Ammonia-free fermented soybean and method for preparing the same

Abstract

The application provides a kind of ammonia-free fermented bean and a preparation method thereof, and belongs to the technical field of food.The fermented bean is mixed and stirred with edible oil, and then powder phospholipid is added and mixed and stirred, so that a deodorizing layer is formed on the surface of the fermented bean, and the odor substances released by the fermented bean are dissolved in the phospholipid in the surface layer, thereby realizing the elimination of the fermented odor of the fermented bean on the basis of maintaining the original nutritional components of the fermented bean, and also improving the functional activity of the fermented bean, which has good market competitiveness.

Description

Technical Field

[0001] This invention belongs to the field of food technology, specifically relating to an ammonia-free fermented soybean and its preparation method. Background Technology

[0002] Fermented soybeans are a type of fermented soybean product made by naturally fermenting high-protein legumes (mainly soybeans) at relatively high temperatures (37-45℃) using microorganisms (primarily Bacillus subtilis) in the natural environment. Fermented soybeans have a nearly thousand-year history of consumption in my country (they are also known as salted soybeans in northern Jiangsu). As a traditional local snack, their safety has been proven over time. After microbial fermentation, soybean protein is hydrolyzed into soybean polypeptides with broad physiological activity, while existing anti-nutritional factors are eliminated, thus improving both their nutritional value and biological activity. Traditional natural fermentation of soybeans in my country includes bacterial and mold-based methods; fermented soybeans belong to the bacterial type, while fermented black beans (douchi) belong to the mold type.

[0003] Safety, nutrition, and flavor are the three major standards Chinese people use for food. Fermented soybeans have been consumed in my country for nearly a thousand years (they are also called salted soybeans in northern Jiangsu). As a traditional snack, their safety has been proven over time. However, this safe and nutritious traditional snack has not been widely popularized in my country, mainly due to the distinctive ammonia odor of fermented soybeans.

[0004] The main flavor compounds in fermented soybeans include free ammonia, pyrazines, and branched-chain fatty acids. Among the pyrazines identified are 2,5-dimethylpyrazine, 2,3,5-trimethylpyrazine, 2,3,5,6-tetramethylpyrazine, and 2,3,5-methyl-6-ethylpyrazine, while branched-chain fatty acids include, but are not limited to, isobutyric acid, isovaleric acid, isohexanoic acid, 2-methylbutyric acid, and methyl isobutyrate. Of these flavor compounds, free ammonia is the main odorant, while branched-chain fatty acids are the main off-odorant; the two work synergistically to create the ammonia odor of fermented soybeans. For consumers accustomed to the ammonia odor of fermented soybeans, this odor is a major obstacle to their acceptance. Common deodorization methods for fermented soybeans include the following:

[0005] 1. Screening for proprietary strains: This involves screening for fermentation strains (Bacillus subtilis) that produce less odor during fermentation [Liu Yanmin et al., Food Science, 2020, 41(2):208-214.]. While this proprietary strain fermentation method can control the flavor of fermented beans, it inevitably comes at the cost of sacrificing the degree and quality of fermentation. The composition and content of nutrients and active ingredients in the fermented beans also differ from those of traditional fermentation. Furthermore, using proprietary strains requires production equipment, conditions, and an environment that can guarantee pure culture. This method is not suitable for the natural fermentation of traditional fermented beans.

[0006] 2. Adding other strains, that is, on the basis of the original Bacillus subtilis fermentation, by adding lactic acid bacteria, molds or yeasts, etc., to carry out secondary fermentation or compound fermentation, so as to improve the flavor (Yang Ye et al., China Brewing, 2019, 38(6):49-53; Lan Guangqun, Guizhou University, 2020; Gao Zexin et al., China Brewing, 2014, 33(9):49-52). However, this process has many problems, because lactic acid bacteria, molds or yeasts have different requirements for the nutritional components of the culture medium and the culture conditions compared with Bacillus subtilis. For example, lactic acid bacteria can only utilize lactose, while soybeans do not contain lactose. In order for lactic acid bacteria to grow well, it is necessary to add lactose to soybeans, which increases the complexity and cost of fermented soybean production. Once Bacillus subtilis forms a dominant bacteria in the early fermentation, it will inhibit the growth of subsequent strains (such as yeast or mold). The addition of microorganisms in the later stages requires a large inoculation volume to ensure successful secondary fermentation. Furthermore, the yeast or mold, during its growth, uses and consumes the original nutrients in the fermented beans (such as amino acids, bioactive peptides, and vitamins), thus altering or even destroying the beans' nutritional composition. Moreover, this process can only alter or mask the flavor; it cannot truly remove unpleasant odors.

