Soybean protein cooked bean curd and low-temperature segmented braising preparation method thereof

Abstract

This invention relates to the field of soybean protein product processing, and discloses a method for preparing steamed soybean protein tofu and its low-temperature segmented braising and roasting process. The method includes premixing soybean protein isolate with an ice-water mixture, sequentially adding sodium pyrophosphate, salt, and D-anhydrous glucose and chopping, adding soybean oil and sodium stearoyl lactylate and chopping, adding cold-soluble κ-carrageenan and glucono-delta-lactone, mixing and discharging, pre-gelling by heat induction, and then demolding and cutting to obtain the embryo. The embryo is then mixed with a compound flavored braising sauce and braised in two stages, followed by a first-stage dehydration and a second-stage roasting. It is then vacuum-packed and sterilized under pressure and cooled under pressure before being removed from the oven. This invention utilizes soybean protein isolate combined with an ice-water mixture and cold-soluble κ-carrageenan to form a microemulsion system. During heat induction and cooling, an interpenetrating double-network gel structure is constructed, controlling the temperature rise to prevent premature thermal denaturation and inducing uniform cross-linking to avoid pores, thereby improving the system's water and oil holding capacity and elasticity.

Description

Technical Field

[0001] This invention relates to the field of soybean protein product processing technology, specifically to a method for preparing steamed soybean protein tofu and its low-temperature segmented braising and roasting process. Background Technology

[0002] Soy protein tofu, as a common plant-based protein product, has a wide consumer base. However, in current soybean protein tofu production processes, the lack of effective temperature control leads to premature thermal denaturation of the protein during shear mixing. Furthermore, the aqueous and oil phases within the system struggle to form a stable microemulsion, resulting in an insufficiently dense gel network structure. Simultaneously, traditional gelation induction methods cause excessively rapid and uneven protein cross-linking, leading to localized excessively rapid gelation and porosity within the product, resulting in insufficient water and oil retention capacity and elasticity.

[0003] In the braising process of dried tofu, existing braising techniques typically employ a single temperature and salinity setting. Under these conditions, the proteins on the surface of the dried tofu are prone to shrinkage and closure due to rapid heating. This premature densification of the surface hinders the deep penetration of flavor compounds into the core area, resulting in a bland internal flavor. Furthermore, the lack of control over osmotic pressure and temperature gradients makes it difficult to effectively seal the limited amount of penetrating flavor compounds within the product, leading to a final product lacking the characteristic chewy exterior and tender interior flavor profile.

[0004] In the later stages of drying and sterilization in the production of dried tofu, conventional processing methods are insufficient to effectively remove surface free water and utilize Maillard browning to improve the product's chewiness. Furthermore, during conventional high-temperature sterilization and unloading processes, the vaporization of moisture within the packaging bag generates saturated vapor pressure. This internal expansion force can easily cause stress tearing of the dried tofu's gel structure, leading to water separation under high temperature and pressure, which in turn causes packaging rupture and changes in product shape, making it difficult to consistently meet commercial aseptic requirements. Therefore, providing a method for preparing steamed dried tofu using soybean protein and its low-temperature segmented braising and roasting process is a problem that needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing steamed soybean protein tofu and its low-temperature segmented braising and roasting process. This method solves the problems of premature thermal denaturation and gel pores in soybean protein tofu during production, the difficulty in deep flavor penetration and lack of layering during single braising, and the vulnerability of the gel structure to stress tearing during conventional drying and sterilization, which leads to packaging breakage and unstable shape.

[0006] To address the above problems, the present invention provides the following technical solution: The first aspect of this invention provides a steamed tofu made with soybean protein, employing the following technical solution: A type of steamed tofu made with soybean protein, comprising the following ingredients by weight percentage: Soy protein isolate: 28.0%–32.0%; Ice-water mixture: 55.15%–61.85%; Soybean oil: 9.0%–10.0%; D-Anhydrous Glucose: 0.5%–1.5%; Salt: 0.1%–0.3%; Cold-soluble κ-carrageenan: 0.20%–0.40%; Glucono-δ-lactone: 0.15%–0.25%; Sodium pyrophosphate: 0.10%–0.20%; Sodium stearoyl lactylate: 0.10%~0.20%.

[0007] By adopting the above technical solution, using soy protein isolate as the base material and a specific ratio of ice-water mixture, not only is a protein matrix for forming a stable gel provided, but the ice-water mixture also controls the heating rate during the subsequent strong shearing process, preventing premature thermal denaturation of the soy protein isolate.

[0008] Sodium stearoyl lactylate, acting as an emulsifier, synergistically with the soy protein isolate to form a stable oil-in-water microemulsion system in the aqueous phase, improving the finished product's softness and juiciness. Sodium pyrophosphate can chelate metal ions in the system, enhancing the protein's solubility and hydration capacity.

[0009] The cold-soluble κ-carrageenan interacts synergistically with the soy protein isolate, forming a protein-polysaccharide interpenetrating double network gel structure during thermal induction and subsequent cooling, significantly improving the system's water- and oil-holding capacity and elasticity. The gluconate-δ-lactone slowly hydrolyzes in aqueous solution to generate gluconic acid, causing the system's pH to gradually decrease to near its isoelectric point, inducing slow and uniform cross-linking of protein molecules, avoiding the problems of excessively rapid localized gelation and porosity caused by traditional brine curing. The D-anhydrous glucose and the salt serve as base flavoring substances, participating in the Maillard reaction in subsequent high-temperature processes, imparting the characteristic color and flavor to the finished product.

[0010] Preferably, the thickness of the steamed soybean protein tofu is 8mm to 12mm, and the length and width are 25mm to 35mm respectively.

[0011] By adopting the above technical solution, the geometric dimensions of the steamed soybean protein tofu are limited to the specific range mentioned above, so that the mass transfer distance between water and flavor substances can be well balanced during the subsequent braising process. This ensures that the salt and flavor in the core area can quickly reach mass transfer balance, while avoiding textural aging on the surface due to prolonged braising. At the same time, the dimensions can ensure a consistent heat penetration rate during the back pressure sterilization stage, and the central cold point temperature can stably meet commercial sterility requirements.

