Fermentation base, leavening agent, corn plant-based yoghurt and preparation method of corn plant-based yoghurt

Abstract

The invention discloses a fermentation base, a leavening agent, corn plant-based yoghurt and a preparation method thereof, and belongs to the technical field of plant yoghurt fermentation. A plant-based yoghurt product is developed by taking a high-oil high-protein micro-endosperm corn variety as a raw material, a micro-endosperm corn fermentation base, a micro-endosperm corn leavening agent and a preparation method of the corn plant-based yoghurt are developed, and the prepared micro-endosperm corn plant-based yoghurt has relatively high nutritional value and better taste and texture. In addition, the preparation process is simple and easy to operate, and has high practicability and market value.

Description

Technical Field

[0001] The invention relates to the technical field of plant yogurt fermentation, and more particularly to a fermentation base, a starter, a corn plant-based yogurt and a preparation method thereof. Background Art

[0002] At present, there are three main quality problems in plant-based yogurt products. The first is poor product texture and stability; the second is the presence of peculiar smell in the product; and the third is unbalanced nutrition in the product. The main reason for these problems is related to the raw material characteristics of plant-based yogurt. Due to the nutritional imbalance of plant raw materials, low protein content, few carbon sources available to microorganisms, many macromolecular particulate matter, and anti-nutritional factors, the microbial fermentation is incomplete and the gel structure is rough and unstable, which in turn leads to poor product texture and stability. The texture of the product often affects the taste, so the taste of plant-based yogurt often has the problem of roughness and heavy powder.

[0003] Protein is the key to the formation of gel system in plant-based yogurt. The functional properties of protein directly affect the texture and stability of plant-based yogurt. However, plant protein often has problems such as large molecular structure, poor solubility, easy precipitation and low bioavailability. It is difficult to form a stable gel system and cannot withstand long-term storage. Therefore, processing protein molecules can effectively improve the texture and stability of yogurt.

[0004] Cruz et al. compared the yogurt made by fermentation after ultra-high pressure homogenization, ultra-high temperature and high pressure sterilization of soy milk. After ultra-high pressure homogenization, the degree of protein molecule denaturation increased, the hardness and water holding capacity of yogurt were the highest, the gel structure was denser, and the product stability was improved. This is because the degree of protein denaturation increases with the increase of pressure, and the interaction force formed between protein molecules also increases accordingly. At the same time, higher pressure reduces the particle size of fat globules, which helps yogurt to form a denser network structure. Hickisch et al. used pasteurization and ultra-high temperature heating to heat lupin protein, respectively. The cross-linking between proteins increased, the network structure formed was denser, the gel hardness was enhanced, and the quality of lupin yogurt was improved. This is because high-temperature heating and homogenization can cause the natural protein structure to denature and unfold, expose hydrophobic groups, and disulfide bonds link amino acids to form soluble aggregates during the temperature increase. These changes can promote gel formation and enhance the cross-linking and density of the yogurt gel network. Nie et al. introduced transglutaminase into the fermentation agent during the fermentation of mung bean protein yogurt. The results showed that the cross-linking of transglutaminase did not significantly improve the water holding capacity of the emulsion gel, but it could significantly increase the hardness of the emulsion gel. Transglutaminase can modify glutamic acid (acyl donor) and lysine (acylation acceptor) through acylation, giving it a strong cross-linking ability, thereby strengthening the gel network structure and improving its gel properties and plasticity.

[0005] In addition to improving the stability by improving the properties of the protein as described above, it can also be improved by adjusting the formulation. The protein content in plant raw materials is low, and the gel structure formed during fermentation is weak, resulting in low product hardness and unstable structure. Appropriate use of additives (protein extracts, thickeners, emulsifiers, inulin, fiber, etc.) can effectively improve this problem. For example, Sung et al. added 4% pea protein and 0.1% citrus fiber to replace the stabilizer in the fermentation of stirred plant-based acid soy milk, improving the viscosity, fluidity, water-holding capacity of the yogurt, and the overall acceptance was 87.1%. A clean-label plant-based stirred soy milk yogurt without additives and with high acceptance was produced.

