A soybean paste embryo production process for reducing free tyrosine content

Abstract

The application discloses a soybean paste embryo production process capable of reducing free tyrosine content. The process improves raw material treatment and koji making procedures, can reduce free tyrosine content in soybean paste embryo to a low enough level under the condition that amino acid nitrogen in the soybean paste is kept at a medium level or above, and thus effectively eliminates the hidden danger of white point precipitation of the soybean paste.

Description

Technical Field

[0001] This invention belongs to the field of soybean paste brewing technology, specifically relating to a soybean paste embryo production process that reduces the content of free tyrosine. Background Technology

[0002] Soybean paste is a traditional Chinese condiment, generally made from soybeans and wheat flour. It undergoes a production process including raw material processing, koji making, and fermentation to create a condiment with a distinctive color, aroma, and flavor. Specific production processes include:

[0003] (1) First, remove impurities from the soybeans and soak them. Then, after removing the soaking water, steam or boil the soybeans.

[0004] (2) The steamed soybeans are mixed with flour, and then inoculated with bacteria to make koji;

[0005] (3) The prepared Daqu is mixed with salt water to form a sauce mash, which is then fermented at room temperature to obtain soybean paste embryo; the soybean paste embryo is then blended to become soybean paste.

[0006] In the above-mentioned production process of soybean paste, soybeans, as the main raw material for providing protein, decompose into a variety of amino acids during fermentation, which are extremely important substances for forming the flavor components of soybean paste. Flour, on the other hand, mainly serves as a starchy raw material, providing carbon source for the growth of microorganisms. Moreover, flour contains 10-14% protein, which can increase the amino acid content in soybean paste. In addition, flour contains a certain amount of bran, which is used to improve the looseness of the mixture and facilitates the provision of sufficient oxygen for the growth of microorganisms.

[0007] The current production process has a significant drawback: the likelihood of white spots appearing in soybean paste is very high. An article published in *China Brewing*, Issue 2, 2005, titled "Analysis and Research on White Substances in Soybean Paste," revealed that about half of the white spots in soybean paste are amino acids, with tyrosine having the highest proportion at 66.4%. However, tyrosine has extremely low solubility in water, only 0.045%. Based on the applicant's production experience and follow-up sampling of each batch of soybean paste, when the tyrosine content in soybean paste reaches or exceeds 100 mg / 100g, free tyrosine is easily released during fermentation and shelf life, forming irregular white crystals, commonly known as white spots, which seriously affect the appearance and quality of the soybean paste. Consumers, unaware of the cause, may mistakenly believe the white spots are mold or spoilage and request returns. Therefore, reducing the appearance of white spots in soybean paste during shelf life has always been an important research topic in soybean paste production and technology.

[0008] However, effectively solving the white spot problem in soybean paste has always been a technical challenge for enterprises, thus limiting the innovation and upgrading of soybean paste processing. This is because flavorful soybean paste generally has a high amino acid nitrogen content, and the content of free tyrosine also increases accordingly. In other words, the higher the amino acid nitrogen content of existing soybean paste, the higher the tyrosine content will be, leading to a higher probability of white spots appearing during the shelf life. Therefore, current technology cannot increase amino acid nitrogen while inhibiting the increase of free tyrosine content. Thus, the white spot problem limits the improvement of the flavor and taste of soybean paste. Therefore, the national standard GB / T24399-2009 for soybean paste only requires an amino acid nitrogen index of ≥0.50g / 100g.

[0009] Nevertheless, due to the unavoidable intervention of miscellaneous bacteria during the fermentation of koji during the koji-making process, the resulting enzyme system is difficult to control. Therefore, existing technology cannot prevent the breakdown of proteins into tyrosine during this process, and the tyrosine content will continue to rise during subsequent fermentation. As a result, although the amino acid nitrogen index of soybean paste is low, it is still impossible to completely eliminate the formation of white spots.

[0010] Currently, to address the white spot problem in soybean paste caused by the difficulty in controlling the enzyme system produced during koji making, the existing technology offers the following improvement measures:

[0011] 1. Screening for new strains: A strain of Aspergillus oryzae was obtained by domesticating and breeding the Japanese soybean paste-specific koji in soybean juice culture medium supplemented with L-tyrosine. When this strain of Aspergillus oryzae was used to ferment soybean paste, no white spots were generated. However, the above method has a low probability of obtaining a specific strain of Aspergillus oryzae, and its horizontal scalability among different companies is very poor.

