Preparation method of ash bean curd leisure food rich in dietary fiber

Abstract

The application relates to the food processing technical field and discloses a preparation method of ash bean curd leisure food rich in dietary fiber, which is prepared from the following raw materials in parts by weight: mature soybean milk 1000 parts; dietary fiber emulsion precursor 180-250 parts; and composite coagulant 3-5 parts; wherein the dietary fiber emulsion precursor is an oil-in-water emulsion with a pH value of 6.8-7.2 formed by shearing and homogenizing water, dietary fiber, vegetable oil, polyphosphate and organic acid. The dietary fiber is adsorbed on the oil-water interface to form an emulsion structure, thereby avoiding the mechanical cutting effect caused by directly dispersing the fiber particles in the protein matrix and maintaining the continuity of the gel network. Meanwhile, the pH value of the emulsion precursor is pre-adjusted by the organic acid, the chemical interference of the alkalinity of the polyphosphate on the acidic coagulant is eliminated, the compact formation of the protein gel is ensured, the content of the dietary fiber is increased, and the delicacy and water retention of the finished product are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method for preparing a gray tofu snack food rich in dietary fiber. Background Technology

[0002] Gray tofu is a soy product processed using a traditional ash-processing technique. Its unique flavor and porous, spongy structure make it popular with consumers. With changes in modern diets, fortifying traditional soy products with dietary fiber has become an important way to improve their nutritional value. However, in actual processing, the introduction of high-fiber content poses a significant challenge to the matrix construction of gray tofu.

[0003] Dietary fiber is mostly insoluble macromolecular particles, and its surface properties differ from those of soy protein. When high-content dietary fiber is directly dispersed in a soy milk system, the fiber particles act as inactive fillers, blocking the cross-linking of protein molecules and disrupting the continuity and integrity of the gel network. This physical structural defect directly results in a rough texture in the finished product, producing a noticeable powdery or grainy feel. It also significantly reduces the gel's water-holding capacity and elasticity, making the product's texture loose or hard, failing to meet the requirements of a smooth texture in snack foods. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing gray tofu snack food rich in dietary fiber, solving the problem of poor taste in products produced by existing preparation technologies.

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a gray tofu snack food rich in dietary fiber, using the following technical solution:

[0007] A type of gray tofu snack food rich in dietary fiber is made from the following raw materials in parts by weight: 1000 parts cooked soy milk; 180-250 parts dietary fiber emulsion precursor; 3-5 parts compound coagulant; wherein the dietary fiber emulsion precursor is formed by shearing and homogenizing water, dietary fiber, vegetable oil, polyphosphate and organic acid to form an oil-in-water emulsion with a pH of 6.8-7.2.

[0008] By employing the above technical solution, this invention utilizes dietary fiber as a solid particle stabilizer to construct a Pickering emulsion system. In this system, dietary fiber is adsorbed at the oil-water interface, forming a microcapsule structure with oil droplets as the core and fiber as the shell. This avoids the mechanical cutting effect caused by fiber particles being directly dispersed in the protein gel matrix, thus maintaining the integrity of the gel matrix.

[0009] Meanwhile, by introducing organic acids to adjust the pH of the system to 6.8-7.2, the alkalinity of polyphosphate is neutralized, the chemical interference of polyphosphate on the acid-induced gelation process is eliminated, and the composite coagulant can induce proteins to form a dense gel network.

[0010] Preferably, the weight ratio of each component in the dietary fiber emulsion precursor is as follows: 1000 parts deionized water; 180-220 parts dietary fiber; 250-350 parts vegetable oil; 15-25 parts polyphosphate; and organic acid: the amount required to adjust the pH of the system to 6.8-7.2.

[0011] By adopting the above technical solution, the emulsion system with this ratio has a suitable interface coverage, which can effectively encapsulate dietary fiber and introduce uniformly distributed elastic microstructure units for the subsequent gel matrix.

[0012] Preferably, the raw materials are selected to meet the following conditions: the dietary fiber is bamboo shoot dietary fiber with a particle size D90 of 20μm-40μm; the polyphosphate is selected from one or a combination of sodium tripolyphosphate, sodium hexametaphosphate, or sodium pyrophosphate; the organic acid is selected from one or a combination of citric acid, malic acid, or lactic acid; and the composite coagulant is composed of transglutaminase and glucono-δ-lactone, with a mass ratio of 1:6-8.

[0013] By adopting the above technical solution, bamboo shoot dietary fiber of a specific particle size can form a stable Pickering emulsion; the covalent cross-linking effect of transglutaminase and the acid induction effect of gluconate-δ-lactone work synergistically to build a rigid-flexible protein network around the oil droplets of the emulsion, which enhances the gel strength and provides mechanical support for subsequent puffing.

[0014] Secondly, the present invention provides a method for preparing a gray tofu snack food rich in dietary fiber, using the following technical solution:

[0015] A method for preparing a gray tofu snack food rich in dietary fiber includes the following steps:

[0016] S1. Dissolve polyphosphate in water, add organic acid to adjust pH, then add dietary fiber, then add vegetable oil and homogenize to obtain dietary fiber emulsion precursor.

[0017] S2. The dietary fiber emulsion precursor is mixed with cooked soy milk, a composite coagulant is added, and the mixture is kept at 50-90℃ for reaction. After pressing and cutting, tofu blocks are obtained.

[0018] S3. Use a two-component isolation ash preparation to bury the tofu blocks, first perform low-temperature treatment, and then perform high-temperature treatment.

[0019] S4. Sieve off the ash, wash, and dehydrate to obtain the final product.

[0020] Preferably, in step S1, the homogenization process is performed at a speed of 10,000-15,000 rpm for 5-8 minutes; the specific operation for adjusting the pH is as follows: add an aqueous solution of organic acid dropwise to the solution after the polyphosphate is dissolved until the pH value of the system stabilizes between 6.8 and 7.2.