[0007] 3. Adding seasonings to mask unpleasant flavors involves adding seasonings and spices to mitigate the unpleasant taste. Different seasonings can be added during fermentation, such as soaking soybeans in water with seasonings like Sichuan peppercorns, thirteen-spice powder, and curry powder, or adding salt, chili peppers, and fennel during the post-fermentation stage (Wu Xuejiao et al., Chinese Seasonings, 2018, 43(12):94-98). However, this method can only mask unpleasant flavors in the early stages of processing. As the fermented soybeans are left to sit for longer, the internal flavors, especially ammonia, are slowly released, and the odor will gradually become apparent.

[0008] Therefore, removing the ammonia odor from fermented soybeans has become a key point in promoting fermented soybeans. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide an ammonia-free fermented bean and its preparation method, which not only preserves the stability of the original nutrients of the fermented bean and enhances its functional activity, but also eliminates the fermented odor of the fermented bean, thus having strong market competitiveness.

[0010] The present invention provides an ammonia-free fermented soybean, comprising fermented soybean and an odor-removing layer coated on the surface of the fermented soybean; the raw materials of the odor-removing layer include edible oils and powdered phospholipids.

[0011] Preferably, the mass ratio of the edible oil to the powdered phospholipid is (1-10):1.

[0012] Preferably, the edible oils include one or more of the following: sesame oil, peanut oil, tea oil, sunflower seed oil, and olive oil.

[0013] Preferably, the mass ratio of the deodorizing layer to the fermented soybeans is (3-30):100.

[0014] Preferably, the method for preparing the fermented soybeans includes the following steps:

[0015] Soak soybeans in sequence, steam them, and then let them ferment naturally under the action of rice straw. After seasoning, fermented soybeans are obtained.

[0016] Preferably, the temperature of the natural fermentation is 30-40°C, and the time of the natural fermentation is 18-24 hours;

[0017] The method of natural fermentation under the action of straw is to spread the steamed soybeans flat on the straw in the fermentation box, spread a layer of straw on the steamed soybeans, and then spread another layer of steamed soybeans until the fermentation box is full.

[0018] Preferably, the moisture content of the fermented soybeans is 5 wt% to 18 wt%.

[0019] This invention provides a method for preparing ammonia-free fermented soybeans, comprising the following steps:

[0020] Mix fermented soybeans with edible oils, then add powdered phospholipids and mix again. Separate the fermented soybeans with powdered phospholipids on their surface to obtain ammonia-free fermented soybeans.

[0021] Preferably, the edible oil added accounts for 1% to 10% of the weight of the fermented soybeans;

[0022] The added powdered phospholipid accounts for 2% to 20% of the weight of the fermented soybeans.

[0023] The present invention provides ammonia-free fermented soybeans, comprising fermented soybeans and an odor-removing layer coating the surface of the fermented soybeans; the raw materials of the odor-removing layer include edible oils and powdered phospholipids. Free ammonia is the main odor-causing substance in fermented soybeans. By using raw materials with similar polarity and the principle of "like dissolves like," and by adding a powdered phospholipid / sesame oil system to coat the fermented soybeans, the free ammonia is adsorbed and dissolved in the system, achieving a dynamic balance between the release of odor-causing substances and the absorption of odor by phospholipids. Therefore, the ammonia-free fermented soybeans provided by the present invention maintain the stability of the original nutritional components of the fermented soybeans and effectively eliminate the fermented odor. Experiments show that the free ammonia content of the ammonia-free fermented soybeans provided by the present invention is only 15-25 mg / kg, which is 7-13 times lower than that obtained by traditional methods. Sensory evaluation results show that the ammonia-free fermented soybeans have a significant taste advantage and are welcomed by consumers. At the same time, the ammonia-free fermented soybeans provided by the present invention have a good effect on enhancing their antioxidant activity. Therefore, the fermented soybeans provided by the present invention effectively solve the ammonia odor problem of traditional fermented soybeans and improve their biological activity, giving them strong market competitiveness.