[0012] Preferably, the steamed tofu made from soybean protein also contains an extract of a compound spice blend, which is composed of star anise, cinnamon, cloves and Sichuan peppercorns.

[0013] By adopting the above technical solution, a compound spice mixture consisting of star anise, cinnamon, cloves and Sichuan pepper is introduced into the soybean protein system in the form of an extract. The alcohol-soluble and water-soluble flavor compounds in the extract can be uniformly dispersed in the protein gel network.

[0014] The method avoids the physical disruption to the continuity of the protein gel network caused by directly adding spice powder, thus maintaining the density of the gel system and the smoothness of the cut surface while ensuring that the product has a complex spice flavor.

[0015] The second aspect of this invention provides a low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu, employing the following technical solution: A low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu includes the following steps: Soy protein isolate was premixed with ice water, sodium pyrophosphate, salt and D-anhydrous glucose were added and chopped in sequence, soybean oil and sodium stearoyl lactylate were added and chopped, cold-soluble κ-carrageenan was added and chopped, and finally gluconate-δ-lactone was added and mixed before discharge to obtain the discharge slurry. The slurry is pumped into a mold box for thermally induced pregelation, then allowed to stand, demolded, and cut to obtain the preform. The embryo and the compound flavored braising liquid are put into a braising pot to form a mixed braising liquid. The mixed braising liquid is then subjected to the first stage of braising. Subsequently, the mixed braising liquid is heated and salt is added for the second stage of braising. The product is then removed and drained to obtain the braised tofu. The braised tofu is dehydrated in the first stage, then baked in the second stage, and then cooled to obtain cooled tofu. The cooled dried bean curd is vacuum-packed, placed in a sterilizing autoclave, heated, and sterilized under back pressure. It is then cooled under pressure and removed from the autoclave to obtain the steamed bean curd made from soybean protein.

[0016] By adopting the above technical solution, the specific order of feeding and segmented mixing ensure that ingredients with different properties are dispersed under suitable rheological conditions. First, the soy protein isolate is hydrated, then salts are added to promote protein dissolution, followed by the addition of soybean oil and emulsifiers to form a homogeneous emulsion. Finally, the coagulant gluconate-δ-lactone is added, ensuring the homogeneity of the slurry.

[0017] The combination of heat induction and static setting allows for the stepwise hydrophobic interactions of proteins and the cold gelation of polysaccharides, endowing the embryo with mechanical strength to withstand subsequent processing. Two-stage brining, through a controlled osmotic pressure gradient of low-temperature, low-salt initial penetration and high-temperature, high-salt compaction, promotes deep penetration of flavor compounds into the gel. In the second stage, moderately high temperatures cause surface proteins to shrink, locking in internal flavor and moisture. The combination of dehydration and baking removes surface free water, promoting surface Maillard reactions and forming a tough outer skin structure.

[0018] Finally, the backpressure sterilization technology balances the internal pressure generated by the vaporization of water vapor inside the packaging bag, effectively preventing water separation, pore expansion, and packaging rupture under high temperature and high pressure conditions, ensuring the product's morphological stability and commercial sterility requirements.

[0019] Preferably, the steps for obtaining the output slurry specifically include: Premix the soy protein isolate with ice water at a speed of 1200 r / min to 1800 r / min for 1 min to 3 min; Add sodium pyrophosphate, salt and D-anhydrous glucose and chop at 2500 r / min to 3200 r / min for 1 min to 3 min; Add soybean oil and sodium stearoyl lactylate and chop at a speed of 3000 r / min to 4000 r / min for 2 min to 4 min; Add cold-soluble κ-carrageenan and chop at 3000 r / min to 4000 r / min for 1 min to 3 min; Add gluconate-δ-lactone and mix at a speed of 500 r / min to 1000 r / min for 0.5 to 1.5 min, controlling the temperature of the discharged slurry to be 10℃ to 12℃.

[0020] By adopting the above technical solution, the stepped rotation speed control matches the variation law of the slurry viscosity. When adding the soybean oil and the cold-soluble κ-carrageenan, a rotation speed of 3000 r / min to 4000 r / min is used for shearing, which can effectively break the oil droplets down to the micron level and allow the carrageenan to fully expand; when adding the glucono-δ-lactone, the speed is reduced to 500 r / min to 1000 r / min, which can avoid excessive shearing and damage to the initially formed hydrolyzed micelles.

[0021] By controlling the final discharge temperature at 10℃~12℃, the hydrolysis rate of lactone was significantly suppressed, ensuring that the discharge slurry maintained good rheological and pumpability before entering the mold box, thus avoiding pipeline blockage and uneven molding caused by premature gelation.

[0022] Preferably, the step of obtaining the embryo specifically includes: The conditions for thermally induced pregelation are a temperature of 40℃~50℃ and a time of 20min~40min. The conditions for standing are a temperature of 4℃ to 7℃ and a time of 10h to 14h.

[0023] By adopting the above technical solution, the thermal induction conditions of 40℃~50℃ can accelerate the hydrolysis of gluconate-δ-lactone, causing the pH of the system to drop rapidly to the isoelectric point region of the protein, promoting disulfide bonds and hydrophobic interactions, and forming a preliminary protein spatial network.

[0024] Subsequently, it was transferred to a refrigerated container at 4℃~7℃ and allowed to stand for 10h~14h, providing sufficient time for the cold-soluble κ-carrageenan to undergo helical transformation and aggregation crystallization of the molecular chains. At the same time, the protein network structure was allowed to complete structural relaxation and release of internal stress at low temperature, forming a dense and elastic macroscopic gel, which ensured the smoothness of the edges during demolding and cutting.

[0025] Preferably, the compound flavored braising liquid is prepared through the following steps: A mixture of star anise, cinnamon, cloves and Sichuan peppercorns is added to a reaction vessel containing water at a mass ratio of 1:15 to 1:50 to form a mixture. The mixture in the reaction vessel is heated to 80℃~105℃ and boiled for 30min~120min to obtain the original extract. The original extract was filtered to obtain a spice extract. D-anhydrous glucose and salt are added to the spice extract, stirred to dissolve and cooled, so that the mass fraction of D-anhydrous glucose in the compound flavor seasoning brine is 0.5% to 2.0% and the mass fraction of salt is 0.3% to 0.8%.

