A method to improve the quality and safety of fermented bean curd

Abstract

This invention discloses a method for improving the quality and food safety of fermented bean curd: Soybeans are soaked and ground to obtain a slurry. After boiling, fermented swill is added for coagulation, followed by initial filtration to obtain fermented bean curd flakes and swill. The fermented bean curd flakes are then mixed with a powder composed of transglutaminase and salt. After pressing and shaping, fermented bean curd blanks are obtained. The bean curd blanks are sprayed with *Mucor* dispersed in the fermented swill and fermented. The fermented bean curd blanks are then salted to obtain salted bean curd blanks, which are then further cured to obtain the finished product. The fermentation broth obtained by this invention has a significant inhibitory effect on *E. coli*. It can inhibit the proliferation of exogenously contaminated *E. coli* during the fermentation of bean curd blanks, thereby avoiding food safety risks caused by *E. coli*. Furthermore, the transglutaminase, uniformly dispersed in the fermented bean curd flakes, dissolves in water under the action of salt and catalyzes the interaction of proteins in the fermented bean curd flakes to form amide bonds, improving the quality of the bean curd blanks.

Description

Technical Field

[0001] This invention relates to the production process of fermented bean curd, and more particularly to a method for improving the quality and safety of fermented bean curd. Background Technology

[0002] Fermented bean curd is a traditional fermented soybean condiment made from traditional food molds such as Mucor or Rhizopus. It is a delicious, uniquely flavorful, delicately textured, and nutritious side dish. Legend has it that fermented bean curd has been brewed for over 1000 years, but detailed records of its production method appear more than 400 years ago in the Ming Dynasty book *Penglong Yehua* written by Li Rihua. Currently, there are many varieties of fermented bean curd in my country, including red, white, green, and soy-sauce-flavored varieties, but their production processes are largely the same. However, due to the traditional nature of fermented bean curd production, modern production processes involve many manual operations that are difficult to mechanize, non-sterile fermentation processes, and susceptibility to environmental microbial contamination. These factors often lead to unstable product quality, a high rate of gas and juice leakage caused by microorganisms, and significant food safety risks.

[0003] Current research on fermented bean curd production processes and technologies largely focuses on preparation techniques and the use of new microbial strains to prepare new fermented bean curd products. For example, Chinese invention patent CN 113142492 A (patent title: A Production Process and Fermented Bean Curd Powder) uses a mixed strain of *Mucor* and *Rhizopus* to ferment the fermented bean curd under multiple stages and different conditions to improve the product's flavor and aroma, and uses this as the main ingredient to prepare fermented bean curd powder. Another example is Chinese invention patent CN110540942 A (patent title: *Mucor rhodotorulata* and its Application in the Production of Green Fermented Bean Curd), which uses a new *Mucor* strain isolated from a fermented bean curd production workshop for fermentation in the production of green fermented bean curd, and inoculates it with *Pediococcus halophilus*, *Staphylococcus aureus*, and *Staphylococcus pasteurellus* for post-fermentation, obtaining a product with a unique flavor and rich taste.

[0004] However, given the susceptibility of fermented bean curd production to external microbial contamination, no research has been reported on controlling such contamination and improving product safety. Furthermore, during the post-fermentation process, the fermentation of fermented bean curd blocks by proteases and Mucor microorganisms in the pickling solution can cause them to gradually soften, even leading to texture problems such as mushyness, chipped corners, and missing edges. No technology has been reported to improve these textures and quality. Summary of the Invention

[0005] To overcome the challenges of contamination by environmental microorganisms, especially E. coli, during the production of fermented bean curd due to the extensive manual operations and the relatively open environment during fermentation and pickling, and to improve the texture and structure of the fermented bean curd blocks and avoid quality problems such as softness, missing edges, and missing corners, this invention provides a method for improving the quality and safety of fermented bean curd.

[0006] This invention utilizes the inhibitory effect of Lactobacillus reuteri on Escherichia coli in the fermentation broth obtained from the reuse of yellow swill discharged during production, combined with the catalytic linkage effect of TG enzyme, to improve the texture and structure of fermented bean curd blocks, thereby avoiding quality problems such as softness, missing edges and corners, and overcoming the high risk of environmental Escherichia coli contamination.