[0006] However, there has never been a study on improving the texture and stability of corn plant-based yogurt. Therefore, developing a fermentation medium, starter culture, and preparation method for improving corn plant-based yogurt is an urgent problem for those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a fermentation medium, starter culture, corn plant-based yogurt, and its preparation method. The present invention uses the "Huajian No. 1" high-oil and high-protein micro-endosperm corn variety as raw material to develop plant-based yogurt products, and through research, a new micro-endosperm corn plant-based yogurt with good fermentation performance, uniform and stable texture, and delicate taste is prepared. While innovating, it meets the dual consumption needs of modern consumers for whole grains and high-protein foods, conforms to the global concept of sustainable food development, reducing carbon emissions, and the general trend of the development of the healthy food market. It is the best breakthrough for promoting the industrialization of micro-endosperm corn and also provides important data support for the research on the preparation process of plant yogurt in China.

[0008] One of the purposes of the present invention is to provide a preparation method for a micro-endosperm corn fermentation medium, including the following steps:

[0009] S11. Select dry corn kernels without moldy grains, add water and boil, time for 30 min for rehydration and swelling, fish out and rinse clean, add pure water 8 times the mass of the dry corn kernels, and wet grind to obtain corn slurry for standby;

[0010] S12. Add flavor protease, transglutaminase, and α-amylase, mix evenly, enzymatically hydrolyze at 45 - 65 °C for 20 - 60 min, and stir the corn slurry 2 - 3 times during the enzymatic hydrolysis;

[0011] S13. After the enzymatic hydrolysis is completed, sterilize at 95 °C for 15 min, cool and filter with a 120-mesh filter cloth to obtain the micro-endosperm corn fermentation medium.

[0012] Preferably, in S12, the enzyme activity of the flavor protease is 5000 - 6000 U / g, and the enzyme activity of the transglutaminase is 100 - 200 U / g; the ratio of the flavor protease to the transglutaminase is 2:1, and the total addition amount is 0.05 - 1.0% of the mass of the corn steep liquor; the enzyme activity of the α-amylase is 20000 U / g, and the addition amount is 0.10 - 0.30% of the mass of the corn steep liquor.

[0013] The beneficial effects of adopting the above technical solution are as follows: The flavor protease and transglutaminase can effectively reduce bitterness before fermentation, enhance the gel network structure of proteins, improve the texture of yogurt. The enzymatic hydrolysis products such as small molecule peptides and amino acids can also provide energy for lactic acid bacteria, promote their reproduction and acid production, improve the fermentability of yogurt, and shorten the time for yogurt to reach the fermentation end point; The enzymatic hydrolysis and liquefaction of α-amylase can hydrolyze part of the starch into dextrin and glucose, increase the sugar content available for fermentation in the corn fermentation medium, promote microbial acid production, improve the utilization rate of raw materials, and improve the texture of yogurt.

[0014] The second object of the present invention is to provide a preparation method of a micro-endosperm corn starter, comprising the following steps:

[0015] S21. Mix casein, glucose and pectin evenly, add an appropriate amount of water to make a mixture.

[0016] S22. Heat the mixture in a water bath to 80 °C, stir constantly for 20 min, cool to room temperature and continue stirring to obtain a gel-like substance.

[0017] S23. Add the mixed bacterial powder to the gel-like substance and mix evenly.

[0018] S24. Ferment for a certain period of time, cool to room temperature, and obtain the micro-endosperm corn starter.

[0019] Preferably, by mass fraction: the casein is 30 - 50%, the glucose is 5 - 15%, the pectin is 6 - 12%, the mixed bacterial powder is 8 - 10%, and the balance is water.

[0020] Preferably, the mixed bacterial powder includes at least two or more mixed bacterial species of Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei, and Lactococcus lactis subsp. diacetylactis.

