a higher specific volume value, more uniform voids and holes inside the bread, softer bread, higher elasticity and cohesion values, and richer flavor. In addition, the starter of the present invention is also refrigerated, which can not only retain nutrients and maintain activity, but also add a unique flavor. At the same time, the fermentation process is easy to control, the time is flexible, and it is more in line with the factory production cycle and convenient for mass production; and technical means such as refrigerated liquid seeds and graded fermentation make the production of bread more flexible, and the flavor and taste are more layered. The present invention increases the gluten strength and toughness by using low-temperature purified water, maintains the temperature of the dough, and forms a stable gluten network; promotes hydration through low-temperature proofing and increases gluten formation.

[0031] In summary, the present invention obtains a composite lactic acid bacteria bread starter by compounding Lactobacillus plantarum, Weissella fusion and Pediococcus pentosaceus. The starter is used together with natural yeast to make multi-grain bread, which can effectively improve the quality of the multi-grain bread, increase the flavor of the multi-grain bread, and improve the texture of the bread while ensuring the nutritional value of the multi-grain bread. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the result of bread texture structure measurement.

[0033] Figure 2 The following are the flavor test results of the bread in Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0034] The Lactobacillus plantarum CICC 21794, Weissella fusiformis CICC 24453 and Pediococcus pentosaceus CICC 22231 involved in the following examples and control examples were all purchased from the China Industrial Microbiological Culture Collection Center.

[0035] The whole wheat flour, oat flour, buckwheat flour and tartary buckwheat flour involved in the following embodiments and comparative examples were all purchased from Shanxi Yanmen Qinggao Food Industry Co., Ltd.

[0036] The liquid culture medium involved in the following examples and control examples is an MRS culture medium with a sucrose addition amount of 50 g / L, composed of: 10.0 g / L peptone, 5.0 g / L beef powder, 5.0 g / L yeast extract, 50 g / L sucrose, pH 6.5, all of which are edible.

[0037] The purified water involved in the following embodiments and comparative examples is purified tap water with a temperature in the range of 4 to 8°C.

[0038] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0039] Example 1

[0040] A composite lactic acid bacteria bread leavening agent, the preparation method is as follows:

[0041] (1) Lactobacillus plantarum CICC 21794, Weissella fusion CICC 24453 and Pediococcus pentosaceus CICC22231 were activated twice until the bacterial concentration reached 10 8 CFU / mL, the mixture was mixed in a ratio of 1:1:1 according to the number of bacterial strains, and then the mixed bacterial solution was inoculated into the liquid culture medium at an inoculum size of 3%, cultured at a constant temperature of 30°C for 20 hours, and then centrifuged at 1000 rpm for 5 minutes to obtain a composite lactic acid bacteria fermentation liquid;

[0042] (2) After buckwheat flour and purified water were mixed at a mass ratio of 1:1.5, 3vt% of the compound lactic acid bacteria fermentation liquid was added, stirred evenly, fermented in a fermentation tank at 30°C for 20 hours, and refrigerated at 4°C for 12 hours to obtain a compound lactic acid bacteria bread starter;

[0043] A composite lactic acid bacteria fermented multi-grain liquid seed bread is prepared from the following raw materials in parts by weight, calculated as 5 kg:

[0044] Multi-grain flour 2.645 kg (52.9%);

[0045] 1.0kg of purified water (20%);

[0046] Yeast 0.075 kg (1.5%);

[0047] White sugar 0.45kg (9%);

[0048] Salt 0.03kg (0.6%);

[0049] 0.8kg (16%) of composite lactic acid bacteria bread starter.

[0050] The specific preparation method is:

[0051] (a) The composite lactic acid bacteria bread starter obtained above is mixed with multi-grain flour, yeast, white sugar, salt and purified water, and beaten for 7 minutes, and the temperature is maintained at 20° C. to obtain a composite lactic acid bacteria fermented multi-grain liquid main dough, and the main dough is patted by hand to discharge gas. After the exhaust is completed, the main dough is cut into 160g doughs of uniform size, and low-temperature proofing is performed at 4° C. for 50 minutes;

[0052] (b) The low-temperature proofed composite lactic acid bacteria fermented multi-grain liquid seed dough is returned to the temperature of 25.5°C, put into an oven, and the upper and lower temperatures are adjusted to 180°C, baked for 22 minutes, and cooled to obtain composite lactic acid bacteria fermented multi-grain liquid seed bread.