[0007] This invention is achieved through the following technical solution:

[0008] A method for improving the quality and safety of fermented bean curd includes the following steps:

[0009] Soybeans are soaked, ground, boiled, coagulated, and initially filtered to obtain soybean curd. The soybean curd is mixed with a certain proportion of powder, then pressed, cut into blocks, and arranged to obtain fermented bean curd blocks. An inoculation solution made by dispersing Rhizopus spores in the fermentation liquid is sprayed onto the fermented bean curd blocks, and the blocks are cultured and fermented in a fermentation room until the Rhizopus mycelium covers the fermented bean curd blocks. The salted fermented bean curd blocks are then mixed with a pickling solution prepared by dissolving baijiu and salt in the fermentation liquid in a certain proportion and packaged in a packaging container for post-fermentation. Once the post-fermentation is complete, the product is ready.

[0010] The soaking process involves soaking soybeans in water at a temperature of 40±1℃ for 6±0.5 hours, after which the soybeans increase in weight by 1.5 times.

[0011] The grinding process involves adding water to soaked soybeans and processing them through a grinding machine to obtain soy milk with a concentration of 7±1 degrees.

[0012] The process of boiling the soy milk involves heating the soy milk to a boil and maintaining that boil for 5 minutes.

[0013] The aforementioned slurry addition involves adding fermentation liquid to a slurry at a temperature not lower than 85°C, with a slurry-to-fermentation liquid ratio of 4:1.

[0014] The initial filtration involves filtering the slurry material through an 80-120 mesh filter to obtain slurry residue, which is called slurry flakes, and the discharged filtrate is called yellow swill.

[0015] The mixing process involves uniformly mixing slurry and mixed powder at a weight ratio of 15-20:1, and the mixed powder is made by uniformly mixing salt and transglutaminase at a weight ratio of 8-6:1.

[0016] The pressing process involves placing the well-mixed pulp material into a pressing device, applying a pressure of 2.0±0.5MPa for 2.5±0.5 hours, and obtaining a material with a moisture content of 68%±2%.

[0017] The aforementioned slicing and arranging involves dividing the pressed material into blocks according to specified dimensions and arranging them as required to obtain fermented bean curd blanks.

[0018] The inoculation process involves uniformly spraying an inoculation solution onto the surface of the fermented bean curd cake, with the amount of inoculation solution being 1.5% to 4.5% (w / w) of the weight of the fermented bean curd cake.

[0019] The fermentation process involves placing the inoculated fermented bean curd blanks in a fermentation chamber and fermenting them for 32±1 hours at a temperature of 24±2℃ and a relative humidity of not less than 90%, to obtain fermented bean curd blanks wrapped with Mucor mycelia.

[0020] The salting process involves sprinkling salt onto the fermented fermented bean curd blocks, with a salt-to-fermented bean curd block weight ratio of 1:12, and salting for 12±1 hours. Then, brine with a salt content of 22%±1% (w / w) is added to submerge the fermented bean curd blocks, and the pickling time is 3±1 hours. After draining the brine, the salted fermented bean curd blocks are obtained.

[0021] The packaging involves placing the fermented bean curd pieces in a packaging container, then pouring in the pickling liquid to submerge the fermented bean curd pieces. The weight ratio of the fermented bean curd pieces to the pickling liquid is 3:2, and then the container is sealed.

[0022] The post-fermentation process involves placing the packaged fermented bean curd at a temperature of 30±2℃ until the amino acid nitrogen content of the pickling liquid is greater than 0.3g / 100mL, at which point the post-fermentation is complete.

[0023] The fermentation broth is made by using yellow swill discharged from the initial filtration as the main raw material, adding white sugar and F55 fructose syrup according to the formula, and then adding Lactobacillus reuteri for fermentation after sterilization and cooling.

[0024] The culture medium for the fermentation broth has the following raw material composition by weight percentage:

[0025] Yellow swill: 88% ~ 92% (w / w)

[0026] White sugar: 6% ~ 8% (w / w)

[0027] F55 high-fructose corn syrup: 2%–4% (w / w)

[0028] The inoculum size of *Lactobacillus reuteri* is 2–5 × 10⁻⁵. 6 CFU / mL (based on culture medium volume).