[0021] By adopting the above technical solutions, high shear force makes the oil droplet size smaller, increasing the specific surface area to load more fiber; precise pH adjustment ensures the chemical stability of the emulsion precursor after mixing with soy milk and prevents local flocculation.

[0022] Preferably, in step S3, the two-component isolated ash preparation is prepared by mixing component A and component B before use; component A includes: plant ash and anhydrous calcium chloride; component B includes: sodium bicarbonate and dried starch; wherein, the amount of anhydrous calcium chloride added is 4%-6% of the mass of plant ash, and the dried starch covers the surface of sodium bicarbonate powder.

[0023] By adopting the above technical solution, calcium chloride in component A provides a high concentration of calcium ion source, enhancing the osmotic power; the dried starch in component B forms a physical isolation layer on the surface of sodium bicarbonate. This isolation layer blocks moisture during the low-temperature treatment stage, preventing premature decomposition and failure of sodium bicarbonate; during the high-temperature treatment stage, the starch layer gelatinizes and breaks down, releasing sodium bicarbonate for thermal decomposition and gas production, thus achieving synchronous matching between the gas production timing and the matrix thermal expansion timing.

[0024] Preferably, in the two-component isolated ash preparation, the mass ratio of plant ash, sodium bicarbonate and anhydrous calcium chloride is 100:2.0-3.0:4.0-6.0.

[0025] By adopting the above technical solution, the synergistic effect of the proportions of each component balances the surface hardening rate and the expansion driving force, avoiding excessive hardening of the skin due to excessive calcium content, which restricts expansion, or structural collapse due to excessive gas-generating agent.

[0026] Preferably, in step S3, the low-temperature treatment temperature is 40-48°C and the time is 3.5-6.0 hours.

[0027] By adopting the above technical solution, this temperature range promotes ion diffusion while avoiding drastic protein denaturation, and mainly facilitates the penetration of calcium ions and the chelation reaction of polyphosphates.

[0028] Preferably, the high-temperature treatment in step S3 is performed at a temperature of 110-125°C for 8-15 minutes.

[0029] By adopting the above technical solution, this temperature range causes the moisture inside the tofu block to undergo a rapid phase change and triggers the decomposition of sodium bicarbonate, thus completing the final volume expansion and structural solidification.

[0030] Preferably, in step S4, the cleaning is performed by spraying with an edible acid solution with a concentration of 0.5%-1.0%, wherein the edible acid solution is selected from citric acid solution or acetic acid solution.

[0031] By adopting the above technical solution, the acid-base neutralization reaction is used to remove the residual alkaline wood ash on the surface of the finished product, thereby improving the product flavor and removing the astringent taste.

[0032] This invention provides a method for preparing a gray tofu snack food rich in dietary fiber. It has the following beneficial effects:

[0033] 1. This invention utilizes dietary fiber adsorbed at the oil-water interface to form an emulsion structure, avoiding the mechanical cutting effect caused by fiber particles directly dispersed in the protein matrix, thus maintaining the continuity of the gel network. Simultaneously, by pre-adjusting the pH of the emulsion precursor with organic acids, the chemical interference of polyphosphate alkalinity on the acidic coagulant is eliminated, ensuring the dense formation of the protein gel. This significantly improves the fineness and water-holding capacity of the finished product while increasing the dietary fiber content.

[0034] 2. This invention achieves high-ratio volume expansion of the finished product through a gradient process of low-temperature chelation retardation and high-temperature phase change puffing. Utilizing the competitive chelation of calcium ions by polyphosphates, the hardening rate of surface proteins in the early stages of ash preparation is slowed down, inhibiting premature surface sealing. This process not only promotes deep penetration of calcium ions into the center of the tofu block but also provides the necessary space for internal moisture vaporization and matrix extension during the high-temperature stage, solving the problems of internal collapse and insufficient puffing caused by the overly hard surface of traditional high-fiber tofu.

[0035] 3. This invention utilizes a two-component isolated ash preparation and post-processing technology to optimize the flavor and structural stability of the product. By physically isolating sodium bicarbonate with dried starch, premature decomposition and inactivation of the gas-producing components in a low-temperature, humid environment are prevented, ensuring concentrated gas release at high temperatures, synchronized with the thermal expansion of the matrix, and supporting a uniform porous structure. Furthermore, combined with an acid spray cleaning step, the acid-base neutralization reaction effectively removes residual alkaline wood ash from the surface of the finished product, eliminating the common alkaline and astringent taste of traditional ash tofu and improving its edible flavor. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the preparation process steps of the present invention. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described 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.

[0038] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0039] Soy protein isolate, protein content (dry basis) ≥90%, PDI dispersibility index ≥85, CAS No.: 9010-10-0. Bamboo shoot dietary fiber, processed by air jet milling, total dietary fiber content ≥95%, particle size D90 20μm-40μm. Transglutaminase, enzyme activity ≥100U / g, CAS No.: 80146-85-6. Sodium tripolyphosphate, food grade, CAS No.: 7758-29-4. Citric acid monohydrate, food grade, CAS No.: 5949-29-1. Glucono-δ-lactone, food grade, CAS No.: 90-80-2. Anhydrous calcium chloride, food grade powder, CAS No.: 10043-52-4. Sodium bicarbonate, food grade, CAS No.: 144-55-8. Corn starch, food grade, moisture ≤14%, CAS No.: 9005-25-8. Plant ash, a byproduct of soybean straw burning, passed through a 100-mesh sieve. Grade 1 soybean oil, commercially available food grade.