[0026] By employing the above technical solution, the characteristic aromatic compounds in the compound spices are fully dissolved through heating and simmering. The filtration and residue removal step eliminates the rough texture caused by solid particles adhering to the surface of the dried bean curd.

[0027] A certain amount of D-anhydrous glucose and salt were pre-dissolved in the spice extract to construct a primary flavoring base liquid with uniform composition and low osmotic pressure, thus establishing stable initial boundary conditions for solid-liquid mass transfer in the subsequent gradient brining process.

[0028] Preferably, the steps for obtaining the braised tofu specifically include: The embryo and the compound flavored brine are added to the braising pot at a mass ratio of 1:3 to 1:6 to form the mixed brine. The first stage of braising conditions is a temperature of 50℃~60℃, an initial salinity of 0.3%~0.8%, and a time of 15min~25min; The mixed brine is heated to 80°C to 90°C within 2 to 4 minutes, and the salt is added to raise the salinity of the mixed brine to 2.5% to 3.5%. The second stage of brining conditions is a temperature of 80℃~90℃ and a time of 15min~25min.

[0029] By adopting the above technical solution, the combination of 50℃~60℃ and low salinity in the first stage avoids the protein from shrinking too quickly when heated, so that the pores inside the embryo are in an open state, and the sugar and spice extracts are deeply infiltrated into the core area by relying on molecular thermal motion.

[0030] The second stage involves rapidly heating the temperature to 80℃~90℃ and establishing a highly saline, osmotic environment. This forces the surface proteins to rapidly denature and shrink due to heat and salting-out effects. As moisture seeps out, the surface becomes denser, effectively sealing the flavor substances that penetrated in the first stage inside, giving the product a layered flavor profile that is tough on the outside and tender on the inside.

[0031] Preferably, the steps for obtaining the cooled dried bean curd specifically include: The first stage of dehydration conditions are: temperature 55℃~65℃, wind speed 1.0m / s~3.0m / s, and time 10min~20min; The second stage baking conditions are: temperature 85℃~95℃, wind speed 1.0m / s~2.0m / s, and time 8min~12min; The cooling conditions are to cool to 20°C to 30°C.

[0032] By adopting the above technical solution, the first stage uses high wind speed and medium temperature to peel off the free water and attached brine from the surface of the dried bean curd, so that a dry microgel film is formed on the surface. The second stage involves baking at 85℃~95℃ using a low airflow rate, which triggers the Maillard browning reaction of the residual D-anhydrous glucose and free amino acids on the surface, generating a baked flavor and deepening the surface color. Simultaneously, it further promotes the vitrification transition of the epidermal tissue, significantly improving the product's chewiness. Cooling to 20℃~30℃ eliminates internal thermal stress, preventing deformation during subsequent vacuum packaging and reducing condensation.

[0033] Preferably, the step of heating in the sterilizing autoclave and sterilizing under back pressure, followed by pressurized cooling and removal from the autoclave, specifically includes: The temperature in the sterilization autoclave is raised to 110℃~115℃; Maintain a back pressure of 0.20MPa to 0.35MPa and keep warm for 20 to 30 minutes for sterilization; The conditions for pressurized cooling and outlet discharge are as follows: Cool under pressure to 35℃~45℃.

[0034] By adopting the above technical solution, heat preservation and sterilization at 110℃~115℃ is sufficient to destroy the spores of pathogenic bacteria and putrefactive bacteria such as thermophilic Bacillus stearothermophilus, thus meeting the requirements for long-term storage and transportation at room temperature.

[0035] During high-temperature sterilization, the moisture inside the packaging bag has a large vapor expansion force. By filling the bag with compressed air to maintain a reverse pressure of 0.20MPa to 0.35MPa, the saturated vapor pressure inside the bag can be effectively offset, protecting the original dense gel structure of the soybean protein steamed tofu from stress tearing and preventing packaging damage. After being cooled under pressure to 35℃~45℃, the product is removed from the reactor. This ensures that the external back pressure remains until the internal temperature of the product drops below the safe temperature, further stabilizing the product's form and preventing the texture from becoming spongy due to boiling during the instant of pressure release.

[0036] This invention provides a method for preparing steamed tofu with soybean protein and its low-temperature segmented braising and roasting process. It offers the following advantages: 1. This invention uses soy protein isolate as a base material and combines it with ice-water mixture, sodium stearoyl lactylate, cold-soluble κ-carrageenan, and glucono-δ-lactone as raw materials. While controlling the heating rate to prevent premature thermal denaturation, it enables soybean oil to form an oil-in-water microemulsion system in the aqueous phase. Then, during the thermal induction and cooling process, a dense proteoglycan interpenetrating double network gel structure is formed. Finally, it induces uniform cross-linking of protein molecules to avoid excessively rapid gelation and pore problems, and improves the water-holding capacity and elasticity of the system.

[0037] 2. This invention involves mixing the embryo with a compound flavored braising liquid and braising it at a lower temperature and lower salinity in the first stage and at a higher temperature and higher salinity in the second stage. This avoids the protein shrinking too quickly due to heat, allowing the flavor substances to penetrate deeply into the core area through molecular thermal motion. Subsequently, a strong penetrating environment is established, forcing the surface protein to denature and shrink due to heat and salting-out effects. This allows the surface to become denser as water seeps out, while simultaneously sealing the penetrating flavor substances inside and giving the product a layered flavor profile that is tough on the outside and tender on the inside.

