A method for preparing soybean paste by reducing white spot precipitation through physical elution

Abstract

The invention discloses a method for preparing soybean paste by reducing white spot precipitation in a physical elution manner. The method combines soybean pretreatment and natural oil elution processes to elute free tyrosine from soybean paste embryos during the fermentation process, thereby effectively reducing the free tyrosine content in the soybean paste, solving the problem of white spot precipitation of soybean paste during the fermentation process and during the shelf life, and ensuring that the soybean paste has a good flavor.

Description

Technical Field

[0001] The invention belongs to the field of food processing, and particularly relates to a method for preparing soybean paste by reducing white spot precipitation in a physical elution manner. Background Art

[0002] Soybean paste is a traditional seasoning sauce in my country. It is generally made from soybeans and flour. It goes through a production process including raw material processing, koji making and fermentation to make a seasoning sauce with special color, aroma and taste.

[0003] The specific production process of soybean paste includes:

[0004] (1) Wash and soak the soybeans, then steam and cook them;

[0005] (2) The steamed soybeans are mixed with flour, inoculated with fungi, and koji is made;

[0006] (3) The prepared Daqu is mixed with salt water to form a sauce mash, which is then naturally fermented in the sun and dew for 60 to 90 days to obtain a soybean paste embryo; the soybean paste embryo is then blended to obtain soybean paste.

[0007] During the koji-making process, the protein in the raw materials breaks down and produces tyrosine, which then increases in content during the subsequent fermentation process. However, because tyrosine has an extremely low solubility in water, at only 0.045%, it easily precipitates during the fermentation and shelf life of soybean paste, forming irregular white crystals commonly known as "white specks." While the presence of white specks in soybean paste typically indicates a high amino acid nitrogen content, rather than mold or spoilage, it's difficult for consumers to distinguish what white specks are in soybean paste. Sensory perception suggests white specks indicate mold and spoilage, severely impacting soybean paste sales and the perception of the company's quality. Therefore, the presence of white specks in soybean paste, whether during production or shelf life, has long been considered substandard. Furthermore, if the free tyrosine content in the soybean paste embryo is detected to be excessively high during fermentation, the embryo becomes unusable, resulting in significant economic losses and no remedial measures are currently available.

[0008] How to effectively reduce the appearance of white spots in soybean paste has always been an important topic in soybean paste production and technical research. It has also been a technical problem that has troubled companies and has therefore restricted soybean paste process innovation and upgrading:

[0009] This is because flavorful soybean pastes typically have high amino acid nitrogen content, which in turn increases the free tyrosine content. In other words, higher amino acid nitrogen content in existing soybean pastes is inevitably accompanied by higher tyrosine content, leading to a higher probability of white spots appearing during the paste's shelf life. Therefore, existing technologies cannot simultaneously increase the amino acid nitrogen content of soybean paste while suppressing the increase in free tyrosine content. This white spot problem limits the improvement of soybean paste's flavor and taste. Therefore, the amino acid nitrogen index for soybean paste specified in the national standard GB / T24399-2009 only requires ≥0.50g / 100g. The amino acid nitrogen content of soybean pastes on the market is generally 0.6-0.7g / 100g.

[0010] In the prior art, if the free tyrosine content of soybean paste after fermentation is high, the product is more likely to develop white spots during its shelf life; if the free tyrosine content of soybean paste after fermentation is low, the product is less likely to develop white spots during its shelf life. Based on the applicant's production experience and follow-up of samples from each batch of soybean paste, the standard line for free tyrosine in soybean paste embryos is 100mg / 100g; as long as the free tyrosine content of soybean paste is higher than 100mg / 100g, the resulting soybean paste is at risk of developing white spots; when the free tyrosine content of soybean paste is lower than 100mg / 100g, the resulting soybean paste generally does not develop white spots.

[0011] At present, the common measures to solve the "white spot" problem of soybean paste are:

[0012] (1) Genetic engineering is used to obtain recombinant bacteria that produce tyrosine ammonia lyase, or to select Aspergillus species that produce less tyrosine by mutagenesis or domestication (Xiao Xiao et al., Study on methods to suppress the production of white crystals in Aspergillus-type soybean paste, School of Chemical Engineering, Shijiazhuang University, Shijiazhuang 050035; 2); This method can fundamentally solve the white spot problem, but genetic engineering is difficult, mutagenesis and domestication of bacterial strains are time-consuming, the strains are unstable, and many companies do not have the conditions to develop such a process; therefore, such a process is difficult to replicate in various production companies;