[0040] Preparation Example 1:

[0041] This preparation example provides a method for preparing a pH-balanced fiber Pickering emulsion precursor, including the following steps:

[0042] The following proportions can be increased proportionally: Weigh 1000g of deionized water, heat to 60℃, add 20g of sodium tripolyphosphate and stir to dissolve. At this point, the pH of the solution is approximately 9.4. Slowly add a 50% citric acid aqueous solution while stirring at 800rpm until the pH of the solution stabilizes at 7.0±0.1. Add 200g of bamboo shoot dietary fiber (D90 is 35μm) to the solution and stir to disperse for 15 minutes to fully hydrate it and form a uniform slurry. Then add 300g of first-grade soybean oil, maintain the temperature at 50℃, and use a high-shear homogenizer at 12000rpm for 6 minutes to obtain a milky white, uniform, and thick Pickering emulsion precursor A1.

[0043] Preparation Example 2:

[0044] This preparation example provides a method for preparing a pH-balanced fiber Pickering emulsion precursor, including the following steps:

[0045] Weigh 1000g of deionized water, heat to 65℃, add 15g of sodium tripolyphosphate and stir to dissolve; add dropwise a 40% citric acid aqueous solution while stirring at 800rpm to adjust the pH of the solution to 6.8±0.1; add 180g of bamboo shoot dietary fiber (D90 of 25μm) to the solution and stir to disperse for 20 minutes; then add 250g of first-grade soybean oil and process with a high-shear homogenizer at 10000rpm for 8 minutes to obtain Pickering emulsion precursor A2.

[0046] Preparation Example 3:

[0047] This preparation example provides a method for preparing a pH-balanced fiber Pickering emulsion precursor, including the following steps:

[0048] Weigh 1000g of deionized water, heat to 60℃, add 25g of sodium tripolyphosphate and stir to dissolve; add dropwise a 50% citric acid aqueous solution while stirring at 800rpm to adjust the pH of the solution to 7.2±0.1; add 220g of bamboo shoot dietary fiber (D90 of 40μm) to the solution and stir to disperse for 10 minutes; then add 350g of first-grade soybean oil and process with a high-shear homogenizer at 15000rpm for 5 minutes to obtain Pickering emulsion precursor A3.

[0049] Preparation Example 4:

[0050] This preparation example provides a method for preparing a two-component isolated ash preparation, including the following steps:

[0051] Preparation of component A: In a dry environment with relative humidity below 40%, weigh 100 kg of dried plant ash that has passed through a 100-mesh sieve, add 5.0 kg of anhydrous calcium chloride powder, mix evenly using a V-type mixer, and then vacuum seal and package.

[0052] Preparation of component B: Weigh 2.5 kg of sodium bicarbonate powder, add 2.0 kg of dry corn starch, mix at low speed for 10 minutes to make the starch evenly cover the surface of sodium bicarbonate, and seal the package.

[0053] Instructions for use: Within 10 minutes before the start of the ash preparation process, open the bag and mix component A and component B evenly to obtain ash preparation B1.

[0054] Preparation Example 5:

[0055] This preparation example provides a method for preparing a two-component isolated ash preparation, including the following steps:

[0056] Preparation of component A: In a dry environment, weigh 100 kg of dried plant ash that has passed through a 100-mesh sieve, add 4.0 kg of anhydrous calcium chloride powder, mix evenly, and then seal and package.

[0057] Preparation of component B: Weigh 3.0 kg of sodium bicarbonate powder, add 2.5 kg of dry corn starch, mix evenly at low speed, and then seal and package.

[0058] Instructions for use: Mix component A and component B evenly before use to obtain ash preparation B2.

[0059] Preparation Example 6:

[0060] This preparation example provides a method for preparing a two-component isolated ash preparation, including the following steps:

[0061] Preparation of component A: In a dry environment, weigh 100 kg of dried plant ash that has passed through a 100-mesh sieve, add 6.0 kg of anhydrous calcium chloride powder, mix evenly, and then seal and package.

[0062] Preparation of component B: Weigh 2.0 kg of sodium bicarbonate powder, add 1.5 kg of dry corn starch, mix evenly at low speed, and then seal and package.

[0063] Instructions for use: Mix component A and component B evenly before use to obtain ash preparation B3.

[0064] Example 1:

[0065] This embodiment provides a method for preparing gray tofu snack food rich in dietary fiber, see attached document. Figure 1 This includes the following steps:

[0066] Take 10 kg of cooked soy milk with a solid content of 12%, cool it to 50°C, add 2.0 kg of Pickering emulsion precursor A1 prepared according to the method of Preparation Example 1, and stir evenly; add 5.0 g of transglutaminase (pre-dissolved in 50 mL of warm water), keep warm and stir for 30 minutes; then add 35 g of gluconate-δ-lactone (pre-dissolved in 100 mL of water), quickly heat to 85°C and keep warm for 20 minutes to form a gel;

[0067] The gel is crushed and placed in a press, then pressed at 0.3 MPa until the moisture content is 72%, and cut into 3cm×3cm×3cm cube tofu blocks.

[0068] Take an appropriate amount of ash preparation B1 prepared according to the method of Preparation Example 4, and completely bury the tofu blank in it; first, place it in a 42℃ constant temperature fermentation room for low temperature chelation retardation treatment for 4.0 hours; then take it out along with some ash, and transfer it to a 115℃ hot air oven for high temperature phase change puffing treatment for 12 minutes.

[0069] Remove the expanded tofu, sift out the ash, spray and wash with a 1.0% citric acid solution for 30 seconds, centrifuge to dehydrate, and then vacuum pack to obtain the finished product.

[0070] Example 2:

[0071] This embodiment provides a method for preparing gray tofu snack food rich in dietary fiber, including the following steps:

[0072] Take 10 kg of cooked soy milk with a solid content of 12%, cool it to 45°C, add 2.5 kg of Pickering emulsion precursor A2 prepared according to the method of Preparation Example 2, and stir evenly; add 6.0 g of transglutaminase, keep warm and react for 35 minutes; then add 40 g of gluconate-δ-lactone, heat to 90°C and keep warm for 15 minutes to form a gel;

[0073] The gel is crushed and placed in a press, then pressed at 0.4 MPa until the moisture content is 70%, and cut into tofu blocks.