[0038] 3. This invention improves the chewiness of the product by first dehydrating the braised tofu and then baking it in the second stage to remove surface free water and induce Maillard browning reaction. Subsequently, the tofu is heated in an autoclave and sterilized under reverse pressure and then cooled under pressure. This effectively counteracts the saturated vapor pressure inside the packaging bag to protect the dense gel structure from stress tearing, ultimately preventing packaging breakage and water separation under high temperature and high pressure, and ensuring product stability and meeting commercial sterility requirements. Attached Figure Description

[0039] Figure 1 The infrared spectrum of the soybean protein cooked tofu composite gel network of the present invention; Figure 2 This is a graph showing the change in the energy storage modulus of the soybean protein cooked tofu gel system of the present invention; Figure 3 This is a low-field nuclear magnetic resonance relaxation time distribution diagram of soybean protein cooked tofu according to the present invention. Figure 4 This is a time-varying force graph of the texture profile of steamed soybean protein from the present invention. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a compound flavored braising sauce, including the following steps: Accurately weigh the compound spice mixture consisting of star anise, cinnamon, cloves, and Sichuan peppercorns, and add it to a jacketed reactor containing purified water at a ratio of 1:50 (spice to water) and stir well.

[0042] Turn on the heating system to raise the temperature of the mixture in the jacketed reactor to 80°C. Maintain this temperature and simmer continuously for 30 minutes to allow the flavor compounds in the spices to initially dissolve into the aqueous phase.

[0043] After the decoction is finished, the extract is filtered through a 200-mesh stainless steel filter to effectively remove spice residue and obtain a clear spice extract.

[0044] Add D-anhydrous glucose and refined salt to the spice extract and stir thoroughly until completely dissolved, so that the mass fraction of D-anhydrous glucose in the final compound flavor seasoning brine is 0.5% and the mass fraction of refined salt is 0.3%. Let it cool naturally before use.

[0045] Preparation Example 2: This preparation example provides a method for preparing a compound flavored braising sauce, including the following steps: Accurately weigh the compound spice mixture consisting of star anise, cinnamon, cloves, and Sichuan peppercorns, and add it to a jacketed reactor containing purified water at a ratio of 1:30 (spice to water) and stir well.

[0046] Turn on the heating system to raise the temperature of the mixture in the jacketed reactor to 95°C, and simmer at this temperature for 60 minutes to allow the flavor compounds in the spices to fully dissolve into the aqueous phase.

[0047] After the decoction is finished, the extract is filtered through a 200-mesh stainless steel filter to effectively remove spice residue and obtain a clear spice extract.

[0048] Add D-anhydrous glucose and refined salt to the spice extract and stir thoroughly until completely dissolved, so that the mass fraction of D-anhydrous glucose in the final compound flavor seasoning brine is 1.0% and the mass fraction of refined salt is 0.5%. Let it cool naturally before use.

[0049] Preparation Example 3: This preparation example provides a method for preparing a compound flavored braising sauce, including the following steps: Accurately weigh the compound spice mixture consisting of star anise, cinnamon, cloves, and Sichuan peppercorns. Add the compound spice mixture to a closed micro-high pressure jacketed reactor containing purified water at a material-to-water ratio of 1:15 and stir until homogeneous.

[0050] Turn on the heating and pressurizing system to raise the temperature of the mixture in the reaction vessel to 105°C. Maintain this temperature for 120 minutes to allow the deep flavor substances in the spices to be deeply extracted into the aqueous phase.

[0051] After the boiling process is complete, the temperature is reduced and the pressure is released. The extract is then filtered using a 200-mesh stainless steel filter to effectively remove spice residues and obtain a clear spice extract.

[0052] Add D-anhydrous glucose and refined salt to the spice extract and stir thoroughly until completely dissolved, so that the mass fraction of D-anhydrous glucose in the final compound flavor seasoning brine is 2.0% and the mass fraction of refined salt is 0.8%. Let it cool naturally before use.

[0053] Examples 1-3:

[0054] Example 1

[0055] This embodiment provides a low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu, including the following steps: A mixture of 28.0% soy protein isolate and 61.85% industrial ice water was added to a chopper and premixed at 1200 rpm for 1 min. Then, 0.10% sodium pyrophosphate, 0.1% refined salt, and 0.5% D-anhydrous glucose were added and chopped at 2500 rpm for 1 min. Next, 9.0% refined soybean oil and 0.10% sodium stearoyl lactylate were added and chopped under strong shear at 3000 rpm for 2 min. Then, 0.20% food-grade cold-soluble κ-carrageenan was added and chopped at 3000 rpm for 1 min. Finally, 0.15% glucono-δ-lactone was added and mixed at 500 rpm for 0.5 min before discharging. The temperature of the discharged slurry was controlled at 10℃. The slurry was pumped into the mold box and pregelatinized by heat in a 40℃ incubator for 20 minutes. Then it was transferred to a 4℃ cold storage and left to stand for 10 hours. After demolding, it was cut into preforms with a thickness of 8 mm and a length and width of 25 mm. The embryo and the compound flavored brine prepared in Example 1 were added into a jacketed braising pot at a mass ratio of 1:3. The first stage of braising was carried out at 50°C and an initial salinity of 0.3% for 15 minutes. Then, the brine was heated to 80°C within 2 minutes and concentrated salt was added to raise the salinity of the system to 2.5%. The second stage of braising was carried out under these conditions for 15 minutes. The embryo was then removed and drained. The braised tofu was laid out in a single layer in a hot air tunnel and dehydrated for 10 minutes at 55°C and 1.0 m / s. Then it was baked for 8 minutes at 85°C and 1.0 m / s. The tofu was then removed and cooled to 20°C. The cooled dried tofu is vacuum-packed in a high-temperature resistant, retortable composite packaging bag and then placed in a reverse-pressure sterilizer. The temperature is raised to 110°C, and the entire process is sterilized under reverse pressure of 0.20 MPa using compressed air for 20 minutes. After that, it is cooled under pressure to 35°C and removed from the sterilizer to obtain soy protein dried tofu.