[0021] Preferably, in S24, the fermentation is carried out at 40 - 45 °C for 6 - 12 h.

[0022] The beneficial effects of adopting the above technical solution are as follows: The mixed bacterial powder is a key component of the starter, which can fully ferment the raw materials of the starter. During the fermentation of the starter, the mixed bacterial powder can ferment carbohydrates such as casein to produce acidic substances such as lactic acid, promoting the fermentation of the corn plant-based yogurt and enriching the nutritional components and sensory substances of the yogurt.

[0023] The third object of the present invention is to provide a preparation method of a corn plant-based yogurt, comprising the following steps:

[0024] S31. Prepare the micro-endosperm corn fermentation base according to the above method and set aside;

[0025] S32. Prepare the micro-endosperm corn starter according to the above method and set aside;

[0026] S33. Blending: Weigh a certain amount of glucose, white sugar, soy protein isolate, and inulin, add them to the micro-endosperm corn fermentation base, and mix evenly by high-speed shearing;

[0027] S34. Homogenization: Homogenize at 45 MPa for 3 min;

[0028] S35. Cooling and inoculation: Naturally cool to 40 - 45 °C, add the micro-endosperm corn starter, and mix evenly;

[0029] S36. Fermentation: Ferment the inoculated mixed milk at 43 °C for 3 - 7 h;

[0030] S37. Cold storage and after-ripening: After the fermentation of the micro-endosperm corn plant-based yogurt is completed, quickly cool it to room temperature and then refrigerate it at 4 °C for after-ripening for 12 h to obtain the micro-endosperm corn plant-based yogurt.

[0031] Preferably, in S33, based on the mass of the micro-endosperm corn fermentation base:

[0032] The addition amounts of the glucose and white sugar are 4 - 8%, and the ratio of glucose: white sugar = 2:3;

[0033] The addition amount of the soy protein isolate is 1.5 - 3.5%;

[0034] The addition amount of the inulin is 3%.

[0035] Preferably, in S35, based on the mass of the micro-endosperm corn fermentation base, the addition amount of the micro-endosperm corn starter is 0.1 - 0.5%.

[0036] The beneficial effects of adopting the above technical solutions are as follows: During the initial enzymatic hydrolysis process of the micro-endosperm corn fermentation substrate, partial glucose is hydrolyzed and can be utilized for lactic acid fermentation. However, compared with the lactose content in milk, the carbohydrates in the micro-endosperm corn raw material that can be utilized by lactic acid bacteria are still relatively few, which directly affects the fermentation rate and product taste of the micro-endosperm corn plant-based yogurt. Therefore, an additional carbon source needs to be supplemented. Lactobacillus bulgaricus cannot directly utilize sucrose to produce acid and can utilize glucose and lactose. The purpose of this invention is to prepare a pure plant-based yogurt without milk components. Therefore, in this experiment, sucrose and glucose are selected for addition; inulin has many hydrophilic groups and can form a good gel structure after binding with water. It can be used as a stabilizer and fat substitute for yogurt, increasing the viscosity and water-holding capacity of yogurt. Inulin also has prebiotic properties and can be added as a prebiotic component to yogurt. It can not only increase the total number of lactic acid bacteria in yogurt but also enhance the survival time of probiotics during storage. Therefore, inulin is selected to replace the stabilizer in the experiment.

[0037] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0038] (1) The casein yogurt starter proposed by the present invention uses a mixed bacterial powder containing Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei, and Lactococcus lactis subsp. diacetylactis. Compared with the yogurt starters sold on the market currently, it is more suitable for the plant-based protein fermentation in the corn syrup system, making the yogurt product have good sensory evaluation values and texture parameter values.

[0039] (2) The micro-endosperm corn plant-based yogurt prepared by the present invention has higher nutritional value, and its taste and texture are also better. In addition, the preparation process of the present invention is simple, easy to operate, and has high practicality and market value.