[0012] 2. Increase the solubility of tyrosine in fermented soybean paste mash: By adding emulsifiers such as PEG, polyethylene glycol, or sucrose fatty acid esters, the solubility of tyrosine can be increased, thus controlling the formation of white spots; however, the above methods are still in the laboratory stage and have not been verified in production.

[0013] 3. Inhibits the production of tyrosine in fermented soybean paste mash:

[0014] ① During the fermentation stage, glacial acetic acid inhibitors are added to inhibit microbial growth and adjust the pH value to reduce protease activity.

[0015] ②Reduce the inoculation amount during koji making, reduce the cooking intensity of soybeans, reduce the moisture content of the mixture, shorten the koji making time, and increase the proportion of soybeans that are not used for koji making, thereby reducing protease activity;

[0016] ③Shorten the koji-making time and increase the brine concentration to inhibit the rate of amino acid nitrogen formation;

[0017] The drawback of this method is that while reducing the concentration of tyrosine, the production of other amino acids also decreases, thereby reducing the flavor of the soybean paste, and it still cannot guarantee that the soybean paste will not develop white spots during its shelf life.

[0018] Based on the applicant's production experience and follow-up sampling of each batch of soybean paste pre-ferment, the standard line for free tyrosine precipitation in soybean paste pre-ferment is 100 mg / 100g. If the free tyrosine content in the soybean paste pre-ferment is higher than 100 mg / 100g, the resulting soybean paste carries a risk of developing white spots. When the free tyrosine content is lower than 100 mg / 100g, the resulting soybean paste generally does not develop white spots, but this does not completely eliminate the risk of white spots forming during the shelf life. The inventors' research found that the free tyrosine content in the soybean paste pre-ferment must be significantly lower than 100 mg / 100g, such as below 60 mg / 100g, to completely eliminate the risk of white spots forming during the shelf life. However, existing technologies make it difficult to reduce the free tyrosine content in soybean paste pre-ferment to 60 mg / 100g while still ensuring that the amino acid nitrogen content of the soybean paste meets national standards. Summary of the Invention

[0019] The purpose of this invention is to provide a production process for soybean paste embryos that reduces the content of free tyrosine. This process, by improving the raw material processing and koji-making processes, enables the free tyrosine content in soybean paste embryos to be reduced to a sufficiently low level while maintaining a moderate or higher level of amino acid nitrogen in the soybean paste, thereby effectively eliminating the potential risk of white spots precipitating in the soybean paste.

[0020] To achieve the above-mentioned objectives, the present invention adopts the following solution:

[0021] A process for producing soybean paste embryos with reduced free tyrosine content, characterized by comprising the following steps:

[0022] (1) Soybeans are first cleaned, soaked, and steamed, and then the steamed soybeans are soaked in water.

[0023] (2) Mix the soybeans treated in step (1) with starchy raw materials evenly, then inoculate with bacteria to make koji and obtain koji; the starchy raw materials, by mass percentage, include 0-20% flour and 80-100% soluble starch.

[0024] (3) Mix Daqu with salt water to obtain soy sauce mash, and after fermentation, obtain soybean paste embryo.

[0025] When researching the white spot problem in soybean paste, the inventors attempted to suppress it by modifying existing koji-making and fermentation conditions, such as increasing the koji-making temperature, shortening the koji-making time, increasing the concentration of fermentation brine, and reducing fermentation time. However, they found that these measures significantly affected the flavor of the soybean paste, and the effect of resolving the white spot problem was inconsistent. Therefore, the inventors further investigated and determined that the following technical measures can effectively solve the problem of white spots appearing in soybean paste during its shelf life:

[0026] ① Using soluble starch to completely or partially replace flour in the production of soybean paste koji: Because starch is a polysaccharide obtained by separating protein and other substances from flour, and the soluble starch is starch that has been treated with a light acid or alkali, so soluble starch does not contain protein components; using soluble starch as the main starch raw material for koji production can provide a carbon source for the growth of microorganisms and meet the needs of microbial growth and reproduction, but it also greatly reduces the activity of protease secreted by the microorganisms, thereby reducing the content of free tyrosine from protein decomposition.