[0029] The culture medium for the fermentation broth was sterilized at 93±2℃ for 20 minutes, then cooled to 37±1℃ and inoculated with Lactobacillus reuteri, and fermented at 37±1℃ for 12 hours.

[0030] The prepared fermentation broth had a pH of 4.0±0.2 and a total acid content of 1.8±0.3 g / 100 mL (calculated as lactic acid). It showed a significant inhibitory effect on Escherichia coli, which was verified by the inhibition zone test method, requiring the inhibition zone diameter to be greater than 15 mm.

[0031] The inoculum consists of *Rhizopus* spores dispersed in the fermentation broth prepared using *Lactobacillus reuteri*. The fermentation broth is boiled and maintained at boiling for 5 minutes, then cooled to room temperature before being thoroughly mixed with the *Rhizopus* spores. The mixture is then filtered through a 40-mesh sieve to obtain a spore count between 1 and 5 × 10⁻⁶ spores per milliliter. 7 Bacterial suspension.

[0032] The preparation process of the pickling liquid is as follows: salt and liquor are dissolved in the fermentation liquid prepared by Lactobacillus reuteri to obtain a solution with a salt content of 4.5% ± 0.5% (w / w) and an alcohol content of 16% ± 2% (v / v). The solution is stirred and heated to boiling and kept at a gentle boil for 10 minutes, and then cooled to below 30°C.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] The yellow swill discharged during the production of fermented bean curd is a soybean solution containing high levels of carbon and nitrogen nutrients. Direct discharge of this solution would increase the pressure on wastewater treatment. Instead, it can be fermented and reused as a fermentation liquid in the production of fermented bean curd. Furthermore, based on the fermentation of yellow swill with added white sugar and F55 fructose syrup using Lactobacillus reuteri, a flavorful fermentation liquid with a pH of 4.0±0.2, a total acid content of 1.8±0.3g / 100mL (calculated as lactic acid), and the ability to inhibit the growth and reproduction of E. coli can be recycled back into the production of fermented bean curd. This not only improves the flavor and quality of the fermented bean curd pickling liquid but also further enhances the safety of the fermented bean curd, reducing the food safety risks posed by E. coli. Ultimately, it also reduces the pressure on wastewater treatment and improves resource utilization.

[0035] In addition, during the preparation of fermented bean curd blocks, a mixture of TG enzyme and salt powder is added to the fermented soybean curd. During pressing, dividing, arranging, inoculation and fermentation, an appropriate amount of salt promotes the dissolution of TG enzyme, thereby playing a catalytic role. This causes the amino acid residues containing amino and carboxyl groups that make up the soybean protein to form amide bonds, which improves the hardness, elasticity and bonding strength of the fermented bean curd blocks, thereby improving its texture and structure. This can enhance the fermented bean curd blocks' resistance to the texture damage caused by salt penetration and protease hydrolysis during pickling and post-ripening, ensuring the softness, hardness and integrity of the fermented bean curd blocks, and avoiding quality problems such as soft texture, missing edges and corners. Attached Figure Description

[0036] Figure 1 This invention provides a process flow diagram of a production technology that effectively improves the quality and safety of fermented bean curd.

[0037] Figure 2 This is a comparison diagram of the texture and structure of the sample produced in Example 3 and the sample produced in a conventional manner. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to specific embodiments.

[0039] Example 1:

[0040] A method for improving the quality and safety of fermented bean curd includes the following steps:

[0041] (1) Soaking: Soak soybeans in water at a temperature of 40±1℃ for 6±0.5 hours. After soaking, the soybeans increase in weight by 1.5 times.

[0042] (2) Grinding: Soaked soybeans are added to water and processed through a grinding machine to obtain soy milk with a concentration of 7±1 degrees.

[0043] (3) Boiling the soy milk: Heat the soy milk to a boil and keep it boiling for 5 minutes.

[0044] (4) Adding fermentation liquid to the slurry at a temperature not lower than 85℃, with the ratio of slurry to fermentation liquid being 4:1.