[0056] Example 2

[0057] This embodiment provides a low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu, including the following steps: A mixture of 29.0% soy protein isolate and 59.50% industrial ice water was added to a chopper and premixed at 1500 rpm for 2 minutes. Then, 0.15% sodium pyrophosphate, 0.2% refined salt, and 1.0% D-anhydrous glucose were added and chopped at 2800 rpm for 2 minutes. Next, 9.5% refined soybean oil and 0.15% sodium stearoyl lactylate were added and chopped under strong shear at 3600 rpm for 3 minutes. Then, 0.30% food-grade cold-soluble κ-carrageenan was added and chopped at 3600 rpm for 2 minutes. Finally, 0.20% glucono-δ-lactone was added and mixed at 750 rpm for 1 minute before discharging. The temperature of the discharged slurry was controlled at 11℃. The slurry was pumped into the mold box and pregelatinized by heat in a 45℃ incubator for 30 minutes. Then it was transferred to a 6℃ cold storage and left to stand for 12 hours. After demolding, it was cut into preforms with a thickness of 10 mm and a length and width of 30 mm. The embryo and the compound flavored brine prepared in Example 2 were added into a jacketed braising pot at a mass ratio of 1:4. The first stage of braising was carried out at 55°C and an initial salinity of 0.5% for 20 minutes. Then, the brine was heated to 85°C within 3 minutes and concentrated salt was added to raise the salinity of the system to 3.0%. The second stage of braising was carried out under these conditions for 20 minutes. The embryo was then removed and drained. The braised tofu was laid out in a single layer in a hot air tunnel and dehydrated for 15 minutes at 60°C and 2.0 m / s. Then it was baked for 10 minutes at 90°C and 1.5 m / s. The tofu was then removed and cooled to 25°C. The cooled tofu is vacuum-packed in a high-temperature resistant, retortable composite packaging bag and then placed in a reverse-pressure sterilizer. The temperature is raised to 112°C, and the entire process is sterilized under reverse pressure of 0.25 MPa using compressed air for 25 minutes. After that, it is cooled under pressure to 40°C and removed from the sterilizer to obtain soy protein tofu.

[0058] Example 3

[0059] This embodiment provides a low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu, including the following steps: A mixture of 32.0% soy protein isolate and 55.15% industrial ice water was added to a chopper and premixed at 1800 rpm for 3 minutes. Then, 0.20% sodium pyrophosphate, 0.3% refined salt, and 1.5% D-anhydrous glucose were added and chopped at 3200 rpm for 3 minutes. Next, 10.0% refined soybean oil and 0.20% sodium stearoyl lactylate were added and chopped under strong shear at 4000 rpm for 4 minutes. Then, 0.40% food-grade cold-soluble κ-carrageenan was added and chopped at 4000 rpm for 3 minutes. Finally, 0.25% glucono-δ-lactone was added and mixed at 1000 rpm for 1.5 minutes before discharging. The temperature of the discharged slurry was controlled at 12℃. The slurry was pumped into the mold box and pregelatinized by heat in a 50℃ incubator for 40 minutes. Then it was transferred to a 7℃ cold storage and left to stand for 14 hours. After demolding, it was cut into preforms with a thickness of 12mm and a length and width of 35mm. The embryo and the compound flavored brine prepared in Example 3 were added into a jacketed braising pot at a mass ratio of 1:6. The first stage of braising was carried out at 60°C and an initial salinity of 0.8% for 25 minutes. Then, the brine was heated to 90°C within 4 minutes and concentrated salt was added to raise the salinity of the system to 3.5%. The second stage of braising was carried out under these conditions for 25 minutes. The embryo was then removed and drained. The braised tofu was laid out in a single layer in a hot air tunnel and dehydrated for 20 minutes at 65°C and 3.0 m / s. Then it was baked for 12 minutes at 95°C and 2.0 m / s. The tofu was then removed and cooled to 30°C. The cooled tofu is vacuum-packed in a high-temperature resistant, retortable composite packaging bag and then placed in a reverse-pressure sterilizer. The temperature is raised to 115°C, and the entire process is sterilized under reverse pressure of 0.35 MPa using compressed air for 30 minutes. After that, it is cooled under pressure to 45°C and removed from the sterilizer to obtain soy protein tofu.

[0060] Comparative Examples 1-5: Comparative Example 1: Compared with Example 2, the difference is that no gluconate-δ-lactone was added, and its corresponding mass fraction was made up by an equal amount of industrial ice-water mixture. All other parameters and steps are the same.

[0061] Comparative Example 2: Compared with Example 2, the difference is that no food-grade cold-soluble κ-carrageenan was added, and its corresponding mass fraction was made up by an equal amount of soy protein isolate. All other parameters and steps are the same.

[0062] Comparative Example 3: Compared with Example 2, the difference is that the braising stage does not involve segmented temperature and salt changes. Instead, after the embryo is put into the braising pot, it is directly braising at a constant temperature and salt of 85°C and 3.0% salinity for 40 minutes. All other parameters and steps are the same.

[0063] Comparative Example 4: Compared with Example 2, the difference is that the baking stage does not involve segmented dehydration and coloring operations. Instead, the braised tofu is directly baked with hot air at 90°C for 25 minutes. All other parameters and steps are the same.

[0064] Comparative Example 5: Compared with Example 2, the difference is that the back pressure sterilization stage does not apply 0.25MPa compressed air back pressure, but directly uses 112℃ physical saturated pure steam at normal pressure without additional back pressure for 25 minutes. All other parameters and steps are the same.

[0065] Test Examples 1-4: Test Example 1: Experimental description: This test case was used to verify the compliance of the macroscopic physicochemical indicators of the soybean protein dried tofu products obtained in each example and comparative example, as well as the effectiveness of the packaging material in protecting against microorganisms after heat sterilization. The final moisture content and total salt content of the finished product were quantitatively measured to evaluate the control of moisture lock-in and flavor penetration by different process routes. A constant temperature insulation test simulating a storage environment and microbial culture and counting were conducted to verify whether the finished product reached a commercially sterile state, providing data support for a shelf life of more than 9 months.