[0027] ② Soaking cooked soybeans to reduce the protein content: Based on the existing soybean processing procedures, this invention soaks the cooked soybeans after steaming, causing some of the soluble proteins in the soybeans to dissolve in the water, thus reducing the protein content in the soybeans. This reduces the protease activity of the koji (fermented soybean starter). At the same time, as soybeans are the main protein source, the reduced protein content leads to a decrease in the amount of free amino acids produced from decomposition. In other words, the free tyrosine in the soybean paste embryo will also decrease simultaneously, thereby reducing the risk of white spots appearing in the soybean paste.

[0028] During the research and development process, the inventors discovered that even with only the first measure, white spots might still appear in the soybean paste embryo. Therefore, considering that the main protein source in soybean paste is soybeans, the inventors tried the second measure: soaking cooked soybeans in water to remove soluble proteins from the raw materials. After extensive testing, it was determined that by adopting the above-mentioned measures ① and ②, the present invention reduces the protein in the raw materials, thereby lowering the protease activity during koji making and fermentation. This ensures that the free tyrosine content in the soybean paste embryo after conventional fermentation is below 100 mg / 100g, thus solving the white spot problem in soybean paste. At the same time, it also keeps the amino acid nitrogen index of soybean paste at a level significantly higher than the national standard.

[0029] In a preferred embodiment of the present invention, the starchy raw material is soluble starch.

[0030] In a further embodiment of the present invention, the soybeans steamed in step (1) are soaked in water for 3 to 5 minutes, and the water can be tap water.

[0031] In the specific embodiment of the present invention, the soybean steaming in step (1) can be carried out using conventional operations. The degree of steaming is such that the cooked soybeans maintain a certain hardness and retain the integrity of the particle size.

[0032] In step (2) of this invention, the ratio of soybeans to starchy raw materials is the same as the existing ratio of soybeans to flour, generally 1:0.3 to 0.4.

[0033] The strains, koji-making, and fermentation in steps (2) and (3) of this invention adopt conventional strains, koji-making, and fermentation processes for soybean paste production, such as using Aspergillus oryzae as the strain and using room temperature fermentation.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention reduces the soluble protein content in the raw materials and lowers the protease activity of the starter culture by using soluble starch to completely or partially replace flour and adding a soaking process to the cooked soybeans. This effectively reduces the free tyrosine content in the soybean paste embryo, making the free tyrosine content in the soybean paste embryo significantly lower than 100mg / 100g. This ensures that no free tyrosine is released during the fermentation process and shelf life of the soybean paste. At the same time, the amino acid nitrogen index can be maintained at a level significantly higher than the national standard, and the flavor of the soybean paste is not diminished. It is the same as or better than the flavor of soybean paste without white spot inhibition measures, thus effectively solving the white spot problem of soybean paste.

[0036] 2. Compared with the prior art, the method of the present invention only replaces the starch raw material and adds a 3-5 minute soaking process for cooked beans. The production process remains basically unchanged and has little impact on production time. Moreover, the present invention does not require additional production equipment and is simple to operate. Therefore, it is highly feasible and easy to promote. Detailed Implementation

[0037] The following embodiments are for illustrative purposes only, and the scope of protection of the present invention is not limited to these embodiments. Those skilled in the art can achieve the objectives of the present invention based on the above disclosure and the ranges of the parameters.

[0038] Note: Because the same production process is used, the physicochemical indicators such as free tyrosine in soybean paste embryos produced at both laboratory and large-scale production levels, as well as different batches produced at the same scale, will fluctuate. Therefore, this invention will conduct repeated experiments at laboratory, large-scale, and production scales to verify that the production process of this invention can reliably ensure that the free tyrosine content in soybean paste embryos is far below 100mg / 100g, thus solving the white spot problem in soybean paste. The control sample is a simple comparative experiment example, without any technical measures to reduce free tyrosine. Because the probability of white spots in the soybean paste embryos produced there is extremely high, it is not the actual process for producing soybean paste embryos. The actual process for producing soybean paste embryos requires the improvement measures described in point 3 of the background art.