[0045] (5) Primary filtration: The material after slurrying is filtered through an 80-120 mesh filter screen to obtain slurry residue as slurry flakes and filtrate as yellow swill.

[0046] (6) Mixing: The mixture of slurry and mixed powder is made by mixing salt and transglutaminase in a weight ratio of 20:1.

[0047] (7) Pressing: Place the well mixed pulp material in the pressing equipment, apply a pressure of 2.0±0.5MPa for 2.5±0.5 hours, and obtain a material with a moisture content of 68%±2%.

[0048] (8) Dividing and arranging the pressed material into blocks according to the specified size and arranging them as required to obtain fermented bean curd blanks.

[0049] (9) Inoculation: The inoculation solution is evenly sprayed onto the surface of the fermented bean curd cake. The amount of inoculation solution sprayed is 1.5% (w / w) of the weight of the fermented bean curd cake. The preparation of the inoculation solution involves first boiling the fermentation broth and maintaining the boiling state for 5 minutes, then cooling it to room temperature before dispersing and mixing it evenly with the Rhizopus spores. The mixture is then filtered through a 40-mesh sieve to obtain a spore count of 5 × 10⁶ spores per milliliter. 7 Bacterial suspension.

[0050] (10) Fermentation: The inoculated fermented bean curd blanks are placed in a fermentation chamber and fermented for 32±1 hours at a temperature of 24±2℃ and a relative humidity of not less than 90% to obtain fermented bean curd blanks wrapped by Mucor mycelium.

[0051] (11) Salting: Sprinkle salt on the fermented fermented bean curd blanks. The weight ratio of salt to fermented bean curd blanks is 1:12. The salting time is 12±1 hours. Then add brine with a salt content of 22%±1% (w / w) to submerge the fermented bean curd blanks. The pickling time is 3±1 hours. Drain the brine to obtain salted fermented bean curd blanks.

[0052] (12) Packaging: Place the fermented bean curd pieces in a packaging container, then pour in the pickling liquid to submerge the fermented bean curd pieces. The weight ratio of fermented bean curd pieces to pickling liquid is 3:2. Then seal the container. Preparation of pickling liquid: Dissolve salt and white wine in the fermentation liquid prepared using Lactobacillus reuteri to obtain a solution with a salt content of 4.5% ± 0.5% (w / w) and an alcohol content of 16% ± 2% (v / v). Stir and heat to boiling and maintain a gentle boil for 10 minutes, then cool to below 30°C.

[0053] (13) Post-fermentation: The packaged fermented bean curd blanks are placed at a temperature of 30±2℃ until the amino acid nitrogen content of the pickling liquid is greater than 0.3g / 100mL, then the post-fermentation is completed.

[0054] (14) Preparation of fermentation broth: Using the yellow swill discharged from the primary filtration as the main raw material, white sugar and F55 fructose syrup are added according to the formula. After sterilization and cooling, Lactobacillus reuteri is added for fermentation. The prepared fermentation broth is reserved for the next batch of fermented bean curd production.

[0055] The fermentation broth culture medium, by weight percentage, consists of the following raw materials:

[0056] Yellow swill: 88% (w / w)

[0057] White sugar: 8% (w / w)

[0058] F55 high-fructose corn syrup: 4% (w / w)

[0059] The inoculum size of *Lactobacillus reuteri* was 2 × 10⁻⁶ 6 CFU / mL (based on culture medium volume).

[0060] The culture medium was sterilized at 93±2℃ for 20 minutes, then cooled to 37±1℃ and inoculated with Lactobacillus reuteri. Fermentation was carried out at 37±1℃ for 12 hours.

[0061] The prepared fermentation broth had a pH of 4.0±0.2 and a total acid content of 1.8±0.3 g / 100 mL (calculated as lactic acid). It showed a significant inhibitory effect on Escherichia coli, which was verified by the inhibition zone test method, requiring the inhibition zone diameter to be greater than 15 mm.

[0062] Example 2:

[0063] A method for improving the quality and safety of fermented bean curd includes the following steps:

[0064] (1) Soaking: Soak soybeans in water at a temperature of 40±1℃ for 6±0.5 hours. After soaking, the soybeans increase in weight by 1.5 times.