[0013] (2) Reduce the koji making time (Xia Yanshi, Xia Yanbin, Yang Fulin, Huang Qun, College of Food Science and Technology, Hunan Agricultural University, 1007-2764 (2004) 02-0163-061); specifically, reduce the three-day koji to two-day koji or even shorter, or adjust the koji making temperature to a temperature that is not conducive to the growth and enzyme production of Aspergillus oryzae; this method can effectively reduce the protease activity of the koji, and the corresponding enzyme that decomposes and produces tyrosine will be reduced, thereby reducing the generated tyrosine and reducing the hidden danger of white spots. However, due to the reduction in protease activity, the utilization rate of protein is reduced, which not only reduces the utilization rate of raw materials, but also seriously affects the flavor of the soybean paste embryo;

[0014] (3) Adding surfactants after the fermentation of soybean paste (Wang Jianming, Zhang Ming, Jia Lei, School of Food Engineering and Biotechnology, Tianjin University of Science and Technology, China Food Quality News / April 24, 2009, Page 006) can reduce the surface tension of soybean paste and enhance its solubilization effect at the interface, making it difficult for some amino acids that are easy to crystallize to precipitate to aggregate, so that they can be dispersed or dissolved in the sauce; however, according to the test results, the addition of surfactants cannot effectively solve the white spot problem. Specifically, although the number of white spots will be reduced to a certain extent, there is still a major hidden danger because tyrosine is still at a high level. Summary of the Invention

[0015] The object of the present invention is to provide a method for preparing soybean paste by reducing the precipitation of white spots by physical elution. The method can effectively reduce the free tyrosine content in the soybean paste, solve the problem of white spot precipitation of the soybean paste during the fermentation process and the shelf life, and ensure that the soybean paste has a good flavor.

[0016] Regarding the white speck problem in soybean paste, the inventors observed unqualified soybean paste embryos and found that the white specks were all located inside the bean skin (i.e., the white specks were enclosed in the bean skin), while soybeans without white specks had damaged or no bean skin (a small number of soybeans had their bean skin damaged or peeled during transportation or processing). They also found that the fermentation liquid contained less free tyrosine, which was due to the fact that the free tyrosine in the soybean paste embryos was mostly concentrated in the bean skin. Therefore, the inventors tried to crack the soybean skins of soybeans to achieve a cracked state before using them to prepare soybean paste embryos. They found that the free tyrosine content in the soybean paste embryos was lower than that of the prior art, while the free tyrosine content in the fermentation liquid was slightly higher.

[0017] At the same time, when the inventors sampled and tested unqualified soybean paste embryos, they added a certain amount of salt water, stirred them, and then sampled them again because of their thick texture. They found that the free tyrosine content of the soybean paste embryos had decreased, but the flavor also declined. Therefore, the inventors began soaking the soybean paste embryos in salt water and other liquids of varying concentrations. They confirmed that the free tyrosine content of the soybean paste embryos after soaking decreased significantly, but the flavor degradation problem persisted.

[0018] Later, the inventors used natural oil to replace the fermentation liquid during the fermentation process, resulting in reduced free tyrosine in the soybean paste embryo but improved flavor.

[0019] Therefore, in order to achieve the above object, the present invention adopts the following technical solutions:

[0020] A method for preparing soybean paste by reducing white spot precipitation by physical elution comprises the following steps:

[0021] (1) Soybean pretreatment: roast the soybeans in a roasting machine until the soybean skins are cracked but the kernels are not cracked;

[0022] (2) Material preparation: Wash and soak the roasted soybeans, then steam and cook the cooked soybeans. After cooling, mix the cooked soybeans with flour and fungus to obtain a mixture;

[0023] (3) Qu making: the mixture is placed in a Quchi for cultivation to obtain Daqu;

[0024] (4) Fermentation: Add salt water to the Daqu and stir evenly to prepare the mash, which is then placed in a fermentation tank for fermentation. During the fermentation process, the solid matter in the mash floats to form a mash layer, while the fermented liquid sinks to the bottom.

[0025] (5) Elution: In the late fermentation stage, the fermentation liquid is released, and then natural oil is added from above the mash layer to replace the fermentation liquid, so that it slowly penetrates into the mash layer from top to bottom, or the mash layer is directly stirred to elute the free tyrosine in the mash layer; then the fermentation is continued, and the mash layer and the fermentation liquid are separated again;

[0026] (6) Post-processing: After fermentation is completed, the fermentation liquid is released to obtain soybean paste embryo, which is then blended to obtain soybean paste.