[0024] The present invention provides a method for preparing ammonia-free fermented soybeans, comprising the following steps: mixing fermented soybeans and edible oils, then adding powdered phospholipids and mixing again, separating the fermented soybeans with powdered phospholipids adhering to their surface, and obtaining ammonia-free fermented soybeans. The present invention involves coating the surface of fermented soybeans with a powdered phospholipid / sesame oil system, which is simple, easy to perform, and highly practical and reproducible. Detailed Implementation

[0025] The present invention provides an ammonia-free fermented soybean, comprising fermented soybean and an odor-removing layer coated on the surface of the fermented soybean; the raw materials of the odor-removing layer include edible oils and powdered phospholipids.

[0026] In this invention, the preferred mass ratio of the edible oil to the powdered phospholipid is (1-10):1, more preferably 2-5:1, and most preferably 3:1. The edible oil preferably includes one or more of the following: sesame oil, peanut oil, tea oil, sunflower seed oil, and olive oil. The function of the edible oil is to form a film on the surface of the fermented soybeans, facilitating the subsequent adhesion of the powdered phospholipid. The powdered phospholipid conforms to the national food safety standard GB 28401-2012, "Food Additives Phospholipids." The powdered phospholipid adheres to the surface of the fermented soybeans through the edible oil. By controlling the amount of powdered phospholipid added, a dynamic balance is achieved between the release of odorous substances and the absorption of the powdered phospholipid, thereby eliminating the fermented odor of the soybeans. The preferred mass ratio of the deodorizing layer to the fermented soybeans is (3-30):100, more preferably 3-10:100, and most preferably 10:100.

[0027] This invention does not impose any particular limitation on the preparation method of fermented soybeans; any fermented soybean preparation method well-known in the art can be used. In the embodiments of this invention, the preparation method of the fermented soybeans preferably includes the following steps:

[0028] Soak soybeans one by one, then steam and boil them. The soybeans are then naturally fermented under the action of rice straw, and seasoned to obtain fermented soybeans.

[0029] In this invention, the soybeans are preferably plump, uniform in size and color, and free from spots, damage, and insect holes. The soybeans are preferably washed before soaking. This invention does not have any particular limitation on the soybean variety; any soybean variety well-known in the art can be used. The soybeans are soaked in three times their weight of water for 6–8 hours, changing the water 1–3 times during this period. After soaking, any peeled, damaged, or unsoaked soybeans are removed. The cooking temperature is 100°C. The cooking time is preferably 30–60 minutes, more preferably 40–50 minutes, and most preferably 45 minutes.

[0030] In this invention, the natural fermentation method using rice straw involves spreading the steamed soybeans evenly on rice straw placed in a fermentation box, then spreading a layer of rice straw on top of the steamed soybeans, followed by another layer of steamed soybeans, until the fermentation box is full. In this invention, the fermentation box is preferably sterilized. The rice straw is preferably blanched. The blanching method is preferably blanching in boiling water for 1-2 minutes. The purpose of blanching is to kill miscellaneous bacteria on the rice straw. The Bacillus subtilis spores produced by the fermentation bacteria on the rice straw are heat-resistant; during the blanching process, the Bacillus subtilis spores can survive and germinate, grow, and ferment the soybeans in the later fermentation process. The thickness of the rice straw layer is preferably 2-3 cm, more preferably 2.5 cm. The thickness of the steamed soybeans is preferably 4-8 cm, more preferably 5-7 cm, and most preferably 6 cm. In each fermentation box, the mass ratio of steamed soybeans to rice straw is preferably 18-22:1, more preferably 20:1. The preferred temperature for natural fermentation is 30–40°C, more preferably 35–38°C, and most preferably 37°C. The preferred fermentation time is 18–24 hours, more preferably 20–23 hours, and most preferably 22 hours.