[0053] Embodiment 2:

[0054] Preparation of multi-grain liquid bread fermented by compound lactic acid bacteria

[0055] Different from Example 1, the raw materials used in the composite lactic acid bacteria fermented multi-grain liquid seed bread in this example are calculated as 5 kg and are prepared from the following raw materials in parts by weight:

[0056] Multi-grain flour 2.095kg (41.9%);

[0057] 1.3kg (26%) of purified water;

[0058] Yeast 0.075 kg (1.5%);

[0059] White sugar 0.45kg (9%);

[0060] Salt 0.03kg (0.6%);

[0061] 1.05 kg (21%) of the composite lactic acid bacteria bread starter described in Example 1.

[0062] Embodiment 3:

[0063] Preparation of multi-grain liquid bread fermented by compound lactic acid bacteria

[0064] Different from Example 1, the raw materials used in the composite lactic acid bacteria fermented multi-grain liquid seed bread in this example are calculated as 5 kg and are prepared from the following raw materials in parts by weight:

[0065] Multi-grain flour 2.195 kg (43.9%);

[0066] Clean water 0.7kg (14%);

[0067] Yeast 0.075 kg (1.5%);

[0068] White sugar 0.45kg (9%);

[0069] Salt 0.03kg (0.6%);

[0070] 1.55 kg (31%) of the composite lactic acid bacteria bread starter described in Example 1.

[0071] Comparative Example 1

[0072] A multi-grain bread is prepared from the following raw materials in parts by weight, calculated as 5 kg of raw materials:

[0073] Multi-grain flour 2.945 kg (58.9%);

[0074] 1.5kg (30%) of purified water;

[0075] Yeast 0.075 kg (1.5%);

[0076] White sugar 0.45kg (9%);

[0077] 0.03kg (0.6%) of table salt.

[0078] The specific preparation method is:

[0079] (a) Mix multi-grain flour, yeast, white sugar, salt and purified water, beat for 7 minutes, maintain the temperature at 18-23° C. to obtain a multi-grain main dough, exhaust and cut into 160 g multi-grain bread dough of uniform size, and proof for 50 minutes at 4° C.;

[0080] (b) returning the multi-grain bread dough that has been proofed at low temperature to 25.5° C., placing it in an oven, adjusting the oven temperature to 180° C. for both the upper and lower heats, baking it for 22 minutes, and cooling it to obtain the multi-grain bread.

[0081] Test example:

[0082] The bread prepared in Examples 1 to 3 and Comparative Example 1 was subjected to specific volume testing, whole texture testing and flavor testing, and the testing methods are as follows:

[0083] (1) Specific volume test: The specific volume is determined by the millet replacement method. Fill a container of appropriate capacity with millet and compact it. Pour out some of the millet, put the bread to be tested into the container, then pour the millet back, fill the container and compact it, and scrape it flat with a ruler. Finally, use a measuring cylinder to measure the remaining millet volume V (mL), which is the actual volume of the bread to be tested. Calculate the specific volume according to the following formula (specific volume = V / m, where V is the volume of the bread; m is the mass of the bread (g)). The test results are shown in Table 1:

[0084] Full texture test: Take three loaves of bread from the same batch and cut them into uniform slices with a thickness of 15 mm using a slicer. Select the second slice of bread near the bottom as the center slice and observe the texture structure of the upper and lower sections (the results are shown in Figure 2). Figure 1As shown), the hardness of the bread slices was measured using a physical property analyzer. The hardness was measured separately and the average value was taken as the bread hardness. The probe used in the physical property analyzer was P / 36R. Settings: mode TPA; speed before test 3mm / s; test speed 1.5mm / s; speed after test 5mm / s; compression depth 5mm; interval time 10s; compression times 2 times. The hardness, elasticity, cohesion, adhesiveness, chewiness, and elasticity data of the bread were obtained, and the test results are shown in Table 1.