[0074] Take an appropriate amount of ash preparation B2 (high-expansion type) prepared according to the method of Preparation Example 5, bury the tofu blanks; place them in a 45°C environment for low-temperature chelation retardation treatment for 5.0 hours; then transfer them to a 120°C converter for high-temperature phase change expansion treatment for 10 minutes; sieve the ash, wash with 0.5% edible acetic acid solution, centrifuge, dehydrate and package.

[0075] Example 3:

[0076] This embodiment provides a method for preparing gray tofu snack food rich in dietary fiber, including the following steps:

[0077] Take 10 kg of cooked soy milk with a solid content of 11%, cool it to 50°C, add 1.8 kg of Pickering emulsion precursor A3 prepared according to the method of Preparation Example 3, and stir evenly; add 4.5 g of transglutaminase, keep warm and react for 25 minutes; then add 30 g of gluconate-δ-lactone, heat to 85°C and keep warm for 20 minutes to form a gel;

[0078] The gel is crushed and placed in a press, then pressed at 0.25 MPa until the moisture content is 75%, and then cut into tofu blocks.

[0079] Take an appropriate amount of ash preparation B3 (strong hardening type) prepared according to the method of Preparation Example 6, bury the tofu blanks; place them in a 40°C environment for low-temperature chelation retardation treatment for 6.0 hours; then transfer them to a 110°C oven for high-temperature phase change puffing treatment for 15 minutes; and then perform routine ash sieving, cleaning and packaging.

[0080] Example 4:

[0081] This embodiment provides a method for preparing gray tofu snack food rich in dietary fiber, including the following steps:

[0082] Take 10 kg of cooked soy milk with a solid content of 12%, cool it to 48°C, add 2.2 kg of Pickering emulsion precursor A1 prepared according to the method of Preparation Example 1, and stir evenly; add 5.5 g of transglutaminase, keep warm and react for 30 minutes; then add 38 g of glucono-δ-lactone, heat to 88°C and keep warm for 18 minutes to form a gel;

[0083] Press the gel until the moisture content is 73%, then cut it into pieces;

[0084] Take an appropriate amount of the ash preparation B1 prepared according to the method of Preparation Example 4, bury the tofu blank; place it in a 48°C environment for low-temperature chelation retardation treatment for 3.5 hours; then transfer it to a 125°C environment for high-temperature phase change puffing treatment for 8 minutes.

[0085] Standard ash screening, cleaning, and packaging.

[0086] Comparative Example 1:

[0087] The difference compared to Example 1 is as follows:

[0088] The process of preparing the Pickering emulsion precursor in step (1) was cancelled. Instead, equal amounts of bamboo shoot dietary fiber powder, grade 1 soybean oil, sodium tripolyphosphate and citric acid (in the proportions in preparation example 1) were directly added to cooked soy milk for mechanical mixing, without high shear homogenization to form an emulsion structure.

[0089] The usage of other raw materials and subsequent processes are the same.

[0090] Comparative Example 2:

[0091] The difference compared to Example 1 is as follows:

[0092] When preparing the Pickering emulsion precursor, sodium tripolyphosphate (STPP) is not added, and correspondingly, citric acid is not added for neutralization; the emulsion is prepared using only fiber and oil-water mixture.

[0093] The usage of other raw materials and subsequent processes are the same.

[0094] Comparative Example 3:

[0095] The difference compared to Example 1 is as follows:

[0096] When preparing the Pickering emulsion precursor, after adding sodium tripolyphosphate, the step of adding citric acid to adjust the pH is omitted, and the pH value of the emulsion precursor is kept at the original alkaline state (about pH 9.4), and it is directly added to the soy milk.

[0097] The usage of other raw materials and subsequent processes are the same.

[0098] Comparative Example 4:

[0099] The difference compared to Example 1 is as follows:

[0100] In preparing ash preparation B1, dry corn starch was not added to component B. Sodium bicarbonate powder was directly mixed with component A (wood ash containing calcium chloride) and used after simulating storage for 24 hours.

[0101] The usage of other raw materials and subsequent processes are the same.

[0102] Comparative Example 5:

[0103] The difference compared to Example 1 is as follows:

[0104] In step (3) gradient ash preparation, the step of “low-temperature chelation retardation treatment for 4.0 hours in a constant temperature fermentation room at 42℃” is cancelled, and the buried tofu blanks are directly placed in a hot air oven at 115℃ for high-temperature puffing treatment.

[0105] The usage of other raw materials and subsequent processes are the same.

[0106] Test Example 1: Construction of Gel Matrix and Verification of pH Equilibrium Mechanism

[0107] This test case aims to verify the effect of the Pickering emulsion precursor described in this invention on the protein gel network structure, and the effectiveness of the acid-base pre-neutralization strategy in resolving chemical compatibility issues. Examples 1-4 and Comparative Examples 1-3 were selected as experimental subjects. Since the only difference between Comparative Examples 4 and 5 is the formulation of the subsequent ash preparation, and their gel matrix construction stage is completely consistent with Example 1, they are not repeated here.

[0108] Soy milk mixtures were prepared according to the methods described in each embodiment and comparative example. After adding gluconate-δ-lactone and mixing evenly, 500 mL of the mixture was immediately sampled and placed in a constant temperature beaker to maintain the gelation temperature described in each example.

[0109] The initial pH value was measured immediately upon addition of GDL using a high-precision pH meter; after standing for 30 minutes, the final pH value of the system was measured again to assess the kinetic environment of the acid-induced gel.

[0110] After the gelation reaction was complete, a texture analyzer was used to perform a puncture test on the formed gel. The test speed was set to 1.0 mm / s, the puncture depth to 10 mm, and the breaking force was recorded as an indicator of gel strength. Each sample was measured in parallel five times, and the average value was taken.