[0039] Example 1: Effect of soluble starch replacing flour on the enzyme activity of Daqu (a type of starter culture)

[0040] Soluble starch was mixed with ordinary flour at mass ratios of 0%, 30%, 50%, 60%, 80%, and 100% as starchy raw materials. Cooked soybeans were then mixed with the above starchy raw materials at a mass ratio of 1:0.35 to prepare a mixture. The mixture was inoculated with 3‰ Aspergillus oryzae by mass, placed in an aluminum box, and incubated in a constant temperature (30.5℃) and constant humidity (99%) incubator for koji making for 44 hours. The effects of different starchy raw materials (different amounts of soluble starch) on the enzyme activity of the koji were compared. Each experimental group with different proportions of soluble starch was tested in triplicate. The results are shown in Table 1.

[0041] Table 1. Protease activity of Daqu prepared with different amounts of soluble starch.

[0042] Soluble starch ratio Daqu moisture content Neutral protease activity (U / g) Acidic protease activity (U / g) 0％ 31 1468 438 30％ 32 1056 354 50％ 33 858 287 80％ 34 654 205 100％ 35 502 168

[0043] The Daqu (fermented starter culture) prepared with different starch addition amounts was mixed with brine to make mash. The material-to-water ratio was 1:2.5, the brine concentration was 18 Baume, and fermentation was carried out at 30℃ for 30 days. The soybean paste embryo was taken and sent for testing of physicochemical indicators. The results are shown in Table 2.

[0044] Table 2. Physicochemical properties of soybean paste starter obtained from fermentation of koji prepared with different amounts of soluble starch.

[0045]

[0046] As shown in Table 1, with the increase of the proportion of soluble starch in starchy raw materials, the neutral and acidic protease activities of the koji made by mixing with cooked beans gradually decreased. Therefore, compared with the koji-making process using ordinary flour, using soluble starch instead of ordinary flour resulted in the lowest koji protease activity.

[0047] Table 2 shows that the amino acid nitrogen and free tyrosine in soybean paste embryos gradually decreased with increasing soluble starch content. Even when the soluble starch content reached 100%, the amino acid nitrogen content of soybean paste embryos was still significantly higher than the standard of 0.5 g / 100 g in GB / T24399-2009 Soybean Paste. When 80-100% of soluble starch replaced ordinary flour in koji making, the tyrosine content of fermented soybean paste was much lower than 100 mg / 100 g, while the optimal soluble starch content was 100%.

[0048] Example 2: Effect of soaking time of cooked soybeans on enzyme activity of Daqu (a type of starter culture)

[0049] Soaked cooked soybeans in water for 1 min, 3 min, 5 min, 10 min, and 15 min, respectively. The soaking time was then 1 min, 3 min, 5 min, 10 min, and 15 min. The mixture was then mixed with ordinary flour at a mass ratio of 1:0.35 to form a koji (fermented soybean paste). The mixture was inoculated with 3‰ Aspergillus oryzae by mass, placed in an aluminum container, and incubated in a constant temperature (30.5℃) and constant humidity (99%) incubator for 44 h. The effect of different soaking times on the koji enzyme activity was compared. Each experimental group with different soaking times was repeated three times. The results are shown in Table 3.

[0050] Table 3. Protease activity of Daqu (a type of starter culture) prepared from cooked soybeans after different soaking times.

[0051] Soaking time for cooked beans Daqu moisture content Neutral protease activity (U / g) Acidic protease activity (U / g) 0min 28 1578 458 1min 29 1256 350 3min 30 843 277 5min 31 840 265 10min 30 798 268 15min 30 825 258

[0052] Soaking cooked soybeans in tap water for different times to make Daqu (a type of starter culture) was carried out. The mature Daqu was mixed with brine to make mash. The ratio of raw material to water was 1:2.5, the brine concentration was 18 Baume, and fermentation was carried out at 30℃ for 30 days. The soybean paste embryo was taken and sent for testing of physicochemical indicators. The results are shown in Table 4.

[0053] Table 4. Physicochemical properties of fermented soybeans obtained from cooked soybeans with different soaking times.