[0065] (2) Grinding: Soaked soybeans are added to water and processed through a grinding machine to obtain soy milk with a concentration of 7±1 degrees.

[0066] (3) Boiling the soy milk: Heat the soy milk to a boil and keep it boiling for 5 minutes.

[0067] (4) Adding fermentation liquid to the slurry at a temperature not lower than 85℃, with the ratio of slurry to fermentation liquid being 4:1.

[0068] (5) Primary filtration: The material after slurrying is filtered through an 80-120 mesh filter screen to obtain slurry residue as slurry flakes and filtrate as yellow swill.

[0069] (6) Mixing: The mixture of slurry and mixed powder is made by mixing salt and transglutaminase in a weight ratio of 15:1.

[0070] (7) Pressing: Place the well mixed pulp material in the pressing equipment, apply a pressure of 2.0±0.5MPa for 2.5±0.5 hours, and obtain a material with a moisture content of 68%±2%.

[0071] (8) Dividing and arranging the pressed material into blocks according to the specified size and arranging them as required to obtain fermented bean curd blanks.

[0072] (9) Inoculation: The inoculation solution is sprayed evenly onto the surface of the fermented bean curd cake. The amount of inoculation solution sprayed is 3.0% (w / w) of the weight of the fermented bean curd cake. The preparation of the inoculation solution involves first boiling the fermentation broth and maintaining the boiling state for 5 minutes, then cooling it to room temperature before dispersing and mixing it evenly with the Mucor spawn. The mixture is then filtered through a 40-mesh sieve to obtain a spore count of 2.5 × 10⁻⁶ per milliliter. 7 Bacterial suspension.

[0073] (10) Fermentation: The inoculated fermented bean curd blanks are placed in a fermentation chamber and fermented for 32±1 hours at a temperature of 24±2℃ and a relative humidity of not less than 90% to obtain fermented bean curd blanks wrapped by Mucor mycelium.

[0074] (11) Salting: Sprinkle salt on the fermented fermented bean curd blanks. The weight ratio of salt to fermented bean curd blanks is 1:12. The salting time is 12±1 hours. Then add brine with a salt content of 22%±1% (w / w) to submerge the fermented bean curd blanks. The pickling time is 3±1 hours. Drain the brine to obtain salted fermented bean curd blanks.

[0075] (12) Packaging: Place the fermented bean curd pieces in a packaging container, then pour in the pickling liquid to submerge the fermented bean curd pieces. The weight ratio of fermented bean curd pieces to pickling liquid is 3:2. Then seal the container. Preparation of pickling liquid: Dissolve salt and white wine in the fermentation liquid prepared using Lactobacillus reuteri to obtain a solution with a salt content of 4.5% ± 0.5% (w / w) and an alcohol content of 16% ± 2% (v / v). Stir and heat to boiling and maintain a gentle boil for 10 minutes, then cool to below 30°C.

[0076] (13) Post-fermentation: The packaged fermented bean curd blanks are placed at a temperature of 30±2℃ until the amino acid nitrogen content of the pickling liquid is greater than 0.3g / 100mL, then the post-fermentation is completed.

[0077] (14) Preparation of fermentation broth: Using the yellow swill discharged from the primary filtration as the main raw material, white sugar and F55 fructose syrup are added according to the formula. After sterilization and cooling, Lactobacillus reuteri is added for fermentation. The prepared fermentation broth is reserved for the next batch of fermented bean curd production.

[0078] The fermentation broth culture medium, by weight percentage, consists of the following raw materials:

[0079] Yellow swill: 92% (w / w)

[0080] White sugar: 6% (w / w)

[0081] F55 high-fructose corn syrup: 2% (w / w)

[0082] The inoculum size of *Lactobacillus reuteri* was 5 × 10⁻⁶.6 CFU / mL (based on culture medium volume).

[0083] The culture medium was sterilized at 93±2℃ for 20 minutes, then cooled to 37±1℃ and inoculated with Lactobacillus reuteri. Fermentation was carried out at 37±1℃ for 12 hours.

[0084] The prepared fermentation broth had a pH of 4.0±0.2 and a total acid content of 1.8±0.3 g / 100 mL (calculated as lactic acid). It showed a significant inhibitory effect on Escherichia coli, which was verified by the inhibition zone test method, requiring the inhibition zone diameter to be greater than 15 mm.