[0111] Take approximately 20g of gel sample and place it in a centrifuge tube with a filter. Centrifuge at 3000 rpm for 15 minutes. Weigh the sample before and after centrifugation and calculate the centrifugal water-holding capacity using the following formula: .

[0112] Table 1: Physicochemical properties and water-holding capacity test data of gel matrix for each group

[0113] Group Initial pH value (when GDL is added) Final pH value (after 30 minutes) gel strength (g) Centrifugal water holding capacity (%) Gel state description Example 1 6.92 5.84 48.7 86.4 The gel is homogeneous, smooth, and elastic. Example 2 6.75 5.72 45.2 84.1 The gel is intact, slightly soft in texture, and does not separate into layers. Example 3 7.15 5.91 51.3 88.7 The gel is firm and has strong toughness. Example 4 6.95 5.81 49.6 85.9 The gel state is stable and similar to that of Example 1. Comparative Example 1 6.88 5.79 18.4 62.3 The gel structure is loose and has a noticeable granular texture. Comparative Example 2 6.64 5.65 32.1 71.5 The gel formation is acceptable, but the water retention is average. Comparative Example 3 9.35 7.42 6.2 24.8 It has a paste-like or semi-fluid consistency and cannot be shaped.

[0114] Based on the data analysis in Table 1, Examples 1-4 all showed significant advantages in terms of gel strength and water retention.

[0115] First, regarding the verification of the pH balance mechanism, comparing the data from Example 1 and Comparative Example 3 shows that the pH environment is crucial for gel formation. In Example 1, the initial pH was controlled at 6.92 by pre-neutralizing sodium tripolyphosphate with citric acid. After adding GDL, the pH of the system successfully dropped to 5.84 within 30 minutes. This pH range is close to the isoelectric point region of soybean protein, promoting the unfolding and aggregation of protein molecules, forming a dense gel network.

[0116] Conversely, although Comparative Example 3 introduced an emulsion structure, no acid-base adjustment was performed. The strong alkaline buffering effect of STPP resulted in an initial pH as high as 9.35. Although GDL hydrolysis produced acid, most of the acid was consumed by the alkaline buffer system, and the final pH only dropped to 7.42. In this slightly neutral or weakly alkaline environment, the surface charge repulsion of soybean protein was relatively large, making it impossible to form an effective gel network. This resulted in a gel strength of only 6.2g, a paste-like consistency, and a lack of basis for processing and shaping.

[0117] Secondly, regarding the verification of the Pickering emulsion interface regulation mechanism, comparing the data from Example 1 and Comparative Example 1 reveals that while their chemical compositions are essentially the same, their physical structures differ fundamentally. Example 1 exhibits a gel strength of 48.7 g and a water-holding capacity as high as 86.4%, while Comparative Example 1 shows only 18.4 g and 62.3%. This difference indicates that the Pickering emulsion formed in Example 1 encapsulates dietary fiber microparticles at the oil-water interface, transforming it from a disruptive element to a supportive one, with the emulsion droplets acting as active fillers to enhance the protein network. In contrast, in the simple physical mixing of Comparative Example 1, the high content of dietary fiber, acting as a foreign substance, directly penetrates the protein network, creating stress concentration points and network defects. This severely weakens the continuity of the gel, leading to a significant decrease in water-holding capacity and difficulty in locking in moisture.

[0118] Furthermore, in Comparative Example 2, although the pH was suitable and gel formation was possible without STPP, its gel strength and water-holding capacity were lower than those of Example 1. This indicates that STPP not only plays a role in regulating pH in the system, but also, as a polyphosphate, assists in the construction of protein networks through cross-linking and improves the water-holding capacity of the system.

[0119] In summary, this invention solves the chemical compatibility problem between STPP and GDL through an acid-base pre-neutralization strategy, and overcomes the destructive effect of high dietary fiber on the gel network by using Pickering emulsion technology, thus constructing a gel matrix with high strength and high water retention capacity, providing the necessary material basis for subsequent gradient ash preparation and expansion processes.

[0120] Test Example 2: Verification of Calcium Ion Osmotic Distribution and Hysteresis Swelling Effect

[0121] This test aims to verify the crucial role of the multivalent ion chelation hysteresis mechanism in overcoming premature surface closure and achieving a gradient structure by quantitatively analyzing the spatiotemporal distribution of calcium ions in the tofu matrix, the surface hardening rate, and the volume change of the final product. Examples 1-4 and Comparative Examples 2, 4, and 5 were selected as test subjects.

[0122] Tofu blanks to be ash-processed were prepared according to the methods described in the various embodiments and comparative examples. During the low-temperature hysteresis stage of the gradient ash-processing, three samples were randomly selected from the ash pile every 1.0 hour, the ash adhering to the surface was quickly removed, and the surface hardness was measured using a texture analyzer. The results were recorded until the low-temperature stage ended or the surface hardness exceeded the instrument's range.

[0123] After the entire ash-setting and puffing process was completed, the samples were cooled to room temperature. The volume of the tofu blocks before ash-setting was determined using the water displacement method. and the volume of the final product Calculate the volume expansion rate: .

[0124] The final product was cut open along the centerline, and the epidermis and middle layer were separated from the surface using a microsurgical scalpel at a distance of 5 mm. Both layers were then dried at 105°C to constant weight. 0.5 g of the dried sample was accurately weighed, digested with nitric acid and perchloric acid, and the calcium content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) to assess the migration depth of calcium ions.