[0027] The natural oil described in the present invention is raw soy sauce, which refers to the crude oil obtained after the fermentation of soy sauce, i.e., the head oil. Its flavor is greater than or equal to the flavor of the soybean paste fermentation liquid. The inventors have experimentally confirmed that using natural oil for elution can improve the flavor of the soybean paste embryo, while using double or triple elution of soy sauce will reduce the flavor of the soybean paste embryo. According to testing, the tyrosine content of the natural oil is less than 100 mg / 100 g.

[0028] In step (1) of the present invention, soybeans are roasted to achieve a state in which the bean skins are cracked but the bean kernels are not cracked. During the fermentation process in step (4), tyrosine originally accumulated in the bean skins flows out from the cracked parts and dissolves into water. Therefore, the fermentation liquid at this time contains a large amount of free tyrosine, and the free tyrosine content in the mash layer is equivalent to that in the fermentation liquid.

[0029] Therefore, in the late fermentation stage of step (5), the fermentation broth with a high free tyrosine content is released, and natural oil is used instead of the fermentation broth to continue the fermentation, and the free tyrosine in the mash layer is eluted out, which can reduce the tyrosine concentration of the entire mash and make the free tyrosine content of the soybean paste embryo always lower than 100 mg / 100 g. This not only solves the problem of white spots appearing during the production process, but also solves the hidden danger of white spots precipitating in the finished soybean paste.

[0030] The inventors have found that the best way to crack the soybean skin is to pre-treat it by roasting. On the one hand, without the step (1) of cracking the soybean skin, the free tyrosine content of the fermented mash layer as a whole will still be higher than the free tyrosine content in the fermentation broth. Even if the elution operation of step (5) is performed, the free tyrosine in the mash layer cannot be effectively eluted. The inventors have experimentally verified that white spots will still precipitate in the soybean paste embryo prepared without pre-treatment. Therefore, pre-treatment of soybeans can effectively ensure the effect of the subsequent elution operation. On the other hand, roasting soybeans produces a unique aroma of fried beans, which can effectively enhance the overall flavor of the soybean paste.

[0031] Furthermore, natural oil, as the crude oil obtained after the fermentation of soy sauce, is rich in flavor substances and has a high content of amino acid nitrogen. In the later stage of fermentation, using it to replace the fermentation liquid for fermentation can enhance the flavor of soybean paste.

[0032] In step (5), after one elution, the free tyrosine content in the mash is lower than 100 mg / 100 g, and another elution operation may not be performed, or another elution operation may be performed to further reduce the risk of white spot precipitation.

[0033] Preferably, in step (5), the elution is performed once or more, more preferably three times; when multiple elutions are performed, the specific operation is as follows:

[0034] ① Release the fermentation liquid first,

[0035] ② Add natural oil from above the mash layer and allow it to slowly penetrate into the mash layer from top to bottom, or stir the mash layer directly so that the natural oil can elute the free tyrosine in the mash layer;

[0036] ③Continue fermentation;

[0037] ④ After the mash layer and natural oil are separated again, the first elution is completed;

[0038] If you need to complete the second or more elutions, just repeat the above steps ① to ④.

[0039] The present invention preferably uses a natural oil with a free tyrosine content of 50 mg / 100 g or less for elution in step (5), and the lower the free tyrosine content of the natural oil, the better. Numerous experiments have shown that using a natural oil with a free tyrosine content of 50 mg / 100 g or less can ensure that the free tyrosine content of the soybean paste embryo is reduced to below 100 mg / 100 g after three or fewer elution operations, thereby avoiding increased production costs due to repeated elutions.

[0040] In step (5), the present invention can adopt a self-rinsing method and a stirring method for elution; the self-rinsing method is to add natural oil from above the mash layer, wait for it to slowly penetrate into the mash layer from top to bottom, and elute the free tyrosine; the stirring method is to add natural oil to the mash layer and then stir it to make the free tyrosine content in the mash layer equivalent to the free tyrosine content in the fermentation liquid (natural oil) (reach an equilibrium state), so that when the mash layer rises again, the natural oil fermentation liquid will elute the higher content of free tyrosine in the mash layer.

[0041] Since the natural oil may penetrate the mash layer during the slow infiltration process when eluting by self-leaching, thus affecting the elution effect, the present invention preferably adopts stirring mode for elution, which can ensure the effect of eluting free tyrosine and improve the qualified rate of soybean paste.