[0085] Example 3:

[0086] A method for improving the quality and safety of fermented bean curd includes the following steps:

[0087] (1) Soaking: Soak soybeans in water at a temperature of 40±1℃ for 6±0.5 hours. After soaking, the soybeans increase in weight by 1.5 times.

[0088] (2) Grinding: Soaked soybeans are added to water and processed through a grinding machine to obtain soy milk with a concentration of 7±1 degrees.

[0089] (3) Boiling the soy milk: Heat the soy milk to a boil and keep it boiling for 5 minutes.

[0090] (4) Adding fermentation liquid to the slurry at a temperature not lower than 85℃, with the ratio of slurry to fermentation liquid being 4:1.

[0091] (5) Primary filtration: The material after slurrying is filtered through an 80-120 mesh filter screen to obtain slurry residue as slurry flakes and filtrate as yellow swill.

[0092] (6) Mixing: The mixture of slurry and mixed powder is made by mixing salt and transglutaminase in a weight ratio of 17.5:1.

[0093] (7) Pressing: Place the well mixed pulp material in the pressing equipment, apply a pressure of 2.0±0.5MPa for 2.5±0.5 hours, and obtain a material with a moisture content of 68%±2%.

[0094] (8) Dividing and arranging the pressed material into blocks according to the specified size and arranging them as required to obtain fermented bean curd blanks.

[0095] (9) Inoculation: The inoculation solution is sprayed evenly onto the surface of the fermented bean curd cake. The amount of inoculation solution sprayed is 4.5% (w / w) of the weight of the fermented bean curd cake. The preparation of the inoculation solution involves first boiling the fermentation broth and maintaining the boiling state for 5 minutes, then cooling it to room temperature before dispersing and mixing it evenly with the Mucor spawn. The mixture is then filtered through a 40-mesh sieve to obtain a spore count of 1×10⁻⁶ per milliliter. 7 Bacterial suspension.

[0096] (10) Fermentation: The inoculated fermented bean curd blanks are placed in a fermentation chamber and fermented for 32±1 hours at a temperature of 24±2℃ and a relative humidity of not less than 90% to obtain fermented bean curd blanks wrapped by Mucor mycelium.

[0097] (11) Salting: Sprinkle salt on the fermented fermented bean curd blanks. The weight ratio of salt to fermented bean curd blanks is 1:12. The salting time is 12±1 hours. Then add brine with a salt content of 22%±1% (w / w) to submerge the fermented bean curd blanks. The pickling time is 3±1 hours. Drain the brine to obtain salted fermented bean curd blanks.

[0098] (12) Packaging: Place the fermented bean curd pieces in a packaging container, then pour in the pickling liquid to submerge the fermented bean curd pieces. The weight ratio of fermented bean curd pieces to pickling liquid is 3:2. Then seal the container. Preparation of pickling liquid: Dissolve salt and white wine in the fermentation liquid prepared using Lactobacillus reuteri to obtain a solution with a salt content of 4.5% ± 0.5% (w / w) and an alcohol content of 16% ± 2% (v / v). Stir and heat to boiling and maintain a gentle boil for 10 minutes, then cool to below 30°C.

[0099] (13) Post-fermentation: The packaged fermented bean curd blanks are placed at a temperature of 30±2℃ until the amino acid nitrogen content of the pickling liquid is greater than 0.3g / 100mL, then the post-fermentation is completed.

[0100] (14) Preparation of fermentation broth: Using the yellow swill discharged from the primary filtration as the main raw material, white sugar and F55 fructose syrup are added according to the formula. After sterilization and cooling, Lactobacillus reuteri is added for fermentation. The prepared fermentation broth is reserved for the next batch of fermented bean curd production.

[0101] The fermentation broth culture medium, by weight percentage, consists of the following raw materials:

[0102] Yellow swill: 90% (w / w)

[0103] White sugar: 7% (w / w)

[0104] F55 high-fructose corn syrup: 3% (w / w)

[0105] The inoculum size of *Lactobacillus reuteri* was 3.5 × 10⁻⁶. 6 CFU / mL (based on culture medium volume).