[0054]

[0055]

[0056] As shown in Tables 3 and 4, when the soaking time of cooked soybeans is 3-5 minutes, the enzyme activity of the Daqu (fermented starter culture) has already reached a low level. Even if the soaking time of cooked soybeans is extended, the enzyme activity of Daqu does not decrease significantly. Therefore, it is only necessary to use cooked soybeans soaked for 3-5 minutes for Daqu production. When the mature Daqu is mixed with salt water, the fermented soybeans can have free tyrosine content below 90 mg / 100g. Therefore, based on the impact on production efficiency, the optimal soaking time for cooked soybeans is 3-5 minutes.

[0057] Example 3: Laboratory-scale efficacy verification experiment

[0058] 1. Laboratory-scale koji-making was conducted using different starchy raw materials, and the protease activity of the resulting koji was compared.

[0059] The koji was made from ordinary flour and cooked beans, and the resulting koji served as a control sample.

[0060] ① Cooked beans were not soaked; soluble starch and cooked beans were used as raw materials to make koji, and the resulting koji was test sample 1.

[0061] ② Soak cooked beans in tap water for 3 minutes, then mix them with regular flour to make koji, which is the test sample 2;

[0062] ③ After soaking cooked soybeans in tap water for 3 minutes, they are mixed with soluble starch as raw materials to make koji, which is test sample 3, i.e. the scheme of this invention;

[0063] In the above koji-making process, the soybean flour mass ratio was 1:0.35, the Aspergillus oryzae inoculation mass was 3‰ of the raw material, the koji-making process was carried out at a constant temperature of 30.5℃, the humidity was 99%, and the koji-making time was 44h. The neutral and acidic protease activities of different samples were compared. Three parallel experimental groups were made for each of the above experimental and control samples. The results are shown in Table 5.

[0064] Table 5. Protease activity of Daqu (a type of starter culture) prepared from different raw materials.

[0065] sample Daqu moisture content Neutral protease activity (U / g) Acidic protease activity (U / g) control sample 31 1521 458 Test sample 1 32 724 354 Test sample 2 32 558 187 Test sample 3 34 354 58

[0066] 2. Physicochemical properties of soybean paste embryos obtained from different raw materials through koji making and fermentation

[0067] The starter culture of the control sample and test samples 1-3 was mixed with brine to make mash. The material-to-water ratio was 1:2.5, the brine concentration was 18 Baume, and fermentation was carried out at 30℃ for 30 days. The soybean paste embryo was taken and sent for testing of physicochemical indicators. The results are shown in Table 6.

[0068] Table 6 Physicochemical properties of soybean paste embryos obtained from fermentation of different raw materials

[0069]

[0070] As shown in Tables 5 and 6, the neutral and acidic protease activities of the control sample Daqu were as high as 1521 U / g and 458 U / g, respectively, and its amino acid nitrogen content was as high as 0.98 g / 100g. However, the free tyrosine content in the soybean paste embryo also increased significantly, reaching 180 mg / 100g, resulting in a high rate of white spot precipitation. The neutral and acidic protease activities of the experimental sample Daqu were reduced by 52% and 23% compared with the control sample, respectively. However, the free amino acid content still exceeded the standard line for free tyrosine precipitation in soybean paste embryo, thus resulting in a high probability of white spot precipitation. This indicates that using soluble starch alone to replace flour is still insufficient to achieve the goal of preventing white spot precipitation in soybean paste during its shelf life. The neutral and acidic protease activities of the experimental sample Daqu were even more significantly reduced, with the neutral protease activity decreasing by 63% and the acidic protease activity decreasing. The free amino acid content in the soybean paste embryo fermented with Daqu was 90 mg / 100g, slightly lower than the standard line of 100 mg / 100g for free tyrosine precipitation in soybean paste embryos. This indicates that the soaking of cooked soybeans is more effective, but there is a risk of tyrosine crystal precipitation. Compared with the control sample, the moisture content of Daqu in the test sample 3 was higher, and the activities of neutral and acidic proteases were significantly reduced. The neutral protease activity decreased by 77%, and the acidic protease activity decreased by 87%. The free tyrosine content in the resulting soybean paste embryo was 40 mg / 100g, meaning that there was no risk of white spot precipitation. The free amino acid content in the soybean paste embryo was still 0.63g / 100g, which is also higher than the standard of 0.5g / 100g in "GB / T24399-2009 Soybean Paste", meeting the flavor standard of soybean paste.