[0042] Preferably, in step (5), the amount of natural oil used for each elution is 1.2 to 2.5 times the weight of the raw materials (i.e. the total weight of soybeans and flour).

[0043] The total fermentation time of the present invention is 60 to 90 days. Preferably, the elution operation in step (5) is performed when the fermentation time is ≥ 40 days.

[0044] In a specific embodiment of the present invention:

[0045] In step (1), the temperature of roasting soybeans is 250-270° C., so that the soybean skins are cracked but the bean kernels are not cracked.

[0046] In step (2), the soaking time of soybeans is 5 to 10 hours, and the weight volume ratio of soybeans to water is 1:2 to 2.5 kg / L.

[0047] In step (2), the weight ratio of soybeans to flour is 1:0.2-0.5; the bacterial strain is koji, and the inoculation amount is 0.5±0.1‰ of the total weight of soybeans and flour.

[0048] In step (3), the Daqu culture time is 33 to 48 hours.

[0049] In step (4), the amount of salt water added is 1.5 to 2.5 times the total weight of soybeans and flour, so that the salt content of the liquid part in the sauce mash is 16.5±0.3g / 100mL.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) Completely different from the traditional process for reducing white spots in soybean paste, this method takes a different approach. By combining soybean pretreatment and natural oil elution processes, free tyrosine is eluted from the soybean paste embryo during the fermentation process, making the free tyrosine content in the soybean paste embryo significantly lower than 100 mg / 100 g, thereby effectively solving the problem of white spot precipitation in soybean paste during the fermentation process and during the shelf life;

[0052] Moreover, the present invention can improve the flavor of soybean paste embryo while solving the problem of white spot precipitation, meet the market requirements for the product, and improve the overall economic benefits of soybean paste.

[0053] (2) The fermentation liquid released in the elution process of the present invention can be recycled for the production of soy sauce. Specifically, the fermentation liquid can be directly blended into soy sauce after being clarified by centrifugation or pressing, or added to soy sauce mash to extract the secondary oil. Therefore, even if the present invention adopts the elution process, no additional waste liquid will be generated, and excessive cost burden on the production enterprise is avoided.

[0054] (3) The method of the present invention can make up for the defect that the soybean paste embryo cannot be used due to the high free tyrosine content during the fermentation process, thereby avoiding the large economic losses caused by this.

[0055] (4) Compared with the existing methods for solving the "white spot" problem mentioned above, the present invention simply and effectively controls the hidden dangers of white spots and has good replicability and promotion. This technology can be applied to the seasoning industry due to the problem of tyrosine precipitation. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0057] Unless otherwise specified, the test methods used in the examples of the present invention are all conventional methods; the materials used are all commercially available materials unless otherwise specified.

[0058] The following examples all used natural oil with a free tyrosine content of ≤50 mg / 100 g for elution.

[0059] Example 1: Effect of elution timing on free tyrosine content in soybean paste embryos

[0060] Soybeans were roasted at 260°C using a roasting machine until the skins were cracked but the kernels remained intact. The washed soybeans were mixed with water at a ratio of 1:2.5 kg / L and soaked for 5 hours. The soybeans were then steamed at a pressure of 0.08±0.1 MPa for 15±1 min. The cooked soybeans were mixed with flour at a weight ratio of 1:0.5, and koji was inoculated at 0.5±0.1‰ of the total weight of the soybeans and flour. The mixture was then placed in a koji pool and cultured for 48 hours to obtain a large Koji; adding salt water in an amount of 2 times the total weight of soybeans and flour to the koji, stirring evenly to obtain a sauce mash, which is placed in a fermentation tank for fermentation, and the salt content of the liquid part in the sauce mash is 16.5±0.3g / 100mL; at different fermentation times, the sauce mash is eluted once, that is, the bottom fermentation liquid is first released, and then natural oil is added from above the sauce mash layer, and stirred, and the amount of natural oil used for elution is 2 times the weight of the raw materials; after 90 days of fermentation, the fermentation liquid is filtered out to obtain the soybean paste embryo.

[0061] The free tyrosine content of the specific soybean paste / soybean paste embryo is shown in Table 1, and the physical and chemical indicators of the soybean paste embryo after fermentation are shown in Table 2.

[0062] Table 1

[0063]

[0064] As shown in the table above, if elution is performed before or during fermentation, the free tyrosine content in the soybean paste will be lower after elution. However, as fermentation continues, the free tyrosine content will continue to increase by the time the paste is released. Elution in the later stages of fermentation is more effective, with the free tyrosine content in the soybean paste at the end of fermentation not significantly higher than on the day of elution. Therefore, the optimal time for elution is when the fermentation has been going on for 40 days or longer.