[0085] Table 1 Bread volume texture analysis results

[0086] index specific volume hardness elasticity Adhesion Adhesion Chewability Responsiveness Comparative Example 1 3.55±0.44 312.76 156.66 234.71 234.71 208.69 312.76 Example 1 3.85±0.08 331.88 166.21 249.05 249.05 221.44 331.88 Example 2 2.92±0.17 413.52 207.04 310.28 310.28 275.87 413.52 Example 3 2.96±0.23 348.09 174.32 261.21 261.21 232.25 348.09

[0087] like Figure 1 , Examples 2 and 3 have darker colors than the control example and Example 1, which affects consumers' desire to buy. In addition, the pores of Examples 2 and 3 are too large and too dense, while Example 1 has not only moderate color, but also smooth and uniform pore surface, small and dense pores, indicating that the structure of Example 1 is more uniform. The fineness and toughness of the internal structure of bread affect the taste, and from Figure 1 It is obvious that the lower cross section of Example 2 is very rough and has the worst toughness, while Example 1 is the most delicate, showing good expansion and lightness. This shows that when the addition amount of the composite lactic acid bacteria bread starter is 16%, the prepared multi-grain flour bread has moderate color, uniform structure and the best sensory quality.

[0088] The specific volume of bread reflects the fluffiness of bread, which directly affects the appearance, mouthfeel and internal organization of bread. As shown in Table 1, the multi-grain liquid bread with a composite lactic acid bacteria bread fermentation agent content of 16% (Example 1) prepared by composite lactic acid bacteria fermentation liquid has the best specific volume, and the chewiness, elasticity and resilience of bread are correspondingly improved, which improves the mouthfeel of bread. It is possible that the addition amount increases the moisture content of the dough, and the moist environment is more conducive to the growth of yeast and lactic acid bacteria. The good hydration effect improves the formation of gluten, making the dough more elastic and ductile. And too high addition, such as the bread prepared by 21% composite lactic acid bacteria bread fermentation agent (Example 2) and the bread prepared by 31% composite lactic acid bacteria bread fermentation agent (Example 3) will make the bread environment overhydrated, causing the bread to collapse. Therefore, 16% composite lactic acid bacteria bread fermentation agent (Example 1) has the best effect on improving the specific volume and texture of bread.

[0089] (2) Flavor detection; flavor compounds were extracted using solid phase microextraction (SPME) method. Before volatile extraction, the CAR / PDMS coated fiber was adjusted at 250°C for 1h. Then, 3g of three breads made in the same batch were weighed and placed in a 20mL headspace sample bottle for 60min of volatile extraction. Chromatographic conditions: He was the carrier gas, passing through a GC-MSDB-Wax capillary column (30m*0.25mm*0.25μm), and the column oven temperature program was an initial temperature of 40°C, maintained for 2min, and then heated to 230°C at 5°C / min. Mass spectrometry conditions: electron energy was -70eV, ion source temperature was 230°C, quadrupole temperature was 150°C, transfer line temperature was 230°C, solvent delay time was 25min, and detection method was full ion scan. Specific results Figure 2 shown.

[0090] like Figure 2 As shown, according to cluster analysis, it can be seen that the flavor clustering of the bread prepared with 16% compound lactic acid bacteria bread starter (Example 1) is closest to that of Control Example 1. Compared with Control Example 1, the compound lactic acid bacteria bread starter addition group can add more flavor substances of wine aroma, floral and fruity aroma, nut aroma and green grass aroma.

[0091] GC-MS was used to measure the presence of a variety of chemical substances in bread, such as isopentanol, phenylethyl alcohol, 3-hydroxy-2-butanone, hexyl formate, benzaldehyde, isobutyl alcohol, 2-n-pentyl furan, nonanal, heptaldehyde, 2,3-butanedione, 1-octen-3-ol, nonanoic acid, phenylacetaldehyde, cis-3-nonen-1-ol, trans-2-nonenal, trans-2-octenal, and 2-heptenal and 1-pentanol. The contents of substances in different breads or doughs are different, and each substance has a corresponding aroma descriptor. For example, the content of phenylethyl alcohol in the bread prepared by 16% composite lactic acid bacteria bread fermentation agent (Example 1) is significantly higher than that of other types, which may give it a unique fruity or floral aroma. The content of 3-hydroxy-2-butanone in the bread prepared by 16% composite lactic acid bacteria bread fermentation agent (Example 1) is also relatively high, which may add a cream or caramel flavor to it. The contents of hexanal and nonanal, which have bad flavor, in the bread prepared with 16% composite lactic acid bacteria bread starter (Example 1) are relatively low, while the contents in Control Example 1 are relatively high.