[0071] Example 4: Large-scale effect verification experiment

[0072] 1. Laboratory-scale koji-making was conducted using different starchy raw materials, and the protease activity of the resulting koji was compared.

[0073] At 60m 3 Each test sample was tested in one fermentation tank. The soybean flour mass ratio was 1:0.35. The mass of Aspergillus oryzae inoculation was 3‰ of the raw material. The fermentation tank was thick-layered and ventilated for koji making, and the koji making time was 42-44 hours.

[0074] ①The koji was made from ordinary flour and cooked beans, and the resulting koji served as a control sample;

[0075] ② Cooked beans were not soaked; soluble starch and cooked beans were used as raw materials to make koji, and the resulting koji was test sample 1.

[0076] ③ Soak cooked beans in tap water for 3 minutes, then mix them with regular flour to make koji, which is the test sample 2;

[0077] ④ After soaking cooked soybeans in tap water for 3 minutes, they are mixed with soluble starch as raw materials to make koji, which is test sample 3, i.e., the scheme of this invention;

[0078] The neutral and acidic protease activities of different samples were compared, and the results are shown in Table 7.

[0079] Table 7. Protease activity of Daqu (a type of starter culture) prepared from different raw materials.

[0080] sample Daqu moisture content Neutral protease activity (U / g) Acidic protease activity (U / g) control sample 28 1221 358 Test sample 1 29 732 301 Test sample 2 30 688 287 Test sample 3 31 254 65

[0081] 2. Physicochemical properties of soybean paste embryos obtained from different raw materials through koji making and fermentation

[0082] The Daqu prepared by the above different processes was mixed with brine to make mash. The material-to-water mass ratio was 1:2.5, the brine concentration was 18 Baume, and fermentation was carried out at 30℃ for 30 days. The soybean paste embryo was taken and sent for testing of physicochemical indicators. The results are shown in Table 8.

[0083] Table 8 Physicochemical properties of soybean paste embryos obtained from fermentation of different raw materials

[0084]

[0085] As shown in Tables 7 and 8, the moisture content of sample 2 did not fluctuate much compared to the control sample, remaining within the normal range. Both neutral and acidic enzyme activities decreased, with neutral enzyme activity decreasing by 40% and acidic enzyme activity decreasing by 44%, a significant decrease. However, the enzyme activity is still relatively high for brewing soybean paste, resulting in relatively high levels of free amino acids in the soybean paste. The moisture content of sample 3 increased compared to the control sample, while neutral and acidic enzyme activities decreased significantly, with neutral enzyme activity decreasing by 79% and acidic enzyme activity decreasing by 82%.

[0086] The free tyrosine content in the soybean paste embryo of test sample 3 was 40mg / 100g, and there was no risk of white spot precipitation. At the same time, the neutral enzyme activity and acid enzyme activity of the koji made from the raw materials of test sample 3 were low, and the free amino acid content of the fermented soybean paste was also higher than the standard of "GB / T 24399-2009 Soybean Paste", which can meet the flavor of soybean paste.

[0087] 3. White spots appearing in soybean paste embryos obtained from fermentation of different raw materials.

[0088] The white spots on the soybean paste embryos during the fermentation process were observed, and the white spots on the soybean paste embryos were observed at room temperature during their shelf life. The results are shown in Table 9.

[0089] Table 9. White Spots in Soybean Paste Base

[0090] sample During fermentation Shelf life (12 months) control sample White spots appear after 15-20 days of fermentation. Not used in soybean paste production Test sample 1 White spots appear after 25-30 days of fermentation. Not used in soybean paste production Test sample 2 White spots appear after 20-30 days of fermentation. Not used in soybean paste production Test sample 3 No white spots appeared No white spots appeared

[0091] Example 6: Soybean Paste Brewing Production Experiment

[0092] With a single 65m 3The effect verification test of the preparation process of low protease activity Daqu was carried out in fermentation tanks. The specific production steps of the test sample were as follows: after soaking cooked soybeans in water for 3 minutes, they were mixed with soluble starch, and 3‰ of Aspergillus oryzae by weight of raw materials were inoculated for Daqu preparation. The mature Daqu was mixed with salt water with a concentration of 18 Baume at a material-to-water ratio of 1:2.5 to make mash, fermented soybean paste embryos, and various physicochemical indicators of soybean paste embryos were tested.