[0065] Table 2

[0066]

[0067]

[0068] If elution is performed in the early and middle stages of fermentation, the total acidity of the soybean paste embryo will be significantly reduced; while if elution is performed in the late stage of fermentation, there will be no significant difference in the physical and chemical indicators of the soybean paste embryo.

[0069] This example further conducted a sensory evaluation of the overall flavor of the soybean paste embryo (organized 10 R&D personnel and sensory evaluators, with each item worth 100 points). The evaluation results are shown in Table 3 below.

[0070] Table 3

[0071]

[0072] The results in Table 3 show that when elution was performed in the early and middle stages of fermentation, the overall flavor of the soybean paste was significantly lower than that of the control, mainly due to poor smell and taste; when elution was performed in the late stage of fermentation, there was no significant difference from the control.

[0073] The possible reason for the situations in Tables 2 and 3 above is that fermentation is still continuing in the early and middle stages, and there are still certain enzymes in the mash. During elution, some enzymes in the mash are eluted, which affects the fermentation and causes the flavor of the soybean paste to deteriorate; while in the later stage, fermentation is basically completed, and elution at this time has little effect on fermentation.

[0074] Example 2: Effect of elution method and number of times on free tyrosine in soybean paste embryo

[0075] Soybeans are roasted at 260° C. using a soybean roaster until the hulls are cracked but the kernels are not; after washing the soybeans, the soybeans are mixed with water at a ratio of 1:2 kg / L and soaked for 10 hours, and then the soybeans are steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked soybeans and flour are mixed at a weight ratio of 1:0.4, and koji essence is inoculated at a ratio of 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for cultivation for 42 hours to obtain daqu; brine is added to the daqu at a ratio of 2 times the total weight of the soybeans and flour, and the mixture is stirred evenly to obtain a sauce mash, which is then placed in a fermentation tank for fermentation, and the salt content of the liquid part of the sauce mash is 16.5±0.3 g / 100 mL; in the later stage of fermentation, the sauce mash is eluted by self-leaching or stirring, and the amount of natural oil used for each elution is 1.5 times the weight of the raw materials; after 80 days of fermentation, the fermentation liquid is filtered out to obtain a soybean paste embryo.

[0076] 1. Elute by self-elution:

[0077] After 40 days of fermentation, the mash is eluted by self-elution, that is, the fermentation liquid is first released at the bottom, and natural oil is added from the surface of the mash layer. The natural oil gradually penetrates into the mash layer from the upper surface, and the mash layer slowly rises. The natural oil brings the free tyrosine in the mash layer into the liquid; after the mash layer and the fermentation liquid are separated again, the above elution operation is repeated.

[0078] In this example, five cans of sauce mash eluted by self-leaching were tested, and the free tyrosine contents thereof are shown in Table 4.

[0079] Table 4

[0080]

[0081] The data from tanks 2 to 5 show that the more elutions, the lower the free tyrosine content in the mash. Furthermore, the higher the free tyrosine content in the uneluted mash, the more elutions are required. When the number of elutions is three, the free tyrosine content is already well below 100 mg / 100 g. This also demonstrates that the self-elution method employed in the present invention can reduce the free tyrosine content and minimize the occurrence of white spots.

[0082] As for Tank 1, perforation occurred during the second and third elution of its mash (i.e., when natural oil was added, the liquid directly pressed through the mash and entered the bottom of the tank), so the elution effect was not achieved, resulting in the free tyrosine content in the mash not being significantly reduced.

[0083] 1. Elution by stirring:

[0084] After 40 days of fermentation, the mash is eluted by stirring, that is, the fermentation liquid is first released at the bottom, natural oil is added from the surface of the mash layer, and it is stirred. At this time, the free tyrosine in the mash layer and the fermentation liquid reaches a state of equilibrium, so when the mash layer slowly rises, the fermentation liquid brings the higher content of free tyrosine in the mash layer into the liquid; after the mash layer and the water yellow are separated again, the above elution operation is repeated.

[0085] In this example, five cans of sauce mash eluted in a stirring manner were tested, and the free tyrosine contents thereof are shown in Table 5.

[0086] Table 5

[0087]

[0088] The data in Table 5 show that the greater the number of elutions, the lower the free tyrosine content in the mash. Furthermore, the higher the free tyrosine content in the uneluted mash, the more elutions required. When the number of elutions was three, the free tyrosine content was significantly lower than 100 mg / 100 g. This demonstrates that the present invention's use of a stirring elution method can effectively reduce the free tyrosine content and minimize the occurrence of white spots.