[0092] In summary, using the composite lactic acid bacteria starter provided by the present invention and natural yeast to prepare multi-grain bread can not only improve the nutritional value of the multi-grain bread, but also effectively improve the quality of the multi-grain bread, increase the flavor of the multi-grain bread, and improve the texture of the bread.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a composite lactic acid bacteria bread starter, characterized in that: The preparation method of the composite lactic acid bacteria bread starter is as follows: mixing tartary buckwheat flour with clean water, adding composite lactic acid bacteria fermentation liquid, stirring, fermenting, and refrigerating to obtain the composite lactic acid bacteria bread starter; The composite lactic acid bacteria fermentation liquid consists of Lactobacillus plantarum, Weissella fusion and Pediococcus pentosaceus.

2. The method for preparing the composite lactic acid bacteria bread starter according to claim 1, characterized in that: The weight ratio of the tartary buckwheat flour to the purified water is 1-1.5:1-1.5; The inoculation amount of the composite lactic acid bacteria fermentation liquid is 2% to 3% of the total mass of tartary buckwheat flour and purified water; The fermentation conditions are: 28-32°C, 16-20h; The refrigeration conditions are: 3-4°C, 10-12h.

3. The method for preparing the composite lactic acid bacteria bread starter according to claim 2, characterized in that: The preparation method of the composite lactic acid bacteria fermentation liquid is as follows: the plant lactobacillus, fusion Weissella and Pediococcus pentosaceus are activated respectively until the bacterial concentration reaches 10 8 ~10 9 CFU / mL, the mixture is mixed according to the number of bacterial strains of 1:1-1.5:1-1.5 to obtain a mixed bacterial solution, and then the mixed bacterial solution is inoculated into a liquid culture medium at an inoculum size of 2-3% at 27-30°C for expansion culture for 16-20 hours, and the solid-liquid is separated to obtain the composite lactic acid bacteria fermentation liquid.

4. The method for preparing the composite lactic acid bacteria bread starter according to claim 3, characterized in that: The Lactobacillus plantarum is Lactobacillus plantarum CICC 21794; the Weissella fusion is Weissella fusion CICC 24453; the Pediococcus pentosaceus is Pediococcus pentosaceus CICC 22231; The number of times the strain is activated is 1 to 3 times; The conditions for the solid-liquid separation are: centrifugation at 800-2000 rpm for 5-10 min.

5. The composite lactic acid bacteria bread starter obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the composite lactic acid bacteria bread starter according to claim 5 in making bread.

7. A composite lactic acid bacteria fermented multi-grain liquid bread, characterized in that: The raw materials include the following mass percentages: 40% to 55% of multi-grain flour, 13% to 27% of purified water, 1.0% to 2.5% of yeast, 5% to 15% of white sugar, 0.3% to 1.2% of salt, and 15% to 35% of the composite lactic acid bacteria bread starter; The multi-grain flour includes one or more of whole wheat flour, oat flour and buckwheat flour.

8. The composite lactic acid bacteria fermented multi-grain liquid bread according to claim 7, characterized in that: When the multi-grain flour is whole wheat flour, oat flour and buckwheat flour, the mass ratio of the whole wheat flour, oat flour and buckwheat flour is 15-17:5:

3.

9. The method for preparing multi-grain liquid bread fermented by compound lactic acid bacteria according to claim 8, characterized in that: The following steps are involved: (a) mixing multi-grain flour, purified water, yeast, white sugar, salt and the composite lactic acid bacteria bread starter, beating at 18-23° C. for 6-7 minutes to obtain a composite lactic acid bacteria fermented multi-grain liquid main dough, exhausting the air and cutting and shaping to obtain a composite lactic acid bacteria fermented multi-grain liquid dough, and proofing at low temperature; (b) after the low-temperature proofed composite lactic acid bacteria fermented multi-grain liquid seed dough is warmed up, it is baked and cooled to obtain composite lactic acid bacteria fermented multi-grain liquid seed bread.

10. The preparation method according to claim 8, characterized in that: The temperature of the purified water in step (a) is 4-8°C; The low temperature proofing condition is 4-7°C, 30-60min; The temperature in step (b) is returned to 24-26° C. for 10-30 min. The baking conditions are: upper and lower fire 180-200° C., 17-22 minutes.

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