[0031] After the natural fermentation is completed, the obtained soybeans are seasoned. The seasonings include the following components in parts by weight: 0.15-0.25 parts salt, 0.35-0.45 parts chili pepper, more preferably 0.2 parts salt and 0.4 parts chili powder. After seasoning, it is preferable to remove moisture from the seasoned soybeans. The method for removing moisture preferably includes drying, sterilization, and dehydration. The drying temperature is preferably 55-75°C, more preferably 60-70°C, and more preferably 65°C. The drying time is 2-4 hours, more preferably 3 hours. The sterilization and dehydration method is preferably microwave treatment. The microwave power of the microwave treatment is preferably 100-300W, more preferably 150-250W, and most preferably 200W. The microwave treatment time is preferably 3-5 minutes, more preferably 4 minutes. The moisture content of the fermented soybeans is preferably 5wt%-18wt%, more preferably 8wt%-15wt%, 10wt%-13wt%, and most preferably 12wt%. Controlling the moisture content of the fermented soybeans is beneficial for the subsequent oil coating process, improving the adhesion of the oil to the surface of the soybeans. Experiments show that if the moisture content of the fermented soybeans is too high, it is not conducive to the later oil coating process, as the oil and water do not mix. On the other hand, if the moisture content of the fermented soybeans is too low, they become hard and difficult to chew, affecting the taste.

[0032] This invention provides a method for preparing ammonia-free fermented soybeans, comprising the following steps:

[0033] Mix fermented soybeans and edible oils, then add powdered phospholipids and mix again. Separate the fermented soybeans with powdered phospholipids on their surface to obtain ammonia-free fermented soybeans.

[0034] In this invention, the edible oil added preferably accounts for 1% to 10% of the weight of the fermented soybeans, more preferably 2% to 8%, further preferably 4% to 6%, and most preferably 5%. The powdered phospholipid added preferably accounts for 2% to 20% of the weight of the fermented soybeans, more preferably 5% to 15%, further preferably 8% to 12%, and most preferably 10%. The mixing order in this invention cannot be changed. Only by mixing the edible oil with the fermented soybeans first, so that the edible oil adheres to the surface of the fermented soybeans, can the coating rate of the powdered phospholipid be improved, thereby achieving the purpose of removing the odor emitted by the fermented soybeans.

[0035] In this invention, obtaining ammonia-free fermented beans preferably also includes repackaging. The repackaging is preferably carried out in a sterile environment. The preferred specifications for the ammonia-free fermented beans are 50g to 200g per bag.

[0036] In this invention, to verify the odor-removing effect of the fermented beans prepared by the method of this invention, the main odor-causing substance, free ammonia, was detected and sensory evaluated. The results showed that the free ammonia content was only 15-25 mg / kg, while the free ammonia content of fermented beans prepared by traditional methods was as high as 105-185 mg / kg. Simultaneously, the sensory evaluation score was 25-28 points (out of 30), while the sensory evaluation score of fermented beans prepared by traditional methods was 11-13 points. It is evident that the ammonia-free fermented beans prepared by this invention have a significant advantage in removing ammonia odor. Furthermore, the bioactivity of the fermented beans was tested. The total antioxidant value of the ammonia-free fermented beans prepared by this invention was 1.7-2.1 (with vitamin C as a reference), while the species antioxidant value of fermented beans prepared by traditional methods was 0.6-0.8 (with vitamin C as a reference). This demonstrates that the ammonia-free fermented beans prepared by this invention can improve their bioactivity.

[0037] The following detailed description, in conjunction with embodiments, illustrates an ammonia-free fermented soybean and its preparation method provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1

[0039] A method for preparing ammonia-free fermented soybeans

[0040] 1. Select 120 kg of plump, uniformly sized Northeast soybeans. Remove any beans or cotyledons that are discolored, have obvious spots, are broken, or have insect holes. Soak the soybeans in 360 kg of water for 8 hours, changing the water once during this period. After soaking, further remove any peeled, broken, or unsoaked beans. Clean the beans thoroughly and then steam them in a steamer for 60 minutes.

[0041] 2. Let the steamed soybeans cool to 40℃, then divide them into 20 kg boxes and put them into sterilized fermentation boxes. Lay out straw that has been blanched in hot water, then lay a layer of straw (2 cm thick) and a layer of soybeans (3 cm thick). The total amount of straw used is 1 kg.

[0042] 3. Place the fermentation box in a 37℃ constant temperature incubator for 24 hours.