[0089] From the results in Tables 3 and 4, it can be seen that when eluting by self-elution, if there is no perforation, the elution effect is not significantly different from that by stirring. However, since perforation may occur in self-elution, stirring is preferred for elution.

[0090] Example 3: Effect of the amount of natural oil used in each elution on free tyrosine in soybean paste embryos

[0091] Soybeans are roasted at 260°C using a soybean roaster until the skins are cracked but the kernels are not; after washing the soybeans, the soybeans are mixed with water at a ratio of 1:2 kg / L and soaked for 8 hours, and then the soybeans are steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked soybeans and flour are mixed at a weight ratio of 1:0.5, and koji essence is inoculated at 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for cultivation for 40 hours to obtain Daqu; brine is added to the Daqu at a ratio of 2.5 times the total weight of the soybeans and flour, and the mixture is stirred evenly to obtain a sauce mash, which is then placed in a fermentation tank for fermentation, and the salt content of the liquid part of the sauce mash is 16.5±0.3 g / 100 mL; on the 50th day of fermentation, the sauce mash is eluted in a stirring manner using different amounts of natural oil; the elution is performed twice (the amount of natural oil used for both times is the same); after 80 days of fermentation, the fermentation liquid is filtered out to obtain a soybean sauce embryo.

[0092] The results of free tyrosine content in the mash after each elution are shown in Table 6.

[0093] Table 6

[0094]

[0095] It can be seen from the above table that the greater the amount of natural oil used in a single elution, the better the elution effect.

[0096] During production, if the amount of natural oil used is too little, the elution effect is not obvious. Since using natural oil for elution will enhance the flavor of soybean paste, the recommended minimum elution water ratio is 1:1.2. When the amount of natural oil used reaches 1:2.5, the effect of elution once is already good. Increasing the amount of elution water will cause certain waste. Taking all factors into consideration, the elution water ratio should be controlled between 1:1.2 and 1:2.5.

[0097] Example 4: Effect of natural oil temperature on tyrosine in soybean paste embryo

[0098] After washing the soybeans, they are mixed with water at a ratio of 1:2 kg / L and soaked for 5 hours, and then the soybeans are steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked soybeans and flour are mixed at a weight ratio of 1:0.5, and koji essence is inoculated at 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for cultivation for 40 hours to obtain Daqu; brine is added to the Daqu at a ratio of 2.5 times the total weight of the soybeans and flour, and the mixture is stirred evenly to obtain a sauce mash, which is then placed in a fermentation tank for fermentation, and the salt content of the liquid part of the sauce mash is 16.5±0.3 g / 100 mL; on the 60th day of fermentation, the sauce mash fermented at different periods is eluted once with natural oil at different temperatures in a stirring manner, and the amount of natural oil used for elution is 2.5 times the weight of the raw materials; after 80 days of fermentation, the fermentation liquid is filtered out to obtain the soybean paste embryo.

[0099] The results of free tyrosine content in the mash after elution are shown in Table 7.

[0100] Table 7

[0101]

[0102]

[0103] As can be seen from the table above, the temperature of the natural oil has the same effect on the elution of the soybean paste embryo, regardless of winter or summer. That is, the natural oil temperature has no effect on the free tyrosine content of the soybean paste embryo. Therefore, in a specific embodiment of the present invention, a natural oil at room temperature (i.e., the natural oil is not temperature-controlled) is used for the elution operation.

[0104] Example 5: Production test to verify the effect

[0105] With a single 65m 3 The effect verification test is carried out on the fermentation tank as a unit. The specific production steps are as follows:

[0106] Roast soybeans at 260°C using a soybean roaster until the skins are cracked but the kernels are intact; wash the roasted soybeans, mix them with water at a ratio of 1:2.5 kg / L and soak for 6 hours, then steam the soybeans at a pressure of 0.08±0.1 MPa for 15±1 min; mix the cooked soybeans with flour at a weight ratio of 1:0.4, inoculate koji with 0.5±0.1‰ of the total weight of the soybeans and flour, and then culture in a koji pool for 40 hours to obtain Daqu; add salt water twice the total weight of the soybeans and flour to the Daqu and stir evenly. A soybean mash is prepared and placed in a fermentation tank for fermentation, wherein the salt content of the liquid part of the soybean mash is 16.5±0.3 g / 100 mL; on the 45th day of fermentation, the fermentation liquid is discharged, and natural oil is added from above the soybean mash layer and stirred to allow the natural oil to elute free tyrosine in the soybean mash layer; after the soybean mash layer and the fermentation liquid are separated again, the elution operation is repeated; elution is performed three times during the fermentation period, and the amount of natural oil used for each elution is twice the weight of the raw material; after 90 days of fermentation, the fermentation liquid is filtered out to obtain soybean paste embryos with a low free tyrosine concentration, and soybean paste is obtained after blending.