[0106] The culture medium was sterilized at 93±2℃ for 20 minutes, then cooled to 37±1℃ and inoculated with Lactobacillus reuteri. Fermentation was carried out at 37±1℃ for 12 hours.

[0107] The prepared fermentation broth had a pH of 4.0±0.2 and a total acid content of 1.8±0.3 g / 100 mL (calculated as lactic acid). It showed a significant inhibitory effect on Escherichia coli, which was verified by the inhibition zone test method, requiring the inhibition zone diameter to be greater than 15 mm.

[0108] Comparative Example 1:

[0109] Fifteen batches of fermented bean curd products were produced simultaneously with those from Examples 1 and 2 and conventional production. The contamination levels of the three production stages most prone to E. coli contamination and proliferation were measured. The specific data on E. coli contamination levels of each sample are shown in Table 1.

[0110] Table 1 Comparison of E. coli contamination between the production process of the example and the conventional production process.

[0111]

[0112] As shown in the table above, the production test results indicate that in Examples 1 and 2, none of the three production stages most prone to E. coli contamination were detected. In contrast, in the conventional production process, all three production stages most prone to E. coli contamination were detected, but the number and proportion of contaminated batches gradually decreased. The fermentation stage, due to its relatively open environment, was more susceptible to contamination and proliferation, resulting in the highest number and proportion of contaminated batches. In the salting stage, the high salt content inhibited and killed E. coli in batches with lower initial contamination levels, significantly reducing the number and proportion of contaminated batches. Finally, in the post-ripening stage, the alcohol and salt in the pickling solution killed E. coli in batches with low initial contamination levels, further reducing the number and proportion of contaminated batches. The results above suggest that the fermentation broth prepared by Lactobacillus reuteri can effectively prevent and inhibit the growth and reproduction of Escherichia coli, thus avoiding the quality risks caused by E. coli contamination in the fermented bean curd production process and effectively improving its food safety.

[0113] Comparative Example 2:

[0114] The regularity of the texture and structure of the fermented bean curd blocks was compared with that of conventionally produced samples, using the sample produced in Example 3.

[0115] from Figure 2It can be clearly seen that the fermented bean curd blocks prepared in Example 3 have a complete texture and structure, a smooth surface without bumps or depressions, and intact edges and corners without damage. In contrast, some fermented bean curd blocks produced in conventional production sometimes have uneven surfaces and cracks due to softening and rotting, and their edges and corners are severely damaged. This shows that the technical method of the present invention can effectively solve the quality problems such as softening and rotting, and edge and corner damage that occur during the production of fermented bean curd.

[0116] As described above, the present invention can be effectively achieved. The present invention utilizes swill to dissolve granulated sugar and F55 fructose syrup, which, after sterilization and cooling, are inoculated with *Lactobacillus reuteri* and fermented at 37°C for 12 hours to obtain a fermentation broth that significantly inhibits *E. coli*. This inhibits the proliferation of exogenously contaminated *E. coli* during the fermentation of fermented bean curd, thus avoiding food safety risks caused by *E. coli*. Furthermore, the transglutaminase, uniformly dispersed in the fermented bean curd curd, dissolves in water under the action of salt and catalyzes the interaction of proteins in the curd curd to form amide bonds, improving the texture and structure of the fermented bean curd curd and preventing quality problems such as softening, chipped corners, chipped edges, and turbidity of the pickling solution during the post-fermentation process.

[0117] The implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for improving the quality and safety of fermented bean curd, characterized in that, Includes the following steps: Soybeans are soaked, ground, boiled, coagulated, and initially filtered to obtain soybean curd. The soybean curd is mixed with mixed powder, then pressed, cut into blocks, and arranged to obtain fermented bean curd blocks. Inoculation solution prepared by dispersing Rhizopus spores in fermentation liquid is sprayed onto the fermented bean curd blocks, and fermentation is carried out in a fermentation room until Rhizopus mycelium covers the fermented bean curd blocks. After salting, the salted fermented bean curd blocks and pickling solution prepared by dissolving baijiu and salt in fermentation liquid are placed in packaging containers for post-fermentation treatment. After post-fermentation is completed, it becomes the finished product. The term "slurry addition" refers to adding fermentation liquid to a slurry at a temperature not lower than 85°C, with a slurry-to-fermentation liquid ratio of 4:

1. The so-called "mixing of pulp and mixed powder" refers to the uniform mixing of pulp and mixed powder at a weight ratio of 15-20:1; the "mixed powder" refers to the uniform mixing of salt and transglutaminase at a weight ratio of 8-6:

1. The fermentation broth refers to the fermentation liquid obtained by using yellow swill discharged from the primary filtration as the main raw material, adding white sugar and F55 fructose syrup according to the formula, and then adding Lactobacillus reuteri for fermentation after sterilization and cooling. The culture medium for the fermentation broth has the following raw material composition by weight percentage: Yellow swill: 88%~92% (w / w); White sugar: 6%~8% (w / w); F55 high-fructose corn syrup: 2%~4% (w / w); The inoculum size of *Lactobacillus reuteri* is 2–5 × 10⁻⁵. 6 CFU / mL; The fermentation broth had a pH of 4.0±0.2 and a total acid content of 1.8±0.3 g / 100mL.

2. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The aforementioned primary filtration refers to filtering the material after slurrying through an 80-120 mesh filter screen to obtain filter residue as slurry flakes and discharge filtrate as yellow swill; The pressing process refers to placing the well-mixed pulp material in a pressing device, applying a pressure of 2.0±0.5 MPa for 2.5±0.5 hours, and obtaining a material with a moisture content of 68%±2%.

3. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The aforementioned slicing and arranging refers to dividing the pressed material into blocks according to specified dimensions and arranging them as required to obtain fermented bean curd blanks; The inoculation refers to the uniform spraying of the inoculation solution onto the surface of the fermented bean curd cake, with the amount of inoculation solution being 1.5% to 4.5% (w / w) of the weight of the fermented bean curd cake.

4. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The aforementioned cultivation and fermentation refers to placing the inoculated fermented bean curd blank in a fermentation chamber and fermenting it for 32±1 hours at a temperature of 24±2℃ and a relative humidity of not less than 90% to obtain fermented bean curd blank wrapped by Mucor mycelium.

5. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The salting process refers to spreading salt on the fermented fermented bean curd blanks, with a salt-to-fermented bean curd blank weight ratio of 1:12, and salting time of 12±1 hours. Then, brine with a salt content of 22%±1% (w / w) is added to submerge the fermented bean curd blanks, and the pickling time is 3±1 hours. After draining the brine, salted fermented bean curd blanks are obtained.

6. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The term "packaged in a container" refers to placing the fermented bean curd pieces inside the container, then pouring in the pickling liquid to submerge the fermented bean curd pieces, with a weight ratio of fermented bean curd pieces to pickling liquid of 3:2, and then sealing the container.

7. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The post-fermentation process refers to placing the packaged fermented bean curd at a temperature of 30±2℃ until the amino acid nitrogen content of the pickling liquid is greater than 0.3g / 100mL, at which point the post-fermentation process is complete. The culture medium for the fermentation broth was sterilized at 93±2℃ for 20 minutes, then cooled to 37±1℃ and inoculated with Lactobacillus reuteri, and fermented at 37±1℃ for 12 hours.

8. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The inoculum solution is prepared by dispersing the *Mucor* spores in the fermentation broth. The fermentation broth is boiled and kept boiling for 5 minutes, then cooled to room temperature before being evenly mixed with the *Mucor* spores. The mixture is then filtered through a 40-mesh sieve to prepare an inoculum with spore counts ranging from 1 to 5 × 10⁻⁶ per milliliter. 7 Bacterial suspension.

9. The method for improving the quality and safety of fermented bean curd according to claim 1, characterized in that, The preparation process of the pickling liquid is as follows: salt and liquor are dissolved in the fermentation liquid to obtain a solution with a salt content of 4.5%±0.5% (w / w) and an alcohol content of 16%±2% (v / v). The solution is stirred and heated to boiling and kept at a gentle boil for 10 minutes, and then cooled to below 30°C.

10. A fermented bean curd product, characterized in that... It is prepared by the method described in claim 1.

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