[0043] 4. After fermentation is complete, remove the fermentation box, remove the straw, take out the fermented beans, and add seasonings (total amount of salt 1.2 kg, total amount of chili powder 2.4 kg, of which each box contains 0.2 kg of salt and 0.4 kg of chili powder) and mix them together.

[0044] 5. After seasoning, dry the seasoned fermented beans with infrared hot air (60℃) for 1 hour, and then further sterilize and dehydrate them with microwave to bring the moisture content to about 12%.

[0045] 6. Mix the sterilized and dehydrated fermented soybeans with sesame oil, stirring to ensure the sesame oil evenly coats the soybeans. The total amount of sesame oil used is 9 kg.

[0046] 7. After the fermented soybeans and sesame oil are evenly mixed, add the powdered lecithin and stir thoroughly to ensure the lecithin adheres evenly to the surface of the fermented soybeans. The total amount of lecithin used is 3 kg.

[0047] 8. The prepared fermented beans are packaged and vacuum-sealed to obtain ammonia-free fermented bean products.

[0048] Note: All operations must be performed in a sterile environment.

[0049] Example 2

[0050] A method for preparing ammonia-free fermented soybeans

[0051] 1. Select 100 kg of plump, uniformly sized Northeast soybeans. Remove any beans or cotyledons that are discolored, have obvious spots, are broken, or have insect holes. Soak the soybeans in 300 kg of water for 8 hours, changing the water once during this time. After soaking, further remove any peeled, broken, or unsoaked beans. Clean the beans thoroughly and then steam them in a steamer for 40 minutes.

[0052] 2. Let the steamed soybeans cool to 40℃, then divide them into 20 kg boxes and put them into sterilized fermentation boxes. Lay out layers of straw that have been blanched in hot water, then add a layer of soybeans. The total amount of straw used is 0.8 kg.

[0053] 3. Place the fermentation box in a 35℃ constant temperature incubator for 36 hours.

[0054] 4. After fermentation is complete, remove the fermentation box, remove the straw, take out the fermented beans, and add seasonings (total amount of 1 kg of salt and 2 kg of chili powder, of which each box contains 0.2 kg of salt and 0.4 kg of chili powder) to season.

[0055] 5. After seasoning, the product is dried with infrared hot air (50℃) for 1.5 hours, and then further sterilized and dehydrated by microwave to achieve a moisture content of about 6%.

[0056] 6. Mix the sterilized and dehydrated fermented soybeans with sesame oil, stirring to ensure the sesame oil evenly coats the soybeans. The total amount of sesame oil used is 8 kg.

[0057] 7. After the fermented soybeans and sesame oil are evenly mixed, add the powdered lecithin and stir thoroughly to ensure the lecithin adheres evenly to the surface of the fermented soybeans. The total amount of lecithin used is 4 kg.

[0058] 8. Divide the prepared fermented beans into portions and vacuum pack them.

[0059] Simultaneously, soybeans are naturally fermented according to this method to prepare fermented soybeans, without subsequent addition of sesame oil and phospholipid coating, as a traditional method.

[0060] Example 3

[0061] Production of ammonia-free fermented soybeans

[0062] 1. Select 80 kg of plump, uniformly sized Northeast soybeans. Remove any beans or cotyledons that are discolored, have obvious spots, are broken, or have insect holes. Soak the soybeans in 240 kg of water for 8 hours, changing the water once during this time. After soaking, further remove any peeled, broken, or unsoaked beans. Clean the beans thoroughly and then steam them in a steamer for 35 minutes.

[0063] 2. Let the steamed soybeans cool to 45℃, then divide them into 20 kg boxes and put them into sterilized fermentation boxes. Lay out layers of straw that have been blanched in hot water, then add a layer of soybeans. The total amount of straw used is 1 kg.

[0064] 3. Place the fermentation box in a 30℃ constant temperature incubator for 48 hours.

[0065] 4. After fermentation is complete, remove the fermentation box, remove the straw, take out the fermented beans, and add seasonings (total amount of salt 1.2 kg, total amount of chili powder 2.4 kg, of which each box contains 0.3 kg of salt and 0.6 kg of chili powder) to season.

[0066] 5. After seasoning, the product is dried with infrared hot air (70℃) for 1 hour, and then further sterilized and dehydrated by microwave to achieve a moisture content of about 8%.