[0125] Table 2: Test data on calcium ion permeation distribution and puffing performance

[0126] Group Initial hardness (g) Surface hardness (g) over 1 hour 4-hour surface hardness (g) Epidermal calcium content (mg / g) Central calcium content (mg / g) Osmotic Ratio (RCa) Volume expansion rate (%) Example 1 48.7 65.2 184.3 24.5 16.8 0.69 284.5 Example 2 45.2 58.9 162.7 22.1 15.4 0.70 276.2 Example 3 51.3 72.1 205.6 26.3 17.9 0.68 268.9 Example 4 49.6 68.4 192.5 25.1 16.2 0.65 291.4 Comparative Example 2 32.1 485.6 >2000 48.7 2.4 0.05 115.3 Comparative Example 4 48.5 67.8 188.2 23.9 15.8 0.66 132.7 Comparative Example 5 48.7 - - 45.2 3.1 0.07 145.6

[0127] According to the data in Table 2, there are significant differences between the example group and the comparative group in terms of calcium ion migration behavior and final puffing effect.

[0128] Regarding the chelation retardation mechanism of multivalent ions, data from Examples 1-4 show that after the introduction of sodium tripolyphosphate (STPP) and low-temperature treatment, the surface hardness of the tofu curd only increased slightly in the initial stage. This indicates that STPP successfully competitively bound some calcium ions in the environment, delaying the rapid cross-linking reaction between calcium and the soybean protein surface. This retardation provides a valuable time window for calcium ions to diffuse inward, resulting in a central layer calcium content of 16.8 mg / g after 4 hours, with an osmotic ratio maintained at around 0.69. This uniform calcium distribution not only strengthens the internal network but also prevents the premature formation of a dense hard shell on the surface, thus allowing internal moisture to vaporize smoothly in the subsequent high-temperature stage and drive matrix expansion, ultimately achieving a high volume expansion rate of 284.5%.

[0129] In contrast, Comparative Example 2, by removing STPP, resulted in a violent reaction of calcium ions upon contact with the tofu surface. The surface hardness surged to 485.6g within 1 hour, forming a dense, eggshell-like barrier layer. This surface sealing effect blocked subsequent calcium ion penetration, leading to extremely low calcium content in the central layer and failure to strengthen the internal protein network through calcium bridging. During the high-temperature puffing stage, due to the excessively hard outer skin and fragile internal structure, steam could not effectively expand the matrix, resulting in a volume expansion rate of only 115.3%, and a product with a hard outer skin and a mushy core.

[0130] Comparative Example 5, while retaining STPP, omitted the low-temperature hysteresis stage and directly subjected it to high-temperature treatment. The high temperature accelerated the chemical reaction rate, rendering the chelation hysteresis effect ineffective. The epidermal calcium content reached as high as 45.2 mg / g, while the central layer only reached 3.1 mg / g, exhibiting a surface sealing phenomenon similar to Comparative Example 2, with the expansion rate limited to 145.6%. This confirms that chemical chelation must work synergistically with low-temperature processing to achieve the desired gradient structure.

[0131] In addition, although Comparative Example 4 had good calcium permeability, it lacked a gas generation system based on sodium bicarbonate and starch microcapsules. It could not generate sufficient expansion driving force by relying solely on water evaporation, and the expansion rate was only 132.7%. This shows that matching the chemical gas generation source with the rheological properties of the matrix is ​​also a necessary condition for achieving high bulkiness.

[0132] In summary, Examples 1-4 successfully constructed a gradient network structure with a moderately hardened outer layer and a uniformly reinforced inner layer by precisely controlling the competitive relationship between the diffusion kinetics of calcium ions and the cross-linking kinetics of proteins. Combined with an isolation-type gas-generating agent, this enabled high-ratio puffing under high dietary fiber loading.

[0133] Test Example 3: Comprehensive Evaluation of Expansion Performance and Texture Properties

[0134] This test aims to comprehensively evaluate the impact of different processing conditions on the quality of high-dietary-fiber gray tofu by quantitatively measuring the volume expansion rate and textural parameters of the final product. Examples 1-4 and Comparative Examples 1-5 were selected as test subjects.

[0135] The finished gray tofu products prepared in each embodiment and comparative example were placed in a desiccator for 24 hours to equilibrate and eliminate the interference of environmental humidity on the surface properties. The volume of the finished product was determined using the millet displacement method. First, a container of known volume was filled with millet and leveled, then poured out and weighed to obtain the millet density. Then, the sample to be tested was placed in the container, filled with millet and leveled, and the mass of the remaining millet was weighed. The volume of the sample was obtained by calculating the difference. Each group of samples was measured in parallel 6 times, and the maximum and minimum values ​​were removed before taking the average value.

[0136] The samples were cut into standard cubic blocks of 20mm × 20mm × 20mm, and full textural profile analysis was performed using a TA.XTPlus texture analyzer. A P / 36R cylindrical probe was selected, and the test mode was set to two-stage compression. The initial velocity was 2.0mm / s, the test velocity was 1.0mm / s, the post-test velocity was 1.0mm / s, the compression deformation was 50%, the interval between the two compressions was 5.0s, and the trigger force was 5.0g.

[0137] Key indicators such as hardness, elasticity, and chewiness are automatically calculated by the instrument software. Ten parallel samples are tested in each group.

[0138] Table 3: Test data on the puffing rate and textural properties of finished products in each group

[0139] Group Volume expansion rate (%) Hardness (g) Elasticity (Ratio) Chewable (g) Remark Example 1 284.5 1156.4 0.89 642.1 Loose structure, good resilience Example 2 276.2 1089.7 0.86 615.3 The texture is relatively soft and the pores are uniform. Example 3 268.9 1245.8 0.91 785.6 Slightly stiff, with strong support Example 4 291.4 1123.2 0.88 630.9 Highest degree of puffing Comparative Example 1 108.3 3852.1 0.42 2154.7 Dense texture, hard and crumbly mouthfeel Comparative Example 2 115.3 4120.5 0.35 2486.2 The outer skin is extremely hard, while the inside is collapsed. Comparative Example 3 N / A 145.6 N / A 89.4 It is soft and mushy, with no elasticity. Comparative Example 4 132.7 2854.3 0.55 1563.8 Although it has hardened, it has not foamed. Comparative Example 5 145.6 1865.9 0.68 1102.5 Uneven puffing, with localized hard lumps

[0140] Based on the data analysis in Table 3, Examples 1-4 all showed significant advantages in terms of expansion rate and textural properties, verifying the synergistic effect of the multiple technical mechanisms of the present invention.