[0107] Example 6: Production test to verify the effect

[0108] With a single 65m 3 The effect verification test is carried out on the fermentation tank as a unit. The specific production steps are as follows:

[0109] The soybeans were roasted at 260°C using a bean roaster until the skins were cracked but the kernels were not; the roasted soybeans were washed, mixed with water at a ratio of 1:2.5 kg / L and soaked for 8 hours, and then steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked soybeans were mixed with flour at a weight ratio of 1:0.3, and koji was inoculated at 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for 42 hours to obtain Daqu; salt water twice the total weight of the soybeans and flour was added to the Daqu and stirred evenly to prepare Daqu. The obtained mash is placed in a fermentation tank for fermentation, and the salt content of the liquid part in the mash is 16.5±0.3 g / 100 mL; on the 50th day of fermentation, the fermentation liquid is released, and natural oil is added from above the mash layer and stirred to allow the natural oil to elute free tyrosine in the mash layer; after the mash layer and the fermentation liquid are separated again, the above elution operation is repeated; elution is performed twice during the fermentation period, and the amount of natural oil used for each elution is 1.5 times the weight of the raw material; after 85 days of fermentation, the fermentation liquid is filtered out to obtain a soybean paste embryo with a low free tyrosine concentration, and the soybean paste is obtained after blending.

[0110] Comparative Example 1

[0111] The soybeans are washed, mixed with water at a ratio of 1:2.5 kg / L and soaked for 6 hours, and then the soybeans are steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked beans are mixed with flour at a weight ratio of 1:0.4, and koji essence is inoculated at 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for cultivation for 40 hours to obtain Daqu; brine twice the total weight of the soybeans and flour is added to the Daqu, stirred evenly to obtain a sauce mash, which is placed in a fermentation tank for fermentation, and the salt content of the liquid part of the sauce mash is 16.5±0.3 g / 100 mL; after 90 days of fermentation, the fermentation liquid is filtered out to obtain a soybean paste embryo with a low free tyrosine concentration, and the soybean paste is obtained after blending.

[0112] Comparative Example 2

[0113] The soybeans were washed, mixed with water at a ratio of 1:2.5 kg / L and soaked for 6 hours, and then steamed at a pressure of 0.08±0.1 MPa for 15±1 min; the cooked soybeans were mixed with flour at a weight ratio of 1:0.4, and koji essence was inoculated at a ratio of 0.5±0.1‰ of the total weight of the soybeans and flour, and then placed in a koji pool for 40 hours to obtain Daqu; salt water twice the total weight of the soybeans and flour was added to the Daqu, stirred evenly to obtain a sauce mash, which was then placed in a fermentation tank for fermentation. The salt content of the liquid part is 16.5±0.3g / 100mL; on the 45th day of fermentation, the fermentation liquid is released, and natural oil is added from above the mash layer and stirred to allow the natural oil to elute the free tyrosine in the mash layer; after the mash layer and the fermentation liquid are separated again, the above elution operation is repeated; elution is performed 3 times during the fermentation period, and the amount of natural oil used for each elution is twice the weight of the raw material; after 90 days of fermentation, the fermentation liquid is filtered out to obtain a soybean paste embryo with a low free tyrosine concentration, and the soybean paste is obtained after blending.

[0114] The physical and chemical indicators of the soybean paste embryos prepared in Example 5 and Comparative Examples 1-2 were tested, and the white spot situation after storage for 12 months (equivalent to the shelf life of soybean paste) was observed. The results are shown in Tables 8 and 9.