[0093] A control sample was prepared using conventional processes to produce soybean paste embryos. The control sample used ordinary flour and cooked soybeans as raw materials for koji making, and the other steps were the same as those for the test sample. The results are shown in Tables 10 and 11.

[0094] Table 10 Comparison of protease activity of soybean paste starter prepared by different processes

[0095] sample Daqu moisture content Neutral enzyme activity (U / g) Acidic enzyme activity (U / g) control sample 30 1098 298 test sample 32 232 29

[0096] Table 11 Comparison of physicochemical properties of soybean paste pre-processed by different processes

[0097]

[0098]

[0099] The white spots on the soybean paste embryos during the fermentation process were observed, and the white spots on the soybean paste embryos were observed at room temperature during their shelf life. The results are shown in Table 12.

[0100] Table 12 White Spots in Soybean Paste Base

[0101] sample During fermentation Shelf life (12 months) control sample White spots appear after 20-25 days of fermentation. Not used in soybean paste production test sample No white spots appeared No white spots appeared

[0102] As shown in Tables 9 and 10, the control sample developed white spots during fermentation, failing to meet factory quality inspection requirements and therefore unsuitable for use in soybean paste production. The process of this invention, when applied to soybean paste brewing, ensures that the free tyrosine content in the soybean paste embryo drops below the standard line (100 mg / 100g), significantly reducing the risk of white spot precipitation and effectively preventing its formation. Table 12 also shows that the soybean paste embryo prepared by this invention does not exhibit white spot problems during its shelf life.

[0103] Example 7 Sensory Evaluation

[0104] For the soybean paste embryos of the control and experimental samples in Example 6, 10 experienced evaluators were gathered to conduct sensory evaluation. The evaluation indicators for sensory evaluation included appearance, color, aroma, umami, sweetness, bitterness, saltiness, sourness and overall taste, with a score of 0-4 points. The higher the score, the better the indicator. The sensory evaluation results are shown in Table 11.

[0105] Table 13 Sensory evaluation results of soybean paste base brewed using different processes

[0106] strains posture Color aroma Umami sweet bitter taste Salty sour Overall taste test sample 3.1 3.0 3.1 3.5 3.2 3.1 3.1 3.6 3.4 control sample 3.1 3.1 3.0 3.6 3.1 3.1 3.1 3.5 3.3

[0107] Table 13 shows the sensory evaluation results. The main sensory indicators such as umami, sweetness, and color of the soybean paste embryo prepared by the process of this invention are not much different from those of soybean paste embryos produced by existing processes, and are within the normal fluctuation range. In other words, the process of this invention will greatly reduce the content of free tyrosine in soybean paste, which not only reduces the risk of white spot precipitation, but also eliminates the hidden danger of white spot precipitation. At the same time, it does not have a significant impact on the taste of soybean paste. This is because the method of this invention reduces the content of free tyrosine in soybean paste embryos without affecting other flavor amino acids.

[0108] This invention can be summarized in other specific forms that do not depart from the spirit or main features of the invention. The above embodiments of the invention are merely illustrative and not restrictive. Therefore, any minor modifications, equivalent variations, and alterations made to the above embodiments based on the essential technology of this invention fall within the scope of the invention's technical solution.

Claims

1. A production process for soybean paste embryos that effectively inhibits the precipitation of white spots in soybean paste, characterized in that, Includes the following steps: (1) Soybeans are first cleaned, soaked, and steamed, and then the steamed soybeans are soaked in water for 3-5 minutes. (2) Mix the soybeans treated in step (1) with soluble starch at a mass ratio of 1:0.3~0.4, then inoculate with the starter culture to make koji and obtain koji. (3) Mix Daqu with salt water to obtain soy sauce mash, and after fermentation, obtain soybean paste embryo.

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