[0040] (3) The present invention provides a fermentation substrate, a starter, and a preparation method suitable for the micro-endosperm corn plant-based yogurt, filling the gap in this field. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0042] Figure 1 For the influence of the addition amount of soy protein isolate in Example 4 on the quality of the micro-endosperm corn plant-based yogurt.

[0043] Figure 2Effect of sugar addition amount on the quality of micro-endosperm corn plant-based yogurt in Example 5.

[0044] Figure 3 Effect of inoculum amount of starter on the quality of micro-endosperm corn plant-based yogurt in Example 6.

[0045] Figure 4 Effect of fermentation time on the quality of micro-endosperm corn plant-based yogurt in Example 7. Specific implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0047] 1. Determination of texture properties

[0048] Use a TA11 / 1000 probe to perform texture analysis on the hardness, elasticity, cohesiveness, chewiness, and adhesiveness of the yogurt. Determination conditions: Select the TPA mode, TA11 / 1000 probe, target value: 10 mm, test speed: 1.0 mm / s; trigger point load: 5 g.

[0049] 2. Determination of water-holding capacity

[0050] Accurately weigh 10 g of the yogurt sample, place it in a 50 mL centrifuge tube, centrifuge at 5000 r / min at 4 °C for 15 min, discard the supernatant, and weigh the remaining precipitate mass. The formula for calculating the water-holding capacity is as follows:

[0051]

[0052] In the formula: WHC - water-holding capacity of the yogurt, %

[0053] m0 - mass of the centrifuge tube, g

[0054] m1 - mass of the yogurt sample, g

[0055] m2 - mass of the remaining precipitate and the centrifuge tube, g

[0056] 3. Determination of titratable acidity

[0057] Accurately weigh 5 g of yogurt sample, add 20 mL of distilled water that has been boiled and cooled to room temperature, then add 2 drops of 0.5% phenolphthalein indicator. After mixing evenly, titrate it with 0.1 mol / L NaOH standard solution until it turns slightly red and does not fade within 30 s. Read the volume of the consumed NaOH standard solution and substitute it into the formula for calculation. The acidity value of the yogurt is expressed in degrees Thörner (°T).

[0058]

[0059] Where: X——Yogurt acidity, °T

[0060] C——Concentration of NaOH standard solution, mol / L

[0061] V——Volume of NaOH standard solution consumed during titration, mL

[0062] M——Mass of yogurt sample, g

[0063] 0.1——Molar concentration of NaOH defined by the theory of acidity, mol / L

[0064] 4. Sensory evaluation criteria

[0065] The sensory evaluation method refers to GB 19302-2010 "National Food Safety Standard Fermented Milk" and is optimized on this basis. A sensory evaluation panel consisting of 10 food professionals (5 males and 5 females) is formed. The panel members score the yogurt samples item by item according to Table 1. The scoring content includes the texture, taste, flavor and color of the yogurt, with a full score of 100 points, and the result is the average value.

[0066] Table 1 Sensory scoring table for micro-endosperm corn plant-based yogurt

[0067]

[0068]

[0069] Example 1

[0070] A preparation method of a micro-endosperm corn fermentation base, comprising the following steps:

[0071] S11. Select dry corn kernels without moldy grains, boil them in water and time for 30 min for rehydration and swelling, fish them out and rinse them clean, add pure water 8 times the mass of the dry corn kernels, and wet grind to obtain corn slurry for standby;

[0072] S12. Add flavor protease, glutamine transaminase and α-amylase, mix evenly, enzymatically hydrolyze at 55 °C for 60 min, and stir the corn slurry 3 times during the enzymatic hydrolysis;

[0073] S13. After the enzymatic hydrolysis is completed, sterilize at 95 °C for 15 min. After cooling, filter with a 120-mesh filter cloth to obtain the micro-endosperm corn fermentation medium.