[0141] Regarding the rheological regulation mechanism of Pickering emulsions, comparing the data from Example 1 and Comparative Example 1, it is evident that the volume expansion rate of Example 1 is as high as 284.5%, while that of Comparative Example 1, which uses simple physical mixing, is only 108.3%. This indicates that although both have the same dietary fiber content, Example 1, through emulsification technology, encapsulates the fiber at the oil-water interface, constructing an elastic network with fiber as the skeleton and oil as the lubricating phase. This structure can withstand the tensile stress generated by bubble expansion at high temperatures without breaking, thus giving the finished product an elasticity value as high as 0.89 and moderate hardness. Conversely, in Comparative Example 1, the exposed fibers directly disrupt the continuity of the protein matrix, forming stress concentration points, resulting in a hard texture, extremely poor elasticity, and an inability to form a sponge-like porous structure.

[0142] Regarding the retardation mechanism of multivalent ion chelation, Comparative Example 2, lacking sodium tripolyphosphate, exhibited the highest hardness (4120.5g) among all groups, and the lowest elasticity. This is because calcium ions, unchelated, rapidly reacted with surface proteins in the early stages of ash preparation, forming a hard and inelastic calcium shell. This hard shell restricted the volumetric work done by internal vapors, resulting in an extremely low expansion rate. The Example Group, on the other hand, delayed surface hardening through STPP, maintaining sufficient ductility in the matrix to accommodate gas expansion, ultimately achieving the ideal texture of a crisp exterior and tender interior.

[0143] Regarding the solid-phase micro-isolation mechanism, although Comparative Example 5 contained gas-producing components, its expansion rate was only 185.4% due to the lack of starch microcapsule isolation, significantly lower than that of Example 1. The data indicates that the unisolated sodium bicarbonate prematurely decomposed and released CO2 in the humid environment during the early ash-processing stage, resulting in insufficient gas source driving force during the high-temperature phase change expansion stage, causing the finished product to collapse and increasing its hardness and chewiness.

[0144] Furthermore, in Comparative Example 3, the gel network failed to be effectively established due to the lack of pH adjustment, resulting in a hardness of only 145.6g. Effective elasticity data could not be measured, and the product was soft and mushy, completely losing its ability to be processed and molded. This further confirms the decisive role of pH balancing strategy in the molding of high-fiber matrices.

[0145] Application Example 1

[0146] This embodiment introduces tea juice or tea flower juice to enhance flavor and function based on the basic process of Example 1. The specific preparation process is as follows:

[0147] First, prepare the plant extract: weigh the dried high-mountain green tea leaves or tea flowers, add them to deionized water at 85℃ at a material-to-water ratio of 1:20 and extract for 15 minutes. Then filter the extract with a 200-mesh filter cloth to remove the residue. Allow the filtrate to cool naturally to room temperature to obtain a high-concentration tea juice or tea flower juice for later use.

[0148] Take 10 kg of cooked soy milk with a solid content of 12% and let it cool naturally to 50°C. Before adding the dietary fiber emulsion precursor, add 5%-10% of the cooked soy milk mass (preferably 8% in this embodiment, i.e., 0.8 kg) of the prepared tea juice or tea flower juice slowly to the cooked soy milk and stir at low speed for 5 minutes until the system is homogeneous.

[0149] Subsequently, 2.0 kg of Pickering emulsion precursor A1 prepared according to Preparation Example 1 was added to the mixture and stirred until homogeneous. 5.0 g of pre-dissolved transglutaminase was added, and the mixture was kept warm and stirred for 30 minutes. Then, 35 g of pre-dissolved glucono-δ-lactone was added, and the mixture was rapidly heated to 85°C and kept at that temperature for 20 minutes to form a flavored gel with a fresh plant aroma. The gel was crushed, pressed at 0.3 MPa until the moisture content reached 72%, and then cut into 3 cm × 3 cm × 3 cm cubes of tofu.

[0150] Take an appropriate amount of ash preparation B1 prepared according to the method in Preparation Example 4, and completely bury the above-mentioned flavored tofu blank in it; first, place it in a constant temperature fermentation room at 42℃ for low-temperature chelation retardation treatment for 4.0 hours; then, take it out along with some ash, and transfer it to a hot air oven at 115℃ for high-temperature phase change puffing treatment for 12 minutes. Finally, sieve out the ash, spray and wash with 1.0% citric acid solution for 30 seconds, centrifuge to dehydrate, and vacuum package to obtain the finished product.

[0151] In this embodiment, the tea juice or tea flower juice is added only after the soy milk has matured and before the coagulant is added. This avoids the volatilization of aromatic substances and degradation of natural pigments caused by cooking the raw soy milk at high temperatures, while ensuring that flavor substances are evenly distributed within the continuous protein aqueous phase. The addition ratio is controlled at 5%-10% to ensure the aroma and coloring effects while avoiding excessive dilution of the soy protein concentration, which would weaken the gel matrix strength.

[0152] The tea polyphenols and aromatic substances in tea or tea flower extracts not only effectively neutralize and mask the inherent beany smell of soybean matrix and the slight alkaline taste from the ash-processing, giving the product a delicate and natural color, but also allow the polyphenolic compounds to interact moderately with the side-chain groups of soybean protein, playing a microscopic synergistic role in the covalent cross-linking network of transglutaminase, thus making the porous sponge structure after high-temperature puffing more chewy and resilient. Furthermore, the introduced natural antioxidants effectively inhibit the oxidative rancidity of the oil components in the system, thereby improving the quality stability of this snack food during its shelf life.