[0066] Experimental steps: Three bags of finished dried bean curd from each group were randomly selected. After opening the bags, the bean curd was quickly and evenly crushed. 5.000g of the sample was accurately weighed and placed in a flat weighing bottle that had been weighed to constant weight. The bottle was then placed in an electric thermostatic drying oven at 105℃ and dried continuously with hot air using the oven drying method. Every hour, the weighing bottle was removed with crucible tongs, placed in a desiccator to cool to room temperature, and then accurately weighed. The constant weight state was considered to be reached when the difference between two consecutive weighings did not exceed 2mg. The final moisture content of the finished product was calculated based on the difference in mass before and after drying. Accurately weigh 10.00g of uniformly pulverized dried bean curd sample, add 70mL of distilled water, and heat in a boiling water bath for 30 minutes to promote the full dissolution and diffusion of internal salts into the aqueous phase. After cooling, transfer to a volumetric flask and dilute to 100mL. Filter the extract to obtain a clear filtrate. Accurately pipette 10.00mL of the filtrate into an Erlenmeyer flask, introduce potassium chromate solution as an indicator, and perform routine quantitative titration using silver nitrate standard titration solution until the solution changes from pale yellow to a stable brick-red precipitate. Calculate the total salt content of the finished product based on the actual volume of silver nitrate standard titration solution consumed. Fifty bags of well-packaged dried bean curd were randomly selected from each group. The samples were divided into two groups. The first group of 25 bags was placed in a constant temperature incubator at 37℃ for 10 consecutive days, and the second group of 25 bags was placed in a constant temperature incubator at 55℃ for 5 consecutive days. During this assessment period, manual inspections were carried out daily and the physical appearance changes of the packaging bags were recorded. The bags were observed to see if they swelled, if there was any material leakage at the sealing line, and if the internal dried bean curd tissue showed signs of rancidity, stratification, or color changes. After the heat preservation period, the bags were aseptically opened and samples were taken in a clean bench. Plate count culture of pathogenic bacteria and conventional spoilage bacteria was carried out in accordance with the national food safety standard for commercial aseptic testing. The amount of microbial residue in each group was counted and recorded.

[0067] Experimental data: Table 1. Physicochemical Indicators and Results of Commercial Aseptic Performance Testing

[0068] Experimental conclusion: Referring to Table 1, the final moisture content and total salt content of Examples 1 to 3 were consistently controlled. After incubation at 37°C and 55°C, the packaging bags remained flat, and no microorganisms were detected, achieving a commercially sterile state. The total salt content of Comparative Examples 1 and 3 was only 0.85% and 0.73%, respectively, indicating that the lack of glucono-δ-lactone slow-release acidification or the direct one-step brining process resulted in a dense, hard shell formed by rapid thermal denaturation of the outer protein layer, hindering salt penetration into the interior. Comparative Example 5 did not apply back pressure during the sterilization stage, leading to significant swelling and rupture of the packaging and excessive microbial residues.

[0069] See attached document Figure 1 3200 to 3500cm -1 The region reflects the intermolecular hydrogen bonding within the system. In Example 2, the absorption peak intensity at this location is significantly higher than that in Comparative Examples 1 and 2, and the peak position exhibits a red shift towards lower wavenumbers. Simultaneously, at 1650 cm⁻¹... -1 The amide I band at 1540 cm -1 The sharp absorption peak of the amide II band indicates that the secondary structure of soybean protein is transforming into a stable β-sheet conformation. Combined with the decrease in moisture content to 45.23% and the obvious water-holding collapse phenomenon in Comparative Example 2, this verifies that the synergistic effect of cold-soluble κ-carrageenan and soybean protein can effectively enhance the water retention and heat distortion resistance of the system.

[0070] Test Example 2: Experimental description: This test case evaluates the continuous molding stability and processing adaptability of the soybean protein dried tofu obtained in various embodiments and comparative examples under industrial production conditions at the 100kg scale. The integrity of the preform pieces after pregelation and cold-cooled demolding is statistically analyzed to examine the resistance of the internal macromolecular cross-linking state to mechanical cutting shear forces. Simultaneously, the total mass of the final qualified product is weighed to calculate the overall yield, providing physical loss analysis and economic data reference for continuous operation in actual large-scale mass production.

[0071] Experimental steps: In a 100kg-class industrial-grade reactor and supporting production line, a scale-up trial production was carried out according to the process parameters set in each embodiment and comparative example, and the physical morphological changes of the preform during the molding and demolding stage were tracked and recorded. After the gel blocks have been refrigerated and settled, they are demolded and placed on the conveyor belt of a fully automatic cutting machine. The corresponding cutting specifications are set for continuous physical cutting. After all the blocks are collected, they are sorted by a combination of manual and machine vision on a high-intensity light inspection table. Standard embryos with smooth surfaces, neat edges, and no cracks or missing corners are selected, weighed, and their proportion of the total embryo mass before cutting is calculated to obtain the cut piece integrity rate. The final qualified finished product, which has undergone all processes of segmented brining, hot air baking and back pressure sterilization and cooled to room temperature, is collected. The total mass of the finished product before packaging is weighed using a high-precision electronic weighbridge. The total mass is then divided by the total mass of the raw material slurry initially fed into the reactor to calculate the overall yield.

[0072] Experimental data: Table 2. Test Results of Slicing Integrity Rate and Overall Yield

[0073] Experimental conclusion: Referring to Table 2, the cut integrity rate of Examples 1 to 3 all reached over 98%, and the overall yield remained stable in the range of 76% to 79%, indicating that the soybean protein system formed a gel state with suitable hardness and toughness after the pre-gel and refrigeration processes, which can effectively resist the mechanical shearing force of the fully automatic cutter. Comparative Example 1, without the addition of glucono-δ-lactone, saw a decrease in cut integrity rate to 83.12%, and a significant decline in the overall yield of the finished product. Comparative Example 2, without the addition of cold-soluble κ-carrageenan, resulted in a soft gel that stuck to the blade, with an integrity rate of only 72.58%, and a final yield reduced to 58.16%.

[0074] See attached document Figure 2The dynamic rheological storage modulus reflects the elastic mechanical strength and resistance to deformation of the gel system before cutting. Within the angular frequency scanning range of 0 to 100 rad / s, the storage modulus curve of Example 2 remained consistently high and stable with frequency, confirming the tight cross-linking of the internal macromolecules. The storage modulus curves of Comparative Examples 1 and 2 shifted significantly downwards, especially Comparative Example 2, which lacked the support of carrageenan, resulting in a low storage modulus and making the preform prone to irreversible deformation and fragmentation during physical cutting.