[0074] Among them, the enzyme activity of the flavor protease is 5000 - 6000 U / g, and the enzyme activity of the transglutaminase is 100 - 200 U / g; the ratio of the flavor protease to the transglutaminase is 2:1, and the total addition amount is 0.2% of the mass of the corn steep liquor; the enzyme activity of the α-amylase is 20000 U / g, and the addition amount is 0.2% of the mass of the corn steep liquor.

[0075] Table 2 shows the corn-based plant yogurt prepared before and after the enzymatic hydrolysis of this fermentation medium under the same conditions. The texture characteristics and mechanical properties of the corn-based plant yogurt are characterized by measuring the hardness, cohesiveness, elasticity, gumminess, and chewiness.

[0076] Table 2 Changes in the texture characteristics of yogurt before and after enzymatic hydrolysis

[0077]

[0078] Note: Different letters in the same column in the table indicate significant differences in the data, P < 0.05.

[0079] As shown in Table 2, the hardness of the yogurt prepared after the enzymatic hydrolysis treatment of the fermentation medium is lower than the measured value of the yogurt prepared before the enzymatic hydrolysis treatment, and there are no significant differences in cohesiveness, elasticity, gumminess, and chewiness. Enzymatic hydrolysis hydrolyzes starch in the system into sugars, and the content of insoluble solids decreases. Starch can increase the hardness of the sample, and after enzymatic hydrolysis, the content decreases, resulting in a decrease in the hardness of the yogurt.

[0080] Example 2

[0081] A micro-endosperm corn starter, by mass fraction, contains the following components: casein 45%, glucose 15%, pectin 10%, the mixed bacterial powder 10%, and the balance is water; the mixed bacterial powder is a mixture containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

[0082] The preparation method of the above-mentioned micro-endosperm corn starter includes the following steps:

[0083] S21. Mix casein, glucose, and pectin evenly, add an appropriate amount of water to make a mixture.

[0084] S22. Heat the mixture in a water bath to 80 °C, stir constantly for 20 min, cool to room temperature and continue stirring to obtain a jelly-like substance.

[0085] S23. Add the mixed bacterial powder to the jelly-like substance and mix evenly.

[0086] S24. Ferment at 45 °C for 8 h, cool to room temperature, and obtain the micro-endosperm corn starter.

[0087] Table 3 shows the extraction rate of yogurt protein, pH value, protein content, fat content, total acidity, number of lactic acid bacteria, and sensory score of yogurt prepared by using this starter culture, a mixed powder of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus respectively under the same conditions.

[0088] Table 3

[0089]

[0090] Table 4 shows the texture properties of yogurt prepared by using this starter culture, a mixed powder of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus respectively under the same conditions.

[0091] Table 4 Influence of Starter Culture on Texture Properties of Yogurt

[0092] Item Hardness / g Cohesiveness Elasticity / mm Adhesiveness / g Chewiness / mJ This starter 21.52±0.55a 0.67±0.08a 8.47±0.41a 16.50±3.08a 1.75±0.31a Mixed bacterial powder 21.00±1.10a 0.61±0.06a 7.71±0.47b 12.00±2.10b 0.84±0.42b

[0093] Note: Different letters in the same column of the table indicate significant differences in data, P < 0.05.

[0094] Generally speaking, this starter culture helps to improve the texture properties, nutritional components, and sensory properties of yogurt.

[0095] Example 3

[0096] A preparation method of a corn plant-based yogurt, comprising the following steps:

[0097] S31. Prepare a micro-endosperm corn fermentation substrate according to Example 1 and set aside;

[0098] S32. Prepare a micro-endosperm corn starter culture according to Example 2 and set aside;

[0099] S33. Blending: Based on the mass of the micro-endosperm corn fermentation substrate:

[0100] Weigh 6% glucose and white sugar, with glucose:white sugar = 2:3, 2.5% soy protein isolate, and 3% inulin, add them to the micro-endosperm corn fermentation substrate, and mix evenly by high-speed shearing;

[0101] S34. Homogenization: Homogenize at 45 MPa for 3 min;

[0102] S35. Cooling and inoculation: Naturally cool to 40 - 45 °C, and add 0.3% of the micro-endosperm corn starter culture based on the mass of the micro-endosperm corn fermentation substrate, and mix evenly;

[0103] S36. Fermentation: Ferment the inoculated mixed milk at 43 °C for 4 h;

[0104] S37. Post - ripening after refrigeration: After the micro - endosperm corn - based yogurt is fermented and completed, it is quickly cooled to room temperature and then post - ripened at 4°C for 12 h to obtain the micro - endosperm corn - based yogurt.