[0067] 6. Mix the sterilized and dehydrated fermented soybeans with peanut oil, stirring to ensure the peanut oil evenly coats the soybeans. The total amount of peanut oil used is 8 kg.

[0068] 7. After the fermented soybeans and peanut oil are evenly mixed, add the powdered lecithin and stir thoroughly to ensure the lecithin adheres evenly to the surface of the fermented soybeans. The total amount of lecithin used is 8 kg.

[0069] 8. Divide the prepared fermented beans into portions and vacuum pack them.

[0070] Simultaneously, soybeans are naturally fermented according to this method to prepare fermented soybeans, without subsequent addition of sesame oil or phospholipid coating.

[0071] Comparative Example 1

[0072] Fermented soybeans were prepared by naturally fermenting soybeans according to the method in Example 1, without subsequent addition of sesame oil and phospholipid coating.

[0073] Comparative Example 2

[0074] Ammonia-free fermented soybeans were prepared according to the method in Example 1, except that sesame oil was replaced with ethanol (30% labeled concentration).

[0075] Comparative Example 3

[0076] Ammonia-free fermented soybeans were prepared according to the method in Example 1, except that sesame oil was replaced with acetic acid (5% labeled concentration).

[0077] Comparative Example 4

[0078] Ammonia-free fermented soybeans were prepared according to the method in Example 1, except that animal fats were used instead of powdered phospholipids.

[0079] Comparative Example 5

[0080] Ammonia-free fermented soybeans were prepared according to the method in Example 1, except that fish oil was used instead of powdered phospholipids.

[0081] Comparative Example 6

[0082] Ammonia-free fermented soybeans were prepared according to the method in Example 1, except that sesame oil and powdered phospholipids were mixed with the fermented soybeans to prepare ammonia-free fermented soybeans.

[0083] Example 4

[0084] Method for determining free ammonia in fermented soybeans

[0085] Free ammonia is the main odor-causing substance in fermented soybeans. By measuring the free ammonia in the product, the degree of odor removal in fermented soybeans prepared by different processes can be objectively determined. The determination of free ammonia is carried out according to the national standard (GB / T5009.44-2003) using the volatile basic nitrogen method, and the removal rate of free ammonia is calculated according to Formula I.

[0086] Free ammonia removal rate (%) = (Free ammonia content in fermented beans prepared by traditional process - Free ammonia content measured in the treatment group) / Free ammonia content in fermented beans prepared by traditional process × 100% Formula I

[0087] The fermented soybeans prepared using traditional methods are made through natural fermentation and are not subsequently treated with added sesame oil or phospholipids.

[0088] The results are shown in Table 1.

[0089] Table 1. Free ammonia content in fermented soybeans prepared by different processes

[0090] Processing group Free ammonia content (mg / kg) Removal rate (%) Example 1 15±1 85.7 Example 2 20±2 80.1 Example 3 25±2 76.2 Comparative Example 1 105±5 - Comparative Example 2 85±4 19 Comparative Example 3 70±3 33.3 Comparative Example 4 75±4 28.6 Comparative Example 5 75±3 28.6 Comparative Example 6 50±2 52.4

[0091] The results above show that the free ammonia content in the ammonia-free fermented soybeans prepared by the present invention is only one-ninth of the free ammonia content in the fermented soybeans prepared by the traditional process (Comparative Example 1), indicating that the method of the present invention can greatly remove the odor from the fermented soybeans.

[0092] Example 5

[0093] Sensory evaluation of fermented soybeans prepared by different methods

[0094] A sensory evaluation panel of twelve members was formed, consisting of six men and six women. Among the men, two were aged 16-26, two were aged 26-36, and two were aged 36-56. Among the women, two were aged 16-26, two were aged 26-36, and two were aged 36-56. Three of the men were R&D personnel (graduates of food science) and three were ordinary consumers. Two of the women were R&D personnel (graduates of food science) and four were ordinary consumers. Sensory evaluations of the color, aroma, and taste of the fermented soybeans were conducted according to the scoring criteria in Table 2. Specific results are shown in Table 2, and the sensory quality evaluation criteria are shown in Table 2 below (total score 30 points). The highest and lowest scores were discarded, and the average score of the remaining ten participants was taken.

[0095] Table 2 Sensory Evaluation Scoring Criteria

[0096]

[0097] The sensory evaluation results are shown in Table 3.