[0075] Based on the data from Comparative Examples 3 to 5, although the cut piece integrity rate remained at a high level, the overall yield showed a significant downward trend. This confirms that the segmented variable-temperature braising and roasting and back-pressure sterilization processes played a positive protective role in reducing material breakage and dehydration losses, thereby stabilizing the final yield in the overall process.

[0076] Test Example 3: Experimental description: This test case was used to verify the physical structural stability and moisture retention capacity of the soybean protein-based dried tofu obtained in each embodiment and comparative example during the backpressure heat sterilization stage. By statistically analyzing the packaging damage after sterilization, the impact of internal and external pressure differences on the physical barrier of the packaging during the process was evaluated. The proportion of free water extracted from the finished product after storage was quantitatively determined to examine the locking effect of the macromolecular cross-linking system on bound water, thereby verifying the actual role of relevant process and formulation parameters in inhibiting thermal collapse and maintaining the product's firm texture.

[0077] Experimental steps: The physical damage and air leakage of each group of packaging bags after sterilization were statistically analyzed, and the proportion of bags damaged due to expansion and deformation to the total number of packaging bags in the batch was calculated to obtain the sterilization bag breakage rate. After sterilization, the intact and undamaged finished product is placed flat in an environment of 25℃ for 24 hours to stabilize the internal structural balance. Wipe the surface of the outer packaging bag dry. After opening the bag, pour the contents of the entire bag of dried tofu into a 200-mesh stainless steel sieve and let it drain naturally for 2 minutes. Use a high-precision balance to collect the residual liquid inside the packaging bag and all the free liquid drained through the sieve, and weigh them accurately. Calculate the percentage of free liquid mass to the total mass of the dried bean curd, and record it as the finished product water separation rate.

[0078] Experimental data: Table 3. Test results of sterilization bag breakage rate and water separation rate

[0079] Experimental conclusion: Referring to Table 3, the sterilization and bag breakage rates of Examples 1 to 3 were all 0.00%, and the finished product water separation rate was controlled within the range of 0.58% to 0.81%, demonstrating good water retention and anti-deformation ability. In Comparative Example 2, no cold-soluble κ-carrageenan was added; the soybean protein could not withstand the high-temperature evaporation pressure, resulting in tissue thermal collapse and the release of a large amount of free water, leading to a significant increase in the water separation rate to 8.43%. In Comparative Example 5, no 0.25 MPa equilibrium back pressure was applied during sterilization; the vaporization of trace amounts of moisture inside the packaging generated expansion pressure, resulting in a bag breakage rate of 18.52%. The internal structure of the unbroken sample was also damaged due to excessive expansion, and the water separation rate increased to 11.16%.

[0080] See attached document Figure 3 The low-field NMR T2 relaxation time distribution spectrum reflects the fluidity and binding state of water within the system. The main peak with relaxation times between 10 ms and 100 ms represents non-flowing water. In Example 2, the signal peak amplitude in this range is significantly higher than that in Comparative Examples 2 and 5, and the peak position shifts to the left towards lower relaxation times. This indicates that the addition of carrageenan effectively improves the physical water-holding capacity of the system, converting more free water into non-flowing water and maintaining the product's firm texture. Combined with the data from Comparative Example 5, this confirms that the backpressure sterilization process plays a crucial role in preventing tissue damage and water loss caused by high-temperature expansion.

[0081] Test Example 4: Experimental description: This test case was used to evaluate the changes in the textural properties of the soybean protein-based dried tofu obtained in each example and comparative example before and after heat sterilization, as well as the uniformity of flavor substance penetration into the product interior. The macroscopic hardness values ​​of the product before and after heat sterilization were measured using analytical instruments, and their retention rate was calculated to verify the product's ability to resist high-temperature damage and maintain a firm structure. The salt concentrations of the surface and core were measured using stratified sampling and titration methods, and the difference was calculated to examine the interference of different process parameters on the electrolyte internal diffusion channels.

[0082] Experimental steps: The texture profiles of each group of dried bean curd samples before and after heat sterilization were analyzed using a food texture analyzer. A cylindrical probe with a diameter of 36 mm was selected, the compression ratio was set to 50%, the test speed was set to 1.0 mm / s, and the maximum peak value in the first compression cycle was extracted as the macroscopic hardness value of the sample. Divide the obtained hardness value after sterilization by the hardness value before sterilization, and then multiply by 100% to obtain the hardness retention rate of each group of samples. Using a precision blade, the outer surface layer of the dried bean curd, with a thickness of 1 mm, and the core block, with a thickness of 2 mm, were cut off in parallel from the center of each group as samples to be tested. The samples were then weighed and recorded precisely. The excised surface tissue and core block samples were ground and pulverized separately. The soluble salts were extracted using a boiling water bath. After cooling to room temperature and making up to a fixed volume and filtering, the salt concentrations of the surface and core samples were quantitatively determined by silver nitrate titration. Calculate the absolute difference between the salt concentration of the surface sample and the salt concentration of the core sample to obtain the salt range between the surface and core of each group of finished products.

[0083] Experimental data: Table 4. Hardness retention rate and surface-to-internal salinity difference test results

[0084] Experimental conclusion: Referring to Table 4, the hardness retention rate of Examples 1 to 3 remained consistently above 90%, and the salt content difference between the surface and interior was controlled within the range of 0.22% to 0.31%, demonstrating good structural thermal stability and uniform internal flavor. Comparative Example 1 did not contain glucono-δ-lactone, and Comparative Example 3 underwent a single-stage brining process. The salt content difference between the surface and interior of these two groups increased to 1.96% and 2.12%, respectively, with the central area appearing whitish due to insufficient salt absorption. This indicates that in the absence of slow-release acidification or staged temperature-controlled brining, the outer layer rapidly shrinks upon heating, forming a hard surface shell that hinders the penetration of external salt into the core area, while the overall hardness retention rate significantly declines.