[0105] Example 4

[0106] Replace step S33 in Example 3 with "Based on the mass of the micro - endosperm corn fermentation medium, weigh respectively: 6% glucose, white sugar, glucose:white sugar = 2:3, 1.5%, 2%, 3%, 3.5% soy protein isolate, 3% inulin, add them into the micro - endosperm corn fermentation medium, and mix evenly by high - speed shearing", and the rest is the same as Example 3.

[0107] Soy protein isolate, as a supplementary nitrogen source for the micro - endosperm corn - based yogurt, can not only increase the protein content in the yogurt, promote the acid production of lactic acid bacteria, but also improve the taste and texture of the yogurt. As Figure 1 shown, the acidity of the yogurt continuously increases with the increase of the addition amount of soy protein isolate, rising from 58.5°T to 72.2°T. When the addition amount is 2.5%, the sensory score reaches the highest of 90.2 points. At this time, the yogurt has a mellow taste, a delicate tissue state, and no granular feeling. When the addition amount of soy protein isolate continues to increase, the texture of the yogurt becomes rough and the taste becomes worse. When the addition amount increases to 3.5%, the sensory score drops to 70.9 points. This may be because an appropriate amount of soy protein powder is decomposed under the action of endogenous protease during the yogurt fermentation process, producing peptides and amino acids, providing energy for the fermentation of microorganisms and promoting yogurt acid production. However, with the increase of the addition amount of soy protein isolate, the interaction between protein molecules interferes with the formation of the gel network structure in the system, resulting in a rough texture of the yogurt, obvious granular feeling, strong pasty taste, and thus leading to a decrease in the sensory score. Considering the test results of the acidity and sensory score of the yogurt, the most suitable addition amount of soy protein isolate is 2.5%.

[0108] Example 5

[0109] Replace step S33 in Example 3 with "Based on the mass of the micro - endosperm corn fermentation medium, weigh respectively: 4%, 5%, 7%, 8% glucose, white sugar, glucose:white sugar = 2:3, 2.5% soy protein isolate, 3% inulin, add them into the micro - endosperm corn fermentation medium, and mix evenly by high - speed shearing", and the rest is the same as Example 3.

[0110] The influence of the sugar addition amount on the quality of the micro - endosperm corn - based yogurt is as Figure 2As shown. The acidity of yogurt continues to rise with the increase of sugar addition. Sugar can provide sufficient carbon source for the growth and metabolism of lactic acid bacteria, promote lactic acid bacteria to be converted into lactic acid through metabolism, and then lead to the continuous increase of yogurt acidity. The amount of sugar added has a significant effect on the sensory score of yogurt. The sensory score of yogurt shows a trend of increasing first and then decreasing. When the sugar addition is 6%, the yogurt has a suitable sour-sweet ratio, a harmonious taste, and a good tissue state. The sensory score reaches a maximum of 88.4 points, with significant changes before and after; at this time, the acidity of yogurt is 65.2°T, and the acidity continues to rise with the increase of sugar addition. The reason for the analysis may be that the right amount of sugar can promote the reproduction of lactic acid bacteria and cover up part of the sour taste, making the prepared yogurt sweet and sour. When the amount of sugar added is too low, most of it is decomposed and absorbed and converted into lactic acid, resulting in insufficient overall sweetness of the yogurt. If the amount of sugar added is too high, the yogurt tastes too sweet and greasy, and the sensory score is reduced. Taking all factors into consideration, the most suitable amount of sugar added is 6%.