[0153] Application Example 2:

[0154] This embodiment, based on the basic process of Example 1, adds subsequent processing steps of high-temperature baking, drying, and frying to further improve the crispness and flavor absorption capacity of the product. The specific preparation process is as follows:

[0155] Take the dehydrated gray tofu from Example 1 that has been treated in step S4 (screening to remove ash, spraying and washing with 1.0% citric acid solution for 30 seconds, and centrifuging to dehydrate), and spread it evenly on a baking tray.

[0156] (1) High-temperature baking: Push the baking tray containing gray tofu into the baking equipment and bake at 170-200℃ for 5-10 minutes. During this stage, the high temperature will cause the surface moisture of the gray tofu to evaporate rapidly, which will promote the Maillard reaction between the free amino acids and reducing sugars on the surface, forming a dense surface solidified layer and characteristic flavor substances, while maintaining the integrity of the internal dietary fiber network structure.

[0157] (2) Drying treatment: The gray tofu after high-temperature baking is transferred to a hot air circulating drying equipment and dried continuously at a temperature of 65-75℃ for 2.5-4.0 hours. This stage allows the internal moisture to slowly migrate outward and evaporate, ensuring the uniformity of the internal and external moisture distribution, reducing the internal moisture mass fraction to between 10% and 15%, and obtaining a dehydrated gray tofu blank with solidified structure.

[0158] (3) Frying treatment: Put the dehydrated gray tofu into edible vegetable oil at 160-180℃ for a short frying treatment of 1-2 minutes, then remove and drain the oil to obtain the finished product.

[0159] The beneficial effects of this embodiment are as follows: The initial ash-processing has already endowed the ash tofu with a unique porous, sponge-like structure rich in dietary fiber. Combined with specific high-temperature baking, drying, and frying processes, a synergistic effect is produced. High-temperature baking at 170-200℃ serves to set the surface and promote the formation of flavor compounds; subsequent drying removes excess moisture and enhances the mechanical strength of the network framework; during the final frying process, residual moisture vaporizes instantly upon heating, and combined with the penetration and displacement of the porous network by hot oil, the high-fiber matrix undergoes secondary micro-expansion. The combination of multiple processes allows the final product to maintain its honeycomb-like porous structure while its overall texture transforms from soft and chewy to crispy, significantly improving the product's sensory quality and flavor profile.

[0160] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A type of gray tofu snack food rich in dietary fiber, characterized in that, Made from the following ingredients in parts by weight: 1000 servings of cooked soy milk; 180-250 parts of dietary fiber emulsion precursor; 3-5 parts of composite coagulant; The dietary fiber emulsion precursor is formed by shearing and homogenizing water, dietary fiber, vegetable oil, polyphosphate and organic acid to form an oil-in-water emulsion with a pH of 6.8-7.

2.

2. The gray tofu snack food rich in dietary fiber according to claim 1, characterized in that: The weight ratio of each component in the dietary fiber emulsion precursor is as follows: 1000 parts deionized water; 180-220 parts dietary fiber; 250-350 parts vegetable oil; 15-25 parts polyphosphate; organic acid: the amount required to adjust the pH of the system to 6.8-7.

2.

3. The gray tofu snack food rich in dietary fiber according to claim 1, characterized in that: The selection of raw materials must meet the following conditions: The dietary fiber is bamboo shoot dietary fiber with a particle size D90 of 20μm-40μm; The polyphosphate is selected from one or a combination of sodium tripolyphosphate, sodium hexametaphosphate, or sodium pyrophosphate. The organic acid is selected from one or a combination of citric acid, malic acid, or lactic acid. The composite coagulant is composed of transglutaminase and gluconate-δ-lactone, with a mass ratio of 1:6-8.

4. A method for preparing a dietary fiber-rich gray tofu snack food, as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Dissolve polyphosphate in water, add organic acid to adjust pH, then add dietary fiber, then add vegetable oil and homogenize to obtain dietary fiber emulsion precursor. S2. The dietary fiber emulsion precursor is mixed with cooked soy milk, a composite coagulant is added, and the mixture is kept at 50-90℃ for reaction. The mixture is then pressed and cut into pieces to obtain tofu blocks. S3. Use a two-component isolation ash preparation to bury the tofu blocks, first perform low-temperature treatment, and then perform high-temperature treatment. S4. Sieve off the ash, wash, and dehydrate to obtain the final product.

5. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 4, characterized in that: In step S1, the homogenization process is performed at a speed of 10,000-15,000 rpm for 5-8 minutes. The specific operation for adjusting the pH is as follows: add an aqueous solution of organic acid dropwise to the solution after the polyphosphate is dissolved until the pH value of the system stabilizes between 6.8 and 7.

2.

6. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 4, characterized in that: In step S3, the two-component isolated ash preparation is prepared by mixing component A and component B before use; Component A comprises: plant ash and anhydrous calcium chloride; Component B comprises: sodium bicarbonate and dried starch; The amount of anhydrous calcium chloride added is 4%-6% of the mass of plant ash, and the dried starch is coated on the surface of sodium bicarbonate powder.

7. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 6, characterized in that: In the two-component isolated ash preparation, the mass ratio of plant ash, sodium bicarbonate and anhydrous calcium chloride is 100:2.0-3.0:4.0-6.

0.

8. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 4, characterized in that: In step S3, the low-temperature treatment temperature is 40-48℃ and the time is 3.5-6.0 hours.

9. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 4, characterized in that: The high-temperature treatment in step S3 is performed at a temperature of 110-125°C for 8-15 minutes.

10. The method for preparing a dietary fiber-rich gray tofu snack food according to claim 4, characterized in that: In step S4, the cleaning is carried out by spraying with an edible acid solution with a concentration of 0.5%-1.0%, and the edible acid solution is selected from citric acid solution or acetic acid solution.

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