[0085] See attached document Figure 4 The pressure-time characteristic curve of the product's texture profile analysis reflects its mechanical response under compression. Within a test period of 0 to 10 seconds, the peak compressive force and corresponding work area of ​​Example 2 were significantly higher than those of Comparative Examples 1 and 3, and the shape of the unloading rebound phase of the curve was also more pronounced. Combined with the changes in various indicators of Comparative Example 4 under single-bake conditions, it is evident that the combination of segmented temperature variation process and slow-release acidification can guide the uniform distribution of internal pores. This is beneficial for deep salt penetration and gives the product a strong and tough texture resistant to high-temperature deformation.

Claims

1. A type of steamed tofu made with soybean protein, characterized in that, It contains the following raw materials by weight percentage: Soy protein isolate: 28.0%–32.0%; Ice-water mixture: 55.15%–61.85%; Soybean oil: 9.0%–10.0%; D-Anhydrous Glucose: 0.5%–1.5%; Salt: 0.1%–0.3%; Cold-soluble κ-carrageenan: 0.20%–0.40%; Glucono-δ-lactone: 0.15%–0.25%; Sodium pyrophosphate: 0.10%–0.20%; Sodium stearoyl lactylate: 0.10%~0.20%.

2. The soybean protein steamed tofu according to claim 1, characterized in that, The thickness of the steamed soybean protein tofu is 8mm to 12mm, and the length and width are 25mm to 35mm respectively.

3. The steamed tofu made with soybean protein according to claim 2, wherein the steamed tofu made with soybean protein further comprises an extract of a compound spice blend, wherein the compound spice blend is composed of star anise, cinnamon, cloves and Sichuan pepper.

4. A low-temperature segmented braising and roasting method for preparing steamed soybean protein tofu as described in any one of claims 1-3, characterized in that, Includes the following steps: Soy protein isolate was premixed with ice water, sodium pyrophosphate, salt and D-anhydrous glucose were added and chopped in sequence, soybean oil and sodium stearoyl lactylate were added and chopped, cold-soluble κ-carrageenan was added and chopped, and finally gluconate-δ-lactone was added and mixed before discharge to obtain the discharge slurry. The slurry is pumped into a mold box for thermally induced pregelation, then allowed to stand, demolded, and cut to obtain the preform. The embryo and the compound flavored braising liquid are put into a braising pot to form a mixed braising liquid. The mixed braising liquid is then subjected to the first stage of braising. Subsequently, the mixed braising liquid is heated and salt is added for the second stage of braising. The product is then removed and drained to obtain the braised tofu. The braised tofu is dehydrated in the first stage, then baked in the second stage, and then cooled to obtain cooled tofu. The cooled dried bean curd is vacuum-packed, placed in a sterilizing autoclave, heated, and sterilized under back pressure. It is then cooled under pressure and removed from the autoclave to obtain the steamed bean curd made from soybean protein.

5. The preparation method according to claim 4, characterized in that, The specific steps for obtaining the output slurry include: Premix the soy protein isolate with ice water at a speed of 1200 r / min to 1800 r / min for 1 min to 3 min; Add sodium pyrophosphate, salt and D-anhydrous glucose and chop at 2500 r / min to 3200 r / min for 1 min to 3 min; Add soybean oil and sodium stearoyl lactylate and chop at a speed of 3000 r / min to 4000 r / min for 2 min to 4 min; Add cold-soluble κ-carrageenan and chop at 3000 r / min to 4000 r / min for 1 min to 3 min; Add gluconate-δ-lactone and mix at a speed of 500 r / min to 1000 r / min for 0.5 min to 1.5 min, controlling the temperature of the discharged slurry to be 10℃ to 12℃.

6. The preparation method according to claim 5, characterized in that, The steps for obtaining the embryo specifically include: The conditions for thermally induced pregelation are a temperature of 40℃~50℃ and a time of 20min~40min. The conditions for standing are a temperature of 4℃ to 7℃ and a time of 10h to 14h.

7. The preparation method according to claim 4, characterized in that, The compound flavor seasoning brine is prepared through the following steps: A mixture of star anise, cinnamon, cloves and Sichuan peppercorns is added to a reaction vessel containing water at a mass ratio of 1:15 to 1:50 to form a mixture. The mixture in the reaction vessel is heated to 80℃~105℃ and boiled for 30min~120min to obtain the original extract. The original extract was filtered to obtain a spice extract. D-anhydrous glucose and salt are added to the spice extract, stirred to dissolve and cooled, so that the mass fraction of D-anhydrous glucose in the compound flavor seasoning brine is 0.5% to 2.0% and the mass fraction of salt is 0.3% to 0.8%.

8. The preparation method according to claim 7, characterized in that, The specific steps for obtaining the braised tofu include: The embryo and the compound flavored brine are added to the braising pot at a mass ratio of 1:3 to 1:6 to form the mixed brine. The first stage of braising conditions is a temperature of 50℃~60℃, an initial salinity of 0.3%~0.8%, and a time of 15min~25min; The mixed brine is heated to 80°C to 90°C within 2 to 4 minutes, and the salt is added to raise the salinity of the mixed brine to 2.5% to 3.5%. The second stage of brining conditions is a temperature of 80℃~90℃ and a time of 15min~25min.

9. The preparation method according to claim 8, characterized in that, The specific steps for obtaining the cooled dried bean curd include: The first stage of dehydration conditions are: temperature 55℃~65℃, wind speed 1.0m / s~3.0m / s, and time 10min~20min; The second stage baking conditions are: temperature 85℃~95℃, wind speed 1.0m / s~2.0m / s, and time 8min~12min; The cooling conditions are to cool to 20°C to 30°C.

10. The preparation method according to claim 9, characterized in that, The steps of heating and sterilizing in the sterilizing autoclave under back pressure, followed by pressurized cooling and removal from the autoclave, specifically include: The temperature in the sterilization autoclave is raised to 110℃~115℃; Maintain a back pressure of 0.20MPa to 0.35MPa and keep warm for 20 to 30 minutes for sterilization; The conditions for pressurized cooling and outlet discharge are: pressurized cooling to 35℃~45℃.

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