[0115] Table 8

[0116]

[0117] Table 9

[0118] sample After fermentation Storage for 12 months Example 5 No white spots No white spots appear Example 6 No white spots No white spots appear Comparative Example 1 White spots appear More white spots appear Comparative Example 2 No white spots A few white spots appear

[0119] For the soybean paste embryos of Example 5 and Comparative Example 1, 10 experienced appraisers were summoned to conduct sensory evaluation. The evaluation indicators of sensory evaluation include body, color, aroma, umami, sweetness, bitterness, saltiness, sourness and comprehensive taste, with a score of 0-4 points. The higher the score, the better the index. The sensory evaluation results are shown in Table 10. (Comprehensive taste refers to whether the overall taste and various flavors are soft and coordinated.) Table 10 Sensory evaluation results of soybean paste embryos brewed by different processes

[0120] sample posture Color aroma Umami sweetness Bitterness salty sour Overall taste Example 5 4 4 4 4 4 4 3 4 4 Comparative Example 1 4 3 2 2 4 4 3 2 3.5

[0121] The results in Table 10 show that the soybean paste obtained in the present invention received better evaluations in terms of aroma, umami, sourness, and overall taste. This demonstrates that the present invention improves the flavor of the soybean paste by replacing the fermentation broth with natural oil and continuing the fermentation process, as well as roasting the soybeans.

[0122] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing soybean paste by physical elution to reduce white spot precipitation, characterized in that: The following steps are involved: (1) Soybean pretreatment: roast the soybeans in a roasting machine until the soybean skins are cracked but the kernels are not cracked; (2) Material preparation: Wash and soak the roasted soybeans, then steam and cook them until cooked. After cooling, mix the cooked beans with flour and fungus to obtain a mixture. (3) Qu making: the mixture is placed in the Quchi for cultivation to obtain Daqu; (4) Fermentation: Add salt water to the Daqu and stir evenly to make the mash, which is then placed in a fermentation tank for fermentation. During the fermentation process, the solid matter in the mash floats up to form a mash layer, while the fermentation liquid sinks to the bottom. (5) Elution: In the late fermentation stage, specifically when the fermentation time is ≥40 days, the fermentation liquid is released, and then natural oil is added from above the mash layer to replace the fermentation liquid, so that it slowly penetrates into the mash layer from top to bottom, or the mash layer is directly stirred to elute the free tyrosine in the mash layer; then the fermentation is continued, and the mash layer and the fermentation liquid are separated again; The elution is carried out by self-elution or stirring; The self-rinsing method is to add natural oil from the top of the mash layer, wait for it to slowly penetrate into the mash layer from top to bottom, and elute the free tyrosine; The stirring method is to add natural oil to the mash layer and then stir it to make the free tyrosine content in the mash layer equal to the free tyrosine content in the fermentation liquid, so that when the mash layer rises again, the natural oil fermentation liquid will elute the higher content of free tyrosine in the mash layer; The natural oil is raw soy sauce, which refers to the crude oil obtained after the soy sauce fermentation is completed; the amount of natural oil used for each elution is 1.2 to 2.5 times the weight of the raw material; (6) Post-processing: After fermentation is completed, the fermentation liquid is released to obtain soybean paste embryo, which is then blended to obtain soybean paste.

2. The method for preparing soybean paste according to claim 1, wherein In step (5), the elution is performed once or more times; When multiple elutions are performed, the specific operations are as follows: ① Release the fermentation liquid first, ② Add natural oil from above the mash layer and allow it to slowly penetrate into the mash layer from top to bottom, or stir the mash layer directly so that the natural oil can elute the free tyrosine in the mash layer; ③Continue fermentation; ④ After the mash layer and natural oil are separated again, the first elution is completed; To perform elution for the second time or more, simply repeat steps ① to ④ above.

3. The method for preparing soybean paste according to claim 2, wherein In step (1), the temperature of roasting soybeans is 250-270° C., so that the soybean skins are cracked but the bean kernels are not cracked.

4. The method for preparing soybean paste according to claim 3, wherein The elution in step (5) was performed using a natural oil having a free tyrosine content of ≤50 mg / 100 g.

5. The method for preparing soybean paste according to claim 4, wherein: In step (2), the soaking time of soybeans is 5 to 10 hours, the weight volume ratio of soybeans to water is 1:2 to 2.5 kg / L; the weight ratio of soybeans to flour is 1:0.2 to 0.5, and the inoculation amount of the bacterial strain is 0.5±0.1‰ of the total weight of soybeans and flour.

6. The method for preparing soybean paste according to claim 5, wherein: In step (3), the Daqu culture time is 33 to 48 hours.

7. The method for preparing soybean paste according to claim 6, wherein In step (4), the amount of salt water added is 1.5 to 2.5 times the total weight of soybeans and flour, so that the salt content of the liquid part in the sauce mash is 16.5±0.3g / 100mL.

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