[0098] Table 3 Sensory evaluation results

[0099] Processing group Sensory evaluation score Example 1 28 Example 2 27 Example 3 26 Comparative Example 1 12 Comparative Example 2 15 Comparative Example 3 13 Comparative Example 4 18 Comparative Example 5 20 Comparative Example 6 22

[0100] The results above show that the ammonia-free fermented beans prepared by the method provided by the present invention have a significantly higher sensory score than those prepared by traditional processes, indicating that the ammonia-free fermented beans provided by the present invention are more likely to be favored by consumers.

[0101] Example 6

[0102] Antioxidant activity assay method

[0103] The antioxidant activity of fermented soybeans prepared by different methods was determined using the TRAP (total peroxyl radical-trapping antioxidant parameter assay). The principle is that ABTS is used as a chromogenic agent. Under the action of hydrogen peroxide initiator AAPH, ABTS free radicals are quantitatively generated. The reaction mixture is blue and exhibits strong absorption at 734 nm. After the antioxidants react with the free radicals, the color of the reaction mixture lightens, and the absorbance at 734 nm decreases. The free radical scavenging effect can be measured colorimetrically to evaluate the antioxidant capacity. Vitamin C was used as a standard reference to quantitatively determine the total antioxidant value. The rate of increase in antioxidant activity of the fermented soybeans was calculated according to Formula II.

[0104] Antioxidant activity enhancement rate (%) = (Antioxidant activity results in fermented beans prepared by different methods - Antioxidant activity results in fermented beans prepared by traditional methods) / Antioxidant activity results in fermented beans prepared by traditional methods × 100% Formula II

[0105] The test results are shown in Table 4.

[0106] Table 4 Results of Antioxidant Activity Detection

[0107] Processing group Increase in antioxidant activity (%) Example 1 240 Example 2 220 Example 3 200 Comparative Example 1 0 Comparative Example 2 0 Comparative Example 3 -10 Comparative Example 4 -20 Comparative Example 5 80 Comparative Example 6 160

[0108] The results above show that the antioxidant activity of the ammonia-free fermented soybeans prepared by this invention is more than twice that of fermented soybeans prepared by traditional methods. This indicates that the preparation process provided by this invention can not only remove the odor from fermented soybeans but also improve their bioactivity. The reason for this may be that phospholipids themselves have antioxidant and blood vessel softening functions.

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ammonia-free fermented soybeans, characterized in that, The ammonia-free fermented soybeans consist of fermented soybeans and an odor-removing layer coating the surface of the fermented soybeans; the odor-removing layer is made of edible oils and powdered phospholipids. The process includes the following steps: mixing fermented soybeans and edible oils, then adding powdered phospholipids and mixing again, separating the fermented soybeans with powdered phospholipids adhering to their surface to obtain ammonia-free fermented soybeans; The mass ratio of the edible oils to the powdered phospholipids is (1~10):1; The mass ratio of the deodorizing layer to the fermented soybeans is (3~30):

100.

2. The preparation method according to claim 1, characterized in that, The amount of edible oil added accounts for 1% to 10% of the weight of the fermented soybeans; The added powdered phospholipids account for 2% to 20% of the weight of the fermented soybeans.

3. The preparation method according to claim 1, characterized in that, The edible oils include one or more of the following: sesame oil, peanut oil, tea oil, sunflower seed oil, and olive oil.

4. The preparation method according to claim 1, characterized in that, The powdered phospholipids include soybean lecithin.

5. The preparation method according to claim 1, characterized in that, The method for preparing fermented soybeans includes the following steps: soaking soybeans in sequence, steaming and boiling them, allowing the steamed soybeans to ferment naturally under the action of rice straw, and then seasoning them to obtain fermented soybeans.

6. The preparation method according to claim 5, characterized in that, The temperature for natural fermentation is 30~40℃, and the time for natural fermentation is 18~48h; The method of natural fermentation under the action of straw is to spread the steamed soybeans flat on the straw in the fermentation box, spread a layer of straw on the steamed soybeans, and then spread another layer of steamed soybeans until the fermentation box is full.

7. The preparation method according to claim 5 or 6, characterized in that, The moisture content of the fermented beans is 5wt% to 18wt%.

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