[0111] Example 6

[0112] The step S35 of Example 3 is replaced by "naturally cooling to 40-45° C., adding 0.1%, 0.2%, 0.4%, and 0.5% of the micro-endosperm corn fermentation agent, based on the mass of the micro-endosperm corn fermentation base, respectively, and mixing evenly", and the rest is the same as Example 3.

[0113] like Figure 3 As shown in the figure, the acidity of yogurt first increases and then tends to be flat with the increase of the inoculum of the starter, reaching a maximum of 67.47°T when the inoculum is 0.4%, and 67.63°T when the inoculum is 0.5%, with no significant change. The sensory score shows a trend of first increasing and then decreasing with the increase of the inoculum, reaching a maximum score of 87.8 points when the inoculum is 0.3%. The reason may be that with the increase of the inoculum of the starter, the density of the strains is also increasing, and the acid production rate is accelerated. However, when the density of lactic acid bacteria in the system reaches a certain concentration, the acid production in the system is too high due to the rapid acid production in the early stage. In the later stage of fermentation, the growth and metabolism of microorganisms are inhibited. The acidity does not increase significantly when the inoculum is continued to increase. If the inoculum of the starter is too low, the acid production rate of yogurt is slow, the yogurt fermentation is incomplete, and the texture is loose; if the amount of starter added is too high, the acid production is too much, the protein denaturation is accelerated, the coagulation time is shortened, the whey precipitation is obvious, and the acidity is too high, the taste is not harmonious, and the sensory score is reduced. Based on the sensory score and acidity, the most suitable addition amount of the starter is 0.3%.

[0114] Example 7

[0115] The step S36 of Example 3 is replaced by "fermenting the inoculated mixed milk at 43° C. for 3 h, 5 h, 6 h, and 7 h respectively", and the remaining steps are the same as those of Example 3.

[0116] like Figure 4As shown, when the fermentation time is 3h to 5h, both the acidity and sensory score of the yogurt show an upward trend. At 4h, the yogurt has a suitable sour and sweet taste, a pleasant corn aroma, and good curdling effect, and the sensory score reaches the highest of 88.2 points. After the fermentation time continues for 5h, the acidity continues to increase, but with the increase of time, the phenomenon of whey separation intensifies and the sensory quality declines. This may be because during the fermentation process, the number of lactic acid bacteria increases, the acidity increases, and the strong gel structure of the yogurt is damaged, resulting in whey separation. A large number of flavor substances are produced during the fermentation of yogurt, but the fermentation time is short, resulting in insufficient accumulation of flavor substances and poor flavor. Considering the production cost, the most suitable fermentation time is 4h.

[0117] The response surface experimental method was comprehensively used to predict the optimal fermentation conditions of micro-endosperm corn plant-based yogurt, and the best results were obtained, that is: the addition amount of soy protein isolate is 2.36%, the addition amount of sugar is 6.333%, the inoculation amount of starter is 0.255%, and the fermentation time is 4.19 hours. The predicted score of the sensory quality of this process is 89.159 points. Considering the feasibility of operation, the process was adjusted to the addition amount of soy protein isolate of 2.4%, the addition amount of sugar of 6.3%, the inoculation amount of starter of 0.26%, and the fermentation time of 4.2h. Under these process conditions, 3 verification tests were carried out, and the results were averaged. The sensory score of the yogurt was 89.1±1.21 points, which is close to the predicted value, indicating that this model can accurately predict the optimal fermentation process conditions of micro-endosperm corn plant-based yogurt.

[0118] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts among the embodiments, reference can be made to each other.

Claims

1. A preparation method of a micro-endosperm corn fermentation substrate, characterized in that, It includes the following steps: S11. Select dry corn kernels without moldy grains, add water and boil, then time for 30 min for rehydration and swelling. Scoop out, rinse clean, add pure water 8 times the mass of the dry corn kernels, and wet grind to obtain corn slurry for standby; S12. Add flavor protease, transglutaminase and α-amylase, mix evenly, and enzymatically hydrolyze at 45 - 65 °C for 20 - 60 min. Stir the corn slurry 2 - 3 times during the enzymatic hydrolysis; S13. After the enzymatic hydrolysis is completed, sterilize at 95 °C for 15 min, cool, and filter with a 120-mesh filter cloth to obtain the micro-endosperm corn fermentation medium.

2. The preparation method of a micro-endosperm corn fermentation substrate according to claim 1, characterized in that In S12, the enzyme activity of the flavor protease is 5000 - 6000 U / g, and the enzyme activity of the transglutaminase is 100 - 200 U / g; the flavor protease:transglutaminase = 2:1, and the total addition amount is 0.05 - 1.0% of the mass of the corn slurry; The enzyme activity of the α-amylase is 20000 U / g, and the addition amount is 0.10 - 0.30% of the mass of the corn slurry.

3. A preparation method of a micro-endosperm corn ferment, characterized in that, It includes the following steps: S21. Mix casein, glucose and pectin evenly, add an appropriate amount of water to make a mixture; S22. Water bath the mixture to 80 °C, stir constantly at a constant temperature for 20 min, cool to room temperature and continue stirring to obtain a jelly-like substance; S23. Add the mixed bacterial powder to the jelly-like substance and mix evenly; S24. Ferment for a certain period of time, cool to room temperature, and obtain the micro-endosperm corn fermentation agent.

4. The preparation method of a micro-endosperm corn ferment as described in claim 3, characterized in that, By mass fraction: the casein is 30 - 50%, the glucose is 5 - 15%, the pectin is 6 - 12%, the mixed bacterial powder is 8 - 10%, and the balance is water.

5. The preparation method of a micro-endosperm corn ferment as described in claim 4, characterized in that, The mixed bacterial powder includes at least two or more mixed bacterial species of Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei, and Lactococcus lactis subsp. diacetylactis.

6. The preparation method of a micro-endosperm corn starter according to claim 3, characterized in that, In S24, the fermentation is carried out at 40 - 45 °C for 6 - 12 h.

7. A method for preparing a corn plant-based yogurt, characterized in that, It includes the following steps: S31. Prepare the micro-endosperm corn fermentation medium according to the method described in any one of claims 1 - 2 for standby; S32. Prepare the micro-endosperm corn fermentation agent according to the method described in any one of claims 3 - 6 for standby; S33. Blending: Weigh a certain amount of glucose, white sugar, soy protein isolate, and inulin, add them to the micro-endosperm corn fermentation medium, and mix evenly by high-speed shearing; S34. Homogenization: Homogenize at 45 MPa for 3 min; S35. Cooling and inoculation: Naturally cool to 40 - 45 °C, add the micro-endosperm corn fermentation agent, and mix evenly; S36. Fermentation: Ferment the inoculated mixed milk at 43 °C for 3 - 7 h; S37. Cold storage and after-ripening: After the fermentation of the micro-endosperm corn plant-based yogurt is completed, quickly cool it to room temperature, and then refrigerate it at 4 °C for after-ripening for 12 h to obtain the micro-endosperm corn plant-based yogurt.

8. A method for preparing a corn plant-based yogurt according to claim 7, characterized in that, In S33, based on the mass of the micro-endosperm corn fermentation medium: The addition amounts of the glucose and white sugar are 4 - 8%, and the glucose:white sugar = 2:3; The addition amount of the soy protein isolate is 1.5 - 3.5%; The addition amount of the inulin is 3%.

9. The preparation method of a corn plant-based yogurt according to claim 7, characterized in that, In S35, based on the mass of the micro-endosperm corn fermentation medium, the addition amount of the micro-endosperm corn fermentation agent is 0.1 - 0.5%.

10. A corn plant-based yogurt, characterized in that, A corn plant-based yogurt obtained by the preparation method according to any one of claims 7 to 9.

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